39.1 DCCP Agents

This section describes the operation of the DCCP agents in ns. At current ns implementation, there are two major congestion control of DCCP agents: CCID2 and CCID3. It is a symmetric two-way agent in the sense that it represents both a sender and receiver. DCCP for ns is still under development.

The files described in this section are too numerous to enumerate here. Basically it covers most files matching the regular expression ~ns/dccp*.{cc, h}.

Applications can access DCCP agents via the []sendmsg function in C++, or via the send or sendmsg methods in OTcl, as described in section 40.2.3.

The following is a simple example of how a DCCP CCID2 agent may be used in a program. In the example, the CBR traffic generator is started at time 1.0, at which time the generator begins to periodically call the DCCP agent []sendmsg function.

        set ns [new Simulator]
        set sender [$ns node]
        set receiver [$ns node]
        $ns duplex-link $sender $receiver 5Mb 2ms DropTail

        set dccp0 [new Agent/DCCP/TCPlike]
        $dccp0 set window_ 7000
        set dccpsink0 [new Agent/DCCP/TCPlike]
        $ns attach-agent $sender $dccp0
        $ns attach-agent $receiver $dccpsink0
      
        set cbr0 [new Application/Traffic/CBR]
        $cbr0 attach-agent $dccp0
        $cbr0 set packetSize_ 160
        $cbr0 set rate_ 80Kb

        $ns connect $dccp0 $dccpsink0
        $ns at 1.0 "$cbr0 start"

The following example uses DCCP CCID3.

        set ns [new Simulator]
        set sender [$ns node]
        set receiver [$ns node]
        $ns duplex-link $sender $receiver 5Mb 2ms DropTail

        set dccp0 [new Agent/DCCP/]
        set dccpsink0 [new Agent/DCCP/TFRC]
        $ns attach-agent $sender $dccp0
        $ns attach-agent $receiver $dccpsink0
      
        set cbr0 [new Application/Traffic/CBR]
        $cbr0 attach-agent $dccp0
        $cbr0 set packetSize_ 160
        $cbr0 set rate_ 80Kb

        $ns connect $dccp0 $dccpsink0
        $ns at 1.0 "$cbr0 start"