3Com Dual 56K manual Using the Modem Channels

Using the Modem Channels 23

If one or more Service Providers are configured as a Multilink-enabled connection, one high-speed call at a time is possible whenever one of these calls is in session, as shown in Figure 9.

Eric’s PC

OfficeConnect¤

Dual 56K LAN Modem

Anne’s PC	MODEM 1MODEM 2	LAN Status	Public telephone
			network

Suhlle’s PC

Combining both

analog lines with Multilink provides a single high-speed connection

Private network

Floyd’s PC

Figure 9 One High-Speed Connection to a Single Location

Sharing an Already In either of the above scenarios, once the dial-out connection is established, up to Established Connection 25 users can share the already-open connection. The LAN Modem is designed to

make use of already-established call connections in order to provide optimal line availability for all users sharing WAN access.

Whenever the LAN Modem receives an information packet requesting WAN access, it looks for an already-established connection to the specified destination (such as an ISP for an Internet connection). If an open connection is available, the LAN Modem uses this for any authorized user. The LAN Modem uses the IP address translation system, Network Address Translation (NAT), to allow multiple users to transmit their individual information packets along this same open channel. If you choose, you can restrict line sharing so that only authorized users have access to an open connection to a specified destination.

Note that speed may be affected when multiple users share a connection and attempt to download data simultaneously.

For a further explanation of NAT and IP address translation in the LAN Modem, see “IP Address Translation Using NAT,” at the end of this section, or refer to the Networking Primer in Appendix A.

Callback Capability When you configure a Service Provider profile to a remote destination, you can choose to enable Callback in the LAN Modem. With Callback enabled, your outgoing call is immediately dropped by the receiving device and then returned, provided the call-receiving device is also set up with this feature. Callback can provide potential cost savings for the dial-out party, as well as security for the call-receiving device and its attached network.