JP2002538675A - Call setup in communication systems - Google Patents

Abstract

(57) Abstract: A method of negotiating the type of coding during setup of a voice call between two MSCs (3, 4) in a communication system, and the setup procedure of the call is indicated via the SSP (13). . An initial address message (IAM) is sent from the originating MSC (3) to the SSP (13). The IAM includes the called number and the identification of the primary and secondary encoding type choices of the originating MSC (3). The SSP (13) determines the identity of the destination MSC (4) based on the called party number, and further determines a candidate for selecting the encoding type of the destination MSC (4). The SSP (13) then determines a call coding type selection candidate based on the destination MSC (4) coding type selection candidate and the source MSC (3) coding type selection candidate. I do. If the so-determined call encoding choice is different from the first-order encoding type choice identified by the IAM, the first-order encoding type is the second-order encoding type. And the IAM is sent to the destination MSC (4).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] Technical Field of the Invention The present invention relates to call setup in a communication system, and more particularly to setting a voice call over the called number converter station to perform the conversion of the called party number.

[0002] The setting of the telephone connection in the background communication system of the present invention and the exchange of negotiation and information between two or more nodes in the network is involved. In particular, for voice calls made across network boundaries, the call setup typically involves negotiation between the originating and terminating exchanges, and the voice to be used for the call. Has been determined. Speech coding of a speech signal is mainly used to reduce a transmission bit rate through a connection.

[0003] Considering the state of communication networks in Japan, the basic speech coding type is known as µ-law coding. In modern mobile digital networks (known as PDC networks), the network can support one or both of two additional coding types, PSI-CELP and VSELP. VSELP is referred to as a "full rate" codec (coder / decoder) and is responsible for a data rate of 11.2 kbit / s. PSI-CELP, on the other hand, is a "half-rate" codec that is responsible for a data rate of 5.6 kbit / s. Usually, PSI-CELP,
It will support both VSELP and μ-law, or only VSELP and μ-law. Unlike conventional networks, in a mobile network, encoding and decoding may be performed at the mobile station rather than at the switch.

[0004] When a mobile station that supports PSI-CELP calls a mobile station that supports PSI-CELP, the voice signal is subjected to intermediate transcoding, ie, from one coding type to another. Is transmitted in both directions without the need for conversion. However, if a mobile station supporting the same PSI-CELP
Mobile station (or network) supporting P (not PSI-CELP)
, The voice data must be transcoded or changed to VSELP encoding if the originating mobile station allows. Of the two options, transcoding introduces distortion into the signal and consumes additional processing power at the terminating switch (usually referred to as the mobile switching center (MSC)), the latter of which. Is more preferred.

[0005] Clearly, negotiation of the encoding type to be used for voice calls is necessary because there may be a mismatch between the encoding types available in the source and destination networks. It is. In addition, such negotiation is necessary to take into account the coding preferences of the network operator. For example, a mobile network operator supporting both PSI-CELP and VSELP may prefer to provide subscribers with high quality voice. Therefore, the operator's preference for coding schemes would be full-rate VSELP coding. Other operators of similar mobile networks may prefer to maximize their ability to handle calls and therefore prefer to use half-rate PSI-CELP coding.

In a mobile network, each MSC knows its own network coding capabilities and coding choices (preferences). In addition, each MSC maintains a database containing coding capabilities and selection candidates for other networks (often referred to as "external" networks). When a call is made from a mobile station, the originating MSC identifies the destination exchange based on the prefix of the called number. The originating switch then determines the preferred coding type based on its own network capabilities and selection candidates, and the capabilities of the destination switch and selection candidates. Based on its preferred coding type, the originating MSC assigns an appropriate voice channel over the air interface to the calling mobile station.

[0007] Call setup is initiated by the originating MSC sending a so-called Initial Address Message (IAM) to the terminating MSC. The IAM contains a number of fields containing various data related to the call. One of these fields is referred to as the "User Service Information" (USI) field and contains the encoding choices as determined by the originating MSC. When receiving the IAM at the destination MSC, the MSC examines the transmitted coding choice and compares it with its own current coding choice. Note that the current MSC selection candidate may be different from the one that was notified to the source MSC and stored, for example, due to a change in traffic level at the destination MSC.

[0008] The endpoint MSC may accept the transmitted choice, or may indicate an alternative choice by returning a Mobile Application (MAP) message to the originating MSC. Note that if the end MSC determines that an alternative selection candidate is to be taken, the selection is limited. Specifically, if IA
If the selection candidate indicated by M is PSI-CELP, the MSC of the end point selects VSELP or μ-law as an alternative, while if the selection candidate indicated by IAM is VSELP, the MSC of the end point is selected. Can only select μ-law as an alternative. That is, the MSC at the end point simply goes down the list, that is, PSI-CELP → VSELP → μ-law. Upon receipt of the MAP message, the originating MSC adopts the encoding type indicated there, or
A default μ-law encoding may be employed.

In some cases, the destination MSC may not return a MAP message to the originating MSC. If the MAP message is not received at the originating MSC prior to the so-called answer message (ANM, which is sent from the terminating MSC and indicates the answer of the call), the originating MSC will receive the default encoding, That is, μ
Assume -law.

[0010] Many modern communication networks incorporate so-called intelligent network (IN) services. An example of such a service is the service number 800, where the dialed number is the service exchange (SSP) where the call setup was initially indicated.
). The SSP performs number translation in connection with the service control station (SCP) to determine the true destination of the call. Once the real destination is determined, SS
P relays the IAM received from the originating switch to the destination switch.

[0011] The use of SSPs in communication networks presents a problem with regard to the type of coding. As already mentioned, before the originating MSC sends the IAM message, the MSC must have determined a candidate for the type of coding to assign to the calling mobile station the appropriate channel. . However, the originating MS
C cannot determine the identity of the destination network from the dialed number. Therefore, the choices have to be determined only for the capabilities of the originating MSC and the choices.

Still further, when the IAM is received by the SSP, the SSP may
Although the identity of C, and therefore the capabilities and choices of its encoding type, can be determined, the current set of choices for the complete set of originating MSCs (which have previously been transmitted to the SSP or other network nodes) (It may differ from time to time compared to the notified choices). Therefore, the SSP cannot make meaningful adjustments to the selection candidates indicated in the IAM. As a result, μ-law coding is often selected even when better quality coding is available at both the source and destination networks. For example, consider the case where the source MSC selection candidate is VSELP coding, but it is also possible to use PSI-CELP. Therefore, in the IAM sent to the SSP, the VSE
LP is identified as the preferred encoding type. The IAM is then relayed from the SSP to the destination MSC. If the destination MSC cannot use VSELP, it will use the PSI-C (since it can only move the coding type selection order down as described above using the returned MAP message).
There is no possibility of reverting to ELP and therefore the call will default to μ-la
The w-encoding type must be used.

[0013] The problems described in the previous paragraph are not limited to path calls through the SSP. Rather, the problem appears wherever the call goes through a path through a network node such as a mobile network gateway mobile switching center (GMSC) where the conversion of the called number is performed.

An object of the Summary of the Invention The present invention overcomes the above disadvantages, at least reduce. It is a further object to allow coding type negotiation to occur between two nodes of a communication network, even when a call is first directed to a number translation node.

According to a first aspect of the present invention, the type of encoding is negotiated during the establishment of a voice call between the originating exchange and the destination exchange of the communication system, and the procedure for setting up the call is controlled. A method is provided that is directed via a caller ID conversion node. The method is as follows: (1) The caller's exchange and the caller's exchange select at least the first-order coding type selection candidate of the caller's exchange and the caller's exchange in the second-order converter. Transmitting a call setup message including identification of a second-ranked encoding type selection candidate if it has a selection candidate of: (2) receiving, at a number conversion node, the call setup message; Determining the identity of the destination exchange based on the called party number; (3) determining, at the translation node for that number, a candidate for selecting the encoding type of the destination exchange; Number conversion based on the coding type selection candidate determined for the destination exchange and the coding type selection candidate of the originating exchange as identified in the call setup message Determining a call encoding type selection candidate at the node; and (5) the first order code identified by the call setup message, wherein the call encoding selection candidate determined in step (4) is identified. In the call setup message, if the selected candidate matches the encoding type selection candidate, the first-order encoding type selection candidate is recognized as the preferred encoding type. And (6) transmitting the call setup message from the translation node of that number to the destination exchange.

According to embodiments of the present invention, an intermediate called party number translation node selects a selection candidate in substantially the same manner as would be done if the called party number translation node were absent. In this way, it is possible to provide a candidate for selecting the coding type of the source exchange and a candidate for selecting the coding type of the destination exchange.

[0017] Preferably, the called number conversion node is a service switching center (SSP) in a sophisticated network. More preferably, in step (2), the identity of the destination exchange is determined using a signaling connection between its SSP and a service control station (SCP).

Preferably, the originating switch is a mobile switching center of a mobile digital network. More preferably, the destination switch is also a mobile switching center of the digital mobile network. One or both of the mobile switching centers (MSCs) are PDs
It may belong to the C network. However, the invention is applicable to fixed line networks and other mobile digital networks.

When the MSC belongs to the PDC network, the selection candidate is PSI-C
ELP or VSELP may be used. In addition, the network and the MSC may have the capability to use the default coding type, i.e., [mu] -law coding.

Preferably, by appropriately setting the user service information prime (USI ′) parameter, the first order encoding type is included in the call setup message sent from the originating exchange to the called number conversion node. Are displayed. By setting the user service information (USI) parameter, a second-ranked encoding type selection candidate may be indicated in the same manner.

If, in step (5), it is found that the choice of call encoding is different from the choice of said first order coding type identified in the call setup message, the destination exchange Is transmitted without changing the USI parameter. On the other hand, if the call coding selection candidate matches the first order coding type selection candidate identified in the call setup message, the USI parameter in the call setup message is the USI ′ parameter. Will be replaced.

Preferably, the call setup message is an initial address message (IAM).

According to a second aspect of the present invention, the type of encoding is negotiated during the establishment of a voice call between the originating exchange and the destination exchange of the communication system, and the procedure for setting up the call is affected. A device is provided which is indicated via a caller ID conversion node. The apparatus includes: a source exchange to a called number conversion node; and a caller ID, a candidate for selecting at least a first-order encoding type of the source exchange, and a source exchange having a second type. Means for transmitting a call setup message including identification of a second-order encoding type selection candidate if it has a rank selection candidate; and receiving a call setup message at the called number conversion node; Means for determining the identity of the terminating exchange based on the called number; means for determining, at the called number translation node, a candidate for selecting an encoding type of the terminating exchange; Based on the coding type selection candidate determined for the calling party and the coding type selection candidate of the originating exchange identified in the call setup message, the conversion of the called number is performed. Means for determining a candidate for the type of call coding in the code, and the first candidate for the coding of the call determined by the conversion node for the called number is identified by the first order identified in the call setup message. If the selected encoding type matches the selected candidate, the call setting message recognizes the first-ranked encoding type selection candidate as the preferred encoding type. Means for recognizing a candidate for selecting a second-order coding type as a preferred coding type, and means for transmitting a call setup message from the called number conversion node to the destination exchange. I do.

According to a third aspect of the present invention, during the setup of a voice call between the originating exchange and the destination exchange of the communication system, the callee number conversion node may select an encoding type selection candidate at the called number conversion node. A method for determining is provided. The method comprises the steps of: (1) at the called number conversion node, transmitted from the originating exchange to select at least the first encoding type of the called number and the originating exchange, and the source of the originating exchange; Receiving a call setup message including an identification of a second order encoding type candidate if the exchange has a second order candidate; and (2) at the called number translation node, Determining the identity of the terminating switch based on the called party number and the choice of the coding type of the terminating switch; (3) the choice of the coding type determined for the terminating switch; Determining a call encoding type selection candidate in the SSP based on the call source encoding type selection candidate identified in the call setup message; and (4) determining in step (3) If the specified call coding selection candidate matches the first order coding type selection candidate identified in the call setup message, the call setup message may include the first coding type as the preferred coding type. Recognizing a choice of a priority encoding type, and if not, recognizing a choice of a second-priority coding type as a preferred encoding type in the call setup message; Transmitting a call setup message from the calling number conversion node to the destination exchange.

[0025] The Detailed Description Figure 1 a specific embodiment is a communication system having a first and a second mobile telephone network 1 is illustrated. For the following description, it is assumed that these networks 1 and 2 are PDC according to Japanese standards. Each of the networks 1, 2 has a “mobile switching center” (MSC) 3, which connects calls to and from mobile stations 5, 6.
4 has one or more switches. One mobile station 5, 6 is connected to the MSC 3, 4 of the network via a base station control station (BSC) 7, 8 and a base station (BTS) 9, 10. The BTSs 9 and 10 have a “cell” configuration in which the mobile stations 5 and 6 are located, while the BSCs 7 and 8 are the mobile stations 5 and 6.
Are associated with a small group of cells (and therefore multiple BTSs), including those located.

The mobile station 5 sends the SETUP message via the BTS 9 and the BSC 7 to the associated M
Requesting a telephone connection by sending to SC3. This message contains the called party number. Assuming that the called party number corresponds to a conventional B-number, i.e., a particular subscriber, and that the called party is a subscriber of some external network, i.e., network 2, MSC 3 has a Prepare a call setup message (specifically IAM) for transmission to the MSC 4 defined by the number prefix.

As described above, the preparation of the IAM requires a suitable coding type (ie, PSI) based on the capabilities and selection options of the source MSC 3 and the capabilities of the destination MSC 4.
-CELP, VSELP, or μ-law).
The latter is maintained in a database 11 that stores capability information related to MSC3. For example, it is assumed that the source MSC 3 can use both PSI-CELP and VSELP, but it is preferable to use PSI-CELP, and the destination MSC 4 can also use both PSI-CELP and VSELP. If
The originating MSC 3 uses the PSI in the user service information parameter (USI) of IAM.
-Indicate selection candidates for CELP. The IAM is then transmitted over the interconnected network 12 to the destination MSC 4. After the coding type selection candidate is determined, and before transmitting the IAM, the source MSC 3 allocates a necessary half-rate channel to the calling mobile station 5.

The destination exchange 4 is defined by USI parameters, ie, in this example, PS
If it has a coding choice that matches the I-CELP, it sends a MAP message back to the originating MSC3. The MAP message has two fields of codec status and codec slew rate information. The former field is set to indicate codec through (i.e., transmitted from mobile station to mobile station without transcoding), while the latter field is half-rate encoded (i.e., PSI-CELP). ). For those skilled in the art,
It will be clear how the fields of the MAP message are set for other choices and capabilities.

The call setup procedure described thus far follows the conventional PDC setup procedure.
However, the setting procedure described below represents a modification to the conventional procedure. Consider the case where the number dialed at the mobile station 5 is related to a number 800 or the like, for example, a certain special service such as toll free or speed dial. In such a case, the dialed number does not directly represent a network subscriber, but rather is a number that requires a translation to determine such a subscriber number.

Upon receiving the SETUP message including the number 800, the originating MSC 3 prepares an IAM message for relaying to the destination exchange. However, when deciding the selection candidate of the coding type, the MSC 4 cannot identify the 800-number switch because the terminal exchange is not directly determined. Source MSC
3 therefore inserts its own speech coding type selection candidate into the user service information prime parameter (USI ') (and assigns the channel to the calling mobile station 5). The selection candidates will be PSI-CELP or VSELP.
In the USI parameters, the originating MSC also inserts alternative speech coding type selection candidates. If MSC3 has only one selection candidate, this is inserted into the USI parameter.

From the dialed number 800, the originating MSC 3 recognizes that the initial destination for the IAM is the service switching center (SSP) 13. The IAM is therefore sent to the SSP 13 where a digit translation is performed on the dialed number 800 to determine the B-number of the subscriber to whom the call is going. Using the translated B-number prefix, SSP 13 can identify the destination exchange 4 for the call.

The SSP 13 has a database 11 for storing capability information corresponding to the capability of the source MSC 3 (and of the destination MSC 4). From source MSC3 to I
When receiving the AM, the SSP 13 queries the database 11 to identify the capabilities of the destination MSC 4. If the destination MSC 4 cannot support the candidate encoding type selection of the originating MSC 3 (as defined by the IAM's USI 'parameter), the USI parameter is left unchanged by the SSP. The USI 'parameter may be deleted (although this is not essential since it is ignored by the endpoint MSC 4 in any case). The IAM is then relayed by the SSP 13 to the destination exchange 4.

A search query of the database 11 that stores the capability information by the SSP causes the destination MSC 4 (as defined by the USI 'parameter of the IAM) to identify the source M
If the SC3 encoding type selection candidate can be supported, the USI
The definition of the encoding type selection candidate in the parameter is USP in SSP13.
Replaced by the selection candidate identified by the I 'parameter. Again, the choice of coding type defined by the USI 'parameter may possibly be deleted before the IAM is relayed to the destination MSC4.

The above process is illustrated by way of example. First, the source MSC3 is PSI-CEL
Consider the case where both P and VSELP can be used, and it is preferable to use PSI-CELP. In the IAM sent from the MSC 3 to the SSP 13, the UAM
The SI 'parameter is set to indicate PSI-CELP, while the USI parameter is set to indicate VSELP. If the SSP 13 determines that the destination exchange can only use VSELP, the USI 'parameter is deleted and the IAM is routed through the interconnect network 12 to the destination exchange 4
Is forwarded to.

Now, consider a similar case except that the SSP 13 determines that the exchange 4 at the end point can use both the PSI-CELP and the VSELP. In this case, USI
The parameters are replaced with USI 'parameters before transferring the IAM to the destination exchange 4.

When receiving the IAM at the destination MSC 4, the setup procedure proceeds in a conventional manner.
That is, the end MSC 4 determines whether the selection candidate identified in the USI parameter matches its own current selection candidate. If they match, this is indicated in the returned MAP message. If the outgoing selection candidate does not match that of the destination MSC 4, an alternative coding type is identified in the MAP.

FIG. 2 is a flow chart diagram illustrating the above-described procedure in which a mobile-to-mobile call is routed through a service switching center.

It will be appreciated by those skilled in the art that various modifications can be made to the embodiments described above without departing from the scope of the invention. For example, while the above embodiments relate to number translation in the SSP, the invention also applies to number translation that occurs in the mobile network gateway MSC (GMSC). When a call is made to a mobile subscriber, the call is routed to the subscriber's home network. The GMSC uses the home location register (H
LR) to determine the location of the subscriber. Assuming that the subscriber is currently registered on the external network, the GMSC will change the directory number to HL
Replace with the roaming number received from R. Again, the originating MSC is not necessarily
It will be appreciated that there is no need to know the identity of the external network, a defect which is avoided in the present invention.

[Brief description of the drawings]

For a better understanding of the invention, reference will be made, for example, to the accompanying drawings, to illustrate how the same may be performed. The drawing is as follows.

FIG. 1 schematically illustrates a communication system in which a call setup procedure is routed through a service switching center.

FIG. 2 is a flowchart illustrating a call setup procedure in the system of FIG. 1;

[Procedural Amendment] Submission of translation of Article 34 Amendment

[Submission date] April 11, 2001 (2001.4.11)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Contents of correction]

[Claims]

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Claims (11)

