Efficient connection of isdn private branch exchanges to a packet-switched network

p0001The invention relates to a method and a peripheral adapter for exchanging signaling information between an ISDN connection and a packet-oriented exchange.

p0002The convergence or the combination of time-division multiplexed networks - also known as TDM (time devision multiplexing) networks and packet-based networks leads to new switching technology requirements with regard to the implementation of signaling and user data.

p0003In the course of the coordination of time-multiplex-based and packet-based networks, interworking, which is taken over from the English language, is often used - both local and node-side adaptations are necessary.

p0004A TDM-based exchange or a TDM-based switching node causes the connection control and the termination or intersection of the user channels. The task spectrum of a switching center for data transmission in the packet network, hereinafter referred to as a packet-related exchange, includes, in addition to the conventional connection control, the control of the associated user channels outside the packet-based exchange via external devices (eg gateways, resource servers, (Eg, using the RTP (Real Time Protocols)) and control (eg using one of the following protocols: MGCP (Media Gateway Control Protocol), H.248, H.323).

p0005For the terminal side, there are, besides the conventional analogue and ISDN terminals and extensions, also terminals suitable for the packet network which allow broadband data access, but which are also capable of supporting the basic performance features known from public telecommunication networks (eg using the H.323 protocol) Or the SIP (Session Initiation Protocol) protocol). A broadband access medium or access network to the subscriber is often found either with subscriber line lines or cable networks operated with xDSL techniques (DSL: Digital Subscriber Line).

p0006The interface between the access network and the transmission network, eg packet-based IP (Internet Protocol) network, is usually formed by adaptation adapters close to the subscriber. The term "peripheral adapter" is frequently also used for adaptation devices closest to the user. Examples of subscriber-specific adaptation devices are IAD (Integrated Access Device) for terminating an xDSL line and MTA (multimedia terminal adapter) on or in the cable modem, which terminate the access network on the transmission network side. Subscriber-friendly adaptation devices and access networks can then be used for the connection of broadband end devices (eg PC with internet access, TV set, videotelephone) as well as classic subscriber terminals, eg analogue telephone, ISDN telephone and analogue and ISDN extension.

p0007In the case of conventional terminals, ie, telephones and PBX systems, packet-oriented switching centers should make available, as far as possible, all the features known from line-connected connection technology so that the integration of packet-oriented networks does not lead to a restriction of the feature spectrum of services. In addition, the non-availability of hardware and software resources, as well as the non-availability of terminals, must be detected and, if necessary, an alarm of the operator. However, structures of the intermediate access networks are usually unknown to the packet-oriented switching node. For example, breakdown situations of components and network components which relate to the signaling path between the packet-oriented switching node and the subscriber terminal are only apparent to the switching node indirectly, ie, by recognizing the non-availability of subscribers and extensions.

p0008Conventional analog and ISDN subscribers that can be reached via a packet network are packet-based for the distinction of purely packet-based subscribers (SIP, H.323) and classical, line-connected analog and ISDN subscribers (eg connections via interfaces V5.1 and V5.2) Are characterized in a particular manner. The peripheral subscriber-oriented adaptation devices have special functions (eg, telephony clients in IADs and MTAs) which enable the transmission of signaling between the terminal and the packet-switched exchange via intermediate access networks and packet-based transmission networks. The packet-switched switching systems and clients in the peripheral adaptation devices (IAD, MTA) can be configured accordingly by the network administration. In the case of the provision of functions in the subscriber-related adaptation devices for the transmission of the signaling, analogue and ISDN interfaces are distinguished from the viewpoint of the switching system. Another distinctive feature from the point of view of the packet-based switching system is the allocation of features of a main connection or a branch exchange connection. From the point of view of the subscriber, either an analog or ISDN terminal operated as a main connection is connected to the peripheral adapter (IAD, MTA), or an analog or ISDN branch exchange facility (also called PBX or private branch exchange) is connected in the same way.

p0009Regarding ISDN interfaces, eg at the peripheral adaptation device, two different connections or interfaces are distinguished:<ul><li>The base connection, also referred to as BRA (Basic Rate Access), has one or two user channels. Often there are two user channels (B-channel) of 64 kbit / s (56 kbit / s in the USA) and a signaling channel (D-channel) of 16 kbit / s.</li><li>The second type of connection, also referred to as PRA (Primary Rate Access), is the primary multiplexing connection, usually consisting of 30 B channels (because of the PCM30 system), a synchronization channel and a signaling channel (D-channel) Up to 4 PCM30 systems with a single D-channel can be combined into a PRA.</li></ul>

p0010The state (layer 1, layer 2, blocking state) of the ISDN connection (BRA, PRA) is known to a conventional local switching center of a TDM network, in contrast to the case of a packet-based switching center due to physical line termination or the interface protocols to subscriber concentrators and access networks.

p0011Also for packet networks, small ISDN extensions must be connected via peripheral adapters via a BRA or a plurality of BRAs; Large ISDN extensions must be connectable via one or a plurality of PRAs, whereby mixtures of BRAs and PRAs must also be supportable with regard to a given ISDN extension. In this case, BRA and PRA may be connected via a uniform or via a specific peripheral adapter and physically terminated. The ISDN signaling can then be exchanged packet-based between peripheral adapter and packet-oriented exchange (eg by means of ISDN user adaptation IUA and SCTP). This is usually done by way of the DSS1 (Digital Signaling System No.1) protocol, to which details are set out in the standard ITU-T Q.931 (ISDN user-network interface layer 3 specification for basic call control).

p0012EP-A-0948236 discloses a method for multiple utilization of a telecommunications channel in which base connections of terminals with user channels and in each case an associated signaling channel are combined by means of a multiplexing additional device and are mapped onto a single primary multiplexer connection. In this case, the multiple-used primary multiplexer connector is directly supplied to a switching device. By corresponding configuration in this switching device, a subscriber channel is assigned to a D16 sub-channel so that the signaling channels and the associated user channels can be treated separately for each logically separate connection on a common physical connection in the switching device.

p0013The object of the invention is to provide a flexible and efficient implementation for the connection of ISDN PBX systems with peripheral adapters to a packet network.

p0014In the invention, signaling information is exchanged via a peripheral adapter between an ISDN connection, for example an ISDN-BRA or ISDN-PRA connection, and a packet-oriented switching center. For example, an ISDN terminal or an ISDN PBX can be connected to the ISDN connection. The processing or processing of the signaling information transmitted by the ISDN connection in the packet-switched exchange is carried out independently of the type of the ISDN connection. For example, there is no distinction between ISDN-BRA and ISDN-PRA connections in the packet-switched exchange. The peripheral adapter is, for example, an IAD or an MTA. For the purpose of the treatment of signaling information independent of the ISDN connection type by the packet-oriented exchange, signaling information transmitted from the ISDN connection to the peripheral adapter is adapted. Correspondingly, signaling information transmitted by the packet-oriented switching center to the peripheral adapter is adapted for further transmission to the ISDN connection in accordance with the ISDN connection type. In this manner, various ISDN connections can be represented by a single port type in the packet-oriented exchange. In general, different ISDN connection types comprise a different number of user data channels. For example, the PRA connection has 30 user data channels and one signaling channel. The BRA port or base port, on the other hand, usually comprises one or two user data channels and a signaling channel. In the adaptation of signaling information in the peripheral adapter according to the invention, an image of the different user data channels can be made on the side of the packet-oriented switching system and of the ISDN connection for different connection types. In this case, user data channels or logical ports in the packet network can be distinguished by the addressing of the packets or the addresses of the packets. In the case of useful data transmission in the TDM and packet network, the term "bearer" borrowed from the English is also frequently used instead of the term "user data channel". According to the invention, there is then an allocation between logical port or user data channel (bearer) and the provision of resources in packet-oriented switching systems. For example, the processing of a switching technology program can be performed in the packet-oriented switching system in accordance with the logical port or the user data channel. On the side of the ISDN connection, physical ports are given as well as user data channels which are assigned to fixed time slots during the transmission over a TDM network. A conversion according to the invention of the user data channels of the PRA to user channels of logical ports as well as a corresponding adaptation of the signaling information in peripheral adapters can be carried out with the aid of a table in the peripheral adapters. Such a table is established, for example, by the network management in the peripheral adapter. This means that the network management knows the hardware interfaces or the physical ports of the ISDN connection in order to set up the table. Usually, the network management has this information already for the reason that the peripheral adapter must be suitably configured. In contrast to network management, the details regarding the ISDN connection are transparent to the packet-oriented exchange. The information on hardware details of the ISDN connection, which is provided by the network administration, need not be available to the packet-oriented exchange. All physical ISDN-connected functions can be handled in the peripheral adapter, whereby the administration of the packet-based exchange can be reduced to a uniform logical ISDN port type or ISDN connection type with a fixed number of user channels.

