PTP Configuration¶
PTP Synchronization¶
Precision Time Protocol (PTP) provides an efficient way to synchronize time on the network nodes. This protocol uses Master-Slave architecture. Grandmaster Clock (Master) is a reference clock for the other nodes, which adapt their clocks to the master.
Using Physical Hardware Clock (PHC) from the Grandmaster Clock, NIC port precision timestamp packets can be served for other network nodes. Slave nodes adjust their PHC to the master following the IEEE 1588 specification.
There are existing implementations of PTP protocol that are widely used in the industry. One of them is PTP for Linux, which is a set of tools providing necessary PTP functionality. There is no need to re-implement the 1588 protocol because PTP for Linux is precise and efficient enough to be used out of the box.
To meet O-RAN requirements, two tools from PTP for Linux package are required: ptp4l and phc2sys.
PTP for Linux* Requirements¶
PTP for Linux* introduces some software and hardware requirements. The machine on which the tools will be run needs to use at least a 3.10 Kernel version (built-in PTP support). Several Kernel options need to be enabled in Kernel configuration:
CONFIG_PPS
CONFIG_NETWORK_PHY_TIMESTAMPING
PTP_1588_CLOCK
Be sure that the Kernel is compiled with these options.
For the best precision, PTP uses hardware timestamping. NIC has its own clock, called Physical Hardware Clock (PHC), to read current time just a moment before the packet is sent to minimalize the delays added by the Kernel processing the packet. Not every NIC supports that feature. To confirm that currently attached NIC support Hardware Timestamps, use ethtool with the command:
ethtool -T eth0
Where the eth0 is the potential PHC port. The output from the command should say that there is Hardware Timestamps support.
To set up PTP for Linux*:
1.Download source code:
git clone http://git.code.sf.net/p/linuxptp/code linuxptp
git checkout v2.0
Note Apply patch (this is required to work around an issue with some of the GM PTP packet sizes.)
diff --git a/msg.c b/msg.c
old mode 100644
new mode 100755
index d1619d4..40d1538
--- a/msg.c
+++ b/msg.c
@@ -399,9 +399,11 @@ int msg_post_recv(struct ptp_message *m, int cnt)
port_id_post_recv(&m->pdelay_resp.requestingPortIdentity);
break;
case FOLLOW_UP:
+ cnt -= 4;
timestamp_post_recv(m, &m->follow_up.preciseOriginTimestamp);
break;
case DELAY_RESP:
+ cnt -= 4;
timestamp_post_recv(m, &m->delay_resp.receiveTimestamp);
port_id_post_recv(&m->delay_resp.requestingPortIdentity);
break;
Build and install ptp41.
# make && make install
3. Modify configs/default.cfg to control frequency of Sync interval to 0.0625 s.
logSyncInterval -4
ptp4l¶
This tool handles all PTP traffic on the provided NIC port and updated PHC. It also determines the Grandmaster Clock and tracks synchronization status. This tool can be run as a daemon or as a regular Linux* application. When the synchronization is reached, it gives output on the screen for precision tracking. The configuration file of ptp4l contains many options that can be set to get the best synchronization precision. Although, even with default.cfg the synchronization quality is excellent.
To start the synchronization process run:
cd linuxptp
./ptp4l -f ./configs/default.cfg -2 -i <if_name> -m
The output below shows what the output on non-master node should look like when synchronization is started. This means that PHC on this machine is synchronized to the master PHC.
