IEEE C37.238-2011 pdf free download – IEEE Standard Profile for Use of IEEE 1588™ Precision Time Protocol in Power System Applications.
5.12.2 Profile specific TLVs
The following profile specific TLV shall be supported:
 IEEE_C37_238 TLV
This TLV shall be used to communicate the following:
 Grandmaster ID
 GrandmasterTimeInaccuracy
 NetworkTimeInaccuracy
The grandmaster ID is user configurable.
The implementation of this TLV shall conform to the terms of 14.3 of IEEE Std 1588-2008.
The IEEE_C37_238 TLV field values shall be as follows:
 tlvType (Enumeration16); ORGANIZATION_EXTENSION value = 0003 hex
 lengthField (UInteger16) value = 000C hex. The number of octets in the dataField
 organizationId (Octet[3]); The OUI value assigned by IEEE RAC = 1C129D hex
 organizationSubType (Enumeration24) value = 000001hex
 dataField (12 octets) as follows:
 grandmasterID (2 octets) value 0003-00FE hex, most significant byte is reserved and shall be 0. Other values are invalid and indicate that grandmasterID is not configured.
 grandmasterTimeInaccuracy (Uinteger32) value 00000000-FFFFFFFF hex, in nanoseconds,where FFFFFFFF indicates the maximum value (approximately 4.29 s) has been exceeded.
 networkTimeInaccuracy 10 (Uinteger32) value 00000000-FFFFFFFF hex, in nanoseconds,
where FFFFFFFF indicates the maximum value (approximately 4.29 s) has been exceeded.
 reserved (2 octets) value 000000000000 hex shall be transmitted.
The IEEE C37.238 Announce messages shall not be sent until the grandmaster clock has been assigned a unique grandmaster ID and data for the ALTERNATE_TIME_OFFSET_INDICATOR TLV has been configured.
IEEE C37.238 Announce messages without two mandatory TLVs attached shall be ignored by the BMC algorithm.
5.13 TimeInaccuracy
IEEE C37.238 TimeInaccuracy provides a mechanism by using profile specific IEEE_C37_238 TLV, defined in 5.12.2, for the applications to determine whether the worst-case error estimate in the delivered time is acceptable.
All clocks shall provide TimeInaccuracy using profile specific IEEE_C37_238 TLV, defined in 5.12.2.
TimeInaccuracy includes the following:
 grandmasterTimeInaccuracy
 networkTimeInaccuracy
GrandmasterTimeInaccuracy is provided by grandmaster clocks. This value shall be a more precise value of the clockAccuracy of the clockQuality field specified in 7.6.2.5 and Table 6 of the IEEE Std 1588-2008.
NetworkTimeInaccuracy is configured at the grandmaster and shall be set to 0 by default. This value may be set to TimeInaccuracy accumulated in the worst network path.
LocalTimeInaccuracy is maximum TimeInaccuracy that the device contributes to the networkTimeInaccuracy. Device manufactures shall specify LocalTimeInaccuracy. This value shall not exceed the value specified in Annex B.
TimeInaccuracy shall be calculated during network engineering stage based on device specifications and network design.
TCs shall not forward any IEEE C37.238 messages, while their LocalTimeInaccuracy exceeds its specified maximum LocalTimeInaccuracy.
NOTE—TCs could use the following parameters to define their TimeInaccuracy:
 Error introduced by the Timestamping hardware.
 Error of the PDelay measurements on the receiving port.
 Syntonization error, i.e., uncertainty combined with the residence time of previous Sync messages.IEEE C37.238 pdf download