LAN interconnection experiments over a cross country switched multi-megabit data service network

Data transfer rates between local area networks connected via a cross-country switched multi-megabit data service (SMDS) experimental prototype network were measured. Private line services from an interexchange carrier were used to support the experimental network. The user-network interface was the DSI subscriber network interface (SNI) (1.17 Mb/s). The maximum measured UDP data transfer rate was up to 1.05 Mb/s for 1024-byte packets. TCP was fine tuned by increasing its maximum packet size to 1 kbyte (from 512 byte) and its maximum window size to 46 kbyte (from 16 kbyte) to accommodate the SMDS network round-trip delay. The maximum TCP user data transfer rate was 0.963 Mb/s for 1024-byte packets. The average round-trip delay between workstations was 400 ms when the 1024-byte packet TCP experiments were being performed. The average round trip delay when no experiments were being performed was 121 ms. The TCP protocol adapted well to the delay characteristics of the experimental SMDS network.<>