to the COM Port Control Protocol
The NetModem, NetDialOut & NetSerial software redirectors
fully supports the "COM Port Control"
protocol (IETF RFC-2217).
COM Port Control increases compatibility between modem access
servers and many PC applications.
In order for COM Port Control to work, both ends of the telnet
connection (the server and client) need to support it. Many
Access Server manufactures support COM Port Control,
including Cisco, Cyclades,
port control is also supported in PC's running NetModem
Server. The COM Port Control Protocol was originally
created by Cisco for use in their AS-series Access Servers.
What is "COM
"COM Port Control" is an extension of the Telnet
Protocol. It allows redirector software to send configuration
information to an Access Server. It also allows the Server
to send the client redirector any serial line status changes,
and allows the client redirector to manage flow control with
the Access Server.
When making a connection without using "COM Port
Control", the client redirector is still able to communicate
with the server, but it will only be able to send and receive
data, which is fine for use with many PC applications.
However by using "COM Port Control" when making
a connection, the client PC application is also able to read
status lines and control signals on the client redirectors
virtual COM port which is exchanged with the Server, allowing
a wider range of PC application software to be used sucessfully.
For example, "COM Port Control" is required to use
Class 2 or 2.0 faxing over a modem server.
COM Port Control
Client redirectors create virtual COM ports using "COM
Port Control" to allow the following port controls:
- Purge Data (empties buffer)
- Suspend/Resume Outbound Flow Control
- Set Flow Control Method (Example: Use DSR Hardware Flow
- Line settings:
Data Length bits
- RTS, Request to Send - This informs the modem the app
is ready to exchange data.
- DTR, Data Terminal Ready. - This informs the modem to
Client redirectors typically use the COM Port protocol to
report the following line conditions:
- Suspend/Resume Inbound Flow Control
- DCD, Data Carrier Detect. - This indicates that the connection
link is successful.
- DSR, Data Set Ready. - This indicates that the modem is
ready to establish a link
- CTS - Clear to Send. - This indicates the modem is ready
to exchange data.
- RI, Ring Indicator. - This indicates the phone is currently
COM Port Control
in the industry
Since Cisco released the COM Port Control specificiations as
an non-propritary open protocol in 1997, many other software
companies have jumped on the RFC-2217 bandwagon, including LabTam
(USA) , Odin (USA), Tactical (USA) , Fabulatech (Ukraine), Eltima
(Ukraine), LabF (Finland), and HWgroup (Czech republic).