5 (g)PTP message delivery
24.5353GPP5G System (5GS)Device-Side Time Sensitive Networking (TSN) Translator (DS-TT) to Network-Side TSN Translator (NW-TT) protocol aspectsRelease 17Stage 3TS
5.1 Overview
For time synchronization, a 5G system (5GS) can be configured to operate in one of the following modes (3GPP TS 23.501 [2]):
a) a time-aware system, for which the 5GS needs to support implementation of (g)PTP requirements (see IEEE Std 802.1AS [4]);
b) a boundary clock, for which the 5GS needs to support implementation of PTP requirements (see IEEE Std 1588-2019 [3];
c) a peer-to-peer transparent clock, for which the 5GS needs to support implementation of PTP requirements (see IEEE Std 1588-2019 [3]; and
d) an end-to-end transparent clock, for which the 5GS needs to support implementation of PTP requirements (see IEEE Std 1588-2019 [3].
Within a 5GS, a (g)PTP message is delivered over the user plane. While the generic mechanisms for the (g)PTP message delivery are according to IEEE Std 802.1AS [4] and IEEE Std 1588-2019 [3], a specific requirement for the DS-TT and the NW-TT is available in terms of the signalling of ingress time. See clause 5.2 for further details.
5.2 Signalling of ingress time for time synchronization and delay measurements
3GPP TS 23.501 [2] describes how to convey an ingress timestamp (TSi) for a (g)PTP event message, where the ingress TT creates a Suffix field with TSi encoded as specified in clause 5.3.1.
For a gPTP message, if the ingress TT is:
a) a NW-TT, support for these operations by the NW-TT is mandatory; or
b) a DS-TT, support for these operations by the DS-TT is optional.
For a PTP message, if the ingress TT is:
a) a NW-TT, support for these operations by the NW-TT is optional; or
b) a DS-TT, support for these operations by the DS-TT is optional.
The DS-TT or NW-TT (i.e. egress TT) creates an egress timestamping (TSe) for every (g)PTP event message. The egress TT uses TSi from the Suffix field of the (g)PTP message to calculate the residence time as specified in 3GPP TS 23.501 [2].
For a gPTP message, if the egress TT is:
a) a NW-TT, support for these operations by the NW-TT is optional; or
b) a DS-TT, support for these operations by the DS-TT is mandatory.
For a PTP message, if the egress TT is:
a) a NW-TT, support for these operations by the NW-TT is optional; or
b) a DS-TT, support for these operations by the DS-TT is optional.
5.3 Encoding of organization specific TLV extensions
5.3.1 General
Organization specific TLV extensions are included the Suffix field of a (g)PTP message as specified in clause 14.3 of IEEE Std 1588-2019 [3]. The Suffix field is coded as shown in figure 5.3.1.1 and table 5.3.1.1.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
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TLV type |
octet 1 octet2 |
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Length of TLV |
octet 3 octet 4 |
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Organization Id |
octet 5 octet 7 |
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Organization Subtype |
octet 8 octet 10 |
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Data field |
octet 11 octet n |
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Figure 5.3.1.1: Suffix field
Table 5.3.1.1: Suffix field
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TLV type (octets 1 to 2) |
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This field indicates the type of TLV extension and shall be coded as follows: – 00003H ORGANIZATION_EXTENSION; All other values are reserved. Length of TLV (octets 3 to 4) This field indicates the length of the value part of the TLV extension (i.e. octets 5 to n) coded in binary over 2 octets. Organization Id (octets 5 to 7) This field indicates the value of the Organizational Unique Identifier (OUI) assigned to 3GPP by the IEEE, coded in binary over 3 octets. Organization Subtype (octets 8 to 10) This field identifies the type of TLV extension included in the Data field and shall be coded as follows: – 00000H Reserved; – 00001H Ingress timestamp |
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All other values are spare. Data field (octets 11 to n) This field contains the contents of the specific TLV extension. Its encoding is specified in the corresponding clause. |
Editor’s note: The value of the OUI for 3GPP needs to be assigned by the IEEE.
5.3.2 Ingress timestamp
The Data field of a TLV extension carrying an Ingress timestamp is coded as shown in figure 5.3.2.1 and table 5.3.2.1.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
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Data field |
octet 11 octet 20 |
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Figure 5.3.2.1: Data field for Ingress timestamp (Organization Subtype = 0001H)
Table 5.3.2.1: Data field for Ingress timestamp (Organization Subtype = 0001H)
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Data field (octets 11 to 20) |
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For Organization Subtype = 0001H, the data field contains the ingress timestamp of the (g)PTP event (Sync) message, encoded over 10 octets as specified in clause 5.3.3. of IEEE Std 1588-2019 [3]. |
Annex A (informative):
Change history
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Change history |
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Date |
Meeting |
TDoc |
CR |
Rev |
Cat |
Subject/Comment |
New version |
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2019-08 |
CT1#119 |
C1-194647 |
Draft skeleton provided by the rapporteur |
0.0.0 |
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2019-09 |
CT1#119 CT#85 |
C1-194650 CP-192258 |
Implementation of an agreed pseudo CR (C1-194650) Addition of the TS number assigned in CT#85 |
0.1.0 |
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2019-11 |
CT1#121 |
Implementation of the following pseudo CRs agreed by CT1: Corrections made by the rapporteur |
0.2.0 |
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2019-12 |
CT#86 |
CP-193151 |
Presentation for information to TSG CT |
1.0.0 |
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2019-12 |
CT#86 |
CP-183288 |
A title corrected |
1.0.1 |
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2020-03 |
CT1#122 |
Implementation of the following pseudo CR agree by CT1: Corrections made by the rapporteur |
1.1.0 |
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2020-03 |
CT-87e |
CP-200167 |
Presentation for approval to TSG CT |
2.0.0 |
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2020-03 |
CT-87e |
Version 16.0.0 created after approval |
16.0.0 |
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2020-06 |
CT-88e |
CP-201137 |
0002 |
1 |
F |
TSN working domain |
16.1.0 |
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2020-09 |
CT-89e |
CP-202170 |
0003 |
D |
Editorial correction |
16.2.0 |
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2020-12 |
CT-90e |
CP-203219 |
0004 |
1 |
F |
Update handling of suffix field |
16.3.0 |
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2020-12 |
CT-90e |
CP-203219 |
0006 |
1 |
F |
TSi handling when the NW-TT generates the gPTP event messages |
16.3.0 |
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2021-06 |
CT-92e |
CP-211136 |
0007 |
2 |
B |
Support for PTP message delivery |
17.0.0 |
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2021-09 |
CT-93e |
CP-212134 |
0008 |
1 |
C |
Correction of timestamping the messages for time synchronization and delay measurements |
17.1.0 |
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2021-12 |
CT-94e |
CP-213035 |
0009 |
C |
Removing unnecessary text in clause 5.2 |
17.2.0 |
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