B.1 General

29.2743GPP3GPP Evolved Packet System (EPS)Evolved General Packet Radio Service (GPRS) Tunnelling Protocol for Control plane (GTPv2-C)Release 18Stage 3TS

This annex provides details on how a GTPv2 entity transparently copies information received from RANAP or S1AP or NGAP into GTPv2 IE or IE field.

RANAP and S1AP ASN.1 encoding details in this annex are informative. The reference specifications are 3GPP TS 25.413 [33], 3GPP TS 36.413 [10] and 3GPP TS 38.413 [84] respectively.

The respective RANAP/S1AP/NGAP Information Elements are transported on the Iu/S1 interface within a "protocol-IE container" which is composed of:

– an Information Element Identity (referred to below as "IE-ID"),

– an indication how the receiver shall react if the Information Element is not comprehended (referred to below as "criticality"),

– and an "open type field" which consists of a length indication ("OT-LI") and the Information Element itself (referred to below as "IE").

RANAP/S1AP/NGAP PDUs and the contained IEs are defined by means of ASN.1, the specified encoding is PER (packed encoding rule), Octet aligned variant:

– PER minimises the information sent on the respective interface to the absolute minimum;

– Hence, type definitions of fixed length are encoded without any type or length indication, only type definitions of variable length contain a length indication, e.g.

– an OCTET STRING with indefinite length would need to contain a length indication (referred to below as "OCT-LI") followed by the actual octets (referred to below as "octets");

– a SEQUENCE neither contains a type, nor a length-indication. Only in case of optional elements it contains a kind of bit string with each position of this bitstring indicating the presence of an OPTIONAL element (an encoded SEQUENCE type is referred to below as "sequence").