Tektronix SPG8000A Operation Instructions Manual - User Manual

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SPG8000A Option PTP operation instructions

This document describes how to con

gure the SPG8000A to operate in your PTP

network and also provides information about the basics of PTP operation. A list
of known bugs and operational limitations are included.

How to con

gure Option PTP on the SPG8000A

General information

The operation of the instrument is intended to be primarily an SPG with the
addition of PTP functionality, and the menu structure re

ects this orientation.

Reference mode.

The Reference mode selection restricts the possible PTP

functions as follows:

If the Reference mode is set to GPS, Genlock or Internal, the primary PTP
function is a master.

If the Reference mode is set to PTP, then the primary PTP function is restricted
to Slave PTP mode.

Automatically adapting between master and slave functions via the BMCA
is not supported.

Secondary PTP engine.

A secondary PTP engine is also available. This allows

implementing two masters when in Internal mode or locked to GPS, and
simultaneous Master and Slave operation.

The primary and secondary PTP systems must be on different domains.

Presets.

Most of the PTP functions are saved in the presets. After con

guring

the instrument, a user can save the Power-on preset so that the desired instrument
state is restored when the instrument is powered on.

Black outputs.

The black outputs support a 1pps mode. This is useful for

measuring timing between systems.

Firmware update.

After a

rmware update, the presets are often not valid and will

usually be erased. Therefore, after an update please use the REF button menu to
reselect either GPS or PTP as the Reference mode, and then use the PTP button
menu to reselect all of the parameters. Next, use the SYSTEM button menu to
resave the Power-on preset with your preferred settings.

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SPG8000A Option PTP operation instructions

Basic setup

recommendations

Use the SYSTEM button menu to set the PTP network IP address using
DHCP or Manual mode. (Press the SYSTEM button, and then press the down
arrow twice to access the menu.)

NOTE.

Both PTP ports share the same network address. See the PTP network

settings section below for information about how to con

gure the two PTP ports.

Use the REF button menu to set the Reference mode depending on whether
the SPG8000A will be a PTP master, slave or both. (Press the REF button,
and then press the left or right arrow to select. Press ENTER to con

rm the

selection.)

If the SPG8000A is to be the PTP master, select either GPS, Genlock or

Internal mode.

If the SPG8000A is to be a PTP slave, select PTP mode.

If the SPG8000A is to be both a PTP master and slave, select PTP mode

and then con

gure the secondary master.

If Genlock mode is selected as the Reference mode, then also set the time to
VITC, LTC, or Internal. In addition, select to use the ST309 data as "input" if
ST309 date information is available in the input timecode. Note the limitations
on Drop Frame time code in the limitations section of this document.

Use the PTP button menu to con

gure the Primary master or slave PTP

pro

le, message rates, etc. (Press the PTP button once, and then use the arrow

keys and the ENTER / BACK keys as necessary to make selections.)

If desired, press the PTP button a second time to access the secondary PTP
engine. Select parameters as needed.

Con

gure the rest of the SPG8000A as per the online manual for the SPG8000.

SPG8000A Option PTP operation instructions

SYSTEM button menu

additions

PTP network settings.

A new submenu in the SYSTEM button menu allows users

to set the Network parameters on the PTP connection. Use this menu to set the
DHCP/Manual and other network selections.

This menu also allows setting the DSCP level on the PTP messages. For most
situations, the default value of 0 for noncritical General messages and 46 for the
Event messages is appropriate. If you are using the AES67 pro

le, it may help to

set both message types to the maximum value of 56. Changing these values resets
all of the PTP systems and will disrupt the PTP operation for about 35 seconds.

This menu also allows control of the internal switch. The RJ45 and SFP ports can
be con

gured as fully cross-linked, isolated or to mirror the RJ45 to the SFP. For

most applications the Isolated setting is appropriate. This setting allows the two
ports to both access PTP functions and not allow cross traf

c. If you want the

ports to work like a normal switch, use the Cross-linked setting. In this setting, all
traf

c into either port will echo out the other port. In Mirror mode, all the traf

in and out of the RJ45 port will be echoed to the SFP port. This is useful if you
need to use Wireshark on a Unicast system. In this case, hook the Wireshark PC
to the SFP port and use the internal switch to mirror the traf

Epoch settings.

