Preliminary Report of Performance Results for TCP over ATM with Congestion

r, through a single switch, causing congestion at one of the switch output ports. Each TCP connection has it's own VC. A topology of five TCP s was chosen to model the case of multiple connections. The number of TCPs was increased to 10 for comparing performance when congestion increases. For all links, the bandwidth is 141 Mbps, chosen instead of 155 Mbps, so that the cell time is an integral number, 3 microseconds. The traffic model used for the initial study is an infinite stream of data, chosen because it represents the worst case for creating congestion. TCP ack packet size is 40 bytes. A LAN environment is modeled, in which the propagation delay is 3 or 5 microseconds from each host to the switch. The switch speedup factor is 2, typical of a LAN switch. Packet size, buffer size, and window size are varied in the experiments. Performance measures include each TCP connection's goodput, i. e., throughput without retransmissions, it's packet retransmission rate, and the number and r

An Overview of RDMA over IP

This paper gives an overview of Remote Direct Memory Access (RDMA) over IP. The first part of the paper is taken from an internet draft [RMTB02] that describes the problem of high system costs due to network I/O copying in end-hosts at high speeds. A review of experience and research over the last ten or so years shows that the problem is due to limits on available memory bandwidth, and the prohibitive cost of additional memory bandwidth, and that it can be substantially improved using copy avoidance. The second part of the paper considers an RDMA over IP solution, giving background and current status. An architecture is described that is that currently being adopted by the RDMA Consortium and the RDDP WG in the IETF. Outstanding issues, some of a research nature, are considered.

Analysis of a Resequencer Model for Multicast over ATM Networks

Multicast delivery saves bandwidth and offers logical addressing capabilities to the applications. The receivers of a multicast group need to differentiate cells sent by different sources. This demultiplexing requirement can be satisfied in an ATM environment using multiple dedicated point-to-multipoint virtual channel connections (VCs), but with certain shortcomings. This paper discusses an alternative resequencing model to solve this problem. It scales well in large networks. Three resequencing methods are are developed and simulation results reported. The strategy is useful for applications spanning large regions where it is desirable to mix streams of cells from different bursty sources onto the same virtual channel

Dynamics of TCP Traffic over ATM Networks

We investigate the performance of TCP connections over ATM networks without ATM-level congestion control, and compare it to the performance of TCP over packet-based networks. For simulations of congested networks, the effective throughput of TCP over ATM can be quite low when cells are dropped at the congested ATM switch. The low throughput is due to wasted bandwidth as the congested link transmits cells from `corrupted' packets, i.e., packets in which at least one cell is dropped by the switch. We investigate two packet discard strategies which alleviate the effects of fragmentation. Partial Packet Discard, in which remaining cells are discarded after one cell has been dropped from a packet, somewhat improves throughput. We introduce Early Packet Discard, a strategy in which the switch drops whole packets prior to buffer overflow. This mechanism prevents fragmentation and restores throughput to maximal levels