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QoS Standards for IP Networks and Services

The migration of telecoms networks from circuit switching and ATM to IP poses major challenges for maintaining the QoS necessary for applications such as voice, video and streaming services. This article describes the key ITU-T and 3GPP standards relating to QoS...

ITU-T and 3GPP QoS Standards

Y.1540 is the recommendation defining the basic common performance parameters for evaluating network performance for IP networks. The specifications of these common parameters are the basis for quantitatively evaluating, measuring, and comparing network QoS performance. Y.1540 was last revised in 2007.

Y.1541 is the recommendation specifying the objectives of end-to-end network performance or performance between user network interfaces (UNI’s) based on Y.1540 parameters. Y.1541 was last revised in 2005.

Y.1542 describes some ideas regarding how the end-to-end performance objectives specified in Y.1541 can be achieved in multiple-carrier environments. This recommendation was originally called G.fepo and received consent in 2006. Notably, Y.1542 is a framework recommendation—i.e., it does not include anything to mandate. It simply discusses approaches for achieving the end-to-end performance objectives. It mainly describes two different approaches: (1) Impairment Allocation, which assigns a subset of end-to-end performance objectives to each provider on the path, thus achieving the total end-to-end performance objectives, and (2) Impairment Accumulation, which accumulates the sum of the performance budget commitment from each provider on the path and evaluates whether the end-to-end QoS requirements are fulfilled.

Y.1543 specifies the measurement methodology for a network with a multi-provider environment.

TS 22.105 defines QoS parameters for bearer services and teleservices, and sets expectations for measures such as delay, delay variation, loss, etc for each of the service types identified

TS 23.107 develops the QoS framework for the UMTS bearer service

ITU-T Y.1540 Performance Parameters

IPTD measures the end-to-end delay of a service, and consists of contributions from several sources. These delays are additive, so the total IPTD value is the sum of all of these contributions. Certain delays are fundamental (such as propagation delay), whereas as other contributors are tractable to design trade-offs, such as transport delay (where queuing and scheduling can have an effect) and jitter buffer delay

IPDV measures the variation in the end-to-end delay between a minimum and maximum (strictly the 99th percentiles, rather than absolute maximums)

IPLR measures the ratio of loss to delivered packets, including packets loss through network congestion (typically dropped by intermediate routers) and packet loss through late arrival at jitter buffers

IPER measures packets delivered to the correct destination but with errors in the packet

Additional measurements are listed in the standard, and it provides flexibility on which percentile points are used, for example, in specifying IPDV

ITU-T Y.1541 QoS Classes

Y.1541 defines a set of classes of services and proposes upper bounds on the QoS parameters for each of these, as shown above. The most recent revision of Y.1541 includes two additional QoS classes (Classes 6 and 7) for further discussion.

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