Specifications
Operat ion
Page
54
4
OPERATION
This section describes the operation that supoorts the various
interfaces. The operation is described in terms of the model section
and uses an Algol-like colloquial, high-level language for
specification of algorithms.
For this version of the specification, operation
is
not presented in
the form of a complete implementation model. Instead, to allow
quicker review, and since the protocols are quite simple, descriptions
are in English or simplified algorithmic form. The descriptions
assume, for example, that transmits and receives will be properly
demultiplexed between the Data Link Layer and the simplified processes
presented here. They also assume that Data Link Open and Close
functions are performed outside themselves.
Operation and message formats are, as much as possible, drawn from the
existing Maintenance Operation Protocol (MOP) Version 2.1. This means
that some algorithms, such as down-line load, are directly drawn from
existing products with proven field records.
4.1
Common Algorithms
In all maintenance protocols, an invalid message
is
treated as
if
it
never arrived or had data errors.
Many of the maintenance algorithms require timeout and retransmission
of a message when a response is not received. There are two
variations of this algorithm. The first is persistent.
It
will not
terminate unless stopped by a hard error or high level intervention.
The second terminates when a fixed retry count
is
exhausted.
In the higher level algorithms they are referred to as
Must-transact, message
for the persistent variety, and
Transact, message
for the fixed retry variety. Message is the message that
is
to be
sent.
A
receive buffer, and other outputs of the call, are assumed to
avoid obscuring the important algorithms. These algorithms also
assume synchronous transmit and receive functions, with a receive
timeout calculated according to channel speed and size of receive
buffer plus 1 second for remote response time.
These algorithms result in either a transmit or receive error or a
message received in response to the message transmitted. The
algorithms assume that the data link has
a
service-timer and a
suggested maximum-retries for maintenance operation. Control of these
parameters
is
outside the scope of this specification.