[Claims] 1. A method of negotiating the type of encoding during the establishment of a voice call between a source exchange and a destination exchange in a communication system, said call establishment procedure being performed via a called number conversion node. A method as instructed, comprising: (1) selecting from the originating exchange to the number translating node the at least first order coding type of the called party number and the originating exchange; Transmitting a call setup message including the candidate and the identification of the second order encoding type selection candidate if the originating exchange has a second order selection candidate; and (2) a translation node for the number. Receiving the call set-up message at and determining the identity of the terminating switch there based on the called party number; (3) at the number translation node, Determining the coding type selection candidate for the point switch; and (4) the originating as identified in the call setup message with the coding type selection candidate determined for the destination switch. Determining a choice of a coding type for the call at the number translation node based on the coding type selection candidate of the original exchange; and (5) the call determined in the step (4). Is the same as the first encoding type selection candidate identified in the call setup message, the call configuration message includes the first encoding type as the preferred encoding type. Recognize the selection candidates of the encoding type of the order, and if they do not match, select the candidate of the encoding type of the second order as the preferred encoding type in the call setup message. How to recognizing step, characterized by a step of transmitting a setup message for the call to (6) exchange of the end-point from the conversion node of the numbers. 2. The method of claim 1, wherein the originating switch is a mobile switching center of a mobile digital network. 3. The method according to claim 1, wherein the destination switch is a mobile switching center of a mobile digital network. 4. The method according to claim 2, wherein one or both of the mobile switching centers belong to a PDC network. 5. The coding type selection candidate is PSI-CELP or VS
The method of claim 4, wherein the method is an ELP. 6. The first order coding type in the call setup message sent from the originating exchange to the number translation node by appropriately setting the user service information prime (USI ') parameter. The method according to any one of claims 1 to 5, further comprising the step of indicating a selection candidate. 7. The method of claim 6, wherein the number translation node is a service switching office (SSP). 8. The method according to claim 6, further comprising the step of setting a user service information (USI) parameter to indicate selection candidates for the second-rank coding type. 9. In the step (5), it has been found that the candidate for coding the call is different from the candidate for selecting the first-order coding type identified in the call setup message. If the USI parameter to the destination exchange is transmitted unchanged, while the call encoding selection candidate matches the first order encoding type selection candidate identified in the call setup message. 9. The method of claim 8, wherein if so, the USI parameter in the call setup message is replaced with the USI 'parameter. 10. A method for negotiating the type of encoding during the establishment of a voice call between an originating exchange and a destination exchange of a communication system, said call establishment procedure being performed via a called number translation node. The apparatus being instructed, wherein the apparatus sends from the originating switch to the called party number conversion node a selection of at least a first order coding type of the called party number and the originating switch. Means for transmitting a call setup message including a candidate and an identification of a second order encoding type selection candidate if the originating exchange has a second order selection candidate; and the called party number conversion node. Means for receiving the call setup message and determining the identity of the destination exchange based on the called number, and at the called number conversion node, Means for determining a candidate for the encoding type of the exchange; and the encoding of the originating exchange identified in the call setup message and the candidate for the encoding type determined for the destination exchange. Means for determining a call encoding type selection candidate at the called number conversion node based on the type selection candidate; and encoding the call determined at the called number conversion node. If the selection candidate matches the first-ranked coding type selection candidate identified in the call setup message, the first-ranked coding type is selected as the preferred coding type in the call setup message. Recognize the type selection candidate, and if they do not match, in the call setup message, recognize the second-ranked encoding type selection candidate as the preferred encoding type. Means and, said method characterized in that it comprises a means for transmitting from the conversion node of the called party number of configuration messages of the call to the exchange of the end point to be. 11. A method for determining a coding type selection candidate at a called number conversion node during the establishment of a voice call between a source exchange and a destination exchange of a communication system, the method comprising: (1) in the called number conversion node, the called party number transmitted from the originating exchange, a candidate for selecting at least a first-order coding type of the originating exchange, and the originating exchange Receiving a call setup message including an identification of a second-order coding type selection candidate if the switch has a second-order selection candidate; and (2) at the called party number conversion node, Determining the identity of the destination exchange based on the called party number and a candidate for selecting the encoding type of the destination exchange; and (3) determined for the destination exchange. Determining a candidate for a coding type of a call in the SSP based on the selected candidate for the coding type and the candidate for the coding type of the originating exchange identified in the call setup message. And (4) if the call encoding choices determined in step (3) match the first order encoding type choices identified in the call setup message, The call setting message recognizes the first-ranked coding type selection candidate as the preferred coding type, and if the two do not match, the call setting message indicates the second-ranking coding type as the preferred coding type. And (5) transmitting the call setup message from the called number translation node to the destination exchange. Method characterized by having.