High Capacity Network Link Emulation Using Network Processors

Network link emulation constitutes an important part of network emulation, wherein links in the topology are emulated to subject the network traffic to different bandwidths, latencies, packet loss distributions, and queuing models. Increasingly, experimenters are creating topologies with substantial emulation bandwidths; contributed both by a large number of low-speed links and a small number of high-speed links. It is a significant challenge for a link emulator to meet this requirement in real time. Existing solutions for link emulation use general-purpose PC-class machines; the well-understood hardware and software PC platform make it attractive for quick implementation and easy deployment. A PC architecture is largely optimized for compute bound applications with large amounts of exploitable instruction-level parallelism (ILP) and good memory reference locality. Networking applications, on the other hand, have little ILP and instead exhibit a coarser packet-level parallelism. In this thesis, we propose using network processors for building high capacity link emulators. Network processors are programmable processors that employ a multithreaded, multiprocessor architecture to exploit packet-level parallelism, and have instruction sets and hardware support geared towards efficient implementation of common networking tasks. To evaluate our proposal, we have designed and implemented a link emulator, LinkEM, on the IXP1200 network processor. We present the design and a mapping of LinkEM’s tasks across the multiple microengines and hardware threads of the IXP1200. We also give a detailed evaluation of LinkEM, which includes validating its emulation accuracy, and measuring its emulation throughput and link multiplexing capacity. Our evaluation shows that LinkEM has a factor of between 1.6 and 4.6 higher throughput for small packets, and link multiplexing capacity between 1.4 and 2.6 higher for low bandwidth links than Dummynet, a popular PC based link emulator, on a comparable PC platform.