Abstract:
A method and apparatus are provided for transferring an ATM call. A first ATM call ( 124 ) is established between a first party ( 120 ) and a second party ( 116 ) and a second ATM call ( 128 ) is established between the second party ( 116 ) and a third party ( 118 ). The first and second ATM calls both include a plurality of segments ( 124   a–d,    128   a–d ) or connections that are coupled to a plurality of ATM switches ( 208, 210, 212, 214 ) over ATM facilities to provide virtual connections. The transfer is accomplished by sending a message to the ATM switch over the ATM facility ( 109 ) to request the transfer of the first party to the third party. The message identifies the first ATM call and the second ATM call. The switch makes a new connection ( 220 ) between the first ATM call and the second ATM call and releases the segments of the first and second ATM calls that connect the ATM switch to the second party. As a result, the first party and the third party are connected for communication.

Description:
FIELD OF THE INVENTION 
   The invention generally relates to telecommunications, and in particular, to the transfer of a switch virtual channel over an ATM facility. 
   BACKGROUND OF THE INVENTION 
   ATM (Asynchronous Transfer Mode) switches are being employed as the switch fabric in telecommunications switches. In particular ATM switches are being used for inter-switch connections and to interconnect access gateways, e.g., line access gateways and trunk access gateways. These ATM services are being used for data and voice connections. 
   Several existing voice capabilities require moving a voice connection once it is established. For example, transferring a call or creating a conference call. Currently there is no capability for moving one end of an ATM communication. In order to provide traditional voice connections and features over ATM facilities, a procedure for movement of an ATM connection must be supported. One proposal for transfer or movement of a voice connection over ATM facilities is accomplished by using an inter-telephony switch signaling protocol to convey to the call control entities (telephone switches) that are connected to the voice connections the request for a transfer. The call control entities then instruct the access gateways to establish new ATM connections using ATM bearer signaling in accordance with the transfer. After the new connections are established, all the old connections are released.  FIG. 1  and  FIG. 2 , which are discussed below, illustrate the problem and the proposed solution, respectively. 
     FIG. 1  is a block diagram of a communication system  100 , including media access gateways (MAGs)  102 , call control entities (CCEs)  104 , and an ATM core  106 . Media access gateways  102  are connected to the ATM core  106  via ATM facilities  109 . The media access gateways  102  provide communication access for terminals, such as telephones  116 , 118  and  120 . The ATM core  106  includes a plurality of ATM switches that are interconnected via ATM facilities  109 . An exemplary arrangement for ATM core  106  shown in  FIG. 1  includes ATM switch one  108 , ATM switch two  110 , ATM switch three  112 , and ATM switch four  114 . The number and arrangement of ATM switches varies. Call control entities  104  control the actions of the associated media access gateways  102 . In addition, the call control entities  104  are coupled to an inter-telephony switch connection network, Signaling System  7  network  122 , which provides the transport for bearer independent call control (BICC) signaling. 
   As shown schematically in  FIG. 1 , telephone  120  has a call path  124  established with telephone  116 . Call path  124  traverses media access gateways  102  coupled to telephones  116  and  120 , plural ATM facilities  109  and ATM core  106 . More specifically, call path  124  includes a first segment  124   a , a second segment  124   b , a third segment  124   c , and a fourth segment  124   d . First segment  124   a  extends from media access gateway  102  over ATM facility  109  to ATM switch three  112 . A switched connection  126   a  connects first segment  124   a  to second segment  124   b  at ATM switch three  112 . Second segment  124   b  extends from ATM switch three  112  over ATM facility  109  to ATM switch two  110 . A switched connection  126   b  connects second segment  124   b  to third segment  124   c  at ATM switch two  110 . Third segment  124   c  extends from ATM switch two  110  over ATM facility  109  to ATM switch one  108 . A switched connection  126   c  connects third segment  124   c  to fourth segment  124   d . Fourth segment  124   d  extends over ATM facility  109  to media access gateway  102 . 
   Another call path  128  traverses media access gateways  102  coupled to telephone  116  and  118 , plural ATM facilities  109  and ATM core  106 . More specifically, call path  128  includes a first segment  128   a , a second segment  128   b , a third segment  128   c  and a fourth segment  128   d . First segment  128   a  extends from media access gateway  102  over ATM facility  109  to ATM switch four  114 . A switched connection  130   a  couples first segment  128   a  to second segment  128   b  at ATM switch four  114 . Second segment  128   b  extends from ATM switch four  114  over ATM facility  109  to ATM switch two  110 . A switched connection  130   b  connects second segment  128   b  to third segment  128   c  at ATM switch two  110 . Third segment  128   c  extends from ATM switch two  110  over ATM facility  109  to ATM switch one  108 . A switched connection  130   c  couples third segment  128   c  with fourth segment  128   b . Fourth segment  128   d  extends from ATM switch one  108  to media access gateway  102 . 
   Call paths  124  and  128  are established in any suitable manner. Typically, call paths  124  and  128  are established using standards specified in ATM User-Network Interface (UNI) Signaling Specification, Version 4.0, af-sig-0061.0000 and ATM Forum Private Network-Network Interface (PNNI) Specification, Version 1.0, af-pnni-0055.00. After call paths  124  and  128  are established, a difficulty arises if one of the call paths is to be transferred or moved. For example, if telephone  116  desires to transfer call path  124  to call path  128  such that telephone  120  and telephone  118  are coupled together for voice communications, then a problem arises as to how the desired connections are to be established. 
   One known proposed solution for transferring call path  124  to call path  128  is illustrated in  FIG. 2 . In summary, a new connection is established between telephone  120  and telephone  118  and the old connections are released. More specifically, BICC signaling between call control entities  104  results in the call control entities  104  instructing the media access gateways  102  to establish the new ATM connection needed. The media access gateways  102  use UNI signaling to establish the new ATM connection. In particular, a new call path  140  is established to connect telephone  118  to telephone  120 . Call path  140  traverses media access gateways  102  that are coupled to telephones  118  and  120 , plural ATM facilities  109  and ATM core  106 . More specifically, call path  140  includes a first segment  140   a  that extends from media access gateway  102  over ATM facility  109  to ATM switch four  114 . A switched connection  142   a  couples first segment  140   a  to second segment  140   b . Second segment  140   b  extends from ATM switch four  114  over ATM facility  109  to ATM switch two  110 . A switched connection  142   b  connects second segment  140   b  to third segment  140   c . Third segment  140   c  extends from ATM switch two  110  over ATM facility  109  to ATM switch three  112 . A switched connection  142   c  couples third segment  140   c  to fourth segment  140   d . Fourth segment  140   d  extends from ATM switch three  112  over ATM facility  109  to media access gateway  102 . After establishing call path  140 , call paths  124  and  128  are released. 
   One problem with the solution described above and illustrated in  FIG. 2  is that the call control entity (switching node) needs to be aware of when another call control entity (switching node) in a call manipulates the call or bearer path. The bearer path, in effect, becomes a shared resource that all switching nodes jointly use to provide their own services. This greatly increases the complexity of implementing services where feature interactions cross switch boundaries. In light of this, a switching node is not able to perform call redirection and insert/remove service circuits in established connections to provide usual features (e.g., N-way bridging, announcement playback, tone generation, tone detection, speech recognition and multicasting) available to traditional time-division multiplexing (TDM) calls. Also, some resources are temporarily duplicated in order to establish the new connection. For example, portions of call path  124  and call path  128  replicate the new call path  140 . The complexity required to establish the new connection using BICC signaling and the utilization of additional resources to establish the new connection makes this solution somewhat undesirable. 
