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The Point-to-Point Protocol (PPP) provides a standard method for transporting multi-protocol 
datagrams over point-to-point links. The base protocol is specified in RFC 1661. Many other 
RFCs define additional capabilities for network protocol negotiation, management information 
databases (MIBs), and PPP operation over different kinds of serial channels.

PPP is comprised of three main components. The first component is a method of 
encapsulating multi-protocol datagrams so that the underlying protocol can be identified; the 
second component is the Link Control Protocol (LCP) that is used for establishing, 
configuring, and testing the datalink connection; the third component is a family of Network 
Control Protocols (NCPs) that are used for establishing and configuring different network-
layer protocols such as IP and IPX.

The implementation of PPP for the Omni Switch/Router WAN Switching Modules supports 
bridging, IP routing and IPX routing. Data compression of the PPP packets is also supported 
when the WSX module contains a STAC 9705 Data Compression Coprocessor.

There are five phases to a PPP connection: Dead, Establish, Authenticate, Network, and 
Terminate:

The first phase is called the “Dead” phase because the physical channel has not yet 

been activated.

 After the physical channel has been activated, the PPP connection enters the second 

phase, called “Establish,” wherein it attempts to negotiate link-level parameters and options 
using the Link Control Protocol (LCP). This phase ends when the LCP enters its own “open” 
state.

 After LCP has reached its “open” state, the PPP connection enters the phase 

called “Authenticate” wherein it tries to identify the peer with which it is attempting to 
establish a connection. If the authentication option is enabled, either the Password 
Authentication Protocol (PAP) or the Challenge Handshake Authentication Protocol (CHAP) is 
used to perform the authentication. If authentication is not enabled, the PPP connection 
proceeds to the next phase, “Network.”

 After the “Authenticate” phase is successful (or when it is not enabled), the PPP 

connection proceeds to the next phase, called “Network,” wherein the network protocols are 
negotiated using the appropriate Network Control Protocol (NCP). For example, to negotiate 
the use of IP over the PPP connection, the Internet Protocol Control Protocol (IPCP) is used. 
The details of the negotiation are specific to each network protocol, but may include such 
tasks as assigning network layer addresses. A network layer protocol must be negotiated 
successfully before the exchange of protocol packets can proceed; but, once negotiated, the 
protocol can begin to freely exchange packets. The PPP connection spends most of its time in 
the “Network” phase, because this is where the active transmission of data occurs.

. The final phase of a PPP connection is called the “Terminate” phase. This phase 

begins when authentication is unsuccessful or the channel becomes inoperative. Very often, 
this phase is simply bypassed, and PPP will return to the idle (Dead) phase when a channel is 
disconnected.