DESCRIPTION OF RELATED ART As Internet is being more and more popular we tend to spend more and more time in front of our computers while connected to Internet. The most common way of connecting to Internet is by using a modem and the connection times are far longer than the time usually spent in a traditional voice conversation. For home users the use of the telephone line for connectiong to Internet can lead to a conflict since most subscribers only have one line which shall serve both computer communication and voice communication.

In the Swedish patent application SE-9602212-4 is a method for enabling a subscriber to make and receive voice calls during an on-going Internet session disclosed.

In the Swedish patent application SE-9603932-6 the methods disclosed in SE-9602212-4 is further developed and additional problems solved.

The general idea of the above mentioned applications is that a user, connected to Internet via a modem using his ordinary telephoneline, register with a service using a special application in his computer. The service connects the users telephone number to a special number activating a IN service so that whenever a call is placed towards the user, it is redirected to the special number. When the IN service is activated it activates a gateway which connects, via Internet, to the application in the users computer and alerts the user who

can the answer the call. Alternatively can the users number be directed direct to a voice gateway.

In a similar manner, the user can place an outgoing call using the gateway to act as a bridge between the IP-based Internet and PSTN. In this situation it seems from the PSTN network point-of- view as if the gateway is making the call and should be charged.

A solution to this problem is presented in SE-9603932-6.

None of the above mentioned applications discloses specific methods for registration or configurations which will increase the reliability of the services and how this can be solved.

SUMMARY OF THE INVENTION The present invention discloses a method and a network for solving the problem with user registration in a network configuration with increased reliability.

The purpose of the present invention is thus to be able to register a user in a network configuration with increased reliability.

The problem described above, with how to achive registration in a network with increased reliability is solved by letting the client register with a first registry function which supplies the client with the adress of a second registry function as well as at least one, preferrably two, adresses of voice gateways and that said client register with said second registry function.

In more detail, the problem described above is solved by letting the client send a first message to a first registry. The registry performs authentication of the client and sends back a message comprising the IP-adress of a second registry function and one or several IP-adresses of voice gateways in dependance of the result of the authentication. The IP-adresses of the

voice gateways received with the second message are arranged in priority order and stored at the client. The client sends a third message to the second registry. The second registry performs authentication of the client and sends a fourth message comprising the IP-adress of the first registry as well as one or several IP-adresses of voice gateways in dependance of the result of the authentication. Since the client knows that it is already registered at the first registry it does not send a message to the first registry. The IP-adresses of the voice gateways received with the fourth message are arranged in priority order and stored at the client.

Through this procedure the client is registered and authenticated at two different registry's. In case of failure of one of them the voice gateways can confirm the authentication with the other functional registry. Likewise, since the client has received at least two IP-adresses to different voice gateways, the client can utilise the other in case of a failure in one of the voice gateways.

An advantages of the present invention is that network security is increased.

Another advantage is that a priority list of voice gateway is established which will enable the client to use the voice gateway which is currently the best choice dependent on traffic situation, congestion or load.

Other advantages will be obviouse to a man skilled in the art in the light of the detailed description given below.

Further scope of applicability of the present invention will become apparent from the detailed description given herein after. However, it should be understood that the preferred embodiments of the invention, are given by way of illustration

only, since variouse changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description BRIEF DESCRIPTION OF DRAWINGS Figure 1 discloses the interfaces for the phone doubler.

Figure 2 discloses a more detailed view of the network configuration of the phone doubler.

Figure 3 shows a network configuration of a preferred embodiment Figur 4 shows a signalling diagram DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 depicts the Phone Doubler network and its external interfaces to external networks, users and units. A User 101 is the person using Phone Doubler at home. The user 101 is also the subscriber of the service. A ISDN 102 (Integrated Services Digital Network) is used as gateway to a PSTN 103 (Public Switched Telephone Network). An SP 104 (Service Provider) is the system, organisation and persons responsible for the successful operation of Phone Doubler 105. Also In figure 1 is the Phone Doubler inner structure showed. Client 106 is the part of Phone Doubler that is located at the user's premises. A Registry 108 is a node within the gateway that is common for all users of the Phone Doubler service. This node is referred to as the registry in the remainder of this document. A VG 107 (Voice Gateway) is the unit that processes all calls and speech transmission. A VG 107 can handle a number of simultaneous calls. In figure 1 are also the interfaces external to the network and nodes identified. A UI 109 (User Interface) is the interface between the User 101 and the Client 106. PRI 110 (ISDN Primary Rate

Interface) is the interface used between the VG 107 and the ISDN 102. OMI 111 (Operation and Maintenance Interface) is the interface between SP 104 and the registry 108 and VG 107. A CLGI 112 (Client Gateway Interface) is the interface between the Client 106 and the registry 108 respectivly the client and the VG 107. A REGI 113 (Registry Interface) is the interface between the registry 108 and the VG 107.