   Therefore, a need exists for an improved transfer capability for ATM virtual channels. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect of the present invention, a method is provided for transferring an ATM call. A first ATM call is established between a first party and a second party and a second ATM call is established between the second party and a third party. The first ATM call includes a plurality of segments that are coupled to a plurality of ATM switches to provide a virtual connection. Similarly, the second ATM call includes a plurality of segments that are coupled to a plurality of ATM switches to provide a virtual connection. To accomplish the transfer, an ATM switch that is coupled to the second party receives a message to transfer the first ATM call to the second ATM call in order to connect the first party and the third party. In response to receiving the message to transfer, the ATM switch connects a first segment of the first ATM call to a first segment of the second ATM call. After successfully connecting a portion of the first ATM call to a portion of the second ATM call, the ATM switch releases a second segment of the first ATM call that extends from the ATM switch to the second party. Similarly, the ATM switch releases a second segment of the second ATM call that extends from the ATM switch to the second party. No separate inter-telephony switch signaling is required. Preferably, a media access gateway is coupled to the ATM switch and the second party. And, a call control entity is coupled to the media access gateway. The media access gateway extends the message to transfer to the ATM switch under control from the media access gateway controller. After transfer is complete, the media access gateway and call control entity may maintain a reference to the call to permit subsequent interaction with the call. 
   In accordance with another aspect of the invention, an apparatus is provided for transferring an ATM call. The apparatus includes an ATM switch that receives over an ATM facility a message to transfer the first ATM call to a second ATM call. In response to receiving the message, the ATM switch connects a first segment of the first ATM call to a first segment of the second ATM call. The ATM switch then releases a second segment of the first ATM call that extends from the ATM switch to a caller. Also, the ATM switch releases a second segment of the second ATM call that extends from the ATM switch to the caller. The new connection established on the ATM switch transfers the first ATM call to be connected for communication with the second ATM call. Preferably a media access gateway is coupled to the ATM switch and the caller. And, a call control entity is coupled to the media access gateway. The media access gateway extends the message to transfer to the ATM switch under control from the media access gateway controller. After transfer is complete, the media access gateway and call control entity may maintain a reference to the call to permit subsequent interaction with the call. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a communication system showing ATM call connections. 
       FIG. 2  is a block diagram of a communication system showing a prior art method for transferring the ATM call connections illustrated in  FIG. 1 . 
       FIG. 3  is a block diagram of a communication system with ATM call connections in accordance with the present invention. 
       FIG. 4  is a block diagram of a communication system with ATM call connections in accordance with the present invention. 
       FIG. 5  is a block diagram of a communication system with ATM call connections in accordance with the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3  is a block diagram of a communication system  200  in accordance with the present invention. Communication system  200  includes media access gateways (MAGs)  202 , call control entities (CCEs)  204 , and an ATM core  206 . Media access gateways  202  are connected to the ATM core  206  via ATM facilities  109 . The media access gateways  202  provide communication access for terminals, such as telephones  116 , 118  and  120 . The ATM core  206  includes a plurality of ATM switches that are interconnected via ATM facilities  109 . In the exemplary arrangement shown in  FIG. 3 , ATM core  206  includes ATM switch one  208 , ATM switch two  210 , ATM switch three  212 , and ATM switch four  214 . The number and arrangement of ATM switches may vary. Call control entities  204  control the actions of the associated media access gateways  202 . A telephony switch or switching node may include one or more call control entities  204 , media access gateways  202 , bridges and the like. Communication system  200  is similar in many respects to communication system  100  of  FIG. 1 . However, communication system  200  includes media access gateways  202 , call control entities  204  and ATM switches in ATM core  206 , all of which are preferably modified to accommodate a transfer function in accordance with the present invention, as described below by way of an example. 
   Media access gateways  202  are preferably trunk access gateways or line access gateways. Call control entities  204  are preferably processor-based apparatus that control one or more media access gateways with modifications to accommodate the present invention. ATM switches in ATM core  206  are preferably any ATM switch modified to accommodate a transfer function in accordance with the present invention. ATM facilities  109  are any transmission medium and protocol for transferring ATM packets. 
