Backbone Design

Backbone Design

Backbone Design

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A babackckbbonone e is is a a mmeaeans ns of of coconnnenecctitinng g ttwo wo or or momore re LALANsNs. . It It prproovividedes s aa transmission channel for

transmission channel for packets being transmitted from packets being transmitted from one LAN to one LAN to another. another. After After  connection to a backbone, a LAN may remain distinct or be merged with another. connection to a backbone, a LAN may remain distinct or be merged with another. Ind

Indiviividuadual l LANLANs s are are conconnecnected ted to to the backbthe backbone one netnetworwork k usiusing ng somsome e typtype e of of  device. The type of device used to connect to the backbone can vary—it may be a device. The type of device used to connect to the backbone can vary—it may be a hub, a repeater, a bridge, a router, or a gateway—depending on the purpose of the hub, a repeater, a bridge, a router, or a gateway—depending on the purpose of the  backbone.

 backbone. ackb

ackbone networkone networks s can be can be applapplied to ied to a a singlsingle e buildbuilding environming environment as ent as well as well as toto campus environments, where the backbone is used to connect LANs in different campus environments, where the backbone is used to connect LANs in different  buildings. It is possible to find both types of

 buildings. It is possible to find both types of backbone networks in a single facilitybackbone networks in a single facility  —there

 —there is is a a backbone backbone network network in in place place in in each each building building and and a a separate separate campuscampus  backbone is used to c

 backbone is used to connect these in!buildonnect these in!building backbones.ing backbones. ac

ackbokbone ne netnetworworks ks may may alsalso o be be useused d to to impimplemlement ent a a LAN LAN envenviroironmenment nt thathatt  provides for

 provides for centrali"ed management. Icentrali"ed management. In such n such an environment, an environment, all network all network serversservers are moved to one central location. The servers are connected to each other via a are moved to one central location. The servers are connected to each other via a high!speed network backbone. The different LANs are also connected to this same high!speed network backbone. The different LANs are also connected to this same  backbone

 backbone using using bridge bridge technologytechnology. . The The network network backbone backbone allows allows the the stations stations onon the LANs to communicate with the servers.

Backbone network classification

A backbone network can be broadly classified into five categories on the basis of  transmission media, topology, access control, transmission mode and speed

#. Transmission $edia

It is recommended that the media to be used as a transmission channel for a local %i.e., non wide!area& backbone network follow the specifications made in the AN'I(TIA()IA!*+!A standard. AN'I(TIA()IA!*+!A recogni"es four backbone transmission media, which shall be used individually or in

combination- #// 0 1T2 backbone cable.  #*/ 0 'T2!A cable.

 +3.*(#3* 4m multi!mode optical fiber cable.  'ingle!mode optical fiber cable.

3.  Topology

As is the case in LAN architecture, the backbone network has both a physical topology and a logical topology. The physical topology describes the actual appearance of the network—the manner in which the transmission media are  placed and how devices are attached to the backbone network. That is, the actual  pathway for transmissions. The logical topology describes how signals are sent over the backbone network. This is largely a factor of the technology used to access the backbone.

Physical design

The physical design of the backbone network differs very little from other LAN designs. 5ften, it follows a linear bus, a ring or a hierarchical star topology.

a& Linear bus backbone

1sing a linear bus configuration for the backbone network re6uires a separate  backbone cable to which backbone access devices are connected. These devices

 b& 7ierarchical star backbone

The hierarchical star is the topology recommended by AN'I(TIA()IA!*+!A. In such a configuration, the devices connecting to the LANs are also connected to a central device, forming the star.

Logical design

The two choices for carrying backbone network traffic are the distributed environment and the centrali"ed environment. They differ in the manner with which multiple networks are connected.

a& 8istributed backbone network 

A distributed backbone network is one where the backbone transmission media is shared among all of the devices accessing this backbone. An e9ample of such an environment is an :88I backbone.

 b& ;entrali"ed optical cabling

ecause of the increased distance capabilities of optical fiber, selected users of fiber!to the! desk are taking the collapsed backbone one step further. This approach allows the telecommunications closet to be entirely passive< however, it does

re6uire a two fiber path in the backbone for each station. =. Accessing the backbone Network 

The various devices used to link LAN segments operate at different layers of the 5'I model. These linking devices, or relay devices, can be categori"ed as

 belonging to one of four basic types. These are as follows- The repeater.

 The bridge.  The router.  The gateway.

a& >epeater 

A repeater is considered to be the simplest form of an interconnection device and is used to link networks at the 2hysical layer of the 5'I model. It is essentially a non! intelligent device used to move all data packets or frames received from one LAN segment to another LAN segment. A repeater makes no decision regarding the source or destination of a packet. The main function of a repeater is to e9tend the length of a network. >epeaters are add!on devices used to strengthen a transmission signal. In the case where digital signaling is used, the repeater  actually regenerates the signal.

 b& ridges

A bridge is a device that provides a communications pathway between two LANs, typically using the same network technology. ridges are used to create a single logical network and are sometimes used to interconnect networks that have already  been e9tended using repeaters. In its simplest form, the bridge is considered to be an intelligent repeater because it is capable of deciding whether to forward a frame or not. A bridge functions at the 8ata Link layer of the seven!layer 5'I reference model.

c& >outers

>outers operate at the Network Layer of the 5'I model. The addressing scheme of  this protocol is used to move data frames through the system from a source device to a destination device. >outers can provide interconnectivity in local and(or wide area environments. They also provide traffic control and filtering functions when there are multiple pathways between the end LANs.

d& ?ateways

?ateways are devices used to translate transmissions between two computer  systems. They are used when there are significant differences between the network  architectures which need to communicate—including differences in communications protocols, data formatting structures, and(or languages. $ost gateways operate at the Application layer of the 5'I model. A common use of  gateways is to interconnect and translate two proprietary protocol stacks such as 'NA %'ystems Network Architecture& to 8NA %8igital Network Architecture& or  AppleTalk to T;2(I2.