EXFO FTB-800 Series for FTB-1 - Manual (Page 551)

Glossary
NetBlazer 541
1588 PTP
If the Master Clock has sufficient capacity to handle the Client Clock
request, it responds with a signaling message containing a GRANT
UNICAST TRANSMISSION TLV.
The REQUEST UNICAST TRANSMISSION TLV contains several
parameters:

messageType is the type of service being requested: Announce,
Sync, or Delay Response.

durationField is the duration of the requested service:
300 seconds by default and configurable from 60 to 1000 seconds.

logInterMessagePeriod: transmission rate of the requested
messages.
If the Master Clock denies the request, e.g. because it has no remaining
capacity, it will send back a GRANT UNICAST TRANSMISSION TLV with the
durationField set to zero.
In the event of being denied service by a Master Clock, or receiving no
response to the service request, a Client Clock should wait a minimum of
one second before issuing a new Unicast request to that Master Clock.
As Unicast service is only granted for a limited time, the Client Clock must
re-request service periodically, before the expiration of the current grant.
The Client Clock should reissue the request sufficiently far in advance of
the expiration to allow the request to be repeated at least twice if no grant
is received. This parameter is called Unicast renewal interval.