3Com 3C892 - OfficeConnect ISDN Lan Modem Router User Manual

Also see for OfficeConnect Series: Product guide Datasheet Datasheet Product guide Product guide

Contents

3Com 3C892 - OfficeConnect ISDN Lan Modem Router User Manual Manual pdf 19 page image

20 CHAPTER 2: ISDN LAN MODEM FUNCTIONALITY DESCRIPTIONCall Routing Protocoland IP AddressTranslationThis section describes the call routing protocol used by the ISDN LAN Modem andexplains how IP addresses are translated.Placing a Call to aPreviously DefinedDestinationTo illustrate how the ISDN LAN Modem routes outgoing data calls, let us assumethat you have set up the following types of service providers.n A direct connection to an Internet Service Providern A direct connection to a remote office LANn A direct connection to a remote office LAN from which you can also access theInternetIf all of those connection types are configured on the ISDN LAN Modem and areassociated with your computer, the following algorithm is performed for each ofthe following scenarios.Call Routing While No Other Calls Are ConnectedIf the ISDN LAN Modem has not established any calls to a remote destination andyou want to access the Internet from your computer, you simply launch your Webbrowser (or whichever networking application you like). When the ISDN LANModem receives the information packet requesting access to the WAN, it mustdetermine which connection type to use. The ISDN LAN Modem looks at thedestination Network ID (which comprises the destination IP address and subnetmask) associated with the packet. If the Network ID of the packet matches theNetwork ID of the remote LAN, with or without Internet access, then the call isplaced 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 thisconnection. The ISDN LAN Modem will translate each individual user’s IP addressinto a single, shared IP address (assigned by the remote location), thereby allowingup to 25 users to access the same remote location.The following example shows three users sharing a connection to the Internet anddepicts the IP translation as it occurs in the ISDN LAN Modem.