Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M7/00—Arrangements for interconnection between switching centres
  • H04M7/12—Arrangements for interconnection between switching centres for working between exchanges having different types of switching equipment, e.g. power-driven and step by step or decimal and non-decimal
  • H04M7/1205—Arrangements for interconnection between switching centres for working between exchanges having different types of switching equipment, e.g. power-driven and step by step or decimal and non-decimal where the types of switching equipement comprises PSTN/ISDN equipment and switching equipment of networks other than PSTN/ISDN, e.g. Internet Protocol networks
  • H04M7/126—Interworking of session control protocols
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M7/00—Arrangements for interconnection between switching centres
  • H04M7/12—Arrangements for interconnection between switching centres for working between exchanges having different types of switching equipment, e.g. power-driven and step by step or decimal and non-decimal
  • H04M7/1205—Arrangements for interconnection between switching centres for working between exchanges having different types of switching equipment, e.g. power-driven and step by step or decimal and non-decimal where the types of switching equipement comprises PSTN/ISDN equipment and switching equipment of networks other than PSTN/ISDN, e.g. Internet Protocol networks
  • H04M7/125—Details of gateway equipment
  • H04M7/1255—Details of gateway equipment where the switching fabric and the switching logic are decomposed such as in Media Gateway Control

Definitions

• the present invention relates to signalling in a telecommunications system and in particular, though not necessarily, to the transmission of signalling data associated with voice or data calls.
• CCS Common Channel Signalling
• PSTN Public Switched Telephone Network
• ISDN Integrated Services Digital Network
• PLMN Public Land Mobile Networks
• SS7 Signalling System Number 7
• ITU-T International Telecommunications Union - Technical
• SS7 is a packet switched system occupying one time slot per frame of the Time Division Multiple Access (TDMA) E.l or T.l transmission formats (the other time slots being available for user data).
• TDMA Time Division Multiple Access
• Individual signalling message packets are associated with respective individual telephone calls.
• a single SS7 channel is able to handle all signalling between two network nodes (termed "signalling points") for several thousands of calls.
• the route taken by a signalling message in the SS7 network may be the same as that over which the associated telephone call is established, or it may be different.
• SS7 (along with other CCS systems) is able to support a number of different telecommunications protocols (e.g. PSTN, ISDN, PLMN).
• SS7 comprises a Message Transfer Part (MTP) which deals with the physical transfer of signalling information over the signalling network, i.e. message formatting, error detection and correction, etc, and user parts and application parts which allow several "users" (i.e. ISDN User Part, Telephony User Part, etc) to send signals in ' the same signalling network.
• MTP Message Transfer Part
• SS7 makes use of addresses known as Point Codes to route signalling data through the "visibility area" of a telecommunications network, the visibility area typically being the network itself together with the interfaces between the network and “foreign” networks under the control of other operators.
• a Point Code is placed in the header of a signalling packet and is examined by a network signalling point (SP) upon receipt of the packet to determine the next hop for the packet en route to its destination.
• SP network signalling point
• any change in the Point Code allocation within the visibility area requires the operator to update the Point Code database (or routing table) which exists in each SP of the network. This however adds significantly to the maintenance overheads of the network.
• the dedicated nature of SS7 makes it in general expensive to install and maintain (in relation to both hardware and software), a significant barrier especially to prospective new telecom operators.
• the bandwidth available for actual user call data is restricted.
• Yet another disadvantage of traditional signalling architectures is that the interoperability of SS7 networks is limited due to the dedicated nature of the MTP physical layers.
• a method of transmitting signalling information between signalling points of a telecommunications system comprising transmitting signalling information between said signalling points via a IP based network.
• the method preferably including the steps of transmitting signalling information from a first signalling point to a first gateway, formatting the signalling information at the first gateway into a format suitable for transmission over an IP network, transmitting the formatted information from the first gateway to a second gateway over an IP network, receiving the formatted information at the second gateway and recovering therefrom the original signalling information, and transmitting the recovered signalling information to a second signalling point.
• Embodiments of the present invention enable the separation of information for transmission through the system into call information and signalling information.
• the use of the IP based network for transmitting signalling information releases capacity in the originating system for use by call information.
• the use of the IP network reduces the need for conventional signalling infrastructure (although this may still be used in part).
• IP based networks offer increased flexibility (e.g. routers of the network have self-updating routing tables) and reduced operating, maintaining, and engineering costs in comparison with conventional telecommunications signalling networks.
• the signalling information being associated with a subscriber-to- subscriber voice or data traffic channel carried by a first transmission network.
