Transport Layer Schemes

Scheme #1:Just transmit the data
Algorithm for sender: Just send the data. Don't worry about overflowing the receiver or transmission errors
Algorithm for receiver: Read all the data as fast as you can. Buffer as needed.
When does this work: Only if the underlying network handles errors for you, or errors are SO rare you don't care
Example: Streaming Media
Speed: Best posible

Scheme #2: Automatic Repeat Request
Algorithm for sender:

While there is data to send ...
           Start the timer
           Send the packet
           If you get an ack
               Move the pointe to the next packet
               Goto 1
            If the timer goes off

Don't move the pointer
Goto 1

Algorithm for Receiver:

Repeat
    Wait for a packet
    If checksum OK
        Send ACK
        If pointer OK
            Accept data
Until Last packet accepted

When does this work: When Latency is low compared to bandwidth and there are few errors
Example: Human conversation
Speed: Very bad if latency is high compared to bandwidth or if there are lots of errors

Scheme #3: Automatic Repeat Request with NAK
Algorithm for sender:

While there is data to send ...
           Start the timer
           Send the packet
           If you get an ack
               Move the pointe to the next packet
               Goto 1
            If the timer goes off or you get a NAK
               Don't move the pointer
               Goto 1

Algorithm for Receiver:

Repeat
    Wait for a packet
    If checksum OK
        Send ACK
     Else
        Send NAK
        If pointer OK
            Accept data
Until Last packet accepted

When does this work: When Latency is low compared to bandwidth
Example: Human conversation
Speed: Very bad if latency is high compared to bandwidth

Scheme #4: Go Back N
Algorithm for sender:

Function Sendpacket
    Start timer[packetnumber]
    Send packet
While there is data to send
    While there are packets yet to send and within N of the last ack'ed packet
        SendPacket for all the unset packets
     If a Timer goes off
        Sendpacket for all packets within the window and >= the timer that went off
     If an ACK arrives
         Cancel the associated timer

Algorithm for Receiver:

Repeat
    Get a packet
    If checksum OK send ACK
    If this is a new packet and contigous with already accepted data
        Accept the data
Until the last packet is accepted

When does this work: There are few errors
Packets are rarely reordered.
There is enough RAM to buffer latency * bandwidth amount of data
Example:
Speed: Fine if there are only a few errors

Scheme #5: Selective Repeat
Algorithm for sender:

Function Sendpacket
    Start timer[packetnumber]
    Send packet
While there is data to send
     While there are packets within the senders window and not yet sent
        SendPacket the packet
    If a Timer goes off
        Sendpacket for all that packet
     If an ACK arrives
         Cancel the associated timer

Algorithm for Receiver:

Repeat
    Get a packet
    If checksum OK send ACK
    If this is a new packet
        Store the data into a buffer
     Accept any data from the buffer contigious with the already acepted data
Until the last packet is accepted

When does this work: Always, if you have time to code it
Example: TCP, except that TCP does byte numbers instead of packet numbers
Speed: Great

Scheme #5: Checksum 'till Finished
Algorithm for sender:

Function Sendpacket
    Repeat
          r = random()
          c = checksum(all_the_data, r)
          send r and c
      Until (receiver tells you to stop)

Algorithm for Receiver:

Repeat
Get a packet containing r and c
Until sizeof(all the 'c's) > sizeof(data)
Send stop command to the server
Decode the data

When does this work: Always, if you have time to code it and love math
Example: None that I know of
Speed: Great for long datas and lossy or corrupting networks