A second new submenu in the SYSTEM button menu controls

the Epoch Selection, which is intended to change the timing on the Black outputs.
For PTP systems, set this to the 1970 epoch.

New PTP button menu

There are two PTP functions: Primary and Secondary. Press the PTP button
repeatedly to toggle between the two functions.

The Primary PTP function will be either Master or Slave depending on the
Reference selection. Adaptive mode between master and slave is not supported.

The Secondary PTP function is only a master. The primary and secondary PTP
functions cannot be on the same domain. The SPG8000A will display an error
message if an attempt is made to set them to the same domain.

The entries in the PTP menu vary depending on modes of the instrument.
Master and Slave modes need different settings. Multicast, Unicast and Mixed
modes have different settings. Different pro

les allow different ranges for

some parameters. The possible PTP menu entries are listed below with a basic
description of their function:

Master can be enabled or disabled. Slave is always on.

Pro

le Type. The following pro

le types are available: General, ST2059,

AVB and AES67. Since each pro

le retains unique settings, each parameter

must be set for each pro

le type.

Press ENTER to set defaults for the selected pro

le. The defaults will set a

nominal value given the selected pro

le.

SPG8000A Option PTP operation instructions

Domain. Defaults to a reasonable setting for each pro

le. Users are not

allowed to set both PTP engines to the same domain.

Communication mode. All of the master and slave devices on a given domain
must use compatible communication modes. For most pro

les, this means

the master and slave communication modes need to match exactly. On the
SMPTE pro

le, the Multicast and Mixed modes are compatible, so a master

in any of these modes will work with a slave in any of those modes.

Unicast is separate and the master and slave must match. Note that the
Unicast, and Mixed without negotiation modes require that the IP address
of all the masters be entered into the Acceptable Master Table (AMT) of
the slave.

Announce interval allows setting the rate at which the master will send
announce messages. For Unicast mode there are two settings: Desired and
Required. The slave will start by requesting the Desired rate. If the master
refuses that rate, the slave will request a slower rate. This continues down
to the Required setting. If the master cannot support the Required setting,
the communication will not start. The default for the Required setting is the
minimum rate / maximum interval allowed in the pro

le.

Sync interval allows setting the rate at which the master will send sync
messages. For Unicast mode there are two settings: Desired and Required.
The slave will start by requesting the Desired rate. If the master refuses that
rate, the slave will request a slower rate. This continues down to the Required
setting. If the master cannot support the Required setting, the communication
will not start. The default for the Required setting is the minimum rate /
maximum interval allowed in the pro

le.

Delay Message allows setting the rate at which the master will send delay
request messages. For Unicast mode there are two settings: Desired and
Required. The slave will start by requesting the Desired rate. If the master
refuses that rate, the slave will request a slower rate. This continues down
to the Required setting. If the master cannot support the Required setting,
the communication will not start. The default for the Required setting is the
minimum rate / maximum interval allowed in the pro

le.

Announce timeout count sets the number of announce messages which can be
missed before the device will assume the master is no longer present. After
that time, all the devices on the domain will start the process of selecting a
new master.

Priority 1 and 2 are used in the BMCA to select the active master. Typically,
all the masters should have the Priority 1 parameter set to the same value,
and then use the Priority 2 parameter to select the primary master if all have
the same clock quality. A lower value is preferred. For example, if you set
the Priority 2 parameter of the primary master to 127, then set the Priority 2
parameter of all other masters to 128.

SPG8000A Option PTP operation instructions

One-step and two-step communication mode controls whether the timestamp
for the sync message is sent in the sync (one-step mode) or sent in a follow-up
message (two-step mode). Some devices, such as transparent clocks, only
work on two-step messages. All slaves are required to work in both one-step
and two-step modes.

Delay Mechanism. Two delay modes are available: Peer-to-Peer and
End-to-End.

