Precision Time Protocol (PTP) IEEE 1588v2

Precision Time Protocol (IEEE 1588v2) allows precise synchronization of clocks in measurement and controls systems implemented with technologies such as network communications, local computing and distributed objects. The protocol supports system wide synchronization accuracy in sub-microseconds range with minimal network and local clock computing resources. The protocol operates in master/subordinate configuration. IEEE1588 deploys Multicast over an Ethernet network, and devices such as routers and switches can sync to the provided timing source.

Supported Load Modules

The following Ixia load modules have the PTP capability:

Supported Messages

The following messages are supported between clocks participating in the PTP protocol.

Supported Features

The following PTP features are supported.

Local Clock synchronization through PTP to another PTP clock

The local clock of the is synchronized to the 's master clock by minimizing the Offset_from_master value of the current data set. The time and the rate characteristics of the local clock are modified upon receipt of either a sync message or follow-up message. The following figure illustrates the PTP communication path.

Figure: PTP Communication Path

PTP Communication Path
Term Value

sync_receipt_time = Ts1

Ts1 =Tm1+O+master_to__delay

preciseOriginTimestamp = Tm1

Tm1

master_to__delay (computed)

Ts1–Tm1

delay_req_sending_time = Ts2

Ts2

delayReceiptTimestamp = Tm2

Tm2 = Ts2 – O + _to_master_delay

_to_master_delay (computed)

Tm2 – Ts2

one_way_delay

{(master_to__delay as computed) + (_to_master_delay as computed)}/2

 

{(Ts1-Tm1) + (Tm2-Ts2)}/2

 

{(O + master_to__delay ) +

 

–O +_to_master_delay)}/2

 

{(master_to__delay ) + (_to_master_delay)}/2

 

master_to__delay if path is symmetrical

 

  1. Offset shall be computed as O= Ts1-Tm1 - one_way_Delay. Offset and One way delay shall be stored.
  2. Offset correction shall be applied to the local clock.

Local clock frequency transfer

In Slave mode of operation, the Ixia port implements a local clock in software (Linux). The frequency of the oscillator is not adjusted but allowed to free-run. The local clock shall be implemented based on time information synchronized from sync/follow_up messages and hardware timestamps associated with these messages. The local clock is associated with a constant and a slope. The rate of a local clock relative to a master clock is illustrated in the figure below in IxExplorer References section.

IxExplorer References

See the IxExplorer User Guide, Chapter 10, Protocol Interfaces, especially topics Protocol Interfaces Tab, PTP Discovered Information, and PTP Clock Configuration.

Figure: Rate of Local Clock Relative to Master

Where T1 is the time synchronized from the master and TS1 is the hardware timestamp associated with sync message 1. T2 and TS2 are corresponding parameters associated with sync message 2. T is the time at any point of time.

With a sync message, the parameters K and the slope are updated. The Clock Offset from master is calculated as discussed above and applied to K for correction.

Timestamps are cleared once when PTP is enabled.

In master mode of operation, server provides timestamp to the ports at the instant timestamps are cleared and slope is 1. OFFSET from master is 0.

If a GPS source is interfaced to the chassis, ports emulating the master are configured as Grand Master.

Local clock time format is seconds (32 bits) and nanoseconds (32 bits). The Ixia port supports a 2-step clock.