3Com 3C892 manual How does a LAN connect to a WAN?

106APPENDIX A: NETWORKING PRIMER

How does a LAN connect to a WAN?

You can connect a LAN to a WAN through a number of devices such as a router or a bridge that can place a call to the remote LAN using a dial-up telephone service such as ISDN. Routers and bridges are devices that link networks. A bridge sends every bit of information across the WAN while a router is considered a more sophisticated device because of its ability to route only the desired bits of information across the WAN while checking the integrity of the data and transmission path.

What is a LAN modem? A LAN modem is a hybrid between a modem that combines the dial-up capabilities of a modem with an Ethernet hub. This eliminates the computer COM port speed bottleneck (the LAN runs at 10 Mbps) while providing local networking between the attached computers on the LAN. Even with this sophisticated functionality, a LAN modem is easy to install and use, making it ideal for small networks.

What is ISDN? The Integrated Services Digital Network (ISDN) provides a digital telephone service which allows both data and voice communication over the same telephone line and at significantly faster speeds than the traditional Plain Old Telephone Service (POTS) or analog service. There are two types of lines which provide access to ISDN, Basic Rate Interface (BRI) and Primary Rate Interface (PRI). The ISDN LAN Modem supports a BRI interface.

OfficeConnect¤

ISDN LAN Modem

		LAN STATUS		OfficeConnect®	3 Com
Alert PWR ISDN B1 B2	Tx	Coll	1 2 3 4
				ISDN LAN Modem

Public telephone

network

ISDN BRI line

Figure 54 ISDN BRI Line

Each BRI telephone line consists of two 64 Kbps bearer or B channels and one 16 Kbps D channel for each ISDN line. The D channel is the signaling channel; it carries messages between the ISDN LAN Modem and your telephone company’s ISDN switch. Note that while the ISDN standard is to have 64 Kbps B channels, some telephone companies or the equipment you are connecting to may use 56 Kbps channels.

OfficeConnect¤
ISDN LAN Modem			64 Kbps B Channel
LAN STATUS		OfficeConnect®3 Com	64 Kbps B Channel	Public telephone
Alert PWR ISDN B1 B2Tx Coll 1 2 3	4	ISDN LAN Modem	16 Kbps D Channel	network

ISDN BRI line

Figure 55 ISDN BRI Line in Detail

A single B channel transmits data or voice traffic at a rate of up to 64 Kbps. The B channels may be used independently to allow two simultaneous connections to different locations as shown in Figure 56.