Method and apparatus for echo compensation in a telecommunication network

The invention relates to a method for echo compensation in a telecommunications network according to the preamble of claim 1 and a corresponding apparatus according to the preamble of claim. 8

Newer communication architectures, the packet- or cell-based A method for speech signal transmission, such as Voice over IP (VoIP) or Voice over ATM (VoATM) use, see the separation of the signaling and call processing Treatment of a communication link one hand, the transport payload on the other hand in front.

Concretely this switching-oriented networks in connectionless service-related units (call feature server) and transport of user information (carrier or bearer) and Units for controlling these useful connections (Bearer Control) divided. To communicate to conventional circuit-switched telecommunications networks or PSTNs (Public Switched Telephone Networks) to enable, is a "Translation" between these two different communication architectures required.

For transmission of the payload in the packet-oriented Data networks are different, in particular high bit rate Transport technologies such as the aforementioned VoIP or VoATM used. Consequently, this is an on IP (Internet Protocol) or ATM (Asynchronous Transfer Mode) based backbone as a remote transmission network Speech signals used between terminals. Usually are signaling information together with the user data transported. For this purpose, each data packet payload, especially in the packet header, and transport controlling information, ie signaling information on. This signaling information for example, the IP address of a Receiver.

However, the signaling can also regardless of the carrier also be made via the IP / ATM backbone. The aim of this division in signaling and payload is reuse telecommunications services today narrowband networks in broadband networks. This allows especially that Participants either directly via for example the DSS1 (Digital Signalling System No.1) or via switching centers For example, according to ISUP (ISDN User Part) to so-called Call Feature Server (CSF) can be connected. Such Call feature servers separate user data from signaling information and so enable the coupling of packet-oriented Data networks with traditional circuit-switched Telecommunications networks.

On coupling point, the user connections using special, called Media Gateways (MG) servers in the used transport technology transformed. own Media Gateways both interfaces to the PSTN / ISDN and IP / ATM networks and thus form the interfaces between circuit-switching and packet-oriented networks. You can in real-time TDM (Time Division Multiplexing) in -Sprachdaten VoIP / VoATM data and convert vice versa. You can usually it merely the simple addition of this transformation for building implement connections required information.

Media gateways are therefore of central authorities, the Media Gateway Controllers (MGC), controlled. These are used in essential to coordinate and monitor the media gateway and control connections between media gateways. The Media Gateway Controller also work as call feature servers, to further telecommunications services building easier connections allow. The control is effected due to the MGCP (Media Gateway Controller Protocol) or also the H.248 protocol or Q.1950 protocol.

Data communication between use the call feature Server an extended ISUP protocol (ISUP +) or the standardized BICC (Bearer Independent Call Control) protocol. Currently, there is the ITU standards Q.1902.x BICC CS2 (Bearer Independent Call Control Capability Set 2, with its own Service Indicator in MTP (Message Transfer Part)) and Q765.5 BAT (Bearer Application Transport). These describe IP Bearer, that is IP-based data networks, the RTP (Real Time Protocol) as a carrier technology and as a Participants are to provide services that he made the conventional circuit-switched networks knows.

In Fig. 1, the connection of two PSTNs 10 and 12 via a packet-oriented data network 20, here the Internet represented. The two PSTNs (Public Switched Telephone Networks) 10 and 12 each have local exchanges LE (Local Exchange), connected to the telephones 14 as the terminal equipment are, and a transition TX 16 or 18 to the Remote connection network serving on data network 20th Transitions TX 16 and 18 are in each case both a Media Gateway Controller 26 and 28 and with a Media Gateway 22 and 24, respectively.

The media gateways 22 and 24 are directly connected to the Internet 20 connected as an IP bearer. They are used essentially for Entund Packing data packets received via the Internet 20 be or sent. With the data packets, the Payload of a connection between the two PSTNs 10 and 12 transferred. The connection is controlled via the Media gateway controllers 26 and 28, the information by means of BICC CS2 or ISUP + exchange. For common-channel signaling (CCS) between the transitions 16 and TX 18 and the Media Gateway Controllers 26 and 28 is used as the ISUP protocol.

