Panasonic UF-E1 Service Manual page 159

6.5.2. Layer Functions and Technology
6.5.2.1. PPP
In recent years, the Point-to-Point Protocol, RFC 1661, or PPP has become popular with internet. PPP is a
bit/byte synchronous or asynchronous link control protocol, using serial lines and it supports various net-
work protocols. There has been the Serial Line Internet Protocol (SLIP) as the same kind of serial line data
link protocol but it has some problems in link control, error processing and use with multiple protocols. PPP
has been conceived to resolve these problems and it is a more powerful protocol in that sense.
As a protocol family with many related protocols, PPP can do the following: making multiple protocols into
capsules; establishment, setting, testing of data link connections using link control protocol (LCP); and
establishing and setting of network protocols by the Network Control Protocol (NCP). Generally speaking,
there are functions of PPP per se and other applications with public networks such as ISDN and X.25.
1. Characteristics of PPP
PPP has the following characteristics:
a. PPP is a High-Level Data Link Control (HDLC) based protocol compatible with both synchronous
and asynchronous signals.
b. PPP supports multiple protocols. On the same link, mixture of protocols can be used: IP, OSI, DEC-
net, IPX (NetWare), XNS (Xerix Network System), etc.
c. PPP conducts negotiation between senders and receivers with IP addresses.
d. Full-duplex/bi-directional communication.
e. PPP has such functions as authentication, compression, and communication quality monitoring.
2. PPP and Data Link Layer Protocol
PPP is a protocol family with the layer structure as shown in Figure 6.5.2.1. As a protocol on the data
link layer on a serial line (full duplex/dedicated, switch board), PPP has the Link Control Protocol (LCP)
and it exercises control over establishment and setting of data link, including negotiations for maximum
length of information and various component information. Also, for controlling multiple network proto-
cols, PPP is equipped with the Network Control Protocol (NCP) for each protocol and this will enable
PPP to establish and configure network connection.
With IP packets, PPP conducts IP negotiation such as IP address negotiation using the Internet Proto-
col Control Protocol (IPCP) and then conducts communication by IP packets. Furthermore, there is the
PPP Multilink Protocol (MP), which provides network service by combining multiple data links as one
data link and the Bridging Control Protocol (BCP) that uses PPP as the bridge between networks.
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