10CLAIMS
1. A method for answering a request to use a feature on a transmission line, comprising the steps of: receiving a request for a feature to be used on a transmission line; attempting to answer to said request by using an external feature from a switch on said transmission line; and if said external feature is not available from said switch, answering said request locally by using a local feature; wherein said request to use a feature on said transmission line is answered by using the external feature on the switch if it is available or is answered locally if it is not available.
2. A method as claimed in claim 1 , wherein said request is a request for holding a call, wherein a first call has been connected and wherein said first call is held using either an external hold or a local hold depending on the availability of said external hold on said line.
3. A method as claimed in any one of claims 1 and 2, further comprising a step of storing an indication of the non-availability of said external feature on said line.
4. A method as claimed in claim 3, further comprising a step of using said indication of the non-availability of said external feature to terminate said step of attempting to answer to said request using said external feature.
5. A method as claimed in any one of claims 3 and 4, further comprising a step of resetting said indication of the non-availability of said external feature after at least one of a next power down and the lapse of a pre-determined time period.
6. A method as claimed in any one of claims 1 to 5, wherein said availability of said external feature is determined by the receipt of an acknowledgment message for a feature request that was sent to a switch on said line. 11
7. A method as claimed in claim 2, wherein the method comprises the steps of: receiving a user command to hold the first call, sending a hold message for the first call to a switch, setting the first call state to held if an acknowledgment message for a hold request is received for the first call, setting the first call state to local_held and muting the first call's B- channel if the acknowledgement message for a hold request is not received for the first call and sending a setup message to the switch to originate a second call on the line, wherein the first call is held using an external hold if the switch supports the hold feature and the first call is held using a local hold if the switch does not support the hold feature.
8. A method as claimed in any one of claims 1 to 7, wherein said transmission line is an ISDN line.
9. An apparatus answering a request to use a feature on a transmission line, comprising: a feature request receiver for receiving a request to use a feature on a transmission line; an external feature requester for attempting to answer to the request by using an external feature from a switch on said transmission line; an external feature status determiner for determining if said external feature is available from said switch on said line; a local manager for answering said request by using a local feature if said external feature is not available on said line; wherein said request to use a feature on said transmission line is answered by using the external feature on the switch if available or is answered locally if not.
10. An apparatus as claimed in claim 9, wherein said request is a request for 12
holding a call, wherein a first call has been connected and wherein said first call is held using either an external hold or a local hold depending on the availability of said external hold on said line.
11. An apparatus as claimed in any one of claims 9 and 10, wherein said external feature status determiner stores an indication of the non-availability of said external feature on said line.
12. An apparatus as claimed in claim 11 , further comprising an attempt reset for using said indication of the non-availability of said external feature to terminate said attempt to answer to said request using said external feature.
13. An apparatus as claimed in any one of claims 11 and 12, further comprising an indication reset for resetting said indication of the non-availability of said external feature after at least one of a next power down and the lapse of a pre-determined time period.
14. An apparatus as claimed in any one of claims 9 to 13, wherein said an external feature status determiner determines the availability of said external feature by the receipt of an acknowledgment message for a feature request that was sent to a switch on said line.
15. An apparatus as claimed in claim 10, wherein: the feature request receiver receives a user command to hold the first call; the external feature requester sends a hold message for the first call to a switch, the external feature status determiner sets the first call state to held if an acknowledgment message for a hold request is received for the first call and sets the first call state to local_held if the acknowledgement message for a hold request is not received for the first call; the local manager mutes the first call's B-channel and sends a setup message to the switch to originate a second call on the line, wherein the first call is held using an external hold if the switch supports 13
the hold feature and the first call is held using a local hold if the switch does not support the hold feature.
16. A method as claimed in any one of claims 9 to 15, wherein said transmission line is an ISDN line.