Specifications

Configuring and Managing Integrated Modems
Managing Modems
DC-93
Cisco IOS Dial Technologies Configuration Guide
Configuring MICA In-Band Framing Mode Control Messages
Dial-in Internet connections typically start in character mode to allow the user to log in and select a
preferred service. When Cisco IOS software determines that the user wants a framed interface protocol
during the call, such as PPP or SLIP, commands are sent to the MICA modem so that it will provide
hardware assistance with the framing. This hardware assistance reduces the Cisco IOS processing load.
To avoid loss or misinterpretation of framed data during the transition, issue these commands at precise
times with respect to the data being sent and received.
MICA modem framing commands can be sent in the data stream itself, which greatly simplifies Cisco
IOS tasks in achieving precision timing. For PPP connections, the common way for modems to connect
to the Internet, total connect time might typically be improved by 2 to 3 seconds. This functionality
reduces timeouts during PPP startup and reduces startup time. If an ASCII banner is sent just before PPP
startup, this feature eliminates problems with banner corruption such as truncation and extraneous
characters, thus improving the performance of terminal equipment.
In earlier software, the modem interface timing rules were not well understood and were difficult or
impossible to implement using the separate command interface of the modem. The practical result is that
the MICA in-band framing mode reduces the number of timeouts during PPP startup, and thus reduces
startup time. MICA in-band framing is supported on MICA modems in Cisco AS5300 and Cisco AS5800
access servers.
To configure the MICA in-band framing mode control messages, use the following commands beginning
in global configuration mode:
The Cisco IOS software offers additional interface commands that can be set to control modem interface
timing. Refer to the Cisco IOS command references for more information about the interface commands
described in the following paragraphs.
When a link goes down and comes back up before the timer set by the carrier-delay command expires,
the down state is effectively filtered, and the rest of the software on the switch is not aware that a
link-down event occurred. Therefore, a large carrier delay timer results in fewer link-up and link-down
events being detected. On the other hand, setting the carrier delay time to 0 means that every link-up and
link-down event is detected.
When the link protocol goes down (because of loss of synchronization, for example), the interface
hardware is reset and the data terminal ready (DTR) signal is held inactive for at least the specified
interval. Setting the pulse-time command enable pulsing DTR signal intervals on serial interfaces, and
is useful for handling encrypting or other similar devices that toggle the DTR signal to resynchronize.
Command Purpose
Step 1
Router(config)# line line-number
[
ending-line-number ]
Specifies the number of modem lines to configure and
enters line configuration mode. If a range is entered, it
must be equal to the number of modems in the router.
Step 2
Router(config-line)# no flush-at-activation
Improves PPP and SLIP startup.
Normally a router avoids line and modem noise by
clearing the initial data received within the first one or
two seconds. However, when the autoselect PPP
feature is configured, the router flushes characters
initially received and then waits for more traffic. This
flush causes timeout problems with applications that
send only one carriage return.