The transport layer for data streams over S1, X2, S4, S5 and S8  is an IP based Transport. The GTP-U  protocol over UDP over IP is supported as the transport for data streams on the user data interfaces. 

Any data link protocol that fulfils the requirements toward the upper layer may be used.

UDP/IP

• The UDP port number for GTP-U is as defined in 3GPP TS 29.281.
• The eNB and the EPC support fragmentation and assembly of GTP packets at the IP layer.
• The eNB and the EPC support IPv6 and/or IPv4.

Protocol specification

3GPP TS 36.410 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1 general aspects and principles

3GPP TS 36.411 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1

3GPP TS 36.414 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 data transport

3GPP TS 36.420 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 general aspects and principles

3GPP TS 36.421 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 layer 1

3GPP TS 36.424 - Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 data transport

IETF RFC 2460: "Internet Protocol, Version 6 (IPv6) Specification"

IETF RFC 791 (September,1981): "Internet Protocol"

IETF RFC 2474 (December 1998): "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers"