Telephonic communications – Plural exchange network or interconnection – Interexchange signalling
Reexamination Certificate
2000-05-16
2003-12-30
Matar, Ahmad F. (Department: 2642)
Telephonic communications
Plural exchange network or interconnection
Interexchange signalling
C370S385000
Reexamination Certificate
active
06671367
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to capability negotiation in a telecommunications network and in particular, though not necessarily, to the negotiation of a suitable speech codec.
BACKGROUND TO THE INVENTION
Telecommunications networks currently rely to a large extent upon the Signalling System no.
7
(SS
7
) as the mechanism for controlling call connections and for handling the transfer of signalling information between signalling points of the networks.
Typically, one or more application and user parts at a given signalling point will make use of SS
7
to communicate with peer application and user parts at some other signalling point. Examples of user parts are ISUP (ISDN User Part) and TUP (Telephony User Part) whilst examples of application parts are INAP (Intelligent Network Application Part) and MAP (Mobile Application Part). The conventional SS
7
protocol stack includes Message Transfer Parts MTP
1
, MTP
2
, and MTP
3
which handle the formatting of signalling messages for transport over the physical layer as well as various routing functions.
There has been considerable interest of late amongst the telecommunications community in using non-standard (i.e. non-conventional within the telecommunications industry) signalling transport mechanisms in telecommunications networks in place of the conventional SS
7
mechanisms. The reasons for this are related both to improvements in efficiency as well as potential cost savings. Much consideration has been given for example to the use of Internet Protocol (IP) networks to transport signalling information between signalling points. IP networks have the advantage that they make efficient use of transmission resources by using packet switching and are relatively low in cost due to the widespread use of the technology (as opposed to specialised telecommunication technology). There is also interest in using other transport mechanisms including AAL1/2/5, FR etc.
The ISUP standard which deals with the setting-up and control of call connections in a telecommunications network is closely linked to the SS
7
signalling transport mechanism and does not readily lend itself to use with other non-standard transport technologies such as IP and AAL2. As such, several standardisation bodies including the ITU-T, ETSI, and ANSI, are currently considering the specification of a signalling protocol for the control of calls, which is independent of the underlying transport mechanism. This can be viewed as separating out from the protocol, Bearer Control functions which relate merely to establishing the parameters (including the start and end points) of the “pipe” via which user plane data is transported between nodes, and which are specific to the transport mechanism. The new protocol, referred to as Transport Independent Call Control (TICC), retains Call Control functions such as the services invoked for a call between given calling and called parties (e.g. call forwarding), and the overall routing of user plane data.
The new network architecture resulting from the separation of the call and Bearer Control levels results in an open interface appearing between a Call Control entity and a Bearer Control entity, where these entities are referred to as a Media Gateway Controller and a Media Gateway respectively. The open interface is referred to hereinafter as X-CP, examples of which are the MEGACO work of the IETF and the H.248 work of ITU Study Group
16
(SG
16
).
Traditionally, fixed telephone networks make use of Pulse Code Modulation to transport user plane data, e.g. voice, facsimile, etc, between network nodes. Modem cellular networks on the other hand often use one or more coders/decoders (referred to as “codecs”) to compress voice signals for efficient transmission across the air interface and within the cellular networks themselves. Where a telephone call connection extends between two networks (or terminals) which support different or multiple speech codecs, a negotiation may be carried out between the terminals to decide upon an appropriate codec. If this negotiation is not carried out, the result may be a requirement for transcoding at the interface between the networks, i.e. conversion from one form of speech coding to another. Transcoding is expensive in terms of resources, significantly degrades speech quality, and introduces a processing time delay. Codec negotiation is therefore the preferred option.
In addition to codec negotiation, there is often a need in conventional telecommunications networks to negotiate other functionality and parameters. For example, it may be desirable to negotiate security capabilities such as voice ciphering and data encryption between terminals or nodes in telecommunications networks.
SUMMARY OF THE PRESENT INVENTION
According to a first aspect of the present invention there is provided a method of negotiating a call capability between signalling points in a telecommunications system, the method comprising:
sending a capability preference or prioritised list of preferences from an originating signalling point to a terminating signalling point or signalling transfer point, at the Call Control level; and
returning a capability acceptance from the terminating signalling point or signalling transfer point to the originating signalling point at the Call Control level, if the terminating signalling point or signalling transfer point accepts a preference sent by the originating signalling point.
It will be appreciated that in some cases, e.g. where the terminating signalling point or signalling transfer point does not accept a capability preference (or one of a list of preferences) sent by the originating signalling point, no acceptance message may be returned in which case a default capability is assumed by both points. Alternatively, a default message may be returned indicating that the default codec is to be used. If no codec can be agreed upon, then in certain situations a call may be released due to network incompatibility.
The present invention is particularly suited to negotiating speech codec capabilities between signalling transfer points located in different telecommunications networks. For example, in Japanese telecommunications networks, the invention may be used to negotiate the use of one of VSELP, PSI-CELP, or &mgr;-law coding, where claw coding is the default coding. However, the invention is also applicable to negotiating other capabilities including security capabilities (e.g. voice ciphering and data encryption).
The protocol used to conduct the negotiation may be TICC, or may be a specific protocol also employed at the CC level, i.e. a User Plane Capability Negotiation protocol.
Where the Call Control and Bearer Control levels are controlled by separate protocols, a signalling point reacts to the selection of a capability at the Call Control level by notifying the Bearer Control level, if the selection affects the bearer level. If appropriate, notifications may be subsequently sent at the bearer level between bearer switching points to enable the establishment of appropriate bearer level resources.
Preferably, the signalling point or signalling transfer point is a Media Gateway Controller. More preferably, the Media Gateway Controller communicates with one or more Media Gateways which exist at the Bearer Control level.
Despite the fact that certain options supported for a capability at the Bearer Control level may be known at the Call Control level, the Call Control level will not necessarily know the current availability of those options at the Bearer Control level. Preferably therefore, upon receipt of a capability preference or prioritised list of preferences at a terminating signalling point or signalling transfer point, the Call Control level conducts a negotiation with the Bearer Control level to determine option availability at the Bearer Control level. More preferably, this negotiation occurs between a Media Gateway Controller of the Call Control level and a Media Gateway of the Bearer Control level.
Where a prioritised list of preferences is sent from an origin
De Nicolo David
Dikic Nebosja
Dingle Barry
Graf Leslie
Groves Christian
Matar Ahmad F.
Nguyen Quynh H.
Telefonaktiebolaget LM Ericsson
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