MagTek MCP - Manual (Page 37)

Section 4. Protocol
31
Rule 5.5
A node that initiated error recovery per Rule 5.2 (using R-frame with poll bit set) processes the
next received R-frame or I-frame the following way: (a) if the N(R) field of the received frame is
equal to the node’s last sent N(S) plus one, then the node accepts this as confirmation according
to Rule 4.8; otherwise (b), it re-sends the outstanding I-frame and again starts waiting for the
response. In case (b), the node sends the I-frame with the same N(S) as the original I-frame and
with N(R) equal to the node’s current receive sequence number, which may have changed since
the original I-frame was sent.
Rule 5.6
If a node that initiated error recovery per Rule 5.2 does not receive either an I-frame or an R-
frame within the block wait timeout, the node shall (a) re-send the R-frame with poll indicator
set using its current receive sequence number or (b) give up.
Rule 5.7
If a node that initiated error recovery per Rule 5.3 does not receive the expected response within
the block wait timeout, the node shall (a) re-send the I-frame per Rule 5.3 or (b) give up.
Rule 5.8
If a node gives up on error recovery per Rule 5.6 or
Rule 5.7 it shall consider the user data
unsent. The node shall (a) consider the connection dissolved and stop sending and receiving user
data until it receives RESYNC request per
Rule 3.2 and Error! Reference source not found.,
(b) initiate connection reset per Rule 3.6, or (c) initiate baud synchronization per Rule 2.2
followed by connection reset per rule Rule 3.6.
Service Indications
Rule 6.1
If a node receives a frame with correct header EDC but incorrect full EDC, the node shall either
(a) ignore the frame or (b) send a RESEND S-frame indication enclosing the PCB byte from the
received frame and specifying the “EDC error” error code.