Specifications

Ethernet Loop Testing
Page E-11
2. Unrecognized function code.
The message is ignored.
In order to provide maximum problem diagnosis capabilities, Loop
Servers must always attempt to receive Ethernet maximum sized
messages.
E.4.2 Loop Requester
The Loop Requester uses receipt numbers to identify requests both back
to the user and in protocol messages. When the system
is initialized,
the next available receipt number
is set to a random value. It is
then incremented each time one is used.
E.4.2.1 LoopDirect Function
A receipt number is assigned and the state of the operation is set to
"not complete". The data, provided via transmitBuffer, is transmitted
to the destination station, identified
by remoteAddress, as a Reply
message encapsulated in
a Forward Data message with the local station
as the forwarding address. If the transmit
is not accepted, the error
code is returned and the receipt number marked complete. If the
transmit succeeded, a receive is pasted. Note that in some
implementations it may be necessary to post the receive first to avoid
a race between the posting of the receive and the receipt of the
message.
The receive is satisfied by the first Reply message received with the
correct receipt number. Additional replies (as in the case of a
LoopDirect to the loopback assistance multicast group) are
automatically ignored since there is no longer an outstanding request
with the receipt number. When the transmit and receive are both
complete,
if they were successful the received data is compared to the
transmitted data, exclusive of loop protocol overhead.
If they do not
match or the receive or transmit failed, the appropriate error
is
recorded; otherwise, success and the responding station address are
recorded.
E.4.2.2 LoopAssisted Function
If the request is for receive assistance, and the assistant address
is
a multicast address, an invalid assistant address error is returned;
otherwise,
a receipt number is taken and the state of the operation is
set to "not complete". The data is put into the form of a Reply
message and encapsulated in a Forward Data message with the local
station address as the forward address. The rest of the operation
depends on the assistance level requested: