For each PTP message type to be exchanged between the router and an external 1588 clock, a unicast session must be established using the unicast negotiation procedures. The router allows the configuration of the message rate to be requested from external 1588 clocks. The router also supports a range of message rates that it grants to requests received from the external 1588 clocks. The IEEE 1588 standard allows the grantor port to respond with a shorter duration than what was in the request. The router can accept such a grant and uses that duration. The router issues a renegotiation before the duration expires.
Table: Message rates ranges and defaults describes the ranges for both the rates that the router can request and grant.
| Message type | Rates requested by the 7450 ESS, 7750 SR, 7950 XRS, and VSR | Rates granted by the 7450 ESS, 7750 SR, 7950 XRS, and VSR | ||
|---|---|---|---|---|
| Min | Max | Min | Max | |
Announce  | 
1 packet every 16 seconds  | 
8 packets/second  | 
packet every 16 seconds  | 
8 packets/second  | 
Sync  | 
1 packet/second  | 
64 packet/second  | 
1 packet/second  | 
128 packet/second  | 
Delay_Resp  | 
1 packet/second  | 
64 packets/second  | 
1 packet/second  | 
128 packets/second  | 
(Duration)  | 
300  | 
300  | 
1  | 
1000  | 
State and statistics data for each PTP peer are available to assist in the detection of failures or unusual situations.