p0015The invention reduces the implementation effort in the packet-oriented exchange, since only a single ISDN connection type has to be handled. The administration of hardware data in the packet-oriented exchange, which must already be managed for the peripheral adapter, is avoided, resulting in a reduction in the operating costs for the network and the exclusion of data inconsistencies between the peripheral adapter and the packet-switched exchange. The reduction of the administration effort is associated with a lesser resource consumption in the packet-switched exchange, which manifests itself, for example, in the memory allocation and results from the fact that information related to ISDN connection need not be stored in the packet-switched exchange. The adaptive function of the peripheral adapter has provided a flexible allocation of the logical resources of the packet-based exchange to the physically available resources of the peripheral adapter, which is adaptable by the network management. The adaptation according to the invention in the peripheral adapter also permits a concentration of user data channels. For example, the 30 useful data channels of a PBX system with PRA connection can be mapped to less than 15 BRA connections in the packet-oriented exchange. In this case, it is assumed that the above-mentioned logical port type of the packet-switched exchange station coincides with the ISDN BRA with up to 2 bearer channels. This is an economical solution with a weak utilization of the useful data channels of the ISDN connection. By configuring the peripheral adapter, the concentration of the user data channels can be flexibly adapted to a changed utilization of the useful data channels of the ISDN connection. The inclusion of PRA with more than 30 user channels is also possible.

p0016In the case of differences between the logical ISDN connections in the packet-oriented switching center and the physical ISDN connections on the subscriber side, an adaptation of the call identifier must often be made in addition to a mapping of the user data channel references, eg channel numbers, into the peripheral adapter. In this case, call identification is the identification information designated as the call reference in ITU-T Q.931, ISDN user-network interface layer 3 specification for basic call control. This call identifier differentiates calls or calls. In contrast to the call number of a subscriber, the call identifier on disjoint partial routes can assume different values ​​for a call. Call connections are assigned to connections. After the end of a connection, the corresponding call ID is free again and can be assigned again. Finally, a call identifier is unique only within a signaling channel. The latter property requires that, in many cases, an implementation of the call identifier in the peripheral adapter must be carried out. For example, switching BRA ISDN lines are used, which each comprise two basic channels and a signaling channel. Several of these logical BRA ISDN connections are then mapped to a PRA-ISDN connection with thirty useful data channels and a signaling channel. Accordingly, the mapping of several signaling channels to a signaling channel takes place, that is, without an adaptation of the call identifiers, the uniqueness of the call identifiers would be questioned.

