Report on Transport Protocols over Mismatched-rate Layer-1 Circuits with 802.3x Flow Control

This report describes our work detailing the operation and performance of TCP-based transport protocols (Reno, BIC, and CTCP) on “Layer-1” circuits, in which a Gigabit Ethernet port on an end host has been directly mapped to a SONET circuit of lower rate (e.g., a 155 Mbps OC3). The switch uses IEEE 802.3x flow control to prevent the sender from overwhelming the switch’s buffer. Current equipment such as Multiservice Provisioning Platforms (MSPPs) can act as virtual-circuit/circuit gateways (G/Ws) that offers both Ethernet and SONET line interface modules (LIMs) with a SONET-based switch fabric. An Ethernet LIM has Ethernet ports on the front end (the left edge of Stage One in Fig. 1) and SONET (virtual) ports on the back end (the right edge of Stage Three in Fig. 1) through which the card is connected to the backplane. The backplane thus brings SONET signals from all interface cards, both Ethernet and SONET, to the switch fabric card where the signals are crossconnected according to programmed configuration information. Generic Framing Procedure (GFP) and virtual concatenation (VCAT) [1] technologies are implemented in the Ethernet interface cards to map Ethernet frames into SONET frames. For a matched-rate circuit, a 1 Gbps (GbE) port would be cross-connected to a 7-OC3c SONET signal. Configuration of a mismatched-rate circuit is allowed, e.g., a GbE port can be mapped to an OC3c SONET signal. Regardless of whether the circuit is a matchedor mismatched-rate circuit, since the whole port is mapped to a SONET signal, these type of circuits are referred to as “port-mapped” or “Layer-1” circuits. In a mismatched-rate circuit, Ethernet frames may arrive at an Ethernet port at a rate faster than the rate of the SONET Sender Receiver 1Gbps 155Mbps Buffer Observation point