Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1998-04-09
2001-05-15
Marcelo, Melvin (Department: 2739)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S524000
Reexamination Certificate
active
06233233
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a packet switch; and, more particularly, to a packet handling apparatus functionally distributed among subscriber modules for use in the packet switch.
BACKGROUND OF THE INVENTION
A data communication technology making use of a “packet” is widely employed in a data communication network, wherein the packet is a sequence of binary digits including data, call control signals and possibly address which are arranged in a specific format. Perhaps the best known and most widely used protocol standard of a data communication is X.25 protocol. The X.25 specifies an interface between a host system and a packet-switched network.
With the improvement in transmission technology and switching facilities, a new packet communication scheme, “frame relay”, has been becoming highlighted and won popularity. The communication scheme using the frame relay, principally based on the X.25, eliminated as many overhead of the X.25 as possible. Thus, the frame relay can be viewed as a streamlined version of the X.25.
As an Integrated Services Digital Network (ISDN) accommodates the frame relay to a large degree, a capability of performing a packet switching for the frame relay is regarded essential in an ISDN switching system.
Since the ISDN switch accommodates a packet switching as well as a circuit switching, in practice, the packet switch can be regarded as sub-functions of the ISDN switch.
A skeleton of the ISDN switch, or the packet switch, is shown in FIG.
1
.
The packet switch incorporates itself into major subsystems such as an access switching subsystem (ASS)
100
, an interconnection network subsystem (INS)
110
and a central control subsystem (CCS)
120
.
The ASS
100
interconnects itself with subscribers on one side and the INS
110
on the other side. The ASS
100
performs call processing, call flow control, time switching functions, and the like.
The INS
22
, connected to the ASS
100
, is designed for performing space switching, network synchronization and the like.
The CCS
120
supervises and controls overall functions performed in each subsystem in the packet switch.
In the ASS
100
, a plurality of access switching subsystems for ISDN subscriber (ASS-I)
101
to
103
are incorporated. The ASS-I provides interfaces by using the ISDN standard interfaces such as I
430
, I
441
and I
451
. An ISDN subscriber is able to gain access to the packet switch and finally reach another ISDN subscriber with the help of these ISDN standard interfaces and protocols.
An access switching subsystem for packet (ASS-P)
104
designed for handling packets is also included in the ASS
100
. All the packets exchanged between subscribers pass and are handled by the ASS-P
104
. The ASS-P
104
is not directly connected to subscribers but is connected to the INS
110
.
Meanwhile,
FIG. 2
provides a closer look at the ASS
100
.
A basic rate subscriber interface block (BSI)
201
, a primary rate subscriber interface block (PSI)
202
and a basic access rate multiplexing interface block (BAMI)
203
provide different types of interfaces to provide services for various kinds of communication services from ISDN subscribers.
An ISDN subscriber access processor (ISAP)
204
is employed in order to control functions of the BSI
201
, the PSI
202
and the BAMI
203
.
An inter-processor communication (IPC) network
205
is designed for communications between processors in the ASS-I
101
.
An access switching processor-ISDN (ASP-I)
206
is designed for controlling operations occurring within the ASS-I
101
. A time switch processor (TSP)
207
controls the operation of a time switch (TSW)
208
.
The TSW
208
performs a time slot interchange as a typical time switch does. The TSW
208
constitutes a typical T-S-T switching structure together with another TSW and a space switch (SSW) (not shown).
A detailed inner structure of the ASS-P
104
is described in FIG.
3
.
The ASS-P
104
presents a layered structure including packet handling modules (PHMs)
301
to
303
, packet layer control processors (PLCPs)
305
to
307
and an access switching processor for packet (ASS-P)
309
.
Herein, the PHMs
301
to
303
handle the X.25 and an X.75 protocol. The PHMs
301
to
303
are classified into a PHM-B for handling a B-channel packets based also on the X.25 protocol, a PHM-D for handling D-channel packets based on the X.25 protocol and a PHM-P for providing inter-working services between the ISDN and a public switched packet data network (PSPDN) based on the X.75 protocol.
The PLCPs
305
to
307
perform call processing for packets, and handle routing information.
The ASP-P
309
controls connection and disconnection between the ASS-P
104
and subscriber modules such as the BSI
201
, the PSI
202
and the BAMI
203
.
A time switch processor (TSP)
310
controls the operation of a time switch (TSW)
311
.
The PLCPs
305
to
307
communicate with the PHMs
301
to
303
via a packet bus (P-bus)
304
; and communicate with the ASP-P
309
and the TSP
310
by using an inter-processor communication (IPC) network
308
.
The above-described conventional packet switch, however, presents some disadvantages.
A packet switching service can be blocked in case of a malfunction or a breakdown of the ASS-P
104
since all the packet data is processed in the ASS-P
104
.
In addition, the conventional packet switch leaves something to be desired. In case that a sending subscriber and a receiving subscriber happen to be connected to the same ASS-I, all the packets to be exchanged between the subscribers must pass the ASS-P
104
. Time for processing packets is rather longer when the sending subscriber and the receiving subscriber are connected to the same ASS-I than connected to different ASS-Is. In other words, the path the packets travel in the packet switch is ASS-I—SSW (in the INS
110
)—ASS-P—SSW (in the INS
110
)—ASS-I. In this case, it is desired to have a scheme that the packet data is processed only at the ASS-I, not passing through the SSW.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide a packet handling apparatus functionally distributed among subscriber modules for use in the packet switch.
In accordance with the present invention, there is provided an integrated services digital network (ISDN) switch capable of switching packets in each of access switching subsystems. The inventive ISDN switch comprises: a plurality of access switching subsystems including a time switch, for providing interfaces with subscriber equipments by using the ISDN standard interfaces; an interconnection network subsystem including a space switch, connected to the access switching subsystems, for performing functions such as space switching and network synchronization; and a central control subsystem, connected to the interconnection network subsystem, for supervising and controlling overall functions performed in each subsystem in the ISDN switch.
REFERENCES:
patent: 5805570 (1998-09-01), Fields et al.
Bacon & Thomas PLLC
Marcelo Melvin
Mercury Corporation
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