Improving TCP performance over asymmetric networks

ABSTRACT

Bandwidth asymmetry is quite common among modern networks; e.g., ADSL, cable TV, wireless, and satellite link with a terrestrial return path. In these networks, the bandwidth over one direction can be orders of magnitude smaller than that over the other. The performance of TCP transfer in the high bandwidth direction can be severly reduced by the delay acknowledgment packets experienced in the reverse direction. In this paper, we describe our proposed solution ACE (Acknowledgement Based on Cwnd Estimation). In comparison to other solutions, ACE requires only modification of the TCP stack at terminals attached to an asymmetric network. We evaluated the performance of ACE over a cable modem network by simulation. We have also implemented ACE on the Linux platform and tested it on a small testbed network with an emulated asymmetric link. The performance improvement was significant especially when there is a high degree of asymmetry.

INDEX TERMS

Primary Classification:
  C. Computer Systems Organization
  C.2 COMPUTER-COMMUNICATION NETWORKS

Additional Classification:
  C. Computer Systems Organization
  C.2 COMPUTER-COMMUNICATION NETWORKS

General Terms:
Documentation, Management, Performance

Keywords:
ADSL, Ack filtering, TCP, asymmetric networking, cable modem, congestion window estimation