PPP operation and protocols

Connections made using Point-to-Point Protocol (PPP) must adhere to standards established in PPP RFCs. For information on PPP RFCs, see "Introduction to TCP/IP" at the Microsoft Windows Resource Kits Web site. (http://www.microsoft.com/) This topic gives an overview of PPP operations and the protocols used in a PPP connection. For information about how to configure PPP settings, see PPP settings.

PPP connection process

After a physical or logical connection is made to a PPP-based remote access server, the following negotiations establish a PPP connection:

Negotiate the use of the link

PPP uses Link Control Protocol (LCP) to negotiate link parameters such as the maximum PPP frame size, the use of Multilink, and the use of a specific PPP authentication protocol.

Authenticate the remote access computer

The remote access client and the remote access server exchange messages according to the negotiated authentication protocol. If EAP is being used, the client and the server negotiate a specific EAP method, known as an EAP type, and then exchange the messages of that EAP type.

Use callback

If callback for the dial-up connection is configured, the physical connection is terminated, and the remote access server calls the remote access client back.

Negotiate the use of network protocols

This process involves using a series of network control protocols (NCPs) to configure the network protocols the remote access client uses. For example, the NCP for TCP/IP is Internet Protocol Control Protocol (IPCP). If the remote access client is configured to use TCP/IP, IPCP is used to assign an IP address to the client and to configure the client with the IP addresses of DNS and WINS servers.

The resulting connection remains active until the line is disconnected for any of the following reasons:

The user or the administrator explicitly hangs up the line.
The line is disconnected due to idle time-out.
An unrecoverable link error occurs.

Link Control Protocols

Link Control Protocol (LCP) establishes and configures PPP framing. PPP framing defines how data is encapsulated before it is transmitted on the wide area network. The PPP standard framing format ensures that remote access software from any vendor can communicate and recognize data packets from any remote access software that adheres to the PPP standards.

PPP and the Microsoft® Windows® Server 2003 family use variants of High-level Data Link Control (HDLC) framing for serial or ISDN connections.

Authentication protocols

Authentication protocols are negotiated immediately after link quality is determined and before the network layer is negotiated. For more information about available authentication protocols, see Authentication protocols and methods.

Network control protocols

Network control protocols establish and configure different network protocol settings for TCP/IP, IPX, and AppleTalk. The following table describes network control protocols used with a PPP connection.

The IPX/SPX protocol is not available on Microsoft XOX or the 64-bit versions of the Windows Server 2003 family.

Network control protocol	Description
Internet Protocol Control Protocol (IPCP)	IPCP is used to configure TCP/IP on the remote access client. Configuration parameters include an IP address and the IP addresses of DNS and WINS servers.
Internetwork Packet Exchange Control Protocol (IPXCP)	IPXCP is used to configure IPX on the remote access client. IPXCP is widely implemented by PPP vendors. Configuration parameters include the IPX network and node numbers.
AppleTalk Control Protocol (ATCP)	ATCP is used to configure AppleTalk on the remote access client. Configuration parameters include an AppleTalk address.

Note

The PPP settings dialog box includes the option Negotiate multi-link for single-link connections. This option enables separation of high and low-priority channels over a single link connection. If your remote access server supports this feature, you might notice improved audio quality. However, because this feature is incompatible with many remote access servers, you should leave it disabled unless instructed otherwise. For more information on PPP settings, see PPP settings.