Switching 2 by Mushtaq 221110

Switching Networks Single Stage Network outlets ,consisting of matrix of The fig shows M inlets and N outlets crosspoints ,these may be separate relays or electronics devices or contacts of crosspoints. lo st unless This switch gives full availability , no call lost outgoing trunks are congested. The system contains M x N crosspoints . If M = N then number of crosspoints is : C1 = N² The cost increased as the square of the size of the switch .The efficiency (N/N² = I/N ) decreases decrease s inversely with N. It is uneconomical to use single stage network netw ork for large number of inlets and outlets.

The world's largest digital library

Try Scribd FREE for 30 days to access over 125 million titles without ads or interruptions! Start Free Trial Cancel Anytime.







Switching Networks Single Stage Network a nd 100 outlets For example a switch with 100 inlets and requires 10, 000 crosspoints and only 1% of these can be used at any time. For making connections between large number of trunks are constructed as network containing several stages of switches.







Switching Networks Two

Stage Network nxg

n nxg

n nxg N inlets

M inlets

n

n nxg

nxg







wo Stage Switching Networks

T

g = N/n o f crosspoints per secondary The No. of crosspoints per primary switch = No. of switch = g n = N The total No. of crosspoints C 2 in the network = No. of switches x crosspoints per switch . C2 = 2 g n = 2N²/n (1) Since there is one link from each primary switch to each secondary switch , the No. of links is equal to No. of primary switch x No. of secondary switches = g² = (N/n (N/n )² (2) The No. of crosspoints varies as 1/n and No. of links varies as 1/N² , if n is made large to reduce the No. of crosspoints . There will be few links to carry








T

he total No. of crosspoints crosspoints from equation (1) is : C2 = 2gn = 2N²/n putting value of n = ¥ N C2 = 2N²/ ¥ N C2 = 2 ( N ) 3/2 (4) Select one of nearest integer to n that is factor of N. Crossbar switch may be of size 10 x 10 or 10 x 20 . It is economic to use the network with more than two stages. T








T

Example : Design a two stage network for connecting 200 incoming trunks to 200 outgoing trunks. Let n = ¥200 = 14.14 ,however ,how ever n must be factor fac tor 200, so nearest possible possible values are n= 10 and and n= 20 . Two possible networks are shown below:

n

10x10

20x20

n










T

n

n 10 10








T

he fig (a) have same No. of outgoing and incoming trunks. However concentrator co ncentrator have more incoming trunks than outgoing trunks and expander have more mor e outgoing trunks than incoming trunks . T








T

No. of links = No. No. of primary switches x No. of secondary switches = MN/ mn. Since traffic capacity is limited by No. of outgoing trunks , there is not feasible to to provide more m ore than this number of








T

When m = ¥M Equation (2) m = n = ¥M (4 ) The No. of crosspoints are minimum if No. of inlets per primary switch No. of outlets per secondary switch , from







hree Stage Switching Networks

T F

IG BELOW SHOWS THREE STAGE SWITCH

B Links Links










T








T







T


Switching 2 by Mushtaq 221110

Recommend Documents