A few main factors drive
network scalability on the campus. First, bandwidth and latency
performance become more important as existing and emerging applications
are and will be requiring higher bandwidth. The typical 80/20 rule (80
percent of the network traffic is local compared to 20 percent to the
backbone) is being reversed such that 80 percent of the traffic is now
destined for the backbone. This setup requires the backbone to have
higher bandwidth and switching capacity.
Both ATM and Gigabit Ethernet
solve the issue of bandwidth. ATM provides a migration from 25 Mbps at
the desktop, to 155 Mbps from the wiring closet to the core, to 622 Mbps
within the core. All this technology is available and shipping today.
ATM also promises 2.4 Gbps of bandwidth via OC-48, which was available
and standard at the end of 1997. Ethernet currently provides 10 Mbps to
the desktop, with 100 Mbps to the core. Cisco has provided Fast
EtherChannel® as a mechanism of scaling the core bandwidth and providing
a migration to Gigabit Ethernet.
Second, a scalable campus
networking architecture must account for existing desktops and
networking protocols. This scenario forces compatibility with current
desktop PCs, servers, mainframes, and cabling plants. Large enterprise
networks have invested millions of dollars into this infrastructure.
Also, in order to ensure a smooth migration, existing LAN protocols must
be supported in some way in order to assure a smooth migration.
Quality of service (QoS) has
increased in visibility, as network managers require some traffic to
have higher-priority access to the network relative to other traffic,
particularly over the WAN. The options for QoS include Guaranteed QoS,
where a particular user or “flow” is guaranteed performance, and class
of service (CoS), which provides best-effort QoS, and finally, increased
bandwidth such that contention for that bandwidth is no longer an issue.
Ethernet promises to provide
CoS by mapping priority within the network to mechanisms such as
Resource Reservation Protocol (RSVP) for IP as well as other mechanisms
for Internetwork Packet Exchange (IPX). ATM guarantees QoS within the
backbone and over the WAN by using such mechanisms as available bit rate
(ABR), constant bit rate (CBR), variable bit rate (VBR), and unspecified
bit rate (UBR).
Both ATM and Ethernet attempt
to solve similar application-type problems. Traditionally, Ethernet and
Fast Ethernet have been utilized for high-speed backbone and riser
connectivity. A common application, for example, is to provide switched
or group-switched 10 Mbps to each desktop, with Fast Ethernet
connectivity to and within the core. This scenario can be accomplished
at a relatively low cost. Gigabit Ethernet promises to continue scaling
that bandwidth further. Recently, ATM has also been utilized to build
campus-wide backbones at a moderate price range. However, the key
benefit of ATM has been seen in the metropolitan-area network and in the
wide-area network. WAN integration and compatibility has been a
significant driver in scaling campus networks. The importance of
integrating data types such as voice, video, and data over a WAN has
been a significant driver for service integration and will be key in
reducing the cost of WAN services and maintenance.