Operation Manual

Reducing Connection Costs
NT/MPRI – 3 Configuration and Operation of the NT/MPRI: The Basics 48
The “Disconnect Timeout” and “Inactivity Timeout” can be set for each
call destination in the NT/MPRI. The “Inactivity Timeout” is the length
of time after which an idle physical connection is cleared; the “Discon-
nect Timeout” is the length of time without transmission activity for
which a logical connection is maintained. These settings are entered in
the configuration of the call destination.
Special Filters and Spoofing Mechanisms
Special filters and “spoofing” mechanisms prevent network packets
which contain information for network protocols and/or operating sys-
tems, but no data of interest to the user, from being transmitted over
ISDN. In the local network such packets are no problem, but transmis-
sion over ISDN would entail significantly higher connection costs.
Special Filters: A number of applications constantly exchange packets,
often leading to frequent and superfluous connection setups. For this
reason the NT/MPRI contains a number of special packet filters for
TCP/IP and IPX/SPX which are activated by default. For instance, SNMP
traps can be filtered out by SNMP filters for IP or IPX to prevent frequent
ISDN calls.
These filters can be activated and deactivated in the call destination
settings (“IP” and “IPX” buttons).
Spoofing Mechanisms: In Microsoft networks, NetBIOS packets are ex-
changed at regular intervals once a client has logged on to a Windows
XP/2000/NT server. This traffic cannot be simply filtered out by the
NT/MPRI, since this would interrupt the client-server connection. The
NT/MPRI therefore answers such packets locally, simulating a re-
sponse from the client. In this way the NT/MPRI supports spoofing of
NetBIOS session keep-alive packets and SMB echo packets (SMB in
NetBIOS).
In the NetWare environment too, certain types of packets which are ex-
changed between NetWare clients and servers, or the server/host part
of distributed applications, require an acknowledgement from the re-
mote station. If these packets were simply filtered out, the communica-
tions link between the client and the host of a service or application
would no longer function.
Example: If Watchdog packets which a NetWare server sends to a client
for confirmation were simply filtered out and not acknowledged locally
by the NT/MPRI, the NetWare server would assume that the client is no
longer connected. Thus the server database designates the client as
non-existent, even though it is still logically connected.
ntmpri-e.book Seite 48 Donnerstag, 28. Februar 2002 11:26 11