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36 Cards in this Set
- Front
- Back
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Three functions of the transport layers |
1. Flow control 2. Error control 3. Congestion control handles process to process connection/communication |
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Well known port numbers |
0-1023 |
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registered |
1024-49151 |
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dynamic/private |
49152-65535 |
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Who checks the port numbers? |
The OS |
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SNMP |
simple network management protocol UDP based to handle printers, devices, etc. |
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tftp |
trivial ftp used to boot router, send to router files like firmware updates etc. |
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Socket address |
1. Port number provided by transport layer 2. IP address provided by network layer |
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Flow control |
control rate of incoming/outgoing packets producer/consumer relationship producer pushes out no matter if consumer can take it. flow control sends a message to producer telling it to stop |
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what kind of requests don't need flow control? |
pull requests |
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Diagram of flow controls |
producer app pushes to consumer transport (flow control) producer transport pushes to consumer transport 2 (flow control) producer application pulls from transport 2 (no flow control) |
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Window size |
amount of the buffer used before stop sending requests if network is under-loaded use larger window size |
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Where does congestion occur? |
routers and switches only |
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Types of errors |
1. packet loss 2. corrupted packet 3. out of order arrival 4. duplicates |
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How to handle loss? |
Sender starts a timer and wait for ACK. if ACK doesn't come before timer expires, resend packet |
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How to handle corrupted? |
checksum used to see if corrupted. Receiver doesn't send anything back to the server. Sender will resend when there is no ACK |
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how to hand out of order arrival? |
append a sequence number to packets if one packet comes in before the other you could just discard that one and wait for a resend in correct order --> higher network traffic as a result |
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how to handle duplicates? |
just discard the duplicate |
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How do you know if you need congestion control? |
if the input rate >= output rate can use the loss rate to determine congestion |
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Sliding window approach |
Use the buffer as a queue. When you get the ACK for first packet sent move pointers to start down one from 1st and down one from end wrap around |
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Connection less communication |
No flow or error. Just pump out a packet as soon as it arrives |
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Stop and Wait |
Window size = 1 supports sequence number timer supported Only need two sequence numbers --> 0,1 |
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Stop and Wait approach |
Send one packet, do not remove from buffer until ACK is recieved |
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What are the sequence numbers used for? |
detecting duplicate packets |
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Range of sequence numbers for stop and wait |
2 = 0,1 |
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What does the receiver send back? |
ACK with next packet number expected. So if it receives packet 0, it will send ACK1 and expect packet 1 next |
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Problem with stop and wait approach |
too slow of bit rate. Bandwidth wasted while waiting for response |
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Network thickness and longness |
thickness - amount of bandwidth long - round trip time |
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Bandwidth delay product |
volume of the pipeline- how many bits in round trip way e.x. 1 Mbps, RTT = 20msec (1*10^6) * (20*10^-3) = 20,000 bits/sec |
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Utilization of stop and wait protocol |
5% if each packet is 1,000 bits and bandwidth delay product is 20,0000 |
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Go back-N protocol utilization (same scenario) |
75% |
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Go back-N protocol |
Sender has multiple spots in window, receiver only has 1 Sender: - sf = first outstanding packet - sn = next packet to send |
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Go back-N protocol on no ACK |
if no ACK is received then it will resend all the packets from sf on to window size disadvantage: waste if only one of multiple is lost |
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Reciever in go back-N protocol |
sends back an ACK with next packet expected. It means that the other packets have arrived successfully window size 1 |
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determining sender window size |
m=2 <-- number of bits (2^m)-1 |
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read textbook before quiz |
read textbook before quiz |
