Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-07-16
2004-06-29
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S352000
Reexamination Certificate
active
06757266
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for setting up connections or calls in a communication system including at least one first communication network having a number of first terminals connected thereto and at least one second communication network having a number of second terminals connected thereto. The connections or calls between a respective first terminal and a respective second terminal are being routed through one or more access servers which may be part of the first or second communication network. The invention can be used in all kinds of packet switched networks (not only in IP-based networks; IP: internet protocol).
In particular the invention relates to terminating calls or connections from a packet switch network to a terminal of a circuit switched network through one or more access servers. For example, the invention relates to a situation where speech (e.g. voice over IP) and data calls terminating from a TCP/IP based network (e.g. Internet) are routed to a subscriber (or respectively to his/her terminal equipment) in a telecommunication network. The telecommunication network may be a public land mobile network PLMN, a public switched telephone network PSTN or an integrated services digital network ISDN. All such telecommunication networks are intrinsically based on circuit switching rather than a packet switching.
1. Background of the Invention
An access server is a well-known functionality in TCP/IP and/or telecommunication networks.
FIG. 4
a
shows a number of terminals TE
1
-TE
4
connected to an internet/intranet. In this case an access server AS provides the functionality to enable direct internet/intranet access. As shown in
FIG. 4
b
, the access server AS may also provide an interface between the packet switched network (e.g. a TCP/IP network) and a circuit switched network (such as a public switched telephone network PSTN). It should be noted in
FIG. 4
b
that geographically the entities of the packet switched network and the circuit switched network will overlap. Therefore, the access server AS provides the functional interconnection between entities in the two networks rather than the geographical interface. It is also not important to which network (packet switched or circuit switched network) the access server AS is attributed as long as it provides the functional interconnection between the first and second network, in the case of an interconnection between a packet switched network and a circuit switched network in particular the mapping of a packet switched call from a terminal TE of the first network to a circuit switched call to be terminated in the terminal MS of the second network.
In case the second network is constituted by a mobile radio communication network (such as the D1, D2 or E-plus network in Germany), there may be provided several access servers AS and furthermore the mobile stations MS constituting the second terminals of the second network are mobile, i.e. they roam from cell to cell in the mobile radio communication network.
TELNET Session According to the Prior Art
When a plurality of access servers AS including one gateway access server GAS are provided, one access server AS is used as the final device for the packet switching of the call and the access server AS then converts the packet switched (call) connection to a circuit switched connection (call) between the access server AS and the terminal of the circuit switched network. This may for example be the case, when a mobile station MS is not connected with an IP address (otherwise packet switching may be used end-to-end).
FIG. 4
c
shows steps {circle around (
1
)}-{circle around (
3
)} to set up a (call) connection from a terminal TE of a TCP/IP network to a terminal MS of a telecommunication network. In
FIG. 4
c
only for illustration purposes the access servers AS
1
, AS
2
are located in the telecommunication network.
The TELNET session is just an example of how such a (call) connection setup can be done. It is also possible to provide a special translation (address translation) even for a telecommunication network that converts from IP address to MSISDN number, e.g. in cases where subscribers have fixed IP addresses.
In step {circle around (
1
)} a call from a terminal of the TCP/IP network can be terminated into the telecommunication network. When sending a call set up message (actually this is the first packet transmitted), the terminal TE also includes an identification of the called mobile station MS to which a call is to be set up. The TELNET session is used to retrieve the IP address (either a fixed IP address or a dynamically allocated IP address when the mobile subscriber accesses the TCP/IP network) by sending as identification for the called mobile station the mobile station subscriber number MSISDN in step {circle around (
2
)} to the access server AS
1
or AS
2
depending on which access server is provided for serving the mobile station MS. (Moreover, instead of the MSISDN also the IMSI may be used (in mobile radio networks); even more generally E.164 numbers are used such that the concept is generally applicable to PSTN and ISDN as well). In step {circle around (
3
)} the access server, e.g. AS
1
, returns the IP address of the mobile station MS. Of course, it will be appreciated that the mobile station MS roams in said telecommunication network such that depending on the location it will be served by a mobile switching center MSC
1
or a mobile switching center MSC
2
as illustrated in
FIG. 4
c.
Whilst the TELNET session can in principle return the IP address of the mobile station, there are some intrinsic problems with the TELNET session.
Firstly, there may be a case where the call set up message is sent to an access server AS which is currently in fact not serving the desired mobile subscriber MS, i.e. the mobile subscriber is not served by the corresponding access server, e.g. AS
1
, but served by another access server AS
2
in the same telecommunication network. Since the call set up message was directed to the access server AS not serving the mobile station MS, no terminating call session can successfully be established. In
FIG. 4
c
it may be noted that a direct call from AS
1
to MS only takes place when the MS is really connected to the AS (with an IP address). Usually, the call connection passes through MSC
1
(circuit switched).
Secondly, as is also indicated in
FIG. 4
c
, when there are several access server AS
1
, AS
2
in the same telecommunication network (which seems to be very likely due to the growing amount of internet calls), the packet switched call from the packet switched network (internet) will be converted into the circuit switched call in the corresponding “called” or “addressed” access server. Although it may be possible to set up the call if the access server happened to be selected which is currently serving the mobile station, another disadvantage may occur. Namely, the “called” or “addressed” access server may not necessarily be the access server which is located most closely to the mobile station when it roams in the mobile radio communication network. This means, that in fact there may be another access server located closer to the present location of the mobile station MS which is however not used since the connection is always built up through the “called” access server. The result is that the distance over which the call is handled as a circuit switched call is much longer than necessary. The above example describes the case that the mobile station is not served by an access server because there is as yet no circuit switched connection of a previously setup call connection. That is, in a case where there exists already one circuit switched connection between one access server AS and the mobile station and a further connection is to be setup, then the access server AS should be selected which is already used for the existing circuit-switched connection.
Thirdly, packet switched calls such as calls from the internet may use a plurality of functionalities (such as bearer services) which may
Chin Wellington
Schultz William
Telfonaktiebolaget LM Ericsson (publ)
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