Next, we compare procedures for certain feature scenarios. In the IS-41 approach, features are handled in three ways: by the HLR upon receiving a

Transcription

1 Next, we compare procedures for certain feature scenarios In the IS-41 approach, features are handled in three ways: by the HLR upon receiving a LOCREQ, a serving upon receiving a ROUTEREQ, or by the serving upon receiving a connection setup message For example, unconditional call forwarding and selective call acceptance are features handled by the HLR upon receiving a LOCREQ, call forwarding on busy is handled by the serving during ROUTEREQ, and call forwarding on no-answer or no response to page are triggered at the serving during connection setup For features handled by the serving s, only service triggers are downloaded Any data associated with the service is retained in the HLR For example, call forwarding on no-answer is triggered at the serving if the user does not answer after connection is setup However, the forwarded number is stored in the HLR Retrieval of this data requires messaging to the HLR This approach is well-suited for some features that have large amounts of associated data For example, speed dial may require the HLR to download a large amount of data if the mobile user has a large database of numbers Such downloading and subsequent movements to new VLRs as the end point moves will generate a high signaling load The cost of extra messaging during call/connection setup delay may be a small penalty in comparison to this increased signaling load On the other hand, for features with small amounts of data, such as a forwarded number for call forwarding on no-answer, the increased call/connection setup delay associated with increased messaging may be more costly than the increased signaling load caused by downloading this data In our solution, the decision of whether to download both service triggers and data, or only the service triggers is done on a feature-by-feature basis, provided the home network provider allows downloads The third procedure is registration In the IS-41 approach, upon receiving a zone-change registration, the HLR sends a cancellation to the old VLR In our approach, the new visitor USS communicates with the old visitor USS to migrate the user process (if there is one) The HLR to VLR downloads during registration is cross-network signaling for roaming mobiles (mobiles visiting in other networks) In our solution, the visitor USS to visitor USS migration makes it easier to move both service triggers and data Thus, for some features, even service data can be downloaded from the home USS unlike in the IS-41 approach Finally, consider the outgoing call/connection setup procedure In IS-41, for many features, the HLR is involved In our approach, we observe that if a dynamic user process is available, most features can be handled by the visitor USS, thus eliminating the message exchange with the home USS and reducing call/connection setup delay We summarize the functional differences between a home USS and an HLR and between a visitor USS and VLR Unlike the HLR, a home USS assigns temporary directory numbers for mobiles, and in mode II operation, provides all the call control needs of a mobile There are three differences between visitor USS and VLRs: unlike VLRs, the visitor USS does not provide a hierarchy in mobile tracking (for improved call/connection setup delays); each visitor USS provides user control functions allowing for dynamically requested signaling services, unlike VLRs; and each visitor USS provides call control functions, unlike VLRs which act as databases with call control being performed in s 5 CONCLUSIONS This paper proposed two types of user signaling servers (USS) for PCS user service profile management The home USS provides location control and call control functions to invoke IN-based services for its mobiles The visitor USS provides call control functions for some services and user control functions to act as a surrogate for its mobiles We described signaling procedures for four modes of operation in which both types, one type, or neither type of USS was involved in the control procedures for a mobile We compared our approach with the data communications approach and the IS-41 wireless intelligent network approach Significant advantages over the data communications approach is that by using the visitor USS, mobiles can save valuable air interface and computing resources, and also subscribe to IN-based services Several procedural differences between the IS-41 approach and ours lead to signaling load and call/connection setup delay reduction References [1] EIA/TIA IS-41 Rev C: Cellular -telecommunications Intersystem Operations, May 1995 [2] J Porter and A Hopper, An ATM based protocol for Wireless LANs, Olivetti Technical Report, April 19, 1994 [3] D Raychaudhuri and N D Wilson, ATM-Based Transport Architecture for Multiservices Wireless Personal Communication Networks, IEEE Journal on Selected Areas in Communications, vol 12, pp , Oct 1994 [4] M Veeraraghavan and T F La Porta, Models for Control of B-ISDN and IN-Supported Services, Proc of ISSLS '93 [5] R Ramjee, T F La Porta, M Veeraraghavan, The Use of Network-Based Migrating User Agents for Personal Communication Services, to appear in IEEE Personal Communications Magazine [6] T F La Porta, M Veeraraghavan, P A Treventi and R Ramjee, Distributed Call Processing for Personal Communication Services, IEEE Communications Magazine, June 1995

