1 Introduction to WANs

1.0 Chapter Introduction

1.0.1 Chapter Introduction

Page 1:
When an enterprise grows to include branch offices, e-commerce services, or global operations, a single LAN network is no longer sufficient to meet its business requirements. Wide-area network (WAN) access has become essential for larger businesses today.

There are a variety of WAN technologies to meet the different needs of businesses and many ways to scale the network. Adding WAN access introduces other considerations, such as network security and address management. Consequently, designing a WAN and choosing the correct carrier network services is not a simple matter.

In this chapter, you will begin exploring some of the options available for designing enterprise WANs, the technologies available to implement them, and the terminology used to discuss them. You will learn about selecting the appropriate WAN technologies, services, and devices to meet the changing business requirements of an evolving enterprise. The activities and labs confirm and reinforce your learning.

Upon completion of this chapter, you will be able to identify and describe the appropriate WAN technologies to enable integrated WAN services over a multilocation enterprise network.

1.0.1 - Chapter Introduction
The diagram depicts the chapter objectives:
- Describe how the Cisco enterprise architecture provides integrated services over an enterprise network.
- Describe key WAN technology concepts.
- Select the appropriate WAN technology to meet different enterprise business requirements.

1.1 Providing Integrated Services to the Enterprise

1.1.1 Introducing Wide Area Networks (WANs)

Page 1:
What is a WAN?

A WAN is a data communications network that operates beyond the geographic scope of a LAN.

WANs are different from LANs in several ways. While a LAN connects computers, peripherals, and other devices in a single building or other small geographic area, a WAN allows the transmission of data across greater geographic distances. In addition, an enterprise must subscribe to a WAN service provider to use WAN carrier network services. LANs are typically owned by the company or organization that uses them.

WANs use facilities provided by a service provider, or carrier, such as a telephone or cable company, to connect the locations of an organization to each other, to locations of other organizations, to external services, and to remote users. WANs generally carry a variety of traffic types, such as voice, data, and video.

Here are the three major characteristics of WANs:

• WANs generally connect devices that are separated by a broader geographical area than can be served by a LAN.
• WANs use the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers.
• WANs use serial connections of various types to provide access to bandwidth over large geographic areas.

Why Are WANs Necessary?

LAN technologies provide both speed and cost-efficiency for the transmission of data in organizations over relatively small geographic areas. However, there are other business needs that require communication among remote sites, including the following:

• People in the regional or branch offices of an organization need to be able to communicate and share data with the central site.
• Organizations often want to share information with other organizations across large distances. For example, software manufacturers routinely communicate product and promotion information to distributors that sell their products to end users.
• Employees who travel on company business frequently need to access information that resides on their corporate networks.

In addition, home computer users need to send and receive data across increasingly larger distances. Here are some examples:

• It is now common in many households for consumers to communicate with banks, stores, and a variety of providers of goods and services via computers.
• Students do research for classes by accessing library indexes and publications located in other parts of their country and in other parts of the world.

Since it is obviously not feasible to connect computers across a country or around the world in the same way that computers are connected in a LAN with cables, different technologies have evolved to support this need. Increasingly, the Internet is being used as an inexpensive alternative to using an enterprise WAN for some applications. New technologies are available to businesses to provide security and privacy for their Internet communications and transactions. WANs used by themselves, or in concert with the Internet, allow organizations and individuals to meet their wide-area communication needs.

1.1.1 - Introducing Wide Area Networks (WAN's)
The diagram depicts a network with a LAN and access area interconnected by a WAN with a cloud in it.

LAN:
Contains multiple interconnected Layer 2 switches, user workstations, and servers as well as Layer 3 switches and routers. The ovals connecting the LAN components are labeled as Building Backbone and Campus Backbone.

WAN:
Contains Layer 3 switches and a router in a network cloud. One of the routers in the LAN connects to the WAN router.

Access Area:
Contains a branch office with PC's, a telecommuter, and a remote user connected to a Layer 3 switch in the WAN network cloud.

1.1.2 The Evolving Enterprise

Page 1:
Businesses and Their Networks

As companies grow, they hire more employees, open branch offices, and expand into global markets. These changes also influence their requirements for integrated services and drive their network requirements. In this topic, we will explore how company networks change to accommodate their changing business requirements.

Every business is unique and how an organization grows depends on many factors, such as the type of products or services the business sells, the management philosophy of the owners, and the economic climate of the country in which the business operates.

In slow economic times, many businesses focus on increasing their profitability by improving the efficiency of their existing operations, increasing employee productivity, and lowering operating costs. Establishing and managing networks can represent significant installation and operating expenses. To justify such a large expense, companies expect their networks to perform optimally and to be able to deliver an ever increasing array of services and applications to support productivity and profitability.

To illustrate, let us look at an example of a fictitious company called Span Engineering, and watch how its network requirements change as the company grows from a small local business into a global enterprise.

Click the tabs in the figure to see each growth stage and the associated network topology.

Small Office (Single LAN)

Span Engineering, an environmental consulting firm, has developed a special process for converting household waste into electricity and is developing a small pilot project for a municipal government in its local area. The company, which has been in business for four years, has grown to include 15 employees: six engineers, four computer-aided drawing (CAD) designers, a receptionist, two senior partners, and two office assistants.

Span Engineering's management is hoping that they will have full scale projects after the pilot project successfully demonstrates the feasibility of their process. Until then, the company must manage its costs carefully.

For their small office, Span Engineering uses a single LAN to share information between computers, and to share peripherals, such as a printer, a large-scale plotter (to print engineering drawings), and fax equipment. They have recently upgraded their LAN to provide inexpensive Voice over IP (VoIP) service to save on the costs of separate phone lines for their employees.

Connection to the Internet is through a common broadband service called Digital Subscriber Line (DSL), which is supplied by their local telephone service provider. With so few employees, bandwidth is not a significant problem.

The company cannot afford in-house information technology (IT) support staff, and uses support services purchased from the same service provider. The company also uses a hosting service rather than purchasing and operating its own FTP and e-mail servers. The figure shows an example of a small office and its network.

Campus (Multiple LANs)

Five years later, Span Engineering has grown rapidly. As the owners had hoped, the company was contracted to design and implement a full-sized waste conversion facility soon after the successful implementation of their first pilot plant. Since then, other projects have also been won in neighboring municipalities and in other parts of the country.

To handle the additional workload, the business has hired more staff and leased more office space. It is now a small to medium-sized business with several hundred employees. Many projects are being developed at the same time, and each requires a project manager and support staff. The company has organized itself into functional departments, with each department having its own organizational team. To meet its growing needs, the company has moved into several floors of a larger office building.

As the business has expanded, the network has also grown. Instead of a single small LAN, the network now consists of several subnetworks, each devoted to a different department. For example, all the engineering staff are on one LAN, while the marketing staff is on another LAN. These multiple LANs are joined to create a company-wide network, or campus, which spans several floors of the building.

The business now has in-house IT staff to support and maintain the network. The network includes servers for e-mail, data transfer and file storage, web-based productivity tools and applications, as well as for the company intranet to provide in-house documents and information to employees. In addition, the company has an extranet that provides project information only to designated customers.

Branch (WAN)

Another five years later, Span Engineering has been so successful with its patented process that demand for its services has skyrocketed, and new projects are now being built in other cities. To manage those projects, the company has opened small branch offices closer to the project sites.

This situation presents new challenges to the IT team. To manage the delivery of information and services throughout the company, Span Engineering now has a data center, which houses the various databases and servers of the company. To ensure that all parts of the business are able to access the same services and applications regardless of where the offices are located, the company now needs to implement a WAN.

For its branch offices that are in nearby cities, the company decides to use private dedicated lines through their local service provider. However, for those offices that are located in other countries, the Internet is now an attractive WAN connection option. Although connecting offices through the Internet is economical, it introduces security and privacy issues that the IT team must address.

Distributed (Global)

Span Engineering has now been in business for 20 years and has grown to thousands of employees distributed in offices worldwide. The cost of the network and its related services is now a significant expense. The company is now looking to provide its employees with the best network services at the lowest cost. Optimized network services would allow each employee to work at high efficiency.

To increase profitability, Span Engineering needs to reduce its operating expenses. It has relocated some of its office facilities to less expensive areas. The company is also encouraging teleworking and virtual teams. Web-based applications, including web-conferencing, e-learning, and online collaboration tools, are being used to increase productivity and reduce costs. Site-to-site and remote access Virtual Private Networks (VPNs) enable the company to use the Internet to connect easily and securely with employees and facilities around the world. To meet these requirements, the network must provide the necessary converged services and secure Internet WAN connectivity to remote offices and individuals.

As we have seen from this example, the network requirements of a company can change dramatically as the company grows over time. Distributing employees saves costs in many ways, but it puts increased demands on the network. Not only must a network meet the day-to-day operational needs of the business, but it needs to be able to adapt and grow as the company changes. Network designers and administrators meet these challenges by carefully choosing network technologies, protocols, and service providers, and by optimizing their networks using many of the techniques we teach in this series of courses. The next topic describes a network model for designing networks that can accommodate the changing needs of today's evolving businesses.

1.1.2 - The Evolving Enterprise
The diagram depicts a growing business and its networks in four stages: small office (single LAN), campus (multiple LAN's), branch (WAN), and distributed (global network).

Small Office (single LAN): A small office with a few employees and devices connected to the Internet using broadband access is shown. A single LAN is used for sharing information, peripherals, and Internet access.

Campus (multiple LAN's): The network has grown and now consists of several subnetworks and multiple LAN's joined to create a company-wide network, or campus, which spans several floors of the building. All LAN's in the building connect to the Internet using a firewall router. A business campus can consist of hundreds of employees on one or more floors and in neighboring buildings.

Branch (WAN): The company has opened a branch office, a remote office, and a regional office in addition to the central office. These are interconnected using an Internet WAN composed of multiple Layer 3 switches and a router.

Distributed (global network): The company has grown to thousands of employees distributed in offices worldwide. Telecommuters, home offices, branch offices, and regional offices all connect to the central office using WAN links, broadband, and the Internet.

1.1.3 The Evolving Network Model

Page 1:
The Hierarchical Design Model

The hierarchical network model is a useful high-level tool for designing a reliable network infrastructure. It provides a modular view of a network, making it easier to design and build a scalable network.

