Media server selection for vocal announcements within a call control system
The present invention relates to the so-called « Next Generation Networks)) (NGN). This concept of "next generation networking" is a broad term for emerging communication network architectures and technologies, which encompass the pure data networks and the plain old voice networks (PSTN for "Public Switched Telephone Network").
Typically, in a NGN architecture, the information is transmitted via data packets, generally based on the IP (Internet protocol) technologies, being pure IP or MPLS (for "Multi-Protocol Label Switching"). The acronym "VoIP" (Voice over IP) is often used to refer to this transmission of voice traffic over an IP-packets infrastructure.
According to the nature of the transmitted information (data, voice, video...), the packets could be handled differently by the communication network equipments, according to some QoS (Quality of Service) policies.
But in general, the transport-layer equipments (IP routers...) are not aware of this nature of the transmitted information, since the NGN architecture relies on a separation between the transport layer (or connectivity) and the call control layer.
Call sessions are typically handled by dedicated apparatus that are called differently according to manufacturers and standards. Usual terms comprise "Softswitch" or "call controller". Hereafter, we will refer to this kind of apparatus as a call control system (CCS).
In addition to the control of call sessions per se, the call control systems are also responsible for higher-level services, like specific billing, call redirections and the like.

Some of these high-level services may require the call control system to play a pre-recorded announcement to the caller.
For instance, when a call is subject to a specific billing rate, it is usual to warn the caller about his/her call being billed higher than usual.
Some services may also require the caller to enter a pin code before allowing him/her the access.
In an NGN network served by "softswitches", the announcements are played using a pool of media servers.
In a large country, these media servers can be located geographically very far apart.
In addition, especially in such countries, the announcement is connected via a satellite connection.
Since satellite connections are expensive and network resource consuming, it becomes highly desirable to connect the announcement from the nearest media server relative to the geographical region of the called subscriber/user.
This is of particularly higher importance where the NGN network covers Intelligent Networks (IN) and local traffic as well, as the quantum of announcements to be played per day/hour would be significantly higher.
Furthermore, the Applicant set itself the problem of providing a call control system enabling to have the nearest media server selected to have the connection of announcements of all types and for all purposes.
The aim of the invention is to solve these issues.
It relates to a call control system having trunks to receive setup
signaling messages for setting up call sessions in a communication
network, means to detect that a setup signaling message corresponds
to a service requiring a vocal announcement to be played to the

originator of said setup signaling message and/or to the called subscriber/user, and means to retrieve a vocal announcement associated to said service from a memory location of a media server.
According to a general definition of the invention, said call control system further comprises means for determining said media server according to the geographical region of said media server, said geographical region being determined at least from a key verification relative to said setup signaling message.
According to embodiments of the invention, this determination of said geographical region of said media server depends on a Calling Line Identity, contained in said setup signaling message, or on the identifier of the trunk from which said setup signaling message has arrived, or on the number of the called party, or on the trunk for which said signaling message is destined.
The call control system may comprise matching table for mapping values of said media servers and said geographical regions.
The call control system may comprise also matching table for mapping values of said geographical regions and said Calling line identities and/or said identifiers of trunks and/or said Called numbers.
The invention consists also on a communication network comprising such a call control system.
At last, another object of the invention is a method for controlling calls comprising a step of transmitting setup signaling message to a call control system for setting up call sessions in a communication network, a step of detection that a setup signaling message corresponds to a service requiring a vocal announcement to be played to the originator of said setup signaling message and/or to the called subscriber/user, and a step for retrieving a vocal announcement associated to said service from a memory location of a media server.

This method is characterized in that it further comprises a step of determining said media server according to the geographical region of said media server, said geographical region being determined at least from a key verification relative to said setup signaling message.
The invention would be more clearly explained in the following description, with the help of the annexed figures.
The figure 1 illustrates a communication network comprising a call control system according to the invention.
The figure 2 is a flowchart illustrating the steps relative to the determination of the nearest media server, according to the invention.
In the figure 1, the communication network CN comprises a call control system CCS. This call control system can receive setup signaling message from various calling devices (telephone, IP terminals, etc.), Tl, T2, T3, located in several geographical areas or regions RG1, RG2, RG3 corresponding to local communication networks, LN1, LN2, LN3, respectively.
Typically, these setup signaling messages may be compliant with the SIP protocol ("Session Initiation Protocol") as defined by the RFC 3261 of the IETF (Internet Engineering Task Force). In case of a converged call control system, like a media gateway control (MGC), the setup signaling messages can arrive from plain-old telecommunication networks (POTN) and be compliant with the ISUP protocol ("ISDN User Part").
The aim of the setup signaling messages (e.g. the "Invite" message of the SIP protocol) is to set up a call session between the calling device and a called device (not shown in the figure). As said previously, before establishing the call session, some services may be needed requiring a vocal announcement to be played to the calling

