Specifications

Protocol Messages
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5 PROTOCOL MESSAGES
This section defines the binary formats of the protocol messages that
support the operation described in the operation section. In order to
operate correctly on exclusive maintenance channels, message
identification codes are taken from a single space. Values
16 and 18
are reserved for compatibility with
MOP implementations not described
here.
Some data links have a minimum message size and many of the
maintenance protocol messages are quite small. Padding must be
requested from the particular data link on the assumption that such a
service is provided if needed. The actual size of received messages
is also provided by the Data Link Layer, so that messages with a
single variable length data field need not include a size field.
The following notation is used to describe the messages:
Description of field
Where:
FIELD Is the name of the field being described.
LENGTH Is the length of the field expressed as one of the following:
. The number of 8-bit bytes.
. The notation wC-n" meaning counted image field with n
being a number that is the maximum length in 8-bit bytes
of the image. The actual length of the image is encoded
into the first byte of the field. Therefore, the minimum
length of the field is one byte. The first byte of the
field may contain information in addition to the length
count.
. The notation "I-n" meaning image field with n being a
number that is the maximum length in 8-bit bytes of the
image. The image is preceded by sufficient information to
compute the length of the field. Image fields are
variable length and may be null
(length=O). All
8 bits of
each byte may be used as information bits.
. An asterisk (*I, indicating that the field consists of the
remainder of the message, i.e., the total message length
less the length of all of the other fields.
CODING
Is the representation type used, as follows:
B Binary
BM Bit map (each bit has independent meaning)