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length that the receiving side allows. Sometimes this information will
be exchanged during handshaking. However, few manufacturers, if
any, have implemented this mechanism.
If the sending side sends packets greater than what the receiving side
allows, the receiving side will discard the frame and reply with a
Frame Reject frame (FRMR). FRMR indicates that the information
received is too long. Both sides will then reset their link layer
negotiation and re-send the frame again. Usually this will happen
repeatedly until the call gets disconnected.
The omni 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 should be used.
Type:
ATCL252<Enter> (Set the frame size to 252 octets, user
value between 1-2048)
TA responds:
OK
Type:
ATCL?<Enter> (To inquire about the current setting of
the packet length)
TA responds:
Maximum user data length in a packet (byte) : 252
Answering a Call using MSN
When answering an incoming call, the call will first be identified if the
caller number matches the MSN settings.
The Multiple Subscriber Number (MSN) supplementary service
enables multiple ISDN numbers to be assigned to a single ISDN BRI
line. It allows the caller to select, via the public network, one or more
distinct terminals from a variety of terminal choices. Since the Omni
ISDN Communication Basics 31
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