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Content for  TS 23.401  Word version:  17.6.0

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5.3  Authentication, security and location managementp. 133

5.3.1  IP address allocationp. 133

5.3.1.1  Generalp. 133

The procedures of clause 5.3.1 apply to UEs activating a PDN connection of PDN Type IPv4, IPv6 or IPv4v6. Part of it also applies for PDN Type Non-IP when SGi PtP Tunnelling based on UDP/IP, see clause 4.3.17.8, is used. The procedures of clause 5.3.1 do not apply to UEs activating a PDN connection of PDN Type Ethernet.
A UE shall perform the address allocation procedures for at least one IP address (either IPv4 address or IPv6 prefix) after the default bearer activation if no IPv4 address is allocated during the default bearer activation.
One of the following ways shall be used to allocate IP addresses for the UE:
  1. The HPLMN allocates the IP address to the UE when the default bearer is activated (dynamic or static HPLMN address);
  2. The VPLMN allocates the IP address to the UE when the default bearer is activated (dynamic VPLMN address); or
  3. The PDN operator or administrator allocates an (dynamic or static) IP address to the UE when the default bearer is activated (External PDN Address Allocation).
The IP address allocated for the default bearer shall also be used for the dedicated bearers within the same PDN connection. IP address allocation for PDN connections, which are activated by the UE requested PDN connectivity procedure, is handled with the same set of mechanisms as those used within the Attach procedure.
PDN types IPv4, IPv6 and IPv4v6 are supported. An EPS Bearer of PDN type IPv4v6 may be associated with one IPv6 prefix only or with both one IPv4 address and one IPv6 prefix. PDN type IPv4 is associated with an IPv4 address. PDN type IPv6 is associated with an IPv6 prefix. PDN types IPv4 and IPv6 are utilised for the UE and/or the PDN-GW support IPv4 addressing only or IPv6 prefix only; or operator preferences dictate the use of a single IP version only, or the subscription is limited to IPv4 only or IPv6 only for this APN. In addition, PDN type IPv4 and IPv6 are utilised for interworking with nodes of earlier releases.
The way that the UE sets the requested PDN type may be pre-configured in the device per APN. Unless otherwise configured (including when the UE does not send any APN), the UE sets the PDN type during the Attach or PDN Connectivity procedures based on its IP stack configuration as follows:
  • A UE which is IPv6 and IPv4 capable shall request for PDN type IPv4v6.
  • A UE which is only IPv4 capable shall request for PDN type IPv4.
  • A UE which is only IPv6 capable shall request for PDN type IPv6.
  • When the IP version capability of the UE is unknown in the UE (as in the case when the MT and TE are separated and the capability of the TE is not known in the MT), the UE shall request for PDN type IPv4v6.
The HSS stores one PDN type per APN in the subscription data. During the Attach or UE requested PDN connectivity procedure the MME compares the requested PDN type to the PDN type in the subscription records for the given APN and sets the PDN type as follows:
  • If the requested PDN type is allowed by subscription, the MME sets the PDN type as requested.
  • If the requested PDN type is IPv4v6 and subscription data only allows PDN type IPv4 or only allows PDN type IPv6, the MME sets the PDN type according to the subscribed value. A reason cause shall be returned to the UE indicating that only the assigned PDN type is allowed. In this case the UE shall not request another PDN connection to the same APN for the other IP version during the existence of the PDN connection.
  • If the requested PDN type is IPv4 or IPv6, and either the requested PDN type or PDN type IPv4v6 are subscribed, the MME sets the PDN type as requested. Otherwise the PDN connection request is rejected.
  • If the requested PDN type is IPv4v6, and both IPv4 and IPv6 PDN types are allowed by subscription but not IPv4v6, the MME shall set the PDN type to IPv4 or IPv6 where the selection between IPv4 and IPv6 is implementation specific. The UE should then initiate the UE requested PDN connectivity procedure to this APN in order to activate a second PDN connection with the other single address PDN type which was not allocated by the network.
The PDN-GW may restrict the usage of a PDN type IPv4v6 as follows.