The Hierarchical Network Model

As you may recall from CCNA Exploration: LAN Switching and Wireless, the hierarchical network model divides a network into three layers:

• Access layer-Grants user access to network devices. In a network campus, the access layer generally incorporates switched LAN devices with ports that provide connectivity to workstations and servers. In the WAN environment, it may provide teleworkers or remote sites access to the corporate network across WAN technology.
• Distribution layer-Aggregates the wiring closets, using switches to segment workgroups and isolate network problems in a campus environment. Similarly, the distribution layer aggregates WAN connections at the edge of the campus and provides policy-based connectivity.
• Core layer (also referred to as the backbone) - A high-speed backbone that is designed to switch packets as fast as possible. Because the core is critical for connectivity, it must provide a high level of availability and adapt to changes very quickly. It also provides scalability and fast convergence.

Click Example Topology button in the figure.

The figure represents the Hierarchical Network Model in campus environments. The Hierarchical Network Model provides a modular framework that allows flexibility in network design, and facilitates ease of implementation and troubleshooting in the infrastructure. However, it is important to understand that the network infrastructure is only the foundation to a comprehensive architecture.

Networking technologies have advanced considerably in recent years, resulting in networks that are increasingly intelligent. The current network elements are more aware of traffic characteristics and can be configured to deliver specialized services based on such things as the types of data they carry, the priority of the data, and even the security needs. Although most of these various infrastructure services are outside the scope of this course, it is important to understand that they influence network design. In the next topic, we will explore the Cisco Enterprise Architecture, which expands upon the hierarchical model by making use of network intelligence to address the network infrastructure.

1.1.3 - The Evolving Network Model
The diagram depicts the hierarchical network model and an example topology.

Hierarchical Network Model:
Shown are three nested ovals. The outermost oval is labeled Access. The Access Layer provides local and remote user workgroup access to network devices.

An oval labeled Distribution is inside the Access oval. The Distribution Layer provides policy-based connectivity.

The innermost oval is labeled Core. The Core Layer provides a high-speed backbone designed to switch packets as fast as possible.

Example Topology:
The topology consists of Access Layer devices at the bottom of the hierarchy. These include six Layer 2 switches, two of which are connected to WAN routers. One is connected to an Internet router, and another is connected to a telephone switch. The two remaining switches have links to end-user access devices.

The Distribution Layer is the next level up and consists of three Layer 3 routing switches connected to each other. Each pair of Layer 2 access switches is connected to a Layer 3 distribution switch. The top of the hierarchy is the Core Layer with two Layer 3 routing switches. The three Distribution Layer switches connect to Core Layer switches with redundant links.

Page 2:
The Enterprise Architecture

As described earlier, different businesses need different types of networks, depending on how the business is organized and its business goals. Unfortunately, all too often networks grow in a haphazard way as new components are added in response to immediate needs. Over time, those networks become complex and expensive to manage. Because the network is a mixture of newer and older technologies, it can be difficult to support and maintain. Outages and poor performance are a constant source of trouble for network administrators.

To help prevent this situation, Cisco has developed a recommended architecture called the Cisco Enterprise Architecture that has relevance to the different stages of growth of a business. This architecture is designed to provide network planners with a roadmap for network growth as the business moves through different stages. By following the suggested roadmap, IT managers can plan for future network upgrades that will integrate seamlessly into the existing network and support the ever-growing need for services.

The following are some examples of the modules within the architecture that are relevant to the Span Engineering scenario described earlier:

• Enterprise Campus Architecture
• Enterprise Branch Architecture
• Enterprise Data Center Architecture
• Enterprise Teleworker Architecture

1.1.3 - The Evolving Network Model
The diagram depicts Cisco enterprise architectures. There are four panels labeled Campus, Branch Sites, Data Center, and Teleworker. The teleworker is connected to the campus network via broadband. the branch sites are connected to the campus network via WAN links. The campus consists of various user and network devices. Campus routers are connected to the data center routers via WAN links. The data center consists of various core network devices.

Page 3:
Modules in the Enterprise Architecture

The Cisco Enterprise Architecture consists of modules representing focused views that target each place in the network. Each module has a distinct network infrastructure with services and network applications that extend across the modules. The Cisco Enterprise Architecture includes the following modules.

Roll over each module in the figure.

Enterprise Campus Architecture

A campus network is a building or group of buildings connected into one enterprise network that consists of many LANs. A campus is generally limited to a fixed geographic area, but it can span several neighboring buildings, for example, an industrial complex or business park environment. In the Span Engineering example, the campus spanned multiple floors of the same building.

The Enterprise Campus Architecture describes the recommended methods to create a scalable network, while addressing the needs of campus-style business operations. The architecture is modular and can easily expand to include additional campus buildings or floors as the enterprise grows.

Enterprise Edge Architecture

This module offers connectivity to voice, video, and data services outside the enterprise. This module enables the enterprise to use Internet and partner resources, and provide resources for its customers. This module often functions as a liaison between the campus module and the other modules in the Enterprise Architecture. The Enterprise WAN and Metropolitan-Area Network (MAN) Architecture, which the technologies covered later in this course are relevant to, are considered part of this module.

Enterprise Branch Architecture

This module allows businesses to extend the applications and services found at the campus to thousands of remote locations and users or to a small group of branches. Much of this course focuses on the technologies that are often implemented in this module.

Enterprise Data Center Architecture

Data centers are responsible for managing and maintaining the many data systems that are vital to modern business operations. Employees, partners, and customers rely on data and resources in the data center to effectively create, collaborate, and interact. Over the last decade, the rise of Internet and web-based technologies has made the data center more important than ever, improving productivity, enhancing business processes, and accelerating change.

Enterprise Teleworker Architecture

Many businesses today offer a flexible work environment to their employees, allowing them to telecommute from home offices. To telecommute is to leverage the network resources of the enterprise from home. The teleworker module recommends that connections from home using broadband services such as cable modem or DSL connect to the Internet and from there to the corporate network. Because the Internet introduces significant security risks to businesses, special measures need to be taken to ensure that teleworker communications are secure and private.

Click the Example Topology button in the figure.

The figure shows an example of how these Enterprise Architecture modules can be used to build a business network topology.

1.1.3 - The Evolving Network Model
The diagram depicts the modules in the enterprise architecture. Six main areas are identified: the enterprise campus, enterprise edge, WAN and Internet, enterprise branch, enterprise data center, and enterprise teleworker. These are presented as a logical arrangement and as an example topology.

Enterprise Campus:
Connects users within the campus, the server farm, and the enterprise edge modules. The enterprise campus network is divided into four submodule areas: building access, building distribution, campus core, and data center, which consists of a server farm and network management.
- Building access submodule: Contains end-user workstations, IP phones, and Layer 2 access switches that connect devices to the building distribution submodule.

- Building distribution submodule: Provides aggregation of building access devices, often using Layer 3 switching. This submodule performs routing, quality control, and access control.

- Campus core submodule: Provides redundant and fast-converging connectivity between buildings, the server farm, and enterprise edge.

- Server farm and data center: Contains e-mail and corporate servers providing applications and file, print, e-mail, and Domain Name System (DNS) services to internal users.

Enterprise Edge:
Aggregates the connectivity from the various functional areas at the enterprise edge, and routes the traffic into the campus core submodule. The enterprise edge network is divided into four areas: e-commerce, Internet connectivity, WAN and metropolitan area network (MAN) site-to-site connectivity, and remote access including VPN.

WAN and Internet:
This is the service provider environment and is divided into three main areas: ISP services, Frame Relay, Asynchronous Transfer Mode (ATM), and MAN services, and the Public Switched Telephone Network (PSTN).

Enterprise Branch: Extends the applications and services found at the campus to remote locations.

Enterprise Data Center: Manages and maintains centralized data systems for the entire enterprise.

Enterprise Teleworker: Connects individual employees to network resources remotely, typically from their homes.


Example Topology:
The topology consists of four main areas: enterprise campus, enterprise branch, enterprise edge, and teleworker.

Enterprise Campus:
Building Access Layer devices are at the bottom of the hierarchy. The next level up is building distribution with four Layer 3 switches. Above that is the campus core with two Layer 3 switches that are connected to the Distribution Layer.

Branch office and teleworker areas interconnect to the enterprise campus through the enterprise edge devices (mainly routers) at the top of the diagram. The branch office connects to the enterprise campus via Frame Relay, and the teleworker connects via broadband.

Page 4:

1.1.3 - The Evolving Network Model
The diagram depicts an activity in which you match the names of enterprise architecture modules with icons and locations representing the areas in the architecture diagram. The modules are based on those described in Page 1.1.3 Diagram Three, and include:

Enterprise Campus
- Building Access.
- Building Distribution.
- Campus Core.
- Server farm and Data Center.
Enterprise Edge
- E-Commerce.
- Internet connectivity.
- WAN and MAN Site-to-Site VPN.
- Remote Access and VPN.
WAN and Internet
Enterprise Branch Architecture
Enterprise Data Center Architecture
Enterprise Teleworker Architecture

Note: Contact your instructor to discuss how best to perform this activity.

1.2 WAN Technology Concepts

1.2.1 WAN Technology Overview

Page 1:
WANs and the OSI Model

As described in relation to the OSI reference model, WAN operations focus primarily on Layer 1 and Layer 2. WAN access standards typically describe both Physical layer delivery methods and Data Link layer requirements, including physical addressing, flow control, and encapsulation. WAN access standards are defined and managed by a number of recognized authorities, including the International Organization for Standardization (ISO), the Telecommunication Industry Association (TIA), and the Electronic Industries Alliance (EIA).

The Physical layer (OSI Layer 1) protocols describe how to provide electrical, mechanical, operational, and functional connections to the services of a communications service provider.

The Data Link layer (OSI Layer 2) protocols define how data is encapsulated for transmission toward a remote location and the mechanisms for transferring the resulting frames. A variety of different technologies are used, such as Frame Relay and ATM. Some of these protocols use the same basic framing mechanism, High-Level Data Link Control (HDLC), an ISO standard, or one of its subsets or variants.

1.2.1 - WAN Technology Overview
The diagram depicts the seven layers of the O S I model and associates WAN services with the Data Link Layer 2 and Physical Layer 1. Frame Relay, ATM, and High-Level Data Link Control (HDLC) WAN services operate at Layer 2. The Physical Layer (O S I Layer 1) protocols describe how to provide electrical, mechanical, operational, and functional connections to the services of a communications service provider.

