3Com SuperStack II Using PPP on Dial-Up and Leased Lines, Using Packet-Switched Network Services

26CHAPTER 2: USING THE BRIDGE/ROUTER IN YOUR NETWORK

Table 4 Dial-Up and Leased Line Services

		Serial Device (Required
Telco Line	Protocol	on Flex-WAN Serial Ports)	Data Transfer Rate
Fractional T1	PPP	CSU/DSU	Up to 24 channels (DS0s) at 64
			Kbps each
Digital Data Service (DDS)	PPP	CSU/DSU	Up to 64 Kbps

* Some ISDN lines support up to 56 Kbps per B channel. For more information, contact your ISDN service provider.

Table 5 Packet-Switched Services

Packet-Switched		Serial Device (Required on
Services/Protocol	Telco Line	Flex-WAN Serial Ports)	Data Transfer Rate
X.25	POTS	Modem	Up to 56 Kbps
Frame Relay	Leased line	CSU/DSU	Up to 2.048 Mbps
SMDS	Leased line	CSU/DSU	Up to 2.048 Mbps

Using PPP on Dial-Up and Leased Lines

All dial-up and leased lines use PPP. If you want to use multiple lines or channels to connect to the same destination, you can use Multilink PPP. Multilink PPP is especially useful for ISDN, as described in the following section.

ISDN ISDN consists of two bearer (B) channels and one delta (D) channel. Each B channel can transmit up to 64 Kbps; the D channel transmits signaling information about the call to computers at the switching system at a rate of 16 Kbps.

With Multilink PPP, you can use both B channels together for a combined data rate of 128 Kbps. With PPP, you can use each 64 Kbps B channel separately.

Some ISDN lines support up to 56 Kbps per B channel. For more information, contact your ISDN service provider.

Using Packet-Switched Network Services

You can use packet-switched services with your bridge/router instead of dial-up or leased lines to take advantage of high performance for a reasonable price. This section describes X.25 and Frame Relay.

X.25 An X.25 packet-switched network is defined by the International Telecommunications Union (ITU) Recommendation X.25, a global standard that began development in the 1970s. The recommendation