docs/PTP-configuration_fh.rst

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PTP configuration
=================

A.5 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 xRAN 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). There are several Kernel options
that 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 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
    
2.Apply patch (this is required to work around issue with some of the
GM PTP packet size.)::

    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;

3.Build and install ptp41::

   # make && make install

4.Modify configs/default.cfg to control frequency of Sync interval to
0.0625s::

    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 |br|
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 good.

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 |br|
machines (O-DU and RU) to start transmission at the
same moment and keep time frames defined by ORAN Fronthaul |br|
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 |br|
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 Section A.6.1 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

1.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

2.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

3. 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

4.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

5.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

6. 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

7. 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

8. 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 current port state and comparing it with the expected
value. This verification should be done before initialization.

*notes. “SLAVE” is the only expected value in this release; only a
non-master scenario is supported currently.*

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