• said first transmission network is a circuit switched network, using for example PSTN, ISDN, or PLMN protocols, or a combination of these protocols.
• said signalling points between which the user call information and the signalling information is transmitted are switching points (e.g. exchanges) of the telecommunication system, or signalling transfer points.
• the IP based network may also be used inter alia to transmit signalling information to and from Intelligent Network nodes.
• Signalling information may be transmitted between said signalling points in part via a packet switched signalling network different from said IP based network, signalling information being converted from one format to another at the network interfaces.
• said packet switched signalling network may be a common channel signalling network such as a Signalling System No.7 (SS7) based network.
• SS7 Signalling System No.7
• signalling information is transmitted between a group of locally arranged signalling points using an SS7 network.
• Signalling information intended for signalling points outside the local area is transmitted to a gateway node which provides an interface between the SS7 network and the IP network.
• the gateway node provides an interface for signalling information transmitted through the IP network to a local signalling point.
• the signalling data transmitted through the IP network comprises signalling information associated with call set-up and call termination in the first transmission network of the telecommunications system.
• Signalling information relating to call charging may also be transmitted through the IP network.
• an apparatus for transmitting signalling information between signalling points of a telecommunications system include an Internet Protocol (IP) based network forming at least part of a transmission link between said signalling points, and means for transmitting signalling information between said signalling points via the IP based network.
• IP Internet Protocol
• the apparatus preferably further include a gateway device coupled to a signalling point and also to an Internet Protocol (IP) based network, wherein the gateway device is arranged to receive signalling information from said signalling point coupled thereto and to convert that information into a format suitable for transmission over the IP network and to perform a reverse conversion for signalling information from the IP network.
• IP Internet Protocol
• the gateway device is a Signalling System No.7 (SS7)/Internet Protocol (IP) gateway device.
• SS7 Signalling System No.7
• IP Internet Protocol
• the gateway devices of the apparatus are standalone devices. In other embodiments, however, the gateway devices may be integrated into a signalling point or a signalling transfer point.
• the gateway nodes may be coupled to the IP network via respective Internet Access Servers. Alternatively, the gateway nodes may be coupled directly to the IP network.
• the gateway nodes are coupled to respective signalling points/signalling transfer points via PCM or TDMA links, e.g. E.1 (2Mb/s, 32 channels) or T.1 (1.5Mb/s, 24 channels).
• the gateway nodes are coupled to respective IASs via packet switched data links, e.g. using ethernet or ATM.
• the gateway devices may be provided with conversion means for converting between the ISUP messaging format and the SIP messaging format; between an H.323 messaging format and the SS7 call set-up format, between ISUP and a network access server control protocol, e.g. etheric; or between ISUP and a voice- over-IP control protocol, e.g. Q.767-H-.
• the gateway devices may be provided with an interface for tunnelling SS7 application part messages over IP.
• the gateway devices may each have one of the following protocol stacks arranged on the SS7 and IP sides:
• the gateway nodes may be arranged to determine the IP routing address for a received message or series of messages from one or more of the Signalling Link Selection + Service Information Octet, Subsystem number, and Global Title Translation.
• the signalling information is associated with a subscriber-to-subscriber voice or data traffic channel carried by a first transmission network.
• a method of communicating voice and other user information between a pair of end users, a first of the end users having a circuit switched connection to a telecommunications network and the second of the end users having a packet switched connection to an IP network comprising exchanging signalling information between the telecommunications network and the IP network via a gateway device arranged to convert the signalling data between a voice-over-IP format and an SS7 format.
• Figure 1 illustrates schematically a telecommunications system comprising two interconnected telecommunications networks
• Figure 2 illustrates functionally the architecture of a gateway device of the system of Figure 1 ;
• FIG. 3 illustrates schematically the signal processing layers of the SS7 protocol
• Figure 4 illustrates the processing layers present at a gateway node of the system of Figure 1 ;
• Figure 5 illustrates the flow of signalling data associated with call set up and termination in the system of Figure 1; and Figure 6 is a flow diagram illustrating the signalling process employed in the system of Figure 1.
• a telecommunications system in which the present invention may be employed typically comprises one or more interconnected telecommunications networks. These networks may make use of the same telecommunications protocols (e.g. ISDN, PSTN, PLMN) or may use different protocols. In addition, the networks may be operated by the same or by different operators. However, the networks have in common that they use Signalling System No.7 for communicating signalling information between internally located signalling points (SP).
• SP Signalling System No.7
• FIG. 1 illustrates a much simplified telecommunications system comprising only two telecommunications networks 1,2.
• Both of these networks 1,2 are assumed to be Integrated Digital Services Networks (ISDN).
• ISDN Integrated Digital Services Networks
• Each network comprises a number of switching exchanges 3 interconnected by trunk lines 4.