ptp4l[1434165.358]: port 1: INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[1434165.358]: port 0: INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[1434166.384]: port 1: new foreign master fcaf6a.fffe.029708-1
ptp4l[1434170.352]: selected best master clock fcaf6a.fffe.029708
ptp4l[1434170.352]: updating UTC offset to 37
ptp4l[1434170.352]: port 1: LISTENING to UNCALIBRATED on RS_SLAVE
ptp4l[1434171.763]: master offset -5873 s0 freq -18397 path delay 2778
ptp4l[1434172.763]: master offset -6088 s2 freq -18612 path delay 2778
ptp4l[1434172.763]: port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED
ptp4l[1434173.763]: master offset -5886 s2 freq -24498 path delay 2732
ptp4l[1434174.763]: master offset 221 s2 freq -20157 path delay 2728
ptp4l[1434175.763]: master offset 1911 s2 freq -18401 path delay 2724
ptp4l[1434176.763]: master offset 1774 s2 freq -17964 path delay 2728
ptp4l[1434177.763]: master offset 1198 s2 freq -18008 path delay 2728
ptp4l[1434178.763]: master offset 746 s2 freq -18101 path delay 2755
ptp4l[1434179.763]: master offset 218 s2 freq -18405 path delay 2792
ptp4l[1434180.763]: master offset 103 s2 freq -18454 path delay 2792
ptp4l[1434181.763]: master offset -13 s2 freq -18540 path delay 2813
ptp4l[1434182.763]: master offset 9 s2 freq -18521 path delay 2813
ptp4l[1434183.763]: master offset 11 s2 freq -18517 path delay 2813
phc2sys¶
The PHC clock is independent from the system clock. Synchronizing only PHC does not make the system clock exactly the same as the master. The xRAN library requires use of the system clock to determine a common point in time on two machines (O-DU and RU) to start transmission at the same moment and keep time frames defined by O-RAN Fronthaul specification.
This application keeps the system clock updated to PHC. It makes it possible to use POSIX timers as a time reference in xRAN application.
Run phc2sys with the command:
cd linuxptp
./phc2sys -s enp25s0f0 -w -m -R 8
Command output will look like:
ptp4l[1434165.342]: selected /dev/ptp4 as PTP
phc2sys[1434344.651]: CLOCK_REALTIME phc offset 450 s2 freq -39119 delay 1354
phc2sys[1434344.776]: CLOCK_REALTIME phc offset 499 s2 freq -38620 delay 1344
phc2sys[1434344.902]: CLOCK_REALTIME phc offset 485 s2 freq -38484 delay 1347
phc2sys[1434345.027]: CLOCK_REALTIME phc offset 476 s2 freq -38348 delay 1346
phc2sys[1434345.153]: CLOCK_REALTIME phc offset 392 s2 freq -38289 delay 1340
phc2sys[1434345.278]: CLOCK_REALTIME phc offset 319 s2 freq -38244 delay 1340
phc2sys[1434345.404]: CLOCK_REALTIME phc offset 278 s2 freq -38190 delay 1349
phc2sys[1434345.529]: CLOCK_REALTIME phc offset 221 s2 freq -38163 delay 1343
phc2sys[1434345.654]: CLOCK_REALTIME phc offset 97 s2 freq -38221 delay 1342
phc2sys[1434345.780]: CLOCK_REALTIME phc offset 67 s2 freq -38222 delay 1344
phc2sys[1434345.905]: CLOCK_REALTIME phc offset 68 s2 freq -38201 delay 1341
phc2sys[1434346.031]: CLOCK_REALTIME phc offset 104 s2 freq -38144 delay 1340
phc2sys[1434346.156]: CLOCK_REALTIME phc offset 58 s2 freq -38159 delay 1340
phc2sys[1434346.281]: CLOCK_REALTIME phc offset 12 s2 freq -38188 delay 1343
phc2sys[1434346.407]: CLOCK_REALTIME phc offset -36 s2 freq -38232 delay 1342
phc2sys[1434346.532]: CLOCK_REALTIME phc offset -103 s2 freq -38310 delay 1348
Configuration C3¶
Configuration C3 27 can be simulated for O-DU using a separate server acting as Fronthaul Network and O-RU at the same time. O-RU server can be configured to relay PTP and act as PTP master for O-DU. Settings below can be used to instantiate this scenario. The difference is that on the O-DU side, the Fronthaul port can be used as the source of PTP as well as for U-plane and C-plane traffic.
