Content for TS 36.458 Word version: 16.0.0
The present document specifies the standards for signalling transport to be used across the SLm interface. The SLm interface is a logical interface between the LMU and the E-SMLC in the E-UTRAN core network. The present document describes how the SLmAP signalling messages are transported over SLm.
The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
For a specific reference, subsequent revisions do not apply.
For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
: "Vocabulary for 3GPP Specifications".
(1998-12): "Internet Protocol, Version 6 (IPv6) Specification".
(1998-12): "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers".
(2007-09): "Stream Control Transmission Protocol".
For the purposes of the present document, the terms and definitions given in TR 21.905
and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905
interface between an LMU and an E-SMLC, providing an interconnection point between the LMU and the E-SMLC. It is also considered as a reference point.
Reference point for the application protocol between LMU and E-SMLC.
For the purposes of the present document, the following abbreviations apply.
E-UTRAN Serving Mobile Location Centre
Mobility Management Entity
Point to Point Protocol
Stream Control Transmission Protocol
SLm Application Protocol
Uplink Time Difference of Arrival
SLm signalling bearer provides the following functions:
Provision of reliable transfer of SLmAP message over SLm interface.
Provision of networking and routeing function
Provision of redundancy in the signalling network
Support for flow control and congestion control
The protocol stack for SLm signalling bearer is shown in Figure 4.1
and details on each protocol are described in the following clauses.
The transport network layer is based on IP transport, comprising SCTP on top of IP.
The support of any suitable data link layer protocol, e.g. PPP, Ethernet, etc. , shall not be prevented.
The LMU and E-SMLC shall support IPv6 (RFC 2460
) and/or IPv4 (RFC 791
The IP layer of SLmAP only supports point-to-point transmission for delivering SLmAP messages.
The LMU and E-SMLC shall support the Diffserv Code Point marking as described in RFC 2474
SCTP (RFC 4960
) shall be supported as the transport layer of SLmAP signalling bearer. The Payload Protocol Identifier assigned by IANA to be used by SCTP for the application layer protocol SLmAP is TBD.
SCTP refers to the Stream Control Transmission Protocol developed by the Sigtran working group of the IETF for the purpose of transporting various signalling protocols over IP network.
There shall be only one SCTP association established between one E-SMLC and LMU pair.
The LMU shall establish the SCTP association. The SCTP Destination Port number value assigned by IANA to be used for SLmAP is TBD.
Within the SCTP association established between one E-SMLC and LMU pair:
a single pair of stream identifiers shall be reserved for the sole use of SLmAP elementary procedures that utilize non UE-associated signalling.
At least one pair of stream identifiers shall be reserved for the sole use of SLmAP elementary procedures that utilize UE-associated signalling. However, a few pairs (i.e. more than one) should be reserved.
A single UE-associated signalling shall use one SCTP stream and the stream should not be changed during the communication of the UE-associated signalling.
Transport network redundancy may be achieved by SCTP multi-homing between two end-points, of which one or both is assigned with multiple IP addresses. SCTP end-points shall support a multi-homed remote SCTP end-point. For SCTP endpoint redundancy an INIT may be sent from E-SMLC, at any time for an already established SCTP association, which shall be handled as defined in Section 5.2 of RFC 4960
The SCTP congestion control may, using an implementation specific mechanism, initiate higher layer protocols to reduce the signalling traffic at the source and prioritise certain messages.