8/16/2019 Routing in Telephone Network

1/27

Routing in Telephone

Network 

 

Advanced Data communication andNetworking

By: AmanuelTadele

8/16/2019 Routing in Telephone Network

2/27

8/16/2019 Routing in Telephone Network

3/27

What’s routing?

• is the process o selecting &est paths in anetwork'

• Or interconnecting (e)ices"*Cs+telephones,'# using &est possi&le path

a)aila&le• Routing is perore( or any kin(s o

networks+ inclu(ing the telephone network"circuit switching#+ electronic (ata networks

"such as the -nternet#+ an( transportationnetworks

• Routing is a critical unction in the glo&al

switche( telephone network'Routing in Telephone Network 3

8/16/2019 Routing in Telephone Network

4/27

Classifcation o Routing

Routing

Telephone

Hierarchical Dynamic

DNHR TSMR RTNR …More

Packet

Static Dynamic

Routing in Telephone Network 4

8/16/2019 Routing in Telephone Network

5/27

Town A

Routing in telephone Networks

• Routing in %echanical $witching .ra

Routing in Telephone Network

Town !

Town "

8/16/2019 Routing in Telephone Network

6/27

Routing in telephone Networks

• /ter intro(uction o autoatic 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 (i4erentplaces5 there was no routing in)ol)e(

•  The nee( or routing arose or two priary reasons0' 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 (irectlyconnecte( links

7' it was recogni8e( that soe trunk groups were less

utili8e( copare( to others5 thus+ i there were any wayto take a()antage o this &y routing calls through lessutili8e( trunk groups+ capacity e9pansion coul( &ea)oi(e('

•  

Routing in Telephone Network #

8/16/2019 Routing in Telephone Network

7/27

Routing in telephone Networks

• *araeters to consi(er when thinking a&out routing

(uring 0123s1. 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 storagenor information exchange was possible

2. looping must be avoided at all ties

2' the call setup was accoplishe( through progressive callcontrol (!!) by forwarding setup signaling from oneswitch 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 controlcannot get bac' to a switch from where it started" therewas no way to loo' bac'ward.

Routing in Telephone Network $

8/16/2019 Routing in Telephone Network

8/27

Routing in telephone Networks

• Consi(er this e9aple

•

How to /)oi( this ;oop?• Di4erentiate .9changes &y setting the to (i4erent

Hierarchy

Routing in Telephone Network %

 A !

" D

loop

8/16/2019 Routing in Telephone Network

9/27

Hierarchical Routing

• .9changes are put at (i4erent Hierarchy

• the trunkgroups in hierarchical routing networks areclassife( into two groups: high#usage ()trunkgroups an( *nal trunkgroups

• H< groups since they are not necessary &ut are

installe( &ecause o the high )olue o tra=c&etween those en( no(es connecting suchtrunkgroups'

• / *nal trun'group eans that there is no other

trunkgroup to o)er>ow to i a call (oes not fn( acircuit on a fnal trunkgroup

Routing in Telephone Network &

8/16/2019 Routing in Telephone Network

10/27

Hierarchical Routing

• Rules o Hierarchical routing are

0' / switch in a higher le)el ust ha)e the switchingunction o the lower le)el in a neste( anner'

 This is known as the multiple switching functionrule'

7' Calls ust &e route( through the (irect switchhierarchy+ &oth at the originating switch an( the(estination switch' This is known as the two#ladderlimit rule.

2' or a call ro one area to another+ a H<trunkgroup ro a switch in the originating area toa switch at the ne9t higher le)el in the (estinationarea is a preerre( selection o)er the fnaltrunkgroup to the switch at a le)el (irectly a&o)eit' This is known as the or(ere( routing rule'Routing in Telephone Network '(

8/16/2019 Routing in Telephone Network

11/27

Hierarchical Routing

• Consi(er e9aple

Routing in Telephone Network ''

 A !

" D ') No*e+ A , ! are on the Same la+tHierarchy an* Name* a+ "entral

o--ice."/0 or 1n* o--ice

2) Trunk roup A!AD ,!" are H5

group+

3) Trunk roup "D i+ 6inal Trunk roup4) 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”

8/16/2019 Routing in Telephone Network

12/27

Hierarchical Routing

• $o ar we ha)e seen two le)el Hierarch &ut in real

Network there are f)e o the

Routing in Telephone Network '2

8/16/2019 Routing in Telephone Network

13/27

Hierarchical Routing

• -n @eographical *erspecti)e

Routing in Telephone Network '3

8/16/2019 Routing in Telephone Network

14/27

;iitation 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 aset o rules+ it also le( to situations in which soetrunkgroups coul( not &e use( or routing e)enthough capacity was a)aila&le

Routing in Telephone Network '4

 A !

