Chapter 2
13
2.7 Point-to-Point Protocol
The ADSL devices support PPP over ATM. PPP is a WAN protocol
transmitting multi-protocol data grams over serial links. PPP addresses are:
• Standardized Internet encapsulation of IP over point-to-point links
• Used in assignment and management of IP address
• Asynchronous (start/stop) and bit-oriented encapsulation
• Network protocol multiplexing
• Based on link configuration
• Link quality tested
• Based on error detection
• An option to negotiate for network layering addresses and data
compression
To accomplish the above functions, PPP includes the following protocols:
• Link Control Protocol (LCP)
: To establish, configure and test the
data link connections.
• Network Control Protocol (NCP): TCP/IP Routing Internet Protocol
Control Protocol (IPCP)
• PAP/CHAP Security Protocols
: Establish a link from the point of
origin to the point of destination.
PPP sends LCP frames to configure and (originally) test the data link. After the
link has been established and facilities have been negotiated, the originating
PPP sends NCP frames to choose and configure IP. This link remains until LCP
or NCP frame close the link. PPP maintains the local address to be translated
and the pool of addresses from which to allocate outside addresses.
