ETSI ETS 300 563 ed.2 (1998-10)

Digital cellular telecommunications system (Phase 2) (GSM); Radio Link Protocol (RLP) for data and telematic services on the Mobile Station - Base Station System (MS - BSS) interface and the Base Station System - Mobile-services Switching Centre (BSS - MSC) interface (GSM 04.22 version 4.5.1)

RE/SMG-040422PR1

Digitalni celični telekomunikacijski sistem (faza 2) – Protokol radijske povezave (RLP) za podatkovne in telematske storitve na vmesniku sistema mobilna postaja-bazna postaja (MS-BSS) in vmesniku sistema bazna postaja-komutacija mobilnih storitev (BSS-MSC) (GSM 04.22, različica 4.5.1)

General Information

• Status: Published
• Publication Date: 21-Oct-1998
• Technical Committee: SMG 4 - Data Services
• Current Stage: 12 - Completion
• Due Date: 30-Oct-1998
• Completion Date: 22-Oct-1998
• Ref Project: SIST ETS 300 563 E2:2003 - Digital cellular telecommunications system (Phase 2) (GSM); Radio Link Protocol (RLP) for data and telematic services on the Mobile Station - Base Station System (MS - BSS) interface and the Base Station System - Mobile-services Switching Centre (BSS - MSC) interface (GSM 04.22 version 4.5.1)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ETS 300 563 E2:2003
01-december-2003
'LJLWDOQLFHOLþQLWHOHNRPXQLNDFLMVNLVLVWHPID]D±3URWRNROUDGLMVNHSRYH]DYH
5/3]DSRGDWNRYQHLQWHOHPDWVNHVWRULWYHQDYPHVQLNXVLVWHPDPRELOQDSRVWDMD
ED]QDSRVWDMD06%66LQYPHVQLNXVLVWHPDED]QDSRVWDMDNRPXWDFLMDPRELOQLK
VWRULWHY%6606&*60UD]OLþLFD
Digital cellular telecommunications system (Phase 2) (GSM); Radio Link Protocol (RLP)
for data and telematic services on the Mobile Station - Base Station System (MS - BSS)
interface and the Base Station System - Mobile-services Switching Centre (BSS - MSC)
interface (GSM 04.22 version 4.5.1)
Ta slovenski standard je istoveten z: ETS 300 563 Edition 2
ICS:
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
SIST ETS 300 563 E2:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 563 E2:2003

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SIST ETS 300 563 E2:2003
EUROPEAN ETS 300 563
TELECOMMUNICATION October 1998
STANDARD Second Edition
Source: SMG Reference: RE/SMG-040422PR1
ICS: 33.020
Key words: Digital cellular telecommunications system, Global System for Mobile communications (GSM)
R
GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS
Digital cellular telecommunications system (Phase 2);
Radio Link Protocol (RLP) for data and telematic services on the
Mobile Station - Base Station System (MS - BSS) interface
and the Base Station System - Mobile-services Switching Centre
(BSS - MSC) interface
(GSM 04.22 version 4.5.1)
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Internet: [e-mail] - http://www.etsi.org
Tel.: [phone] - Fax: [phone]
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1998. All rights reserved.

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Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Standards Making Support Dept." at the address shown on the title page.