However, particularly in VoIP connections between Media gateways such large maturities occur that echo cancellation is required to achieve a sufficiently high to maintain quality of a voice connection. Currently it is assumed that, for a VoIP connection is always a Echo cancellation, forming, for example, in the IP endpoints Media gateways is necessary. Therefore, it is usually starting from a fixed delay and the echo cancellation at this delay aligned. echo cancellation however, requires an extra effort, if it is permanently active.

The invention is therefore based on the object, the effort, of the echo canceller in the generic telecommunications networks is required to decrease.

This object is achieved by a method for echo cancellation in a telecommunications network having the features of claim 1 and by a corresponding apparatus with the Features dissolved claim 10th Preferred embodiments result from the dependent claims.

An essential point of the invention is a dynamic, not static use or needed, activation of echo cancellation. It could be found namely that echo cancellation, contrary to previous assumptions not is always required.

The previous assumption is mainly based on the current expansion of packet-oriented data networks such as the Internet, can but disregarded that in future a rapidly progressive Development of such data networks due to the increasing Data transfer volume is expected. Than it will be the Quality also of Service (QOS) of voice connections over these data networks increase. This is where the invention with the Thought of to activate a complex echo cancellation only if it is really necessary. this makes possible the operators of such telecommunications networks a cost-effective utilization of existing resources, particular resources for echo cancellation.

Specifically, the invention relates to a method for echo cancellation in a telecommunications network, in which a traffic channel via a packet-oriented data network between a first and a second media gateway. Further a media gateway controller is provided, which at least the first MG controls. The echo canceling is performed at a Voice connection, if necessary, activated when this actually is necessary because the runtime of data packets via a packet-oriented data network is large. Preferably the echo compensation is switched on, when the runtime of data packets exceeds a predetermined threshold.

During the existence of this are traffic channel a jitter buffer and (known per se) means for detecting the so-called "round trip delay" as a run-time measurement means for observed the traffic channel and on exceeding a predetermined delay value ( "Propagation Delay") a sent message and optionally the echo cancellation to be activated. The length of the jitter buffer enters this In addition to the half of the current "round trip" a, so that with the observation of the jitter buffer a watchdog timer is possible. The detection of the current runtime value is especially in a "Encapsulated Notification Request" with the RTP package initiated.

For MGCP following event in the RTP package is re-proposed: Package Name: R <u>Symbol Definition R S Duration</u><u>PD (###) Propagation delay exceeded X</u>

Propagation delay exceeded: The MG is requested, from a Delay ### (in ms) the MGC with the actual delay (###) to report (in ms). Here, the propagation delay is from half round trip and the jitter buffer together.

When applying to a communication between MGC and MG locally based on MGCP or H.248 or echo cancellers removed by use of ISUP (ISDN User Part, Q.761-Q.764) and optionally BICC or ISUP + dynamic at requirement are switched on.

Before activating an echo compensation and at the beginning of Construction of the traffic channel is in a preferred Embodiment of the method, a measurement of the round-trip delay carried out between the first and second MG to the (Initial) duration of data packets on the traffic channel to determine. After this initial measurement process the transit time measurements during data transfer continuously continued.

Besides the application of BICC protocol for communication between MGCs can also ISUP + be applied. H.248 can next MGCP as the protocol for communication between MGC and MG are used, in particular, after an appropriate Protocol extension.

The method is not limited to the preferred RTP bearer as Bearerprotokoll but may in principle also be applied to other Bearertechnologien.

An inventive apparatus for echo compensation in a Network in which a user channel on a packet-oriented Data network between a first and a second Mg, and an MGC, the MG controls at least the first, is provided, has control means needed 'activation an echo cancellation on in the user channel. The control means may constructed soft- or hardware be. Preferably, the control means are part of the MGC.

An essential component of the echo compensation control means is a comparison unit, which has a first Input (Messignaleingang) runtime metrics about a message receives from the MG, and via a second input (comparison input signal) with a runtime threshold memory for storing a preprogrammed duration threshold value connected is. The comparator unit are in the Result the comparison of the current term with the reference prestored term threshold value a control signal, which activation or inactive Stay the echo canceller causes.

