ELEC-E7321
In this task you need to send largish amount of data using UDP protocol. Like
previous assignments, your client starts by opening a connection to
adnet-agent, and sending a control message: TASK-003 keyword. The server
replies with string
Each UDP datagram should be structured from a 6-byte header and payload as follows:
Four bytes that indicate sequence number of the datagram, in network byte order. The sequence number calculation starts from 1, and should be increased by one for each new datagram sent. If you decide to retransmit a datagram that has been transmitted earlier, it should re-use the same sequence number as originally.
Two bytes that indicate the number of bytes in payload, in network byte order. The maximum length of the payload is 1200 bytes.
After this you should include the payload, repeating the character indicated by adnet-agent.
The adnet-agent server listens to UDP datagrams in UDP port 20000. For each received datagram the server replies by 5-byte UDP acknowledgment with following content:
four bytes that indicate the highest consecutive sequence number received so far, i.e., if there is a datagram missing in the sequence number space, or they otherwise arrive at incorrect order, the server may repeat the same sequence number as previously. In other words, we are using cumulative acknowledgments similar to TCP.
one byte that contain seemingly random number (but is not). Note the content of the last acknowledgment finishing the transmission. This number will be asked in the MyCourses task assignment for grading.
You should run your implementation in three different mininet configurations, as described below. Be prepared to the possibility that some of the datagrams may be lost in the network and in such case need to be retransmitted. The queue length in bottleneck link is limited, therefore it is not a good idea to try to send all datagrams back-to-back, but slow down the transmission of datagrams according to some strategy. You may study how TCP takes care of this, but it is not required to implement a full-fledged modern congestion control algorithm. Something simple suffices.
You should repeat the assignment applying the following four scenarios:
Long delay. The bottleneck link has one-way delay of 200 ms, no limits on
the transmission speed:
sudo aalto/simple_topo.py --delay=200ms
Slow transmitter The bottleneck link has one-way delay of 50 ms, but
transmission speed is limited to 100 kbps:
sudo aalto/simple_topo.py --delay=50ms --bw=0.1
Lossy link The bottleneck link has one-way delay of 200 ms. Packet loss
rate is 10%:
sudo aalto/simple_topo.py --delay=200ms --loss=10
The assignment is successful if you can get acknowledgments for all datagrams in all three scenarios. Measure also the time from the start of the transfer until last acknowledgment is received. There is a lighthearted competition on who can implement the most efficient protocol (not affecting grading).