All experiments were performed on Sun Microsystems SPARCstation 20 model 61 workstations (60MHz SuperSPARC+, 36KB L1, 1MB L2, SPECint92 98.2). The workstations are equipped with 32MB of memory and run SunOS 4.1.3_U1. A 155 Mbit/s ATM local area network connects the workstations, using FORE Systems SBA-200 network adaptors. These network adaptors include an Intel i960 processor that performs cell fragmentation and reassembly of protocol data units (PDUs). Note that LRP does not depend on a specific network adaptor or ATM networks. SOFT-LRP can be used with any network and NI.
The LRP architecture was implemented as follows. We modified the TCP/UDP/IP network subsystem that comes with the 4.4 BSD-Lite distribution [24] to optionally implement LRP. The resulting code was then downloaded into the SunOS kernel as a loadable kernel module and attached to the socket layer as a new protocol family (PF_LRP). A custom device driver was developed for the FORE network adaptor. The 4.4 BSD-Lite networking subsystem was used because of its performance and availability in source form. (We did not have access to SunOS source code.) The 4.4 BSD networking code was slightly modified to work with SunOS mbufs. At the time of this writing, the prototype implementation uses a kernel process to perform asynchronous protocol processing for TCP.
Since we were unable to obtain source code for the SBA-200 firmware, we could not integrate our own demultiplexing function in this network adaptor. However, we know enough about the interface's architecture to be confident that the function could be easily integrated, given the source code. To evaluate packet demultiplexing in the network adaptor (NI demux), we used instead the SBA-200 firmware developed by Cornell University's U-Net project [1]. This firmware performs demultiplexing based on the ATM virtual circuit identifier (VCI). A signaling scheme was used that ensures that a separate ATM VCI is assigned for traffic terminating or originating at each socket. The resulting implementation of NI-LRP is fully functional.