tel:+31-161-242286 f%+31-161-229821 Broadband communication has become a hot issue during the last few years. The Asynchronous Transfer Mode (ATM) will be the most important switching technology for broadband networks, both in the private and public area. The work of the ATM Forumhas considerably accelerated the developments of ATM products. Many equipment vendors have announced ATM products. In the hype around ATM, a clear distinction must be made between private networks and public networks. In the private area (e.g.. LANs), a rapid growth of ATM can be seen already today. The market for public ATM-based services does not yet show such a development. This is partly due to the tariffs for public broadband services, and partly due to the fact that the ATM technology is not yet seen by public operators as a mature technology. It is expected that the market for public broadband services will start growing after 1997. The introduction of broadband capabilities in public networks will enable a wide range of new services, such as broadband LAN-interconnect and interactive video- services. The Intelligent Network concept, offering flexibility and rapid service introduction, will be a very important issue in these broadband networks. Some of the major questions in Broadband Intelligent Networks is: which are the requirements for IN development and what are the main service drivers for Broadband IN ?In this contribution we will focus on these issues. Lets start with a brief introduction in broadband signaling. 0-7803-3230-x/96$5.0001996 EEEY There are several reasons why the control system (and thus: the signaling protocols) in a broadband network will be different from a narrowband network. Assuming that the broadband network is based on the ATMtechnology, these reasons can be summarized as follows: The most obvious impact of broadband networks on signaling protocols is the fact that communication channels have a higher bit rate. New parameters are needed in the signaling messages that control the connections. The capacity of a connection in a broadband network can have anyvalue (e.g. between 1 kb/s and 155 Mb/s) and can even have a variable value. In addition, several Qualities of Service can be offered for a particular connection. It is for this reason that new parameters are needed in several signaling messages. The second class of requirements for broadband signaling systems comes from the fact that the ATM-technology will not only cany the user data, but also the signaling data. In other words: the signaling transport network uses ATM technology, and can even be integrated with the communication network. The third reason why signaling protocols in broadband networks will be different from narrowband networks is the most important: the support of new services and applications. While the PSTN or ISDN has been designed to support merely point-to- point bi-directional connections, this will be completely different in broadband networks. Because of the higher bandwidth, broadband networks allow a wide range of new applications, such as interactive multimedia and multiparty services. The capability to support high quality video signals opens the door to a new category of applications. Functional model signaling Protocols S Ideally spoken, a broadband network should be such flexible, that it would support any telecommunication application, any call configuration (multi-connection, multi- party), any quality of service and any communication bandwidth. This would require a complete newly developed signaling system. Many studies have been carried out and several protowe signaling systems have been developed, that were intended to make the system as flexible and generic as possible. Still, the reality of standardized broadband signaling protocols tends to a go a different way. Broadband signaling protocols are being standardized according to so-called Capability sets. Although IN is developed in a similar way, thecapability sets in broadband and IN are not synchronized. B-ISDN signalling Capability Set 1 was finished by ITU-Tin September 1994. It supports only simple point-to-point single-connection calls, with a constant bit rate only. ATh4 Forum however released an alternative specification, that was based on ITU-T,with a few modifications. One of the main differences is, that ATM-Forum specification U N3.1supports point-to-multipoint calls; this is needed in order to support data-services (e.g.LAN-emulation uses several broadcast procedures). Capability set 2 of ITU-T is being developed in various steps, and includes point-to- multipoint calls, variable bit rate connections and in-call modification procedures (i.e. modification of parameters during the active phase of a call). Requirements for capability set 3 are still unstable. If we look at the Distributed Functional Plane in Intelligent Networks, we can say that this model has been based upon the basic call model in Narrowband ISDN (ITU-T Rec. 4.71). It is important to realize this when developing Broadband IN. In the development of broadband signaling protocols, thebasic call model could be changed very radically. In order to develop a broadband signaling system that would support maximum flexibility for various types of telecommunication calls, one of the concepts is the separation between Call Control and Bearer Control. The separation between Call Control and Bearer Control (or Connection Control) means a functional split between two types of functions: Call Control involves functions that control