ETSI TS 148 103 V13.0.0 (2016-01)

Digital cellular telecommunications system (Phase 2+); Base Station System - Media GateWay (BSS-MGW) interface; User plane transport mechanism (3GPP TS 48.103 version 13.0.0 Release 13)

RTS/TSGG-0248103vd00

General Information

• Status: Published
• Publication Date: 24-Jan-2016
• Technical Committee: 3GPP GERAN 2 - Protocol aspects
• Current Stage: 12 - Completion
• Due Date: 20-Jan-2016
• Completion Date: 25-Jan-2016

Standards Content (Sample)

ETSI TS 1148 103 V13.0.0 (201616-01)






TECHNICAL SPECIFICATIONION
Digital cellular telecocommunications system (Phahase 2+);
Base Station System - MMedia GateWay (BSS-MGW)W) interface;
User planlane transport mechanism
(3GPP TS 48.1.103 version 13.0.0 Release 13 13)

R
GLOBAL SYSTTEME FOR
MOBILE COMMUUNNICATIONS

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3GPP TS 48.103 version 13.0.0 Release 13 1 ETSI TS 148 103 V13.0.0 (2016-01)



Reference
RTS/TSGG-0248103vd00
Keywords
GSM
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3GPP TS 48.103 version 13.0.0 Release 13 2 ETSI TS 148 103 V13.0.0 (2016-01)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or
GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables.
The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under
http://webapp.etsi.org/key/queryform.asp.
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
ETSI

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3GPP TS 48.103 version 13.0.0 Release 13 3 ETSI TS 148 103 V13.0.0 (2016-01)
Contents
Intellectual Property Rights . 2
Foreword . 2
Modal verbs terminology . 2
Foreword . 4
1 Scope . 5
2 References . 5
3 Definitions, symbols and abbreviations . 6
3.1 Definitions . 6
3.2 Abbreviations . 6
4 Transport over TDM . 7
4.1 General . 7
4.2 Transport during local switching . 7
5 Transport over IP . 7
5.1 General . 7
5.2 IP . 8
5.3 UDP . 8
5.4 Transport without RTP multip lexing . 8
5.4.1 Introduction. 8
5.4.2 RTP . 8
5.4.2.1 RTP Header . 8
5.4.2.1.1 Version . 8
5.4.2.1.2 Padding . 8
5.4.2.1.3 Extension . 8
5.4.2.1.4 Contributing Source (CSRC) count . 8
5.4.2.1.5 Marker Bit . 9
5.4.2.1.6 Payload Type . 9
5.4.2.1.7 Sequence Number . 9
5.4.2.1.8 Timestamp . 9
5.4.2.1.9 Synchronisation Source (SSRC) . 9
5.4.2.1.10 CSRC list . 9
5.4.2.2 RTP Payload . 9
5.4.2.3 RTP Packetization Time . 10
5.4.3 RTCP . 10
5.5 Transport with RTP multiplexing . 10
5.5.1 Introduction. 10
5.5.2 RTP . 11
5.5.2.1 Transport format for multiplexing without RTP header compression. 11
5.5.2.2 Transport format for multiplexing with RTP header compression . 12
5.5.3 RTCP . 13
5.5.3.1 General . 13
5.5.3.2 Multiplexing negotiation via RTCP . 13
5.5.3.3 RTCP Multiplexing packet . 14
5.6 Transport of CSData . 15
5.6.1 Introduction. 15
5.6.2 Transport formats for CSData . 16
5.6.2.1 Transport format for CSData without redundancy . 16
5.6.2.2 Transport format for CSData with redundancy . 17
5.6.2.3 Start and Stop of RTP streams with redundancy . 18
5.7 Transport during local switching . 19
Annex A (informative): Change History . 20
History . 21
ETSI

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3GPP TS 48.103 version 13.0.0 Release 13 4 ETSI TS 148 103 V13.0.0 (2016-01)
Foreword
rd
This Technical Specification has been produced by the 3 Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
ETSI