   As shown schematically in  FIG. 3 , telephone  120  has a call path  124  established with telephone  116 . Call path  124  traverses media access gateways  102  coupled to telephones  116  and  120 , plural ATM facilities  109  and ATM core  206 . More specifically, call path  124  includes a first segment  124   a , a second segment  124   b , a third segment  124   c , and a fourth segment  124   d . First segment  124   a  extends from media access gateway  202  over ATM facility  109  to ATM switch three  112 . A switched connection  126   a  connects first segment  124   a  to second segment  124   b  at ATM switch three  212 . Second segment  124   b  extends from ATM switch three  212  over ATM facility  109  to ATM switch two  210 . A switched connection  126   b  connects second segment  124   b  to third segment  124   c  at ATM switch two  210 . Third segment  124   c  extends from ATM switch two  210  over ATM facility  109  to ATM switch one  208 . A switched connection  126   c  connects third segment  124   c  to fourth segment  124   d . Fourth segment  124   d  extends over ATM facility  109  to media access gateway  202 . 
   Another call path  128  traverses the media access gateways  202  coupled to telephone  116  and  118 , plural ATM facilities  109  and ATM core  206 . More specifically, call path  128  includes a first segment  128   a , a second segment  128   b , a third segment  128   c  and a fourth segment  128   d . First segment  128   a  extends from media access gateway  202  over ATM facility  109  to ATM switch four  214 . A switched connection  130   a  couples first segment  128   a  to second segment  128   b  at ATM switch four  114 . Second segment  128   b  extends from ATM switch four  214  over ATM facility  109  to ATM switch two  210 . A switched connection  130   b  connects second segment  128   b  to third segment  128   c  at ATM switch two  210 . Third segment  128   c  extends from ATM switch two  210  over ATM facility  109  to ATM switch one  208 . A switched connection  130   c  couples third segment  128   c  with fourth segment  128   d . Fourth segment  128   d  extends from ATM switch one  208  to media access gateway  102 . 
   Call paths  124  and  128  are established in any suitable manner. 
   Preferably, call paths  124  and  128  are established using UNI and PNNI signaling for establishment of ATM bearer connections. After call paths  124  and  128  are established, a transfer of call path  124  to call path  128  is accomplished in accordance with the present invention. More specifically, under control of, and at the request of telephone  116 , telephone  118  and telephone  120  are coupled together for communication. 
   Preferably, a user at telephone  116  request that telephone  120  and  15  telephone  118  be interconnected. That is, telephone  116  request that call path  124  be interconnected to call path  128 . The request may take any suitable form, for example, a flash hook signal from a touch-tone terminal or telephone. 
   The request is received by media access gateway  202 , which preferably sends the request to call control entity  204  for interpretation. Call control entity  204  receives the request and determines that it is a transfer request. In response to the request, the call control entity  204  directs the media access gateway  202  to send a transfer request to the ATM switch one  208  directly coupled to the media access gateway  202 . The transfer request preferably takes the form of a message that is sent over the ATM facility  109 . Most preferably, the transfer message includes identifiers, such as call references, for both call path  124  and call path  128 . 
   ATM switch one  208  receives the transfer message with the call identifiers over ATM facility  109 . In response to the transfer message, ATM switch one  208  connects a first portion of call path  124  to a first portion of call path  128 . This connection is shown as switched connection  220 . The first portion of call path  124  that is connected to switch connection  220 , includes third segment  124   c , switched connection  126   b , second segment  124   b , switched connection  126   a  and first segment  124   a . The first portion of call path  128  that is connected to switched connection  220  includes third segment  128   c , switched connection  130   b , second segment  128   b , switched connection  130   a , and first segment  128   a.    
