Routing in Telephone Network

Advanced Data communication and Networking

Routing in Telephone Network  By: Amanuel

Routing in Telephone Network Outline: • What’s routing? • Classifcation o routing • Routing in telephone Networks • Hierarchical Routing • Dynaic Non!Hierarchical Routing "DNHR# •  T  Trunk runk $tatus %ap Routing Routing "T$%R#

What’s routing? •

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is the process o selecting &est paths in a network' Or interconnecting (e)ices"*Cs+ telephones,'# using &est possi&le path a)aila&le Routing is perore( or any kin(s o networks+ inclu(ing the telephone network "circuit switching#+ electronic (ata networks "such as the -nternet#+ an( transportation networks Routing is a critical unction in the glo&al switche( telephone network'

Classifcation o Routing

Routing

Telephone

Hierarchical

DNHR

TSMR

Packet

Static

Dynamic

RTNR

Dynamic

…More

Routing in telephone Networks •

Routing in %echanical $witching .ra

Town !

Town A

Town "

Routing in telephone Networks /ter intro(uction o autoatic switching the nee( or any or o routing (i( not arise until the 0123s • essentially point!to!point (irect links "trunk groups# were set up to connect calls &etween (i4erent places5 there was no routing in)ol)e( •  The nee( or routing arose or two priary reasons •

0' point!to!point links lea( to the pro&le+ i'e'+ i there are N no(es in a network+ we nee( N(N 60 )/ 7 (irectly connecte( links 7' it was recogni8e( that soe trunk groups were less utili8e( copare( to others5 thus+ i there were any way to take a()antage o this &y routing calls through less utili8e( trunk groups+ capacity e9pansion coul( &e a)oi(e('

Routing in telephone Networks •

*araeters to consi(er when thinking a&out routing (uring 0123s 1. During these days switches did not have ability to compute and store routing tables thus routing was to be  performed in an age when neither information storage nor information exchange was possible 2. looping must be avoided at all ties 2' the call setup was accoplishe( through progressive call control (!!) by forwarding setup signaling from one switch to the next" this is to be done in an information# less setting$that is% nodes did not have any ability to exchange any status information. &hus% a call control cannot get bac' to a switch from where it started" there was no way to loo' bac'ward.

Routing in telephone Networks •

Consi(er this e9aple "

D

loop

 A •

!

How to /)oi( this ;oop? •

Di4erentiate .9changes &y setting the to (i4erent Hierarchy

Hierarchical Routing • •

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.9changes are put at (i4erent Hierarchy the trunkgroups in hierarchical routing networks are classife( into two groups: high#usage () trunkgroups an( *nal trunkgroups H< groups since they are not necessary &ut are installe( &ecause o the high )olue o tra=c &etween those en( no(es connecting such trunkgroups' / *nal trun'group eans that there is no other trunkgroup to o)er>ow to i a call (oes not fn( a circuit on a fnal trunkgroup

Hierarchical Routing Rules o Hierarchical routing are 0' / switch in a higher le)el ust ha)e the switching unction o the lower le)el in a neste( anner'  This is known as the multiple switching function rule' 7' Calls ust &e route( through the (irect switch hierarchy+ &oth at the originating switch an( the (estination switch' This is known as the two#ladder limit rule. 2' or a call ro one area to another+ a H< trunkgroup ro a switch in the originating area to a switch at the ne9t higher le)el in the (estination area is a preerre( selection o)er the fnal trunkgroup to the switch at a le)el (irectly a&o)e it' This is known as the or(ere( routing rule' •

Hierarchical Routing Consi(er e9aple

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"

D

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2) 3) 4)

 A

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No*e+ A , ! are on the Same la+t Hierarchy an* Name* a+ "entral o--ice."/0 or 1n* o--ice Trunk roup A!AD ,!" are H5 group+ Trunk roup "D i+ 6inal Trunk roup A call -rom " to D can only take Trunk roup "D a+ it cannot go to lower le7el -or routing

Loop is avoided in this system by the rule “It is not allowed to go down toward its immediate lower-level switch for routing”

Hierarchical Routing •

$o ar we ha)e seen two le)el Hierarch &ut in real Network there are f)e o the

Hierarchical Routing •

-n @eographical *erspecti)e

;iitation o Hierarchical Routing •

hierarchical routing a)oi(e( the looping pro&le &y cle)er use o no(es at (i4erent le)els along with a set o rules+ it also le( to situations in which soe trunkgroups coul( not &e use( or routing e)en though capacity was a)aila&le

"

D

A Call from C to D can only take the route C-D Cannot overflow through C--D or C-A-D even though andwidth is available on the trunk groups C-! -d! C-A and A-D

 A

!

"his is inefficient use of resource

Roa( to Dynaic Routing Due to (i4erent tie 8ones in the