2 4 COMPARISON WITH CELLULAR AND DATA NETWORK APPROACHES In this section of the paper, we describe how the inclusion of user signaling servers overcomes the drawbacks of existing approaches for user service profile management First, we address the data communications model Relative to the four modes of operation offered to an end point in our solution, the data communications model only supports mode IV It does not support IN-based services, such as closed user group, and thus does not support modes II or III It does not support mode I, since it offers no means by which a mobile can dynamically request signaling services Server D C OFFER CONNECTIONS Offer connections response Mail Server B Figure 5 Transit Switches An Example Service SETUP Source End point A : signaling : data path In Figure 5, we demonstrate how mode I operation using our solution saves valuable air interface and mobile computing resources when compared to the data communications model for a simple service An end point A requests a connection to mobile C for mail service using the SETUP message End point A indicates that this connection is for mail service using either the broadband high layer information or the user-to-user information parameter Connection setup proceeds through transit switches as shown in Figure 5 When the serving for mobile C receives the Initial Address Message (), it offers the connection to the user process of mobile C located in visitor user signaling server D If mobile C had instructed its user process a-priori to redirect its mail to mail server B, this information is returned by the user process in the Offer connections response, allowing the to route the connection to the mail server By having its user process act on its behalf, mobile C saves computing and air interface resources The IS-41 cellular approach supports only mode III operation, while our solution supports four modes of operation, leading to greater user flexibility while still supporting IN-based services There is no provision to allow mobiles to upload data and request services dynamically for mode I operation as is possible with the visitor USS in our solution Mode II operation is not supported because s provide call control processing along with connection control in IS-41 networks necessitating downloads of service triggers from HLRs In our solution, by separating these functions and locating call control functions in the USS, and limiting functionality in s to only connection control, mode II operation can be supported Thus, a service provider which disallows downloads of service triggers for its mobiles 1 can provide all the call control functions from its home USS even for its mobiles roaming in other networks Finally, mode IV operation in our solution provides fast incoming or outgoing connection setup for mobiles who do not subscribe to or request dynamic signaling services By limiting functionality in the s to include only connection control, no service trigger checks are performed for mobiles operating in mode IV, thus improving connection setup delay Even in mode III operation, there are signaling procedural differences between our solution and the IS-41 approach We describe the differences in four procedures In cellular networks, the mobile location procedure during call/connection delivery consists of a three-hop process Upon receiving a LOCREQ request, the HLR sends a ROUTEREQ to the VLR which forwards this to an The allocates a TLDN (Temporary Local Directory Number) for the mobile Even though one function of the VLR is to provide a hierarchy in mobile tracking, its other function of making available user service profile information to the, leads to the collocation of VLRs with s as is done in most current implementations Having observed this phenomenon, we remove the hierarchy in mobile tracking, and thus eliminate the need for the first ROUTEREQ message Secondly, we observe that TLDNs assigned by the are used primarily to route the connection from the originating/home to the serving Since the home USS knows the on which the mobile is located, in our approach, we assign the functionality of selecting a temporary directory number identifying the on which the mobile is located to the home USS Part of this temporary directory number is a predetermined default value to alert the that the incoming connection request is to a mobile This eliminates the need for the third message (ROUTEREQ) from the VLR to the Thus, the mobile location function is handled by the home USS without requiring the involvement of the visitor USS or the serving This lowers both signaling load and call/connection setup delay 1 Information regarding services subscribed to by a mobile can be considered competitive information

3 this feature, the home USS returns the forwarded number in the Locate&Call_rqst response message Examples of other features checked at the home USS include CUG (Closed User Group) service and selective call acceptance The home or originating then uses standard SS7 signaling to establish the connection The serving sends a page message out to its radio ports to locate the mobile since it know that this mobile has no dynamic user process Call/connection setup to a end point operating in mode III involves both home and visitor USS An end point may operate in this mode either by explicitly requesting a user process in a visitor USS while also subscribing to some INbased services, or if the home USS creates a user process based on the mobile s subscribed service needs The message flow for an incoming call/connection setup to an end point operating in mode III is very similar to that shown in Figure 2 The only difference in that upon receiving a LOCATE&CALL_RQST, the home USS performs both location control and call control and returns a Locate&Call_rqst response (as in Figure 3) and not a Locate