|
when there are no losses
|
|
|
when every second acknowledgment is discarded due to transmission errors
|
|
|
Transmission links have sometimes different upstream and downstream bandwidths. A typical example are access networks that use ADSL (Asymmetric Digital Subscriber Lines). Consider two hosts connected via an ADSL link having an upstream bandwidth of 1 Mbps and a downstream bandwidth of 50 Mbps. The propagation delay between the two hosts is 10 milliseconds. What is the maximum throughput, expressed in frames/second, that the alternating bit protocol can obtain on this link if each data frame has a length of 125 bytes and acknowledgments are 25 bytes long. Same question if the protocol is modified to support 1500 bytes long data frames.
|
|
|
there are no transmission errors
|
|
|
the Internet checksum used by UDP, TCP and other Internet protocols which is defined in :rfc:`1071` and implemented in various libraries.
|
|
|
The delay between the two hosts is `s` seconds in both directions
|
|
|
The Cyclic Redundancy Checks (CRCs) are efficient error detection codes that are able to detect :
|
|
|
The bandwidth of the two directions of the link is set to `B` bits per second
|
|
|
the 16 bits or the 32 bits Cyclical Redundancy Checks (CRC) that are often used on disks, in zip archives and in datalink layer protocols. See http://rosettacode.org/wiki/CRC-32 for CRC-32 implementations in various languages.
|
|
|
ten frames
|
|
|
Same question when using selective repeat instead of go-back-n. Note that the answer is not necessarily the same.
|
|
|
Same question as above, but assume now that both the sender and the receiver implement selective repeat. Note that the answer can be different from the above question.
|
|
|
Reliable transfer
|
|
|
Reliable protocols rely on different types of checksums to verify whether frames have been affected by transmission errors. The most frequently used checksums are :
|
|
|
Reliable protocols depend on error detection algorithms to detect transmission errors. The following questions will reinforce your understanding of these algorithms.
|
|
|
Practice
|
|
|
Open questions
|
|
|
one frame
|
|
|
Is it possible for a selective-repeat receiver to inter-operate with a go-back-n sender ? Justify your answer.
|
|
|
Is it possible for a go-back-n receiver to inter-operate with a selective-repeat sender ? Justify your answer.
|
|
