Tektronix SPG8000A, User Manual

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160 SPG8000A User Manual
Domains
The IEEE1588 standard defines “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 profiles. For example, domain 0 might be an AES67 profile,
dom ain1 could be a master using the AVB (802.1AS) profile, and domain 127
could be a master on the SMPTE ST2059 profile.
Since the SPG8000A has two PTP engines, the instrument can provide PTP
mastering on two domains and two profiles simultaneously. With multipl e
SPGs, more domains and profiles 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 can embed 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 i nto 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 profiles, such as some telecom profiles and the SMPTE ST2059
profile, a mixture of Multicast and Unicast are allowed. On the SMPTE profile
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