3Com 10014299 manual Isdn BRI Interface, Idle coding of synchronous serial interface is 7E

128CHAPTER 10: CONFIGURING WAN INTERFACE

12Configure MTU

MTU of synchronous serial interface affects the fragmentation and reassembling of IP network protocol message on this interface.

Please use the following commands in the view of the synchronous serial interface.

Table 121 Set MTU of synchronous serial interface

Operation	Command
Set MTU of synchronous serial interface	mtu size
Recover the default value of MTU	undo mtu

The unit of mtu is byte, ranging between 128-1500, with 1500 as default.

13Configure the time interval for sending keepalive packets

The serial interface will send keepalive packets to the opposite end at every keepalive interval to check if the link is in normal state or not.

Perform the following configuration in serial interface view.

Table 122 Set the time interval for sending keepalive packets

Operation	Command
Set the time interval for sending keepalive packets	timer hold seconds
Disable keepalive packet sending	undo timer hold

The time interval for sending keepalive packets is 10 seconds by default.

CAUTION: When the serial interface is encapsulated with HDLC protocol, the keepalive interval set on both ends of the link must be the same.

14Set the idle coding of synchronous serial interface

Perform the following configuration in serial interface view.

Table 123 Set the idle coding of synchronous serial interface

Operation	Command
Set the idle coding of synchronous serial interface	idle-mark
to "FF"
Restore the idle coding of synchronous serial	undo idle-mark
interface to "7E"

The idle coding of synchronous serial interface is "7E".

ISDN BRI Interface	Technical Background
	Integrated Services Digital Network (ISDN) is a new technology developed from
	the 1970’s. It can provide all-digital services from terminal user to terminal user
	and fulfill an all-digital transmission mode integrating services such as voice, data,
	graphics and video.
	ISDN is different from conventional PSTN. In conventional PSTN, information is
	sent to the switch via analog user loop, converted to digital signal through A/D
	conversion and then resumed to analog signal when reaching the destination user.
	ISDN realizes the digital transmission of user loop to implement digital end-to-end
	communication. This will enable various digital and analog information to transmit
	via the standard digital interface. Besides, ITU-T standardizes ISDN services and
	formulates such recommendations as I.430, Q.921 and Q.931 to make any