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3GPP TS 48.103 version 13.0.0 Release 13 5 ETSI TS 148 103 V13.0.0 (2016-01)
1 Scope
The present document specifies the User Plane data transport protocols used between BSSs and the Core Network
(MGWs) across the A interface. The main purpose of the present document is the AoIP description, however for the
sake of completeness the AoTDM case is described as well.
UTRAN \
Iu

GERAN Iu mode
MGW
MGW
Nb
Iu
Mc
Mc
A
Nc
GERAN A/Gb mode
MSC server
GMSC server
A
Signalling
Interface
Signalling and Data Transfer
Interface

Figure 1.1: CS core network logical architecture
Note that the present document does not preclude any Core Network Session Control Protocol implementation (BICC
or SIP-I).
2 References
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.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] IETF RFC 791: "Internet Protocol (IP)".
[3] IETF RFC 2460: "Internet Protocol, Version 6 (IPv6)".
[4] IETF RFC 768: "User Datagram Protocol. (UDP)".
[5] IETF RFC 3550: "RTP: A Transport Protocol for Real Time Applications".
[6] 3GPP TS 29.414: "Core network Nb Interface data transport and transport signalling".
[7] IETF RFC 3551: "RTP Profile for Audio and Video Conference with Minimal Control".
[8] 3GPP TR 29.814: "Feasibility Study on Bandwidth Savings at Nb Interface with IP transport".
[9] IETF RFC 4040: "RTP Payload Format for a 64 kbits/s Transparent Call"
[10] IETF RFC 4867: "RTP Payload Format and File Storage Format for the Adaptive Multi-Rate
(AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs"
ETSI

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3GPP TS 48.103 version 13.0.0 Release 13 6 ETSI TS 148 103 V13.0.0 (2016-01)
[11] IETF RFC 2198: "RTP Payload for redundant Audio Data"
[12] 3GPP TR 43.903 A-Interface over IP Study (AINTIP)
[13] 3GPP TS 48.001 "Base Station System – Mobile-services Switching Centre (BSS - MSC)
interface; General aspects"
[14] ITU-T Recommendation G.705: "Characteristics of plesiochronous digital hierarchy (PDH)
equipment functional blocks".
[15] ANSI T1.102-1993: "Digital Hierarchy - Electrical Interface".
[16] ITU-T Recommendation G.711: "Pulse Code Modulation (PCM) of voice frequencies".
[17] 3GPP TS 48.020: "Rate adaption on the Base Station System - Mobile-services Switching Centre
(BSS - MSC) interface".
[18] IETF RFC 5993 (2010) "RTP Payload Format for Global System for Mobile Communications
Half Rate (GSM-HR)".
[19] 3GPP TS 48.008: "Mobile Switching Centre - Base Station System (MSC-BSS) interface; Layer 3
specification".
[20] 3GPP TS 26.102: "Adaptive Multi-Rate (AMR) speech codec; Interface to Iu, Uu and Nb".
[21] 3GPP TS 23.284: "Local Call Local Switch; Stage 2".
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply.
Intra-BSS call: A mobile to mobile voice call involving two mobile stations connected to the same BSS.
Local call: An Intra-BSS call that can be locally switched by the BSS. For details on the Local Switch Service
see 3GPP TS 23.284 [21].
Access MGW: The MGW interfacing to the Radio Access Network
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
TR 21.905 [1].
AoIP A (interface) over IP
AoTDM A (interface) over TDM
APP APPlication
BICC Bearer Independent Call Control
BSS Base Station Subsystem
CS Circuit-Switched
CSData CS Data and fax
IETF Internet Engineering Task Force
IP Internet Protocol
IPv4 Internet Protocol version 4
IPv6 Internet Protocol version 6
ITU-T International Telecommunications Union-Telecommunication sector
MGW Media GateWay
PCM Pulse-Coded Modulation
RFC Request For Comment
ETSI