" D A Call from C to D can only take theroute 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

"his is inefficient use of resource

8/16/2019 Routing in Telephone Network

15/27

Roa( to Dynaic Routing

• Due to (i4erent tie 8ones in the

8/16/2019 Routing in Telephone Network

16/27

Roa( to Dynaic Routing

•  Three iportant (ri)ers that le( to all (ynaic

routing etho(s to liit calls to a a9iu o twolinks are:

0' /n issue was how to han(le the looping pro&le' -t iseasy to see that the looping pro&le can &e easilyhan(le( with a a9iu o two links or a call:

• a call can &e going (irectly ro the ingress switch to theegress switch on a (irect link5

• i this link is &usy+ the call can try another route going rothe ingress switch to an intere(iate switch' Theintere(iate switch on recei)ing the call knows that the call

nee(s to &e sent (irectly to the egress switch+ not anotherintere(iate switch+ (ue to the liit on the nu&er o links'

7' keep the cople9ity (own+ or e9aple+ i the loopingpro&le coul( &e a((resse( easily without intro(ucingsotware cople9ity'

2' -ntro(ucing ore than two links +gain was not signifcant+i'e'+ the &locking woul( go (own ro 0 to a&outRouting in Telephone Network '#

8/16/2019 Routing in Telephone Network

17/27

Roa( to Dynaic Routing

•  Two New intro(uctions (ue to Dynaic routing are

+riginating !all !ontrol(+!!) an( !ran' bac' • -n OCC Call setup is controlle( &y originating switch

an( not progressi)ely orwar(e( to ne9t hop

• the unctionality o returning a call to the

originating switch an( trying another route is calle(!ran'bac'

• with Dynaic routing we ha)e an option to use OCCan( Crank &ack which were not a)aila&le in

Hierarchical routing schees

Routing in Telephone Network '$

8/16/2019 Routing in Telephone Network

18/27

*CC )s' OCC with crank&ack

Routing in Telephone Network '%

3

2

4

'

Call from 1 to 2 uing !CC

"ine #uy

  "  i  n e   #  u    y

" i  n e  # u     y  Elocke(

$uccess

8/16/2019 Routing in Telephone Network

19/27

*CC )s' OCC with crank&ack

Routing in Telephone Network '&

3

2

4

'

Call from 1 to 2 uing $CC with Crank#ack

"ine #uy

" i  n e  # u     y  

$uccess

"rank8ack

8/16/2019 Routing in Telephone Network

20/27

Dynaic Nonhierarchical Routing"DNHR#

• is the frst ipleente( (ynaic routing schee' -t

was frst (eploye( in /TFT’s long!(istancetelephone network in 01G an( was retire( in 0110'

• DNHR is a tie!(epen(ent routing' This eans thatthe set o routes a)aila&le "an( their or(er# at

(i4erent ties o the (ay is (i4erent'• 7!hour tie perio( spanning a A!(ay week was

(i)i(e( into 0I loa( set perio(s: 03 or theweek(ays an( I or weeken(s' The (i4erent

nu&er o loa( set perio(s was (eterine( &ase(on un(erstan(ing tra=c patterns'

• /ll No(es Eelong to the sae ;e)el" Class less#

Routing in Telephone Network 2(

8/16/2019 Routing in Telephone Network

21/27

Dynaic Nonhierarchical Routing"DNHR#

• or each loa( set perio(+ &ase( on tra=c proJection+

a set o routes is copute( ahea( o tie' Typically+tra=c proJection an( routing coputation werecopute( o4!line 0 week in a()ance an( therouting ta&le is then uploa(e( to each switch in the

network'•  These are reerre( to as engineered paths

•  To alle)iate Real tie Eurst tra=c new paths areprepare( in real!tie &asis' these a((itional paths

are reerre( to as real#time paths'• - the &locking &etween a pair o switching no(es goes &eyon(

an accepta&le threshol(+ a new estiation o tra=c o)ere)ery I!in win(ow is in)oke('

• Ease( on this (ata new paths are copute( an( then loa(e(

into the network switches'Routing in Telephone Network 2'

8/16/2019 Routing in Telephone Network

22/27

Dynaic Nonhierarchical Routing"DNHR#

Routing in Telephone Network 22

8/16/2019 Routing in Telephone Network

23/27

 Trunk $tatus %ap Routing"T$%R#

• is an .9tension o the DNHR uses centrali8e( Trunk

$tatus %ap to pro)i(e Real tie routing (ecision inDNHR network

• @ets up(ate ro $*C switches a&out nu&er o-(le trunks e)ery T secon(s

•  These up(ates are sent only when the nu&er o-(le trunks in the trunk group has change('

• -n return T$% perio(ically sen(s to $*C switchesor(ere( routing seBuence to &e use(

•  These routes are (eterine( in real tie &y T$%Rstrategy an( uch ore Dynaic than DNHR

Routing in Telephone Network 23

8/16/2019 Routing in Telephone Network

24/27

 Trunk $tatus %ap Routing"T$%R#

•  There are our alternati)e approaches or T$%R

0' Route each call on the least loa(e( path"*ath ha)ingore nu&er o i(le circuits#

7' Route Call frst on Direct *ath i it e9ists an( a)aila&le+ orelse selecte least loa(e( path

2' Route .ach call frst on *ath assigne( &y

8/16/2019 Routing in Telephone Network

25/27

 Trunk $tatus %ap Routing"T$%R#

Routing in Telephone Network 2

9 :- we u+e DNHR call routing +e;uence -rom A to D i+ AD→ A"

D→

 A!D thi+ lea7e+ no trunk -or call A to " or " to D9 !ut TSMR routing +e;uence will 8e AD→ A!D→ A"D) +o Ne

8/16/2019 Routing in Telephone Network

26/27

 Trunk $tatus %ap Routing"T$%R#

• /)erage Elocking DNHR )s' T$%R on a)erage

&usiness (ay

Routing in Telephone Network 2#

8/16/2019 Routing in Telephone Network

27/27

 Thank Kou

2$

धनयवद