Referring to figure 2, the client 201 is running on a PC (not shown), connected to the ISP's (Internet Service Provider) AS 207 (Access Server) at the ISP's POP (Point Of Presence) via a modem 202 and PSTN 203. The PC is given an IP address by the ISP. This is normally done dynamically when connecting to the POP. In the present preferred embodiment the ISP and the SP 104 is the same organisation or service provider. The VG 203,204 is connected to the ISP's IP network, typically on the same ES 205, 206 (Switched Ethernet) as the POP. Several VGs 203,204 can be connected at one POP. Each VG 203,204 is connected to ISDN 208 via PRI 209,210. One Registry node 211,212 can handle several VG: s 203,204. The Registry node 211,212 can physically be remotely placed. The VG 203,204 and Registry 211,212 are then typically connected to each other via the ISP's backbone IP network 213. The Registry node 211,212 is normally duplicated for redundancy reasons. Several Routers are denoted with an R in figure 2.

In figure 3 the client 301 is connected to Internet 302 as is a first registry 303 and a second registry 304. Also connected to Internet are a first voice gateway 305, a second voice gateway 306 and a third voice gateway 307. The first 305, second 306 and third 307 voice gateway are also connected to the ISDN network 307 which in turn has connection with the PSTN network 308.

Associated with the client 301 is also a table 309 comprising the different voice gateways and their IPadresses.

In figure 4 is a signalling scheme for the registration shown.

The following association between numbers in the figure 4 and messages names apply.

1. MSG1 comprising a request for registration. When MSG1 arrives at the first registry 303 an authentication process is started which might involve further signalling towards the cliant 301 not shown here.

2. MSG2 comprising the IP-adress of the second registry 304 and the IP-adresses of voice gateways 304 and 305. In this preferred embodiment only two voice gateways are shown but a configuration with any number of voice gateways is of course possible. When MSG2 arrives to the client 301 the IP-adresses are stored in the client.

3. MSG3 comprising a request for registration. When MSG1 arrives at the second registry 304 an authentication process is started which might involve further signalling towards the cliant 301 not shown here.

4. MSG4 comprising the IP-adress of the first registry 303 and the IP-adress of voice gateway 306. In this preferred embodiment only one voice gateway is shown but a configuration with any number of voice gateways is of course possible. When MSG4 arrives to the client 301 the IP-adresses are stored in the client.

Through this procedure the client 301 has two registrys 303 and 304 to choose from and three different voice gateways 304,305 and 306.

The central registry nodes may serve several distributed voice gateway modules and form a wide area distributed gateway.

Wide-area distribution issues

As long as the gateway contains a single set of VGs collocated with the POP access server, sufficient IP throughput between modems and VGs is simple to ensure (all devices reside in the same LAN environment). A single ISDN group number will also be sufficient to server all VGs.

When the Phone Doubler service is scaled up to form a wide area gateway, each POP has one or several VGs, served by a central registry node. This ensures that voice traffic is guaranteed to have minimum latency and jitter, since the voice traffic through routers is avoided.

Client data The client has the following data: * Telephone number, made up from country code, area code1, and local number. Example :"46-08-6678054" * Authentication data which is in the present preferred embodiment a ONF (ONe way Function) applied to the concatenation of country code, area code, local number and password. (optional, persistent) * Client IP address (volatile) * Host name 1 of registry.

"Host name 2 of registry.

* Primary VG IP address (volatile) Secondary VG IP address (volatile) Reject incoming calls (volatile) All of these data can be obtained at the sign-on procedure except for Telephone number and Authentication data.

'Optional in markets such as Denmark, where area codes are not used.

The combination of country code, area code, and local number identifies each subscriber uniquely.

The VG IP address attribute also represents the state of the client: A null address indicates signed-off, any other address indicates signed-on.

REGISTRY DATA Subscriber record Both the registry nodes holds an identical collection of subscriber records with the following attributes: telephone number (key, persistent, made up from country code, area code, and local number) authentication data, A ONF applied to telephone number concatenated with password (persistent) 'state. Enabled or disabled.

