Abstract:
A network architecture for a next generation network which contains at least two domains and a method of transmitting a call using voice over IP technique over at least two network domains are presented, wherein instead of point-to-point connections between the two network domains, an interconnection domain is provided which contains a number of Session Border Controllers and at least one Softswitch for provisioning connections between selected ones of said Session Border Controllers.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention is based on a priority application EP 05291699.6 which is hereby incorporated by reference.  
         [0002]     The present invention relates to the field of telecommunications a more particularly to a network architecture for a Next Generation Network comprising at least two network domains and to a method of transmitting a call using voice over IP technique over at least two network domains.  
       BACKGROUND OF THE INVENTION  
       [0003]     While public telephone networks were for a long time exclusively build on circuit switching technology, with the advent of what is known as the Next Generation Network (NGN), a move will be made towards packetized transport, i.e. Voice over IP (VoIP).  
         [0004]     NGNs and VoIP networks have been described in several standardization bodies, defining network models and an architecture of the new network. These standardization bodies include 3GPP with IMS (IP Multimedia Subsystem), ETSI with TISPAN (Telecoms &amp; Internet Converged Services &amp; Protocols for Advanced Networks) and MFS who are defining the architectural aspects.  
         [0005]     By looking at the architecture and network models it becomes obvious that the standardization activities are focused on a single network while basically neglecting any peering models.  
         [0006]     NGN is mainly based on two key aspects, i.e. separation of signaling and media on the one hand and packetized transport (Voice over IP) on the other hand. Session Border Controllers (SBCs) are new elements in NGN networks, which are in general used to interconnect two conversational IP networks. A Session Border Controller is used for example as the demarcation point between the residential IP domain of a subscriber and the domain of the operator to overcome certain limitations which arise due to the use of Network Address and Port Translation (NAPT) in the residential domain. Session Border Controllers are on the other hand used as some sort of packet-to-packet gateways at the interconnect between two operators to avoid the (expensive) need of de-packetization to TDM, use a TDM interconnect and re-packetization, since the latter would result in reduced perceived voice quality and increased delay. In other words, a Session Border Controller may be installed in the Access and is then referred to as an Access Gateway, which will represent the demarcation point between the private IP domain and the operators domain, and another Session Border Controller may be installed in the Core, representing the demarcation point between two independent operators domains.  
         [0007]     This is shown for example in an MFS Technical report entitled “IMS Reconciliation White Paper” by Chris Daniel, April 2005, which shows in  FIG. 4 a  physical network architecture wherein Session Border Controllers are used at the demarcation point towards the subscriber and at the interconnection point towards a second IP network service provider.  
         [0008]     Session Boarder Controllers of the above described type are also described in the publications by J. Hardwick in “Session Border Controllers—Enabling the VoIP Revolution”, by the ETSI Standard TISPAN; NGN Release 1: Functional architecture for PSTN/ISDN Emulation”, and by G. Camarillo in the Internet Draft “Functionality of Existing Session Border Controller (SBC)”.  
         [0009]     Session/border control functionality is also described by K. Sohel et al in the Internet Draft “Conceptual Deployment Scenarios of Session/Border Control (S/BC) Functions” and by M. Bhatia et al in the Internet Draft “SIP Session Border Control Requirements”.  
         [0010]     The text book “Telekommunikationstechnik, Handbuch für Praxis und Lehre” by G. Otfried generally describes different network structures and routing including also hierarchical structure, which are typically used in public telephone and data networks or for coupling LANs over a backbone.  
         [0011]     EP 1113619 describes a broadband cable IP telephony network architecture which includes a central controller connected to a number of peripheral gateways interfacing different networks such as IP networks, classical PSTN and SS7 networks, and the Internet, for instance.  
         [0012]     DE 102 45 643 describes an integrated control unit that contains gateways modules interfacing different networks supporting different transport protocols.  
