Method for transmitting signaling information within a broadband

The transmission of signaling information between network nodes connected to one another ensues in separate signaling channels. A signaling protocol corresponding to a broadband ISDN layer model is respectively defined for such signaling information. Among other things, an ATM adaption layer (S-AAL) is defined therein which, in addition to having a general adaption sub-layer (AAL5), also has two service-specific sub-layers (SSCOP, SSCF) available to it. One of these service-specific sub-layers (SSCF) is thereby modified, as compared to ITU Recommendation Q.2140, each that, for a call set up, a communication over the respective signaling channel occurs between two network nodes connected to one another without a previous check of the transmission link.

BACKGROUND OF THE INVENTION 
The present invention is directed to a method for transmitting signaling 
information on transmission links of a broadband ISDN communication 
network operating in an asynchronous transfer mode (ATM). Such a method 
has already been disclosed in "ATM-Netzwerke-Aufbau, Function, 
Performance", Othmar Kyas, DATACOM Buchverlag GmbH Bergheim, 1995. 
A multitude of protocol procedures for the second sub-layer (service 
specific coordination function, SSCF) of the ATM adaption layer are known 
from ITU Recommendation Q.2140 for the adaptation of the adaption layer to 
the first sub-layer (service specific connection oriented protocol, SSCOP) 
that likewise belongs to the ATM adaption layer and for the implementation 
of a portion of the signaling protocol determined by the adaption layer. 
These protocol procedures at least partially require a substantial 
development outlay as well as a considerable utilization of software and 
hardware resources, this increasing the costs for the individual nodes of 
a broadband ISDN communication network. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method that reduces 
the control outlay and, thus, the outlay for the software and hardware 
resources in the individual nodes of a broadband ISDN communication 
network. 
In general terms the present invention is a method for transmitting 
signaling information on transmission links of a broadband ISDN 
communication network operating according to an asynchronous transfer mode 
(ATM). Signaling channels deviating from useful channels are employed and 
a signaling protocol corresponding to a broadband ISDN layer model is 
respectively defined on the signaling channels for the set up and clear 
down of connections. Accordingly, a physical layer, an ATM layer, an ATM 
adaption layer and an application layer that controls the set up and clear 
down of connections are defined. In addition to a general adaption 
sub-layer, a first service-specific sub-layer that essentially serves for 
message protection and flow control, as well as a second sub-layer for 
adaption of this service-specific sub-layer to the application layer and 
for the implementation of a part of the signaling protocol are provided. 
Protocol procedures defined by ITU Recommendation Q.2140 for the second 
sub-layer are modified such that the second sub-layer, in response to a 
call request from the appertaining application layer, initiates a call set 
up by the first sub-layer. After the call set up has ensued, information 
indicating readiness to operate is immediately transmitted via the 
signaling channel under consideration and without a previous proving phase 
that serves the purpose of checking the transmission path. The appearance 
of information in the appertaining signaling channel corresponding to this 
information is monitored and the appertaining application layer is 
signaled as confirmation for the successful call set up. In response to a 
call request transmitted via the signaling channel, the second sub-layer 
has the call request signaled to it from the appertaining, first 
sub-layer, and, after acceptance thereof, the second sub-layer immediately 
transmits information indicating the readiness to operate over the 
signaling channel under consideration as confirmation for the readiness to 
operate without an aforementioned proving phase. 
The present invention is also a method for transmitting signaling 
information on transmission links of a broadband ISDN communication 
network operating according to an asynchronous transfer mode (ATM). 
Signaling channels deviating from useful channels are employed and a 
signaling protocol corresponding to a broadband ISDN layer model is 
respectively defined on the signaling channels for the set up and clear 
down of connections. Accordingly, a physical layer, an ATM layer, an ATM 
adaption layer and an application layer that controls the set up and clear 
down of connections are defined. In addition to a general adaption 
sub-layer, a first service-specific sub-layer that essentially serves for 
message protection and flow control, as well as a second sub-layer serving 
for the adaption of this service-specific sub-layer to the application 
layer and for the implementation of a part of the signaling protocol are 
provided. Protocol procedures defined by ITU Recommendation Q.2140 for the 
second sub-layer are modified such that the second sub-layer, in response 
to a call request from the appertaining application layer, first initiates 
a call set up by the first sub-layer. After the call set up has ensued, 
information indicating readiness to operate is immediately transmitted via 
the signaling channel under consideration and without a previous proving 
phase that serves the purpose of checking the transmission path. The 
appearance of information corresponding to this information or of useful 
information for the appertaining application layer in the appertaining 
signaling channel is monitored and the appertaining application layer is 
signaled as confirmation for the successful call set up. In response to a 
call request transmitted via the signaling channel, the second sub-layer 
has the call request signaled to it from the appertaining, first 
sub-layer, and, after acceptance thereof, the second sub-layer immediately 
transmits information indicating the readiness to operate over the 
signaling channel under consideration as confirmation for the readiness to 
operate without an aforementioned proving phase. 