* client IP address (secondary key, volatile) * user-id (optional) 'primary VG (volatile) * secondary VG (volatile) 'number of sign-ons (persistent) * number of incoming calls (persistent) * number of outgoing calls (persistent) * first sign-on (persistent) last sign-on (persistent) The client IP address attribute also represents the state of the subscriber record (a null IP address represents signed-off, any other address represents signed-on).

E. 164- IP-address association

When a user is connected to the Internet, the IP address of the client is entered into the subscriber record in both registry nodes. Since both the telephone number and this IP address are keys, an E. 164-IP-address association between the telephone number are and IP address is maintained in the subscriber record.

Registry configuration data The following data are configurable in the registry: Data that are to identical in both registry nodes: 'User provisioning mode, automatic or manual.

* Auto sign-off period (optional, must be greater than the PPP inactivity time-out) Number of password retries * Auto removal period (optional) Country code Trunk prefix (optional) * SMTP-mail server (for e-mail-based alarm handling) * Mail receivers (list of e-mail addresses that will receive alarms) * Time synchronization host. Host name to time synchronisation host Data that are unique for each registry node 'Host name of redundant registry node. (optional) * FTP account in redundant registry node Emergency numbers Data that may be equal in both nodes: Hosts granted access to the WWW-server * Hosts granted access to the FTP-server

VG record The gateway configuration is defined by a set of VG records.

This set of records is held by the registry, and updated on certain events such as start-up and shut-down of VGs.

* IP Address (key) Name Primary client networks (only clients in these networks are served by this VG during normal operation) Secondary up client networks (clients in these networks may be served by this VG when an other VG fails) Maximum signed-on users Currently primary signed-on users Currently secondary signed-on users VG configuration data The VG holds a set of configuration data that are unique for each VG: Dial out prefix * IP-addresses of registry. Optionally two, if redundant register.

Monitor interval.

Number extraction method (calling (A), called (B) or redirecting number) Hosts granted access to the FTP-server * Network charging Registry redundancy To make it possible to maintain the service in a single registry node failure mode.

* The registry peer host name is set in each registry * The VGs are configured with the IP-addresses of both the registry nodes.

'The client nodes are initially configured with the host names of one of the registry nodes. The host name of the second will be send to the client on sign-on to the first.

The subscriber management function usage cases is performed towards one of the nodes. This node replicates the changes to the other node via FTP.

Alarms will be sent from both nodes. The registry log can be fetched from any of the nodes.

Sign-on and sign-off requests from the client is issued to both the registry nodes. In this way are both equally updated.

The auto sign-off function runs in both nodes and are not synchronised.

ERROR MODES Single node error In this case one of the two registry nodes is unavailable due to a SW or HW error in the node or in the IP network.

Detection: The VG detects it by supervising the registry nodes with its monitor interval.

The other registry node will detect it when trying to replicate a subscriber or VG data or when receiving an alarm form a detecting VG.

The client detects it when the client can not access one of the registry nodes for sign-on

Consequences: 'The end user service fully operational.

* The subscriber management function is disabled * The VGs and clients uses the operating node * The registry node must be dimensioned to serve all VGs in this situation.

* The VGs enter an sleep and retry loop in which them try to get in contact with the failing node with its monitoring interval.

* The clients enter an sleep and retry loop in which them try to get in contact with the failing node each 120 s. They do their first try after 120 s.

Recovery: The subscriber management function is enabled.

The VGs will re-establish contact and thus start load sharing of registry queries.

Also the clients which has signed-on during the error situation will within 120 s update their sign-on to the recovered registry node.

Communication error Three situations can occur: 1. The two registry nodes looses contact with each other, but clients and VG can still access both. This is rather odd error, which only can occur in odd designed networks.

2. One or several VGs and a group of clients looses contact with one of the registry nodes.

3. One or several VGs and a group of clients looses contact with both of the registry nodes

It is recommended to have redundancy also in the communication system. The described situations will, if so, less likely to occur.

Detection (1) : Both registry nodes will detect it when trying to replicate a subscriber management function 'The clients and VGs does not discover any error.

Consequences (1) : 'The end user service is fully operational * The subscriber management function is disabled Recovery (Situation 1) * The subscriber management function is enabled.

The registry to registry communication (clearance) alarm is sent from the registry that initiated the established contact.

Detection (2): VG detects when the registry query TCP connection is lost.

