3Com OfficeConnect 3C892A User Manual page 103

Table 9 Symptoms, Causes, and Solutions
Symptom
Cannot hear dial tone when
attempting to place a call using
an ISDN LAN Modem phone
port.
Cannot receive an incoming
call.
The analog modem connected
to the ISDN LAN Modem is
unable to detect dial tone
when attempting to place an
analog call while a Multilink
PPP call is established.
Sending e-mail is occasionally
slow when more than one
workstation is sending e-mail
to the same SMTP server.
Compression does not work
Possible Cause
Bandwidth Allocation may be set
to Use two B Channels.
Bandwidth Allocation may be set
to Use two B Channels.
The standard period of time most
modems are set to wait for a dial
tone before hanging up the call is
2 seconds, which is about the
same amount of time it takes the
ISDN Modem to drop the second
B channel from a Multilink PPP
call and re-establish a dial tone.
A limitation of NAT, the SMTP
server uses a different port
number than the one requested
by the workstations sending
e-mail so the LAN Modem does
not know which of the 2 (or
more) workstations to forward
the response to. Therefore, the
request is discarded.
After 30 seconds, the SMTP
server responds, this time using
the port number specified by the
workstation allowing the e-mail
to be sent.
Compression is not configured.
Compression negotiation was not
successful.
Evaluating Symptoms and Solutions
Solution
Go to the appropriate Service Providers page and
change the Bandwidth Allocations setting to Add
second B channel as required.
Adjust the analog modem setting as follows: Change
S-Register 6 (Wait Time for Blind Dialing) on the analog
modem to a value of 3 or higher (the default is usually
2) to increase the period of time your analog modem is
set to wait before hanging up the call.
Co-ordinate the sending of your e-mail with the other
workstations, or have each workstation use a different
SMTP mail server.
Go to the appropriate Service Provides page and ensure
compression is enabled.
Although compression is enabled on the LAN Modem,
the device the LAN Modem is dialing into must also
have compression enabled and also support the same
type of compression (hi/fn LZS) otherwise compression
negotiation will not be successful.
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