response (as in Figure 2) In this response, it returns the temporary directory number identifying the serving as well as any parameters resulting from its call control invocation of subscribed-to services and subsequent service processing If a separate call control protocol is defined for ATM networks for negotiation or other functionality, separate messages may be sent directly to the user process in the visitor USS prior to connection establishment [6] By having the user process handle these messages, air interface and mobile computing resources are saved The message flow for an incoming call/connection setup to an end point that has no subscribed-to or dynamically requested services operating in mode IV is similar to the one shown in Figure 3 The only difference is that instead of responding to the LOCATE&CALL_RQST message with a Locate&Call_rqst response, the response is simply a Locate response (similar to that shown in Figure 2) The implication is that the home USS only provides the location, the temporary directory number identifying the on which the mobile is located It does not perform any call control functions since end points operating in mode IV have no user service profiles 33 Outgoing Call/Connection Setup Procedure Port SETUP Server (User Process) CHECK FEATURES Next Switch Check features response ACM Figure 4 Outgoing Call/Connection Setup for a Type I End Point We now consider the setup procedure originated from end points operating in each of the four modes A call/connection setup request from an end point operating in mode I is sent via the radio-port to the as shown in Figure 4 The serving sends a request to the user process for this mobile in its visitor USS to check for any features Examples of services that may be triggered here include speed dial, where the numbers are stored in the user process allowing for the mobile end point to use shorter numbers to place outgoing calls, and automatic call back, where the user process stores the last called party number and allows the mobile to redial this number using a short code The user process can also fill in signaling message parameters, such a broadband high layer information (HLI) based on knowledge about the mobile s application layer interfaces This reduces the number of parameters that need to be specified in the SETUP request received over the air interface For end points operating in mode II, the message flow for outgoing call/connection setup is similar to that shown in Figure 4 The only difference is that the visitor USS in Figure 4 is replaced by the home USS Features are checked in the home user signaling server For example, if speed dial is a subscribed-to service, the home user signaling server stores the required data and provides the service For end points operating in mode III, the CHECK FEATURES operation needs to be performed at both the visitor and home USS For end points operating in mode IV, the CHECK FEA- TURES operation is not required at all Instead the serving simply continues setting up the connection by sending the to the next switch on the path For end points operating in mode III, given that a visitor USS is involved, if all outgoing call features are downloaded to the user process in the visitor USS, outgoing call/connection setup delay can be reduced by eliminating the need to query the home USS for call control However, we have retained the possibility of mode III operation even for outgoing calls in order to accommodate any explicit user requests or provider mandates not to download service profile data and triggers

4 32 Incoming Call/Connection Setup Procedure This procedure is described for the four modes of operation described above First, we consider mode I operation Typically, an end point that has no subscribed-to services which requests a dynamic user process during registration operates in this mode The home USS is involved in the setup procedure only to provide location information, while Ports PAGE Page response Server (User Process) Figure 2 OFFER CONNECTIONS Offer connections response Home User Server LOCATE&CALL_RQST Locate response the visitor USS provides services that are dynamically requested from the user process during registration As shown in Figure 2, the originating or home sends a LOCATE&CALL_RQST to the home USS of the called party Since the mobile has no subscribed-to services, the home USS simply returns the location of the mobile as a temporary directory number This number identifies the on which the mobile is located Connection setup proceeds from the originating/home to the serving using the SS7 ( System No 7) Initial Address Message () Routing of the connection and the signaling messages is based on the identity of the serving indicated in the temporary directory number Note that the user plane connection to the mobile from the originating or home passes through transit switches, a serving, and a radio port The visitor USS and home USS are simply nodes involved in the signaling control plane communication Since the knows that the mobile is registered as an end point with a dynamic user process, upon receiving an, the serving offers the connection to this process in its visitor USS The user process pages the mobile after invoking appropriate service control features For example, if call forwarding on busy is a feature that was dynamically requested by the end point, the user process can check to see if the mobile is busy and thus answer the OFFER CONNECTIONS message with a forwarded number allowing the to continue routing the connection to the appropriate forwarded number Features such as call forwarding on no-answer require the involvement of the user