p0017The D-channel protocol DSS1 (Digital Subscriber Signaling System no. 1) is used for signaling between ISDN and peripheral adapters. In this protocol, the transmission layer (layer 1), the protection layer (layer 2) and the switching layer (layer 3) can be distinguished according to the OSI (Open Systems Interconnection) model. The backup layer is described in ITU-T Q.920 (ISDN user-network interface data link layer - General aspects) and ITU-T Q.921 (SDN user-network interface data link layer specification). As an optimization known from ISDN extensions, it is proposed in analogy not to perform a new connection setup on the backup layer (data link connection in Q.920) for each call between the ISDN connection and the peripheral adapter, but instead of transporting it permanently or over a longer period of time Signaling messages on the switching layer through the fuse layer without new adaptations on the fuse layer. Signaling messages of layer 3, which are described in the standards ITU-T Q.930 (ISDN user-network interface layer 3 - General aspects) and ITU-T Q.931 (SDN user-network interface layer 3 specification for basic call control) , Are then transmitted on the packet side by means of the SCTP (stream control transmission protocol) protocol and suitable DSS1 adaptations (IUA), if necessary, in the peripheral adapter.

p0018The invention is explained in more detail below with the aid of figures in the context of an exemplary embodiment. Show it:<dl id="dl0001"><dt>FIG. 1:</dt><dd>An arrangement of network elements with treatment according to the invention of ISDN connections in a packet-based exchange,</dd><dt>FIG. 2:</dt><dd>Inventive rearrangement of the user channels in the course of an ISDN connection independent representation in the packet-oriented exchange,</dd><dt>FIG. 3:</dt><dd>A rearrangement of the user channel control corresponding to FIG. 2,</dd><dt>FIG. 4:</dt><dd>According to the invention, of the call identifications.</dd></dl>

p0019In the figures, like reference numerals designate like elements.

p0020In FIG. 1, two ISDN extensions ISDN-PBX1 and ISDN-PBX2 are connected to a packet network IPNET via two peripheral adapters or subscriber-connected devices TNE1 and TNE2. The peripheral adapters TNE1 and TNE2 are, for example, IADs or MTAs. Between the two peripheral adapters TNE1 and TNE2, user data can be exchanged, for example in the course of a telephone call, which is routed via the packet-based network IPNET. In this way, two subscribers connected to the extensions ISDN-PBX1 or ISDN-PBX2 can communicate with one another. The ISDN-PBX1 extension is connected to the peripheral adapter TNE1 with a PRA connection with thirty useful data channels and a signaling channel. The second branch ISDN-PBX2, on the other hand, is connected to the peripheral adapter TNE2 by means of a BRA connector with two user data channels and a signaling channel. Both different connections are represented in the packet-oriented exchange P-Vst in a uniform manner, namely as BRA connections. For the purpose of the user data transmission control, the packet-oriented exchange P-Vst exchanges signaling information ISDN-sig with the peripheral adapters TNE1 and TNE2. The user data transmission is controlled, for example, using the MGCP (Media Gateway<b>Control</b> Protocol) protocol or the H.248 protocol. In contrast to the packet-oriented exchange P-Vst, the network management NetMg distinguishes different ISDN connection types. The network management NetMg administrates or configures the information on the physical connections and / or ports of the PBX1 and ISDN PBX2 PBXs connected to the peripheral adapters TNE1 and TNE2. In addition, the logical representation of the ISDN user data channels or the logical ports of the ISDN user data channels in the packet-oriented exchange P-Vst is established or managed by the network management NetMg. The transport of ISDN signaling messages between the peripheral adapters TNE1 and TNE2 and the packet-oriented exchange P-Vst can be carried out with the aid of the SCTP (Stream Control Transmission Protocol) protocol and ISDN-specific adaptation layer (eg IUA). With the help of the SCTP protocol, signaling messages can be efficiently transmitted in IP (Internet Protocol) networks SS7. The DSS1 (Digital Signaling System No. 1) protocol is used, for example, for signaling between the ISDN extensions ISDN-PBX1 and ISDN-PBX2 and the associated peripheral adapter TNE1 or TNE2, respectively. For the representation of the PRA connection in FIG. 1 by means of BRA connections in the packet-switched exchange P-Vst, adjustments are made according to the invention in the peripheral adapter TNE1.

