Reiner Ludwig

Ericsson

The recent rise in data traffic volumes being carried by mobile communication networks is tremendous. Some mobile communication networks have already turned from voice dominance to data dominance in terms of carried traffic volume. In 2008 the increase was up to a factor of five, and large operators' networks are now carrying on the order of 5-10 T...

Current cellular networks based on Third Generation Partnership Project (3GPP) and 3GPP2 technologies provide evolution from circuit-switched technologies, originally developed for voice communications, to packetswitched technologies. Next-generation networks need to deliver IP-based services (voice, video, multimedia, data, etc.) for all kinds of...

Simple and cost efficient means for providing and controlling quality of service (QoS) are important for 3GPP operators. This is particularly important for operators planning to provide a wide range of IP-based services across 3GPP broadband shared channels. We point out shortcomings of today's (Rel. 5) 3GPP QoS concept and, based on these, explain...

This paper discusses the requirements on future radio access and, based on the requirements, proposes a framework for such a system. The proposed system based on orthogonal frequency-division multiplexing supports very low latencies and data rates up to 100 Mb/s with wide area coverage and 1 Gb/s with local area coverage. Spectrum flexibility is id...

A framework for future radio-access systems, enabling user data rates up to 100 Mbps with wide-area coverage and up to 1 Gbps for local-area coverage, is presented. The proposed framework supports flexibility in system bandwidth and duplex arrangements. Furthermore, support for relaying and advanced antenna solutions is integrated in the design of...

Wireless multi-hop communication has recently gained a lot of interest in the research community as an approach to provide improved coverage compared to single-hop wireless networks. While most studies focus on routing protocols, ARQ mechanisms for multi-hop wireless links have found little attention so far. In this paper, we propose a novel link l...

We analyze the RTO algorithm standardized for TCP and SCTP (V. Paxon et al., 2000) that is widely deployed in the Internet, referred to as the RFC2988-RTO in this paper. We briefly demonstrate three well-known problems of the RFC2988-RTO. We then develop a new RTO algorithm called the peak-hopper-RTO (PH-RTO) that eliminates the mentioned problems....

Network anomalies such as packet reordering and delay spikes can result in spurious retransmissions and degrade performance of reliable transport protocols such as TCP and SCTP. Past research showed that in certain networks or paths, such anomalies were fairly common. The result was a series of proposals (Eifel, DSACK-based, F-RTO) targeted towards...

this paper, we only consider using the packet lifetime for discarding stale and duplicate data. When the real-time server is located in the Internet, clock synchronization between the lasthop router and the server would typically be required. The Network Time Protocol (NTP) [34] can provide sufficient accuracy for our purposes. When the realtime se...

We study the performance of TFRC-based traffic running across a 3G network. The goal is to evaluate the impact of three different queue management schemes on the end-to-end performance provided by TFRC. We show that drop-on-full queuing is absolutely inappropriate for TFRC traffic running over 3G links since it leads to burst packet drops and oscil...

Radio resource management functions in third generation cellular systems allocate capacity based on both demand and available capacity. A 3G wireless link may therefore be subject to considerable rate variations. These rate variations impose particular challenges on the buffer design. A well performing buffer should secure a high degree of link uti...

We propose a novel active queue management scheme tailored to the specific characteristics of third generation (3G) cellular networks. Such links are often the bottleneck for an end-to-end connection and dedicated to one host. Taking advantage of these specific characteristics, we developed a queuing scheme that is simpler than popular random early...

Techniques for modeling and simulating channel conditions play an essential role in understanding network protocol and application behavior. In [11], we demonstrated that inaccurate modeling using a traditional analytical model yielded suboptimal error control protocol parameters choices. In this paper, we demonstrate that time-varying effects on w...

Delays on Internet paths, especially including wireless links, can be highly variable. On the other hand, a current trend for modern TCPs is to deploy a fine-grain retransmission timer with a lower minimum timeout value than 1 s suggested by RFC2988. Spurious TCP timeouts cause unnecessary retransmissions and congestion control back-off. The Eifel...

Pure end-to-end error recovery fails as a general solution to opti- mize throughput when wireless links form parts of the end-to-end path. It can lead to decreased end-to-end throughput, an unfair load on best-effort networks, and a waste of valuable radio resources. Link layer error recovery over wireless links is essential for reliable flows to a...

Large and sudden variations in packet transmission delays are often unavoidable in GPRS. This may cause spurious timeouts in TCP. Spurious timeouts affect TCP performance in two ways: (1) the TCP sender unnecessarily reduces its load, and (2) the TCP sender is forced into a go-back-N retransmission mode. The Eifel algorithm avoids these consequence...

Techniques for modeling and simulating channel conditions play an essential role in understanding network protocol and application behavior. We demonstrate that time-varying effects on wireless channels result in non-stationary wireless traces. We present an algorithm that divides traces into stationary components in order to provide analytical cha...

We analyze two alternative retransmission timers for the Transmission Control Protocol (TCP). We first study the retransmission timer of TCP-Lite which is considered to be the current de facto standard for TCP implementations. After revealing four major problems of TCP-Lite's retransmission timer, we propose a new timer, named the Eifel retransmiss...

We propose an enhancement to TCP's error recovery scheme, which we call the Eifel algorithm. It eliminates the retransmission ambiguity, thereby solving the problems caused by spurious timeouts and spurious fast retransmits. It can be incrementally deployed as it is backwards compatible and does not change TCP's congestion control semantics. In env...

We propose an enhancement to TCP's error recovery scheme, which we call the Eifel algorithm . It eliminates the retransmission ambiguity, thereby solving the problems caused by spurious timeouts and spurious fast retransmits. It can be incrementally deployed as it is backwards compatible and does not change TCP's congestion control semantics. In en...

It is well-known that TCP performance may degrade over paths that include wireless links, where packet losses are often not related to congestion. We examine this problem in the context of the GSM digital cellular network, where the wireless link is protected by a reliable link layer protocol. We propose the use of multi-layer tracing as a powerful...

This paper has two main contributions. First the extremely high latency of the GSM link is revealed which through measurements is determined to have a magnitude usually only known from satellite links. This greatly impacts the link configuration time of packet framing protocols for serial links like the point-to-point protocol (PPP). The key idea o...

The General Packet Radio Service (GPRS) is one of the services being standardized by ETSI for GSM Phase 2+. This paper briefly presents the status of the GPRS standard giving special attention to the link control/medium access control (RLC/MAC) protocol layer. Subsequently, an analytical evaluation of the GPRS downlink performance is presented. Fac...

The speed of Internet access over GSM can be improved by optimizing the performance of TCP/IP connections over the air link, and by using smart proxies for HTTP transfers or other high-level protocols. The goal is to improve the performance as perceived by the user, which implies the minimization of the end-to-end latency. This document describes t...

The convergence of traditional voice-oriented telecommunications networks and data-oriented computer communications networks is yielding new challenges for building systems equally adept at han- dling voice and data applications. While there is much discussion about packetized voice over IP networks, a little explored opportu- nity is the ability t...

Drahtlose Kommunikation und konkreter: die Leistungsprobleme, die entstehen wenn Internet-Protokolle über Mobilfunkstrecken eingesetzt werden, besitzt derzeit als Forschungsthema höchste Prioriät in akademischen und industriellen Untersuchungen. Dennoch sind heute immer noch eine Reihe von Problemen ungelöst. Der Grund dafür liegt in ineffizienten...