Recursive temporal (RT) namespaces extend spatial namespaces such as IP with the notion of a nested time interval. RT namespace is an architectural approach to dealing with the uncertainty associated with changes to distribution, syntax or semantics of large-scale namespaces that are associated with high cost and probability of failure. We discuss the abstract design issues associated with RT namespaces and two existing approaches that are special cases of the general design. We also propose a variant of IP based on RT namespaces that supports open-ended evolution.

The recursive network architecture (RNA) explores the relationship of layering to protocol and network architecture. RNA examines the implications of using a single, tunable protocol, called a metaprotocol, for different layers of the protocol stack, reusing basic protocol operations across different protocol layers to avoid reimplementation. Its primary goal is to encourage cleaner cross-layer interaction, to support dynamic service composition, and to gain an understanding of how layering affects architecture. This paper provides a description of RNA and a recently completed initial prototype. The prototype extends the Click modular router with control capabilities including dynamic composition and discovery. These capabilities are used to demonstrate simple but flexible stacks of instances of a metaprotocol that are customizable at runtime.

The three papers in this special section were originally presented at the IEEE INFOCOM 2006 conference in Barcelona. The augmented papers, which address issues in wireless networks and mobile computing, represent the high quality of research presented at the conference.

Recently there has been some interest in optical CDMA (OCDMA) for optical networks. A major drawback of OCDMA systems is their low spectral efficiency. This paper explores a novel modulation scheme for OCDMA systems which increases the spectral efficiency called code-cycle modulation (CCM) which uses different cyclic shifts of the spreading sequence assigned to each user to transmit an M-ary information. While the idea of using M-ary OCDMA modulation has been proposed using other means, most of these modulation schemes need M different receiver units to recover the data which causes complexity and power issues in the receiver. The advantage of our scheme is that we propose a supporting receiver architecture which doesn't suffer from complexity and power issues as mentioned above. In the rest of the paper we analyze the performance of this modulation scheme.

This paper presents the idletime scheduler; a generic, kernel-level mechanism for using idle resource capacity in the background without slowing down concurrent foreground use. Many operating systems fail to support transparent background use and concurrent foreground performance can decrease by 50% or more. The idletime scheduler minimizes this interference by partially relaxing the work conservation principle during preemption intervals, during which it serves no background requests even if the resource is idle. The length of preemption intervals is a controlling parameter of the scheduler: short intervals aggressively utilize idle capacity; long intervals reduce the impact of background use on foreground performance. Unlike existing approaches to establish prioritized resource use, idletime scheduling requires only localized modifications to a limited number of system schedulers. In experiments, a FreeBSD implementation for idletime network scheduling maintains over 90% of foreground TCP throughput, while allowing concurrent, high-rate UDP background flows to consume up to 80% of remaining link capacity. A FreeBSD disk scheduler implementation maintains 80% of foreground read performance, while enabling concurrent background operations to reach 70% throughput.

Optical burst switching presents challenges to the design of optical routers. This paper considers how to dimension a router of N input data ports with an additional M fiber delay lines (N+M internal ports) in a hop-and-span constrained network. The router incorporates tunable FDLs that can vary their size to fit the burst being buffered. Tunable fiber delays achieve up to 20% higher throughput than static fiber delays at high input port load. Multiple recirculations are a critical requirement; when packets can circulate only once through the buffer, no measurable improvement is achieved after the number of as FDLs becomes equal to the number of data ports. When recirculation is permitted, throughput increases by up to 40%, depending on a combination of the number of FDLs added and the recirculation limit, which must increase in tandem. For a given number of FDLs, there is an optimal recirculation limit beyond which there is no measurable throughput benefit.

Optical CDMA local area networks allow shared access to a broadcast medium. Every node is assigned an optical orthogonal codeword (OOC) to transmit or receive on. Optical CDMA systems have low throughput under moderate to heavy offered load due to interference between codewords. Interference sensing is a media access architecture where nodes on the network sense the amount of interference on the line before transmission. Nodes defer transmissions if there is interference on the line. This paper discusses and analyzes three algorithms for interference sensing. Through simulation it is shown that these algorithms reduce or eliminate throughput degradation at high loads. The study shows that simple algorithms such as selfish or threshold based algorithms are sufficient to eliminate throughput degradation.

Optical CDMA local area networks allow shared access to a broadcast medium. Every node on the network is assigned an optical orthogonal codeword (OOC) to transmit or receive on. OOCs are designed to be pseudo-orthogonal, i.e., the correlation (and therefore the interference) between pairs of codewords is constrained. This paper demonstrates that the use of optical CDMA does not preclude the need for a media access control (MAC) layer protocol to resolve contention for the shared media. OOCs have low spectral efficiency. As more codewords are transmitted simultaneously, the interference between codewords increases and the network throughput falls. This paper analyzes a network architecture where there is virtually no MAC layer, except for choice of the codeset, and shows that its throughput degrades and collapses under moderate to heavy load. We propose an alternate architecture called interference avoidance where nodes on the network use media access mechanisms to avoid causing interference on the line, thereby improving network throughput. Interference avoidance is analyzed and it is shown that it can provide up to 30% improvement in throughput with low delays and no throughput collapse. We validate our analysis through simulation with realistic network traffic traces.

