However, upgrading the physical wiring can be expensive...

Consequently, network designers generally deploy a campus design that is optimized for the fastest functional architecture that runs on existing physical wire. They might also upgrade wiring to meet the requirements of emerging applications. For example, higher-speed technologies, such as Fast
Ethernet, Gigabit Ethernet, and ATM as a backbone architecture, and Layer 2 switching provide
dedicated bandwidth to the desktop.
Trends in Campus Design
In the past, network designers had only a limited number of hardware options—routers or
hubs—when purchasing a technology for their campus networks. Consequently, it was rare to make
a hardware design mistake. Hubs were for wiring closets and routers were for the data center or main telecommunications operations.
Recently, local-area networking has been revolutionized by the exploding use of LAN switching at
Layer 2 (the data link layer) to increase performance and to provide more bandwidth to meet new
data networking applications. LAN switches provide this performance benefit by increasing
bandwidth and throughput for workgroups and local servers. Network designers are deploying LAN
switches out toward the network’s edge in wiring closets. As Figure 1-3 shows, these switches are usually installed to replace shared concentrator hubs and give higher bandwidth connections to the end user.
Figure 1-3
Example of trends in campus design.
The new wiring closet
Traditional wiring closet
Si
Shared hub
Multilayer switch
(Layers 2 and 3)
LAN switch (Layer 2)
Hub
ATM campus
CDDI/FDDI
switch
concentrator
Cisco router
Cisco router
Traditional backbone
The new backbone
Shared hub
Layer 3 networking is required in the network to interconnect the switched workgroups and to
provide services that include security, quality of service (QoS), and traffic management. Routing integrates these switched networks, and provides the security, stability, and control needed to build functional and scalable networks.
Introduction 1-3
Designing WANs
Traditionally, Layer 2 switching has been provided by LAN switches, and Layer 3 networking has
been provided by routers. Increasingly, these two networking functions are being integrated into
common platforms. For example, multilayer switches that provide Layer 2 and 3 functionality are
now appearing in the marketplace.
With the advent of such technologies as Layer 3 switching, LAN switching, and virtual LANs
(VLANs), building campus networks is becoming more complex than in the past. Table 1-1
summarizes the various LAN technologies that are required to build successful campus networks.
Cisco Systems offers product solutions in all of these technologies.
Table 1-1
Summary of LAN 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
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
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.
Network designers are now designing campus networks by purchasing separate equipment types (for
example, routers, Ethernet switches, and ATM switches) and then linking them together. Although
individual purchase decisions might seem harmless, network designers must not forget that the entire network forms an internetwork.
It is possible to separate these technologies and build thoughtful designs using each new technology, but network designers must consider the overall integration of the network. If this overall integration is not considered, the result can be networks that have a much higher risk of network outages,
downtime, and congestion than ever before.
Designing WANs
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 the WAN. WAN communication is often called a service because the network provider often charges users for the services provided by the WAN (called tariffs). WAN