         [0013]     In all known NGN/VoIP architectures, however, Session Border Controllers are only suited and used to provide point-to-point interconnections between networks or network domains. With the growth of NGN networks, the number of point-to-point connections will soon exceed a manageable size. Moreover, the use of dedicated SBCs for individual point-to-point connections is inefficient and not very flexible.  
         [0014]     It is therefore an object of the present invention to provide a scalable network architecture comprising at least two network domains and a corresponding method of transmitting a call, which both do not suffer from the limitations of the known solutions.  
       SUMMARY OF THE INVENTION  
       [0015]     These and other objects that appear below are achieved by a network architecture for a next generation network which contains at least two domains and by a method of transmitting a call using voice over IP technique over at least two network domains, wherein instead of point-to-point connections between the two network domains, an interconnection domain is provided which contains a number of Session Border Controllers and at least one Softswitch for provisioning connections between selected ones of said Session Border Controllers. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     Preferred embodiments of the present invention will now be described with reference to the accompanying drawings in which  
         [0017]      FIG. 1  shows a prior art NGN interfacing with a traditional circuit switched TDM network;  
         [0018]      FIG. 2  shows a prior art NGN interfacing with a second NGN;  
         [0019]      FIG. 3  shows a prior art NGN interfacing with multiple other NGNs;  
         [0020]      FIG. 4  shows an NGN connected to an interconnection network which interfaces according to the invention multiple other NGNs; and  
         [0021]      FIG. 5  shows a second embodiment of an NGN owned by operator A interfacing via an interconnection network with another NGN of an operator B.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Next-Generation Network is a generic term used to describe the emerging packet-based networks. Such networks feature mixed traffic types such as voice, video, and data, and each traffic type receives an appropriate class of service.  
         [0023]     In the NGN model there exist gateway functions such as Residential Gateways, Access Gateways, Trunking Gateways, or Signaling Gateways. Softswitches, which are also known as Media Gateway Controllers, serve for call control functions. A Signaling Gateway can also be integrated into a Softswitch.  
         [0024]     With the advent of IMS (IP Multimedia Subsystem), a dedicated model has been developed, which standardizes the core and access network by defining closed functional blocks. The present invention provides a peering model on which IMS or “legacy” NGN based networks interoperate properly. Legacy NGN networks are usually defined in a closed zone. Access Gateways, Residential Gateways or SIP (Session Initiation Protocol) phones are connected to the NGN “cloud” and exit the network at a Trunking Gateway to the “rest of the world”. This is shown schematically in  FIG. 1 .  
         [0025]     A telephone set  100  is connected via a telephone line (e.g. ISDN) to an Access Gateway  105 , which converts the TDM signal from the telephone line to IP packets and sends the signaling information to a Softswitch  103  using the H.248 signaling protocol. H.248, which is also known as Megaco (see RFC 3015), is a standard protocol for handling the signaling and session management needed during a multimedia conference. An alternative would be the Media Gateway Control Protocol (MGCP) defined in RFC 2885.  
         [0026]     The Softswitch  103  determines a route through the IP network  101 , which, since the call in this example is destined for a subscriber connected to a circuit switched public telephone network  110  outside the IP network  101 , leads to Trunking Gateway  107 . The Softswitch  103  then provisions an RTP connection (Real-time Transport Protocol) by requesting the Access Gateway  105 , the Trunking Gateway  107 , and any intermediate IP Router along the chosen route (not shown) to reserve a certain capacity for the packetized voice signal. RTP is the Internet-standard protocol for the transport of real-time data, including audio and video. It is a packet based communication protocol that adds timing and sequence information to each packet to allow the reassembly of packets to reproduce real time audio and video information. Moreover, the Softswitch forwards the signaling information to a Signaling Gateway  109  using a SIGTRAN protocol, i.e., a Protocol stack such as SCTP defined by the SIGTRAN working group of IETF (Internet Engineering Task Force), which is a protocol aiming at providing an ETSI no. 7 protocol over IP (see RFC 2960 published October 2000). An alternative would be the M2UA signaling protocol.  
