Campus Arrangement Models
A campus arrangement is an action arrangement consisting of abounding LANs in one or added buildings,
all affiliated and all usually in the aforementioned geographic area. A aggregation about owns the entire
campus network, as able-bodied as the concrete wiring. Campus networks usually abide of Ethernet,
Token Ring, and FDDI LANs and higher-speed Fast Ethernet, Fast EtherChannel, and Gigabit
Ethernet LANs.
An compassionate of cartage breeze is a basic allotment of the campus arrangement design. While high-speed
LAN technologies can be leveraged to advance any cartage movement, the accent should be
on accouterment an all-embracing architecture acquainted to known, studied, or predicted cartage flows. The network
traffic again can be finer confused and managed, and the campus arrangement can be scaled to
support approaching needs.
24 Chapter 2: Campus Arrangement Architecture Models
The abutting sections present assorted arrangement models that can be acclimated to allocate and additionally to design
campus networks. Beginning with acceptable aggregate networks, the models body on anniversary other
to advantage cartage movement and accommodate anticipated behavior.
Shared Arrangement Model
Campus networks accept commonly been complete of a distinct LAN for all users to connect
to and use. All accessories on the LAN were affected to allotment the accessible bandwidth. LAN media
such as Ethernet and Token Arena both accept ambit limitations, as able-bodied as limitations on the
number of accessories that could be affiliated to a distinct LAN.
Network availability and achievement both beneath as the cardinal of affiliated devices
increased. For example, an Ethernet LAN appropriate all accessories to allotment the accessible 10-Mbps
half-duplex bandwidth. Ethernet additionally acclimated the carrier faculty assorted admission blow detect
(CSMA/CD) arrangement to actuate back a accessory could abode abstracts on the aggregate LAN. If two
or added accessories approved to abode at the aforementioned time, arrangement collisions occurred and all devices
had to become bashful and delay to retransmit their data. This blazon of LAN is a blow domain
because all accessories were affected to collisions. Token Arena LANs are not affected to
collisions because they are deterministic and acquiesce stations to abode alone back they receive
a “token” that passes about the ring.
One band-aid acclimated to abate arrangement bottleneck was to articulation or bisect a LAN into discrete
collision domains. This band-aid acclimated cellophane bridges, which alone forwarded Band 2 data
frames to the arrangement articulation area the destination abode was located. Bridges enabled the
number of accessories on a articulation to be reduced, lessened the anticipation of collisions on
segments, and added the concrete ambit limitations by acting as a repeater.
Bridges commonly advanced frames to the LAN articulation area the destination abode is located.
However, frames absolute the advertisement MAC abode (ff:ff:ff:ff:ff:ff) charge be abounding out to
all affiliated segments. Advertisement frames are usually associated with requests for information
or services, including arrangement account announcements. IP uses broadcasts for Address
Resolution Agreement (ARP) requests to ask what MAC abode is associated with a accurate IP
address. Added examples of advertisement frames accommodate IPX Get Nearest Server (GNS) requests,
Service Advertising Agreement (SAP) announcements, Routing Information Agreement (RIP—both
IP and IPX) advertisements, and NetBIOS name requests. A advertisement area is a accumulation of
network segments area a advertisement is flooded.
Multicast cartage is cartage that is destined for a specific set or accumulation of users, behindhand of their
location on the campus network. Multicast frames charge be abounding to all segments because they
are a anatomy of broadcast. Although end users charge accompany a multicast accumulation to accredit their
applications to action and accept the multicast data, a arch charge flood the cartage to all
segments because it doesn’t apperceive which stations are associates of the multicast group. Multicast
frames will use aggregate bandwidth on a segment, but will not force the use of CPU assets on
every affiliated device. Alone the CPUs that are registered as multicast accumulation associates will
actually action those frames. Some multicast cartage is sporadic, as in the case of various
Campus Arrangement Models 25
routing agreement advertisements, while added cartage such as Cisco IP/TV multicast video can
consume best or all the arrangement assets with a abiding beck of real-time data.
Broadcast cartage presents a two-fold achievement botheration on a bridged LAN because all
broadcast frames flood all bridged arrangement segments. First, as a arrangement grows, the broadcast
traffic can abound in admeasurement and absorb the accessible bandwidth. Secondly, all end-user
stations charge accept to, decode, and action every advertisement frame. This action is performed
by the CPU, which charge attending added into the anatomy to see with which high band agreement the
broadcast is associated. While today’s CPUs are able-bodied and ability not appearance a noticeable
degradation from processing broadcasts, banishment accidental advertisement endless aloft every end
user is not wise.
NOTE For a altercation of assay performed by Cisco on the furnishings of assorted agreement broadcasts
on CPU performance, accredit to http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/
nd20e.htm