process after the connection is set up to the mobile The determines that the mobile user does not answer only after completion of connection setup to the mobile In this case, it must notify the user process in the visitor USS to check for the call forwarding on no-answer feature If this feature is activated, the user process returns a forwarded number to the allowing it to redirect the connection setup procedure If an end point starts in this mode of operation, and requests many services dynamically involving significant amounts of service data, migrating this data from one visitor USS to the next as the end point moves may cause excessive signaling load A modification of the mode of operation to involve a home USS as well (mode III) may be justified based on the amount of service data Next, we describe the procedure for incoming call/connection setup to a end point operating in mode II where only ACM Incoming Call/Connection Setup for a Type I End Point Transit Switches Originating or Home Ports PAGE Page response Figure 3 ACM Home User Server Originating or Home LOCATE&CALL_RQST Locate&Call_rqst response Transit Switches Incoming Call/Connection Setup for a Type II End point the home USS is involved without a visitor USS, as shown in Figure 3 Typically, end points that register without requesting a dynamic user process, and that have subscribed to IN-based services none of which require the home USS to create a user process in a visitor USS operate in this mode The LOCATE&CALL_RQST is sent by the originating or home to the home user signaling server of the called party This server returns a temporary directory number identifying the on which the mobile is located It also checks for any IN-based features and triggers service control if required For example, if the called mobile had subscribed to unconditional call forwarding and had activated

5 Home User Servers Home User Servers Server ATM Switching Center () ATM Switching Center () Server Port Port Fixed End points (such as signaling transfer points in System No 7 networks) This network architecture is flexible and supports different types of users End points that have subscribed-to services as well as end points that have no such services are supported in these networks Either type of end point may request that a visitor USS provide user control functions on its behalf For such mobiles, as well as mobiles that subscribe to services that require call control functionality to be executed at a visitor USS, we introduce the notion of a user process One such process is created for each such mobile in the visitor USS associated with the at which the mobile is located The involvement of the home USS and the visitor USS are both optional for call control and user control functions However, home user signaling servers are needed for location control for all mobiles While the home user signaling servers and visitor user signaling servers appear similar to the home location register (HLR) and visitor location register (VLR) of the IS-41 cellular networks, there are some important differences in their functionality These differences are described in Section 4 3 PROCEDURES In this section of the paper, we describe various procedures to track mobiles, deliver incoming calls/connections to mobiles (requires mobile location), and handle call/connection requests originated by mobiles 31 Registration Figure 1 ATM-based PCS Network Architecture When a mobile powers-on, a registration message is sent to the home USS of the mobile through a radio port and This message indicates whether a dynamic user process should be created in a visitor USS or not Both types of end points, with or without subscribed-to services, may choose this option If a dynamic user process is created, it acts as surrogate for the mobile and limits communication over the air interface to the mobile whenever possible The user process corresponding to a mobile is migrated as the mobile changes zones, thus ensuring its easy access by the mobile for frequent data changes [5] Since a visitor USS is associated with each, the user process is migrated from the visitor USS associated with the old (zone) to the visitor USS associated with the new (zone) Using home and visitor user signaling servers, both telephony-oriented and data-oriented users can be supported in these PCS networks Based on whether both types of USS, one type of USS, or no USS, are involved in handling user service profiles for a mobile, end points operate in one of four modes In mode I operation, only a visitor USS is involved for service profile data management In mode II operation, only a home USS is involved In mode III operation, the end point uses the services of both a home USS and a visitor USS Finally, end points operating in mode IV do not require either type of USS for user service profile data management An end point may operate in any of these modes, irrespective of whether it is a simple data laptop, sophisticated multimedia laptop, or a phone Also, an end point does not have to explicitly request a specific mode of operation For end points that have subscribed to certain IN-based services which are dependent on the state of called party or other dynamic information, the home USS may choose to create a user process upon receiving a power-up registration even if the registration message from the mobile does not have an explicit request for such a process For example, the home USS of an end host that has subscribed to services such as call forwarding on no-answer, may choose to create a user process for this end point at the serving visitor USS in order to eliminate excessive messaging to the home USS during call/connection setup These features can be supported even if the home USS does not download service triggers or data although at the cost of increased call/connection setup delay Incoming and outgoing call/connection setup procedures are described for the different modes of operation in the next two sections