  • If the PDN-GW receives a request for PDN type IPv4v6, but the PDN-GW operator preferences dictate the use of IPv4 addressing only or IPv6 prefix only for this APN, the PDN type shall be changed to a single address PDN type (IPv4 or IPv6) and a reason cause shall be returned to the UE indicating that only the assigned PDN type is allowed. In this case the UE shall not request another PDN connection to the same APN for the other IP version during the existence of the PDN connection.
  • If the PDN-GW receives a request for PDN type IPv4v6, but the MME does not set the Dual Address Bearer Flag due to the MME operator using single addressing per bearer to support interworking with nodes of earlier releases the PDN type shall be changed to a single IP version only and a reason cause shall be returned to the UE indicating that only single IP version per PDN connection is allowed. In this case the UE should request another PDN connection for the other IP version using the UE requested PDN connectivity procedure to the same APN with a single address PDN type (IPv4 or IPv6) other than the one already activated.
During inter-RAT mobility between E-UTRAN and UTRAN/GERAN, an EPS bearer with PDN type IPv4v6 shall be mapped one-to-one to PDP type IPv4v6.
During inter-RAT mobility between E-UTRAN and UTRAN/GERAN, an EPS bearer with PDN type IPv4 shall be mapped one-to-one to a PDP context of PDP type IPv4. An EPS bearer with PDN type IPv6 shall be mapped one-to-one to a PDP context of PDP type IPv6.
It is the HPLMN operator that shall define in the subscription whether a dynamic HPLMN or VPLMN address may be used.
The EPS UE may indicate to the network within the Protocol Configuration Options element that the UE wants to obtain the IPv4 address with DHCPv4, which is a deferred IPv4 address allocation option, or during the default bearer activation procedure. This implies the following behaviour both for static and dynamic address allocation:
  • the UE may indicate that it prefers to obtain an IPv4 address as part of the default bearer activation procedure. In such a case, the UE relies on the EPS network to provide IPv4 address to the UE as part of the default bearer activation procedure.
  • the UE may indicate that it prefers to obtain the IPv4 address after the default bearer setup by DHCPv4. That is, when the EPS network supports DHCPv4 and allows that, it does not provide the IPv4 address for the UE as part of the default bearer activation procedures. The network may respond to the UE by setting the PDN Address to 0.0.0.0. After the default bearer establishment procedure is completed, the UE uses the connectivity with the EPS and initiates the IPv4 address allocation on its own using DHCPv4. However, if the EPS network provides IPv4 address to the UE as part of the default bearer activation procedure, the UE should accept the IPv4 address indicated in the default bearer activation procedure.
  • if the UE sends no Address Allocation Preference, the PDN-GW determines whether DHCPv4 is used between the UE and the PDN-GW (for the deferred IPv4 address allocation) or not, based on per APN configuration
Both EPS network elements and UE shall support the following mechanisms:
  1. IPv4 address allocation via default bearer activation, if IPv4 is supported.
  2. /64 IPv6 prefix allocation via IPv6 Stateless Address autoconfiguration according to RFC 4862, if IPv6 is supported;
Furthermore, the Protocol Configuration Options may be used during bearer activation to configure parameters which are needed for IP address allocation.
Both EPS network elements and UE may support the following mechanisms:
  1. IPv4 address allocation and IPv4 parameter configuration after the attach procedure via DHCPv4 according to RFC 2131 and RFC 4039;
  2. IPv6 parameter configuration via Stateless DHCPv6 according to RFC 3736.
  3. Allocation of IPv6 prefixes using DHCPv6 according to RFC 3633.
EPS network elements may support the following mechanism:
  1. Allocation of a static IPv4 address and/or a static IPv6 prefix based on subscription data in the HSS.
If the static IP address/prefix is not stored in the HSS subscription record, it may be configured on a per-user per-APN basis in the DHCP/Radius/Diameter server and the PDN-GW retrieves the IP address/prefix for the UE from the DHCP/Radius/Diameter server. In this case, static IP address/prefix is allocated by the same procedures as the dynamic IP address/prefix allocation (i.e. in such cases it is transparent to the PDN-GW if the IP address is static or dynamic).
