TCP Interface To RHTP - A Zero-Copy Approach To Gigabit Networking Via Myrinet

28.02.2000

Abstract

The Internet has made TCP/IP the standard protocol for WAN networking communication. Because of this development most communication-based applications developed over the recent years, use the IP protocol for communication.

TCP was originally developed for interconnecting several different networks. To the extent this protocol is used today was never thought of when it was originally developed. Interconnecting several networks, with greatly varying error rates, latency and throughput characteristics require processing that is unnecessary in a homogenous network with very low error rate and latency. This processing will pose as a thread to achieving gigabit networking, and will increase latency.

This paper argues that the CPU/memory data path is a potential throughput bottleneck with non zero-copy TCP/IP implementations connected to a gigabit-networking device. The paper will present the Myrinet technology, which offers a gigabit-networking device with processing capabilities. The protocol RHTP will be presented as an improvement of current TCP/IP implementation under Linux. To achieve this the RHTP implements zero-copy and utilize the onboard network possessing capabilities of the Myrinet technology.

RHTP is to achieve better utilization of current LAN configuration with networking hardware, capable of doing processing as well as gigabits transfer rates and fault rates, similar to the internal bus on a standard PC. The current version RHTP protocol is split up into three layers RHTP, TCEP (TCP emulation protocol), and the MLP (Myrinet Linklayer Protocol) or driver. The protocol is partially implemented at the network-card itself.

This paper will present the design and the implementation of the protocol RHTP. With the view to demonstrate a possible, efficient solution to gigabit is networking. The paper will also introduce other schemes and ideas on the subject of gigabit networking in addition to the presentation of the RHTP implementation.

The RHTP protocol will be compared against the Loopback device. The results will show that the RHTP protocol gives both better bandwidth and latency the the Loopback device over the current TCP/IP implementation.

This paper aims at showing that the TCP/IP implementation under Linux is not able to fully utilize new networking hardware with processing capabilities and gigabit transfer rates. The conclusion of this paper is that better utilization of networking hardware like the Myrinet can be achieved by zero-copy technology and by utilizing the network device capabilities.