# communication skill (DOC)

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```					ATM Networks                                                     CSE
884
Homework 1                                                       20
marks

1. Why do ATM networks use cell switching?[1]

2. Why is virtual circuit switching critical for ATM networks? (Please
list three reasons )[1]

3. What are the "adaptation layers"? Are they in the switches? Are
they in the end-hosts?[1]

4. Is it practical to build a large (i.e., with lots of ports) input buffered
ATM switch with fast links? Why or why not?[2]

5. Is it practical to build a large (i.e., with lots of ports} outputbuffered
ATM switch with fast links? Why or why not?[2]

6. How many low-bit-rate calls can be supported by AAL2 in a single
ATM connection?[2]

7. Estimate the bit rate of the connection if an AAL2 carries the
maximum number of calls carrying voice at 12 kbps.[2]

8. Compare the overhead of AAL3/4 with that of AAL5 for a 64Kbyte
packet.[2]

9. Explain how the three-bit sequence number in the AAL1 header can
be used to deal with lost cells and with miss inserted cells.[2]

10. Suppose that an ATM connection carries voice over AAL-1.
Suppose that the packetization delay is to be kept below 10
ms.Calculate the percentage of overhead if the voice is encoded
using PCM.[2]

11. Explain how the header error checksum can be used to synchronize
to the boundary of a sequence of contiguous ATM cells. What is the
probability that an arbitrary five-odd block will satisfy the header
error checksum? Assume bits are equally likely to be 0 or 1. What is
the probability that two random five-octet blocks that correspond to
two consecutive headers pass the error check?[3]

```
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