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Contents
Foreword . 5
1 Scope. 7
2 Normative references . 7
2.1 Definitions and abbreviations . 9
3 Introduction . 9
4 Frame Structure. 10
4.1 Basic frame structure .10
4.2 RLP header . 10
4.3 Order of transmission.10
4.4 Frame check sequence. 10
5 Elements and procedure. 11
5.1 Modes. 11
5.1.1 Asynchronous Balanced Mode (ABM) . 11
5.1.2 Asynchronous Disconnected Mode (ADM). 11
5.2 Header and parameters . 11
5.2.1 Generally used bits . 11
5.2.1.1 Command/response bit, C/R. 12
5.2.1.2 Poll/Final bit, P/F . 12
5.2.2 Unnumbered frames, U . 12
5.2.2.1 Set asynchronous balanced mode SABM (11100) . 12
5.2.2.2 Unnumbered Acknowledge. UA (00110). 13
5.2.2.3 Disconnect, DISC (00010) . 13
5.2.2.4 Disconnected Mode, DM (11000) . 13
5.2.2.5 Unnumbered Information, UI (00000) . 13
5.2.2.6 Exchange Identification, XID (11101). 13
5.2.2.7 Test, TEST (00111). 15
5.2.2.8 Null information, NULL (11110). 15
5.2.3 Supervisory frames, S, and numbered information transfer and
supervisory frames combined, I+S . 15
5.2.3.1 Send Sequence number, N(S) . 15
5.2.3.2 Receive sequence number, N(R). 15
5.2.3.3 Receive ready, RR (00). 16
5.2.3.4 Reject, REJ (01). 16
5.2.3.5 Receive not ready, RNR (10) . 16
5.2.3.6 Selective reject, SREJ (11) . 16
5.3 Error Recovery . 17
5.3.1 Improper frames . 17
5.3.2 N(S) sequence error . 17
5.3.3 Time-out and checkpointing. 17
5.3.3.1 Treatment of errors during link establishment, link reset
and link disconnect. 17
5.3.3.2 Treatment of errors during numbered information transfer. 18
5.3.4 Contentious situations. 18
5.4 List of system parameters . 18
5.4.1 Timer T1 . 18
5.4.2 Maximum number of retransmissions N2. 18
5.4.3 Maximum number of outstanding I frames k . 19
5.5 Support for discontinuous transmission (DTX). 19
6 Service Definitions . 20
6.1 Introduction. 20
6.2 Conventions. 20

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6.3 Queue Model .21
6.4 List of Primitives.22
6.5 Possible RLP time sequence diagrams.23
Annex A (Informative): RLP SDL Diagrams .26
A.1 List of RLP entity states.27
A.1.1 (main) states .27
A.1.2 state variables.27
A.2 List of RLP entity events.31
Annex B (Informative): Change history .63
History.64

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Foreword
This European Telecommunication Standard (ETS) has been produced by the Special Mobile Group
(SMG) of the European Telecommunications Standards Institute (ETSI).
This ETS specifies the Radio Link Protocol (RLP) for data transmission over within the digital cellular
telecommunications system.
The specification from which this ETS has been derived was originally based on CEPT documentation,
hence the presentation of this ETS may not be entirely in accordance with the ETSI rules.
Transposition dates
Date of adoption of this ETS: 23 October 1998
Date of latest announcement of this ETS (doa): 31 January 1999
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 July 1999
Date of withdrawal of any conflicting National Standard (dow): 31 July 1999

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1 Scope
This Specification specifies the Radio Link Protocol (RLP) for data transmission over the GSM PLMN.
RLP covers the Layer 2 functionality of the ISO OSI Reference Model (IS 7498). It is based on ideas
contained in IS 3309, IS 4335 and IS 7809 (HDLC of ISO) as well as X.25 and Q.92x (LAP-B and LAP-D
of CCITT, resp.) RLP has been tailored to the special needs of digital radio transmission. RLP provides to
its users the OSI Data Link Service (IS 8886).
RLP is intended for use with non-transparent data-transfer. Protocol conversion may be provided for a
variety of protocol configurations. Those foreseen immediately are:
- Character-mode protocols using start-stop transmission (IA5)
- X.25 LAP-B.
For reasons of better presentation, material about protocol conversion has been placed within those
Specifications concerned with the relevant Terminal Adaptors, i.e. GSM 07.02 for the asynchronous case
and GSM 07.03 for the synchronous case. Care must be taken that that material also applies to
Interworking Functions; see GSM 09.04 - 09.07.
2 Normative references
This ETS incorporates by dated and undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references, the
latest edition of the publication referred to applies.
[1] GSM 01.04 (ETR 100): "Digital cellular telecommunication system (Phase 2);
Definitions, abbreviations and acronyms".
[2] GSM 04.21 (ETS 300 562): "Digital cellular telecommunication system
(Phase 2); Rate adaption on the Mobile Station - Base Station System (MS -
BSS) interface".
[3] GSM 07.02 (ETS 300 583): "Digital cellular telecommunication system
(Phase 2); Terminal Adaptation Functions (TAF) for services using
asynchronous bearer capabilities".
[4] GSM 07.03 (ETS 300 584): "Digital cellular telecommunication system
(Phase 2); Terminal Adaptation Functions (TAF) for services using synchronous
bearer capabilities".
[5] GSM 09.04 (ETS 300 601): "Digital cellular telecommunication system
(Phase 2); Interworking between the Public Land Mobile Network (PLMN) and
the Circuit Switched Public Data Network (CSPDN)".
[6] GSM 09.05 (ETS 300 602): "Digital cellular telecommunication system
(Phase 2); Interworking between the Public Land Mobile Network (PLMN) and
the Packet Switched Public Data Network (PSPDN) for Packet
Assembly/Disassembly facility (PAD) access".
[7] GSM 09.06 (ETS 300 603): "Digital cellular telecommunication system
(Phase 2); Interworking between a Public Land Mobile Network (PLMN) and a
Packet Switched Public Data Network/Integrated Services Digital Network
(PSPDN/ISDN) for the support of packet switched data transmission services".
[8] GSM 09.07 (ETS 300 604): "Digital cellular telecommunication system
(Phase 2); General requirements on interworking between the Public Land
Mobile Network (PLMN) and the Integrated Services Digital Network (ISDN) or
Public Switched Telephone Network (PSTN)".

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[9] CCITT Recommendation I.440 (Redbook): "ISDN user-network interface data
link layer - General aspects".
[10] CCITT Recommendation I.441 (Redbook): "ISDN user-network interface, data
link".
[11] CCITT Recommendation Q.920 (Redbook): "ISDN user-network interface data
link layer - General aspects".
[12] CCITT Recommendation Q.921 (Redbook): "ISDN user-network interface - data
link".
[13] CCITT Recommendation Q.921bis: "Abstract test suites for LAPD conformance
tests".
[14] CCITT Recommendation Q.922: "ISDN data link layer specification for frame
mode bearer services".
[15] CCITT Recommendation X.25 (Redbook): "Interface between Data Terminal
Equipment (DTE) and Data Circuit Terminating Equipment (DCE) for terminals
operating in Packet Mode and connected to Public Data Networks by dedicated
Circuit".
[16] ISO/IEC Recommendation 4335: "Information technology - Telecommunications
and information exchange between systems - High level data link control
(HDLC) procedures - Elements of procedures".
[17] ISO Recommendation 3309: "Information technology - Telecommunications and
information exchange between systems - High level data link control (HDLC)
procedures - Frame structure".
[18] ISO Recommendation 7498: "Information processing systems - Open Systems
Interconnection - Basic Reference Model".
[19] ISO Recommendation 8885: "Information technology - Telecommunication and
information exchange between systems - High-level data link control (HDLC)
procedures - General purpose XID frame information field content and format".
[20] ISO Recommendation 8886: "Information technology - Telecommunication and
information exchange between systems - Data link service definitions for Open
Systems interconnection".
[21] ISO Recommendation 8509: "Information processing systems - Open Systems
Interconnection - Service conventions".
[22] ISO/IEC Recommendation 7809: "Information technology - Telecommunication
and information exchange between systems - High-level data link control
(HDLC) procedures - Classes of procedures".
[23] ISO Recommendation 7776: "Information processing systems - High-level data
link control procedures - Description of the X.25 LAPB-compatible DTE data link
procedures".