If the static IP address/prefix is stored in the HSS subscription record, during the default bearer establishment the PDN-GW receives this static IP address/prefix from Serving-GW. In this case the PDN-GW shall deliver the received address/prefix to the UE. The static IP address/prefix is delivered to the UE in the same way as a dynamic IP address/prefix. Thus it is transparent to the UE whether the PLMN or the external PDN allocates the IP address and whether the IP address is static or dynamic.
The following clauses describe how the above listed IP address allocation mechanisms work when GTP based S5/S8 is used. The way of working of the IP address allocation mechanisms for PMIP based S5/S8 can be found in TS 23.402.The procedures can be used both for PLMN (VPLMN/HPLMN) or external PDN based IP address allocation.
In order to support DHCP based IP address configuration, the PDN-GW shall act as the DHCP server towards the UE for both HPLMN assigned dynamic and static IP addressing and for VPLMN assigned dynamic IP addressing. When DHCP is used for external PDN assigned addressing and parameter configuration, the PDN-GW shall act as the DHCP server towards the UE and it shall act as the DHCP client towards the external DHCP server. The Serving-GW does not have any DHCP functionality. It forwards packets, including DHCP packets, between the UE and the PDN-GW.
IPv6 Stateless Address autoconfiguration specified in RFC 4862 is the basic mechanism to allocate /64 IPv6 prefix to the UE.
During default bearer establishment, the PDN-GW sends the IPv6 prefix and Interface Identifier to the S-GW, and then the S-GW forwards the IPv6 prefix and Interface Identifier to the MME or to the SGSN. The MME or the SGSN forwards the IPv6 Interface Identifier to the UE. The MME does not forward the IPv6 prefix to the UE. If the UE receives the IPv6 prefix from the SGSN during PDP Context Activation procedure, it shall ignore it.
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5.3.1.2  IP address allocation, renewal and release mechanisms for GTP based S5/S8p. 135

5.3.1.2.1  IPv4 address allocation via default bearer activation and release via PDN connection releasep. 135
An IPv4 address may be provided to the UE as part of the default bearer activation and the IPv4 address is released when PDN connection associated with the IPv4 address is released.
When the PLMN allocates an IPv4 address, it is the PDN-GW responsibility to allocate and release the IPv4 address. The PDN-GW may use an internal IPv4 address pool in this case. The PDN-GW allocates an IPv4 address upon default bearer activation and it releases the IPv4 address upon PDN connection release associated with the IPv4 address for a given UE.
When an IPv4 address is allocated from an external PDN, it is the PDN-GW responsibility to obtain the IPv4 address from the external PDN, and to allocate, renew and release the IPv4 address. The PDN-GW may use DHCPv4 to obtain, renew and release the IPv4 address from the external PDN. If RADIUS or Diameter is used towards the external PDN, as described in TS 29.061, the IP address can be obtained, renewed and released as part of these procedures. If DHCPv4 is used, the PDN-GW functions as a DHCPv4 Client. If RADIUS is used, the PDN-GW functions as a RADIUS Client. If Diameter is used, the PDN-GW functions as a Diameter Client.
After releasing the IPv4 address, the PDN-GW should not assign that IPv4 address to other user immediately.
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5.3.1.2.2  Allocation, renewal and release of the IPv6 default prefix via IPv6 stateless address autoconfigurationp. 136
When the PLMN allocates an IPv6 prefix, it is the PDN-GW responsibility to allocate and release the IPv6 prefix. The PDN-GW may use an internal IPv6 prefix pool in this case. The PDN-GW allocates a globally unique /64 IPv6 prefix via Router Advertisement to a given UE.
When an IPv6 prefix is allocated from an external PDN, it is the PDN-GW responsibility to obtain the IPv6 prefix from the external PDN and to allocate, renew and release the IPv6 prefix. The PDN-GW may use DHCPv6 to obtain the IPv6 prefix from the external PDN. In this case, the PDN-GW functions as a DHCPv6 client. If RADIUS or Diameter is used towards the external PDN as described in TS 29.061, the IPv6 prefix can be obtained, renewed and released as part of these procedures. If RADIUS is used, the PDN-GW functions as the RADIUS Client. If Diameter is used, the PDN-GW functions as the Diameter Client.
