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Homework 3
Out: Wednesday October 10
Due: Monday October 15
Turnin: Online; details TBA
- Suppose you were designing a protocol intended to be carry digital
telephone calls. What approach to reliable transmission would you take?
Briefly explain your reasons.
- Describe, in (just) enough detail to make clear it works, a sliding
window protocol that uses selective ACKs. That is, instead of ACKing each
arriving frame with the number of the first missing frame, another scheme (of
your design) could be used in an attempt to reduce the number of frames that
are retransmitted when an error occurs.
For the purposes of this question, you can assume that transmitted frames
arrive in the order sent, except for those that are lost.
Also, you have no information about what the error rate might be.
Your protocol should work correctly (reliably delivering all frames
to the receiver-side application, in order, and reasonably promptly)
using finite resources, no matter what the error rate is.
You should think about frame formats when designing your protocol, and
your description should include enough information that we understand
how the sender and receiver will be able to decode any frames they receive.
Also, in any reasonable design frame sequence numbers will be limited to
a finite range. Your protocol needs to deal with that restriction.
-
Just like Ethernet and 802.11 wireless, USB has a protocol specification.
In contrast to those other protocols, USB addresses are handed out
dynamically: when a device is connected, the host picks a currently unused
7-bit address and assigns it to the device. That 7-bit address is then
used in all frames involving that device so long as it remains connected.
(The next time it is connected it may get a different address.)
Besides the fact that 7 bits is smaller than 48 bits, what advantage is
there to this dynamic assignment scheme, relative to the 802.2 addresses
used by Ethernet and 802.11?
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