In Peer-to-Peer mode, the Pdelay request and Pdelay response messages

are local to each link in the network. Each device determines the local link
and device delays. The sync message from the master then collects the
corrections as it propagates from the master to slave. Peer-to-Peer mode
is useful in PTP networks where the routing con

guration changes. For

Peer-to-Peer mode to work well, all of the devices need to be PTP aware.

In End-to-End mode, the sync, follow up, delay request and delay

response messages go through the network all the way between the master
and slave. End-to-End mode is useful in PTP networks where some or all
devices are not PTP aware.

Acceptable Master Table is required in Unicast and Mixed without Negotiation
modes. Enter the IP address of all masters into the AMT of the slaves. The
AMT can support up to eight IP addresses.

Asymmetric delay allows correcting the slave timing for any asymmetric
delay in the network. Use the 1 pps or other timing signal to determine the
required delay. This should not be necessary if the network is PTP aware.

ST2059 pro

le menu selections.

When ST2059 is the selected pro

le and the

SPG8000A is con

gured as a PTP master, these additional menu selections

appear. These settings only drive the Synchronization Metadata message content
and have no effect on the operation of the master. Each of these menu selections
can be set to “Auto” to ensure that the metadata bits are sent in a valid state.

ST2059 SM Default Frame. Sets the metadata message

elds to indicate the

selected frame rate: 23.98, 24, 25, 29.97, 30, 47.95, 48, 50, 59.94, 60, 71.92,
72, 100, 119.9, or 120.

ST2059 SM Drop Frame Flag. Sets the metadata message bit for the Drop
Frame Flag to enabled or disabled.

ST2059 SM CFID. Sets the metadata message bit for the Color Frame ID to
enabled or disabled.

SPG8000A Option PTP operation instructions

Status menu

Press the STATUS button then use the down arrow to select different types of
status. The PTP master and PTP slave status sections have multiple pages that can
be displayed using the left and right arrow.

The master status reports the clock quality and some of the ST2059-2
metadata parameters it is sending.

The slave status reports the clock quality and some of the ST2059-2 metadata
parameters it is receiving.

Web UI and SNMP

The Web UI and SNMP allow users to control of most of the instrument functions
that are available from the front panel. See the

SPG8000A User Manual

for more

information on the SNMP command set.

Known bugs and

limitations

The following is a list of known bugs and operational limitations:

Genlock to PAL with VITC or 25 Hz LTC is fully functional. Genlock to
NTSC with VITC or 30 Hz Drop Frame LTC basically works but is not fully
accounting for the drop frame compensation. Therefore, there may be a few
frames of error until the scheduled jam sync had occurred.

The Peer-to-Peer delay mode has had limited testing. The basic messages are
present but a full system has not been demonstrated.

ST2059-2 SM leap seconds are not fully implemented. The other messages
should be working.

Slave Lock takes about 2.5 minutes.

The AVB and AES67 pro

les have had limited testing.

SPG8000A Option PTP operation instructions

PTP operational overview

PTP introduction

Option PTP for the SPG8000A adds two Precision Time Protocol (PTP) engines
to the SPG system. The primary PTP engine has the capability to be a master
PTP source or lock the SPG to the PTP as a slave. The secondary PTP engine
can only be a master.

PTP operating modes.

The basic operating mode of the SPG is set in the

Reference Select menu. The reference selection drives the allowed function of the
primary PTP engine as follows:

If the SPG reference selection is set to internal, or to lock to an external GPS,
NTSC, PAL, Tri-level or CW signal, then the primary PTP engine can only
be a master.

If the SPG reference selection is set to lock to an external PTP signal, then the
primary PTP engine can only be a slave.

PTP master selection.

In a PTP network, all the masters on the network are

evaluated by the Best Master Clock Algorithm (BMCA). The BMCA runs
on all devices, and chooses a master based on several parameters. Some of
the parameters relate to clock quality; conversely the Priority 1 and Priority 2
parameters are set by the user to in

uence the choice of a master:

Priority 1. This parameter de

nes which clocks are allowed to be considered

as masters. To be considered as a master, the value should be set to 128 or
less. Priority 1 is the

rst criteria in the BMCA, so if Priority 1 is set to a

lower value than other devices on the system, then it will be chosen even if
the clock quality is poor. Typically, all the masters in a domain should have
the same value for the Priority 1 parameter.