   The new switched connection  220  made at ATM switch one  208  sends data received on third segment  124   c  to third segment  128   c . And, switched connection  220  sends data received on third segment  128   c  to third segment  124   c . This generally entails changing the routing of ATM cells and the mapping of ATM headers to establish the desired connections. 
   After the new connection  220  is established, the portions of the call paths that are no longer necessary are released. In particular, switched connection  126   c  and fourth segment  124   d , which coupled media access gateway  202  to ATM switch one  208  for call path  124 , are released. Also, switched connection  130   c  and fourth segment  128   d , which coupled media access gateway  202  to ATM switch one  208  for call path  128 , are released. Release completion messages are preferably sent to the media access gateway  202  after successful completion of the transfer. 
     FIG. 4  shows communication system  200 , including the transferred call path that results from the new connection and released connections described above. Notably, the existing call paths are reused in the transferred call path to the extent necessary. This conserves valuable resources. Also, no communication with switches other than ATM switch one  208  is necessary, which conserves resources and reduces the time required to cause the transfer. Also, the complexity of inter-telephony switch communication is avoided. 
   In an alternate embodiment, transfer messages are also sent between ATM switches to minimize the switching resources required to effect a transfer. That is, if a switch receives a transfer message and it determines that the call paths that are to be joined originate from the same ATM switch, then the transfer message, including the appropriate call identifiers is sent to the ATM switch that supplies both calls. For example, ATM switch one  208 , upon receiving the transfer message from media access gateway  202  determines that call path  124  and call path  128  both originate from ATM switch two  210 . Therefore, ATM switch one  208 , optionally sends a transfer message to ATM switch two  210 . In response to receiving the transfer message, ATM switch two  210  connects the required portions of call path  124  to the required portions of call path  128 . This connection  230  is illustrated in  FIG. 5  and is accomplished in a manner analogous to the connection  220 . The portions of the call paths no longer necessary are released after connection  230  is established. In particular, as shown in  FIG. 5 , switched connection  126   b , third segment  124   c , switched connection  126   c  and fourth segment  124   d  of call path  124  are released. And, switched connection  130   b , third segment  128   c , switched connection  130   c  and fourth segment  128   d  of call path  128  are released. After successful completion of the connection and releases, release complete messages are sent from ATM switch two  210  to ATM switch one  208 , and subsequently from ATM switch one  208  to media access gateway  202 . The alternate arrangement discussed above and shown in  FIG. 5  advantageously reduces resources required for the transfer, but adds some complexity in tracking the calls, effecting the transfer and other areas, such as billing. 
   A variation on the transfers discussed above with respect to  FIGS. 3–5  is preferred for some calls. In particular after resources are released and the transfer of the call path is complete, rather than remove all references to the call from the media access gateway that no longer has a call path to the transferred call, the media access gateway maintains references to the transferred call and maintains some control over the call. In the embodiments and examples discussed above, media access gateway  102  connected to telephone  116  preferably maintains control over the transferred call between telephone  120  and telephone  118 . By maintaining control, the media access gateway is able to subsequently modify or interact with the call or bearer path without the set up of a new call or connection. For example, the media access gateway may connect to the transferred path to play an announcement or set up a bridge. Where the media access gateway maintains control after a transfer, the call control entity coupled to the media access gateway preferably perceives the call as though it is joined through that media access gateway. 
   As described above, a new transfer capability is added to ATM communications. The transfer reduces the inter-telephony switch and inter-ATM switch signaling required to effect a transfer of ATM calls. ATM resources are used efficiently in effecting the transfers. The basic transfer capability is utilized with any ATM communications, including communications with bridges and other conference circuits. The transfer capability is readily integrated into higher level functions, such as establishment of conference calls, where a transfer is required to establish the conference call. 
   Whereas the present invention has been described with respect to specific embodiments thereof, it will be understood that various changes and modifications will be suggested to one skilled in the art and it is intended that the invention encompass such changes and modifications as fall within the scope of the appended claim.