1.2.2 WAN Physical Layer Concepts

Page 1:
WAN Physical Layer Terminology

One primary difference between a WAN and a LAN is that a company or organization must subscribe to an outside WAN service provider to use WAN carrier network services. A WAN uses data links provided by carrier services to access the Internet and connect the locations of an organization to each other, to locations of other organizations, to external services, and to remote users. The WAN access Physical layer describes the physical connection between the company network and the service provider network. The figure illustrates the terminology commonly used to describe physical WAN connections, including:

• Customer Premises Equipment (CPE)-The devices and inside wiring located at the premises of the subscriber and connected with a telecommunication channel of a carrier. The subscriber either owns the CPE or leases the CPE from the service provider. A subscriber, in this context, is a company that arranges for WAN services from a service provider or carrier.
• Data Communications Equipment (DCE)-Also called data circuit-terminating equipment, the DCE consists of devices that put data on the local loop. The DCE primarily provides an interface to connect subscribers to a communication link on the WAN cloud.
• Data Terminal Equipment (DTE)-The customer devices that pass the data from a customer network or host computer for transmission over the WAN. The DTE connects to the local loop through the DCE.
• Demarcation Point-A point established in a building or complex to separate customer equipment from service provider equipment. Physically, the demarcation point is the cabling junction box, located on the customer premises, that connects the CPE wiring to the local loop. It is usually placed for easy access by a technician. The demarcation point is the place where the responsibility for the connection changes from the user to the service provider. This is very important because when problems arise, it is necessary to determine whether the user or the service provider is responsible for troubleshooting or repair.
• Local Loop-The copper or fiber telephone cable that connects the CPE at the subscriber site to the CO of the service provider. The local loop is also sometimes called the "last-mile."
• Central Office (CO)-A local service provider facility or building where local telephone cables link to long-haul, all-digital, fiber-optic communications lines through a system of switches and other equipment.

1.2.2 - WAN Physical Layer Concepts
The diagram depicts WAN Physical Layer terminology and equipment found at a company (subscriber) and a WAN service provider.

Company (subscriber) equipment:
- Customer Premises Equipment (CPE) - The devices and inside wiring located at the premises of the subscriber and connected with a telecommunication channel of the carrier.
- Data Communications Equipment (DCE) - Also called data circuit-terminating equipment, the DCE consists of devices that put data on the local loop. In the diagram, the DCE is a modem.
- Data Terminal Equipment (D T E) - The customer devices that pass the data from a customer network or host computer for transmission over the WAN. The D T E connects to the local loop through the DCE. In the diagram, the D T E is a router.

WAN Service Provider equipment:
- Demarcation Point (Demarc) - A point established in a building or complex to separate customer equipment from service provider equipment. Physically, the demarcation point is the cabling junction box, located on the customer premises, that connects the CPE wiring to the local loop.
- Local Loop - The copper or fiber telephone cable that connects the CPE at the subscriber site to the C O of the service provider.
- Central Office (C O) - A local service provider facility or building where local telephone cables link to long-haul, all-digital, fiber-optic communications lines through a system of switches and other equipment. In the diagram, the C O is a building.
- C O Switch - A network device located in the C O that connects the service provider to the customer over the local loop.
- WAN Service Provider Network - Consists of high-speed data routers and switches. In the diagram, this is represented by a cloud filled with a router and several multilayer switches .

Page 2:
WAN Devices

WANs use numerous types of devices that are specific to WAN environments, including:

• Modem-Modulates an analog carrier signal to encode digital information, and also demodulates the carrier signal to decode the transmitted information. A voiceband modem converts the digital signals produced by a computer into voice frequencies that can be transmitted over the analog lines of the public telephone network. On the other side of the connection, another modem converts the sounds back into a digital signal for input to a computer or network connection. Faster modems, such as cable modems and DSL modems, transmit using higher broadband frequencies.
• CSU/DSU-Digital lines, such as T1 or T3 carrier lines, require a channel service unit (CSU) and a data service unit (DSU). The two are often combined into a single piece of equipment, called the CSU/DSU. The CSU provides termination for the digital signal and ensures connection integrity through error correction and line monitoring. The DSU converts the T-carrier line frames into frames that the LAN can interpret and vice versa.
• Access server-Concentrates dial-in and dial-out user communications. An access server may have a mixture of analog and digital interfaces and support hundreds of simultaneous users.
• WAN switch-A multiport internetworking device used in carrier networks. These devices typically switch traffic such as Frame Relay, ATM, or X.25, and operate at the Data Link layer of the OSI reference model. Public switched telephone network (PSTN) switches may also be used within the cloud for circuit-switched connections like Integrated Services Digital Network (ISDN) or analog dialup.
• Router-Provides internetworking and WAN access interface ports that are used to connect to the service provider network. These interfaces may be serial connections or other WAN interfaces. With some types of WAN interfaces, an external device such as a DSU/CSU or modem (analog, cable, or DSL) is required to connect the router to the local point of presence (POP) of the service provider.
• Core router-A router that resides within the middle or backbone of the WAN rather than at its periphery. To fulfill this role, a router must be able to support multiple telecommunications interfaces of the highest speed in use in the WAN core, and it must be able to forward IP packets at full speed on all of those interfaces. The router must also support the routing protocols being used in the core.

1.2.2 - WAN Physical Layer Concepts
The diagram depicts WAN devices. A network cloud labeled WAN contains two WAN switches connected to four interconnected core routers. One PC is connected to a DSL modem and then to a WAN switch via the PSTN. Another PC is connected to a cable modem. The cable modem is then connected to a WAN switch via the cable network. The WAN switch is connected to a channel service unit / data service unit (CSU/DSU) via a T1 dedicated, leased line. The CSU/DSU is then connected to a router. Three PC's are each connected to a modem. The modems are then connected to a WAN switch via an access server.

Page 3:
WAN Physical Layer Standards

WAN Physical layer protocols describe how to provide electrical, mechanical, operational, and functional connections for WAN services. The WAN Physical layer also describes the interface between the DTE and the DCE. The DTE/DCE interface uses various Physical layer protocols, including:

• EIA/TIA-232-This protocol allows signal speeds of up to 64 kb/s on a 25-pin D-connector over short distances. It was formerly known as RS-232. The ITU-T V.24 specification is effectively the same.
• EIA/TIA-449/530-This protocol is a faster (up to 2 Mb/s) version of EIA/TIA-232. It uses a 36-pin D-connector and is capable of longer cable runs. There are several versions. This standard is also known as RS422 and RS-423.
• EIA/TIA-612/613-This standard describes the High-Speed Serial Interface (HSSI) protocol, which provides access to services up to 52 Mb/s on a 60-pin D-connector.
• V.35-This is the ITU-T standard for synchronous communications between a network access device and a packet network. Originally specified to support data rates of 48 kb/s, it now supports speeds of up to 2.048 Mb/s using a 34-pin rectangular connector.
• X.21-This protocol is an ITU-T standard for synchronous digital communications. It uses a 15-pin D-connector.

These protocols establish the codes and electrical parameters the devices use to communicate with each other. Choosing a protocol is largely determined by the service provider's method of facilitation.

Click the WAN Cable Connectors button in the figure to see the types of cable connectors associated with each Physical layer protocol.

1.2.2 - WAN Physical Layer Concepts
The diagram depicts WAN Physical Layer standards and WAN cable connectors that operate on the link between the D T E (router in the diagram) and DCE (modem in the diagram). These include:
- EIA/T IA-232.
- EIA/T IA-449/530.
- EIA/T IA-612/613, commonly referred to as HSSI.
- V.35.
- X.21.

Pictures of the various WAN cable connector types represent WAN physical standards. These include male and female versions of the standards listed above.

1.2.3 WAN Data Link Layer Concepts

Page 1:
Data Link Protocols

In addition to Physical layer devices, WANs require Data Link layer protocols to establish the link across the communication line from the sending to the receiving device. This topic describes the common data link protocols that are used in today's enterprise networks to implement WAN connections.

Data Link layer protocols define how data is encapsulated for transmission to remote sites and the mechanisms for transferring the resulting frames. A variety of different technologies, such as ISDN, Frame Relay, or ATM, are used. Many of these protocols use the same basic framing mechanism, HDLC, an ISO standard, or one of its subsets or variants. ATM is different from the others, because it uses small fixed-size cells of 53 bytes (48 bytes for data), unlike the other packet-switched technologies, which use variable-sized packets.

The most common WAN data-link protocols are:

• HDLC
• PPP
• Frame Relay
• ATM

ISDN and X.25 are older data-link protocols that are less frequently used today. However, ISDN is still covered in this course because of its use when provisioning VoIP network using PRI links. X.25 is mentioned to help explain the relevance of Frame Relay. As well, X.25 is still in use in developing countries where packet data networks (PDN) are used to transmit credit card and debit card transactions from retailers.

Note: Another Data Link layer protocol is the Multiprotocol Label Switching (MPLS) protocol. MPLS is increasingly being deployed by service providers to provide an economical solution to carry circuit-switched as well as packet-switched network traffic. It can operate over any existing infrastructure, such as IP, Frame Relay, ATM, or Ethernet. It sits between Layer 2 and Layer 3 and is sometimes referred to as a Layer 2.5 protocol. However, MPLS is beyond the scope of this course but is covered in the CCNP: Implementing Secure Converged Wide-area Networks.

1.2.3 - WAN Data Link Layer Concepts
The diagram depicts data-link protocols divided into three categories: dedicated point-to-point, packet switched, and circuit switched. Examples are provided for each category:

Dedicated Point-to-Point: Cisco HDLC and P P P.

Packet Switched: X.25, Frame Relay, and ATM.

Circuit Switched: ISDN.

A tabular list of data-link protocols and their usage is also provided.

Protocol: Link Access Procedure Balanced (LAPB).
Usage: X.25.

Protocol: Link Access Procedure D Channel (LAPD).
Usage: ISDN D channel.

Protocol: Link Access Procedure Frame (LAPF).
Usage: Frame Relay.

Protocol: High-Level Data Link Control (HDLC).
Usage: Cisco default.

Protocol: Point-to-Point Protocol (P P P).
Usage: Serial WAN switched connections.

Page 2:
WAN Encapsulation

Data from the Network layer is passed to the Data Link layer for delivery on a physical link, which is normally point-to-point on a WAN connection. The Data Link layer builds a frame around the Network layer data so that the necessary checks and controls can be applied. Each WAN connection type uses a Layer 2 protocol to encapsulate a packet while it is crossing the WAN link. To ensure that the correct encapsulation protocol is used, the Layer 2 encapsulation type used for each router serial interface must be configured. The choice of encapsulation protocols depends on the WAN technology and the equipment. HDLC was first proposed in 1979 and for this reason, most framing protocols which were developed afterwards are based on it.

Click the Play button in the figure to view how WAN data-link protocols encapsulate traffic.