'The client detects it when the client can not access one of the registry nodes for sign-on Consequences (2): The XXX (error) alarm is sent from VG The end user service is fully operational Recovery (2) When the error is fixed the VGs will within its monitor interval re-establish contact and thus start load sharing of registry queries.

Also the clients which has signed-on during the error situation will within 120 s and update their sign-on to the recovered registry node.

Detection (3): * VG detects when both the registry query TCP connection is lost.

'The client detects it when the client can not access any of the registry nodes for sign-on Consequences (3): Users signed-on to the concerned VGs can not place and receive calls.

Recovery (3) When the error is fixed the VGs will re-establish contact with the two registry nodes. If only one is found the single node case or communication failure (2) case is entered Also the clients which has signed-on during the error situation will within 120 s and update their sign-on to the recovered registry nodes Double node error Detection: * The VG detects it by supervising the registry query TCP connection.

* The client detects it when trying to sign on.

Consequences: * The subscriber management function is unavailable Existing calls are unaffected * Its not possible to place and receive calls

User's trying to sign-on is asked to try later.

* The VGs enter an sleep and retry loop in which them try to get in contact with the failing node.

Recovery: When the error is fixed the VGs will within re-establish contact with the two registry nodes. If only one is found the single node case or communication failure (2) case is entered.

Users can start sign on again.

Users signed on when the error occurred will not receive any calls and if they try to place a call they will be informed that they need to first sign-on again.

We will thus in this error mode have a sever service outage.

VG redundancy To make it possible to offer end user service to all users, even if a single VG fails.

To achieve VG redundancy the system must be configured with at least two VGs.

Configure the primary and secondary client networks so that the desired redundancy is achieved.

When a user sign-on, it will be allocated to a primary and secondary VG. The primary VG is selected as described in the sign-on usage cases. The secondary is selected in the same way but with the additional condition that it is selected from the secondary client networks.

Error modes

One node stop In this case a VG fails, due to some HW or SW error.

Detection: The registry nodes detects that the VG fails by supervising the TCP connection to the VG.

The clients which has the VG as primary VG detects it when trying to place outgoing calls.

The ISDN detects that the VG's PRI does not respond.

Consequences: The clients uses the secondary VG. But will also remain to first try the primary VG when placing calls.

The registry marks the VG as disabled it the VG record, which will prevent new users to be assigned to the disabled VG.

ISDN can be set up to route calls to other VGs.

The blocking ratio will increase proportional to the ratio between the total number of VGs and the number of failed VGs.

The delays and jitter will increase for those calls routed a longer distance in the IP network.

Recovery : When the failing VG is up and running again, it will establish TCP connection with the registry node (s). The VG will be marked as enabled.

Clients will use the VG for outgoing calls as soon as it is available.

ISDN will detect it as soon as the PRI is alive.

Sign-on and sign-off functions Purpose To make it possible for the user to be connected to the Internet Service Provider's point-of-presence (POP), using his telephone line, and still be able to use that line and number for incoming and outgoing telephone calls.

The following addresses are of importance in these functions: * the user's telephone number * the client IP address * the ISDN number of the gateway General The sign-on and sign-off functions comes in two flavours, depending on the setting of the authentication mode attribute of the registry configuration.

In the auto provisioning mode the user is allowed to use the service if it's IP-address matches any client networks attribute of the VG-records. In this case the PoP's authentication is trusted and once passed, the user is trusted.

In this mode only charging on IP-addresses may be used and thus network charging. We can't trust the telephone number the user states.

The other, manual, mode means that user must be registered in the system by some administrative procedure into the system, see the subscriber management function. In order to use the service in this mode the users have to go through an authentication procedure also in the Phone Doubler system.

The authentication procedure is based on the challenge response mechanism [Ref. Computer Communications Security, Warwick Ford, Prentice Hall, ISBN 0-13-799453-2]. As ONF the MD5 algorithm can be used [RSA Data Security, Inc. MD5 Message-Digest Algorithm].

ONF (X+Y) denotes below the application of the one way function to the concatenated string X+Y.

Sign-on in auto provisioning mode This usage case may only be entered if the state of the client is signed-off. Prior to this usage case the user is assumed to have set up Call Forwarding or (better) Call Forwarding on Busy to the ISDN number of the VG. This can be done with a telephone set or otherwise (software support for this is not provided in the product). In another embodiment the Call Forwarding is handled automatically by the service.

The client checks that the user's Internet session is active.

