Establishing a communications path via a multi-homed communications network
View Patent ↗The present invention is concerned with situations in which call signalling follows an indirect path between an originating party and a destination party. Such an indirect path can occur when multi-homed communications networks are used. For example, where a service is provided to an enterprise which has a private address domain and that service is hosted by a service provider whose equipment is located in a public address domain connected to the enterprise domain by two or more address translators. Previously, in this type of situation, resulting media paths also follow the indirect path of the call signalling. This is wasteful of network resources. The present invention enables a direct media path to be set-up. This is achieved by enabling network address translators between two address domains to retain information in call set-up messages about the relevant address in the previous address domain and also by adding network identifier information to call set up messages.
1. A method of enabling the establishment of a communications path between a first entity and a second entity in a communications network comprising at least two address domains, said address domains being connected by two or more network address translators, said method comprising the steps of:
i) sending a call set-up message from the first entity to a first one of the network address translators via only a first one of the address domains, said call set-up message containing an address of the first entity within the first address domain;
ii) receiving the call set-up message at the first network address translator and retaining the address of the first entity in the call set-up message as well as adding information indicating the identity of the first address domain to the call set-up message;
iii) forwarding the call set-up message with said added information to the second entity via a second one of the address domains and a second one of the network address translators, such that the information in the call set-up message can be used to establish a communications path from the second entity to the first entity which excludes a second one of the address domains when it is determined, using the added information, that the second entity is within the first address domain.
2. A method as claimed in claim 1 wherein said step (ii) of receiving further comprises creating a binding between a second address domain address for a port at the first network address translator and the first address domain address of the first entity; and once said binding is created adding the second address domain address of that port to the call set-up message.
3. A method as claimed in claim 1 which further comprises, after said step (ii) of receiving, forwarding the call set-up message to a third address domain via a third network address translator.
4. A method as claimed in claim 3 which further comprises at the third network address translator, adding information about an identity of the third address domain to the call set-up message.
5. A method as claimed in claim 1 wherein said first network address translator is arranged to access information from another network entity in order to carry out the method of step (ii) of claim 1 in respect of adding information about the identity of the first address domain to the call set-up message.
6. A method as claimed in claim 1 wherein said communications path is arranged to provide a service that is hosted by one or more servers within the communications network but not within the first address domain.
7. A method as claimed in claim 1 wherein said first address domain is provided in a private region of the communications network and said second address domain is provided in a public region of the communications network.
8. A method as claimed in claim 1 wherein said communications network is selected from an internet protocol communications network or an asynchronous transfer mode communications network.
9. A network address translator suitable for connection between a first and a second address domain in a communications network, said network address translator comprising:
an input arranged to receive a call set-up message from a first entity in the first address domain, said call set-up message comprising an address of the first entity;
a processor arranged to modify the received call set-up message by adding information indicating the identity of the first address domain whilst retaining the address of the first entity; and also adding an address of the network address translator within the second address domain to the call set-up message; said address of the network address translator being bound to the address of the first entity;
a output arranged to forward the modified call set-up message to a second entity via the second address domain, such that the information in the call set-up message can be used to establish a communications path from the second entity to the first entity which excludes a second one of the address domains when it is determined, using the added information, that the second entity is within the first address domain.
10. A network address translator as claimed in claim 9 wherein said processor is provided externally to the network address translator and is connected to the network address translator by a communications network.
11. A method of operating a network address translator which is connected between a first and a second address domain in a communications network, said method comprising the steps of:
i) receiving a call set-up message from a first entity in the first address domain, said call set-up message comprising an address of the first entity;
ii) modifying the received call set-up message by adding information indicating the identity of the first address domain whilst retaining the address of the first entity in the call set-up message; and also adding an address of the network address translator within the second address domain to the call set-up message; said address of the network address translator being bound to the address of the first entity;
iii) forwarding the modified call set-up message to a second entity via the second address domain, such that the information in the call set-up message can be used to establish a communications path from the second entity to the first entity which excludes a second one of the address domains when it is determined, using the added information, that the second entity is within the first address domain.