More specifically, the present invention relates to ad- dressing gateway types from within a packet net- work/intranet.

Prior art and related problems New emerging standard within video and audio conferencing now makes it possible to have audio and video confer- ences/calls within PSTN (ISDN) networks, the internet, intranets and Local Area Networks.

Since other network domains now support making audio and video conferences/calls, the need for ways of interwork- ing between these different kind of networks has emerged.

These interworking units are called gateways, and they provide the conversions necessary (protocol, audio for- mat, video format etc.) for endpoints/terminals residing in different kind of networks to be able to communicate with each other.

There are no limitations on the number of gateways which can be connected to these networks, which means that an intranet can have access to several gateways in order for a terminal inside the intranet to call e. g. an ISDN

video-conferencing terminal. In addition, different gateways are needed for different destinations. E. g. an audio only call to an ordinary POTS telephone would use a different gateway than an audio and video call to an H. 320 (ref 2) (ISDN video-conferencing) terminal.

This indicates that a call initiated from within the intranet needs to know what kind of equipment the receiv- ing party is using. This is particularly true for calls to POTS telephones and H. 320 terminals (ref 2) since both reside within PSTN network but have different features.

POTS telephones support only audio, while H. 320 terminals normally support video and data-conferencing as well.

This in turn means that the calling party within an intranet/LAN must be able to manually route the call to the correct gateway depending on what kind of equipment the calling party knows that the receiving party outside the intranet/LAN has. This invention suggests a method for manually routing the call to the correct gateway by adding information to the called number.

Objects of the invention A main object of the present invention is to propose a way to manually route interworking calls (i. e. over gate- ways) through the gateway suited for the equipment of the receiving party.

Another object of the present invention is to establish such routing in a simple but expedient manner.

Still another object of the present invention is to han- dle said routing information at an appropriate location in the routing path.

Brief summarv of the invention The above objects are achieved in a method as stated in the preamble, which according to the present invention is characterized in that there is added a prefix, given by the caller in the first telecommunication network, to the called number in the external telecommunication network, to inform the routing means or so-called gatekeeper (GK) in the first telecommunication network which type of gateway (GW) is best suited to handle the call depending on the related resource service level.

In an appropriate manner the invention suggest that said routing informing prefix comprises for example a two- digit code.

More specifically, it is according to the invention sug- gested that said prefix is adapted to inform the routing means (GK) that e. g. audio-only calls should be routed to a gateway suited for audio-only, while calls involving both audio and video should be routed to a gateway suited for calls involving both audio and video.

Further features and advantages of the present invention will appear from the following description of an example of an embodiment taken in conjunction with the enclosed drawing, as well as from the attached patent claims.

Brief disclosure of the drawings Fig. 1 is a schematical drawing illustrating an embodi- ment of the method according to the present invention, wherein the routing of calls can take place between a multimedia telephone network and a PSTN (or H. 320) net- work.

Detailed description of an embodiment General description The invention proposes a way to manually route interwork- ing calls (i. e. over gateways) through the gateway suited for the equipment of the receiving party.

Description of solution The solution lies in giving the user an easy way to tell which type of gateway to route the call to. This inven- tion suggests to solve this by adding a prefix to the called number (E. 164 address-ref. 3). The user adds a two-digit code in front of the called number telling which type of gateway is best suited to handle calls, e. g. audio-only calls to ordinary POTS telephone should be routed to an H. 323 (ref. 1)/PSTN gateway, while an H. 320 (ref. 2) call involving both video and audio should be routed to a H. 323/H. 320 gateway.

Since this is redundant information for the gateway, this prefix will be removed by the gatekeeper before the gate- keeper routes the call to the correct gateway.

Explanation of Fig. 1 where two types of gateways towards PSTN is shown for illustrational purposes: a) Caller A wishes to call a person outside the intra- net with number 66842634. The receiving party is using a POTS telephone. The call must go through the PSTN GW, since the H. 320 gateway is based on video- conferencing according to H. 320 (ref. 2) and in which case a H. 320 terminal is needed on the PSTN side to accept the call.

The caller dials 0166842634, where 01 is the prefix to make the gatekeeper route the call to the PSTN gateway.

b) The gatekeeper looks at the prefix, sees that this is a PSTN call and routes the call to the PSTN gateway after having stripped off the prefix.

Avantages The invention gives the owner of the intranet the possi- bility to host several types of gateways and still be able to route the calls to the correct type of gateway.

Broadenina The invention is not limited to the number of gateway types that can be connected from an intranet/LAN (comply- ing to H. 323 ref. 1) towards a PSTN network, but rather to how many types of networks can be connected to an intranet/LAN where gateways are needed to support trans- fer of audio/video/data-calls (e. g. internet, PSTN).

References 1 ITU-T Recommendation H. 323 (1996):"Visual Telephone Systems and Equipment for Local Area Networks which provide a non-guaranteed Quality of Service" 2 ITU-T Recommendation H. 320 (1995):"Narrow-band ISDN visual telephone systems and terminal equipment" 3 ITU-T Recommendation E. 164 (1991):"Numbering Plan for the ISDN Era" 4 ITU-T Recommendation H. 225.0 (1996):"Media Stream Packetization and Synchronization for Visual Telephone Systems on Non-Guaranteed Quality of Service LANs" 5 ITU-T Recommendation Q-931 (1993):"Digital Subscri ber Signalling System No. 1 (DSS1)-ISDN User- Network Interface Layer 3 Specification for Basic Call Control"