– 132 – 61850-8-1 IEC:2004(E)
G.3 ISO 9506-2 (Protocol specification)
G.3.1 Add UTC as a new time type
Insert, in Subclause 14.4.2, below the line
mMSString [16] MMSString
the following new text
utc-time [17] IMPLICIT UtcTime --UTC Time
Add, at the end of Subclause 14.4.2.3, the following new subclause:
14.4.2.4 UTC Time
The UtcTime type shall be an OCTET STRING of length eight (8) octets. The value shall be
encoded as defined in RFC 1305. The format of the value is as a 64-bit fixed point number.
The integer part contains: elapsed number of whole seconds since GMT midnight January 1,
1970(s). The fractional part contains the portion of a second elapsed since the last whole
second.
The integer seconds since January 1, 1970 shall be contained within the most significant four
(4) octets (e. g., octets 0 through 3). The value of the time field shall be derived by numbering
the bits of these octets, starting with the least significant bit of the last octet as bit zero and
ending the numbering with the most significant bit of the first octet as bit thirty one. Each bit
shall be assigned a numerical value of 2**N, where N is the position of the bit in this
numbering sequence. The value of the time shall be obtained by summing the numerical
values assigned to each bit for those bits which are set to one.
The fraction of second value shall be contained in the least significant four octets (e.g. octets
4 through 7). The value of the fraction field shall be derived by numbering the bits of these
octets, starting with the most significant bit of octet 4 as bit one and ending the numbering
with the least significant bit of octet 7 as bit 32. Each bit shall be assigned a numerical value
of 2**-N, where N is the position of the bit in this numbering sequence. The value of the time
shall be obtained by summing the numerical values assigned to each bit for those bits which
are set to one (1).
NOTE This representation corresponds to the format which is commonly used in many contexts such as Internet
protocols and GPS satellite time services. For most real implementations in the foreseeable future, the least
significant octet of the fraction of a second value (fractional parts below 2**-24) are beyond the limits of time
accuracy. Some time protocol standards recommend setting the values of these fractional bits to random values.
Other standards may make use of these least significant bits to meet other application requirements (for example
source of the time stamp, clock quality information, etc.). Use of these least significant 8 bits of the fractional part
for any other purpose should be under local agreement and is beyond the scope of this standard.
G.3.2 Enlarge the MMS Identifier size
Replace, in Subclause 7.5.2, the line
maxIdentifier INTEGER ::= 32
by the following new text
maxIdentifier INTEGER ::= 64
G.3.3 Allow application-dependent use of MMSString data type
Replace, in Subclause 14.4.2, the line
mMSString [16] MMSString