The procedure of stateless IPv6 address autoconfiguration is the following: After default bearer establishment the UE may send a Router Solicitation message to the PDN-GW to solicit a Router Advertisement message. The PDN-GW sends a Router Advertisement message (solicited or unsolicited) to the UE. The Router Advertisement messages shall contain the same IPv6 prefix as the one provided during default bearer establishment. If the UE receives an IPv6 prefix from a SGSN during the PDP Context activation procedure, it shall ignore it.
After the UE has received the Router Advertisement message, it constructs a full IPv6 address via IPv6 Stateless Address autoconfiguration in accordance with RFC 4862. To ensure that the link-local address generated by the UE does not collide with the link-local address of the PDN-GW, the PDN-GW shall provide an interface identifier (see RFC 4862) to the UE and the UE shall use this interface identifier to configure its link-local address. For stateless address autoconfiguration however, the UE can choose any interface identifier to generate IPv6 addresses, other than link-local, without involving the network. However, the UE shall not use any identifiers defined in TS 23.003 as the basis for generating the interface identifier. For privacy, the UE may change the interface identifier used to generate full IPv6 address, as defined in TS 23.221 without involving the network.
Any prefix that the PDN-GW advertises to the UE is globally unique. The PDN-GW shall also record the relationship between the UE's identity (IMSI) and the allocated IPv6 prefix. Because any prefix that the PDN-GW advertises to the UE is globally unique, there is no need for the UE to perform Duplicate Address Detection for any IPv6 address configured from the allocated IPv6 prefix. Even if the UE does not need to use Neighbor Solicitation messages for Duplicate Address Detection, the UE may, for example, use them to perform Neighbor Unreachability Detection towards the PDN-GW, as defined in RFC 4861. Therefore, the PDN-GW shall respond with a Neighbor Advertisement upon receiving a Neighbor Solicitation message from the UE.
In order to renew the allocated IPv6 prefix, the PDN-GW sends a Router Advertisement (solicited or unsolicited) to the UE with the same prefix and new non-zero values in preferred and valid lifetime fields.
In order to release the allocated IPv6 prefix, the PDN-GW shall initiate the PDN connection release procedure. Upon release of the PDN connection, the UE shall implicitly release the prefix for the corresponding PDN connection.
After releasing the IPv6 prefix, the PDN-GW should not assign that IPv6 prefix to other user immediately.
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5.3.1.2.3  IPv6 parameter configuration via stateless DHCPv6p. 136
The UE may use stateless DHCPv6 for additional parameter configuration. The PDN-GW acts as the DHCP server. When PLMN based parameter configuration is used, the PDN-GW provides the requested parameters from locally provisioned database. When external PDN based parameter configuration is used, the PDN-GW obtains the requested configuration parameters from the external PDN as described in the previous clauses. When the PDN-GW acts as a DHCPv6 server towards the UE, the PDN-GW may act as DHCPv6 client towards the external PDN to request the configuration parameters for the UE. If RADIUS or Diameter is used towards the external PDN as described in TS 29.061, the requested configuration parameters can be fetched as part of these procedures.
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5.3.1.2.4  IPv4 address allocation, renewal and release and IPv4 parameter configuration via DHCPv4p. 137
When the PLMN allocates an IPv4 address, it is the PDN-GW responsibility to allocate, renew and release the IPv4 address.
When external PDN allocation is used, the PDN-GW functions as a DHCPv4 server towards the UE. The PDN-GW may act as a DHCP Client when interacting with a DHCPv4 server in the external PDN in order to obtain, renew and release the IPv4 address and to obtain the configuration parameters. Or, if RADIUS or Diameter is used towards the external PDN as described in TS 29.061, the IPv4 address and the requested configuration parameters can be obtained, renewed and released as part of these procedures.
If dynamic policy provisioning is deployed, and the PCRF was not informed about the IPv4 address at IP-CAN session establishment, the PDN-GW shall initiate an IP-CAN Session Modification procedure to inform the PCRF about an allocated IPv4 address. If the IPv4 address is released, the PDN-GW shall inform the PCRF about the de-allocation of an IPv4 address.