1.2.3 - WAN Data Link Layer Concepts
The animation depicts WAN encapsulation where network Layer 3 packet data, for example, a web request, is encapsulated into an HDLC data link Layer 2 frame. When the encapsulation is complete, the fields in the frame are from left to right:
- Flag.
- Address.
- Control.
- Data.
- FCS.
- Flag.

Page 3:
WAN Frame Encapsulation Formats

Examining the header portion of an HDLC frame will help identify common fields used by many WAN encapsulation protocols. The frame always starts and ends with an 8-bit flag field. The bit pattern is 01111110. The address field is not needed for WAN links, which are almost always point-to-point. The address field is still present and may be 1 or 2 bytes long. The control field is protocol dependent, but usually indicates whether the content of the data is control information or Network layer data. The control field is normally 1 byte.

Together the address and control fields are called the frame header. The encapsulated data follows the control field. Then a frame check sequence (FCS) uses the cyclic redundancy check (CRC) mechanism to establish a 2 or 4 byte field.

Several data-link protocols are used, including subsets and proprietary versions of HDLC. Both PPP and the Cisco version of HDLC have an extra field in the header to identify the Network layer protocol of the encapsulated data.

1.2.3 - WAN Data Link Layer Concepts
The diagram depicts WAN frame encapsulation formats. The frame fields shown are from left to right:
- Flag.
- Header.
- Data.
- FCS.
- Flag.

The Header field is expanded to show the following three fields:
- Address.
- Control.
- Protocol.

A WAN header address is usually a broadcast on a point-to-point link. The control field identifies the data portion as either information or control. The protocol field identifies the intended Layer 3 protocol, for example, IP or IPX.

1.2.4 WAN Switching Concepts

Page 1:
Circuit Switching

A circuit-switched network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate.

As an example, when a subscriber makes a telephone call, the dialed number is used to set switches in the exchanges along the route of the call so that there is a continuous circuit from the caller to the called party. Because of the switching operation used to establish the circuit, the telephone system is called a circuit-switched network. If the telephones are replaced with modems, then the switched circuit is able to carry computer data.

The internal path taken by the circuit between exchanges is shared by a number of conversations. Time-division multiplexing (TDM) gives each conversation a share of the connection in turn. TDM assures that a fixed capacity connection is made available to the subscriber.

If the circuit carries computer data, the usage of this fixed capacity may not be efficient. For example, if the circuit is used to access the Internet, there is a burst of activity on the circuit while a web page is transferred. This could be followed by no activity while the user reads the page, and then another burst of activity while the next page is transferred. This variation in usage between none and maximum is typical of computer network traffic. Because the subscriber has sole use of the fixed capacity allocation, switched circuits are generally an expensive way of moving data.

PSTN and ISDN are two types of circuit-switching technology that may be used to implement a WAN in an enterprise setting.

Click the Play button in the figure to see how circuit switching works.

1.2.4 - WAN Switching Concepts
The animation depicts circuit switching and how dialing sets up a physical circuit through the system. A circuit switching cloud is shown with multiple interconnected phone switches. Two conventional analog phones, Phone A and Phone B, are connected to opposite sides of the cloud. Phone A dials Phone B and a circuit is set up between the switches to connect to Phone B. Phone B is shown ringing after the circuit is set up.

Page 2:
Packet Switching

In contrast to circuit switching, packet switching splits traffic data into packets that are routed over a shared network. Packet-switching networks do not require a circuit to be established, and they allow many pairs of nodes to communicate over the same channel.

The switches in a packet-switched network determine which link the packet must be sent on next from the addressing information in each packet. There are two approaches to this link determination, connectionless or connection-oriented.

• Connectionless systems, such as the Internet, carry full addressing information in each packet. Each switch must evaluate the address to determine where to send the packet.
• Connection-oriented systems predetermine the route for a packet, and each packet only has to carry an identifier. In the case of Frame Relay, these are called Data Link Connection Identifiers (DLCIs). The switch determines the onward route by looking up the identifier in tables held in memory. The set of entries in the tables identifies a particular route or circuit through the system. If this circuit is only physically in existence while a packet is traveling through it, it is called a virtual circuit (VC).

Because the internal links between the switches are shared between many users, the costs of packet switching are lower than those of circuit switching. Delays (latency) and variability of delay (jitter) are greater in packet-switched than in circuit-switched networks. This is because the links are shared, and packets must be entirely received at one switch before moving to the next. Despite the latency and jitter inherent in shared networks, modern technology allows satisfactory transport of voice and even video communications on these networks.

Click the Play button in the figure to see a packet switching example.

Server A is sending data to server B. As the packet traverses the provider network, it arrives at the second provider switch. The packet is added to the queue and forwarded after the other packets in the queue have been forwarded. Eventually, the packet reaches server B.

Virtual Circuits

Packet-switched networks may establish routes through the switches for particular end-to-end connections. These routes are called virtual circuits. A VC is a logical circuit created within a shared network between two network devices. Two types of VCs exist:

• Permanent Virtual Circuit (PVC)-A permanently established virtual circuit that consists of one mode: data transfer. PVCs are used in situations in which data transfer between devices is constant. PVCs decrease the bandwidth use associated with establishing and terminating VCs, but they increase costs because of constant virtual circuit availability. PVCs are generally configured by the service provider when an order is placed for service.
• Switched Virtual Circuit (SVC)-A VC that is dynamically established on demand and terminated when transmission is complete. Communication over an SVC consists of three phases: circuit establishment, data transfer, and circuit termination. The establishment phase involves creating the VC between the source and destination devices. Data transfer involves transmitting data between the devices over the VC, and the circuit termination phase involves tearing down the VC between the source and destination devices. SVCs are used in situations in which data transmission between devices is intermittent, largely to save costs. SVCs release the circuit when transmission is complete, which results in less expensive connection charges than those incurred by PVCs, which maintain constant virtual circuit availability.

Connecting to a Packet-Switched Network

To connect to a packet-switched network, a subscriber needs a local loop to the nearest location where the provider makes the service available. This is called the point-of-presence (POP) of the service. Normally this is a dedicated leased line. This line is much shorter than a leased line directly connected to the subscriber locations, and often carries several VCs. Because it is likely that not all the VCs require maximum demand simultaneously, the capacity of the leased line can be smaller than the sum of the individual VCs. Examples of packet- or cell-switched connections include:

• X.25
• Frame Relay
• ATM

1.2.4 - WAN Switching Concepts
The animation depicts packet switching. A cloud is shown with multiple interconnected WAN switches. Server A and Server B are connected to opposite sides of the cloud. Server A sends data to Server B while data from other sources contend for the same links between switches. Labeled data is passed from switch to switch. It may have to wait its turn on a link. Server B is shown receiving data from Server A.

Page 3:

1.2.4 - WAN Switching Concepts
The diagram depicts an activity in which you fill in the BLANK in the statement with the correct term. Not all answers are used, and some statements have more than one correct answer.

Statements:
- WAN operations occur at the BLANK and BLANK Layers of the O S I model.
- A copper or fiber cable connects customer premise equipment, or CPE, to the service provider's nearest BLANK.
- The physical BLANK point is the place where the responsibility for the connection changes from the user to the service provider.
- A BLANK is a WAN device that converts digital signals to analog format for transmission over an analog line and then converts this analog signal back to digital form so that it can be received and processed by the receiving device on the network.
- The BLANK field in WAN frame formats is not needed because WAN links are almost always point-to-point.
- A BLANK switching network is one that establishes a dedicated channel between nodes and terminals before the users may communicate.
- A BLANK switching network does not require a dedicated channel between nodes. Many pairs of nodes can communicate over the same channel.

Terms:
Physical.
Circuit.
Protocol.
Modem.
Central office.
Control.
Demarcation.
Packet.
Exchange.
Control center.
Data link.
Address.

1.3 WAN Connection Options

1.3.1 WAN Link Connection Options

Page 1:
Many options for implementing WAN solutions are currently available. They differ in technology, speed, and cost. Familiarity with these technologies is an important part of network design and evaluation.

WAN connections can be either over a private infrastructure or over a public infrastructure, such as the Internet.

Private WAN Connection Options

Private WAN connections include both dedicated and switched communication link options.

Dedicated communication links

When permanent dedicated connections are required, point-to-point lines are used with various capacities that are limited only by the underlying physical facilities and the willingness of users to pay for these dedicated lines. A point-to-point link provides a pre-established WAN communications path from the customer premises through the provider network to a remote destination. Point-to-point lines are usually leased from a carrier and are also called leased lines.

Switched communication links

Switched communication links can be either circuit switched or packet switched.

• Circuit-switched communication links-Circuit switching dynamically establishes a dedicated virtual connection for voice or data between a sender and a receiver. Before communication can start, it is necessary to establish the connection through the network of the service provider. Examples of circuit-switched communication links are analog dialup (PSTN) and ISDN.
• Packet-switched communication links-Many WAN users do not make efficient use of the fixed bandwidth that is available with dedicated, switched, or permanent circuits because the data flow fluctuates. Communications providers have data networks available to more appropriately service these users. In packet-switched networks, the data is transmitted in labeled frames, cells, or packets. Packet-switched communication links include Frame Relay, ATM, X.25, and Metro Ethernet.

Public WAN Connection Options

Public connections use the global Internet infrastructure. Until recently, the Internet was not a viable networking option for many businesses because of the significant security risks and lack of adequate performance guarantees in an end-to end Internet connection. With the development of VPN technology, however, the Internet is now an inexpensive and secure option for connecting to teleworkers and remote offices where performance guarantees are not critical. Internet WAN connection links are through broadband services such as DSL, cable modem, and broadband wireless, and combined with VPN technology to provide privacy across the Internet.

1.3.1 - WAN Link Connection Options
The diagram depicts WAN link connection options using a hierarchical organizational chart. At the top of the chart is the WAN block, which splits into two categories: public and private.

Beneath the public section of the chart is Internet. Under Internet is broadband VPN. Examples include DSL, cable, and broadband wireless.

The private section of the chart is split into two sub-categories, dedicated and switched. Leased lines in under the dedicated sub-category. An example of a leased line is a T1.

The switched sub-category is split into two more sub-categories, circuit-switched and packet-switched. Examples under circuit-switched include PSTN and ISDN. Examples under packet-switched include Frame Relay, X.25, and ATM.

1.3.2 Dedicated Connection Link Options

Page 1:
Leased Lines

When permanent dedicated connections are required, a point-to-point link is used to provide a pre-established WAN communications path from the customer premises through the provider network to a remote destination. Point-to-point lines are usually leased from a carrier and are called leased lines. This topic describes how enterprises use leased lines to provide a dedicated WAN connection.

