14
Features
Packet Data in the D Channel
Some business applications, for instance POS terminals, cash reg-
isters or credit card terminals, require a permanent data connec-
tion over the X.25 packet data network. Packet data transfer
through the ISDN D channel (according to X.31 via SAPI 16) can
also be established between several S
0
interfaces of the
Forum 525/526. Simultaneous connections are distinguished by
means of a TEI (Terminal Endpoint Identifier).
X.31 packet data can be forwarded between two S
0
interfaces (for
instance an internal and external S
0
interface). Equally, data can
be forwarded (“routed”) over permanent Q.SIG lines. Data can
also be routed over an S
2M
interface. It is possible to operate mul-
tiple terminals with the same TEI on different internal S
0
inter-
faces. A TEI mapping table allows these X.31 connections to be
routed to the same external S
0
interface.
The routing table for X.31 packet data is set in the Configurator
under Telephony: Extended: X.31. Additional information can
be found in the Configurator online help files.
Internet Access
It is possible to connect individual PCs to the Forum 525/526 via
the internal S
0
ports, or to connect an entire LAN to the
Forum 525/526 via the Ethernet port. These PCs can access the
Internet via the Forum 525/526. If Internet access is already
available from an Internet service provider, this can be configured
in the Forum 525/526. If the client network is not IP-capable, the
Forum 525/526 can administer the IP configuration necessary for
Internet access. The Forum 525/526 has an integrated DHCP
server and a DNS server, which in this case take over IP address
administration and name resolution for the client PCs.
The Forum 525/526 enables Internet access for all connected PCs
by means of a common IP address. Only this is externally visible.
The local IP addresses of the client PCs are translated to the IP
address of the Forum 525/526 by network address translation
(NAT). In this way the client PCs in the LAN cannot be reached
directly from the Internet. This protects them from direct external
attack. The LAN is additionally protected by the Forum 525/526
filter lists, which can be customised individually (firewall function).