1. Follow the steps in Appendix B.1.1, PTP for Linux* Requirements to install PTP on the O-RU server.
2. Copy configs/default.cfg to configs/default_slave.cfg and modify the copied file as below:
diff --git a/configs/default.cfg b/configs/default.cfg
old mode 100644
new mode 100755
index e23dfd7..f1ecaf1
--- a/configs/default.cfg
+++ b/configs/default.cfg
@@ -3,26 +3,26 @@
# Default Data Set
#
twoStepFlag 1
-slaveOnly 0
+slaveOnly 1
priority1 128
-priority2 128
+priority2 255
domainNumber 0
#utc_offset 37
-clockClass 248
+clockClass 255
clockAccuracy 0xFE
offsetScaledLogVariance 0xFFFF
free_running 0
freq_est_interval 1
dscp_event 0
dscp_general 0
-dataset_comparison ieee1588
+dataset_comparison G.8275.x
G.8275.defaultDS.localPriority 128
maxStepsRemoved 255
#
# Port Data Set
#
logAnnounceInterval 1
-logSyncInterval 0
+logSyncInterval -4
operLogSyncInterval 0
logMinDelayReqInterval 0
logMinPdelayReqInterval 0
@@ -37,7 +37,7 @@ G.8275.portDS.localPriority 128
asCapable auto
BMCA ptp
inhibit_announce 0
-inhibit_pdelay_req 0
+#inhibit_pdelay_req 0
ignore_source_id 0
#
# Run time options
Start slave port toward PTP GM:
./ptp4l -f ./configs/default_slave.cfg -2 -i enp25s0f0 –m
Example of output:
./ptp4l -f ./configs/default_slave.cfg -2 -i enp25s0f0 -m
ptp4l[3904470.256]: selected /dev/ptp6 as PTP clock
ptp4l[3904470.274]: port 1: INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[3904470.275]: port 0: INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[3904471.085]: port 1: new foreign master fcaf6a.fffe.029708-1
ptp4l[3904475.053]: selected best master clock fcaf6a.fffe.029708
ptp4l[3904475.053]: updating UTC offset to 37
ptp4l[3904475.053]: port 1: LISTENING to UNCALIBRATED on RS_SLAVE
ptp4l[3904477.029]: master offset 196 s0 freq -18570 path delay 1109
ptp4l[3904478.029]: master offset 212 s2 freq -18554 path delay 1109
ptp4l[3904478.029]: port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED
ptp4l[3904479.029]: master offset 86 s2 freq -18468 path delay 1109
ptp4l[3904480.029]: master offset 23 s2 freq -18505 path delay 1124
ptp4l[3904481.029]: master offset 3 s2 freq -18518 path delay 1132
ptp4l[3904482.029]: master offset -169 s2 freq -18689 path delay 1141
Synchronize local timer clock on O-RU for sample application
./phc2sys -s enp25s0f0 -w -m -R 8
Example of output:
./phc2sys -s enp25s0f0 -w -m -R 8
phc2sys[3904510.892]: CLOCK_REALTIME phc offset 343 s0 freq -38967 delay 1530
phc2sys[3904511.017]: CLOCK_REALTIME phc offset 368 s2 freq -38767 delay 1537
phc2sys[3904511.142]: CLOCK_REALTIME phc offset 339 s2 freq -38428 delay 1534
phc2sys[3904511.267]: CLOCK_REALTIME phc offset 298 s2 freq -38368 delay 1532
phc2sys[3904511.392]: CLOCK_REALTIME phc offset 239 s2 freq -38337 delay 1534
phc2sys[3904511.518]: CLOCK_REALTIME phc offset 145 s2 freq -38360 delay 1530
phc2sys[3904511.643]: CLOCK_REALTIME phc offset 106 s2 freq -38355 delay 1527
phc2sys[3904511.768]: CLOCK_REALTIME phc offset -30 s2 freq -38459 delay 1534
phc2sys[3904511.893]: CLOCK_REALTIME phc offset -92 s2 freq -38530 delay 1530
phc2sys[3904512.018]: CLOCK_REALTIME phc offset -173 s2 freq -38639 delay 1528
phc2sys[3904512.143]: CLOCK_REALTIME phc offset -246 s2 freq -38764 delay 1530
phc2sys[3904512.268]: CLOCK_REALTIME phc offset -300 s2 freq -38892 delay 1532
Modify configs/default.cfg as shown below to run PTP master on Fronthaul of O-RU.
