The transport layer for data streams over S1 is an IP based Transport. The following Figure shows the transport protocol stacks over S1.
The GTP-U (
TS 29.281) protocol over UDP over IP shall be supported as the transport for data streams on the S1 interface. The data link layer is as specified in
clause 4.
The transport bearer is identified by the GTP-U TEID (
TS 29.281) and the IP address (source TEID, destination TEID, source IP address, destination IP address).
The GTP-U (
TS 29.281) protocol shall be used over the S1 interface toward the EPC.
The path protocol used shall be UDP (
RFC 768).
The UDP port number for GTP-U shall be as defined in
TS 29.281.
The eNB and the EPC shall support fragmentation and assembly of GTP packets at the IP layer.
The eNB and the EPC shall support IPv6 (
RFC 2460) and/or IPv4 (
RFC 791).
There may be one or several IP addresses in the eNB and in the EPC. The packet processing function in the EPC shall send downstream packets of a given E-RAB to the eNB IP address (received in S1-AP) associated to that particular E-RAB. The packet processing function in the eNB shall send upstream packets of a given E-RAB to the EPC IP address (received in S1-AP) associated to that particular E-RAB.
The Transport Layer Address signalled in S1-AP messages is a bit string of
-
32 bits in case of IPv4 address according to RFC 791; or
-
128 bits in case of IPv6 address according to RFC 2460; or
-
160 bits if both IPv4 and IPv6 addresses are signalled, in which case the IPv4 address is contained in the first 32 bits.
IP Differentiated Services code point marking (
RFC 2474) shall be supported. The mapping between traffic categories and Diffserv code points shall be configurable by O&M based on QoS Class Identifier (QCI) Characteristics and other E-UTRAN traffic parameters (e.g. ARP). Traffic categories are implementation-specific and may be determined from the application parameters.