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TECHNICAL SPECIFICATION
LTE;
Protocol for Reliable Data Service between UE and SCEF;
Stage 3
(3GPP TS 24.250 version 15.1.0 Release 15)
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3GPP TS 24.250 version 15.1.0 Release 15 1 ETSI TS 124 250 V15.1.0 (2019-03)
Reference
RTS/TSGC-0124250vf10
Keywords
LTE
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3GPP TS 24.250 version 15.1.0 Release 15 2 ETSI TS 124 250 V15.1.0 (2019-03)
Intellectual Property Rights
Essential patents
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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
.
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 24.250 version 15.1.0 Release 15 3 ETSI TS 124 250 V15.1.0 (2019-03)
Contents
Intellectual Property Rights . 2
Foreword . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
2 References . 6
3 Definitions and abbreviations . 6
3.1 Definitions . 6
3.2 Abbreviations . 6
4 Overview . 6
4.1 General . 6
4.2 Reference Model . 7
4.3 Description of RDS protocol . 7
4.3.1 Protocol functions . 7
4.3.2 Acknowledged operation . 8
4.3.3 Unacknowledged operation . 8
5 Frame structure and format of fields . 8
5.1 General . 8
5.2 Address and Control field . 8
5.2.1 Address and Control field format . 8
5.2.2 Protocol Discriminator bit (PD) . 10
5.2.3 Address bit (ADS) . 10
5.2.4 Source port number (Source Port) . 10
5.2.5 Destination port number (Destination Port) . 10
5.2.6 Information transfer frame - I . 10
5.2.7 Supervisory frame - S . 10
5.2.8 Unconfirmed Information frame - UI . 10
5.2.9 Unnumbered frame - U . 10
5.2.10 Command / Response bit (C/R) . 11
5.3 Control field parameters and associated state variables . 11
5.3.1 Acknowledgement request bit (A) . 11
5.3.2 Acknowledged operation variables and parameters . 11
5.3.2.1 Send state variable V(S) . 11
5.3.2.2 Acknowledge state variable V(A) . 11
5.3.2.3 Send sequence number N(S) . 11
5.3.2.4 Receive state variable V(R). 11
5.3.2.5 Receive sequence number N(R) . 12
5.3.2.6 Selective Acknowledgement (SACK) bitmap R(n) . 12
5.3.3 Unacknowledged operation variables and parameters . 12
5.3.3.1 Unconfirmed send state variable V(U) . 12
5.3.3.2 Unconfirmed sequence number N(U) . 12
5.3.3.3 Unconfirmed receive state variable V(UR) . 12
5.3.3.4 Other parameters and variables . 12
5.4 Commands and responses . 12
5.4.1 General . 12
5.4.2 Unnumbered (U) frames . 13
5.4.2.1 SET_ACK_MODE command . 13
5.4.2.2 DISCONNECT command . 13
5.4.2.3 ACCEPT response . 13
5.4.2.4 ERROR command / response . 13
5.4.2.5 SET_PARAMETERS command / response . 13
5.4.3 Information (I) and Supervisory (S) frames . 14
5.4.3.1 General . 14
5.4.3.2 Selective Acknowledgement (SACK) command / response . 14
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3GPP TS 24.250 version 15.1.0 Release 15 4 ETSI TS 124 250 V15.1.0 (2019-03)
6 Protocol procedures . 14
6.1 Overview . 14
6.2 Procedures . 14
6.2.1 Types of RDS procedures . 14
6.2.2 Establishment of acknowledged transfer procedure . 15
6.2.2.1 General . 15
6.2.2.2 Establishment of acknowledged transfer procedure initiation . 15
6.2.2.3 Establishment of acknowledged transfer procedure accepted by receiver . 15
6.2.2.4 Establishment of acknowledged transfer procedure completed by originator . 16
6.2.2.5 Establishment of acknowledged transfer procedure not accepted by receiver . 16
6.2.3 Acknowledged information transfer procedure . 16
6.2.3.1 General . 16
6.2.3.2 Transmitting I frames and requesting acknowledgements . 16
6.2.3.3 Receiving I frames and sending acknowledgements . 17
6.2.3.4 Receiving acknowledgements . 17
6.2.4 Termination of acknowledged transfer procedure . 18
6.2.4.1 General . 18
6.2.4.2 Termination of acknowledged transfer procedure initiation . 18
6.2.4.3 Termination of acknowledged transfer procedure accepted by receiver . 18
6.2.4.4 Termination of acknowledged transfer procedure completed by originator . 19
6.2.4.5 Termination of acknowledged transfer procedure not accepted by receiver . 19
6.2.5 Unacknowledged information transfer procedure . 19
6.2.5.1 General . 19
6.2.5.2 Unacknowledged information transfer procedure initiation . 19
6.2.5.3 Unacknowledged information transfer procedure accepted by receiver . 19
6.2.5.4 Unacknowledged information transfer procedure completed by originator . 19
6.2.5.5 Unacknowledged information transfer procedure not accepted by receiver . 19
