Mikael Degermark

Small forwarding tables for fast routing lookups

For some time, the networking community has assumed that it is impossible to do IP routing lookups in software fast enough to support gigabit speeds. IP routing lookups must find the routing entry with the longest matching prefix, a task that has been thought to require hardware support at lookup frequencies of millions per second.We present a forwarding table data structure designed for quick routing lookups. Forwarding tables are small enough to fit in the cache of a conventional general purpose processor. With the table in cache, a 200 MHz Pentium Pro or a 333 MHz Alpha 21164 can perform a few million lookups per second. This means that it is feasible to do a full routing lookup for each IP packet at gigabit speeds without special hardware.The forwarding tables are very small, a large routing table with 40,000 routing entries can be compacted to a forwarding table of 150-160 Kbytes. A lookup typically requires less than 100 instructions on an Alpha, using eight memory references accessing a total of 14 bytes.

Low-loss TCP/IP header compression for wireless networks

Wireless is becoming a popular way to connect mobile computers to the Internet and other networks. The bandwidth of wireless links will probably always be limited due to properties of the physical medium and regulatory limits on the use of frequencies for radio communication. Therefore, it is necessary for network protocols to utilize the available bandwidth efficiently. Headers of IP packets are growing and the bandwidth required for transmitting headers is increasing. With the coming of IPv6 the address size increases from 4 to 16 bytes and the basic IP header increases from 20 to 40 bytes. Moreover, most mobility schemes tunnel packets addressed to mobile hosts by adding an extra IP header or extra routing information, typically increasing the size of TCP/IPv4 headers to 60 bytes and TCP/IPv6 headers to 100 bytes. In this paper, we provide new header compression schemes for UDP/IP and TCP/IP protocols. We show how to reduce the size of UDP/IP headers by an order of magnitude, down to four to five bytes. Our method works over simplex links, lossy links, multi‐access links, and supports multicast communication. We also show how to generalize the most commonly used method for header compression for TCP/IPv4, developed by Jacobson, to IPv6 and multiple IP headers. The resulting scheme unfortunately reduces TCP throughput over lossy links due to unfavorable interaction with TCPs congestion control mechanisms. However, by adding two simple mechanisms the potential gain from header compression can be realized over lossy wireless networks as well as point‐to‐point modem links.

Advance reservations for predictive service in the Internet

Abstract. We extend a measurement-based admission control algorithm suggested for predictive service to provide advance reservations for guaranteed and predictive service, while retaining the attractive features of predictive service. The admission decision for advance reservations is based on information about flows that overlap in time. For flows that have not yet started, the requested values are used, and for those that have already started measurements are used. This allows us to estimate the network load accurately for the near future. To provide advance reservations we ask users to include durations in their requests. We present simulation results to show that predictive service with advance reservations provides utilization levels significantly higher than those for guaranteed service, and comparable to those for predicted service without advance reservations. Those utilization levels are reached without any preemption of other admitted flows. Finally, we discuss how to setup advance reservations over multiple hops in the Internet using resource reservation setup protocols.

Advance Reservations for Predictive Service

We extend a measurement-based admission control algorithm suggested for predictive service to provide advance reservations for guaranteed and predictive service while keeping the attractive features of predictive service. The admission decision for advance reservations is based on information about flows that overlap in time. For flows that have not yet started, the requested values are used, and for those that have already started measurements are used. This allows us to estimate the network load accurately for the near future. To provide advance reservations we ask users to include durations in their requests. We provide simulation results to show that predictive service with advance reservations provides utilization levels significantly higher than those for guaranteed service.

Evaluation of CRTP performance over cellular radio links

To make mobile IP telephony over cellular radio systems an economically viable alternative to circuit-switched voice, it is an absolute requirement that the 40-octet IP/UDP/RTP headers on IP telephony packets be reduced in size to conserve bandwidth and radio spectrum. We evaluate the performance of the default header compression scheme for IP/UDP/RTP, CRTP (RFC-2508), over links built on cellular radio access technology. We find that CRTP does not perform adequately over such links, and suggest that a more robust header compression scheme must be developed to make IP telephony over cellular economically viable.

Wireless real-time IP services enabled by header compression

The world of telecommunications is currently going through a shift of paradigm from circuit switched, connection oriented information transfer towards packet switched, connection-less transfer. For application independence and to decrease costs for transport and switching it is attractive to go IP all the way over the air interface to the end user equipment, i.e., to not terminate the IP protocols before the air interface. A major reason to avoid using voice over IP over the air interface has, up to now, been the relatively large overhead imposed by the IP/UDP/RTP headers of voice packets. This paper presents a novel header compression scheme, ROCCO, that can compress the large headers to a minimum of one octet and is robust against the errors imposed by cellular links. Its performance is excellent both in terms of robustness and compression efficiency. Moreover, system capacity simulations are presented, which show that ROCCO gives significantly higher system capacity than the other current header compression candidate, CRTP. Finally it is argued that with ROCCO voice over IP over wireless becomes feasible from a spectrum-efficiency point of view.

Issues in the Design of a New Network Protocol

We describe some of the issues in the design of a new packet switched network protocol. Adaptation to various network technologies along the dimensions of speed, error model, robustness, etc., is a goal for this new protocol. We look at the adaption in size of the packet header to the speed and robustness of the underlying network to allow efficient communication on low-speed wireless networks, for example. We also explore issues in resource reservation and multicast for real-time multimedia, the notion of a network “flow”, a hybrid of datagrams and virtual circuits, and suggest common solutions for both mobile and multicast routing. The authors are engaged in the design of a network protocol, NP++, whose goal is flexibility over a wide dynamic range of speeds and varying kinds of hardware switching elements.

Requirements on the TCP/IP Protocol Stack for Real-Time Communication in Wireless Environments

A strong trend in the Internet is to provide wireless Internet access to handheld devices. Radio spectrum is a scarce and expensive resource, and a wide-area cellular system that provides satisfying quality for a data service based on the traditional TCP/IP protocol stack will be expensive. This becomes especially problematic for real-time communication based on UDP. To design an economically viable system, different approaches are available. New protocols can be designed that take wireless systems into account. The Wireless Application Protocol (WAP) is an example of such a protocol. Alternatively, the existing TCP/IP protocols can be modified to better support cellular systems. The development of WAP is tempting since it does not have to modify the TCP/IP Protocol stack. However, to provide future proofing, it is a better idea to base the protocol architecture for wireless on TCP/IP since this will be the dominant Internet protocol stack for years to come. This paper discusses requirements on various layers in the TCP/IP protocol stack to better support real-time data services. One key component is a transport layer designed to use limited bandwidth more efficiently for real-time services. Changes are required to other layers as well, but these can be deployed where needed without disturbing the rest of the Internet. By applying these changes, it becomes possible to provide cost efficient, real-time services based on IP in cellular systems.