RFC 2217 (rfc2217) - Page 2 of 14
Telnet Com Port Control Option
Alternative Format: Original Text Document
RFC 2217 Telnet Com Port Control Option October 1997
Many new business functions require a person to connect to remote
services to retrieve or deposit information. By in large, these
remote services are accessed via an async dial up connection. This
new class of functions include:
- dial up connections to the Internet
- connecting to bulletin boards
- connecting to internal and external databases
- sending and receiving faxes.
The general nature of this new class of function requires an
interactive, character-oriented communications session via an async
modem. This is typically known as outbound modem dialing.
To help defer the cost of installing and maintaining additional phone
lines which may be used very little per person, many equipment
manufacturers have added the ability to establish a Telnet session
directly to the outbound ports on many of the most popular access
servers and routers, here after referred to as access servers.
However, the current Telnet protocol definitions are not sufficient
to fully support this new use. There are three new areas of
functionality which need to be added to the Telnet protocol to
successfully support the needs of outbound modem dialing. These are:
- The ability for the client to send com port configuration
information to the access server which is connected to the
outbound modem. This is needed to ensure the data being
transmitted and received by the modem is formatted correctly
at the byte level.
- The ability for the access server to inform the client of any
modem line or signal changes such as RLSD changes (carrier
detect). This information is vital, since many client software
packages use this information to determine if a session with the
remote service has been established. RLSD changes are also
used for signaling in Class I faxing [6].
- The ability to manage flow control between the client and
the access server which does not interfere with the flow
control mechanisms used by the session between the client and
the remote service. Unfortunately RFC 1372 "Telnet Remote
Flow Control Option" [2] can not be used for this purpose
because it relies on sending XON/XOFF style characters which
maybe transmitted or received as a normal course of the
client / remote service session.
Clark Experimental