Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-12-16
2003-06-10
Kizou, Hassan (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S252000, C379S088170
Reexamination Certificate
active
06577637
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method, a switching means and a telecommunication system for performing data communications between a first subscriber station of a mobile radio communication network and a second subscriber station which is connectable to said mobile radio communication network. The second subscriber station can be connected to the mobile radio communication network through the internet and/or a conventional public switched telephone network.
In particular, the invention relates to performing data communications between a mobile station of the mobile radio communication network and a second subscriber station connected to a data network (such as a data network running internet protocol (IP)). Such a second subscriber station can e.g. be an internet telephone constituted by a special internet telephone hardware or software on a workstation capable of supporting the internet protocol.
The mobile radio communication network can be a GSM-based mobile radio network (GSM: Global System of Mobile Communications), such as a D1, D2 or E-plus radio communication network in Germany.
BACKGROUND OF THE INVENTION
In public switched telephone networks (PSTNs), conventionally each subscriber participating in a call has a separate telephone hand set into which the subscriber talks and from which speech is reproduced. Such conventional telephone hand sets can be radio telephones (which allow a free movement of the subscriber at home) which may use analog or digital transmission techniques even when being connected to a conventional public switched telephone network, such as German Telecom in Germany. Several conventional telephones may be interconnected in a private branch exchange system which interconnects the several telephones to one or more outside lines (conventional lines or ISDN lines).
Additionally, most subscribers nowadays also own a mobile radio telephone together with a subscription to a mobile radio communication network. The mobile radio telephone uses entirely digital transmission techniques for communicating with entities in the mobile radio communication network, e.g. with the mobile switching center thereof. Calls between mobile radio telephones or between a conventional telephone hand set and a mobile radio telephone are routed through the mobile radio communication network and the public switched telephone network.
Instead of just routing a telephone call from a public switched telephone network to a private branch exchange system (PBX), it is now also possible to route a call first to a computer network. Such a computer network can e.g. be constituted by a company intranet. Normal workstations of the computer network which have been upgraded with software or hardware to operate as a conventional telephone and/or as an internet telephone can be part of the computer network. Such computer-based telephones become more and more widespread such that it is soon anticipated that at least one party in a telephone communication is using a computer-based telephone instead of a conventional telephone hand set. Some computer networks or intranetworks as well as their interconnected workstations including the telephone software/hardware already use internet protocols for communication. This is e.g. described in an overview article by Linden decarmo “Internet Telephone Standards”, PC Magazine, Feb. 18, 1997, pages 185 to 187.
Although the workstation running the telephone software and/or the mobile radio telephone of the mobile radio communication network constitute quite advanced units with respect to their digital speech coding/decoding units, the analog voice—when spoken into the microphone of the respective telephone—must still be digitized and compressed due to the restrictions imposed on the bandwidth in the available transmission channels, e.g. when the call still needs to be routed through the public switched telephone network. If e.g. a call is originated from a mobile radio telephone of a digital mobile radio communication network, the call will undergo several speech coding/decoding stages before reaching the final called subscriber station. Since each coding/decoding introduces errors, such several stages of decoding/coding processes drastically deteriorate the speech quality received at the called subscriber station.
For example, the compression protocols used in the GSM network and internet telephony are not the same and therefore there is a need for several coding/decoding (audio data compression/decompression) stages.
If internet telephones become more and more common in the future, it might be wise from the network utilization point of view to route the call from the telephone network to the IP-network (IP: Internet Protocol) from the network unit where the call is originated from. The possibility to route the call to a mobile subscriber in an IP-network directly to the serving mobile switching center opens new possibilities for cooperation between owner of IP-networks and mobile operators. For example, an international call from an internet telephone can be routed in the IP-network instead of the public switched telephone network PSTN.
Call Set-Up Between Mobile Station and Workstation
Presently, several possibilities for setting up a call between a mobile radio telephone (a first subscriber station) of a mobile radio communication network and a workstation running a telephone or internet telephone software (a second subscriber station connectable to the mobile radio communication network) can be imagined, as will be explained below with reference to
FIGS. 7
to
11
. The invention uses all such call set-up possibilities.
a) Call from a Mobile Station to a Workstation Connected to an Internet Protocol Network
FIG. 7
a
shows an example of a telephone communication system where a mobile station is transmitting digitally (via a TDMA method) digitally coded speech via an antenna ANT to a switching means BSC/MSC of the mobile radio communication network PLMN. Here the switching means comprises a base station controller BSC and a mobile switching center MSC. The base station controller BSC inherently comprises an audio data (speech) coding/decoding means which is indicated with CODEC in
FIG. 7
a.
Basically, as will be explained in more detail with reference to
FIG. 7
b
, the call originated from the mobile station MS is decompressed in the audio data coding/decoding means such that a data rate of a bandwidth of 64 Kbit/s is transmitted through the public switched telephone network PSTN to the company intranet. Here, the call may be routed through a private branch exchange system PBX to the data network (IP-network), to which the individual workstations WS
1
, WS
2
, . . . , WSn are connected. Since the workstations WS
1
, WS
2
, . . . , WSn run a digital telephone network, the data arriving from the PSTN is digitally decoded after which an audio data (speech) coding/decoding means CODEC in the workstations WS perform the final digital/analog conversion. The PBX in
FIG. 7
a
has a CODEC which can compress (i.e. code) the received speech using a protocol supported by the WS.
The call set-up in
FIG. 7
a
is as follows. The mobile station MS sends a call set-up message including a calling number of the second subscriber station WS which is served by the PBX. Thus, the PBX must have the information that the called second subscriber station—i.e. the workstation running the telephone software—wants all calls arriving for it to be diverted to the internet telephone software running on the workstation. In this case, the PBX needs protocol translation and speech coding between the PSTN and the internet telephone software running on the workstation. Since e.g. the internet telephone uses a packet-based transmission, the PBX must also perform the analog-to-packet conversion. Although the mobile station MS on one side and the workstation WS on the other side each run very advanced digital coding and transmission techniques, intermediate speech coding/decoding is still performed in the base station controller BSC and the PBX. This can deteriorate
Kizou Hassan
Pezzlo John
Telefonaktiebolaget LM Ericsson (publ)
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