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3GPP TS 48.103 version 13.0.0 Release 13 7 ETSI TS 148 103 V13.0.0 (2016-01)
RTP Real-Time Transport Protocol
RTCP Real-Time Transport Control Protocol
SIP-I Session Initiation Protocol with encapsulated ISUP
SSRC Synchronisation Source
SVC Switched Virtual Circuit
TDM Time-Division Multiplexing
UDP User Datagram Protocol
UP User Plane
4 Transport over TDM
4.1 General
The present chapter describes the transport on the A Interface UP over E1/T1 interface; for more information see 3GPP
TS 48.001 [13]. Figure 4.1 shows the protocol stack for the transport network user plane on the A interface.
Payload
(PCM encoded speech or CSData)
E1 or T1

Figure 4.1: TDM Protocol stack for the A interface user plane
Layer 1 shall utilise digital transmission:
- at a rate of 2 048 kbit/s with a frame structure of 32 x 64kbit/s time slots, as specified in ITU-T
Recommendation G.705 [14] clause 3 for E1 interface; or
- at a rate of 1 544 kbit/s with a frame structure of 24 x 64 kbit/s time slots, as specified in T1.102 specification for
T1 interface [15].
The payload is either PCM encoded speech (see ITU-T Recommendation G.711 [16]) or CSData (see 3GPP TS 48.020
[17]).
4.2 Transport during local switching
When a local switch path is established in the BSS for a local call, the user plane between the BSS and the Access
MGWs for both the call legs in uplink and downlink shall not be released.
5 Transport over IP
5.1 General
The present chapter describes the transport of the A-Interface User Plane Payload by RTP/UDP/IP. Figure 5.1 shows
the protocol stack.
Payload (PCM-coded speech, or
compressed speech or CSData)
RTP
UDP
IPv4 or IPv6

Figure 5.1: IP Protocol stack for the A-Interface user plane
The specific carrying way at physical/link layer of the IP protocol is not limited by the present document; if Ethernet is
adopted, link layer will be MAC protocol while if IPoE1 or POS is adopted, link layer will be PPP protocol.
Nevertheless at least Ethernet should be supported.
ETSI

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3GPP TS 48.103 version 13.0.0 Release 13 8 ETSI TS 148 103 V13.0.0 (2016-01)
5.2 IP
IPv4 (RFC 791 [2]) shall be supported
IPv6 (RFC 2460 [3]) may be supported as an option.
One BSS/MGW pair may be connected via several IP interfaces.
5.3 UDP
The UDP Protocol (see RFC 768 [4]) shall be applied.
Two consecutive port numbers shall be used at each BSS/MGW for the RTP connection and for the optional RTCP
connection that corresponds to a single A interface UP connection. Two such consecutive port numbers are termed "port
number block" in what follows. The first port number shall be even and shall be assigned to the RTP protocol. For a
given BSS/MGW, the same port shall be used to send and to receive RTP PDUs. The next port number shall be
assigned to the RTCP protocol. This port shall be reserved even if the optional RTCP protocol is not used.
If multiplexing is applied with or without header compression, the source UDP port number shall indicate the local
termination used to combine the multiplexed packet and the destination UDP port number shall indicate the remote port
number where PDUs are demultiplexed. The negotiation of whether multiplexing is applied and of the destination UDP
port is described in sub-clause 5.5.3.2. If multiplexing was negotiated for an A interface UP user plane connection, the
BSS/MGW may apply multiplexing by sending all packets of the user plane connection (multiplexed with other user
plane connections packets) towards the negotiated destination UDP port.
5.4 Transport without RTP multiplexing
5.4.1 Introduction
User Plane transport without RTP multiplexing is default and shall be supported. It shall be applied after call setup, until
a User Plane transport with RTP-multiplexing is negotiated via RTCP, see clause 5.5. RTCP, see RFC 3550 [5] may be
applied in AoIP, it is optional. A BSS or MSC may ignore incoming RTCP packets on AoIP.
5.4.2 RTP
The RTP protocol (see RFC 3550 [5]) shall be applied.
5.4.2.1 RTP Header
The RTP Header Fields shall be used as described in the following sub-clauses:
5.4.2.1.1 Version
RTP Version 2 shall be used.
5.4.2.1.2 Padding
Padding shall not be used.
5.4.2.1.3 Extension
The RTP Header extension shall not be used.
5.4.2.1.4 Contributing Source (CSRC) count
There is zero CSRC.
ETSI