The client saves its current IP address in the client IP address attribute of the client, for reference by other usage cases (outgoing call set-up and sign-off). The client connects to the registry and transfers the telephone number of the user. The registry retrieves the IP address of the client as a parameter of the ongoing TCP session. Note that the client IP address will be different between Phone Doubler sessions if DHCP is in use.

The registry selects a VG and hands over its IP address to the client. The selection of a VG is done by the registry as follows: (1) select those VG records for which the user's IP address match the primary client networks attribute of the VG, (2) select the VG record having the greatest difference between maximum signed-on users and primary signed-on users, (3) check that the maximum signed-on users limit will not be exceeded for the selected VG, and (4) check that the selected VG is not

disabled. The selected VG record's currently primary signed-on attribute is incremented.

The registry checks for the existence of a subscriber record with the stated telephone number. A check is made that the client IP address is not associated with any telephone number in the registry at this point. A check is made that the state of the subscriber record is enabled and signed-off.

The subscriber record is updated (the client IP address, number of sign-ons, and last sign-on attributes are updated). The PSTN- IP association is thereby established, and the previous checks ensure that it is unambiguous in both directions. The currently signed-on users attribute of the VG record is incremented. The VG IP address is set in the client. The client disconnects from the registry.

If the Internet session is not active the user is advised to start an Internet session and try to sign on again. If the registry is not accessible, the user is informed of this and asked to retry later. The incoming and outgoing call functions will not be available until the client has been successfully signed on. The usage case is terminated.

If the client IP address is not acceptable according to any of the client networks parameters in the VG-records the usage case is terminated. No information is presented to the user, as this exception may be a case of illegal use.

If, due to lack of resources, no VG is available to select, the user is informed of this. The client disconnects from the registry and the usage case is terminated.

If no subscriber record exists for the telephone number provided by the client, a new subscriber record is created. The following

attributes are filled in: telephone number, client IP address, first sign-on. Obvious default values are filled in for the remaining attributes. After this the present usage case may proceed. In another embodiment is no new subscriber record created but rather the usage case terminated.

If, prior to this usage case, the client IP address is associated to some user's telephone number in the registry, this association is obviously invalid. The forced sign-off usage case is executed repeatedly for every such telephone number, until no association from the client IP address to some user's telephone number remains. After this the present usage case may proceed.

If the subscriber record indicates that the user is already signed on (from any client IP address), the forced sign-off usage case is executed. After this the present usage case may proceed.

If the subscriber's state is disabled the user is rejected access and the usage case is terminated.

Sign-on manual mode The difference in this case is that the user has to be defined by the service provider prior to sign-on. In the below the addition to the auto mode case is described.

The client first request to start the sign-on procedure by signalling this to the registry. In this message the telephone number is transferred.

The registry checks that a subscriber record, with that telephone number as key, exists and retrieves a non repeating value (NRV) and associates that NRV with the subscriber. This

NRV is sent to the client which then responds with ONF (ONF (telno+password) +NRV).

NRV can be for instance current time is milliseconds.

ONF (telno+password) is either fetched from the client configuration or calculated as result of a password prompt dialogue with the user. Which mechanism to use is user defined.

The registry takes the authentication data (AD) in the subscriber record, then compares ONF (AD+NRV) with the value received from the client. If these values are equal the user is authenticated and a counter of authentication failures to zero.

If the user is non existing the user is informed that he has to contact the service provider to be registered.

On authentication failure a counter authentication failures is incremented. If this counter exceeds number of password retries the user is disabled.

If the user already is signed on he is informed of this.

In all other parts the exceptions from the auto case remains.

Sign-off, auto mode The client checks that its state is signed-on.

A reminder to cancel his Call Forwarding setting is presented to the user. Unfortunately, cancellation of Call Forwarding cannot be done until the Internet session is finished (outside the scope of the Phone Doubler product).

The forced sign-off usage case is executed.

The client disconnects from the registry.

If the client state is not signed-on, the usage case is terminated with no further action (shutdown of the client may proceed).

If the registry is not accessible, the usage case is terminated.

Shutdown of the client may proceed. This will lead to an invalid association between the user's telephone number and the client IP address, lasting until it is cleared by a sign-on, auto-sign- off or incoming call set-up usage case.

Sign-Off, manual mode The client checks that its state is signed-on.

A reminder to cancel his Call Forwarding setting is presented to the user. Unfortunately, cancellation of Call Forwarding cannot be done until the Internet session is finished (outside the scope of the Phone Doubler product).

The forced sign-off usage case is executed.

The client disconnects from the registry.

