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The main purpose of this TCS was to introduce students to the whole concept of Wide Area Networking. The students learned about common WAN encapsulation types and how they function. The students also learned about WAN connections and the hierarchical WAN model.

The main learning objectives of the TCS were the following:

1. Describe the three major characteristics of a Wide Area Network

WAN's are designed to operate over large geographical areas, allow access over serial interfaces operating at lower speeds, provide full-time and part-time connectivity, and connect devices separated over wide, even global areas. The network operates beyond the local LAN's geographic scope. It uses the services of carriers such as Regional Bell Operating Companies (RBOCs). The WAN devices that connect these large geographic areas include routers, switches, modems, and communications servers.

2. List four common data link layer WAN protocols.

PPP is usually common for dialup single-user-to-LAN or LAN-to-LAN (router-to-router) access. PPP is standardized, so it supports vendor interoperability. It also supports the encapsulation of multiple upper-layer protocols including IP and IPX. HDLC is the Cisco default encapsulation type on point-to-point links. It is used typically when communicating with another Cisco device. If communicating with a non-Cisco device, synchronous PPP is a viable option. LAPB is used for packet-switched networks, the LAPB protocol is used to encapsulate X.25 packets. It can also be used over point-to-point links, if the link is unreliable or there is an inherent delay associated with the link, such as in a satellite link. LAPB provides reliability and flow control on a point-to-point basis. Cisco/IETF is used to encapsulate Frame Relay traffic.

3. Describe how Time Division Multiplexing works and what WAN technology uses it.

TDM is a technique in which information from multiple channels can be allocated bandwidth on a single wire based on prearranged time slots. Bandwidth is allocated to each channel regardless of whether the station has data to transmit. What this means is that multiple channels can be created on a single line by assigning time slots for each channel to transmit on. This is the way that ISP's can increase bandwidth usage over a single line.

4. Describe the data encapsulation process across a WAN link.

There are multiple methods of encapsulating data over a WAN link. The reason for this is that there is multiple WAN encapsulation protocol.

PPP is the common type of encapsulation for dialup single user LAN to LAN access. Since PPP is standardized it supports multivendor interoperability. It also supports the encapsulation of multiple upper layer protocols including IP and IPX. PPP uses another of its major components, the Link Control Protocol (LCP), to negotiate and setup control options on the WAN data link.

HDLC is Cisco's default encapsulation type on point-to-point links. It is used typically when communicating with another Cisco device. HDLC specifies data encapsulation method on serial synchronous serial lines using frame characters and checksums. Frame Relay can transmit data very rapidly by using a simplified framing with no error correction mechanisms over high-quality digital facilities. Frame relay is a common WAN protocol and it is very widely used.

5. Describe what a hierarchical WAN design model is and what are the major benefits.

Network designs tend to follow one of two general design strategies: mesh or hierarchical. In a mesh structure the net topology is flat; all router perform essentially the same functions, and there is usually no clear definition of where specific functions are performed. Expansion of the network tends to proceed in a haphazard, arbitrary manner. In a hierarchical structure the network is organized in layers that each have one or more specific functions. Benefits to using a hierarchical model include the following:

• Scalability
• Ease of Implementation
• Ease of Trouble Shooting
• Predictability
• Protocol Support
• Manageability

6. Describe the functions of each layer in a three layer hierarchical WAN model.

Core - Provides fast wide-area connections between geographically remote sites, tying a number of "campus" networks together in a corporate or enterprise WAN. Core links are usually point-to-point, and there are rarely any hosts in the core layer. Core services are typically leased from a telecom service provider.

Distribution - Refers to the distribution of network services to multiple LANs within a campus network environment. This layer is where the "campus backbone" network is found, typically based on Fast Ethernet. This layer is implemented on sites that are large and is used to interconnect buildings.

Access - Usually a LAN or a group of LANs, typically Ethernet or Token Ring, that provide users with frontline access to network services. The access layer is where almost all hosts are attached to the network, including servers of all kinds and user workstations.

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