3com 3C886 Manual Do Utilizador

C

HAPTER

 2: 56K LAN M

ODEM

 F

UNCTIONALITY

 D

ESCRIPTION

This section describes the call routing protocol used by the 56K LAN Modem and 
explains how IP addresses are translated. 

The 56K LAN Modem distinguishes between three types of destinations:

■

A direct connection to an Internet Service Provider

■

A direct connection to a Remote Office LAN

■

A direct connection to a Remote Office LAN with Internet Access

If all of these connection types are configured on the 56K LAN Modem and are 
associated with your computer, the following algorithm is performed for each of 
the following scenarios.

If the 56K LAN Modem has not established any calls to a remote destination and 
you want to access the Internet from your computer, you simply launch your Web 
browser (or whichever networking application you like). When the 56K LAN 
Modem receives the information packet requesting access to the WAN, it must 
determine which connection type to use. The LAN Modem looks at the destination 
Network ID (destination IP address and subnet mask) associated with the packet. If 
the Network ID of the packet matches the Network ID of the Remote Office LAN, 
with or without Internet access, then the call is placed to the remote LAN. If it 
does not match the Network ID of the remote LAN, with or without Internet 
access, then the call is routed to the direct ISP connection.

Once the connection is established, any authorized user on the LAN can use this 
connection. The 56K LAN Modem will translate each individual user’s local IP 
address into a single, shared IP address (assigned by the remote location), allowing 
shared access to the remote location. The following example shows three users 
sharing a connection to the Internet and depicts the IP address translation as it 
occurs in the LAN Modem.