Lesson 4: Supporting Multilink Connections | MCSE Training Kit(c) Microsoft Windows 2000 Accelerated 2000

Multilink was first introduced in Windows NT 4.0 Remote Access Service. It enables multiple physical links to be combined into one logical link. Typically, two or more ISDN lines or modem links are bundled together for greater bandwidth. In this lesson, you learn about Multilink connections.

After this lesson, you will be able to

Explain Multilink connections

Estimated lesson time: 10 minutes

Point-to-Point Protocol

The PPP was designed to send data across dial-up or dedicated point-to-point connections. PPP encapsulates IP, IPX, and NetBEUI packets within PPP frames, and then transmits the PPP-encapsulated packets across a point-to-point link. PPP can be used between routers over dedicated links or by a Remote Access Service client and server over dial-up links. PPP is made up of the following three main components, whose functions are described in the following list.

Encapsulation. This allows the multiplexing of multiple transport protocols over the same link.
LCP. PPP defines an extensible LCP for establishing, configuring, and testing the Data-Link connection. LCP provides the handshake for encapsulation format, packet size, bringing up or dropping the link, and authentication. Some examples of authentication protocols include PAP, CHAP, and EAP.
Network Control Protocol. Network Control Protocols (NCPs) provide specific configuration needs for their respective transport protocols. For example, IPCP is the IP Control Protocol.

NOTE
More information can be found on PPP and Multilink in RFC 1661: The Point-to-Point Protocol, and RFC 1990: PPP Multilink.

Multilink PPP

A new LCP option. The ability to support Multilink is negotiated during PPP's LCP phase.
A new PPP network protocol. A new PPP network protocol was created called MP (Multilink PPP). MP appears to PPP as a normal PPP payload. MP will resequence and recombine packets before handing them off to the actual transport protocol such as TCP/IP.

MP is encapsulated in PPP Data-link layer frames with the 003D hex protocol field. This information may be useful when reading PPP logs.

Lesson Summary

Multilink was first introduced in Windows NT 4.0 Remote Access Service. It allows the combining of multiple physical links into one logical link. Typically, two or more ISDN lines or modem links are bundled together for greater bandwidth.