Priority 2. This parameter is used to break the tie between masters that have
the same clock quality. Several values may be used to de

ne a hierarchy of

devices. Most pro

les use 128 as a default, so a value of 127 or lower would

indicate a preferred master.

The

nal tie-breaker in the BMCA is the clock ID. This is usually the MAC

address so it provides a unique value by which the BMCA can choose.

Network topology.

In a typical IEEE1588 PTP network, many devices may be

either masters or slaves. If the current master stops working, all the devices that
are capably of being a master broadcast their clock quality and a new master is
selected.

For video networks it may make sense to depart from the telecom-style PTP
topology and dedicate devices to be only masters or slaves. This is the approach
supported by the SPG8000A, which allows for a more traditional primary and
backup master structure controlling a range of slave devices. The BMCA is still
used to select the active master and the network still takes the place of the ECO in
the legacy Black-burst/Tri-level network. See the

SPG8000A User Manual

for

suggestions on possible network topologies.

SPG8000A Option PTP operation instructions

The

ve basic PTP timing

messages

There are

ve basic timing messages in a PTP system: Announce, Sync,

Follow-up, Delay request, and Delay response. Other messages are present in
some instances. For example, grant requests and responses appear in unicast
systems, and Type Length Value (TLV) management messages appear in SMPTE
ST2059 pro

le systems.

Announce message.

The Announce message is sent by the master to advertise its

capability. This message contains the clock quality and priority settings needed
for the BMCA to evaluate which device is the best master.

Sync message.

The Sync message is sent by the master and is used to measure

the propagation delay from the master to slave. The sync message may contain
the timestamp indicating when it was sent, or that time may be in the Follow-up
message. The receiver must timestamp the sync message upon receipt. These
two timestamps are usually called “t1” and “t2” and provide the

rst delay

measurement.

Follow-up message.

The Follow-up message is sent only in cases where the

PTP network hardware is not capable of inserting the timestamp into the Sync
message. (See page 10,

One-step and two-step operation

Delay request message.

The Delay request is sent by the slave. The time at which

it is sent is noted by the slave, but is not included in the message. This time is
usually called “t3.” When the delay request is received by the master, the master
timestamps the receive time. This timestamp is usually called “t4.”

Delay response message.

The delay response is sent from the master to the

slave. The response contains the t4 time stamp from when the master received
the delay request. Once the slave receives the delay response, it has the second
pair of timestamps needed to calculate the second delay measurement of the
slave to master delay.

SPG8000A Option PTP operation instructions

Message timing.

The following

gure show the relationships between the

PTP timing messages.

Pro

les

The IEEE1588 standard de

nes multiple parameters, such as the rates for Sync

and Announce messages, and optional functions such as grandmaster clusters.
Speci

c industries wanting to use PTP are encouraged to de

ne their own

“pro

le,” which allows the PTP standard to be tuned for speci

c applications.

The pro

le de

nes the default and range of each parameter, and de

nes with

options are required, allowed or prohibited.

In the SPG8000A, the pro

le can be initialized to the default value for a given

pro

le and mode. After setting the reference mode, the user should go to the PTP

menu and select the pro

le. The user then has the options to initialize the pro

parameters to the default value for both the selected pro

le and operating mode

(Master, Slave or Adaptive). After initialization, the user can modify the pro

parameters and save as part of an instrument preset. The allowed range of the
parameters is restricted to that which is allowed for the given pro

le type.

SPG8000A Option PTP operation instructions

Domains

The IEEE1588 standard de

nes “domains,” which allow multiple PTP services

to coexist simultaneously on one physical Ethernet connection. For example, on
a given network one master and several slaves can be using domain 0 while a
second master and other slaves are using domain 1. These two PTP services are
independent. One use for this is to have masters on different domains provide PTP
on different pro

les. For example, domain 0 might be an AES67 pro

le, domain 1

could be a master using the AVB (802.1AS) pro

le, and domain 127 could be a

master on the SMPTE ST2059 pro

le.