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2.1 Definitions and abbreviations
Abbreviations used in this specification are listed in GSM 01.04.
Definitions:
command: An instruction represented in the RLP header, causing the receiving RLP entity to execute a
specific function.
frame check sequence: A field of redundant information based on a cyclic code, used for error detection.
I + S frame: An RLP frame that is used for user information transfer, carrying supervisory information
piggyback.
improper frame: An RLP frame having an FCS error or having a header the contents of which is
inconsistent with this Specification.
non-transparent: In PLMN data transmission, a configuration where at layer 2, protocol information of the
fixed network is mapped on RLP elements, and vice versa.
piggybacking: Means by which one and the same frame can carry both user information and RLP related
supervisory information.
response: A reply represented in the RLP-header, by which the sending RLP entity reports back about its
status.
RLP frame: A sequence of contiguous bits, representing an RLP procedural element.
RLP header: That part of an RLP frame that encodes either a command or a response, located at the
beginning of the RLP frame.
S frame: An RLP frame that contains supervisory information in the absence of user information.
transparent: In PLMN data transmission, a configuration where at layer 2 (and also at the layers above)
no protocol conversion takes place.
U frame: An RLP frame that contains unnumbered protocol control information.
3 Introduction
RLP makes use of an underlying FEC (Forward Error Correction) mechanism. For RLP to perform
adequately it is assumed that the basic radio channel together with FEC provides for a block error rate of
less than 10 %, where a block consists of 240 bits.
RLP frames are sent in strict alignment with the radio transmission. (For details, see GSM 04.21). RLP
frames are of fixed size of 240 bits. Whenever such a 240 bit frame is to be sent, the RLP entity has to
provide the necessary protocol information to be contained in it. Provision is made for discontinuous
transmission (DTX).
RLP spans from the mobile station (MS) to the interworking function (IWF), located at the nearest mobile
switching centre (MSC), or beyond. Depending on the exact location of the IWF, handover of the MS may
result in link-reset or even total loss of the connection.
The MS shall initiate the RLP link. In addition the MSC/IWF may initiate the RLP link.
In the terminology of HDLC, RLP is used in a balanced configuration, employing asynchronous operation,
i.e. either station has the right to set-up, reset, or disconnect a link at any time. Procedural means are
provided for to deal with contentious situations, should they ever occur.
RLP is full-duplex in the sense that it allows for information to be transferred in both directions
simultaneously.

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4 Frame Structure
4.1 Basic frame structure
An RLP-frame has a fixed length of 240 bits consisting of a header (16 bits), an information field (200
bits), and an FCS (frame check sequence) field (24 bits). As a benefit of using strict alignment with
underlying radio transmission there is no need for frame delimiters (like flags etc.) in RLP. In
consequence, there is no "bit-stuffing" necessary in order to achieve code transparency. Frames cannot
be aborted while being transmitted.
Header Information FCS
16bit 200 bit 24bit
Figure 1: Frame structure
4.2 RLP header
An RLP-header carries one of three types of control information, the first being unnumbered protocol
control information (U frames), the second being supervisory information (S frames), the third being user
information carrying supervisory information piggybacked (I + S frames).
4.3 Order of transmission
The header, as defined in section 5.2, shall be transmitted from left to right. The FCS shall be transmitted
commencing with the highest order term. The order of bit transmission for the information field is from left
to right.
4.4 Frame check sequence
The FCS shall be the ones complement of the modulo 2 sum of
a) the remainder of
216 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7
x (x + x + x + x + x + x + x + x + x + x + x + x + x + x + x + x + x
6 5 4 3 2
+ x + x + x + x + x + x + 1)
divided modulo 2 by the generator polynomial
24 23 21 20 19 17 16 15 13 8 7 5 4 2
x + x + x + x + x + x + x + x + x + x + x + x + x + x + 1
and
b) the remainder of the division modulo 2 by the generator polynomial
24 23 21 20 19 17 16 15 13 8 7 5 4 2
x + x + x + x + x + x + x + x + x + x + x + x + x + x + 1
24
of the product of x by the content of the frame, excluding the FCS field. (The first bit transmitted
corresponds to the highest order term.)
Implementation note: As a typical implementation, at the transmitter, the initial content of the register of
the device computing the remainder of the division is preset to all ones and is then modified by division by
the generator polynomial (as described above) of the header and information field; the ones complement
of the resulting remainder is transmitted as the 24 bit FCS sequence.
At the receiver, the initial content of the register of the device computing the remainder is preset to all
24
ones. The final remainder after multiplication by x and then division (modulo 2) by the generator
polynomial
24 23 21 20 19 17 16 15 13 8 7 5 4 2
x + x + x + x + x + x + x + x + x + x + x + x + x + x + 1

