Quiz Notes
CS-652, Previous Midterm, Answers 1. Consider a 512x512 Time-Space-Time (TST) switch. It is given that this TST switch uses 16x16 Time Switches in the 1st stage, the RAM access time is 60 nsec, and the forwarding delay through its Cross-Bar switching module is 8 nsec. What is the total time to forward bytes from the input to the output ports? Since 16x16 we will have 512 :16 = 32 32x32 cross bar switch. Delay: 16*60 +16*(60+8) +16*60 = 960*2 + 1088= 3008 nsec = 3.008 µsec
2. A Time Division switch uses a Time Slot Interchange with Random Access Memory time of 50 nanosec. How many T1 lines can this switch handle?
The switch should be able to handle N inputs so that: 2*N*50 ≤ 125000 1250/24 = 52 T1s Each T1 brings in 24 bytes N = 1250
3. We want to design a 1200x1200 three stage switch. If we use 40x20 crossbar switches in the 1st stage, then what types of cross bar switches must be used in the 2nd and 3rd stage? How many crossbar switches are needed in each stage? What is the total number of cross points in all three stages of this switch? Now consider input port 250 and output port 512. How many different paths between these two ports does this switch provide? (Explain why)
We need 1200/40 = 30 40x20 switches in the 1st stage 30 20x40 switches in the 3rd stage. 20 30x30 switches in the 2nd stage and
Total number of cross points: 30 x 40x20 + 20 x 30x30 + 30 x 20x40 = 2*30*800 + 20*900 = = 48000+18000 = 66000 cross points Each out port of a 40x20 crossbar of the 1st stage can reach any output port 20 different paths
4. A video application generates a byte stream at a constant rate of 400 Kbytes/sec. You want to build a 18x18 Time Division Circuit Switch that will enable the simultaneous switching of 18 such video applications. If your switch uses Time Slot Interchange (TSI), then what should be the RAM access time of the TSI that will enable you to do that? Note that a circuit switch forwards only one byte per input port at a time. (Show your
2. A Time Division switch uses a Time Slot Interchange with Random Access Memory time of 50 nanosec. How many T1 lines can this switch handle?
The switch should be able to handle N inputs so that: 2*N*50 ≤ 125000 1250/24 = 52 T1s Each T1 brings in 24 bytes N = 1250
3. We want to design a 1200x1200 three stage switch. If we use 40x20 crossbar switches in the 1st stage, then what types of cross bar switches must be used in the 2nd and 3rd stage? How many crossbar switches are needed in each stage? What is the total number of cross points in all three stages of this switch? Now consider input port 250 and output port 512. How many different paths between these two ports does this switch provide? (Explain why)
We need 1200/40 = 30 40x20 switches in the 1st stage 30 20x40 switches in the 3rd stage. 20 30x30 switches in the 2nd stage and
Total number of cross points: 30 x 40x20 + 20 x 30x30 + 30 x 20x40 = 2*30*800 + 20*900 = = 48000+18000 = 66000 cross points Each out port of a 40x20 crossbar of the 1st stage can reach any output port 20 different paths
4. A video application generates a byte stream at a constant rate of 400 Kbytes/sec. You want to build a 18x18 Time Division Circuit Switch that will enable the simultaneous switching of 18 such video applications. If your switch uses Time Slot Interchange (TSI), then what should be the RAM access time of the TSI that will enable you to do that? Note that a circuit switch forwards only one byte per input port at a time. (Show your