As "duration-measuring equipment", at least one media gateway have at least one jitter buffer, in which data packets the traffic channel is cached. The length the jitter buffer can then - together with the abovementioned "Round Trip Delay" - on as a criterion for decision serve the sending of a message (NTF). It describes the Variance of the arrival of packets at a receiving point and forms the first term of a "Propagation Delay" in the as addend half of the current "round trip" (as in RFC1889, section 6.3.1. on the timestamp = timestamp determined) enters.

The invention is described using an exemplary embodiment explained in connection with the drawings. The Drawings in<sl><li>Fig. 1 shows a known from the prior art telecommunication network, packet-oriented in the speech signals transmitted be and a division or separation of signaling used and switching from payload transport is, and </li><li>Fig. 2 shows an embodiment of a telecommunications network, in which a division or separation of signaling and switching from the payload transport and the invention The method is used for echo cancellation.</li></sl>

For a description of FIG. 1 is the introductory referenced. The following can be used for the same elements and Elements with the same functionality, the same reference numerals be used. For an explanation of the abbreviations used was on the list of reference numerals and abbreviations referenced.

The basic processes of the method can be found in Fig. 2, wherein the sake of clarity, it was decided not to reproduce the acknowledgment messages from MGCP. It is only essential aspects of the application of turning the echo cancellers received. Of the fundamental connection is assumed to be known.

In FIG. 2, a telecommunications network is shown which two PSTNs 10 and 12 having the packet-oriented a Data network 42, here an intranet, communicate with each other can. (The networks can two telecommunications networks of his company in different locations.) To cost voice communication between the sites to allow, be voice calls between the PSTN 10 and the PSTN 12 performed by VoIP. It is essential therefore, that a conventional circuit-switched in the PSTNs 10 and 12 Communication takes place, while in the data network 42 packet-cost as remote network voice signals be transmitted.

The PSTNs 10 and 12 each have local exchanges LE and a transition TX 16 and 18, respectively. At the local exchanges LE are phones 14 as terminals to connected voice communication. The transitions TX 16 and 18 serve to couple the PSTNs 10 and 12 to the packet-oriented Data network 42nd

A transition from a circuit switched to a packet-oriented Voice connection enable media gateways 34, 36, 38 and 40. For this purpose the media gateways 34, 36 and 38, 40 with the junctions 16 and 18 of the PSTN 10 or 12 connected.

In FIG. 2, the control of the media gateways 36 and is further 38 on media gateway controllers or call feature server 44 and 46 shown. The media gateway controller or call Feature Server 44 and 46, as units of one or more conventional switching systems be designed, for example as a special plug-in cards.

With the reception of the message "IAM" of ISUP or BICC / ISUP + in the two media gateway controllers 44 and 46 is in each case after evaluation of the TMR's the message "CRCX" (Create Connection) the MGCP * by saying no echo cancellers turn, sent; at the same time in the "Encapsulated Notification Request "with the RTP package detection changes in new proprietary MGCP "Requested Event" "Propagation Delay Exceeded" activated in the media gateway 36th

Then, when the media gateway 38 later finds that the Buffer is larger, it signals this event to the Media Gateway controller 44, with a NTFY. In Media Gateway Controller 44 is then examined whether the size of the Buffers beyond the recommended duration is, from the echo cancellers are about to turn.

According to the possibilities of the signaling network, in which the media gateway controller 44 is, he can now either own Media Gateway 36 locally using the Message "MDCX" 50 of the echo canceller MGCP turn, or on the "Enhanced Echo Control Procedure" Chapter 2.7.2 of ITU-T standards Q.764 using the message "NRM" (Network Resource Management) on ISUP and / or BICC and ISUP + a further to the media gateways 36 and 38 defined endpoints of the voice call out or even Enable away beyond lying of this echo canceller.

Thus, the echo cancellers are only activated if the Maturities of existing voice connection become too big are. It is to be noted that if the message by the would not be applied "NRM" triggered procedure (ie local switching only), it in a cascading TDM IP-TDM-IP connections can not be prevented, that several echo cancellers are inserted.