Click the Line Types and Bandwidth button in the figure to view a list of the available leased line types and their bit rate capacities.

Leased lines are available in different capacities and are generally priced based on the bandwidth required and the distance between the two connected points.

Point-to-point links are usually more expensive than shared services such as Frame Relay. The cost of leased line solutions can become significant when they are used to connect many sites over increasing distances. However, there are times when the benefits outweigh the cost of the leased line. The dedicated capacity removes latency or jitter between the endpoints. Constant availability is essential for some applications such as VoIP or Video over IP.

A router serial port is required for each leased line connection. A CSU/DSU and the actual circuit from the service provider are also required.

Leased lines provide permanent dedicated capacity and are used extensively for building WANs. They have been the traditional connection of choice but have a number of disadvantages. Leased lines have a fixed capacity; however, WAN traffic is often variable leaving some of the capacity unused. In addition, each endpoint needs a separate physical interface on the router, which increases equipment costs. Any changes to the leased line generally require a site visit by the carrier.

1.3.2 - Dedicated Connection Link Options
The diagram depicts a leased line WAN topology and a table of line types with bit rate capacity.

Leased Line WAN Topology:
Two buildings, the New York office and the London office, are connected through a WAN service provider.

A router in the New York office connects to a CSU/DSU, which then connects to a T3 link, a standard in the U.S. The T3 link connects to the service provider's network cloud.

A router in the London office connects to a CSU/DSU, which then connects to an E3 link, a standard in Europe. The E3 link connects to the service provider's network cloud.

Line Types and Bandwidth (Bit Rate Capacity):

Line Type: 56, Bit Rate Capacity: 56 kilobits per second.
Line Type: 64, Bit Rate Capacity: 64 kilobits per second.
Line Type: T1, Bit Rate Capacity: 1.544 Megabits per second.
Line Type: E1, Bit Rate Capacity: 2.048 Megabits per second.
Line Type: J1, Bit Rate Capacity: 2.048 Megabits per second.
Line Type: E3, Bit Rate Capacity: 34.064 Megabits per second.
Line Type: T3, Bit Rate Capacity: 44.736 Megabits per second.
Line Type: O C-1, Bit Rate Capacity: 51.84 Megabits per second.
Line Type: O C-3, Bit Rate Capacity: 155.54 Megabits per second.
Line Type: O C-9, Bit Rate Capacity: 466.56 Megabits per second.
Line Type: O C-12, Bit Rate Capacity: 622.08 Megabits per second.
Line Type: O C-18, Bit Rate Capacity: 933.12 Megabits per second.
Line Type: O C-24, Bit Rate Capacity: 1244.16 Megabits per second.
Line Type: O C-36, Bit Rate Capacity: 1866.24 Megabits per second.
Line Type: O C-48, Bit Rate Capacity: 2488.32 Megabits per second.
Line Type: O C-96, Bit Rate Capacity: 4976.64 Megabits per second.
Line Type: O C-192, Bit Rate Capacity: 9953.28 Megabits per second.
Line Type: O C-768, Bit Rate Capacity: 39813.12 Megabits per second.

Page 2:

1.3.2 - Dedicated Connection Link Options
The diagram depicts an activity in which you determine if the statement regarding leased lines is true or false.

Statements:
Are dedicated WAN links.
Best used to connect users over a great distance.
Consist of many switched virtual circuits.
Have lower latency and jitter compared to other WAN links.
Can operate at very high bit rates.
Do not require any call setup because they are always on.
Lowest cost WAN links for interconnections.
Most often used as backup for dialup circuits.

1.3.3 Circuit Switched Connection Options

Page 1:
Analog Dialup

When intermittent, low-volume data transfers are needed, modems and analog dialed telephone lines provide low capacity and dedicated switched connections. This topic describes the pros and cons of using analog dialup connection options, and identifies the types of business scenarios that benefit most from this type of option.

Traditional telephony uses a copper cable, called the local loop, to connect the telephone handset in the subscriber premises to the CO. The signal on the local loop during a call is a continuously varying electronic signal that is a translation of the subscriber voice, analog.

Traditional local loops can transport binary computer data through the voice telephone network using a modem. The modem modulates the binary data into an analog signal at the source and demodulates the analog signal to binary data at the destination. The physical characteristics of the local loop and its connection to the PSTN limit the rate of the signal to less than 56 kb/s.

For small businesses, these relatively low-speed dialup connections are adequate for the exchange of sales figures, prices, routine reports, and e-mail. Using automatic dialup at night or on weekends for large file transfers and data backup can take advantage of lower off-peak tariffs (line charges). Tariffs are based on the distance between the endpoints, time of day, and the duration of the call.

The advantages of modem and analog lines are simplicity, availability, and low implementation cost. The disadvantages are the low data rates and a relatively long connection time. The dedicated circuit has little delay or jitter for point-to-point traffic, but voice or video traffic does not operate adequately at these low bit rates.

1.3.3 - Circuit-Switched Connection Options
The diagram depicts analog dialup WAN topology. This WAN is built with an intermittent connection using a modem and the voice telephone network.

Analog Dialup WAN Topology:
Two buildings are connected using analog dialup through a PSTN WAN link.

A PC and a server in one office connect to a router that is connected to a dialup modem. The modem connects to a telephone line and then to a PSTN switch in the cloud. Three PC's in another office connect to a router that is connected to a dialup modem. The modem connects to a telephone line and then to a PSTN switch in the cloud.

Page 2:
Integrated Services Digital Network

Integrated Services Digital Network (ISDN) is a circuit-switching technology that enables the local loop of a PSTN to carry digital signals, resulting in higher capacity switched connections. ISDN changes the internal connections of the PSTN from carrying analog signals to time-division multiplexed (TDM) digital signals. TDM allows two or more signals or bit streams to be transferred as subchannels in one communication channel. The signals appear to transfer simultaneously, but physically are taking turns on the channel. A data block of subchannel 1 is transmitted during timeslot 1, subchannel 2 during timeslot 2, and so on. One TDM frame consists of one timeslot per subchannel. TDM is described in more detail in Chapter 2, PPP.

ISDN turns the local loop into a TDM digital connection. This change enables the local loop to carry digital signals that result in higher capacity switched connections. The connection uses 64 kb/s bearer channels (B) for carrying voice or data and a signaling, delta channel (D) for call setup and other purposes.

There are two types of ISDN interfaces:

• Basic Rate Interface (BRI)-ISDN is intended for the home and small enterprise and provides two 64 kb/s B channels and a 16 kb/s D channel. The BRI D channel is designed for control and often underused, because it has only two B channels to control. Therefore, some providers allow the D channel to carry data at low bit rates, such as X.25 connections at 9.6 kb/s.
• Primary Rate Interface (PRI)-ISDN is also available for larger installations. PRI delivers 23 B channels with 64 kb/s and one D channel with 64 kb/s in North America, for a total bit rate of up to 1.544 Mb/s. This includes some additional overhead for synchronization. In Europe, Australia, and other parts of the world, ISDN PRI provides 30 B channels and one D channel, for a total bit rate of up to 2.048 Mb/s, including synchronization overhead. In North America, PRI corresponds to a T1 connection. The rate of international PRI corresponds to an E1 or J1 connection.

For small WANs, the BRI ISDN can provide an ideal connection mechanism. BRI has a call setup time that is less than a second, and the 64 kb/s B channel provides greater capacity than an analog modem link. If greater capacity is required, a second B channel can be activated to provide a total of 128 kb/s. Although inadequate for video, this permits several simultaneous voice conversations in addition to data traffic.

Another common application of ISDN is to provide additional capacity as needed on a leased line connection. The leased line is sized to carry average traffic loads while ISDN is added during peak demand periods. ISDN is also used as a backup if the leased line fails. ISDN tariffs are based on a per-B channel basis and are similar to those of analog voice connections.

With PRI ISDN, multiple B channels can be connected between two endpoints. This allows for videoconferencing and high-bandwidth data connections with no latency or jitter. However, multiple connections can be very expensive over long distances.

Note: Although ISDN is still an important technology for telephone service provider networks, it is declining in popularity as an Internet connection option with the introduction of high-speed DSL and other broadband services.

1.3.3 - Circuit-Switched Connection Options
The diagram depicts an ISDN WAN topology. ISDN basic rate interface, BR I, and primary rate interface, PRI, are shown.

ISDN Dialup WAN Topology:
Two buildings are connected using ISDN through a public ISDN WAN link.

A PC and a server in one office connect to a router that is connected to an ISDN terminal adapter, T A. The T A connects to a telephone line and then to an ISDN switch in the PSTN cloud. Three PC's in another office connect to a router, which connects to a telephone line and then to an ISDN switch in the PSTN cloud.

In the diagram, the ISDN BR I is two 64 kilobits per second B channels and one 16 kilobits per second D channel. The ISDN PRI is 23 64 kilobits per second B channels, T1, or 30 64 kilobits per second B channels, E1, and one 64 kilobits per second D channel. The T1 provides 1.544 megabits per second, and the E1 provides 2.048 megabits per second, which includes sync.

Page 3:

1.3.3 - Circuit-Switched Connection Options
Activity One:
The diagram depicts an activity in which you determine if the statement regarding analog dialup is true or false.

Statements:
Is a switched WAN link.
Based on cell-switching technology.
Capable of establishing a connection in a very short time.
Sends digital signals over the telco local loop.
Requires a modulator/demodulator to send digital signals to the PSTN.
Advantages include low cost and availability.

Activity Two:
The diagram depicts an activity in which you determine if the statement regarding ISDN dialup is true or false.

Statements:
Is a dedicated WAN link.
Based on circuit-switching technology.
Short call setup time.
Consists of B channels and a D channel.
Not suitable for use as a backup link.

1.3.4 Packet Switched Connection Options

Page 1:
Common Packet Switching WAN Technologies

The most common packet-switching technologies used in today's enterprise WAN networks include Frame Relay, ATM, and legacy X.25.

Click the X.25 button in the figure.

X.25

X.25 is a legacy Network layer protocol that provides subscribers with a network address. Virtual circuits can be established through the network with call request packets to the target address. The resulting SVC is identified by a channel number. Data packets labeled with the channel number are delivered to the corresponding address. Multiple channels can be active on a single connection.

Typical X.25 applications are point-of-sale card readers. These readers use X.25 in dialup mode to validate transactions on a central computer. For these applications, the low bandwidth and high latency are not a concern, and the low cost makes X.25 affordable.