party and/or to the Called party. In such a situation, it is the responsibility of the call control system CCS to trigger the play of this vocal announcement.
Typically again, the vocal announcements are stored in a least one media server MS, separated from the call control system itself. A media server MS is basically a database comprising many vocal announcements (and possibly other kind of media). Each vocal announcement is stored in a memory location of this media server and could be retrieved thanks to a memory address.
The communication between the call control server CCS and a media server MS could be based on the HTTP protocol (HyperText Transfer Protocol). In such a case, the memory address could be an URL (Uniform Resource Locator).
Knowing the memory address of the announcement to be played, the call control server CCS can retrieve it from the media server MS and play it to the calling party that has emitted the setup signaling message.
In practice, the entire country is divided into regions RG, and for each region RG a least one corresponding media server MS is associated.
For example, the media server MSI corresponds to region RG1.
The determination of the nearest media server able to serve the vocal announcement to be played depends on the region corresponding to the setup signaling message (i.e. requested by the calling party and/or the called party).
In practice, the call center system CCS uses information relatives to the setup signaling message and extracts the region RG in which the announcement is to be played. A free media server MS within the identified region RG is then selected and the announcement is triggered.

As shown in the figure 1, trunk Tl links the call control system CCS to the local communication network LN1 belonging to region RG1; the trunk T2 links it to the local communication network LN2 belonging to region RG2; and the trunk T3 links it to the local communication network LN3 belonging to region RG3.
According to the trunk identifier, the call control server CCS can determine which media server MS is present within the region RG corresponding to the local communication network LN.
For instance, if the media server MSI is located in a region RG1 where the local communication network LN1 is identified by the trunk identifier, then the media server MSI would be chosen.
The Calling Line Identity (CLI) could also be used for selecting the media server. This Calling Line Identity CLI is typically the number of the party initiating the call, as defined by the recommendation E.I64 of the ITU-T (International Telecommunication Union). This number is made of several parts as defined by the numbering plan. The prefix of the Calling Line identity CLI represents the region (geographical area). Using this prefix, the call control system CCS can therefore determine the media server.
However, this calling line identity CLI is not mandatory and
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could be not present in the setup signaling message.
With reference to figure 2, a flowchart has been represented illustrating the selection of the appropriate media server.
At step SOI, during the active phase of the call, the calling line identity CLI is examined.
If received, the CLI is extracted to find out the region identifier RG id of the region it belongs to (step S02).
In practice, CLI is the key to a table (for example called " TRANSLAREACOD") used for translation of received CLI (area code) into the corresponding region identifier RG id.

In case the CLI is not present, the unique trunk group identity (trunkgroup id) is used to obtain the region identifier RG id (step S03).
In practice, trunkgroup id is the key to a table (for example called "TKGIDLANID") used for translation of received trunkgroup identifier into the corresponding region identifier.
At step 504, the region identifier RG id thus obtained is processed.
If the region identifier RG id thus obtained is found in a table (called "Media server table") for mapping of region id to media server id (step S05), said corresponding media server identifier MS id is used (step S06) to select the appropriate media server (step S07).
In case the region identifier RG id is not present in the media server table or in case the media server is not found, any media server would be selected (step 508).
In practice, each time the media server table is accessed, first a check is performed on whether the media server is active, enabled, etc. before a comparison is made on the required region identifier RG id and the region identifier RG id entry provided for the media server entry accessed in the table. After the entire table is scanned, if no match is found, then any found valid media server (for example, the last or the first active, enabled, etc. media server that is found) is selected.
In a variant, in case there is no media server found within the desired region, instead of selecting any media server, a solution is to select a media server from the neighboring region.
For announcements to be provided to called subscriber, the called number or outgoing trunkgroup identifier can be used to access the tables to obtain the region identifier id. The region identifier to media server identifier mapping is the same as that for the CLI case. The tables themselves can be generic, and do not distinguish

