The document discusses a time multiplexed time switch that allows time slot interchange (TSI) of sample values, resulting in inherent delays between input and output samples. It explains the operation, memory access, and cost efficiency compared to a traditional space division switch, highlighting the significant cost advantage of using a TSI switch. An example illustrates the operational parameters and costs, demonstrating the benefits of the TSI approach in multiplexing channels.

2. Time Multiplexed Time Switch
• Unlike time multiplexed space switches, it
permits time slot interchange (TSI) of
sample values.
• Such an operation necessarily implies a
delay between the reception and the
transmission of a sample.
• Illustration in next graph.

3.  M channels are multiplexed on
each trunk
 The switch is organized in
sequential write/ random read
fashion
 Time slot duration, tTS= 125/M
 Time slot clock runs at the time
slot rate
 Time slot counter is incremented
by 1 at the end of each time slot.
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TIME SLOT INTERCHANGE SWITCH

4. COMPONENTS
 Contents of counter provides location addresses
for the data memory and the control memory.
 Data memory and control memory access take
place simultaneously at the starting of the time
slot.
 Contents of the control memory are used as the
address of the data memory and the data read out
to the output trunk
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5.  Even if there is no time slot interchange, a sample
is delayed by a minimum of one time slot in action.
 Depending on the output time slot, delay range is
tTS to MtTS microsec.
 In the example given in figure 1st location in CM
contains value 1 which implies that the contents of
input time slot 1 is switched to output time slot 1.
Delay for this sample is tTS microsec
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6.  Location 2 contains 7. Therefore, input time slot 7
is switched to output time slot 2.
Delay for this sample: (M – (7-2) + 1)tTS μ s
=(M – 4)tTS μ s
 Location 3 contains 4. Therefore, input time slot 4
is switched to output time slot 3.
Delay for this sample: (M – (4-3) + 1)tTS μ s
=MtTS μ s = 125 μ s
There are two sequential memory access per time
slot. So, time constraint may be stated as
tTS = 2tm, 125 = 2Mtm
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7. Cost estimation
 No switching elements!
 Cost is equal to the number of memory locations.
 There are M locations each in the control and data
memory
 So, total cost is given by
C = 2M units
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8. EXAMPLE
 Suppose there is a TSI switch with a single input and single
output trunk multiplexing 2500 channels.
So,
tm =125µs/2M=(125*10-6)/(2500*2) = 25 ns
and C = 2 * 2500 = 5000 units
This switch is non-blocking and fully available.
 An equivalent single stage Space Division Switch uses a
matrix of 2500 X 2500. So, cost is 6.25 million units!
Cost advantage of time switch = (6.25*106)/5000 = 1250
Thus a TSI switch is a lot cheaper.
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9. THANK YOU