X.25 link speeds vary from 2400 b/s up to 2 Mb/s. However, public networks are usually low capacity with speeds rarely exceeding above 64 kb/s.

X.25 networks are now in dramatic decline being replaced by newer Layer 2 technologies such as Frame Relay, ATM, and ADSL. However, they are still in use in many portions of the developing world, where there is limited access to newer technologies.

Click the Frame Relay button in the figure.

Frame Relay

Although the network layout appears similar to X.25, Frame Relay differs from X.25 in several ways. Most importantly, it is a much simpler protocol that works at the Data Link layer rather than the Network layer. Frame Relay implements no error or flow control. The simplified handling of frames leads to reduced latency, and measures taken to avoid frame build-up at intermediate switches help reduce jitter. Frame Relay offers data rates up to 4 Mb/s, with some providers offering even higher rates.

Frame Relay VCs are uniquely identified by a DLCI, which ensures bidirectional communication from one DTE device to another. Most Frame Relay connections are PVCs rather than SVCs.

Frame Relay provides permanent, shared, medium-bandwidth connectivity that carries both voice and data traffic. Frame Relay is ideal for connecting enterprise LANs. The router on the LAN needs only a single interface, even when multiple VCs are used. The short-leased line to the Frame Relay network edge allows cost-effective connections between widely scattered LANs.

Frame Relay is described in more detail in Chapter 3, "Frame Relay."

Click the ATM button in the figure.

ATM

Asynchronous Transfer Mode (ATM) technology is capable of transferring voice, video, and data through private and public networks. It is built on a cell-based architecture rather than on a frame-based architecture. ATM cells are always a fixed length of 53 bytes. The ATM cell contains a 5 byte ATM header followed by 48 bytes of ATM payload. Small, fixed-length cells are well suited for carrying voice and video traffic because this traffic is intolerant of delay. Video and voice traffic do not have to wait for a larger data packet to be transmitted.

The 53 byte ATM cell is less efficient than the bigger frames and packets of Frame Relay and X.25. Furthermore, the ATM cell has at least 5 bytes of overhead for each 48-byte payload. When the cell is carrying segmented Network layer packets, the overhead is higher because the ATM switch must be able to reassemble the packets at the destination. A typical ATM line needs almost 20 percent greater bandwidth than Frame Relay to carry the same volume of Network layer data.

ATM was designed to be extremely scalable and can support link speeds of T1/E1 to OC-12 (622 Mb/s) and higher.

ATM offers both PVCs and SVCs, although PVCs are more common with WANs. And as with other shared technologies, ATM allows multiple VCs on a single leased-line connection to the network edge.

1.3.4 - Packet-Switched Connection Options
The diagram depicts common packet-switching WAN technologies, including Frame Relay, ATM, and legacy X.25.

X.25 Network Topology:
Three buildings are shown, Branch Office A, Branch Office B, and the corporate head office. They are interconnected by three X.25 switches in a cloud using switched virtual circuits (SVC's) and permanent virtual circuits (PVC's). A router in each office connects to a CSU/DSU, which connects to one of the X.25 switches in the cloud.

Frame Relay Network Topology:
Two buildings are shown, a branch office and corporate head office. They are interconnected by an ISP router in a cloud using Frame Relay. A router (D T E) in each office connects to the ISP router, which acts as a Frame Relay switch and provides the DCE for each connection. This creates a Frame Relay virtual circuit that is identified at the branch office by data-link connection identifier DLCI 201 and at the corporate head office by DLCI 102.

ATM Network Topology:
Two buildings are shown, a branch office and corporate head office. They are interconnected by a service provider ATM network cloud. At the corporate head office, e-mail, a V o IP phone, a Web server, and an IP TV broadcast are all funneled through a router to an ATM switch at the edge of the cloud. The different transmission packets are broken into ATM cells and are interleaved as they traverse the service provider ATM network to another ATM switch to reach the branch office LAN.

Page 2:

1.3.4 - Packet-Switched Connection Options
The diagram depicts an activity in which you determine if the statements regarding Frame Relay are true or false.

Statements:
Is a connection-oriented digital WAN link.
Based on packet-switching technology.
Less overhead and latency than X.25.
May be used to interconnect LAN's.
Mostly implemented using permanent virtual circuits.
Used on circuits ranging from 56 kilobits per second up to 45 megabits per second.
Costs are based solely on the distance that the packets travel.
Not flexible and cannot handle bursts of data.
Can use one physical interface for multiple connections.

1.3.5 Internet Connection Options

Page 1:
Broadband Services

Broadband connection options are typically used to connect telecommuting employees to a corporate site over the Internet. These options include cable, DSL, and wireless.

Click the DSL button in the figure.

DSL

DSL technology is an always-on connection technology that uses existing twisted-pair telephone lines to transport high-bandwidth data, and provides IP services to subscribers. A DSL modem converts an Ethernet signal from the user device to a DSL signal, which is transmitted to the central office.

Multiple DSL subscriber lines are multiplexed into a single, high-capacity link using a DSL access multiplexer (DSLAM) at the provider location. DSLAMs incorporate TDM technology to aggregate many subscriber lines into a single medium, generally a T3 (DS3) connection. Current DSL technologies use sophisticated coding and modulation techniques to achieve data rates of up to 8.192 Mb/s.

There is a wide variety of DSL types, standards, and emerging standards. DSL is now a popular choice for enterprise IT departments to support home workers. Generally, a subscriber cannot choose to connect to an enterprise network directly, but must first connect to an ISP, and then an IP connection is made through the Internet to the enterprise. Security risks are incurred in this process, but can be mediated with security measures.

Click the Cable Modem button in the figure.

Cable Modem

Coaxial cable is widely used in urban areas to distribute television signals. Network access is available from some cable television networks. This allows for greater bandwidth than the conventional telephone local loop.

Cable modems provide an always-on connection and a simple installation. A subscriber connects a computer or LAN router to the cable modem, which translates the digital signals into the broadband frequencies used for transmitting on a cable television network. The local cable TV office, which is called the cable headend, contains the computer system and databases needed to provide Internet access. The most important component located at the headend is the cable modem termination system (CMTS), which sends and receives digital cable modem signals on a cable network and is necessary for providing Internet services to cable subscribers.

Cable modem subscribers must use the ISP associated with the service provider. All the local subscribers share the same cable bandwidth. As more users join the service, available bandwidth may be below the expected rate.

Click the Broadband Wireless button in the figure.

Broadband Wireless

Wireless technology uses the unlicensed radio spectrum to send and receive data. The unlicensed spectrum is accessible to anyone who has a wireless router and wireless technology in the device they are using.

Until recently, one limitation of wireless access has been the need to be within the local transmission range (typically less than 100 feet) of a wireless router or a wireless modem that has a wired connection to the Internet. The following new developments in broadband wireless technology are changing this situation:

• Municipal WiFi-Many cities have begun setting up municipal wireless networks. Some of these networks provide high-speed Internet access for free or for substantially less than the price of other broadband services. Others are for city use only, allowing police and fire departments and other city employees to do certain aspects of their jobs remotely. To connect to a municipal WiFi, a subscriber typically needs a wireless modem, which provides a stronger radio and directional antenna than conventional wireless adapters. Most service providers provide the necessary equipment for free or for a fee, much like they do with DSL or cable modems.
• WiMAX-Worldwide Interoperability for Microwave Access (WiMAX) is a new technology that is just beginning to come into use. It is described in the IEEE standard 802.16. WiMAX provides high-speed broadband service with wireless access and provides broad coverage like a cell phone network rather than through small WiFi hotspots. WiMAX operates in a similar way to WiFi, but at higher speeds, over greater distances, and for a greater number of users. It uses a network of WiMAX towers that are similar to cell phone towers. To access a WiMAX network, subscribers must subscribe to an ISP with a WiMAX tower within 10 miles of their location. They also need a WiMAX-enabled computer and a special encryption code to get access to the base station.
• Satellite Internet-Typically used by rural users where cable and DSL are not available. A satellite dish provides two-way (upload and download) data communications. The upload speed is about one-tenth of the 500 kb/s download speed. Cable and DSL have higher download speeds, but satellite systems are about 10 times faster than an analog modem. To access satellite Internet services, subscribers need a satellite dish, two modems (uplink and downlink), and coaxial cables between the dish and the modem.

DSL, cable, and wireless broadband services are described in more detail in Chapter 6, "Teleworker Services."

1.3.5 - Internet Connection Options
The diagram depicts common broadband services, including DSL, cable modem, and broadband wireless.

DSL Network Topology:
A teleworker is shown communicating with the company head office using Digital Subscriber Line (DSL). The teleworker connects to a router that is connected to a DSL modem via Ethernet. The DSL modem connects to a phone line that terminates at a DSL access multiplexer (D SLAM) at the service provider's Point of Presence (POP) for access to the Internet cloud. A WAN service provider cloud and router completes the connection to the company head office router.

Cable Modem Network Topology:
A teleworker is shown communicating with the company head office using a cable modem. The teleworker connects to a router, which connects to a cable modem. The cable modem connects to the cable service provider network, which terminates at a cable head-end for access to the Internet cloud. A WAN service provider cloud and router complete the connections to the company head office router.

Broadband Wireless Network Topology:
A home LAN connects to a wireless modem that is connected (non line-of-sight) to a WiMAX 802 dot 16 transmitter. The WiMAX 802 dot 16 transmitter connects to the ISP network via land lines. The ISP location provides access to the Internet. Also shown are Internet data satellites communicating with ground stations in various world locations and then to the ISP.

Page 2:
VPN Technology

Security risks are incurred when a teleworker or remote office uses broadband services to access the corporate WAN over the Internet. To address security concerns, broadband services provide capabilities for using Virtual Private Network (VPN) connections to a VPN server, which is typically located at the corporate site.

A VPN is an encrypted connection between private networks over a public network such as the Internet. Instead of using a dedicated Layer 2 connection such as a leased line, a VPN uses virtual connections called VPN tunnels, which are routed through the Internet from the private network of the company to the remote site or employee host.

VPN Benefits

Benefits of VPN include the following:

• Cost savings-VPNs enable organizations to use the global Internet to connect remote offices and remote users to the main corporate site, thus eliminating expensive dedicated WAN links and modem banks.
• Security-VPNs provide the highest level of security by using advanced encryption and authentication protocols that protect data from unauthorized access.
• Scalability-Because VPNs use the Internet infrastructure within ISPs and devices, it is easy to add new users. Corporations are able to add large amounts of capacity without adding significant infrastructure.
• Compatibility with broadband technology-VPN technology is supported by broadband service providers such as DSL and cable, so mobile workers and telecommuters can take advantage of their home high-speed Internet service to access their corporate networks. Business-grade, high-speed broadband connections can also provide a cost-effective solution for connecting remote offices.

