Circuit-switched network

Details Circuit-switched network Circuit-switched network

1998-12-04

2001-11-27

Olms, Douglas (Department: 2661)

Multiplex communications

Pathfinding or routing

Through a circuit switch

C370S355000, C370S351000, C370S400000

Reexamination Certificate

active

06324175

ABSTRACT:

BACKGROUND OF THE INVENTION
This application claims priority from Japanese Patent Applications No. 9-334444 filed Dec. 4, 1997 in Japan, No. 9-337205 filed Dec. 8, 1997 in Japan, No. 9-345242 filed Dec. 15, 1997 in Japan and No. 9-351431 filed Dec. 19, 1997 in Japan, the contents of all four applications being incorporated herewith by reference.
1. Field of the Invention
The present invention relates to Synchronous Transfer Mode (STM) communications networks, and in particular to techniques for transferring data with an Internet Protocol (IP) address by way of an STM connection.
2. Description of Related Art
A characteristic of STM-based circuit-switched networks is that because a signal on a physical channel is multiplexed into time slots and circuit-switched, the delay during communication is extremely short and there is no overhead such as the header required in Asynchronous Transfer Mode (ATM) where virtual paths and cells are employed. In telephones, for example, voice quality problems arise and echo cancelers may be required if there is a delay of more than 20-30 ms. In telephones, video conferencing and other bidirectional services in general, it is preferable for delay to be short. From this point of view, STM is a transport mode which is well suited to digital telephone networks.
The operation of a conventional STM network will be explained with reference to FIG.
1
and FIG.
2
.
FIG. 1
shows the main components of a conventional STM-based circuit-switched network, while
FIG. 2
shows the main components of a conventional local switch.
As shown in
FIG. 1
, in a conventional STM-based circuit
5
switched network, a user operating telephone
11
transmits dialing information
15
(the telephone number of the called party) to source switch
13
in STM network
12
via common channel signaling network
16
. This is signaling system No. 7 as defined in ITU-T recommendations. Switch
13
receives the dialing information via software
14
and maps it to an E.164 address (an ISDN address as standardized by the ITU-T) for physical transmission, whereupon STM-based communication is carried out. Namely, source switch
13
establishes an STM connection in STM network
12
and uses this connection to map data from telephone
11
to the E.164 address and transfer it to destination switch
13
.
In a conventional STM-based circuit-switched network of this sort, switching is performed by transposing time slots which have been multiplexed into frames, each time slot comprising 8 bytes of data. By way of example, this operation can be implemented by a sequential write random read, as shown in FIG.
2
. Namely, time slots can be switched by using sequential counter CTR to write the data at sequential addresses to data buffer memory DBM, and then using address control memory ACM to change the order in which this data is read.
As mentioned above, compared with ATM and the like, the advantages of a conventional STM-based circuit-switched network of this sort are that delay is extremely short and there is no overhead.
However, a conventional STM-based circuit-switched network of this sort requires that data is transferred via an STM connection which has been set up in advance from a source user terminal to a destination user terminal. Its applicability is therefore restricted, and such circuit-switched networks are only being considered for leased data circuits between large businesses.
FIG. 3
illustrates a schematic of a dedicated STM connection.
On the other hand , in data communications based on an IP architecture , by writing the IP address, which is the identification number of a terminal, in the header of a packet and sending this to a network such as the Internet which supports IP, each router of a switch or the like simply looks for the immediate transfer destination corresponding to the address. The datagram is successively transferred without requiring a connection to be set up between the two terminals which want to communicate. Thus no dedicated connection is required and data can be transferred by means of an extremely simple procedure. However, under this scheme there is a longer delay than in an STM-based circuit-switched network, and overhead is necessary.
SUMMARY OF THE INVENTION
It has been an intention of the inventors to construct a novel circuit-switched network which combines the advantages of an STM-based circuit-switched network and the advantages of data communications based on IP addresses.
It is therefore an object of the present invention to offer a circuit-switched network capable of providing STM circuits dynamically. This is a service which previously could only be offered for simple leased lines by providing an STM-based trunk network based on the logical addresses, and in particular the IP addresses, used in data communications. It is a further object of this invention to provide a circuit-switched network in which delay and overhead requirements are slight.
One characteristic of the present invention is that it analyzes logical addresses in an STM network and performs routing on a burst-by-burst basis on the basis of these logical addresses. One significant feature of the present invention relates to how connections are created and used, and the procedure whereby a user requests a connection.
Namely, a circuit-switched network according to this invention comprises, in an STM network, a plurality of local switches each serving at least one terminal and at least one transit switch connected between these local switches. Logical addresses, and in particular IP addresses, for sending and receiving burst data (packets) between the terminals of these local switches are allocated to at least some of these terminals. Each of the local switches comprises: means for receiving burst data which has been given a logical address and which arrives from a terminal served by that switch; means for managing the logical addresses of the terminals served by that switch; means for acquiring time slot information (the time-slot-relay, i.e., information relating to the route to the destination local switch) which has been allocated in respect of the STM network to the local switch which serves the terminal constituting the destination of this burst data, this allocation being carried out in accordance with the logical address of the received burst data; and means for transferring the burst data through the STM network in accordance with the time slot information obtained by the acquisition means.
The aforesaid acquisition means can comprise means for transferring information relating to the logical address of the received burst data to another local switch. The acquisition means also may comprise means which, if it receives logical address information from another local switch and the logical address concerned is a logical address managed by the local switch to which the acquisition means belongs, returns the time slot information allocated to this local switch to the local switch which is the source of that logical address information.
Alternatively, STM connections can be set up in advance between the aforesaid plurality of local switches, and a table, in which is recorded the time slot information corresponding to these STM connections, can be provided. The aforesaid acquisition means can comprise means for acquiring the aforesaid time slot information by looking up information from this table. In this case, because the time required to transfer logical address information to other local switches is eliminated, time slot information can be obtained rapidly.
If such a table is provided, each local switch can comprise means for monitoring, for each STM connection, whether that connection is busy or not, and for releasing an STM connection which has not been used for more than a set time. As a result, if one of the STM connections which have been set up in advance has not been used for a long period of time, this connection can be released, whereby effective utilization of network resources can be achieved.
Each local switch can comprise: table means in which is recorded,

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