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of the serial incoming protected bits and the FCS will be
0 1 1 0 1 1 0 1 1 0 0 0 1 0 0 1 0 0 1 1 0 0 0 0 (x23 to x0, resp.)
in the absence of transmission errors.
5 Elements and procedure
5.1 Modes
An RLP entity can be in one of two modes:
- Asynchronous Balanced Mode (ABM)
- Asynchronous Disconnected Mode (ADM)
5.1.1 Asynchronous Balanced Mode (ABM)
In ABM, which is the data link operational mode, either RLP entity may send commands at any time and
may initiate response frame transmission without receiving explicit permission to do so from the other
RLP-station. In ABM, frames shall be used for information field transfer and/or to indicate status changes
in the RLP-station.
5.1.2 Asynchronous Disconnected Mode (ADM)
In ADM, which is the data-link non-operational mode, the RLP entity shall be logically disconnected from
the data link and shall, therefore, neither transmit nor accept numbered information frames.
The RLP entity shall, however, be permitted to transmit and accept NULL, DM, UI, TEST and XID frames.
Either RLP entity can issue an SABM command at any time, in order to terminate the ADM state. In that
case, entrance of the ABM state will be indicated by a UA response from the opposite station. If the
opposite station is not able to enter ABM, it will indicate this by a DM response. All commands other than
those mentioned above and any unsolicited response will be ignored in ADM under all circumstances.
5.2 Header and parameters
The formats defined for the header are listed in Figure 2 below.
5.2.1 Generally used bits
NOTES: C/R = COMMAND/RESPONSE BIT
X  = DON'T CARES
N(S) : Bit 4 low order bit
N(R) : Bit 11 low order bit

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U C/R X X 1 1 1 1 1 1 P/F M1 M2 M3 M4 M5 X
______________ ______________
S C/R S1 S2 01 11 11 P/F N (R)
______________ ______________ ______________ ______________
I+S C/R S1 S2 N (S) P/F N (R)
bit 1 2 3 4 5 6 7 8 9 1011 1213 141516
M M M M M
1 2 3 4 5
1 1 1 0 0 S A B M
0 0 1 1 0 U A
0 0 0 1 0 D I S C
S S 1 1 0 0 0 D M
1 2
0 0 R R 1 1 1 1 0 NULL
0 1 R E J 0 0 0 0 0 U I
1 0 R N R 1 1 1 0 1 X I D
1 1 S R E J 0 0 1 1 1 T E S T
Figure 2 Header format
5.2.1.1 Command/response bit, C/R
The C/R-bit is used to indicate whether the frame is a command or response frame and whether the P/F-
bit is to be interpreted as a poll or final bit, resp. For commands, the C/R bit shall be set to "1", for
responses it shall be set to "0".
5.2.1.2 Poll/Final bit, P/F
The P/F-bit is used to mark a special instance of command/response exchange. With a command, it is
called the P-bit, with a response, it is called the F-bit. In any one direction, only one P/F-bit exchange may
be outstanding at any time. A response with the F-bit set to "1" shall always reflect the latest receive status
of the RLP entity.
A P/F-bit exchange always starts with a command frame with the P-bit set to "1", which shall be answered
by a response frame with the F-bit set to "1" at the earliest response opportunity.
No unsolicited F-bit = "1" is allowed. Such a frame shall be considered "improper" (see 5.3.1). In ABM, the
use of the P/F-bit with numbered information exchange is only allowed for checkpoint-recovery (see
5.3.3).
5.2.2 Unnumbered frames, U
5.2.2.1 Set asynchronous balanced mode SABM (11100)
The SABM encoding is used as a command only. It is always used with the P-bit set to 1.
The SABM command is used either to initiate a link for numbered information transfer, i.e. to go from
ADM to ABM, or to reset a link already established for numbered information transfer. With an SABM
command, no information transfer is allowed.

