协议25.003
地址：
http://www.3gpp.org/ftp/Specs/archive/23_series/23.003/
9Definition of Access Point Name
In the GPRS backbone, an Access Point Name (APN) is a reference to a GGSN. To support inter-PLMN roaming, the internal GPRS DNS functionality is used to translate the APN into the IP address of the GGSN.
9.0General
Access Point Name as used in the Domain Name System (DNS) Procedures defined in 3GPP TS 29.303 [73] is specified in subclause 19.4.2.2.
9.1Structure of APN
The APN is composed of two parts as follows:
The APN Network Identifier; this defines to which external network the GGSN/PGW is connected and optionally a requested service by the MS. This part of the APN is mandatory.
The APN Operator Identifier; this defines in which PLMN GPRS/EPS backbone the GGSN/PGW is located. This part of the APN is optional.
NOTE 1:The APN Operator Identifier is mandatory on certain interfaces, see the relevant stage 3 specifications.
The APN Operator Identifier is placed after the APN Network Identifier. An APN consisting of both the Network Identifier and Operator Identifier corresponds to a DNS name of a GGSN/PGW; the APN has, after encoding as defined in the paragraph below, a maximum length of 100 octets.
The encoding of the APN shall follow the Name Syntax defined in RFC 2181 [18], RFC 1035 [19] and RFC 1123 [20]. The APN consists of one or more labels. Each label is coded as a one octet length field followed by that number of octets coded as 8 bit ASCII characters. Following RFC 1035 [19] the labels shall consist only of the alphabetic characters (A-Z and a-z), digits (0-9) and the hyphen (-). Following RFC 1123 [20], the label shall begin and end with either an alphabetic character or a digit. The case of alphabetic characters is not significant. The APN is not terminated by a length byte of zero.
NOTE 2:A length byte of zero is added by the SGSN/MME at the end of the APN before interrogating a DNS server.
For the purpose of presentation, an APN is usually displayed as a string in which the labels are separated by dots (e.g. "Label1.Label2.Label3").
9.1.1Format of APN Network Identifier
The APN Network Identifier shall contain at least one label and shall have, after encoding as defined in subclause 9.1 above, a maximum length of 63 octets. An APN Network Identifier shall not start with any of the strings "rac", "lac", "sgsn" or "rnc", and it shall not end in ".gprs", i.e. the last label of the APN Network Identifier shall not be "gprs". Further, it shall not take the value "*".
In order to guarantee uniqueness of APN Network Identifiers within or between GPRS/EPS PLMN, an APN Network Identifier containing more than one label shall correspond to an Internet domain name. This name should only be allocated by the PLMN if that PLMN belongs to an organisation which has officially reserved this name in the Internet domain. Other types of APN Network Identifiers are not guaranteed to be unique within or between GPRS/EPS PLMNs.
An APN Network Identifier may be used to access a service associated with a GGSN/PGW. This may be achieved by defining:
-an APN which corresponds to a FQDN of a GGSN/PGW, and which is locally interpreted by the GGSN/PGW as a request for a specific service, or
-an APN Network Identifier consisting of 3 or more labels and starting with a Reserved Service Label, or an APN Network Identifier consisting of a Reserved Service Label alone, which indicates a GGSN/PGW by the nature of the requested service. Reserved Service Labels and the corresponding services they stand for shall be agreed between operators who have GPRS/EPS roaming agreements.
9.1.2Format of APN Operator Identifier
The APN Operator Identifier is composed of three labels. The last label (or domain) shall be "gprs". The first and second labels together shall uniquely identify the GPRS/EPS PLMN.
For each operator, there is a default APN Operator Identifier (i.e. domain name). This default APN Operator Identifier is derived from the IMSI as follows:
"mnc<MNC>.mcc<MCC>.gprs"
where:
"mnc" and "mcc" serve as invariable identifiers for the following digits.
<MNC> and <MCC> are derived from the components of the IMSI defined in subclause 2.2.
This default APN Operator Identifier is used for home routed inter-PLMN roaming situations when attempting to translate an APN consisting only of a Network Identifier into the IP address of the GGSN/PGW in the HPLMN. The PLMN may provide DNS translations for other, more human-readable, APN Operator Identifiers in addition to the default Operator Identifier described above.
Alternatively, in the roaming case if the GGSN/PGW from the VPLMN is to be selected, the APN Operator Identifier for the UE is constructed from the serving network PLMN ID. In this case, the APN-OI replacement field, if received, shall be ignored.
In order to guarantee inter-PLMN DNS translation, the <MNC> and <MCC> coding used in the "mnc<MNC>.mcc<MCC>.gprs" format of the APN OI shall be:
<MNC> = 3 digits
<MCC> = 3 digits
If there are only 2 significant digits in the MNC, one "0" digit is inserted at the left side to fill the 3 digits coding of MNC in the APN OI.
As an example, the APN OI for MCC 345 and MNC 12 will be coded in the DNS as "mnc012.mcc345.gprs".
The APN-OI replacement is only used for selecting the GGSN/PGW from the HPLMN. The format of the domain name used in the APN-OI replacement field (as defined in 3GPP TS 23.060 [3] and 3GPP TS 23.401 [72]) is the same as the default APN-OI as defined above except that it may be preceded by one or more labels each separated by a dot.
EXAMPLE 1:province1.mnc012.mcc345.gprs
EXAMPLE 2:ggsn-cluster-A.provinceB.mnc012.mcc345.gprs
The APN constructed using the APN-OI replacement field is only used for DNS translation. The APN when being sent to other network entities over GTP interfaces shall follow the rules as specified in 3GPP TS 23.060 [3] and 3GPP TS 23.401 [72].
9.2Definition of the Wild Card APN
The APN field in the HLR may contain a wild card APN if the HPLMN operator allows the subscriber to access any network of a given PDP Type. If an SGSN has received such a wild card APN, it may either choose the APN Network Identifier received from the Mobile Station or a default APN Network Identifier for addressing the GGSN when activating a PDP context.
9.2.1Coding of the Wild Card APN
The wild card APN is coded as an APN with "*" as its single label, (i.e. a length octet with value one, followed by the ASCII code for the asterisk).
9.3Definition of Emergency APN
The Emergency APN (Em-APN) is an APN used to derive a PDN GW selected for IMS Emergency call support. The exact encoding of the Em-APN is the responsibility of each PLMN operator as it is only valid within a given PLMN.
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