Communications system and method

Details Communications system and method Communications system and method

1998-07-08

2002-08-13

Kizou, Hassan (Department: 2662)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S252000, C370S477000, C375S240000

Reexamination Certificate

active

06434151

ABSTRACT:

This invention relates to telecommunications systems and in particular to an apparatus and method for selecting voice encoding algorithms in such systems.
BACKGROUND OF THE INVENTION
A recent development in telecommunications technology has been the introduction of asynchronous networks in which traffic is carried in packets or cells, the technique generally being referred to as the asynchronous transfer mode (ATM). In such a network, user traffic is packaged into cells each of which is provided with a header containing supervisory or overhead information. As each packet is filled, it is routed across the network to its desired destination, the routing being determined from the packet header information. A potential problem in such a system is the assembly delay inherent in filling a packet with user information or traffic. For high bit rate users the packets are filled rapidly and the delay is therefore insignificant. For low bit rate users, for example voice traffic which is typically carried in 64 kbit/channels, the assembly delay required to fill a packet can become unacceptably long. One approach to this problem is the insertion of padding or dummy traffic into the packets so as to increase the rate at which they are filled. This is considered undesirable as it is an inefficient use of the available bandwidth. To address this problem various workers have introduced ATM transmission techniques in which information streams, typically voice traffic, from a number of low bit rate users is multiplexed on to a single ATM connection. This increases the rate at which individual ATM packets are filled thus overcoming the assembly delay problem. A particular protocol defining this form of transmission is that described in the ITU-T AAL2 standard recommendation 1.363.2.
In the multiplexed connection, each individual information stream can carry voice information that has been encoded using one of a number of available algorithms. This encoding reduces the bit rate and thus frees up bandwidth to allow higher volume of voice traffic to be accommodated. The range of algorithms available for this purpose enables voice calls to be transported at a corresponding range of bit rates. This offers users the ability to reduce or increase the amount of bandwidth required to support voice calls with a corresponding loss or gain in voice quality. This also allows operators to offer premium voice services at a higher cost to the user. In addition to voice encoding, silence suppression may also be used to reduce the amount of bandwidth required for calls.
It will be appreciated that where a number of users share a single ATM connection for voice traffic, they will not in general all use the same algorithm for voice encoding. Each user will use an algorithm appropriate to the particular call and to the class of service that he or she enjoys. Further, it is possible for more than one algorithm to be employed during an individual call, e.g. to overcome temporary congestion where a call may be ‘downspeeded’ to reduce its coding rate and thus save on bandwidth. As soon as this congestion disappears, the call can be ‘upsped’ back to the original coding rate. In order to ensure satisfactory operation of such a system, it is of course necessary that the interworking functions (IWF) at both ends of the ATM connection are made aware of the encoding algorithm currently in use on each individual call. This is at present performed from explicit protocol control information carried in the headers of the AAL2 packets transporting the user information streams. The AAL2 Negotiation Procedure (ANP) as defined in the ITU-T standard draft recommendation I.anp is used to define, during the call set up procedure, the meaning of this protocol control information. This meaning is conveyed by reference to a standard profile.
As discussed above, a number of coding algorithms may be used in the course of a single call. To address this scenario, the ITU-T recommendation currently designated as I.trunk defines a number of coding profiles each containing a number of coding algorithms that belong to a particular coding family. A predetermined profile is selected for a call and conveyed from the transmitting IWF to the receiving IWF by means of the ANP. Any algorithm within that profile is then available for use during that call. Each of the algorithms within a profile can be identified within the header of an AAL2 CPS packet (or minicell) by reference to two fields. These are the Length Indicator (LI) field and the User-to-User Information (UUI) field whose meanings are fixed by the ANP such that each algorithm can be uniquely identified from CPS packet to CPS packet throughout a call. However, it is a prerequisite of this procedure that only the standard algorithm profiles can be employed.
While this approach provides an effective method of identifying coding algorithms to the receiving interworking function (IWF), it suffers from the disadvantage that only a small number of encoding algorithm profiles can be identified in this way and there is no mechanism for identifying a non-standard profile of encoding algorithms. A voice call may thus have to employ a less than ideal profile as this is all that is currently available from the standard profile set.
SUMMARY OF THE INVENTION
An object of the invention is to minimise or to overcome the above disadvantage.
A further object of the invention is to provide an improved method of identifying algorithms used for voice encoding in a telecommunications system.
According to the invention there is provided a method of transmitting a plurality of narrow band digital traffic channels in packets over an asynchronous packet switched network between a transmitter station and a receiver station, wherein each said channel is encoded via one of a set of encoding algorithms associated with that channel, wherein the identity of the algorithnms in each channel set of algorithms is conveyed to the receiver at call set-up between the transmitter and receiver, and wherein the identity of that algorithm emploed to encode a said channel is conveyed via header information provided in the packets carrying that channel.
According to another aspect of the invention there is provided a method of transmitting a plurality of narrow band digital traffic channels over an asynchronous packet switched network between a transmitter station and a receiver station, the method comprising;
at the transmitter station, selecting a group or profile of encoding algorithms for each said channel from a set of encoding algorithms;
encoding each said channel with an algorithm selected from its corresponding group of algorithms;
multiplexing the encoded channels into a common connection over the asynchronous network;
providing a service specific convergence sublayer (SSCS) selection parameter field incorporating for each said channel a plurality of encoding algorithm identifier fields each indicative of a respective algorithm in the group selected for that channel and carrying further information whereby the receiver station may uniquely identify the algorithm currently in use on that channel;
at a receiving station demultiplexing the encoded channels;
determining from the information in the SSCS parameter field the identity of the encoding algorithm currently employed for that channel; and decoding and recovering each said channel via its respective algorithm.
The service specific convergence sublayer selection parameter field is conveyed via an AAL2 negotiating procedure (ANP) established between the transmitter and receiver for allocating user channels therebetween.
According to another aspect of the invention there is provided a method of transmitting a narrow band digital traffic channel between a transmitter station and a receiver station over an asynchronous broad band network, the method including:
at the transmitting station, selecting a group or profile of encoding algorithms for said channel from a set of encoding algorithms and encoding said channel with an algorithm selected from its corresponding group of algori

Affiliated with

Also associated with

Rating

Communications system and method does not yet have a rating. At this time, there are no reviews or comments for this patent.

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

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2876858