Exchange for communication network

Details Exchange for communication network Exchange for communication network

1996-10-29

2002-09-10

Ton, Dang (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S395100

Reexamination Certificate

active

06449278

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to telecommunication exchanges, methods of using such exchanges, switching systems for communication networks, methods of using such systems, and methods of routing traffic in networks.
BACKGROUND OF THE INVENTION
Known switched telecommunication networks, in general, consist of a hierarchical structure as shown in
FIG. 1
, and comprise some of the following set of elements:
local exchanges
trunk exchanges
gateway exchanges
international exchanges
trunk routes and trunk circuits
Local exchanges are nodes in the network to which subscribers are connected. The low calling rates generated by subscribers are concentrated into streams of traffic which are routed onwards to trunk exchanges.
Trunk exchanges do not have subscribers connected to them. They operate on traffic which has been received from other exchanges and which has been pre-concentrated by the local exchanges.
Between any two exchanges (of any type), there exists a trunk route; each trunk route consists of a set of trunk circuits. Each trunk circuit, at any one time, carries the voice (or data) samples for one telephone call.
Trunk exchanges can act as either transit exchanges or tandem exchanges, depending upon their position in the network. It is also possible for an exchange to be a hybrid; for example, a local exchange can include some tandem functions. Occasionally, subscribers are connected directly to a trunk exchange; this can be in order to offer special services or for special reasons of topology or efficiency. The location and type of exchanges is a balance between transmission and switching costs, and the availability of sites.
Specialised trunk networks may also be employed to offer services where such services are not available on the main trunk exchanges or where significantly different calling patterns apply. A good example of such a specialised network is BT's Digital Derived Services Network which offers freephone 0800 and local rate 0345 services. Specialised networks are used when the traffic volumes make it difficult to justify the expense of upgrading the main trunk network or where service features are offered by a different vendor. However, the cost of switching through both trunk exchanges and specialised exchanges may be high if traffic starts to rise significantly. In some cases, the services will then be added in to the main trunk exchanges, and the specialised exchanges can be developed further or re-engineered to provide other services.
Signalling System No.7 (SS No.7) is based upon ITU-T Recommendations Q701-706, Q721-725 and Q761-767. SS No.7 is designed for digital communication networks, including ISDN, which use stored program control exchanges. SS No.7 is optimised for 64 kbit/s bearers, however it can be used on 56 kbit/s bearers and can be operated at lower rates over analogue bearers (e.g. 4.8 kbit/s). It is currently widely used in the UK to set up and clear down telephone calls over 64 kbit/s trunk circuits between digital exchanges. SS No.7 is constructed on a modular basis. SS No.7 (in a narrowband environment) consists of a four-level hierarchy in two main parts: the message transfer part (MTP) which covers levels 1 to 3, and the application-dependent user part (e.g. telephone user part or ISDN user part) which is at level 4.
FIG. 2
is a schematic of the overall SS No.7 structure in which the four levels correspond approximately to the first four levels of the well known seven-layer OSI model.
SS No.7 can also be used in a broadband environment. In such a situation, the broadband version of ISUP (commonly known as B-ISUP) would be used (based upon ITU-T Recommendations Q1761-1764) together with the same MTP-L3 as is used for narrowband. At the levels below MTP-L3, ATM would be used; with, for example, the ATM SAAL (based upon ITU-T Recommendations Q2100, etc.) being used instead of MTP-L2.
A brief summary pertaining to SS No.7 in a narrowband environment follows.
SS No.7 conveys information within signal units (SU), which are delimited by flags. There are three types of signal units, namely FISUs, LSSUs and MSUs. MSUs are the type of signal units which carry the signalling messages which are generated or handled by level 3, level 4 and above.
Level 1 (MTP-L1) defines the physical and functional characteristics of the signalling data link and the access to it. The signalling data link is a full duplex link which can operate over terrestrial or satellite channels. Normally a signalling data link is TS16 in the 32 time-slot 2048 kbit/s PCM system; however TS67-70 in the higher-order 8 Mbit/s multiplex can also be used; the signalling bit rate being 64 kbit/s in both cases. Lower rate signalling data links can also be used.
Level 2 (MTP-L2) carries out the signalling link functions. These include the adaptation between the processor's signal units and the continuous bit stream which is used over the signalling data link (including the insertion and removal of flags plus bit stuffing). Level 2 deals with alignment, with error detection and correction (using cyclic redundancy code x
16
+x
12
+x
5
+1), and with the monitoring of the bit error rate. Where necessary, level 2 generates and receives LSSUs and FISUs. Level 2 transfers MSUs to and from level 3.
Level 3 (MTP-L3) carries out the signalling message handling functions; that is, it directs signalling messages to the correct signalling link or user part. Level 3 also carries out signalling network management functions; that is, it reconfigures signalling links after a failure or recovery, and generates and receives MTP-L3 network management signalling messages.
Level 4 is the user part; for example, it can be the TUP (telephone user part) or ISUP (ISDN user part).
All signal units (SU) include the following fields:
F =
Flag (01111110)
CK =
Check bits
LI =
Length indicator
FIB =
Forward indicator bit
FSN =
Forward sequence number (this is achieved by
incrementing the previous FSN by 1 in modulo
128)
BIB =
Backward indicator bit
BSN =
Backward sequence number
In addition, MSUs include the following fields:
SIO =
Service information octet
SIF =
Signalling information field.
The service information octet and the signalling information field constitute the real contents of the signalling message as seen by the user parts and above. The service information octet identifies the type of user part. The signalling information field contains a routing label and the information content of the signalling message. The routing label includes the originating point code and the destination point code. (Note that the routing label for broadband SS No.7 is exactly the same as for narrowband SS No.7.)
The routing of messages such as MSUs, either for controlling telephone calls, for managing the signalling network, or for other purposes (e.g. accessing special services or data-bases), requires that the signalling points in the signalling network are given unique addresses. With SS No.7, these unique addresses are called point codes. In the SS No.7 signalling network, telephone exchanges are examples of signalling points.
The originating point code and the destination point code in a signalling message identify the sender and receiver of that signalling message. Thus this pair of point codes identify the signalling route set between the sending signalling point and the receiving signalling point. The signalling route set consists of all possible signalling paths between those two signalling points.
If the user part associated with the signalling message is the TUP or ISUP (or B-ISUP), then the pair of point codes within the signalling message identifies the sending exchange and the receiving exchange, and identifies the signalling route set between those two exchanges. This same pair of point codes also identifies the trunk route between those two exchanges (used by the telephone call with which the signalling message is associated).
In the situation where associated SS No.7 signalling is used, then the signal

Affiliated with

Also associated with

Rating

Exchange for communication network does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Exchange for communication network, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exchange for communication network will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2816553