• a trunk line 5 provides a link between exchanges 3 of the two networks 1,2.
• Each traffic channel is a circuit switched channel, i.e. comprising a reserved time slot in each consecutive transmission frame, and as such the network through which a call is routed is referred to here as a "circuit-switched network".
• an SS7 network 8 is provided in each of the telecommunications networks 1,2.
• Each SS7 network 8 handles the flow of signalling information between signalling points (e.g. exchanges 3) of the associated network.
• Signalling information may be routed directly between two signalling end points, or it may be routed through intermediate Signalling Transfer Points (STP) 9.
• STP Signalling Transfer Points
• Each of the networks 1,2 comprises a gateway device 10 which provides an interface for the SS7 network 8 to an IP network 1 1.
• the gateway devices 10 are coupled to the IP network 1 1 via respective Internet Access Servers 12, although it will be appreciated that this coupling may be achieved directly without intervening Internet Access Servers 12.
• IP network is intended to include networks utilising the current de facto IP standard as defined by the Internet Engineering Taskforce or a future derivative thereof (including the TCP or UDP protocol layers).
• the network 11 may be a closed network under the control of the telecommunications network operator(s), i.e. an intranet, or an open network accessible through the World Wide Web (i.e. the Internet).
• the substitution of the IP network for a significant part of the SS7 network provides a number of significant advantages, chiefly a reduction in the signalling traffic and processing required in the conventional telecommunications network and replacement of expensive, dedicated telecommunications infrastructure with low cost, flexible datacom infrastructure.
• the gateway device 10 is coupled on the one side to the Internet Access Server 12, and on the other side to STPs 9 of the SS7 network 8. Whilst the gateway device 10 may be connected to every STP 9 of the SS7 network 8, it is preferred that connection is made to only a subset of all STPs 9 of the SS7 network 8, such that signalling information to be transmitted between a give STP 9 and the gateway device 10 may require routing through one or more intermediate STPs 9.
• Figure 2 illustrates schematically a possible architecture for the gateway devices 12.
• signalling information to be transmitted from a signalling point of one network 1,2, to a signalling point of the other network, through the TCP/IP network 11, requires protocol conversion at both of the gateway devices 10. More particularly, it is necessary to process signalling messages such that the physical message construction, and associated enor detection and correction processes etc., are appropriate for the medium over which the message is next to be transmitted.
• FIG 3 illustrates the seven layers (or levels) which compose the SS7 protocol. These layers will not be described here in detail, but rather the reader should make reference to the ITU-T recommendations starting with Q.700. It is sufficient here to note that layers 1 to 3 provide the physical, datalink, and network layers, whilst layers 4 to 7 provide user parts and application parts which are generally network specific (in particular, the TCAP provides transaction capabilities for services such as INAP, MAP, OMAP, etc.).
• FIG. 4 illustrates the processing layers which are provided at the gateway device
• this user part generated data is passed by the MTP to an intermediate processing layer (identified by reference numeral 13).
• This layer 13 adds to each signalling message a header (9bits) indicating the number of octets which the message contains.
• the processed messages are then passed to the TCP/IP protocol layers where they are organised for transmission over the TCP/IP network
• a single TCP/IP datagram may contain several signalling messages, such that the datagram has the structure illustrated in Table 1 below, and where SIF is the Signalling Information Field and SIO is the Signalling Information Octet.
• the signalling information is processed through the TCP/IP layers to recover the user part generated data, with the signalling message length header being removed in the intermediate layer 13, before passing the data to the MTP in preparation for transmission over the SS7 network 8.
• Figure 4 illustrates a user part(s) layer above the MTP and TCP/IP layers.
• this layer is not normally utilised in the gateway device unless the device is directly connected to a switching exchange 3 such that signalling information can be passed directly from the user parts (e.g. TUP, ISUP, etc.) to the TCP/IP layers and vice versa.
• the user parts e.g. TUP, ISUP, etc.
• Gateway devices may therefore be provided with a database mapping point codes to IP addresses, using dynamic updating if necessary.
• Figure 5 illustrates the flow of signalling information associated with set up and termination of a call between the two telephones 6,7 of Figure 1, where the signalling points are identified using the same symbols as are used in Figure 1.
• Figure 6 is a flow diagram illustrating the signalling process described above.
• this channel may be provided, in whole or in part, by a packet switched channel, e.g. where the call is made from or to a mobile telephone registered with a mobile network utilising the proposed General Packet Radio Service (GSM phase 2+).
• GSM phase 2+ General Packet Radio Service

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Data Exchanges In Wide-Area Networks (AREA)
• Telephonic Communication Services (AREA)

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• 1998
  • 1998-10-30 FI FI982368A patent/FI107216B/fi not_active IP Right Cessation
• 1999
  • 1999-09-24 EP EP99969873A patent/EP1121798A2/de not_active Withdrawn
  • 1999-09-24 WO PCT/FI1999/000790 patent/WO2000019694A2/en not_active Application Discontinuation
  • 1999-09-24 AU AU59858/99A patent/AU5985899A/en not_active Abandoned

Non-Patent Citations (1)

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