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 why that demand is currently not met. Based on a set of requirements identified for an evolved 3GPP QoS concept, we propose four small additions to the 3GPP specifications. The resulting evolved QoS concept is a realization of DiffServ for 3GPP access networks enhanced with the integration with session admission control. Operator QoS control is exercised from the policy charging rule function (PCRF) and through pre-configuration via the management plane. The evolved QoS concept provides a 3GPP operator with capabilities beyond those found in state-of-the-art fixed broadband access networks

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 identified as one main requirement for future systems, and the proposed framework can be deployed in a wide range of spectrum allocations with bandwidths ranging from 2.5 to 100 MHz. Multihop relaying, useful to extend the range for the high data rates, and multiple-antenna configurations are integral parts of the framework. A packet-centric approach is taken for the dataflow processing, implying that the scheduling mechanism and the retransmission protocol operate on complete packets rather than segments thereof, thus allowing for cross-layer optimization. Finally, numerical evaluations are provided, illustrating the feasibility of future very wideband radio access.

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. Through extensive simulations in ns2, we evaluate the effectiveness of both RTO algorithms. The key advantage of the PH-RTO over the RFC2988-RTO is its predictability. Although the RFC2988-RTO often exhibits low loss detection times, it also exhibits frequent "RTO outliers" that can lead to exceptionally long loss detection times. The loss detection times of the PH-RTO are much more closely spread around the mean. Finally, our results show that the PH-RTO is much more robust to sudden delay spikes that are particularly common in wireless networks.

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 algorithm detects spurious TCP timeouts and recovers by restoring the connection state saved before the timeout. This paper presents an enhanced version of the Eifel response to spurious timeouts and illustrates its performance benefits on paths with a high delay-bandwidth product. The refinements concern the following issues (1) an efficient operation in presence of packet losses (2) appropriate restoration of congestion control, and (3) adapting the retransmit timer to avoid further spurious timeouts. In our simulations the Eifel algorithm on paths with a high delay-bandwidth product can increase throughput by up to 250% and at the same decrease the load on the network by 3%. The proposed response also shows adequate performance on heavily congested paths.

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 detection (RED) schemes. Despite its simplicity, our solution yields superior performance for 3G links in terms of high link utilization, low queuing delay, and high end-to-end throughput for TCP bulk data transfers. Our simulation results show a clear win over both conventional drop-tail queuing and also a comparable RED scheme.

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 significant errors in error control protocol parameters choices. In this paper, we demonstrate that time-varying effects on wireless channels result in wireless traces which exhibit non-stationary behavior over small window sizes. We then present an algorithm that divides traces into stationary components in order to provide analytical channel models that, relative to traditional approaches, more accurately represent characteristics such as burstiness, statistical distribution of errors, and packet loss processes. Our algorithm also generates artificial traces with the same statistical characteristics as actual collected network traces. For validation, we develop a channel model for the circuit-switched data service in GSM and show that it: (1) more closely approximates GSM channel characteristics than a traditional Gilbert model and (2) generates artificial traces that closely match collected traces' statistics. Using these traces in a simulator environment enables future protocol and application testing under different controlled and repeatable conditions.

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 of the proposed solution-Quickstart-PPP-is to break the strict sequential order of the different signalling phases while ensuring that protocol semantics are not violated and interoperability with existing PPP implementations is preserved. As a result the link configuration delay can be completely eliminated. The second contribution uncovers a fundamental problem which is that the GSM circuit-switched data service is not capable of satisfying different reliability requirements simultaneously. More precisely it is not possible to use applications requiring the GSM link to operate in reliable mode together with loss-tolerant but delay-sensitive applications at the same time. The developed solution-Link Sniffer-suggests a mechanism that can be added to the implementation of GSM's reliable link layer protocol which allows to "sniff" on packet headers to determine the reliability mode to be used. The key advantage of this solution is that the link layer protocol itself does not have to be changed.

We present the results of a performance evaluation of link layer error recovery over wireless links.Our analysis is based upon a case study of the circuit-switched data service implemented in GSM digital cellular networks.We collected a large set of block erasure traces in different radio environments and used a measurement-based approach to derive real-world models of the wireless link.We show that the throughput of the GSM circuit-switched data channel can be improved by up to 25 percent by increasing the (fixed) frame size of the reliable link layer protocol.Our results also suggest that adaptive frame length control could further increase the channel throughput.In general, our case study shows that pure end-to-end error recovery fails to optimize throughput when wireless links form parts of the end-to-end path.In many cases, it leads to decreased end-to-end throughput, an unfair load on a best-effort network, such as the Internet, and a waste of valuable radio resources (e.g., spectrum and transmission power).In fact, we show that link layer error recovery over wireless links is essential for reliable flows to avoid these problems.

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 methodology to analyze the complex protocol interactions between the layers. Our measurements show that TCP throughput over GSM is mostly ideal and that spurious timeouts are extremely rare. The multi-layer tracing tool we developed allowed us to identify the primary causes of degraded performance: (1) inefficient interactions with TCP/IP header compression, and (2) excessive queuing caused by overbuffered links. We conclude that link layer solutions alone can solve the problem of “TCP over wireless links”. We further argue that it is imperative to deploy active queue management and explicit congestion notification mechanisms in wide-area wireless networks; which we expect will be the bottleneck in a future Internet.