between CLI/called number or incoming/outgoing trunkgroup id. In other words, the present invention is similar when announcements have to be played to called party ("CLI" replaced by called number, "incoming trunk id" replaced by "outgoing trunk id").
According to one embodiment of the invention, the Calling Line identity is used when it is present. When it is not, then the trunk identifier is used instead for determining which media server to select.
According to the invention, the call control system CCS contains means to match with each possibility of value for the calling line identity CLI and/or trunk identifiers, an address to the appropriate media server. These means could for instance be a simple matching table (s).
It is therefore quite easy for the operator of the system to modify this table in order to change a region to another, to add a new media server etc.
The present invention provides tremendous savings for both the network operator as well as the end user.
For network operator, savings in usage of expensive network resources (especially in large countries), both in term of number as well as the duration of use, for e.g., in case of satellites, can be freed up more quickly for other calls/services that increase the operator revenue.
As an example, the typical price for satellite connection is 20 € / minute for an IMASAT satellite connection. In the case of TELEMAR network (in Brazil), announcement connections via satellite varies in the range of one million to five millions (only successful connections are taken into account for this figure) per 24 hours, depending on the occasion of the day. These millions of saved satellite links can according to the present invention be used to generate real voice

traffic, which means higher revenue income for the operator of the network.
Furthermore, since the present invention steers to have the nearest media server selected to have the connection of announcements, the media server equipment can be dimensioned to the real needed capacity of that location or area. As an example, for the price of a large fully equipped media server, smaller media server can be distributed over various locations or areas to steer the needs for public or even product placement announcements of that area. Consequently, the operator of the network can generate additional revenues via product placement/publicity announcements of that area.
For end user, the savings are in terms of call charges due to the faster connection of the announcement.
Furthermore, cost savings are also obtained in case of optical fiber connections to the distant media server.

CLAIMS
1) Call control system (CCS) having trunks to receive setup
signaling messages for setting up call sessions in a
communication network, means to detect that a setup
signaling message corresponds to a service requiring a
vocal announcement to be played to the originator of said
setup signaling message and/or to the called
subscriber/user, and means to retrieve a vocal
announcement associated to said service from a memory
location of a media server (MS), characterized in that it
further comprises means for determining said media server
(MS) according to the geographical region of said media
server (MS), said geographical region being determined at
least from a key verification relative to said setup signaling
message.
2) Call control system according to claim 1, in which said the
determination of said geographical region (RG) of said
media server (MS) depends on a Calling Line Identity (CLI),
contained in said setup signaling message.
3) Call control system according to claim 2, in which said
determination of said geographical region (RG) of said
media server (MS) depends on the identifier of the trunk
from which said setup signaling message has arrived, when
the Calling Line Identity (CLI) is not available.

4) Call control system according to claim 1, in which said
determination of said geographical region of said media
server (MS) depends on the number of the called party.
5) Call control system according to claim 4, in which said
determination of said geographical region of said media
server (MS) depends on the trunk for which said signaling
message is destined, when the called number is not present.
6) Call control system according to one of the previous claims,
further comprising a matching table, mapping values of
said media servers and said geographical regions.
7) Call control system according to claim 2, further comprising
a matching table, mapping values of said geographical
regions and said Calling line identities.
8) Call control system according to claim 3 or claim 5, further
comprising a matching table, mapping values of said
geographical regions and said identifiers of trunks.
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9) Call control system according to claim 4, further comprising
a matching table, mapping values of said geographical
regions and said Called numbers.
10)Communication network comprising a call control system according to one of the previous claims.
11)Method for controlling calls comprising a step of transmitting setup signaling message to a call control system (CCS) for

setting up call sessions in a communication network, a step of detection that a setup signaling message corresponds to a service requiring a vocal announcement to be played to the originator of said setup signaling message and/or to the called subscriber/user, and a step for retrieving a vocal announcement associated to said service from a memory location of a media server (MS), characterized in that it further comprises a step of determining said media server (MS) according to the geographical region of said media server (MS), said geographical region being determined at least from a key verification relative to said setup signaling message.