ATM transmission equipment

Details ATM transmission equipment ATM transmission equipment

1999-04-09

2003-09-02

Kizou, Hassan (Department: 2662)

Multiplex communications

Diagnostic testing

Fault detection

C370S250000, C370S395100, C370S466000

Reexamination Certificate

active

06614760

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to ATM (asynchronous transfer mode) transmission apparatus used in communication networks wherein digital service units (DSUs) and exchange (LT unit) having STM (synchronous transfer mode) line interfaces are connected by ATM, and more specifically to ATM transmission equipment wherewith the transmission path portion of the line interface is replaced with an ATM network, LT unit, DSU, and terminal, etc., can be accommodated, and a T-point interface is provided in the interest of reducing DSU installation costs, so that 1.5M dedicated line service, for example, can be efficiently accommodated in the ATM network.
2. Description of the Related Art
Private networks are recently being widely developed by communication businesses (carriers), and for in-house communication, utilizing the statistical multiplexing benefits and flexible network operability of ATM technology. During the transition period while this type of networking using ATM technology is proliferating, however, there are existing networks, such as communication networks using high-speed digital lines or ISDN lines. Hence a scheme is needed for handling the equipment of these existing networks.
When a carrier is to expand its network, for example, one approach is to set up an ATM network beforehand to provide lines for connecting between the carrier equipment and in-home unit such as terminals, in preparation for the transition to the future ATM network. In such cases, it is important that the ATM network be configured so that it can accommodate the preexisting station exchange (LT unit) and digital service units (DSUs) that make up the carrier equipment and the in-home unit.
In
FIG. 43
is given a simplified block diagram of an ordinary conventional communication network configured with STM lines.
Specifically, in
FIG. 43
, in-home unit. (user terminals)
12
-
1
and
12
-
2
are connected respectively through digital service units (DSUs)
11
-
1
and
11
-
2
to the station exchange (LT unit)
10
having an:STM line interface. In this diagram, U points configure the.subscriber line interfaces (hereinafter called U point interfaces). These U-point interfaces comprise metallic wire or optical fiber and connect between the LT unit
10
and remotely located DSUs
11
-
1
and
11
-
2
. T points configure so-called T point interfaces.
Now, when an ATM network is set up beforehand to provide lines for connecting carrier equipment with terminals and other in-home unit with a view to transition to the future ATM network, as described in the foregoing, one possible configuration involves installing the ATM network at the U points configuring the line interfaces in FIG.
43
. In this configuration, in the first place, it must be possible to emulate the existing transmission paths, and, in the second place, it must be possible to provide T point interfaces for the in-home unit. In the prior art, however, no suitable transmission apparatus exists that satisfies these requirements.
Furthermore, in a network wherein an ATM network is provided for the line interfaces in an StM network, what is ordinarily done is to perform cell assembly and cell disassembly on all data strings (including frame F bits) on the STM lines and to transmit these into the ATM network. When this is done, however, network resources are wasted because the ATM network becomes occupied by bands having the speeds of the STM lines.
In communication systems designed so that conventional video, audio, and text data, etc., are assembled into cells or packets of fixed length and then transmitted from the transmitting equipment to the receiving equipment, when some kind of trouble develops on a line or communication path on the way from the transmitting side to the receiving side, resulting in a situation wherein the desired transmission quality can no longer be guaranteed, the measure of interrupting that line must be taken so that line or communication path is not used.
One conventional method of detecting faults in lines or communication paths, for example, is that disclosed in Japanese Patent Laid-open No. H5-63761/1993 (gazette), whereby, when transmission data are transmitted, information on the time until the next transmission data is added at the beginning thereof. If the time information can be normally verified at the receiving end, a normal reception confirmation signal is returned to the transmitting end. When the time information cannot be normally verified, a retransmit request is transmitted back to the transmitting end, or a line fault state ensues and that fact is output to the outside.
In an ATM network system, on the other hand, when a line break or synchronization fault is detected at the receiving terminal, and alarm information indicating line fault is transmitted back to the opposite end, i.e. to the transmitting equipment, an OAM cell (operation and maintenance cell) is inserted in the ATM cell flow. This alarm information is inserted into the OAM cell and transmitted to the opposite ATM exchange, whereupon, in that opposing ATM exchange, that OAM cell is-resolved, the alarm information extracted, and the resulting data are transmitted to the receiving terminal line end.
There are also, however, systems wherein nodes that configure an ATM network are linked in a ring shape, as diagrammed in FIG.
44
. In the system diagrammed here, multiple nodes
261
-
264
are connected by an outside ring transmission path
265
and by an inside ring transmission path
266
. To each node are connected terminals A and B, i.e.
267
and
268
, such as cameras or personal computers for inputting and outputting image;data, text data, and audio and video data, etc., so that, for example, image data or text data, etc., can be transmitted on the ATM network from terminal A
267
to terminal B
268
. Each of the nodes here,
261
-
264
, comprises ATM exchange with an existing STM line interface that can handle 64 Kbps, 1.5 Mbps, or 2 Mbps, etc.
In an ATM network linked by ring-shaped transmission paths such as this, ordinarily, when transmitting data from terminal A
267
to terminal B
268
, one of the ring transmission paths (the outside ring transmission path
264
in the example diagrammed in
FIG. 46
) is used, as indicated by the broken lines in the drawing. In the event that a fault occurs in a relay transmission path or at the node
264
which is a relay node in the transmission path from the terminal A
267
to the terminal B
268
, indicated by the “X” in
FIG. 45
, a loop-back is effected at the relay node
264
, as indicated by the broken line in this figure, activating the transmission path to the terminal B along the stand-by inner ring transmission path
266
, whereupon data can be transmitted from the terminal A to the terminal B.
However, in the event that a fault occurs at the node
261
to which the terminal B is connected, as indicated by the “X” in
FIG. 46
, loop-backs are effected at node
264
and node
262
, as indicated by the broken line in
FIG. 46
, so that the data output by the terminal A are returned to that terminal A. Thus the fault at the terminal B
268
cannot be detected, and no alarm information is output to the terminal A. This constitutes a problem.
To deal with this problem, there is a method, called BLSR (bidirectional line switched ring), which uses loop-back switches to recover from transmission path faults that occur in ring-shaped network systems. With BLSR, line switching is performed using a so-called squelch table. This squelch table comprises node chaining information that indicates how the nodes are connected in the ring system, and squelch information indicating to which nodes signals ADDed or DROPped in line units are assigned.
FIGS.
50
(
a
)-
50
(
c
) diagram the configuration of such a squelch table. This squelch table comprises node chaining information, cross-connect type information, squelch information, and WORK line information.
The node chaining information indicates how the nodes are connected in the ring system. The cross-co

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