Nortel T1/SMDI Configuration Manual page 174

CallPilot T1/SMDI interfaces
The ASCII character set is not specifically covered by the RS-232
specification, but the requirements for serial ASCII character transmission
(and, therefore, SMDI protocol) fall within the definitions of the RS-232
standard as defined in reference 2 on page 188.
SMDI Link RS-232 connections at the CallPilot demarcation
point
If external SMDI link RS-232 terminating equipment is in close proximity
(for example, less than or equal to 15 meters using low capacitance shielded
RS-232 cable), a sufficient condition for the SMDI link RS-232 connection
medium is a direct connect RS-232 cable conforming to all of the
requirements of this document, (for example, the case of a coresident PBX),
including a crossover cable (that is, null modem) if the terminating
equipment is also of type DTE.
The null modem must be of the no-handshaking type to ensure that far-end
SMDI link RS-232 terminating equipment is not dependent on handshaking
signals from CallPilot. If a null modem with handshaking is employed,
downstream modem equipment can be unable to communicate with
CallPilot because CallPilot does not support hardware handshaking.
SMDI link transmission equipment for distant connections
If the SMDI link terminating equipment cannot be directly connected by
means of an RS-232 cable conforming to this document (for example,
terminating equipment proximity exceeds 15 meters), consider the
following: an external modem or other equipment as described in Reference
Number 1 on page 188 can be used to extend the connection range further
than that allowed by this document for the RS-232 physical link at the
demarcation point.
174
Standard 1.13
CallPilot