         [0027]     The Signaling Gateway  109  converts the signaling information to SS7 (Signaling System No. 7), i.e. the common protocol by which network elements in the public switched telephone network (PSTN) exchange information over a digital signaling network  120  in order to handle call setup, routing, and control. The Trunking Gateway  107  converts the VoIP signals to and from IP network  101  into TDM signals having the common IMT format and sends these to the bearer network  110 , where the called subscriber is located. The call is then processed and established in a conventional manner by the PSTN  110  and its SS7 signaling network  120 .  
         [0028]     In the future, circuit switched PSTN domains will be replaced bit by bit with NGN domains.  FIG. 2  shows the situation that bearer PSTN  110  and its SS7 network  120  is replaced by an IP network B  210  having its own Softswitch  213 . Instead of Signaling and Trunking Gateways  109 ,  107  of  FIG. 1 , a Session Border Controller (SBC)  207  interconnects the IP network A  201  and the IP network B  210 . If a user  200  wishes to call another user who is located in IP network B, an RTP connection from his Access Gateway  205  to the SBC  207  is established under control of Softswitch A  203  and another RTP connection is established from SBC  207  via IP network B to the Access Gateway of the called party (not shown) under control of Softswitch B  213 . Softswitch A  203  communicates for this purpose the signaling information via SBC  207  to Softswitch B  213  using the SIP/SIP-I protocol (SIP: Session Initiation Protocol), i.e., a signaling protocol for Internet conferencing, telephony, presence, events notification and instant messaging developed by the IETF.  
         [0029]     The architecture of a Session Border Controller can either follow the NGN approach of a decomposed model, with a separation of Signaling and Media, or SBCs can be designed as combined boxes. In the access an SBC typically comes along in an integrated model where the signaling and the media part are integrated on the same physical device. While in the network core the SBC is a decomposed SBC with a signaling SBC and a media SBC, which is also referred to as a Media Proxy.  
         [0030]     The key features of an SBC will be the following separated into functions of a Media Proxy Controller and functions of a Media Proxy as such. It has to be noted, however, that depending on the actual application not all but only a subset of these features may be implemented in an actual network implementation.  
         [0031]     Media Proxy High level functions: 
        Bandwidth allocation and CAC functions     Policing and marking (DSCP)     Firewall (Media Pin hole Control)     Network Address and Port Translation (NAPT) and NAT/FW traversal     DSP services     Quality and SLA monitoring     Support lawful Interception     DOS protection        
 
         [0040]     Media Proxy Controller High Level Functions: 
        Signaling protocol translation and interworking     Message scrubbing for end-user identity and address hiding     Topology and infrastructure hiding     Authentication Authorization Accounting (AAA)     Firewall (Media Pin hole Control)     Privacy     Session based routing     Load related services (sharing and balancing)     DSP service control     Call statistics maintenance     Support for lawful intercept     DOS protection        
 
         [0053]     However, as soon as a growing number of networks evolve towards NGN, more NGN provider will ask for peering interfaces and the networks will rapidly become unmanageable. Such a situation is shown schematically in  FIG. 3 , where eight neighboring networks  320   b - 320   i  are connected to IP network A  301  via respective SBCs  307   b - 307   i . Security issues will be a main obstacle to share SBCs among several operators. Issues will arise whether the SBCs have to know the network topology and to which Softswitch the SIP/SIP-I messages have to be forwarded. Same is true for the addressed Media Proxy.  
         [0054]     Therefore, a basic idea of the present invention is to provide instead of a plurality of point-to-point connections a new network which serves to interconnect with other operators. This interconnection network can be used as security line between the home network (trusted zone) and the foreign network (un-trusted zone). The new interconnection network will hence acts as a De-Militarized Zone (DMZ).  
