Networks

Figure 6 shows 100Mbps links connecting the traffic sources to the routers, and 45Mbps links connecting the routers to each other and to the supercomputer sites. The 45Mbps links running between routers are configured as point-to-point links; the 45Mbps links connecting the supercomputing centers to the routers are parameterized Ethernets. We call these networks ``parameterized'' Ethernets because the parmeters we specify in the xsim.data file change the characteristics of these networks from those of the default 10Mbps Ethernet.

The time associated with each link in the figure represent latency times for packets traveling across the link; this latency is proportional to distance. From San Francisco, it is much farther to Chicago than to Los Angeles, so the latency to Chicago (28ms) is four times as great as that to L.A. (7ms).

We now give an example specification for each kind of link, as it appears in xsim.data. The entries specifying networks are found at the end of the file. First, the 45Mbps point-to-point link from San Francisco to Chicago:

    set prate = 45Mb;
    set pdelay1 = 28ms;

    net PP 192.0.51.0;
      connections = SF 0.0.0.1, CH 0.0.0.2;
      args = rate=$prate, delay=$pdelay1;

This entry is straighforward. The first line identifies it as a point-to-point link with network address 192.0.51.0; the two routers SF and CH attach at addresses 192.0.51.1 and 192.0.51.2, respectively. The bandwidth and latency of the link are set by the rate and delay parameters.

Next, we show how the parameterized Ethernets that connect the supercomputer centers to the routers are configured. This one connects the router in Cleveland to the Pittsburgh Supercomputing Center:

    set erateBig = 45Mbps;
    set edelay42 = 780us;
    set emaxpkt = 1500;
    set ehdrsize = 12;
    set coll = off;

    net ETH 192.0.42.0;
      connections = CL 0.0.0.100, h1n42 ethd 0.0.0.1;
      args = rate=$erateBig, delay=$edelay42, maxPacket=$emaxpkt, hdrSize=$ehdrs
             collisions=$coll;

This network is identified as an Ethernet, with net address 192.0.42.0. We change its bandwidth from the default 10Mbps to 45Mbps, and specify a latency of 780 microseconds. The CL router connects at address 192.0.42.100; host h1n42, a host at the PSC that will engage in bulk transfers, has address 192.0.42.1.

Finally, each of the traffic sources is connected to a router by a 100Mbps parameterized Ethernet. Here is an entry for a network that connects a traffic source consisting of three hosts to the router in L.A.:

    set erate = 100Mbps;
    set edelay1 = 1120us;
    set emaxpkt = 1500;
    set ehdrsize = 12;
    set coll = off;

    net ETH 192.0.1.0;
      connections = LA 0.0.0.100, h1n1 ethd 0.0.0.1, h2n1 ethd 0.0.0.2, 
                h3n1 ethd 0.0.0.3;
      args = rate=$erate, delay=$edelay1, maxPacket=$emaxpkt, hdrSize=$ehdrsize, 
             collisions=$coll;

This entry is almost the same as the one given above for the 45Mbps parameterized Ethernet. The three hosts h1n1, h2n1, and h3n1 will generate traffic connections during the simulation; together they make up a single ``traffic source'' in Figure 6.