
Reference Guide for the Model XM128 ISDN Digital Modem
Determining the Packet Length
The user’s information is sent on a
If the sending side sends packets greater than what the receiving side allows, the receiving side discards the frame and replies with a Frame Reject Frame (FRMR). The FRMR indicates that the information received is too long. Both sides then reset their link layer negotiation and send the frame again. Usually this process repeats until the call gets disconnected.
The Model XM128 modem has a fixed maximum receiving frame size of 2048 octets, which is larger than most devices can support. The default maximum sending frame size is 252 octets for V.120 and 2048 for X.75. If you need to change the maximum sending frame size, the ATCL command is used.
To change the maximum sending frame size, use the following commands and follow these steps:
1.Enter ATCL252 (set the frame size to 252 octets, user value between 1 and 2048).
You should receive this message:
OK
2.Enter ATCL? (to inquire about the current setting of the packet length).
You should receive this message:
Maximum user data length in a packet (byte) : 252
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