5 GA-RC elementary procedures for GANC Discovery

3GPP44.318Generic Access Network (GAN)Mobile GAN interface layer 3 specificationRelease 17TS

5.1 Purpose of the Discovery Procedure

The purpose of the Discovery procedure is to allow the network to allocate a Default GANC to a MS. This allocation consists of the IP address or FQDN of the Default GANC-SEGW, and the IP address or FQDN and TCP port of the Default GANC to be used for the Registration procedure. As long as the Default GANC is available in the network the MS shall not perform Discovery procedure again. The Discovery procedure is performed using the IPsec tunnel that is established between the MS and the Provisioning GANC-SEGW as defined in sub-clause 4.2.

5.2 Discovery procedure

The Discovery procedure is performed between the MS and the Provisioning GANC. The Discovery procedure is initiated by the MS in order to receive information about the Default GANC to be used for future instances of the Registration Procedure.

Figure 5.2: Discovery procedure

5.3 Discovery Request initiation by the MS

This procedure shall be triggered after the MS has gained IP connectivity (i.e. an IP address is allocated to the MS in the "transport IP" layer) and the MS has either no stored information about a Default GANC or if the previous Registration procedure towards the Default GANC was unsuccessful.

The MS may initially be provisioned with information (i.e. an IP address or a FQDN) about the Provisioning GANC and the corresponding Provisioning SEGW related to that GANC. The provisioning of this information in the MS is out of the scope of this document. This information can be in the format of either a FQDN or an IP-address or any combination of these.

The MS shall:

– If the MS holds an IP address of the Provisioning SEGW, the MS establishes the secure connection towards the Provisioning SEGW according to sub-clause 4.2;

– If the MS holds a FQDN of the Provisioning SEGW, the MS performs a public DNS query to retrieve the IP-address of the Provisioning SEGW and establish the secure connection towards the Provisioning SEGW according to sub-clause 4.2. The MS shall not store the IP address retrieved from DNS for subsequent procedures (apart from DNS resolver caching);

– In case the MS is not provisioned with information about the Provisioning SEGW, derive a FQDN of the Provisioning SEGW from the IMSI (as described in [3]);

The MS performs a public DNS Query to retrieve the IP-address of the Provisioning SEGW and establish the secure connection towards the Provisioning SEGW according to sub-clause 4.2. The MS shall not store the IP address retrieved from DNS for subsequent procedures (apart from DNS resolver caching);

– Following successful establishment of secure connection to the Provisioning SEGW:

– If the MS holds an IP address of the Provisioning GANC, the MS shall establish a TCP connection to the Provisioning GANC using the well-known TCP port for Discovery as defined in sub-clause 12.2.1

– If the MS holds a FQDN of the Provisioning GANC, the MS shall perform a DNS query "inside the secure connection" to retrieve the IP-address of the Provisioning GANC. The MS shall establish a TCP connection to the Provisioning GANC using this IP address and a TCP port defined for Discovery (see sub-clause 12.2.1). The MS shall not store the IP address retrieved from DNS for subsequent procedures (apart from DNS resolver caching).

– In cases where the MS is not provisioned with information about the Provisioning GANC, the MS derives a FQDN of the Provisioning GANC from the IMSI (as described in [3]).

A DNS query is performed "inside the secure connection" to retrieve the IP-address of the Provisioning GANC. The MS shall not store the IP address retrieved from DNS for subsequent procedures (apart from DNS resolver caching).A TCP connection is then established inside the IPsec tunnel, to the Provisioning GANC using the TCP port defined for Discovery procedure (see sub-clause 12.2.1).

– In all cases the MS shall establish only a single TCP connection to the GANC over the IPsec tunnel.

– After successful establishment of a secure connection to the SEGW and a TCP connection to the GANC the MS shall proceed as follows:

– If the Discovery Procedure is due to the MS failing to register with a GANC, the MS includes the following information elements in the GA-RC DISCOVERY REQUEST message: Register Reject Cause IE, Redirection Counter IE and Default GANC IE,

– Send a GA-RC DISCOVERY REQUEST message to the Provisioning GANC on the established TCP connection.

– When GA-RC layer has submitted the GA-RC DISCOVERY REQUEST message to the TCP layer, it shall start timer TU3901.

5.4 Discovery Request processing by the network

When receiving the GA-RC DISCOVERY REQUEST message the Provisioning GANC may either accept or reject the Discovery request from the MS.

