Overview

In this chapter, we discuss the basic ANSI-41 mobile telecommunications network functions related to intersystem handoff. These functions are divided into the following categories: ^[1]

• Handoff measurement

• Handoff forward

• Handoff back

• Path minimization

• Call release

We also examine the ANSI-41 application processes that support these basic network functions. While there are other handoff-related processes in ANSI-41 for authentication, voice feature, and short-message services support we treat these separately in later chapters. In this chapter we focus on the basic functions required to hand off a call from one system to another.

ANSI-41 does not include complete specifications for each of the basic intersystem handoff processes; for example, ANSI-41 does not define the circumstances under which an MSC should attempt path minimization, leaving this as an implementation issue. This is a deliberate omission and an example of the standards approach taken in ANSI-41: It is intended that the procedures defined address only the required intersystem transactions without infringing on the right of individual system operators and manufacturers to design their internal methods and procedures as they may deem best. ^[2]

In the course of describing the processes, we identify the ANSI-41 mobile application part (MAP) operations (e.g., FacilitiesDirective) used to accomplish intersystem handoff process tasks. We summarize this information at the end of the chapter. Note that we employ the ANSI-41 convention for operation component acronyms; the Invoke component acronym is in all capital letters (e.g., FACDIR), while the Return Result component acronym is in all lowercase...