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When issuing an SABM, the RLP entity has set to zero its internal variables for sending and receiving
numbered information. The other RLP entity, on receiving an SABM command, will either confirm it by
setting to zero its internal variables for sending and receiving numbered information and then issuing an
UA (unnumbered acknowledgement) response or reject it by sending a DM (disconnected mode)
response. In the former case, both entities have entered ABM and numbered information transfer may
commence. In the latter case, both entities are in ADM.
When an SABM command is issued, a loss of information may occur. Appropriate action is in the
responsibility of the layers above.
5.2.2.2 Unnumbered Acknowledge. UA (00110)
The UA encoding is used as a response only. It is used to positively acknowledge an SABM or DISC
command. With the UA response, no information transfer is allowed.
5.2.2.3 Disconnect, DISC (00010)
The DISC encoding is used as a command only. It is used to disestablish a link, previously established for
numbered information transfer, i.e. to terminate ABM and go into ADM. With the DISC command, no
information transfer is allowed.
The other RLP-entity shall answer with a UA response before actioning the DISC command. When a
DISC command is actioned, loss of information may occur. It is the responsibility of the layers above, to
provide for a "graceful" disconnect.
5.2.2.4 Disconnected Mode, DM (11000)
The DM encoding is used as a response only. It is used by RLP entity to report that it is in ADM and, as an
answer to SABM, that it is unable to action a mode setting command. With the DM response, no
information transfer is allowed.
5.2.2.5 Unnumbered Information, UI (00000)
The information field is to be interpreted as unnumbered information. Unnumbered information (UI)
frames can be sent in both ADM and ABM. There is no acknowledgement of receipt of UI-frames within
RLP.
5.2.2.6 Exchange Identification, XID (11101)
The information field is to be interpreted as exchange identification. This frame is used to negotiate and
renegotiate parameters of RLP and layer 2 Relay function. XID frames can be sent in both ADM and ABM.
The negotiation procedure is one step i.e. one side will start the process by sending an XID command,
offering a certain set of parameters from the applicable parameter repertoire (see table 1) the sending
entity wants to negotiate proposing values within the allowed range. In return, the other side will send an
XID response, either confirming these parameter values by returning the requested values, or offering
higher or lower ones in their place (see Table 1 for sense of negotiation), except when the indicated RLP
version is a lower one where a limited set of those parameters presented in the XID command may be
answered according to the negotiated version. This normally will end the negotiation process. XID frames
are always used with the P/F-bit set to "1".
Without any prior XID exchange, default values will apply (see section 5.4).
In the case of a collision of XID commands, all XID commands shall be ignored. The Mobile Station shall
restart the parameter negotiation on expiry of T1, while the Interworking Function shall do so on expiry of
twice the value of T1. An unsuccessful XID exchange shall be repeated on expiry of T1. After N2 times of
unsuccessful repetition, the link shall be disconnected.
In the following, a list of parameters is given which constitute the parameter repertoire for this RLP
version. In addition, the format of the XID information field is given.

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