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Is it suported to have a multicast PTP Grandmaster for boundary/ordinary clock setup?


I'm trying to setup an EXOS device as boundary or ordinary clock, but our grandmaster is set up to work in multicast. Reading documentation, I've just seen examples for unicast grandmasters. Is it possible to sync to a multicast grandmaster?

7 replies

Userlevel 6
EXOS does not currently support multicast PTP operation.

A list of EXOS PTP supported features can be found here:
http://documentation.extremenetworks.com/exos/EXOS_21_1/Slots_and_Ports/c_supported-ptp-features.sht...

A list of EXOS PTP limitations can be found here:
http://documentation.extremenetworks.com/exos/EXOS_21_1/Slots_and_Ports/c_limitations-of-ptp.shtml
Thanks Chad,

It's a pity, because for audio&video, the ptp profiles used (SMPTE ST-2059-2 and AES-67) require the use of multicast.

This makes our EXOS switches useless for this scenario.

Kind regards,

Toni
Userlevel 6
Toni,

This is a common misconception. AES67 has been developed to work on any standard ethernet switch. It has no requirement for PTP on the switching infrastructure. There is a PTP requirement on the endpoints. An excerpt from this FAQ.

"What is the difference between AES67 and AVB?The AVB standards define improvements to the standard Ethernet layer 2 protocol to provide synchronization, Quality of Service (QoS) and an admission control behaviour that prevents the network from becoming overloaded by media traffic; an AVB network requires use of specific AVB Ethernet switches. AES67 utilizes protocols on layer 3 or above, so is able to function using standard Ethernet switches. While it is entirely possible for AES67 to function over an AVB network, AES67 will not receive any performance benefits from the capabilities of the AVB network, except if the AES67 device fully supports the AVB layer 2 protocol stack."

I am not as familiar with SMPTE ST-2059-2, but I know it uses AES67 for the audio transport and therefore I suspect it has similar requirements (standard network switch).
Yes, both have similar requirements. It's true that there is no requirement for PTP aware switches, but if your network is big, with routing, and heavy traffic (and for video the traffic is around 1,5gb per stream, similar to AVB), manufacturers recommend PTP aware switches to be sure they will be sync issues. On top of that, boundary clocks help to offload requests from the grandmaster. That's why we were trying EXOS PTP features.

Kind regads,

Toni
Userlevel 6
Yes if boundary clocks are needed due to the scale of the network, we wouldn't be able to support that functionality.
Anyway, I take this opportunity to ask another question. Transparent clock works in multicast? That is, the switch adds the time correction information to the PTP packets when working in multicast?
Userlevel 6
Toni Comerma wrote:

Anyway, I take this opportunity to ask another question. Transparent clock works in multicast? That is, the switch adds the time correction information to the PTP packets when working in multicast?

The hardware supports this functionality and therefore it may work. However, it is not officially supported.

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