6 User Servers for ATM-based PCS Networks M Veeraraghavan & T F La Porta R Ramjee AT&T Bell Laboratories Department of Computer Science 101 Crawfords Corner Road University of Massachusetts Holmdel, NJ Amherst, MA Abstract Different models for user service profile management exist in telephony wireless intelligent networks and in data networks This paper presents a balanced solution to this problem by providing PCS subscribers access to a new element called a user signaling server Two types of user signaling servers, home and visitor, are defined to provide users both the flexibility of the data networking model in which services are requested as needed as well as the option to subscribe to IN-based services as in the telephony model This approach provides mobile PCS users savings in air interface and computing resources, reduces signaling load (air interface and network) and call/connection setup delay 1 INTRODUCTION Network architectures are being designed to support Personal Communication Services (PCS) for mobile users Upgrades to both cellular telephony networks and wireless data networks are being planned to support multimedia PCS applications Telephony networks and data communication networks have adopted different approaches for managing user service profiles Telephony users have relied on Intelligent Networks to store user profiles and trigger services, such as call forwarding In IS-41-based wireless intelligent networks [1], signaling procedures are used during mobile registration and call origination/delivery to provide services based on prestored triggers and user profile data On the other hand, data network users have relied on their intelligent end equipment to store their user profiles for similar services, such as mail forwarding This approach requires communication with the end point for service control It entails using valuable air interface and mobile end point computing resources Both telephony and data users are expected to coexist in multimedia PCS networks Asynchronous Transfer Mode (ATM) is becoming increasingly prevalent as a key technology for multimedia applications, and is hence being considered for next-generation PCS networks [2][3] Neither of the two models for user service profile management, the telephony/in-based model or the data communications model, is well-suited for multimedia applications in ATMbased PCS networks Some information, such as current execution environment (is X-windows running?), may be relevant before an end point accepts or rejects a connection request Such information is dynamic and cannot be prestored in the network, making the telephony model unsuitable for such end points On the other hand, PCS users may want to subscribe to IN-based services, such as the closed user group (CUG) service or call forwarding on busy Such services are not supported by the data communications model In this paper, we describe a new architectural element, called the User Server, to manage user service profiles in PCS networks Our solution accounts for the drawbacks listed above We describe how our solution manages user profiles and supports multiple modes of operation for different end points in PCS networks 2 ARCHITECTURE Figure 1 shows a network architecture with mobile and fixed end points, radio ports and ATM mobile switching centers (s) In ATM networks, call control is expected to be separate from connection control Call control consists of the functionality that triggers services prior to connection establishment and supports end-to-end negotiation [4] To handle call control and location control (tracking and responding to location queries) functions, we introduce a new type of element called a User Server (USS) These elements are of two types: home user signaling servers and visitor user signaling servers A mobile s home user signaling server tracks its current location There is only one level of mobile tracking whereby the home USS tracks the on which the mobile is located Each is designated to be a zone and mobiles generate zone-change registrations as they move The home USS also stores any (semi-)static service profile information, including triggers and data (such as closed user group information or call forwarding number), for its mobiles During call origination or delivery, it provides the call control function of service invocation based on the triggers stored The visitor user signaling servers are used to temporarily store user profile data and service triggers for mobile end points This information is either downloaded from the home USS or uploaded from the mobile during registration In the former case, the visitor USS is seen to provide the call control function of service invocation for the service triggers downloaded from the home USS In the latter case, it is viewed as providing user control functions by acting as a surrogate for the mobile in order to reduce air interface signaling Since ATM networks will support heterogeneous end points, end-to-end negotiation may be needed prior to connection setup The visitor USS performs such negotiations as part of its user control functions As shown in Figure 1, a visitor USS is collocated with each, while the number of home USS is dependent on the number of mobiles The home USS are connected to the s/visitor USS via direct ATM signaling logical links or via datagram routers