ITU-T - Y.1541
Network performance objectives for IP-based services
|Publication Date:||1 February 2006|
This Recommendation specifies network (UNI-UNI) IP performance values for each of the performance parameters defined in [ITU-T Y.1540]. The specific performance values vary, depending on the network QoS class. This Recommendation defines eight network QoS classes, two of which are provisional. This Recommendation applies to international IP network paths (UNI-UNI). The network QoS classes defined here are intended to be the basis of agreements between end-users and network service providers, and between service providers. The classes should continue to be used when static agreements give way to dynamic requests supported by QoS specification protocols.
The QoS classes defined here support an extremely wide range of applications, including the following: conversational telephony, multimedia conferencing, digital video, and interactive data transfer. Designers of new user applications should first consider using the existing QoS classes, and possibly include technologies to mitigate packet transfer impairments in their design. If one or more packet transfer requirements is not satisfied, then a new class may be considered rather than modifying the current/stable classes. However, any desire for new classes must be balanced with the requirement of feasible implementation, and the number of classes must be small for implementations to scale in global networks. Thus, the extent of user application coverage may expand over time, and readers of this Recommendation are urged to consult the latest version, including the appendices.
Since the QoS classes have been developed to support user applications, their numerical objectives are likely to support the same applications on networks using alternate technologies or combinations of technologies, providing that the fundamental transfer unit has a one-to-one correspondence with IP packets as used here (no fragmentation), and that the overhead of the alternate technology is a non-substantial addition to the IP header (e.g., multi-protocol label switching (MPLS) label and Ethernet frame overhead).
The QoS objectives are primarily applicable when access link speeds are at the T1 or E1 rate and higher. This limitation recognizes that IP packet serialization time is included in the definition of IP packet transfer delay (IPTD), and that sub-T1 access rates can produce serialization times of over 100 ms for packets with 1500 octet payloads. Also, this Recommendation effectively requires the deployment of network QoS mechanisms on access devices in order to achieve the IP packet delay variation (IPDV) objective, especially when the access rate is low (e.g., T1 rate). Network designs may include lower access rates if:
1) Network planners understand the effect of additional serialization time on the user network interface (UNI) to UNI objective for IPTD.
2) QoS mechanisms limit the access contribution to IPDV, and the UNI to UNI objective for IPDV is met. The current IPDV objective is necessary to achieve high quality application performance, as Appendices III and VII clearly show.
This Recommendation provides the network QoS classes needed to support user-oriented QoS categories. Accordingly, this Recommendation is consistent with the general framework for defining quality of communication services in [ITU-T G.1000], and with the end-user multimedia QoS categories needed to support user applications given in [ITU-T G.1010].
NOTE - This Recommendation utilizes parameters defined in [ITU-T Y.1540] that can be used to characterize IP services that are provided using IPv4 and IPv6. [ITU-T Y.1540] was used as the foundation of MPLS performance parameters in [ITU-T Y.1561] and Ethernet service performance parameters in [ITU-T Y.1563]. Applicability or extension to other protocols is for further study.