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3GPP TS 48.103 version 13.0.0 Release 13 9 ETSI TS 148 103 V13.0.0 (2016-01)
5.4.2.1.5 Marker Bit
The marker bit shall be used as specified for the RTP profile applicable for the used payload. If AMR or AMR-WB
speech is received via the GSM radio interface, then an ONSET frame precedes the first speech frame. This ONSET
Frame is transported in a separate RTP packet and shall also have the Marker Bit set to "1". Also the next RTP packet,
which contains the first speech frame of the talkspurt, shall have the Marker Bit set to "1". In case of lost speech frames
due to radio errors or due to FACCH frame stealing the Marker bit shall not be set in the first speech frame after that
interruption.
5.4.2.1.6 Payload Type
See sub-clause 5.4.2.2.
5.4.2.1.7 Sequence Number
The sequence number shall be supplied by the source (BSS or MGW) of an RTP packet. RTP sequence numbering is
based on sent RTP packets, not on expected speech frames. If frames are lost or stolen on the radio interface and the
codec does not support Bad or No_Data frame types, no RTP packet is sent in uplink direction and the RTP Sequence
Number is not incremented, until a next frame is sent in RTP. This ensures that the receiver of the RTP stream can
detect lost RTP packets by inspecting the RTP Sequence Number.
5.4.2.1.8 Timestamp
The timestamp shall be supplied by the source (BSS or MGW) of a RTP PDU. Depending of the (pseudo) codec used a
clock frequency of either 8 or 16 kHz shall be used, as described in sub-clause 5.4.2.2. In case of lost or stolen frames
on the radio interface or in case of an interruption of the RTP stream due to handover, the RTP Timestamp shall be
incremented as if no frame would have been lost. This ensures that the receiver of the RTP stream can regenerate the
time signal correctly.
NOTE: IETF RFC 3550 [5] specifies that the RTP timestamp is based on the sampling instant of the source
Encoder. In case of a circuit switched radio interface the source Encoder for the uplink is within the
mobile station. But the radio interface does not support the transfer of a RTP Timestamp. The clock
synchronisation between mobile station and BSS is, however, very precise and so the BSS can take the
role of the source Encoder and provide the RTP time stamp.
5.4.2.1.9 Synchronisation Source (SSRC)
The source (BSS or MGW) of a RTP PDU shall supply a SSRC. The receiver of a RTP PDU may ignore the SSRC if it
does not use RTCP.
5.4.2.1.10 CSRC list
This list is empty, i.e. not present.
5.4.2.2 RTP Payload
The packing of the RTP Payload for each Speech Codec Type is specified in TS 26.102 [20].
When defined as such by IETF for a given Speech Codec (see RFC 3550 [5]) and RFC 3551 [7]) the "Static" Payload
Type is used; otherwise for RTP profiles for which IETF defines the Payload Type as "Dynamic" (e.g. for AMR codecs,
see RFC4867 [10]) a fixed Payload Type is defined for AoIP in the range of the dynamic Payload Types, see below.
The mapping between transported RTP payloads and their associated Payload Type is as follows:
ETSI

