scope:

This Recommendation defines IP-layer and sub-IP-layer performance parameters for communication scenarios where one or more network technologies provide the access path between a user's communication device and an IP-based network (the Internet is the most common example), where the number of access paths to the IP-based network is changing (possibly due to mobility or to other factors such as failure or overload).

The performance parameters defined here build on the foundation of point-to-point parameters defined in [ITU-T Y.1540] and point-to-multipoint parameters defined in [ITU-T Y.1544].

One way to view the coverage of this Recommendation in comparison with [ITU-T Y.1540] is to view them both in the context of the 3-by-3 matrix of communication phases and performance categories of speed, accuracy and dependability.

Whereas [ITU-T Y.1540] covers the important phase of communication when the user device has activated a network interface and performed sub-IP layer and IP layer configurations, this Recommendation recognizes the importance of metrics for access network activation and deactivation corresponding to a user device's mobility into and beyond coverage areas, and the policy of a user device to use access networks it deems suitable.

Furthermore, this Recommendation recognizes that when more than one access network is accessible to the user device, the device policy may be to:

• hand-over communications to one network and deactivate others;
• prefer one access network but keep the other networks active or in back-up/standby;
• use the information transfer capabilities of all networks simultaneously.

New performance parameters are needed to accommodate all the policies above. At the core of hand-over performance is the simple activation speed and accuracy of the newly accessible network, followed by the implementation of policy, or policy action followed by deactivation.

Policy implemented before activation, based on a priori knowledge or field strength measurements is beyond the scope of this Recommendation. This phase of operation is often referred to as access network "discovery".

Thus, this Recommendation recognizes policy as an element of activation, prior to hand-over or possibly precluding hand-over when all information transfer capabilities will be used simultaneously.