Designing Wans

By Author: pangsiyan
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WAN communication occurs between geographically separated areas. In enterprise internetworks,

WANs connect campuses together. When a local end station wants to communicate with a remote

end station (an end station located at a different site), information must be sent over one or more

WAN links. Routers within enterprise internetworks represent the LAN/WAN junction points of an

internetwork. These routers determine the most appropriate path through the internetwork for the

required data streams.

WAN links are connected by switches, which are devices that relay information through the WAN

and dictate the service provided by theWAN.WAN communication is often called a service because

the network provider often charges users for the services provided by theWAN (called tariffs).WAN

services are provided through the following three primary switching technologies:

LAN Technology Typical Uses

Routing technologies Routing is a key technology for connecting LANs in a campus network. It can be

either Layer 3 switching or more traditional routing with Layer ...
... 3 switching and

additional router features.

Gigabit Ethernet Gigabit Ethernet builds on top of the Ethernet protocol, but increases speed ten-fold

over Fast Ethernet to 1000 Mbps, or 1 Gbps. Gigabit Ethernet provides high

bandwidth capacity for backbone designs while providing backward compatibility for

installed media.

LAN switching technologies

Ethernet switching

Token Ring switching

Ethernet switching provides Layer 2 switching, and offers dedicated Ethernet

segments for each connection. This is the base fabric of the network.

Token Ring switching offers the same functionality as Ethernet switching, but uses

Token Ring technology. You can use a Token Ring switch as either a transparent

bridge or as a source-route bridge.

ATM switching technologies ATM switching offers high-speed switching technology for voice, video, and data. Its

operation is similar to LAN switching technologies for data operations. ATM,

however, offers high bandwidth capacity. Introduction 1-5

Trends in WAN Design

Circuit switching

Packet switching

Cell switching

Each switching technique has advantages and disadvantages. For example, circuit-switched

networks offer users dedicated bandwidth that cannot be infringed upon by other users. In contrast,

packet-switched networks have traditionally offered more ?exibility and used network bandwidth

more ef?ciently than circuit-switched networks. Cell switching, however, combines some aspects of

circuit and packet switching to produce networks with low latency and high throughput. Cell

switching is rapidly gaining in popularity. ATM is currently the most prominent cell-switched

technology. For more information on switching technology for WANs and LANs, see Chapter 2,

Internetworking Design Basics.