Paul Jacob

Comparative Study of Real-Time Multimedia Transmission over Multi-homing Transport Protocols

The availability of multimedia applications suitable for deployment using 3G and GPRS networks has led to a requirement for end-to-end quality of service. More efficient mechanisms are needed in order to provide the required end user quality of service in wireless data networks. This paper investigates the performance implications of transmitting real-time multimedia content over a multi-homed transport protocol in a manner which is tolerant of network failure. It evaluates video quality with different retransmission policies combined with various path failure detection thresholds, path bandwidths, delays and loss rate conditions through Partial Reliable Stream Control Transmission Protocol (PR-SCTP). A solution called Evalvid-SCTP, which is a trace driven simulation of MPEG-4 video over SCTP, was designed to achieve the performance evaluation.

An Analysis of Alterations to the SCTP RTO Calculation Mechanism for WLAN Environments

As a connection oriented transport layer protocol the Stream Control Transmission Protocol (SCTP) inherits many of the features of the Transmission Control Protocol (TCP) including the mechanism by which Retransmission Timeout (RTO) is calculated. Previous investigations have established that the mechanism through which SCTP calculates RTO is inappropriate in Wireless LAN (WLAN) environments. This paper investigates the performance implications of changes to the SCTP RTO calculation mechanism. In particular alterations to the parameters α, the smoothing factor, and β, the delay variance factor are investigated. Results indicate that performance improvements are achievable through careful selection of α and β values. Throughput improvements of 63% over the default mechanism defined in RFC 4960 are described. These performance improvements however, while significant, still can not address the switchover delays which result from the distortions caused by continuously increasing RTT values in WLAN environments.

Using 802.11 MAC Retransmissions for Path Selection in Multi-Homed Transport Layer Protocols

The Stream Control Transmission Protocol (SCTP) is a transport layer protocol which can support mobility through its multi-homing feature. One of the key parameters used by SCTP to manage path selection is Retransmission Time Out (RTO). We illustrate that SCTPs evaluation of underlying paths using end to end metrics, results in the calculation of excessive RTO for degraded wireless paths. This excessive RTO causes SCTP to behave in a counter intuitive manner which delays path switchover. Our investigation shows that the increased Round Trip Time (RTT) is as a result of retransmissions at the 802.11 MAC. We illustrate that when a connectionless 802.2 LLC service is utilized, 802.11 independently implements positive frame acknowledgement resulting in significantly increased RTT. We propose a cross layer path selection algorithm, which recognizes increased 802.11 MAC retransmissions as an indicator of imminent path failure. Results presented indicate that our cross layer approach has excellent performance in comparison to standard SCTP strategies.

An Adaptive Optimized RTO Algorithm for Multi-homed Wireless Environments

As a transport layer protocol SCTP uses end to end metrics, such as Retransmission Time Out (RTO), to manage mobility handover. Our investigation illustrates that Wireless LAN (WLAN) mobility causes continuously increased Round Trip Times (RTT) resulting from 802.11 MAC retransmissions, regardless of the service specified by upper layers. We present scenarios where the current understanding of SCTP switchover aggressiveness is invalid; spurious failovers together with excessive RTO result in new forms of receiver buffer blocking communication failure. Given wireless mobility performance issues, together with the ambiguity of end to end metrics, we propose an Adaptive Optimized RTO algorithm for wireless Access Networks (AORAN) which uses local as well as end to end metrics to manage mobility. AORAN measures RTT between the mobile node and Access Point (AP) to calculate wireless and Internet RTO subcomponents. We also show binary exponential backoff has negative effects on SCTP with increased wireless RTT; AORAN introduces a decision mechanism which implements backoff on RTO subcomponents only when appropriate.

Path Failure Effects on Video Quality in Multihomed Environments

The networking capabilities of mobile devices have increased dramatically in recent years. A wide range of mobile devices now provide the capability to simultaneously connect to multiple underlying networks. The increasingly ubiquitous deployment of WLAN technologies, particularly in urban and campus scenarios, has allowed mobile developers to enhance their application functionality based on the characteristics of wireless rather than mobile networks. This increase in capability comes at a cost however as the provision of seamless mobility for wireless networks remains an open research area. Multi-homing technologies which exploit multiple underlying networks in an application transparent manner, have the potential to overcome many of the issues relating to wireless network mobility. There are a number of mechanisms through which a multi-homed session can be achieved. This paper compares two approaches to multi-homing support; transport layer multi-homing utilising the Stream Control Transmission Protocol (SCTP) and application layer multi-homing utilising the Session Initiation Protocol (SIP). Multimedia streaming experimental evaluations are undertaken which compare the performance of SCTP against a number of increasingly aggressive SIP based handover strategies in response to a path failure. Results indicate that the transport layer SCTP based strategy has significantly better performance within the handover period than the application layer SIP based strategies achieving up to 22.5% better performance than the SIP based strategies.

A Unified Notification Service Utilizing Explicit Wireless Degradation Notifications

The dynamic characteristics of heterogeneous networks require cross layer solutions to optimize performance. Many cross layer solutions however, have tightly coupled Upper Layer Protocols (ULP) to lower layer performance metrics. Such an approach hinders the introduction of potential performance enhancements. In this paper we propose a Unified Notification Service (UNS) which will enable cross layer solutions while decoupling ULPs from lower layer performance metrics. UNS is designed as an open extensible framework to accommodate both existing and emerging notification plug-ins. UNS will also enable the integration of existing protocols to form new notification types. We illustrate how the general purpose solution provided by UNS can incorporate a new Wireless Degradation Notification (WDN) plug-in. We compare the performance of MAC layer retransmissions and Received Signal Strength (RSS) as network performance indicators, and illustrate that a retransmission based metric outperforms an RSS based approach.

Extracting Bulk Configuration Data from a Relational UMTS Management Database

The rapid evolution of 3G technology demands an adaptive, robust network management system. In the 3G UMTS (Universal Mobile Telecommunications System) system, a new radio access network (RAN) called UTRAN (UMTS terrestrial radio access network) is introduced based on W-CDMA (instead of TDMA/FDMA) air interface transmission. The normal network management functionality needs to be supported that is, fault configuration, accounting, performance and security management (FCAPS). The network resource model for UMTS is defined by 3GPP [1] and is object oriented Output data for bulk configuration has a standard XML format defined by the 3GPP. By applying standard software engineering techniques for exporting XML from a relational database we demonstrate that using a relational database for storing management data can achieve very good performance for bulk configuration management export.