Congestion control over ATM local area networks
Asynchronous Transfer Mode (ATM) has emerged as a standard which offers integration of different classes of service as well as scalability in terms of network size and speed. While the early focus on ATM was mainly on wide-area networks, the driving force behind this new technology is increasingly coming from local-area applications. The need for an ATM LAN to support existing protocols (e.g., TCP/IP) transparently is key to its adoption in the local-area environment. In traditional shared medium LANS, congestion control on the medium is handled by medium access control (MAC) protocol. Once a network device gains access to the shared medium, it has the full bandwidth to itself. Other contending network devices must wait until the shared medium becomes free. In ATM LANS, the MAC protocol is removed, and as a result the congestion control it provides is also removed. Each network device can transmit at the full link bandwidth, and can thus potentially cause congestion at some output ports of an ATM switch. This report presents some simulation results and demonstrates the importance of congestion control in ATM networks. First, we show the effects of cell loss on TCP performance in a congested ATM LAN. When congestion results in switch buffer overflow, cells are dropped. The effect of a small cell loss rate is found to translate into a much larger TCP packet retransmission rate, resulting in poor TCP performance. Secondly, we will describe a credit-based, per virtual circuit, per hop flow control algorithm proposed by Digital Equipment Corporation (DEC). We show that when flow control is employed, cell loss and TCP retransmissions are eliminated, resulting in greatly improved TCP performance.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 48631
- Report Number(s):
- SAND-95-8218; ON: DE95010343; TRN: 95:003808
- Resource Relation:
- Other Information: PBD: Mar 1995
- Country of Publication:
- United States
- Language:
- English
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