Quality of Service Methods for IP Networks


This article provides an analysis of the methods and protocols used to improve the Quality of Service (QoS) in Internet Protocol (IP) networks. The challenges of achieving a high level of QoS in IP networks are examined. The traditional methods for QoS are presented along with current and proposed methods for QoS in IP networks. The goal of the article is to educate the reader on the various methods of achieving QoS and to examine the best options for the future. As Internet bandwidth requirements grow and high quality IP applications such as real-time video and Voice over IP (VoIP) become widespread, QoS will be critical to the success of providing high quality Internet Protocol (IP) services.

Quality of Service

The Internet Engineering Task Force (IETF) defines Quality of Service (QoS) as a service agreement (or a guarantee) to provide a set of measurable networking service attributes, including end to end delay, delay variation (jitter), and available bandwidth. The International Telecommunication Union (ITU) defines QoS as the collective effect of service performance which determines the degree of customer satisfaction. Cisco defines QoS as the capacity of a network to provide better service to selected network traffic.

This article defines QoS as the capability of an IP network to classify and prioritize traffic flows in order to ensure that the technical characteristics of packet loss, delay, error rate and jitter are met for each customer. Quality of Service (QoS) methods are based on the ability of an IP network to identify and classify traffic that is higher priority so that the technical requirements of the customer are met. QoS methods are based on having an adequate amount of bandwidth (i.e. low network utilization) to prevent traffic congestion and to permit the setup of priority traffic flows.

Traditional QoS Methods for IP Networks managed service providers in woodbridge

In the early days of the Internet, the applications were low bandwidth and not real-time in nature, so a high quality of service was easy to maintain. The early Internet applications of email, File Transfer Protocol (FTP) and web browsing were low-speed bursty IP traffic so delay, latency and bit error rates were not critical. The early networks relied on the Transmission Control Protocol (TCP) to provide flow control, error checks and retransmission of data packets when necessary. TCP provides a best-effort level of QoS that is acceptable for email and web browsing. However, the TCP protocol alone will not provide an acceptable level of QoS for real-time high bandwidth applications such as video or VoIP. Another method used to improve the QoS in early TCP/IP networks was the First-In First-Out (FIFO) buffer. FIFO buffers provided a simple method to store packets when there was temporary network congestion, but FIFO buffers make no intelligent decision about the priority of traffic. This section will examine some of the traditional methods of QoS to include the Transmission Control Protocol (TCP), IP Routing Protocols, First-In First-Out (FIFO) buffers, the Real Time Protocol (RTP) and the Explicit Congestion Notification (ECN) protocol.

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