GENERAL ASPECTS AND PRINCIPLES RELATING TO DIGITAL
PLMN ACCESS SIGNALLING REFERENCE POINTS
1 General
1.1 Recommendation I.120 provides the conceptual principles on which an ISDN is based. The main
feature of an ISDN is the support of a wide range of service capabilities, including
voice and non- voice applications, in the same network by offering end-to-end digital
connectivity.
1.2 The ISDN concept supports a wide range of service capabilities within the same network such as:
packet-switched and circuit-switched connections up to and including 64 kbits/sec on
a bearer (B) channel. A digital PLMN network supports the same wide range of service
capabilities, including reliable end-to-end digital connectivity and contains
specialized supporting functions, e.g. speech bit rate reduction processing. However, due to
the limited resources associated with radio channels nominal circuit-switched
connections may have to be limited to rates lower than 64 kbit/s (e.g. connections up to and
including 16 kbits/sec).
1.3 The key element of service integration for a digital PLMN is the provision of a set of standard, multipurpose user network interfaces. These interfaces present a focal point
for the development of digital PLMN components and configurations that result in PLMN
ISDN-like terminal equipment and applications.
1.4 A digital PLMN is recognized by the service characteristics available through the user-network
interfaces, rather than by its internal architecture, configuration and technology.
This concept plays a key role in permitting user and network technologies and
configurations to evolve separately.
The service definitions are provided in separate Recommendations.
1.5 The digital PLMN user-network interface point should provide:
a) flexibility of user terminals with respect to digital PLMN network interconnection;
b) flexibility of separate user terminal evolution and PLMN technology evolution;
Fascicle VI.13 - Rec. Q.1061 1
c) flexibility of definition and provisioning for PLMN basic bearer services, teleservices and
supplementary services; and
d) operation and maintenance capabilities.
1.6 wInterface applicationsw
Figure 1/Q.1061 shows some examples of digital PLMN interfaces. The following cases are identified:
1) access of individual digital PLMN terminals (i.e., hand-portable or vehicle-mounted terminals);
2) access of multiple digital PLMN terminal installation;
3) access of a mobile PABX or LAN;
4) dedicated service networks; and
5) land-line ISDN networks.
1.7 A number of digital PLMN signalling reference points are specified and any one of these reference points may be used as the user to network interface point. Figure 2/Q.1061
illustrates the major signalling reference points in a digital PLMN.
a) Xm - TEm to mobility management reference point;
b) Sm - mobility management to RF transmission management reference point; and
c) Um - mobile station (MS) to base station (BS) reference point.
The description of the functional entities is given in 2.
1.8 The MS-BS interface for the digital PLMN mobile station includes both the logical part of the
communication between the MS and the BS, and the control and physical requirements of
the radio channel.
It should be noted that the Um reference point is the traditional radio-based network interface
and is very much RF technology dependent.
The detailed Um reference point will be specified in separate Recommendations.
2 Functional entities between signalling reference points
2.1 PLMN call control adaptation functions are those functions necessary to convert standard CCITT
call control signalling into call control signalling appropriate in the digital PLMN
environment. For example, some parameters of standard CCITT call control signalling
messages need to be translated or some new parameters need to be added, such as IMSI,
mobile serial number.
2.2 Mobility management functions are those functions necessary to support the mobility of the user
terminal, such as informing the network of its present location, and managing user
terminals during handover. In addition, because of the "open" connection via radio, some
functions such as user authentication are included in this functional entity.
2.3 RF transmission management includes those functions associated with providing a radio connection to the BS based on cellular technology, such as selecting the channel coding,
controlling transmitter power, seizing a channel, changing a channel, etc.
2.4 The relationship of these four functional entities is envisaged as of a nested nature and can
be illustrated in Figure 3.Q.1061.
2 Fascicle VI.13 - Rec. Q.1062
FIGURE 1/Q.1061
Digital PLMN interfaces
FIGURE 2/Q.1061
Signalling reference points in a digital PLMN
Fascicle VI.13 - Rec. Q.1061 3
FIGURE 3/Q.1061
Relationship between functional entities
3 Signalling reference point characteristics
The PLMN signalling reference points are specified by a comprehensive set of characteristics,
including:
1) channel structures and access capabilities;
2) signalling protocols; and
3) performance characteristics.
The definition of the digital PLMN interfaces at the signalling reference points follows the
ISDN layered approach to the S and T interfaces according to the OSI reference model.
4 Signalling reference point capabilities
In addition to the multi-service capability, a digital PLMN signalling reference point may
allow for capabilities such as the following:
1) multidrop and other multiple terminal arrangements;
2) choice of information bit rate, switching mode, coding method, etc., on a call-by-call or
other basis (e.g. semi-permanent or subscription time option); and
3) capability for compatibility checking in order to check whether calling or called terminals
can communicate with each other.
5 Relation of signalling reference points to the user network interface(s)
5.1 Signalling reference points are functional interfaces where the user-network interface(s) may
be specified.
5.2 The choice of the user-network interface is based on service definitions in the relevant