         [0055]     The invention is on the one hand based on the decomposed model for the SBCs, i.e., splitting the Session Border Controller into the Media Proxy (MP) responsible for RTP relaying and the Media Proxy Controller (controlling the Media Proxy). On the other hand, the invention introduces a new network between the trusted home domain and the un-trusted foreign domain.  
         [0056]     In  FIG. 4 , a first IP network A  401  is connected at three points via respective SBCs  406 ,  406 ′, and  406 ″ to an interconnection network  410 . In the interconnection network  410 , there are eight SBCs  407   b - 407   i , each of which interfaces a further IP network C-I  420   b - 420   i , respectively. The SBCs  407   b - 407   i  are controlled by a mutual Media Proxy Controller, which acts as the Softswitch of the interconnection network  410 .  
         [0057]     If a subscriber located in IP network A places a call from his telephone set  400  to another subscriber who is located in another IP network, Softswitch  403  provisions an RTP connection from Access Gateway  405  to one of the SBCs, say to SBC  406  and forwards the signaling information to Softswitch  411  of the interconnection gateway  411 . Softswitch  411  in turn provisions a connection to the SBC that connects to the corresponding IP network of the called subscriber and the Softswitch of the addressed network (not shown) provisions an RTP connection to the called subscriber.  
         [0058]     Another embodiment of the invention is shown schematically in  FIG. 5 . A POTS subscriber (Plain Old Telephone System)  500  is connected via an Access Gateway  505  to an IP network  501  of an operator A. In IP network  501 , there are also shown a Softswitch  503  and a SBC  506 , which builds the interface to the network of an operator B  520 . The network operator B  520  has an IP network domain  521  and an own interconnection network  510 . The interconnection network  510  contains five SBCs  507 ,  508   a - 508   d  and a Softswitch  511  for call control. The four SBCs  508   a - 508   d  connect to respective four SBCs  509   a - 509   d  in the IP network domain B  521 , while SBC  507  is connected to SBC  506  in the IP network domain A  501 . Softswitch  522  controls call set-up in IP network domain B  521 . Subscriber equipment  550 ,  551  is connected to the network, i.e., a Residential Gateway  550  and a SIP phone  551  of the subscriber.  
         [0059]     If subscriber  500  whishes to place a call to subscriber  551  who is located in IP network domain B  521 , Softswitch  503  provisions an RTP connection to SBC  506 , Softswitch  511  provisions an RTP connection from SBC  507  to let say SBC  508   d  and Softswitch  522  provisions a connection from SBC  509   d  to the Residential Gateway  550  at the called subscriber&#39;s premises.  
         [0060]     As can be seen from  FIG. 5 , there are four parallel connections between interconnection network  510  to the managed IP domain B  521 . This allows to use the shortest path to a called subscriber. Softswitch  511  is thus equipped with an intelligent database  512 .  
         [0061]     Enhancing this network with more routing intelligence enables least-cost-routing, congestion control, short-cut finder, paired with constraints of network resource, available bandwidth, costs and other, which provides a new network model for International VoIP provider and opens up new applications in the network, such as bandwidth brokers, selling minutes of usage on IP links, redefined worldwide “least-cost-routing”, and sharing of worldwide services.  
         [0062]     The intelligent database  512  is a key for optimized routing in an interconnected NGN with several network domains. It can be fed with latest updates by the network itself and is capable of routing in a optimized way.  
         [0063]     One application of the interconnection network will be to sell and buy minutes wherever it is needed and hence act as a Bandwidth Broker. Within the NGN/VoIP area different subscribers may be handled differently. For example, teens who are paying less for lower service quality will be routed in a different way than other user groups paying for premium service. The intelligent routing capabilities will enable faster provisioning in almost real-time, using not only E164 telephone numbers, but also “sipto:”, alias, ENUM and many other types of identifiers to route calls properly.  