Since the SPG8000A has two PTP engines, the instrument can provide PTP
mastering on two domains and two pro

les simultaneously. With multiple SPGs,

more domains and pro

les can coexist on the same network.

One-step and two-step

operation

Some PTP messages have a time stamp associated with them. This time stamp
indicates the time of the local clock when the message was sent or received.
In some cases, the hardware is capable of embedding the time stamp in the
message as it is sent. This is known as “one-step” mode since the message and
its associated time are sent together.

In other cases, the hardware is not capable of inserting the time into the message,
so instead it is sent in a second follow-up message. This is called “two-step” mode
since there are two messages.

It is interesting to note that in End-to-End mode, only the Sync message is
effected by the one-step and two-step setting since it is the only message that
needs the transmit time stamp inserted. This means that other than masters, all
devices should be able to process either one-step or two-step message types.
In a similar fashion, Peer-to-Peer mode has some messages that may require
follow-up support.

Multicast, Unicast, and

Mixed Communication

modes

There are three basic message modes for PTP: Multicast, Unicast, and mixed
Multicast and Unicast. For full Multicast or Unicast modes, all of the PTP
messages are sent in the selected mode type.

For some pro

les, such as some telecom pro

les and the SMPTE ST2059 pro

le,

a mixture of Multicast and Unicast are allowed. On the SMPTE pro

le unique

mixed mode, the Announce and Sync messages are sent as multicast. However,
the Delay request and Delay Response messages are sent as Unicast.

Some points to understand about communication modes:

Whatever mode is chosen, the master and slave must match or be compatible

Multicast and Mixed mode may need IGMP joins and leaves

Full Unicast must have the master address in all slave AMTs

Unicast without negotiation does not allow master to regulate load

Two masters can be used on different domains to serve slaves on different
communication modes

SPG8000A Option PTP operation instructions

Multicast system messages.

Multicast messages are broadcast and so they can be

received without knowing the address of the sender. This allows a slave to hook
up to the network, receive the announce messages and discover the identity of
the master. Multicast in some networks requires the devices to use IGMP to join
and leave the multicast group.

In Multicast PTP systems, the master sets the rate of the announce and sync
messages. The master also sends the maximum allowed delay request rate in the
delay response message. Ideally, the slave will use that value to set the delay
request rate although some slave set this rate independently. The delay request
rate is typically the same as the sync rate, but may be higher or lower.

Unicast system messages.

Unicast messages require the address of the master

be entered into the Acceptable Master Table (AMT) in each slave. If there are
multiple masters, the IP address for each master must be entered in the AMTs
of all the slaves.

In Unicast PTP systems, the slave must have the address of the master in its
acceptable master table. The slave sends several grant requests to the master
requesting speci

c rates for each message type. If the master accepts the grant

requests, it will send grant acknowledges. If the master denies the grant, the slave
may send a new grant request at a lower rate. This process may continue for
several iterations until the master and slave agree on a rate. The master and slave
will then start exchanging the PTP messages. If the master cannot support any of
the rates requested by the slave, then the slave will not be able to lock to the master.

Mixed mode system messages.

In Mixed Mode systems, some messages are

Multicast and some are Unicast. For the SMPTE ST2059 pro

le, the Announce

and Sync messages are sent as Multicast. This allows devices to discover the
active master. The Delay Request rate is con

gured for Unicast, so the slave and

master must exchange grant messages before the system will start the full range
of messages.

In Mixed mode without negotiation, the delay request rate set by the slave must
be equal to or less than the Sync rate set by the master. Otherwise, the slave will
not be able to connect to the master.

SMPTE pro

le system messages.

For SMPTE pro

le systems, a given domain

must use one type of message for all Announce, Sync and Follow up messages.
Therefore, all masters and slaves on that domain must be con

gured for either

Multicast or they all must be con

gured for Unicast.

For SMPTE mixed mode, the Announce, Sync, and Follow up messages are
con

gured as Multicast so that the delay requests can be Multicast, Unicast, or

Unicast without negotiation. To use this combination, set the master and slave to
any of the modes: Multicast, Mixed, or Mixed without negotiation. The masters
will support all of the slave modes simultaneously.