Types of VPN Access

There are two types of VPN access:

• Site-to-site VPNs-Site-to-site VPNs connect entire networks to each other, for example, they can connect a branch office network to a company headquarters network, as shown in the figure. Each site is equipped with a VPN gateway, such as a router, firewall, VPN concentrator, or security appliance. In the figure, a remote branch office uses a site-to-site-VPN to connect with the corporate head office.
• Remote-access VPNs-Remote-access VPNs enable individual hosts, such as telecommuters, mobile users, and extranet consumers, to access a company network securely over the Internet. Each host typically has VPN client software loaded or uses a web-based client.

Click the Remote Access VPN button or the Site-to-Site VPN button in the figure to see an example of each type of VPN connection.

1.3.5 - Internet Connection Options
The diagram depicts VPN technology, including site-to-site VPN's and remote access VPN's.

Site-to-Site VPN's:
Three buildings are shown, the company head office, Branch Office A, and Branch Office B. The company head office building contains a VPN gateway or concentrator. One side of the gateway is connected to an external router and the other to an internal router. The internal router is connected to a switch and an Intranet Web/TFTP server. The external router is connected to router ISP A for access to the Internet.

Branch Office A contains a LAN and a router connected to ISP C on the Internet. Branch Office B contains a LAN and a router connected to ISP B on the Internet.

A site-to-site VPN tunnel is set up between the company head office router through ISP A to the Internet to ISP B and then to the Branch Office B router.

Another site-to-site VPN tunnel is set up between the company head office router through ISP A to the Internet to ISP C and then to the Branch Office A router.

Remote-Access VPN's:
The company head office building contains a VPN gateway or concentrator. One side is connected to an external router and the other to an internal router. The internal router is connected to a switch and an Intranet Web/TFTP server. The external router is connected to ISP A for access to the Internet.

Teleworker One connects to the ISP using DSL. Teleworker Two connects to the ISP using a cable modem. A remote access VPN tunnel is established from the Teleworker One PC, through the ISP router, to the router at the company head office building, and then to the VPN gateway. A VPN client is installed on the PC that requires a user name and password to gain access to the VPN.

Page 3:
Metro Ethernet

Metro Ethernet is a rapidly maturing networking technology that broadens Ethernet to the public networks run by telecommunications companies. IP-aware Ethernet switches enable service providers to offer enterprises converged voice, data, and video services such as IP telephony, video streaming, imaging, and data storage. By extending Ethernet to the metropolitan area, companies can provide their remote offices with reliable access to applications and data on the corporate headquarters LAN.

Benefits of Metro Ethernet include:

• Reduced expenses and administration-Metro Ethernet provides a switched, high-bandwidth Layer 2 network capable of managing data, voice, and video all on the same infrastructure. This characteristic increases bandwidth and eliminates expensive conversions to ATM and Frame Relay. The technology enables businesses to inexpensively connect numerous sites in a metropolitan area to each other and to the Internet.
• Easy integration with existing networks-Metro Ethernet connects easily to existing Ethernet LANs, reducing installation costs and time.
• Enhanced business productivity-Metro Ethernet enables businesses to take advantage of productivity-enhancing IP applications that are difficult to implement on TDM or Frame Relay networks, such as hosted IP communications, VoIP, and streaming and broadcast video.

1.3.5 - Internet Connection Options
The diagram depicts Metro Ethernet technology. A Metro Ethernet service provider cloud contains five high-speed IP-aware Ethernet switches. Four buildings are connected via the Metro Ethernet cloud. These include a head office downtown, a branch office on Main Street, one in an industrial park, and another in a suburb.

Page 4:
Choosing a WAN Link Connection

Now that we have looked at the variety of WAN connection options, how do you choose the best technology to meet the requirements of a specific business? The figure compares the advantages and disadvantages of the WAN connection options that we have discussed in this chapter. This information is a good start. In addition, to help in the decision-making process, here are some questions to ask yourself when choosing a WAN connection option.

What is the purpose of the WAN?

Do you want to connect local branches in the same city area, connect remote branches, connect to a single branch, connect to customers, connect to business partners, or some combination of these? If the WAN is for providing authorized customers or business partners limited access to the company intranet, what is the best option?

What is the geographic scope?

Is it local, regional, global, one-to-one (single branch), one-to-many branches, many-to-many (distributed)? Depending on the range, some WAN connection options may be better than others.

What are the traffic requirements?

Traffic requirements to consider include:

• Traffic type (data only, VoIP, video, large files, streaming files) determines the quality and performance requirements. For example, if you are sending a lot of voice or streaming video traffic, ATM may be the best choice.
• Traffic volumes depending on type (voice, video, or data) for each destination determine the bandwidth capacity required for the WAN connection to the ISP.
• Quality requirements may limit your choices. If your traffic is highly sensitive to latency and jitter, you can eliminate any WAN connection options that cannot provide the required quality.
• Security requirements (data integrity, confidentiality, and security) is an important factor if the traffic is of a highly confidential nature or if provides essential services, such as emergency response.

Should the WAN use a private or public infrastructure?

A private infrastructure offers the best security and confidentiality, whereas the public Internet infrastructure offers the most flexibility and lowest ongoing expense. Your choice depends on the purpose of the WAN, the types of traffic it carries, and available operating budget. For example, if the purpose is to provide a nearby branch with high-speed secure services, a private dedicated or switched connection may be best. If the purpose is to connect many remote offices, an public WAN using the Internet may be the best choice. For distributed operations, a combination of options may be the solution.

For a private WAN, should it be dedicated or switched?

Real-time, high-volume transactions have special requirements that could favor a dedicated line, such as traffic flowing between the data center and the corporate head office. If you are connecting to a local single branch, you could use a dedicated leased line. However, that option would become very expensive for a WAN connecting multiple offices. In that case, a switched connection might be better.

For a public WAN, what type of VPN access do you need?

If the purpose of the WAN is to connect a remote office, a site-to-site VPN may be the best choice. To connect teleworkers or customers, remote-access VPNs are a better option. If the WAN is serving a mixture of remote offices, teleworkers, and authorized customers, such as a global company with distributed operations, a combination of VPN options may be required.

Which connection options are available locally?

In some areas, not all WAN connection options are available. In this case, your selection process is simplified, although the resulting WAN may provide less than optimal performance. For example, in a rural or remote area, the only option may be broadband satellite Internet access.

What is the cost of the available connection options?

Depending on the option you choose, the WAN can be a significant ongoing expense. The cost of a particular option must be weighed against how well it meets your other requirements. For example, a dedicated leased line is the most expensive option, but the expense may be justified if it is critical to ensure secure transmission of high volumes of real-time data. For less demanding applications, a cheaper switched or Internet connection option may be more suitable.

As you can see, there are many important factors to consider when choosing an appropriate WAN connection. Following the guidelines described above, as well as those described by the Cisco Enterprise Architecture, you should now be able to choose an appropriate WAN connection to meet the requirements of different business scenarios.

1.3.5 - Internet Connection Options
The diagram depicts a table with characteristics of various WAN technology options for use in choosing a WAN link connection.

Option: Leased line.
Description: Point-to-point connection between two computers or LAN's.
Advantages: Most secure.
Disadvantages: Expensive.
Sample protocols used: P P P, HDLC, SDLC, HNAS.

Option: Circuit switching.
Description: A dedicated circuit path is created between endpoints. Best example is a dialup connection.
Advantages: Less expensive.
Disadvantages: Call setup.
Sample protocols used: P P P, ISDN.

Option: Packet switching.
Description: Devices transport packets via a shared single point-to-point or point-to-multipoint link across a carrier interwork. Variable length packets are transmitted over PVC's or SVC's.
Advantages: None listed.
Disadvantages: Shared media across link.
Sample protocols used: X.25, Frame Relay.

Option: Cell relay.
Description: Similar to packet switching, but uses fixed-length cells instead of variable-length packets. Data is divided into fixed-length cells and then transported across virtual circuits.
Advantages: Best for simulated use of voice and data.
Disadvantages: Overhead can be considerable.
Sample protocols used: ATM.

Option: Internet.
Description: Connectionless packet switching using the Internet as the WAN infrastructure. Uses network addressing to deliver packets. Because of security issues, VPN technology must be used.
Advantages: Least expensive and globally available.
Disadvantages: Least secure.
Sample protocols used: VPN, DSL, cable modem, wireless.

Page 5:

1.3.5 - Internet Connection Options
The diagram depicts an activity in which you match the type of WAN link to the technology category:

WAN Link:
PSTN.
ISDN.
Cable.
Frame Relay.
DSL.
X.25.
ATM.

Technology category:
Circuit Switched.
Packet Switched.
Broadband / VPN.

1.4 Chapter Labs

1.4.1 Challenge Review

Page 1:
In this lab, you will review basic routing and switching concepts. Try to do as much on your own as possible. Refer back to previous material when you cannot proceed on your own.

Note: Configuring three separate routing protocols-RIP, OSPF, and EIGRP-to route the same network is emphatically not a best practice. It should be considered a worst practice and is not something that would be done in a production network. It is done here so that you can review the major routing protocols before proceeding, and see a dramatic illustration of the concept of administrative distance.

1.4.1 - Challenge Review
Link to Hands-on Lab: Challenge Review Lab

1.5 Chapter Summary

1.5.1 Chapter Summary

Page 1:
A WAN is a data communications network that operates beyond the geographic scope of a LAN.

As companies grow, adding more employees, opening branch offices, and expanding into global markets, their requirements for integrated services change. These business requirements drive their network requirements.

The Cisco Enterprise Architecture expands upon the Hierarchical Design Model by further dividing the enterprise network into physical, logical, and functional areas.

Implementation of a Cisco Enterprise Architecture provides a secure, robust network with high availability that facilitates the deployment of converged networks.

WANs operate in relation to the OSI reference model, primarily on Layer 1 and Layer 2.

Devices that put data on the local loop are called data circuit-terminating equipment, or data communications equipment (DCE). The customer devices that pass the data to the DCE are called data terminal equipment (DTE). The DCE primarily provides an interface for the DTE into the communication link on the WAN cloud.

The physical demarcation point is the place where the responsibility for the connection changes from the enterprise to the service provider.

Data Link layer protocols define how data is encapsulated for transmission to remote sites and the mechanisms for transferring the resulting frames.