If the client state is not signed-on, the usage case is terminated with no further action (shutdown of the client may proceed).

If the registry is not accessible, the usage case is terminated.

Shutdown of the client may proceed. This will lead to an invalid association between the user's telephone number and the client IP address, lasting until it is cleared by a sign-on, auto-sign- off or incoming call set-up usage case.

Forced sign-off

Other usage cases relying on this one are: Sign-on, Sign-off, Incoming call set-up, Auto-sign-off.

The association between the user's telephone number and the client IP address is broken (The subscriber record is updated).

In the VG records, corresponding to the subscriber record's primary and secondary VG, the current primary and secondary signed-on users is decremented.

The registry log is updated.

Auto-sign-off This usage case is executed periodically in the registry, without manual intervention. The purpose is to remove incorrect information from the subscriber records. The periodicity is given by the auto sign-off period attribute of the registry. It should be reasonably short, since this is how an accidentally disconnected user gets salvaged and can sign on again. It must however be longer than the PPP inactivity time-out, in order not to interfere with that function of the ISP's Internet service.

Examine each subscriber record and carry out the steps below: If the state of the subscriber record is signed-on, verify that the client is actually alive by connecting to it. If the client is not alive, execute the forced sign-off usage case for this subscriber.

If the client is alive but its telephone number does not match the telephone number attribute in the subscriber record, issue a number inconsistency at auto-sign-off alarm and execute the forced sign-off usage case for the subscriber indicated by the subscriber record.

If the client has not been signed on for a very long time (according to the auto removal period defined in the registry), the subscriber record is deleted.

Relation between client UI and usage cases The UI of the client is closely related to the sign-on and sign- off usage cases.

When the client is started it will establish a connection to the ISP's IP network, if not done already by some other application.

The sign-on usage case will then be executed automatically.

The client UI also provides a menu choice or push-button by which the user may request a sign-on. This is meaningful e. g. if the initial sign-on failed for some reason.

When the client is terminated the sign-off usage case is executed automatically.

Incoming call function The incoming call function makes it possible for the user to be connected to the point-of-presence (POP), using his telephone line, and still be able to receive telephone calls on that line and number.

The A-party is the party calling the user's telephone number, which is diverted to the ISDN group number of a VG cluster. In another embodiment the telephone number of the user may be diverted to a IN service.

Addresses The following addresses are of importance in this function: * the user's telephone number

'the client IP address 'the A-part's telephone number 'the voice gateway's ISDN-number Usage cases Incoming call set-up A-part dials B-part's telephone number, which is forwarded to the UAN (Universial Access Number).

The call is originated from the PRI interface. During call set- up the B-part's telephone number is extracted from the Q. 931 signalling over PRI. The type of number to extract is configured in the number extraction method.

If the trunk prefix parameter is present its value is prepended to the B-number.

Then the country code parameter is prepended to the B-number.

The VG connects to the registry and looks up the subscriber record of the B-part's telephone number. The client IP address is retrieved from this record.

The VG disconnects from the registry.

A connection is established to the client, using the IP address that was fetched from the registry.

The client indicates an incoming call to the user via the UI.

The A-party's telephone number is not presented.

Any of the following usage cases are then possible: 'Incoming call answer * Incoming call reject

* Incoming call A-part hangs up during ringing * Incoming call ISDN time-out during ringing If the VG is disabled the B-part is signalled to be busy in PRI and the usage case is terminated.

If the B-parts telephone number is not provided in PRI the call cannot be handled. The B-part is then signalled to be congestion in PRI and the usage case is terminated.

If VG fails to connect to the registry and the registry is redundant this usage case continues with the using the other registry.

If the VG fails to connect to the registry the B-part is signalled to be busy in PRI and the usage case is terminated.

If there is no subscriber record for the provided B-number, the call cannot be handled. The VG disconnects from the registry, the B-part is signalled to be busy in the PRI and the usage case is terminated.

If the B-part's telephone number is not associated with an IP address, the VG disconnects from the registry and the B-part is signalled to be busy in the PRI. The usage case is then terminated. This exception will occur for a user who has signed off and forgotten to cancel his call forwarding.

If the establishment of a connection to the client on the indicated IP address fails, the B-part is signalled to be busy in PRI. The present usage case is then terminated.

If the connection to the client succeeds, but the telephone number of the client is not equal to the B-part's telephone number, the B-part is signalled to be busy in PRI. The present usage case is then terminated.

If the reject incoming calls flag is set in the client the B- part is signalled to be busy in PRI and the usage case is terminated.