6.3 Abnormal cases . 20
6.3.1 Expiry of timer T200 . 20
6.3.2 Expiry of timer T201 . 20
6.4 List of RDS Parameters . 20
6.4.1 General . 20
6.4.2 RDS version number (Version) . 20
6.4.3 Retransmission timers (T200 and T201) . 20
6.4.4 Maximum number of retransmissions (N200) . 20
6.4.5 Maximum number of outstanding I frames (k) . 20
6.4.6 Maximum length of Information Field (N201) . 20
Annex A (informative): Change history . 21
History . 22
ETSI
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3GPP TS 24.250 version 15.1.0 Release 15 5 ETSI TS 124 250 V15.1.0 (2019-03)
Foreword
This Technical Specification has been produced by the 3rd 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 24.250 version 15.1.0 Release 15 6 ETSI TS 124 250 V15.1.0 (2019-03)
1 Scope
The present document specifies a Reliable Data Service (RDS) protocol between the UE and Service Capability
Exposure Function (SCEF) or P-GW.
The present document defines the frame structure, format of fields and procedures for operation of the RDS protocol.
RDS is mainly intended to be used for acknowledged data transfer, but it also supports unacknowledged data transfer.
The present document is applicable to the UE, the SCEF and to the P-GW in the Evolved Packet System (EPS).
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] 3GPP TS 23.682: "Architecture enhancements to facilitate communications with packet data
networks and applications".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in 3GPP TR 21.905 [1] and the following
apply. A term defined in the present document takes precedence over the definition of the same term, if any, in 3GPP
TR 21.905 [1].
For the purposes of the present document, the following terms and definitions given in 3GPP TS 23.682 [2] apply:
SCEF
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in 3GPP 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
3GPP TR 21.905 [1].
RDS Reliable Data Service
4 Overview
4.1 General
The Reliable Data Service (RDS) protocol supports the following requirements:
- RDS supports peer-to-peer data transfers and shall provide reliable data delivery between the UE and the SCEF
or P-GW. The data is transferred via a PDN connection between the UE and SCEF or P-GW.
- A UE can connect to multiple SCEFs or P-GWs. A UE can connect to multiple SCS/AS via the SCEF or P-GW.
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3GPP TS 24.250 version 15.1.0 Release 15 7 ETSI TS 124 250 V15.1.0 (2019-03)
- RDS shall support multiple applications on the UE to simultaneously conduct data transfers with their peer
entities on the SCEF or P-GW using a single PDN connection between the UE and SCEF or P-GW.
- RDS shall support both acknowledged and unacknowledged data transfers.
- RDS shall support variable-length frames and shall allow detection and elimination of duplicate frames at the
receiving endpoint.
4.2 Reference Model
Application
Application
RDS RDS
NAS
NAS
Diameter
Relay Diameter
RRC
S1AP
RRC S1AP
PDCP PDCP SCTP SCTP SCTP SCTP
IP IP
RLC RLC IP IP
L2 L2
MAC MAC L2 L2
L1 L1 L1 L1 L1 L1
LTE-Uu S1-MME T6a
UE eNb MME SCEF
Figure 4.2-1: Protocol layering for reliable data transfer between UE and SCEF via E-UTRAN
The reference model showing the protocol layering for reliable data transfer between UE and SCEF is illustrated in
figure 4.2-1. The RDS operates above the NAS and Diameter layers in the reference architecture.
4.3 Description of RDS protocol
4.3.1 Protocol functions
RDS establishes a peer-to-peer logical link between the UE and SCEF or P-GW. The logical link is identified by a pair
of port numbers and EPS bearer ID. Each port number is used to identify an application on the UE side or at the
network (SCEF or P-GW) side and is carried in the address field of each frame. The source port number identifies the
application on the originator and the destination port number identifies the application on the receiver. When a single
application on the originator conducts data transfer with a single application on the receiver, the source port number and
destination port number need not be used. Each RDS frame shall consist of a header and an information field of variable
length. The header shall contain information about port numbers and the frame number that is used to identify the frame
and provide reliable transmission. The information field contains the payload to be transferred between the UE and
SCEF or P-GW.
