last updated March 8, 04 M. Veeraraghavan 1

TSI (Time Slot Interchange)

• Let the contents of time slots 1 through 24 be as shown on the incoming line.• The switch configuration requires data in slot 1 to be read into slot 24 and vice

versa, and data in slot 2 to be read into slot 23 and vice versa

1224abc

1224cda

d

b23

23a

b

c

d

1

2

23

24

writes inorder of arrival

permutes as per switch configurationand reads out

last updated March 8, 04 M. Veeraraghavan 2

From space switch to T-S-T switch

• The intermediate stage switch is a single switch of size:

n 12....

n 12....

n 12....k 12....

k 12....k 12....

k 12....

k 12....

k 12.... n 12....

n 12....

n 12....

TSI 1

TSI 2

TSI N/n TSI N/n

TSI 2

TSI 1n

N

n

N

n

N

n

N

The intermediate stage switch is reprogrammed for each of the k time slots.

Replace each first-stage and every last-stage switch by a TSI. Replace multipleintermediate-stage switch with a single time-shared space switch.

last updated March 8, 04 M. Veeraraghavan 3

B

VIEW WITH ANIMATION

A C

D

Program the two sets of TSI stages and the intermediate space stage accordingly A->C, B->A, C->D, D->B

The time to send three slots between 1st stage and 2nd stage is the same as the time to receive two slots into the 1st stage.

D1 could have been sent in the first slot on L2 because it could have been sent out on L4 in time slot 1 and then switched around by TSI 4 to the appropriate slot going to D

2 x 3(TSI 1)

B1 A1Connected to A and B

B1 A1

L1

2 x 3(TSI 2)

D1 C1Connected to C and D

D1 C1

L2

t=1

A1

L3

L4

3 x 2(TSI 3)

3 x 2(TSI 4)

Connected to C and D

Connected to A and B

A1

B1

C1

C1

B1

t=2

D1

D1

t=3

last updated March 8, 04 M. Veeraraghavan 4

Programming the switch

• Means setting the operational behavior of all the TSIs and the time-shared space switch

• Previous slide example:– TSI1: TS1->TS1; TS2->TS2; blank->TS3– TSI2: blank->TS1; TS1->TS2; TS2->TS3– TSI3: TS1->unmapped; TS2->TS1; TS3->TS2– TSI4: TS1>TS1; TS2->TS2; TS3->unmapped– time-shared switch

• at time = 1, cross-over• at time=2, direct• at time=3, cross-over