diff --git a/configs/default.cfg b/configs/default.cfg old mode 100644 new mode 100755 index e23dfd7..c9e9d4c --- a/configs/default.cfg +++ b/configs/default.cfg @@ -15,14 +15,14 @@ free_running 0 freq_est_interval 1 dscp_event 0 dscp_general 0 -dataset_comparison ieee1588 +dataset_comparison G.8275.x G.8275.defaultDS.localPriority 128 maxStepsRemoved 255 # # Port Data Set # logAnnounceInterval 1 -logSyncInterval 0 +logSyncInterval -4 operLogSyncInterval 0 logMinDelayReqInterval 0 logMinPdelayReqInterval 0 @@ -37,7 +37,7 @@ G.8275.portDS.localPriority 128 asCapable auto BMCA ptp inhibit_announce 0 -inhibit_pdelay_req 0 +#inhibit_pdelay_req 0 ignore_source_id 0 # # Run time options
Start PTP master toward O-DU:
./ptp4l -f ./configs/default.cfg -2 -i enp175s0f1 –m
Example of output:
./ptp4l -f ./configs/default.cfg -2 -i enp175s0f1 -m
ptp4l[3903857.249]: selected /dev/ptp3 as PTP clock
ptp4l[3903857.266]: port 1: INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[3903857.267]: port 0: INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[3903863.734]: port 1: LISTENING to MASTER on ANNOUNCE_RECEIPT_TIMEOUT_EXPIRES
ptp4l[3903863.734]: selected local clock 3cfdfe.fffe.bd005d as best master
ptp4l[3903863.734]: assuming the grand master role
7.Synchronize local NIC PTP master clock to local NIC PTP slave clock.
./phc2sys -c enp175s0f1 -s enp25s0f0 -w -m -R 8
Example of output:
./phc2sys -c enp175s0f1 -s enp25s0f0 -w -m -R 8
phc2sys[3904600.332]: enp175s0f1 phc offset 2042 s0 freq -2445 delay 4525
phc2sys[3904600.458]: enp175s0f1 phc offset 2070 s2 freq -2223 delay 4506
phc2sys[3904600.584]: enp175s0f1 phc offset 2125 s2 freq -98 delay 4505
phc2sys[3904600.710]: enp175s0f1 phc offset 1847 s2 freq +262 delay 4518
phc2sys[3904600.836]: enp175s0f1 phc offset 1500 s2 freq +469 delay 4515
phc2sys[3904600.961]: enp175s0f1 phc offset 1146 s2 freq +565 delay 4547
phc2sys[3904601.086]: enp175s0f1 phc offset 877 s2 freq +640 delay 4542
phc2sys[3904601.212]: enp175s0f1 phc offset 517 s2 freq +543 delay 4517
phc2sys[3904601.337]: enp175s0f1 phc offset 189 s2 freq +370 delay 4510
phc2sys[3904601.462]: enp175s0f1 phc offset -125 s2 freq +113 delay 4554
phc2sys[3904601.587]: enp175s0f1 phc offset -412 s2 freq -212 delay 4513
phc2sys[3904601.712]: enp175s0f1 phc offset -693 s2 freq -617 delay 4519
phc2sys[3904601.837]: enp175s0f1 phc offset -878 s2 freq -1009 delay 4515
phc2sys[3904601.962]: enp175s0f1 phc offset -965 s2 freq -1360 delay 4518
phc2sys[3904602.088]: enp175s0f1 phc offset -1048 s2 freq -1732 delay 4510
phc2sys[3904602.213]: enp175s0f1 phc offset -1087 s2 freq -2086 delay 4531
phc2sys[3904602.338]: enp175s0f1 phc offset -1014 s2 freq -2339 delay 4528
phc2sys[3904602.463]: enp175s0f1 phc offset -1009 s2 freq -2638 delay 4531
8. On O-DU Install PTP for Linux tools from source code the same way as on O-RU above but no need to apply the patch for msg.c
9. Start slave port toward PTP master from O-RU using the same default_slave.cfg as on O-RU (see above):
./ptp4l -f ./configs/default_slave.cfg -2 -i enp181s0f0 –m
Example of output:
./ptp4l -f ./configs/default_slave.cfg -2 -i enp181s0f0 -m
ptp4l[809092.918]: selected /dev/ptp6 as PTP clock