SPG8000A Option PTP operation instructions

BMCA

The Best Master Clock Algorithm (BMCA) is used to choose the active master on
the domain. This is partially explained in the introduction to this document. The
BMCA operation varies somewhat as function of communication mode.

Multicast mode.

In Multicast mode, the active master sends announce messages

that all other masters and slaves can receive. So all devices can evaluate the
BMCA and decide on the best master. If any device detects that its BMCA
rating is better than the current master, it will send an announce and take over as
the active master.

Unicast mode.

In Unicast mode, slaves only get Announce messages if they

establish a grant from the master. Therefore, each slave must set up a grant
with every device in its AMT. Since the masters do not set up grants from other
masters, they do not have the information to evaluate the BMCA and know if
they are the active master. It is up to the slaves to evaluate the BMCA based on
the announce message they get from each master in their AMT. Each slave then
decides which master is the best and then set up grants for the other message
types. If slaves on a given network have a different list of masters in their AMT,
then they may choose a different master.

Mixed mode.

In a SMPTE ST2059 mixed environment, the announce message is

Multicast. Therefore, the BMCA can follow the Multicast conventions.

Compensating for causes

of asymmetric delay

Several factors can cause the PTP message delay to be different for the messages
sent from the master to slave as opposed to the messages the other direction from
the slave to master. Unless corrected, this propagation delay asymmetry will
cause an offset in the clock phase equal to ½ the difference in the two path delays.
There are 4 main causes of asymmetric delay: Rate mismatch in the ports on a
switch, Traf

c mismatch on the two paths, message type mismatch, and cable

delay variation. The paragraphs below contain hints on how to design the system
to minimize the delay asymmetry. Alternatively, the SPG8000A provides a way to
manually enter a correction value to cancel the delay error.

Rate mismatch.

Rate mismatch in a switch causes a delay asymmetry due to the

fact that the switch does a “store and forward” on messages. This means the
entire message must be stored in the buffer before it starts to be “forwarded” or
sent out. For example, for a 100 Mb input and 1 Gb output, the switch must wait
for the entire message to clock in at the slow rate before it can start outputting
the message at the high rate. Conversely for a 1 Gb/s input and 100 Mb/s output,
the entire packet is quickly read in at the faster rate, so then the output can start
sooner, albeit at a lower rate.

While the total time is the same for both directions, the delay on the fast-in,
slow-out direction is shorter on the packets which contain the PTP timestamps.
This effect is signi

cant on a 100 Mb/1 Gb rate mismatch, but much less

signi

cant on a 1 G/10 G switch since the message time at 1 Gb/s is quite short. If

the switch supports Transparent Clock (TC) mode, then this rate mismatch delay
effect is corrected by the TC delay correction.

SPG8000A Option PTP operation instructions

Traf

c mismatch.

Another cause of asymmetric delay is traf

c mismatch on the

two paths. If there is a high percentage of traf

c utilization on the master to slave

path, then most of the PTP messages may be delayed signi

cantly. If the traf

on the other direction is signi

cantly different, then the messages on the path

may not suffer the same delay.

This effect can be quite large depending on the traf

c, the quality of the switch,

and the number of switches in the network. To reduce this effect, a user should
avoid large loading on the PTP network, use high-quality switches that avoid this
delay variance, or use PTP Transparent mode switches which will insert residence
time information to allow the slave to correct for this delay.

Message type mismatch.

Another cause of delay asymmetry is message type

mismatch. For example, if the sync message is Multicast and the delay request is
Unicast, then some switches may process the messages differently and cause a
differential delay. Since the SMPTE pro

le allows a mixed mode operation,

switches should be evaluated to ensure they do not have this effect. If transparent
mode switches are used, then this effect should be corrected by the slave.

Cable delay variation.

The actual propagation delay through Cat 5 cable can be

signi

cantly different in one direction versus the other direction. This can be

due to the twist rate on the pairs, routing inside the sheath, material differences,
etc. The PTP system is incapable of removing this effect, so the best way to
prevent this is to use high-quality cable with a minimum variation in the physical
propagation delay.

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