The invention thereby yields the advantage that the second sub-layer of the 
ATM adaption layer modified compared to the ITU Recommendation Q.2140 is 
compatible with a second sub-layer implemented fully in accord with the 
ITU Recommendation Q.2140 with respect to the message exchange via a 
transmission link but other complex functions are not provided. 
Another advantage of the method is that the second sub-layer modified 
according to the present invention can also cooperate with an ATM adaption 
layer of a remote station connected via a transmission link wherein no 
second sub-layer is implemented, in that the modified second sub-layer (in 
response to the output of a ready-to operate-information) also interprets 
the immediate appearance of useful information as confirmation of 
readiness to operate on the part of the remote station.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In a broadband ISDN communication network operating according to the 
asynchronous transfer mode (ATM), signaling channels departing from the 
useful channels on transmission links between the individual network nodes 
are used for setting up and clearing down connections. A signaling 
protocol, for example according to the broadband ISDN layer model, is 
thereby defined for such a signaling. This layer model for the signaling 
is shown in FIG. 1, indicating the ITU Recommendations that are relevant 
for the individual layers. According thereto, the lowest layer is formed 
by the physical layer. This is followed by an ATM layer by which the 
format of the ATM cells to be transmitted within the communication network 
is essentially defined according to ITU Recommendation I.361. This is 
followed by an ATM adaption layer S-AAL for the signaling ("Signaling ATM 
Adaptation Layer"). This is divided into three sub-layers, namely a 
general adaption sub-layer, as well as two further service-specific 
adaption sub-layers. 
The general adaption sub-layer that is defined by ITU Recommendation I.363 
and is referenced as AAL5 (ATM adaption layer 5) essentially divides the 
information to be transmitted during the course of a signaling onto ATM 
cells or, respectively, recovers these from ATM cells and also implements 
a check of ATM cells for error-free transmission, for example on the basis 
of what is referred to as a "cyclic redundancy check code" that is 
respectively attached to the ATM cells. 
A first of the service-specific adaption sub-layers that is referenced 
SSCOP (service specific connection oriented protocol) and that is defined 
by ITU Recommendation Q.2110 essentially serves the purpose of message 
protection and flow control. This is followed by the second 
service-specific adaption sub-layer defined in ITU Recommendation Q.2140, 
that is referred to as SSCF (service specific coordination function) and 
with which the adaption of the first service-specific adaption sub-layer 
(SSCOP) to a higher application layer is essentially undertaken and a part 
of the signaling protocol is implemented. Both service-specific adaption 
sub-layers are thereby in communication with a "layer management" defined 
by ITU Recommendation Q.2144. 
Finally, the ATM matching layer S-AAL is followed by the adaption layer 
that has just been mentioned and that has what is referred to as a 
"message transfer part level 3" (MTP Level 3) defined by ITU 
Recommendation Q.2210 as the interface to the ATM adaption layer. The 
sub-layers of the adaption layer additionally indicated in FIG. 1 and 
referenced SCCP, TC, INAP and B-ISUP essentially realize signaling 
protocol parts and are defined for SCCP by ITU Recommendation Q.71x, for 
TC by ITU Recommendation Q.77x and for B-ISUP by ITU Recommendation 
Q.276x. Since these signaling protocol parts are defined and are not the 
subject matter of the present invention, they shall not be discussed in 
greater detail below. 