If the UE sends DHCPv4 lease renewal message to renew the lease of the allocated IPv4 address, the PDN-GW shall renew the lease of the allocated IPv4 address. If the IPv4 address was obtained from an external PDN, the PDN-GW shall perform the DHCPv4 lease renewal procedure with the external PDN if DHCPv4 was used for obtaining IPv4 address from external PDN. If Diameter or RADIUS procedures where used to obtain the IPv4 address from external PDN, the PDN-GW may perform corresponding update procedures as applicable. If the external PDN extends lease of the allocated IPv4 address, the PDN-GW responds accordingly to the UE. Otherwise, if the external PDN does not extend the lease of the allocated IPv4 address, the PDN-GW responds with the remaining lease time of the IPv4 address. If there is no PDN address allocated to the UE for this PDN connection, the PDN-GW shall perform PDN-GW initiated bearer deactivation procedure as defined in clause 5.4.4.1.
If the UE sends DHCPv4 release message to release the allocated IPv4 address for the PDN connection, the PDN-GW may any time thereafter release the IPv4 address. If the PDN connection has no allocated PDN address, the PDN-GW may at any time initiate PDN-GW initiated bearer deactivation procedure as defined in clause 5.4.4.1.
If the PDN connection is released without any DHCPv4 release signalling with the UE, the UE and the PDN-GW shall release the IPv4 address implicitly, as soon as the PDN connection is released.
After releasing the IPv4 address, the PDN-GW should not assign that IPv4 address to any other user immediately.
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5.3.1.2.5Void
5.3.1.2.6  IPv6 Prefix Delegation via DHCPv6 |R10|p. 137
Optionally a single network prefix shorter than the default /64 prefix may be assigned to a PDN connection. In this case, the /64 default prefix used for IPv6 stateless autoconfiguration will be allocated from this network prefix; the remaining address space from the network prefix can be delegated to the PDN connection using prefix delegation after the default bearer establishment and IPv6 prefix allocation via IPv6 stateless address autoconfiguration as defined in clause 5.3.1.2.2. When PLMN based parameter configuration is used, the PDN-GW provides the requested IPv6 prefix from a locally provisioned pool. When external PDN based IPv6 prefix allocation is used, the PDN-GW obtains the prefix from the external PDN.
The address space provided is maintained as an IPv6 address space pool available to the PDN connection for DHCPv6 IPv6 prefix requests with the exclusion of the IPv6 prefix that is allocated to the PDN connection during default bearer establishment as defined in clause 5.3.1.2.2. The total IPv6 address space available for the PDN connection (UE default bearer prefix and UE PDN connection IPv6 address space pool) shall be possible to aggregate into one IPv6 prefix that will represent all IPv6 addresses that the UE may use. If the UE had indicated that it supports prefix exclusion and the prefix to be delegated to the UE includes the /64 prefix that was allocated to the PDN Connection, the PDN-GW shall utilise the prefix exclusion feature as specified for DHCPv6 Prefix Delegation in RFC 6603.
The UE uses DHCPv6 to request additional IPv6 prefixes (i.e. prefixes in addition to the default prefix) from the PDN-GW after completing stateless IPv6 address autoconfiguration procedures. The UE acts as a "Requesting Router" as described in RFC 3633 and inserts one or more IA_PD option(s) into a DHCPv6 Solicit message sent from the UE to the PDN-GW. The PDN-GW acts as the DHCP server and fulfils the role of a "Delegating Router" according to RFC 3633. The UE optionally includes the RAPID_COMMIT option in the DHCPv6 Solicit message to trigger two-message DHCPv6 procedure instead of the four-message DHCPv6 procedure. The UE shall include OPTION_PD_EXCLUDE option code in an OPTION_ORO option to indicate support for prefix exclusion. In response to the DHCPv6 Solicit message, the UE receives a DHCPv6 Reply message with one or more IA_PD prefix(es) for every IA_PD option that it sent in the DHCPv6 Solicit message. The PDN-GW delegates a prefix excluding the default prefix with help of OPTION_PD_EXCLUDE. Prefix exclusion procedures shall follow RFC 6603.
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