The UE establishes a PDN connection with the SCEF or P-GW either during Attach or through UE requested PDN
connectivity. The UE shall use the EPS bearer ID to select the bearer to transfer RDS PDUs to the SCEF or P-GW. The
EPS bearer ID identifies the destination (at the UE or at the SCEF or P-GW) and is not carried in the frame as it is
already included in the NAS ESM message header. Once the UE and network successfully negotiate to use RDS for a
particular PDN connection, the PDN connection shall transfer data only using RDS protocol.
RDS shall support both single and multiple applications within the UE. RDS shall provide fuctionality for flow control
and sequence control to maintain the sequential order of frames across the logical link.
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3GPP TS 24.250 version 15.1.0 Release 15 8 ETSI TS 124 250 V15.1.0 (2019-03)
4.3.2 Acknowledged operation
In acknowledged operation the information is transmitted in order in numbered Information (I) frames. The I frames are
acknowledged at the RDS layer. Error recovery and reordering mechanisms based on retransmission of acknowledged I
frames are specified. Several I frames can be acknowledged at the same time. Flow control is implemented via a sliding
window mechanism.
The procedure for establishment of acknowledged transfer is described in clause 6.
4.3.3 Unacknowledged operation
In unacknowledged operation the information is transmitted in numbered Unconfirmed Information (UI) frames. The UI
frames are not acknowledged at the RDS layer. Error recovery and reordering mechanisms are not defined. Duplicate
UI frames are discarded. Flow control procedures are not defined.
5 Frame structure and format of fields
5.1 General
The peer-to-peer transfers using RDS shall conform to the frame format as shown in figure 5.1-1. The frame header
shall consist of the Address and Control field and is a minimum of 1 octet and a maximum of 3 octets long. The
Information field is of variable length.
8 7 6 5 4 3 2 1
Address and Control field
(variable length, max. 3 octets)
Information field
(variable length, max. N201 octets)
Figure 5.1-1: RDS frame format
5.2 Address and Control field
5.2.1 Address and Control field format
The Address and Control field identifies the type of frame and consists of minimum of 1 octet and maximum of 3
octets. The following types of control field frames are specified:
- confirmed information transfer (I frame);
- supervisory functions (S frame);
- unconfirmed information transfer (UI frame); and
- control functions (U frame).
The address and control field format for RDS is shown in figure 5.2.1-1.The description of address and control field bits
is shown in Table 5.2.1-1.
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3GPP TS 24.250 version 15.1.0 Release 15 9 ETSI TS 124 250 V15.1.0 (2019-03)
Address and Control Field Bits
Format 1
8 7 6 5 4 3 2
Octet
PD 0 A X ADS N(S) 1
I Format
N(R) R1 R2 R3 S1 S2
2
Source Port Destination Port
3
1
S Format PD 1 1 0 ADS A X X
N(R) R1 R2 R3 S1 S2
2
Source Port Destination Port 3
UI Format 1
PD 1 0 X ADS N(U)
Source Port Destination Port
2
U Format 1
PD 1 1 1 ADS CR X X
X X X X M4 M3 M2 M1
2
Source Port Destination Port 3
Figure 5.2.1-1: Address and Control field format
Table 5.2.1-1: Address and Control field bits description
Control field bits Description
A Acknowledgement request bit
M
n Unnumbered function bit
N(R)
Receive sequence number
N(S)
Send sequence number
N(U)
Unconfirmed sequence number
S
n Supervisory function bit
R
n Selective acknowledgement bitmap bit
PD Protocol Discriminator bit
C/R Command / Response bit
ADS Address bit
Source Port Source port number
Destination Port Destination port number
X
Spare bit
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3GPP TS 24.250 version 15.1.0 Release 15 10 ETSI TS 124 250 V15.1.0 (2019-03)
5.2.2 Protocol Discriminator bit (PD)
The PD bit indicates whether a frame is an RDS frame or belongs to a different protocol. RDS frames shall have the
PD bit set to 0. If a frame with the PD bit set to 1 is received, then it shall be treated as an invalid frame.
5.2.3 Address bit (ADS)
The ADS bit controls if the Source Port and Destination Port are included in the frame format. When a single
application on UE side conducts data transfer with a single application on SCEF or P-GW side, the source and
destination port numbers need not be used. The source and destination port numbers enable multiple applications on the
UE side to simultaneously communicate with their peer entities on the SCEF or P-GW side using the same PDN
connection. Source Port and Destination Port are included in the frame format only if the ADS bit is set to 1.
5.2.4 Source port number (Source Port)
When a UE application starts to use the PDN connection to transmit RDS frames, the UE and the SCEF or P-GW
establish which source port number will be used for the application on the UE side for MO traffic
...