thecomplete communication session, e.g. involved parties and equipment compatibility issues. Bearer Control involves functions that control single connections link-by-link. A call may exist of more than one connection in parallel. The separation between Call Control and Bearer Control would result in a new basic call model. A new basic call model would have an impact on the IN-functionalities (SSF, SCF and SRF) and the way the interact with the Basic Call Process. This issue has been raised before in several conferences and standardization meetings. The result would be a model as shown above: Broadband IN, making a distinction between Service Control, Call Control and Bearer Control. As things look today, it is very likely that B-ISDN signaling CS2 will NOT be based upon the separation between Call Control and Bearer Control. That means that the IN- modelfor Broadband will still bebased upon 4.1204. The development of broadband signaling protocols in ITU-T and ATM-Forum did not lead to a complete newly designed control system. Instead of that, next generation signaling protocols are being developed in a backward compatible way. Broadband ISUP is based on ISUP with a number of modifications; the next capability set of Broadband ISUP will be an extension of the present one. An overview of the signaling protocol stacks for UN1 and NNI is shown above. Stage 3 (the signalling protocol specification) is developed with little reference to a stage 2 (functional model) description. At the moment, standardiization bodies are working on defming the interworking between ISUP (narrowband) and INAP. Since B-ISUP is a mofication of ISUP, most of this work will prove to be useful for solving the interworking problems between B- ISUP and I NN. Still, some extra issues will have to be solved due to the extra functionalities in B-ISUP basic call process, such as point-to-multipoint connections and in-call bandwidth renegotiation. Many studies have been carried out in order to investigate the demand for broadband services. Which are thebroadband services that the market is asking for - and willing to pay for ? During the last few years it becomes clear that data-services will be the most important driver for broadband communication, for the short term. The enormous growth in Local Area Networks during thelast five years is leading to a demand for interconnection between LANs at high speeds. At the same time, processing power and development of advanced desktop-applications has led to a growing demand for bandwidth in the Local Area Networks as well. ATM is becoming popular as a technology in Local Area Networks AND as a technology to support high-speed LAN-interconnectservices in the public network. Data-services can be offered by the public infkastructure as a transport service only. Intelligent functionality such as routing, address translation and configuration management can be implemented locally. Still, these functions could also be offered on a larger scale, in the public network. It is for this reason, that data services can be a driver for IN capabilities in broadband networks. Another service that will require both large bandwidth and network intelligence is Video-on-demand. This service is mainly interesting for the consumer market (entertainment), and can be implemented in various ways. Oneway would be to use IN capabilities for service brokery and service deliverance. In this paper we will not expand on that. Third, a broadband network should be able to support narrowband services, such as telephony. Todays IN-services mustbe implemented in Broadband IN as well. Lets consider datacommunication in a broadband network. As explained before, ATM is becoming a popular technology for Local Area Networks. Legacy LANs usually make use of shared mediumprotocols, such as Ethemet and Token Ring. ATM is being introduced as a switched technology, offering dedicated bandwidth to the users, and thus improving network performance. However, todays PC applications have been developed for LAN environments. When introducing ATM in the LAN, it is very important to be backward compatible: this means that ATM supports a LAN-emulation service, in such a way that applications can still work in the same way. The LAN-emulation service, that is offered on top of ATM, works exactly as a legacy LAN. For example, addressing is done by MAC-addresses (Medium Access Control). Since the underlying ATM layer makes use of E.164 addresses, an address resolution function is required. This function is offered by the LES (LANEmulation Server). Another important issue in legacy LANs is broadcasting. Because the underlying ATM network is connection-oriented, extra functionality is needed to broadcast connectionless messages from a source to all destinations. (For example if the destination address is not known.) This function is implemented in the BUS (Broadcast and Unknown Server). Finally, a LECS (LAN Emulation Configuration Server) is needed in order to register and manage the configuration of the network and the PCs. Each PC that is being connected to the ATM-based LAN, will automatically be registered in the LECS. The figure above shows an ATM-LAN with the LAN- emulation functions. These functions are usually private functions, and so is the ATM-LAN. Because of the high-speed ATM backbone, the ATM-LAN can be extended across various sites. Although the LAN-emulation functions (LES, BUS and LECS) will usually be implemented in the private ATM-LAN, another scenario would be to implement these