ptp4l[809092.934]: port 1: INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[809092.934]: port 0: INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[809092.949]: port 1: new foreign master 3cfdfe.fffe.bd005d-1
ptp4l[809096.949]: selected best master clock 3cfdfe.fffe.bd005d
ptp4l[809096.950]: port 1: LISTENING to UNCALIBRATED on RS_SLAVE
ptp4l[809098.363]: port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED
ptp4l[809099.051]: rms 38643 max 77557 freq +719 +/- 1326 delay 1905 +/- 0
ptp4l[809100.051]: rms 1134 max 1935 freq -103 +/- 680 delay 1891 +/- 4
ptp4l[809101.051]: rms 453 max 855 freq +341 +/- 642 delay 1888 +/- 0
ptp4l[809102.052]: rms 491 max 772 freq +1120 +/- 752 delay 1702 +/- 0
ptp4l[809103.052]: rms 423 max 654 freq +1352 +/- 653 delay 1888 +/- 0
ptp4l[809104.052]: rms 412 max 579 freq +1001 +/- 672 delay 1702 +/- 0
ptp4l[809105.053]: rms 441 max 672 freq +807 +/- 709 delay 1826 +/- 88
ptp4l[809106.053]: rms 422 max 607 freq +1353 +/- 636 delay 1702 +/- 0
ptp4l[809107.054]: rms 401 max 466 freq +946 +/- 646 delay 1702 +/- 0
ptp4l[809108.055]: rms 401 max 502 freq +912 +/- 659
10. Synchronize local clock on O-DU for sample application or l1 application.
./phc2sys -s enp181s0f0 -w -m -R 8
Example of output:
./phc2sys -s enp181s0f0 -w -m -R 8
phc2sys[809127.123]: CLOCK_REALTIME phc offset 675 s0 freq -37379 delay 1646
phc2sys[809127.249]: CLOCK_REALTIME phc offset 696 s2 freq -37212 delay 1654
phc2sys[809127.374]: CLOCK_REALTIME phc offset 630 s2 freq -36582 delay 1648
phc2sys[809127.500]: CLOCK_REALTIME phc offset 461 s2 freq -36562 delay 1642
phc2sys[809127.625]: CLOCK_REALTIME phc offset 374 s2 freq -36510 delay 1643
phc2sys[809127.751]: CLOCK_REALTIME phc offset 122 s2 freq -36650 delay 1649
phc2sys[809127.876]: CLOCK_REALTIME phc offset 34 s2 freq -36702 delay 1650
phc2sys[809128.002]: CLOCK_REALTIME phc offset -112 s2 freq -36837 delay 1645
phc2sys[809128.127]: CLOCK_REALTIME phc offset -160 s2 freq -36919 delay 1643
phc2sys[809128.252]: CLOCK_REALTIME phc offset -270 s2 freq -37077 delay 1657
phc2sys[809128.378]: CLOCK_REALTIME phc offset -285 s2 freq -37173 delay 1644
phc2sys[809128.503]: CLOCK_REALTIME phc offset -349 s2 freq -37322 delay 1644
phc2sys[809128.629]: CLOCK_REALTIME phc offset -402 s2 freq -37480 delay 1641
phc2sys[809128.754]: CLOCK_REALTIME phc offset -377 s2 freq -37576 delay 1648
phc2sys[809128.879]: CLOCK_REALTIME phc offset -467 s2 freq -37779 delay 1650
phc2sys[809129.005]: CLOCK_REALTIME phc offset -408 s2 freq -37860 delay 1648
phc2sys[809129.130]: CLOCK_REALTIME phc offset -480 s2 freq -38054 delay 1655
phc2sys[809129.256]: CLOCK_REALTIME phc offset -350 s2 freq -38068 delay 1650
Support in xRAN Library¶
The xRAN library provides an API to check whether PTP for Linux is running correctly. There is a function called xran_is_synchronized(). It checks if ptp4l and phc2sys are running in the system by making PMC tool requests for the current port state and comparing it with the expected value. This verification should be done before initialization.
“SLAVE” is the only expected value in this release; only a non-master scenario is supported currently.