5.4.1 Discovery accepted

If the Provisioning GANC accepts the Discovery request from the MS, it shall send the GA-RC DISCOVERY ACCEPT message to the MS. When the GA-RC layer in the Provisioning GANC has submitted the GA-RC DISCOVERY ACCEPT message to the TCP layer, it may initiate release of its half of the bidirectional TCP connection.

The Provisioning GANC may use the Redirect Counter IE, Register Reject Cause Value IE and Default GANC IE received in the GA-RC DISCOVERY REQUEST message to assign a different Default GANC for the MS.

5.4.2 Discovery rejected

If the Provisioning GANC rejects the Discovery request from the MS, it shall send the GA-RC DISCOVERY REJECT message to the MS. When the GA-RC layer in the Provisioning GANC has submitted the GA-RC DISCOVERY REJECT message to the TCP layer and the value of the Discovery Reject Cause IE included in the message was not ‘Network Congestion’, it may initiate release of its half of the bidirectional TCP connection.

The Provisioning GANC may use the Redirect Counter IE, Register Reject Cause Value IE and Default GANC IE received in the GA-RC DISCOVERY REQUEST message to detect a problem and reject the MS.

5.5 Discovery response processing by the MS

5.5.1 Discovery accepted

When the MS receives GA-RC DISCOVERY ACCEPT message, it shall:

– stop the timer TU3901.

– set the timer value for TU3903 to the default value,

– store the information about Default GANC in persistent storage:

– The Default GANC information consists of the Default GANC, SEGW associated with the Default GANC and optionally a TCP port to be used with that Default GANC. If a specific TCP Port is not received in the message, the defined port for Registration is used (see sub-clause 12.2.1)

– release the TCP connection towards the Provisioning GANC

– the secure connection to the Provisioning SEGW can be reused as follows;

– If the MS is provisioned with an IP address of the Provisioning GANC-SEGW and it matches the received Default GANC-SEGW IP address IE, the MS shall reuse the existing secure connection.

– If the MS is provisioned with a FQDN of the Provisioning GANC-SEGW or derived a FQDN for the Provisioning GANC-SEGW and it matches the received Default GANC-SEGW FQDN IE, the MS shall reuse the existing secure connection.

– otherwise the MS shall release the existing secure connection towards the SEGW of the Provisioning GANC as defined in sub-clause 4.5

– initiate the registration procedure towards the Default GANC as defined in sub-clause 6.2.

5.5.2 Discovery rejected

When the MS receives GA-RC DISCOVERY REJECT message it shall:

– stop the timer TU3901,

– set the timer value for TU3903 to the default value,

– If the value of the Reject Cause IE indicates ‘Network Congestion’ , the MS shall:

– Maintain the secure connection to the GANC-SEGW and the TCP connection to the GANC.

– Create a random value between zero and the received value in TU3902 Timer IE, and

– Add this value to the received value in TU3902 Timer IE, this becomes the new value for TU3902.

– Start timer TU3902 according to the new calculated value.

– If the value of the Reject Cause IE indicates ‘IMSI not allowed’ or "Unspecified", then the MS shall:

– Release the TCP connection established to the Provisioning GANC, if still established.

– Release the secure connection towards the SEGW associated with the Provisioning GANC as defined in sub-clause 4.5.

– Not initiate a new Discovery procedure until the next power-on.

5.6 Abnormal cases

5.6.1 TU3901 expiry

If timer TU3901 has expired in the MS, the MS shall:

– release the TCP connection towards the Provisioning GANC,

– release the secure connection towards SEGW of the Provisioning GANC as defined in sub-clause 4.5,

– double the current value for timer TU3903 but not exceeding the maximum value defined for this timer as defined in sub-clause 12.1.1 and

– start timer TU3903 and wait for it to expire.

5.6.2 Lower layer failure in the MS

Lower layer failure in the MS can be for example related to DNS, IPsec or TCP. If any lower layer failure happens in the MS, the MS shall:

– release the TCP connection towards the Provisioning GANC, if established,

– release the secure connection towards SEGW of the Provisioning GANC, if established, as defined in sub-clause 4.5,

– double the current timer value for TU3903 but not exceeding the maximum value defined in sub-clause 12.1.1,

– stop timer TU3901 if running and

– start timer TU3903 and wait for it to expire.

5.6.3 TU3902 expiry

If timer TU3902 has expired in the MS, the MS shall:

– if the TCP connection to the Provisioning GANC is still established:

– send a GA-RC DISCOVERY REQUEST message and

– start timer TU3901

– otherwise, restart the Discovery procedure as defined in sub-clause 5.3.

5.6.4 TU3903 expiry

If timer TU3903 has expired in the MS, the MS shall restart the Discovery procedure as defined in sub-clause 5.3.