10 IP – The Networking Technology used by GTP

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

10.1 IP Version

GTPv2 entities shall support both versions of the Internet Protocol, version 4 (IPv4) as defined by IETF RFC 791 [6], and version 6 (IPv6) as defined by IETF RFC 2460 [16].

10.2 IP Fragmentation

It is specified here how the fragmentation mechanism shall work with GTP-C.

Fragmentation should be avoided if possible. Examples of fragmentation drawbacks are:

– Fragmentation is inefficient, since the complete IP header is duplicated in each fragment.

– If one fragment is lost, the complete packet has to be discarded. The reason is that no selective retransmission of fragments is possible.

Path MTU discovery should be used, especially if GTPv2-C message is encapsulated with IPv6 header. The application should find out the path MTU, and thereby utilise more efficient fragmentation mechanisms.

10.3 DSCP

Based on operator policy, if:

– GTPv2 entities support using the GTPv2 message priority mechanism as specified in clause 5.4 and clause 12.3.9.3.4 for DSCP marking,

– the transport network utilizes DSCP marking, and

– message-dependant DSCP marking is possible for the protocol stack for transporting GTPv2 messages,

then the DSCP marking as defined by IETF RFC 2474 [81] shall be set for IP packet carrying this GTPv2 messages based on the priority set in the GTPv2 message header.