The X-Bone dynamically deploys and manages Internet overlays to reduce their configuration effort and increase network component sharing. The X-Bone discovers, configures, and monitors network resources to create overlays over existing IP networks. Overlays are useful for deploying overlapping virtual networks on a shared infrastructure and for simplifying topology. The X-Bone extends current overlay management by adding dynamic resource discovery, deployment, and monitoring and allows simultaneous participation in multiple overlays. Its two-layer IP in IP tunneled overlays support existing applications and unmodified routing, multicast, and DNS services in unmodified operating systems. This two-layer scheme uniquely supports recursive overlays, useful for fault tolerance and dynamic relocation. The X-Bone uses multicast to simplify resource discovery, and provides secure deployment as well as secure overlays. This paper presents the X-Bone architecture, and discusses its components and features, and their performance impact.

Hosts providing important network services such as HTTP and FTP incur a per-connection memory load from TCP that can adversely affect their connection rate and throughput. The memory requirement is directly tied to the number of connections; caching and other sharing methods will not alleviate it. We have observed HTTP throughput reductions of as much as 50% under SunOS 4.1.3 due to this loading. This paper advocates off-loading the memory requirements to the growing number of clients. This reduces server memory requirements as connection rate at that server grows due to increases in the number of clients and the bandwidth available on the network. These approaches control server memory load better with growing client load than per-transaction techniques such as persistent HTTP connections. These approaches also interoperate with persistent connections to take advantage of their other benefits. This paper describes the causes of the memory loading, called TIME-WAIT loading, and defines three methods of alleviating it that scale with increasing number of clients. We present measurements of the systems and a comparison of their properties.

Many high-speed networks are in a development stage, compared to established technologies like Ethernet. Use of these networks for production service provides substantial benefits to the developers, e.g., for large-scale testing. However, most users are not tolerant of pre-production network outages, even in exchange for the higher bandwidth these networks afford. This paper describes ISI's experience in deploying such a network, Myricom's Myrinet, for production service. A configuration is described that encourages participation in advanced deployment, and provides dynamic backup to a conventional, production-quality network. Each machine individually and transparently reverts to a stable backup network in the event that the prototype network fails. The system is composed of existing tools, and requires no operating system modifications. Alternate configurations are discussed, and recommendations presented to support such deployment more easily in the future.

This paper considers the interaction of HTTP with several transport protocols, including TCP, Transaction TCP, a UDP-based request-response protocol, and HTTP with persistent TCP connections. We present an analytic model for each of these protocols and use that model to evaluate network overhead carrying HTTP traffic across a variety of network characteristics. This model includes an analysis of the transient effects of TCP slow-start. We validate this model by comparing it to network packet traces measured with two protocols (HTTP and persistent HTTP) over local and wide-area networks. We show that the model is accurate within 5% of measured performance for wide-area networks, but can underestimate latency when the bandwidth is high and delay is low. We use the model to compare the connection-setup costs of these protocols, bounding the possible performance improvement. We evaluate these costs for a range of network characteristics, finding that setup optimizations are relatively unimportant for current modem, ISDN, and LAN users but can provide moderate to substantial performance improvement over high-speed WANs. We also use the model to predict performance over future network characteristics.

MD5 is an authentication algorithm proposed as the required implementation of the authentication option in IPv6. This paper presents an analysis of the speed at which MD5 can be implemented in software and hardware, and discusses whether its use interferes with high bandwidth networking. The analysis indicates that MD5 software currently runs at 85 Mbps on a 190 Mhz RISC architecture, a rate that cannot be improved more than 20-40%. Because MD5 processes the entire body of a packet, this data rate is insufficient for current high bandwidth networks, including HiPPI and FiberChannel. Further analysis indicates that a 300 Mhz custom VLSI CMOS hardware implementation of MD5 may run as fast as 256 Mbps. The hardware rate cannot support existing IPv4 data rates on high bandwidth links (800 Mbps HiPPI). The use of MD5 as the default required authentication algorithm in IPv6 should therefore be reconsidered, and an alternative should be proposed. This paper includes a brief description of the properties of such an alternative, including a sample alternate hash algorithm.

The First IEEE Gigabit Networking (GBN) Workshop defined a set of characteristics of "Interesting" high-speed applications. The GBN criteria ensure that the application addresses a significant problem, and that it actually requires a gigabit network. This paper presents five challenges that augment the GBN criteria. These challenges ask whether gigabit applications require new research into different protocols, or can be supported by existing protocols that merely run faster. It shows a class of applications, interactive distributed multimedia, namely interactive real-time World Wide Web (WWW) access, that survive the challenges. It also shows how source presenting is a way to use excess bandwidth-delay product to reduce the browser response time, and how this is one example of a truly gigabit protocol.>

Communication latency can be reduced by increasing bandwidth via a sender-based anticipation technique called Parallel Communication. The authors apply this method to anonymous FTP. Their analysis of log files indicates that latency can be reduced to 2 round-trip times, as small as 0.6 round-trip time/file, for a 7x increase in bandwidth. This technique applies to up to 95% of the FTP traffic. This method is expected to be especially useful in reducing latency in automated FTP access. Such as in the World-WideWorld-Wide Web.>

Advances in communication rates exceed the ability of a single source to fully utilize a gigabit WAN channel with existing deterministic protocols. A method called parallel communication, which reduces latency by managing indeterminism and increasing channel utilization, given a surplus bandwidth-delay product, is presented. It involves a nondeterministic state mechanism with a modified protocol interface.>