If the client software is busy the B-part is signalled to be busy in PRI and the usage case is terminated.

If the client cannot allocate any audio device a message is presented to the user. This message informs him that there is an incoming call, and that he has two options: (1) terminate the application that uses audio and pick up the call, or (2) reject the call. If (2) is selected, the B-part is signalled to be busy in PRI and the usage case is terminated. If (1) is selected, another attempt is made to set up the call. Should this attempt also fail because the audio device is not free, the same message and options are presented repeatedly.

Incoming call answer This usage case can only occur after the incoming call set-up has succeeded. The user chooses to answer the call. The client updates its status message. Speech transmission starts.

Incoming call reject This usage case can only occur after the incoming call set-up has succeeded.

The B-part is signalled to be busy in the PRI.

All resources that were allocated for the call are released in the client and the VG. The VG disconnects from the client.

Incoming call A-part hangs up during ringing

This usage case can only occur after the incoming call set-up has succeeded.

This usage case is triggered from the PRI.

All resources that were allocated for the call are released in the client and the VG. The user is informed that the A-part has hung up.

The VG disconnects from the client.

Incoming call ISDN time-out during ringing This usage case can only occur after the incoming call set-up has succeeded.

This usage case is triggered from the PRI. It occurs after a while if the B-part (i. e., the Phone Doubler user) does not act at all, and the A-part does not hang up.

All resources that were allocated for the call are released in the client and the VG. The user is informed that the call was disconnected.

The VG disconnects from the client.

Incoming call B-part hangs up during talking This usage case can only occur after the incoming call answer has succeeded, i. e. when speech transmission has been established.

All resources that were allocated for the call are released in the client and the VG, and on-hook is signalled in the PRI. The VG disconnects from the client.

Incoming call A-part hangs up during talking

This usage case can only occur after the incoming call answer has succeeded, i. e. when speech transmission has been established.

This usage case is triggered from the PRI. All resources that were allocated for the call are released in the client and the VG.

The user is informed that the A-part has hung up (the VG does not wait for user confirmation of this message).

The VG disconnects from the client.

Outgoing call function To allow a user to make outgoing telephone calls to PSTN/ISDN while being connected over his telephone line to the ISP's point-of-presence (POP).

The following addresses are of importance in this function: 'the B-part's telephone number * the A-part's IP address To understand how these addresses are managed please refer to the configuration management function.

Usage cases The client performs a very limited number analysis of the B- number.

Outgoing call set-up It is required that the state of the client is signed-on.

A-part dials B-part's telephone number. No number analysis is performed in the client.

The client checks that its current IP address, as reported by the operating system, equals the previously saved client IP address attribute of the client.

The client checks for the existence of a free audio device on the client platform and reserves it.

A connection is established to the VG that was assigned to the client at sign-on.

A check is made that the IP address of the client may actually be served by the VG.

The dialled number is transferred to the VG. A very limited number analysis is performed as follows: If the trunk prefix parameter of the VG is non-empty. A check is made that the leading digits of the dialled number do match the trunk prefix.

If the dial-out parameter is present its value is prepended to the dialled number.

An ISDN call is set up to the called number.

If the network charging parameter is true the user's telephone number is signalled as user provided A-number in the PRI.

If the current client IP address differs from the previously saved client IP address attribute, the state of the client is set to signed-off. The user is advised to sign on again, and the usage case is terminated. This situation may arise if a user signs on, the PPP connection goes down, and a new PPP connection with a different client IP address is established.

If the client cannot allocate any audio device the user is informed of the reason and asked to close any application using the audio devices and then retry.

If the connection to the VG cannot be established, or if the state of the VG is disabled, the client tries to connect to the secondary VG. If this fails the user is advised to close the client and restart it (on the hypothesis that the user will thus be assigned another and better suited VG). The audio device is released and the usage case is terminated.

If the client IP address is not accepted by the VG a rejected IP address at outgoing call alarm is issued. The audio device is released and the usage case is terminated.

If the VG has no free capacity the user is informed of this and advised to retry later. A VG capacity exceeded alarm is issued.

The audio device is released and the usage case is terminated.

If the trunk prefix parameter of the VG is non-empty and the leading digits of the dialled number do match the trunk prefix a check is made if the dialled number is an emergency number. If it is an emergency number the usage case continues other wise the user is informed of that the number has an illegal format and the usage case is terminated.

If the called number cannot be reached the user is informed of the reason (busy, congestion, etc.). The audio device is released and the usage case is terminated.