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3GPP TS 48.103 version 13.0.0 Release 13 10 ETSI TS 148 103 V13.0.0 (2016-01)
Table 5.4.2.2.1: Type of data transported versus RTP Payload Type
Type of data transported RTP Payload Type Clock frequency
PCM μ-law encoded speech (G.711) 0 (see RFC 3551 [7]) 8 kHz (see RFC 3551 [7])
PCM A-law encoded speech (G.711) 8 (see RFC 3551 [7]) 8 kHz (see RFC 3551 [7])
Compressed GSM FR codec 3 (see RFC 3551 [7]) 8 kHz (see RFC 3551 [7])
Speech (3GPP TS 46.010)
GSM EFR codec 110 8 kHz (see RFC 3551 [7])
(3GPP TS 46.060)
GSM HR codec 111 8 kHz (see [18])
(3GPP TS 46.020)
Narrow Band AMR codecs (i.e. FR AMR, 112 8 kHz (see RFC4867 [10])
HR AMR and OHR AMR codecs)
(3GPP TS 29.190)
Wide Band AMR codecs (i.e. AMR-WB, 113 16 kHz (see RFC4867 [10])
OFR AMR-WB and OHR AMR-WB codecs)
(3GPP TS 29.190)
CSData Without RTP redundancy (redundancy 120 8 kHz (see RFC 4040 [9])
(Clear Mode level = 1)
pseudo-codec (3GPP TS 48.008 and TS 48.020)
– see RFC
4040 [9])
With RTP redundancy (redundancy level = 121 8 kHz (see RFC 4040 [9]
2 or 3) and RFC 2198 [11])
(3GPP TS 48.008 and TS 48.020)
See sub-clause 5.6 for the format
description

5.4.2.3 RTP Packetization Time
The RTP Packetization Time is not negotiated for AoIP, but set to a predefined fixed value, see TS 26.102 [20].
For compressed speech on the A-Interface the Packetization Time is identical to the Speech Frame length and that is
20ms for all 3GPP Codec Types.
For PCM-coded speech (ITU-T G.711, A-law and μ-law) the Packetization Time is predefined to 20ms for AoIP.
For CSData the Packetization Time is predefined to 20ms, when no redundancy is used. In case of RTP Redundancy
more than one consecutive data block are included in one RTP packet. But for each of these data blocks the
Packetization Time is predefined to 20ms.
5.4.3 RTCP
RTCP (see RFC 3550 [5]) may be applied. The use of the RTCP protocol is optional.
A BSS/MGW may ignore incoming RTCP PDUs.
5.5 Transport with RTP multiplexing
5.5.1 Introduction
This sub-clause specifies an optional transport format for the A interface and IP transport that allows transporting
several RTP payload PDUs of different user plane connections within one UDP/IP packet, and the corresponding
backward compatible signalling extensions required to negotiate the use of this transport option. Use of this transport
format saves bandwidth in the IP network (bandwidth gains for the Nb interface are evaluated in 3GPP TR 29.814 [8]).
Bandwidth saving is achieved by multiplexing several RTP payload PDUs within one UDP/IP packet. As an option, the
RTP header may be compressed in addition. Two transport formats are specified accordingly.
As specified in sub-clause 5.5.3.1 RTP multiplexing shall not be applied if RTP redundancy has been negotiated.
ETSI

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3GPP TS 48.103 version 13.0.0 Release 13 11 ETSI TS 148 103 V13.0.0 (2016-01)
5.5.2 RTP
5.5.2.1 Transport format for multiplexing without RTP header compression
Several RTP payload PDUs sent to the same IP address are multiplexed within one single UDP/IP packet over the A
interface. If DiffServ is applied, all multiplexed PDUs also need to share the same Diffserv class. The multiplexing shall
only be used with RTP packets. RTCP shall be transported normally by UDP/IP packets.
Use of multiplexing shall be negotiated between BSS and MGW, as specified in sub-clause 5.5.3.2.
Before each multiplexed RTP/codec payload PDU inserted into the UDP/IP packet a "Multiplex Header", which
identifies the multiplexed packet, shall be inserted.
Bits Number
7 6 5 4 3 2 1 0 of Octets
Source IP, Dest IP, . 20/40 IP
Source Port, Dest Port = , Length 8 UDP
T=0 Mux ID = 2 Multiplex
(Destination UDP Port of non-multiplexed PDU) /2 Header
Length Inidicator (LI) = n
R Source ID = 2
(Source UDP Port of non-multiplexed PUD) /2
Full RTP packet n RTP
header
RTP
Payload
Multiplex Header 5 Multiplex
Header
Full RTP packet m RTP
Header
RTP
Payload
...

Figure 5.5.2.1.1: UDP/IP Packet with multiplexed
...