Packet-switched telephony with circuit-switched backup

• US 6,781,983 B1
• Filed: 05/03/1999
• Issued: 08/24/2004
• Est. Priority Date: 05/03/1999
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Armistead, R. Ashby
• Primary Examiner(s): VANDERPUYE, KENNETH N
• Application Number:
  US09/304,032
• Time in Patent Office: 1,940 Days
• Field of Search: 370/353, 370/354, 370/355, 370/356, 370/401, 370/352
• US Class Current: 370/353
• CPC Class Codes: H04L 12/5692 Selection among different networks
• CPC Class Codes: H04L 12/6418 Hybrid transport
• CPC Class Codes: H04L 2012/6424 Access arrangements
• CPC Class Codes: H04L 2012/6481 Speech, voice
• CPC Class Codes: H04M 7/0057 Services where the data services network provides a telephone service in addition or as an alternative, e.g. for backup purposes, to the telephone service provided by the telephone services network

Abstract

A packet voice switch 60 and method for its operation are disclosed. The switch comprises a network switching means, preferably implemented within its host processor 78, that allows calls to be routed between a circuit-switched connection at circuit-switched interface 74 and either another circuit-switched connection at interface 74 or a packet-switched connection at packet-switched interface 76. The network switching means selects call routing for calls based on a comparison of the current quality of service for the call over the packet-switched connection vs. the extra cost of connecting the call over the circuit-switched connection. Preferably, the comparison can be adjusted for call distance, the user'"'"'s own quality of service preference, and current system load.

In a preferred embodiment, switch 60 communicates with a similar packet voice switch (handling the other end of the same call) in order to initiate a mid-call network switch that is transparent to the calling and called parties. This embodiment provides a guaranteed minimum quality of service for packet voice applications, and provides a reliable backup in case of a packet data route failure.

In a second embodiment, users may initiate network switching themselves if they desire higher quality, by entering an appropriate sequence on their DTMF keypad.

Claims

1. A method of operating a telephony switch connected to both a circuit-switched network and a packet-switched network, the method comprising steps of:

calculating an estimated quality of a packet-switched connection for a given call;

selecting, based at least partially on the estimated quality, either the packet-switched connection or a circuit-switched connection for the call; and

connecting the call over the selected network,

wherein the estimated quality is dependent upon the physical distance of the call and increases with increasing physical distance.

2. A method of operating a telephony switch connected to both a circuit-switched network and a packet-switched network, the method comprising steps of:

calculating an estimated quality of a packet-switched connection for a given call;

selecting, based at least partially on the estimated quality, either the packet-switched connection or a circuit-switched connection for the call; and

connecting the call over the selected network,

wherein the selecting step comprises computing a first figure merit for connection of the call over the circuit-switched network, computing a second figure of merit, including a factor related to the estimated quality, for connection of the call over the packet-switched network, and selecting the network with the most favorable figure of merit.

3. The method of claim 2, wherein the first figure of merit is based at least partially on the cost of connection of the call over the circuit-switched network.

4. A method of operating a telephony switch connected to both a circuit-switched network and a packet-switched network, the method comprising steps of:

calculating an estimated quality of a packet-switched connection for a given call;

selecting, based at least partially on the estimated quality, either the packet-switched connection or a circuit-switched connection for the call; and

connecting the call over the selected network,

wherein the result of the selecting step depends at least partially on the current utilization of signal processing resources within the switch.

5. A method of operating a packet voice switch connected to both a local circuit-switched network and a packet-switched network, the method comprising steps of:

receiving an original call request over the local circuit-switched network;

routing the call request over the packet-switched network to a remote packet voice switch for call connection to a called party;

responding to a network change request by rerouting the call over a long-distance circuit-switched network to the remote packet voice switch;

processing incoming audio for the presence of a user-generated in-band signal; and

generating a network change request when an appropriate in-band signal is detected in the incoming audio.

6. A method of operating a packet voice switch connected to both a local circuit-switched network and a packet-switched network, the method comprising steps of:

receiving an original call request over the local circuit-switched network;

routing the call request over the packet-switched network to a remote packet voice switch for call connection to a called party;

responding to network change request by rerouting the call over a long-distance circuit-switched network to the remote packet voice switch;

monitoring the health of the packet voice switch; and

upon detection of a failure of switch hardware necessary to support one or more active packet-switched calls, generating a network change request for one or more active packet-switched calls.

7. A method of operating a packet voice switch connected to both a circuit-switched network and a packet-switched network, the method comprising the steps of:

receiving a network switch request, from a second packet voice switch, the request related to a packet-switched call existing between the two packet voice switches;

sending a request acknowledgment to the second packet voice switch;

associating an incoming circuit-switched connection from the second packet voice switch with the packet-switched call; and

switching call voice data between the two packet voice switches from the packet-switched connection to the circuit-switched connection.

8. A packet voice switch comprising:

a telephony interface for connection to a circuit-switched network;

a packet data interface for connection to a packet-switched network;

coding/decoding means in communication with the packet data interface, for converting voice data from a circuit-switched format to a packet-switched format and converting voice data from a packet-switched format to a circuit-switched format;

call switching means for routing call between the telephony interface and the coding/decoding means; and

network switching means for selecting whether to route calls received at the telephony interface through the coding/decoding means to the packet data interface or back through the telephony interface.

9. The packet voice switch of claim 8, wherein the network switching means has the capability to reroute a call from its selected interface to a different interface while that call is in progress.

10. The packet voice switch of claim 8, further comprising latency measurement means for determining the apparent latency of a connection over the packet-switched network, wherein the latency measurement means supplies latency measurements to the network switching means.

11. The packet voice switch of claim 10, wherein the latency measurement means estimates latency based on packet statistics for an existing packet data connection.

12. The packet voice switch of claim 8, further comprising an in-band signal processor that detects in-band signals and supplies them to the network switching means.

13. The packet voice switch of claim 8, further comprising database communication means for retrieving quality of service factors for a selected call from a database, and supplying these factors to the network switching means.

14. The packet voice switch of claim 8, wherein the network switching means is responsive to requests, received from other packet voice switches, for switching a call currently handled by both switches from a packet-switched to a circuit-switched voice data connection.

15. The packet voice switch of claim 14, wherein the network switching means is responsive to requests, received from other packet switches, for switching a call currently handled by both switches from a circuit-switched to a packet-switched voice data connection.

16. A method of operating a telephony switch connected to both a circuit-switched network and a packet-switched network, the method comprising steps of:

calculating an estimated quality of a packet-switched connection for a given call, wherein the calculating step comprises estimating the latency of the packet-switched connection;

selecting, based at least partially on the estimated quality, either the packet-switched connection or a circuit-switched connection for the call;

connecting the call over the selected network; and

when the circuit-switched connection is selected, maintaining the packet-switched connection at a reduced packet transmission rate and estimating the latency of the packet-switched connection from the reduced packet transmission rate.

17. The method of claim 16, further comprising recalculating the estimated quality periodically while the call is in progress, reselecting either the packet-switched connection or the circuit-switched connection using the recalculated estimated quality, and switching the call to the packet-switched connection when the reselection selects the packet-switched connection.