3Com OfficeConnect 3C891A Release Note page 13

Understanding the
Three Dial-in
Scenarios
Before you can use the Dial-in Wizard to set up the LAN Modem for dial-in access,
you should understand the three dial-in scenarios available for each of your ten
authorized dial-in users. The scenarios are as follows.
Single User Dial-in (terminal adapter or LAN Modem running NAT)
LAN Modem Site-to-Site Dial-in (LAN to LAN bidirectional connectivity)
Advanced Dial-in (unknown router accessing a LAN Modem)
Single User Dial-in
Single User Dial-in describes a scenario where a client workstation dials into a
LAN Modem via a single ISDN terminal adapter (or another LAN Modem, see
below). With Single-User Dial-in the server-side LAN Modem assigns a single IP
address to the incoming client, as shown in Figure 5.
OfficeConnect
ISDN LAN Modem
Small office LAN
Figure 5 Single User Dial-in
Single-User Dial-in from Another LAN Modem: While Single-User Dial-in
provides only one IP address to the dial-in client, the dial-in client may still be
another LAN Modem with several attached workstations. In this case, the
client-side LAN Modem uses NAT to share the single IP address provided by the
server-side LAN Modem, similar to a typical ISP connection, as shown in Figure 6.
Note that unlike the LAN Modem Site-to-Site scenario, the Single User scenario
does not provide for bidirectional LAN-to-LAN connectivity. While authorized
workstations attached to the client LAN Modem can share the connection to the
server LAN Modem, workstations connected to the server LAN Modem cannot
access client-side resources.
OfficeConnect
ISDN LAN Modem
Server side LAN
Figure 6 Single User Dial-in with NAT
Understanding the Three Dial-in Scenarios
Public telephone
network
ISDN BRI line
192.168.254.1 192.168.254.1
Public telephone
network
Server LAN Modem issues
single IP address to
incoming client
3ComImpact IQ ¤ 3 Com
PWR TEST D B1 B2 SD RD DTR
Terminal adapter
(ISDN modem)
Telecommuter
Client
OfficeConnect
ISDN LAN Modem
Client
Client LAN Modem
uses NAT to translate
Client side LAN
issued IP address
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