p0021FIG. 2 shows how an adaptation of the user data references for the purpose of the representation of a PRA connection can be performed by means of BRA connections in the packet-oriented exchange P-Vst. Of the<b>PRE</b>Terminal has thirty basic channels or user data channels and a signaling channel or D-channel. In FIG. 2 reproduced by the reference character 30B + 1D. This<b>PRE</b>Port is represented by fifteen BRA terminals BRA1... BRA15 in the packet-oriented exchange station PVST, each having two user data channels and a signaling channel or D channel (reference symbol for BRA configuration: 2B + 1D). An assignment or mapping of the fifteen logic BRA terminals BRA1... BRA15 to the physical PRA connection is carried out in the peripheral adapter TNE1 by means of a conversion table. The two basic channels of the first BRA terminal BRA1 are mapped onto the useful data channels 1 and 2 of the PRA terminal. The two base channels of the second BRA connection BRA2 are then transferred to the user data channels 3 and 4 of the<b>PRE</b>Connector. Thus, two base channels of the BRA connections are connected to two user data channels of the<b>PRE</b>Port. For the numbering according to the conversion table, please note that the channel with the number 16 of the<b>PRE</b>Port is reserved for the signaling and consequently does not have to be taken into account when the user data references are changed. The table shown gives a rule for the change of user data references, such as the user data channel number, to the signaling messages. The referencing of the user data channels is adjusted. User data itself does not need to be subject to any adaptation. The exchange of signaling information, for example the transmission of a connection set-up message, between peripheral adapter TNE1 and packet-oriented exchange P-Vst is performed by means of the SCTP protocol. In the case of a concentration of the user data channels on the switching-station side, less than fifteen BRA connections would be applied to the<b>PRE</b>Port. This is flexible and easy to implement in that the BRA connections are logical but not physical connections. A concentration is, for example, useful when the data throughput of the PRA connection is significantly lower than the maximum capacity and thus even in load situations only a small part of the user data channels of the PRA is simultaneously occupied.

p0022FIG. 3 shows a corresponding conversion of signaling information for user data control, eg, user data routing, in the packet network. The protocol used on the exchange-site side is, for example, the MGCP protocol in which each B-channel is defined as a separate endpoint.

p0023FIG. 4 shows the treatment according to the invention of the call identifiers (call references) for the scenario according to FIGS. 1 to 3. Call identifications are assigned temporarily and connection-dependent per connection or D-channel. Therefore, the same call identifiers can be transmitted to different D channels of the BRA ports from the packet-oriented exchange to the peripheral adapter TNE1. Such a situation can occur, for example, when an A subscriber calls a B subscriber connected to the extension ISDN-PBX2. Call identifiers from the BRA ports which are transmitted to the peripheral adapter TNE1 are adapted by a call identifier management RKVltg of the peripheral adapter TAE1 for the ISDN site-side further use. Identical call identifiers, for example, nCRef1 for the connections BRA1 and BRA2, are mapped to different call identifiers CRefl1 and CRefl2 in order to establish uniqueness within the D-channel of the PRA-connection. On the side of the ISDN extension ISDN-PBX1 newly assigned call identifiers, such as, for example, nCRefx, can be adopted unchanged on the exchange side, ie, on the packet network side. The call references transmitted over the D-channel of the PRA line direction packet-oriented exchange P-Vst are unambiguous within the D-channel and of course retain this uniqueness even after division into the D-channels of the various logical BRA connections. The transmission of the call identifications or of signaling messages which contain call identifications between the peripheral adapters TNE1 and the packet-oriented exchange P-Vst is preferably implemented with the aid of the SCTP protocol and ISDN-specific adaptation layer (eg IUA).