Unimax MA-2025-4G, Руководство пользователя

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4 . P R O T O C O L S & E N C R Y P T I O N S
4.1 PPP (Point-to-Point Protocol)
PPP (Point-to-Point Protocol) is a protocol for communication between two computers
using a serial interface, typically a personal computer connected by phone line to a
server. For example, your Internet service provider may provide you with a PPP
connection so that the provider's server can respond to your requests, pass them on to
the Internet, and forward the requested Internet responses back to you. PPP uses the
Internet protocol (IP) and is designed to handle others. It is sometimes considered a
member of the TCP/IP suite of protocols. Relative to the Open Systems Interconnection
(OSI) reference model, PPP provides layer 2 (data-link layer) services. Essentially, it
packages your computer's TCP/IP packets and forwards them to the server where they
can actually be put on the Internet.
PPP is a full-duplex protocol that can be used on various physical media, including
twisted pair or fiber optic lines or satellite transmission. It uses a variation of High Speed
Data Link Control (HDLC) for packet encapsulation.
4.2 PPPoE (Point-to-Point Protocol over Ethernet)
PPPoE (Point-to-Point Protocol over Ethernet) is a specification for connecting multiple
computer users on an Ethernet local area network to a remote site via a modem. PPPoE
can be used to have an office or building-full of users share a common Digital
Subscriber Line (DSL), cable modem, or wireless connection to the Internet. PPPoE
combines the Point-to-Point Protocol (PPP), commonly used in dialup connections, with
the Ethernet protocol, which supports multiple users in a local area network. The PPP
protocol information is encapsulated within an Ethernet frame.
PPPoE has the advantage that neither the telephone company nor the Internet service
provider (ISP) needs to provide any special support. Unlike dialup connections, DSL and
cable modem connections are "always on." Since a number of different users are
sharing the same physical connection to the remote service provider, a way is needed
to keep track of which user traffic should go to and which user should be billed. PPPoE
provides for each user-remote site session to learn each other's network addresses
(during an initial exchange called "discovery"). Once a session is established between
an individual user and the remote site (for example, an Internet service provider), the
session can be monitored for billing purposes.