functions in the public network and share them with multiple customers. The LAN Emulation Configuration Service (LECS) could be implemented as an SCF/SDF node. In addition, the address resolution function (LES) is very well suited for implementation in a SCF/SDF it shows many similarities with todays Voice VPN services (especially abbreviated dialing and address translation). The implementation of the BUS is an option. Furthermore, firewall mechanisms should beimplemented in order to create multiple Closed User Groups, sharing the same SCF/SDF functionality. Volume charging will most likely be provided by the public access node, but billing and tariffiig support could very well beimplemented in an IN-manner. This implementation will have an impact on the SIBs. new SIBs will have to be developed in order to support LAN-emulation functions such as address resolution and configuration administration. In addition to that, connection monitoring and billing support would also require new SIBs. For reasons of simplicity, the scenario above shows a centralized IN-control. Similar requirements would also bevalid for a future distributed IN-control. Even though telephony (POTS) is a narrowband service, the introduction of ATM will definitely have an impact on it. In the mediumterm, it is very likely that ATM will be used as an access technology to residential customers. This can be implemented in various ways, e.g. using UTP copper infrastructure with ADSL modems, or using CATV access networks. A multiplexer (MUX) will take care for service multiplexing functions, in order to connect PC, telephone and TV set to the same access. This MUX could be a Set Top Box, that is connected to the CATV inhtructure. Since ATM offers a multiservice access network, it will support 64 kb/s voice traffk, broadband video services and data services(e.g. Intemet access). In the figure above a broadband network is shown, with ATM-based multiservice access to users A and B. An Interworking Unit (rwu) provides connectivity to POTS and ISDN. It is assumed that both the broadband network and narrowband network are IN-based. Lets consider the case thatuser A want to set up a telephony call (IN controlled) with user B. The question is: how can this be implemented and which node controls the call ? There are various scenarios. In scenario 1, the telephony call will be switched and controlled by the narrowband network. ATMtechnology is only applied at the broadband access, but not as switching technology for telephony. The ATM access switch should be able to detect narrowband telephony connections and switch themvia the IN-based PSTNBSDN. The following signaling protocols are used: 4.293 1 at the ATMaccess, B-ISUP and ISUP between the ATMswitch and thePSTN switch, and INAP. This scenario is called overlay ATM access. It has no impact on existing IN functionality. In scenario 2, the call is switched by the ATM network, but controlled by the narrowband IN node. Just like scenario 1, this implementation has no further impact on the IN functionality. This scenario would only be used if the broadband network is not (yet) equipped with IN-functionality. In scenario 3, the integrated scenario, the telephony call is switched and controlled by the ATM network. The B-SCP controls IN-functionalities of the telephony service. In this scenario, a connection is needed between the ATMswitch and the B-SCP. Primarily this could bebased on a narrowband SS7 protocol stack, but preferably it should be an ATM connection. I NN should support specific broadband parameters in order to interwork with other ATM-based service in the B-SCP. Scenario 3 is preferred, in particular when the B-SCP will also be used for other ATM-based services, such as Video-on-demand or high-speed data services. Summarizing we can state the following: Although a number of forces try to introduce a separation between Call control and Bearer Control in the standardized protocols, it is not very likely to be implemented in the short- and medium term network implementations. A separation between CC and BC would Raverequired a new distributed functional model for IN. Instead of that, it has become more likely that Q.1204 will be the basis for Broadband IN. It is expected that the service drivers for broadband I N are: data communication (e.g. LAN-emulation or Internet access), video-on-demand services and plainold telephony. There is a trend to implement intelligent functionality in the private network, in a non-shared way. Service providers could position themselves offering more advanced services by implementing theintelligent functions in their (public) infiastmcture. The Intelligent Network concept is therefore a very good basis for implementing functions for LAN-interconnect and Video-on-Demand. New SIB s will need to be developed. An SCP in a broadband network should also be able to control telephony services, even though these arent broadband services. An integrated scenario would require at least similar IN-capabilities as in narrowband networks. For the short- and medium-term, it is more likely that telephony calls will be switched and controlled by narrowband networks, while ATMis merely used as a multi-service access technology. Standardization of Intelligent Networks is very much telephony oriented, so far. From an IN point of view, there are a lot of new opportunities in broadband networks. It is required that standardization bodies start paying more attention to this matter, now thatbroadband network start to become a reality.