A circuit-switching network establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate.

A packet-switching network splits traffic data into packets that are routed over a shared network. Packet-switching networks do not require a circuit to be established and allow many pairs of nodes to communicate over the same channel.

A point-to-point link provides a pre-established WAN communications path from the customer premises through the provider network to a remote destination. Point-to-point links use leased lines to provide a dedicated connection.

Circuit-switching WAN options include analog dialup and ISDN. Packet-switching WAN options include X.25, Frame Relay, and ATM. ATM transmits data in 53-byte cells rather than frames. ATM is most suited to video traffic.

Internet WAN connection options include broadband services, such as DSL, cable modem or broadband wireless, and Metro Ethernet. VPN technology enables businesses to provide secure teleworker access through the Internet over broadband services.

1.5.1 - Summary and Review
In this chapter, you have learned to:
- Describe how the Cisco enterprise architecture provides integrated services over an enterprise network.
- Describe key WAN technology concepts.
- Select the appropriate WAN technology to meet different enterprise business requirements.

Page 2:

1.5.1 - Summary and Review
This is a review and is not a quiz. Questions and answers are provided.
Question One. Describe the three layers of the hierarchical network model.
Answer:
Access Layer:
- Grants user access to network devices.
- In a network campus, the Access Layer generally incorporates switched LAN devices with ports that provide connectivity to workstations and servers.
- In the WAN environment, it may provide teleworkers or remote sites access to the corporate network across WAN technology.
Distribution Layer:
- Aggregates the wiring closets, using switches to segment workgroups and isolate network problems in a campus environment.
- Similarly, the Distribution Layer aggregates WAN connections at the edge of the campus and provides policy-based connectivity.
Core Layer (also referred to as the backbone):
- High-speed backbone that is designed to switch packets as fast as possible.
- Because the core is critical for connectivity, it must provide a high level of availability and adapt to changes very quickly. It also provides scalability and fast convergence.

Question Two.
Describe the five modules of the Cisco enterprise architecture.
Answer:
Enterprise Campus Architecture:
- An enterprise campus network is a building or group of buildings connected into one network that consists of many LAN's.
- It is generally limited to a fixed geographic area, but it can span several neighboring buildings.
- The architecture is modular and scalable and can easily expand to include additional buildings or floors as required.
Enterprise Branch Architecture:
- This module allows businesses to extend the applications and services found at the enterprise campus to thousands of remote locations and users or to a small group of branches.
Enterprise Data Center Architecture:
- Data centers are responsible for managing and maintaining the many data systems that are vital to modern business operations.
- This module centrally houses the data and resources to enable users to effectively create, collaborate, and interact.
Enterprise Teleworker Architecture:
- This module leverages the network resources of the enterprise from home using broadband services such as cable modem or DSL to connect to the corporate network.
-Typically implemented using remote access VPN's.
Enterprise Edge Architecture
-This module often functions as a liaison between the campus module and the other modules in the enterprise architecture.

Question Three.
Compare and contrast the following WAN terms: CPE, C O, local loop, DCE, D T E, and demarcation point.
Answer:
Customer Premises Equipment (CPE):
- The devices and inside wiring located at the premises of the subscriber and connected with a telecommunication channel of a carrier.
- The subscriber either owns the CPE or leases it from the service provider.
Central Office (C O):
- A local service provider facility or building where local telephone cables link to long-haul, all-digital, fiber-optic communications lines through a system of switches and other equipment.
Local Loop:
- Often referred to as the last mile, it is the copper or fiber telephone cable that connects the CPE at the subscriber site to the C O of the service provider.
Data Communications Equipment (DCE):
- Also called data circuit-terminating equipment, the DCE consists of devices that put data on the local loop.
- The DCE primarily provides an interface to connect subscribers to a communication link on the WAN cloud.
Data Terminal Equipment (D T E):
- The customer devices that pass the data from a customer network or host computer for transmission over the WAN.
- The D T E connects to the local loop through the DCE.
Demarcation Point:
- Physically, it is the cabling junction box located on the customer premises that connects the CPE wiring to the local loop and separates the customer equipment from service provider equipment.
- It is the place where the responsibility for the connection changes from the user to the service provider.

Question Four.
Compare and contrast the following WAN devices: modem, CSU/DSU, access server, WAN switch, and router.
Answer:
Modem:
- A voiceband modem converts and reconverts the digital signals produced by a computer into voice frequencies that can be transmitted over the analog lines of the public telephone network.
- Faster modems, such as cable and DSL, transmit using higher broadband frequencies.
CSU/DSU:
- Digital lines, such as T1 or T3 carrier lines, require a channel service unit (CSU) and a data service unit (DSU).
- The two are often combined into a single piece of equipment, called the CSU/DSU.
- The CSU provides termination for the digital signal and ensures connection integrity through error correction and line monitoring. The DSU converts the T-carrier line frames into frames that the LAN can interpret.
Access server:
- Concentrates dial-in and dial-out user communications and may have a mixture of analog and digital interfaces. It can support hundreds of simultaneous users.
WAN switch:
- Multiport internetworking device used in carrier networks to support Frame Relay, ATM, or X.25.
Router:
Provides internetworking and WAN access interface ports that are used to connect to the service provider network.
These interfaces may be serial connections or other WAN interfaces and may require an external device such as a DSU/CSU or modem (analog, cable, or DSL) to connect to the service provider.

Question Five.
Compare and contrast X.25, Frame Relay, and ATM.
Answer:
X.25 :
- Older low-capacity WAN technology with a maximum speed of 48 kilobits per second, typically used in dialup mode with point-of-sale card readers to validate transactions on a central computer.
- For these applications, the low bandwidth and high latency are not a concern, and the low cost makes X.25 affordable.
- Frame Relay has replaced X.25 at many service provider locations.
Frame Relay:
- Layer 2 WAN protocol that typically offers data rates of 4 Megabits per second or higher.
- It provides permanent, shared, medium-bandwidth connectivity using virtual circuits capable of carrying both voice and data traffic.
- VC's are uniquely identified by a DLCI, which ensures bidirectional communication from one D T E device to another.
ATM:
- Asynchronous Transfer Mode (ATM) technology is based on a cell-based architecture rather than a frame-based architecture, using fixed length cells of 53 bytes.
- These small, fixed-length cells are well suited for carrying delay-sensitive voice and video traffic.

Page 3:
This activity covers many of the skills you acquired in the first three Exploration courses. Skills include building a network, applying an addressing scheme, configuring routing, VLANs, STP and VTP, and testing connectivity. You should review those skills before proceeding. In addition, this activity provides you an opportunity to review the basics of the Packet Tracer program. Packet Tracer is integrated throughout this course. You must know how to navigate the Packet Tracer environment to complete this course. Use the tutorials if you need a review of Packet Tracer fundamentals. The tutorials are located in the Packet Tracer Help menu.

Detailed instructions are provided within the activity as well as in the PDF link below.

Activity Instructions (PDF)

Click the Packet Tracer icon for more details.

1.5.1 - Summary and Review
Link to Packet Tracer Exploration: Packet Tracer Skills Integration Challenge

1.6 Chapter Quiz

1.6.1 Chapter Quiz

Page 1:

1.6.1 - Chapter Quiz
1.Which three items are considered to be WAN devices? (Choose three.)
A.Bridges
B.Modems
C.Routers
D.Layer 2 switches
E.Communication servers
F.Repeaters

2.Which layer of the hierarchical network design model is often referred to as the backbone?
A.Access
B.Distribution
C.Network
D.Core
E.Workgroup
F.WAN

3.Match the description to the associated term.
Descriptions:
A. A switching technology where each switch must evaluate the address of the packet to determine where to send it.

B. A switching technology where a virtual circuit is only physically in existence while a packet is traveling through it.

C. A switching technology that establishes routes through the switches for particular end-to-end connections.

D. A switching technology that has a pre-established dedicated circuit (or channel) between nodes and terminals.

Terms:
Circuit Switching
Packet Switching
Connection-oriented Packet Switching
Connectionless Packet Switching

4.Match the description of the packet-switched technology to the associated term.
Descriptions:
A. Provides a high-bandwidth Layer 2 network capable of managing data, voice, and video all on the same infrastructure.

B. Built on a cell-based architecture in which the cell has a fixed length of 53 bytes.

C. Operates at the Data Link Layer, and the PVC is identified by a DLCI.

D. Operates at the network layer, and the SVC is identified by a channel number.

Terms:
X.25
Frame Relay
ATM
Metro Ethernet

5.Which device is commonly used as Data Terminal Equipment?
A.ISDN
B.Modem
C.Router
D.CSU/DSU

6.Which type of WAN connection should be chosen when a dedicated point-to-point WAN communications path from the customer premises through the provider network to a remote destination is required?
A.ISDN
B.Analog dialup
C.ATM
D.Frame Relay
E.Leased line

7.How are Frame Relay virtual circuits identified?
A.C I R
B.DLCI
C.VPI
D.MAC
E.SPID

8.What WAN technology is designed for delivering data, voice, and video simultaneously over a TDM infrastructure?
A.ATM
B.Cable
C.Frame Relay
D.ISDN

9.Which Cisco architecture enables enterprises to offer important network services, such as security, new communication services, and improved application performance to every office regardless of its size or proximity to headquarters?
A.Enterprise Campus Architecture
B.Enterprise Data Center Architecture
C.Enterprise Branch Architecture
D.Enterprise Teleworker Architecture

10.At which layer of the hierarchical design model do users connect to the network?
A.Application
B.Access
C.Distribution
D.Network
E.Core

11.ISDN PRI is composed of how many B channels in North America?
A.2
B.16
C.23
D.30
E.64

12.The ability to connect securely to a private network over a public network is provided by which WAN technology?
A.DSL
B.Frame Relay
C.ISDN
D.PSTN
E.VPN

13.Which hierarchical design model layer is responsible for containing network problems to the workgroups in which they occur?
A.Application
B.Access
C.Distribution
D.Network
E.Core

14.Which term describes the cabling that connects the customer site to the nearest exchange of the WAN service provider?
A.CPE
B.C O
C.Local loop
D.DCE
E.D T E

15.Which goal can be accomplished by the implementation of the Cisco Enterprise Teleworker Architecture?
A.It allows the enterprise to add large branch sites that span large geographic areas.
B.It allows the enterprise to deliver secure voice and data services to workers no matter where or when they work.
C.To reduce remote security threats, it forces users who are located at main sites to log on to the resources.
D.It satisfies telephony requirements for users who are located at medium to large enterprise sites.