Outgoing call answer This usage case can only occur after the outgoing call set-up usage case has succeeded.

The B-part chooses to answer the call.

The client updates its status message.

Speech transmission starts.

Outgoing call reject This usage case can only occur after the outgoing call set-up usage case has succeeded.

The B-part chooses to reject the call (as may occur if the B- part uses a GSM telephone). The VG sees a busy signal in the PRI.

All resources that were allocated for the call are released in the client and the VG. The user is informed that the B-part rejected the call (the VG does not wait for user confirmation of this message).

The VG disconnects from the client.

Outgoing call A-part hangs up during ringing This usage case can only occur after the outgoing call set-up usage case has succeeded.

The user hangs up before the B-part has acted.

All resources that were allocated for the call are released in the client and the VG. The status message in the client is reset to the idle message.

The VG disconnects from the client.

Outgoing call ISDN time-out during ringing This usage case can only occur after the outgoing call set-up usage case has succeeded.

This usage case is triggered from the PRI. It occurs after a while if the B-part does not act at all, and the A-part does not hang up.

All resources that were allocated for the call are released in the client and the VG. The user is informed that the call was disconnected by ISDN.

The VG disconnects from the client.

Outgoing call A-part hangs up during talking This is how successful outgoing calls are usually terminated.

This usage case can only occur after the outgoing call answer has succeeded, i. e. when speech transmission has been established.

All resources that were allocated for the call are released in the client and the VG. The status message in the client is reset to the idle message.

The VG disconnects from the client.

Outgoing call ISDN disconnect during talking This usage case occurs only infrequently.

This usage case can only occur after the outgoing call answer has succeeded, i. e. when speech transmission has been established.

The B-part hangs up. After a while the ISDN network disconnects the call (the VG sees this in the PRI).

All resources that were allocated for the call are released in the client and the VG. The user is informed that the call was disconnected by the B-part (the VG does not wait for user confirmation of this message).

The VG disconnects from the client.

Subscriber management function To make it possible to administrate the subscribers of the service. The need for service is expected to be small, consisting of occasionally deleting a subscriber record for which the password has been lost.

Usage cases Automatic subscriber removal The subscriber record of a user that does not sign on for a very long time gets deleted from the registry. See the auto-sign-off usage case under Fault Management. This will limit the subscriber table in the registry to consist of reasonably active Phone Doubler users. A user that gets removed from the registry can sign on again at any time.

Subscriber provision A management system can add a specified users via the OMI FTP- interface.

A human administrator can remove a specified user via the OMI HTTP-interface.

Changes made in one registry node are replicated to the redundant registry node.

Subscriber removal A management system can remove a specified users via the OMI FTP-interface.

A human administrator can remove a specified user via the OMI HTTP-interface.

Changes made in one registry node are replicated to the redundant registry node.

Add and remove subscriber to/from blacklist The subscription's state is set to disabled/enabled.

Can be done via HTTP and FTP Change password of subscriber Can be done via HTTP and FTP.

Subscriber analysis A human administrator can retrieve the subscriber-records via the OMI HTTP-interface.

Authentication function The authentication scheme is described in the sign-on and sign- off function.

To prohibit illegitimate use of the service. In particular, to reduce the risk that someone states the telephone number of another Phone Doubler user at sign-on.

Charging function Charging is supported in a number of ways: Registry logs is generated and can be retrieved for the purpose of charging periodical fees or statistical purposes.

Call logs are generated and can be retrieved for the purpose of charging per call charges or statistical purposes.

In manual provisioning mode users can be authenticated to be the legitimate user of its telephone number or user-id.

Users can charged based on their IP-address if the charging system can determine the user of a certain IP-address at a certain time. This must be based on logs from the access servers if DHCP is used.

Incoming calls can be charged based on service rates on the UAN.

In manual provisioning mode outgoing calls can be made with user provided A-number which can be used in the telephone networks charging system for charging of outgoing calls.

Performance management function To make it possible for the SP to monitor and adjust the resource utilisation of this service in the network.

Traffic in and out of the gateway is measured on the ISDN side, for which well known and understood tools and methods exist.

The registry log can be used for statistical analysis of sign-on and sign-off behaviour.

The call logs can be used as complement to the ISDN tools to analyse the telephony behaviour.

An alarm is sent if capacity was exceeded at outgoing call.

The invention being thus described, it will be obviouse that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvoiuse to a man skilled in the art are intended to be included within the scope of the following claims.