         [0064]     The Media Proxy itself may implement a Signaling Firewall, checking the signaling messages for corect content, flood DOS attacks, rate control and other security threats. The Media Proxy itself only allows bearer (based on RTP flows) to enter the Media Proxy.  
         [0065]     Another important aspect of the invention is that the new interconnection network allows to interface a number of “foreign” networks. Such networks that need to be interfaced are also called OLOs (Other Licensed Operators). The Softswitch of the interconnection network acts now as a default Softswitch for all OLOs, so that the Softswitches of the local domain do not need any knowledge of “foreign” subscribers, anymore. The new interconnect network will perform signaling conversion (SIP to SIP-I, etc) and media conversion (for example conversion of the coding from G.711-20 ms to G.729). This architecture is well suited for national as well as international interconnections between independent network domains.  
         [0066]     One or more of the following functions may be provided by the interconnection network: 
        Firewalling 
            Media (RTP, RTCP, UDP, IP, etc)     Signaling (SIP, SIP-I, H248,     Rate Control on TCP/UDP     Rate Control on Signaling (SIP, SIP-I, etc)     Rate Control on Media (RTP, RTCP)     Address filtering on source/destination and hop    
            Mediation and Interworking 
            Transport Interworking 
                IPv4-2-IPv6 adaptation     NAPT—Network Address and Port Translation     QoS adaptation 
                    ToS, RSVP    
                    Virtual Network adaptation 
                    MPLS, VPN, VLAN    
                   
                Signaling Interworking 
                SIP-2-SIP-I and vica versa     SIP-2-H323     MGCP and H248     M3UA-2-M2UA    
                Media Interworking 
                Codec conversion and adaptation 
                    G711-2-G729, G729-2-AMR, etc    
                    Codec characteristic adapatation 
                    G711; 10 ms-2-G711; 20 ms, etc    
                   
               
            Operator Control 
            For business rev. assurance (avoid controller bypass)     QoS level assurance (no uncontrolled network traffic)     Detection &amp; termination of hanging calls    
            Security Proxy &amp; Brokerage 
            Masking of internal (architectural) info to outside networks (privacy &amp; topology hiding)     Separation of change impact     Simplify subscriber mobility     Call Routing (source based) 
                Network (type) selection     New domain (other Softswitch) selection (based on called party ID)    
                Service Resolution 
                Softswitch type    
                Location Resolution     Identity Resolution     Virtual BGW in the concentrated access domain to be controlled by different BGC/SX in the core domains (different OLO&#39;s)    
            QoS/SLA Manager 
            Initial Granting Check 
                What is requested?    Is this according to SLA?    Is the network able to provide? (network actual capabilities)    
                SLA Realization 
                QoS level marking (ToS, VLAN, MPLS . . . )    
                SLA Enforcement 
                Detect SLA violation     React (terminate, rate limit, . . . )    
               
            Monitoring &amp; Supervision 
            Call Statistics 
                Number of calls     Successful/unsuccessful     Duration of calls     Number of Packets send during call     Ratio Silence Suppression—Voiced Time    
                Service Statistics 
                Type of services used     Volumes, . . .    
                SLA monitoring 
                Access (subscriber)     Peering (to OLO)    
                QoS monitoring (passive Voice measurement based on statistics)     QoV monitoring (active Voice measurement signals)     Network (traffic, BW,) monitoring    
            Security 
            Encryption 
                SIP     H.248     SNMP     RTP     RTCP    
                Encryption method 
                TLS     SSL     IPSec    
                Key management    
            Lawful Intercept 
            Signaling     Y-GW function    
            Accounting Support 
            CDR related information generation     SLA coupled statistics    
            Effectiveness increase 
            RTP multiplexing     Header compression    
               
 
         [0155]     Having described embodiments of the present invention in detail, it should be clear to those skilled in the art that various modification, substitutions, and enhancements would be possible without departing from the concepts of the invention. It should be clear that the invention is not limited to voice communication between end-users but will equally apply to any kind of multi-media sessions between any kind of subscribers.