3Com 520 - Manual (Page 49)

Examples of Typical ISDN Networking Applications 1-35
several IP hosts to generate autocalls to the remote
site. When combined with the problem described
above, you could find your ISDN line permanently
connected.
To avoid this situation you need to be sure that no
devices or applications exist on your local site that
could make unnecessary and costly calls to your
remote site. You can also configure the
OfficeConnect Remote units at both ends of the link
to implement a Firewall and/or Call Guillotine to
reduce the amount of traffic permitted to pass across
the link. See the Software Reference guide for more
information about these features.
Alternatively, you may wish to configure the
OfficeConnect Remote to operate as a router to
prevent this problem occurring altogether. This
however requires that each site consists of separate
subnets. See the next section for more information
about IP routing.
IP Host on Another IP Network
Most organizations using TCP/IP protocols on their
network, choose to subnet remote sites or even to
have them on different networks. This requires that
connections to remote sites are routed rather than
bridged. The advantage of routing over bridging is
that calls to the remote site are only made when
data is specifically addressed to a remote network.
Bridging passes any data not known to be for the
local network to the remote network whether that is
its destination or not.
Because the ISDN number can be associated with a
remote network rather than just a specific IP host,
any data for the remote network can generate an
autocall and be routed over the OfficeConnect
Remote. If you need to connect to IP hosts on several
networks, you will need to use routing to be able to
communicate with the different hosts.
The example shown in Figure 1-18 shows the Local
Site connected to two Remote sites over ISDN. All
sites are connected using OfficeConnect Remote
units.
Rc.bk : RC01.FRM Page 35 Thursday, July 10, 1997 9:53 AM