Within the aforementioned service-specific adaption sub-layer SSCF of the 
ATM adaption layer, protocol procedures for a part of the signaling 
protocol are provided at what is referred to as a "network node interface" 
(NNI). This is provided in addition to protocol procedures for adaption 
functions that require no communication with the remote station (node) via 
a transmission link. What is thereby involved, for example, is what is 
referred to as an "initial alignment" that is implemented at the beginning 
of a requested call set up. In accord therewith, the service-specific 
adaption sub-layer SSCF (in response to a call request from the 
appertaining application layer (MTP Level 3)) first initiates a call set 
up by the second adaption sub-layer. After the call set up has ensued, the 
service-specific adaption sub-layer SSCF implements a proving phase 
wherein a check of the transmission path for freedom from error or, 
respectively, adequate transmission quality is implemented via a message 
exchange over the signaling channel coming into consideration for the 
respective connection. A relatively high control outlay and, thus, a high 
outlay for software and hardware resources is thus required for this check 
and the time monitoring connected therewith. After this check, the 
adaption sub-layer SSCF can then transmit information (in service) 
indicating readiness to operate over the appertaining signaling channel to 
the remote station, and the arrival of information from the remote station 
corresponding to this information is monitored. When such information 
arrives, then this is signaled to the appertaining application layer as 
confirmation for a successful call set up. The application layer can then 
begin with the transmission of messages defined by the signaling protocol. 
In a corresponding way, the adaption sub-layer SSCF (in response to a call 
request transmitted via the signaling channel) signals the call request to 
the appertaining adaption sub-layer SSCOP and an afore-mentioned proving 
phase is implemented after the acceptance thereof. Information indicating 
readiness to operate is only transmitted after the successful 
implementation thereof as confirmation for the readiness to operate. This 
information transmitted via the signaling channel under consideration. 
According to the present invention, the method that has just been explained 
and that is provided according to ITU Recommendation Q.2140 is modified 
such that the described message exchange between the adaption sub-layers 
SSCF of two remote stations is implemented without the above-recited 
proving phase in the respective remote station. This yields the advantage 
that the adaption sub-layer SSCF is compatible with respect to the message 
exchange with an adaption sub-layer SSCF fully conforming with ITU 
Recommendation Q.2140 but is substantially reduced in view of the outlay 
and need not realize any time monitoring functions, so that the employment 
of counters and timers can be omitted. This derives, for example, by 
comparing the status diagram for this sub-layer SSCF shown in FIG. 2 to 
the corresponding status diagram according to ITU Recommendation Q.2140. 
An adaption sub-layer SSCF that is reduced according to the present 
invention also yields the advantage over and above this that this, for 
example, can be employed in network configurations wherein taking the 
afore-mentioned proving phase into consideration is not necessary or, 
respectively, yields no advantages. As an example, let ATM pilot projects 
be cited here, the same quality demands often not being made of these as 
of communication networks in full commercial use, or let transmission 
links be cited for which there are no standby transmission links, wherein, 
thus, a shut down or, respectively, non-utilization of a transmission link 
because of poor quality would yield no advantages but, rather, would yield 
disadvantages. 
As already set forth above, it is provided in the above-explained exemplary 
embodiment that the adaption sub-layer SSCF transmits information ("in 
service") indicating the readiness to operate to a remote station via a 
signaling channel and monitors the arrival of information from the remote 
station corresponding to this information as confirmation for the 
readiness thereof to operate. In a further exemplary embodiment, this is 
modified to the effect that, as confirmation for the readiness of a remote 
station to operate, the adaption sub-layer SSCF either interprets 
aforementioned information received from this remote station or, without 
such information, interprets directly received useful information, that 
is, a useful information output from the application layer belonging to 
this remote station according to the defined signaling protocol. It is 
thus possible that the adaption sub-layer SSCF can also collaborate with 
the ATM adaption layer S-AAL of a remote station that has no adaption 
sub-layer SSCF available to it. This, for example, also creates the 
possibility of converting networks or, respectively, transmission links 
(that do not use an adaption sub-layer SSCF at all) successively to 
networks or, respectively, transmission links that employ a full adaption 
sub-layer SSCF according to ITU Recommendation Q.2140. First, the network 
or, respectively, the transmission link is successively reequipped to the 
reduced adaption sub-layer SSCF according to the present invention. 
Proceeding from this status, subsequently, the introduction of the full 
adaption sub-layer SSCF according to ITU Recommendation Q.2140 can 
successively ensue. A complex and costly, quasi-simultaneous adaptation 
can thus be avoided. 
It was stated above that no time monitoring is implemented in the adaption 
sub-layer SSCF modified according to the present invention. However, the 
appertaining application layer, for example the sub-layer MTP Level 3, can 
monitor the call set up in terms of time with the output of a call 
request. Alternatively thereto, at least the call set up can be monitored 
in terms of time by the adaption sub-layer SSCF. 
The invention is not limited to the particular details of the method 
depicted and other modifications and applications are contemplated. 
Certain other changes may be made in the above described method without 
departing from the true spirit and scope of the invention herein involved. 
It is intended, therefore, that the subject matter in the above depiction 
shall be interpreted as illustrative and not in a limiting sense.