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In networking
Computer network

A computer network is a group of interconnected computers. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of some types and categories and also presents the basic components of a network....
, the Point-to-Point Protocol, or PPP, is a data link
Data link layer

The Data Link Layer is layer 2 of the seven-layer OSI model of computer networking.The Data Link Layer is the protocol layer which transfers data between adjacent network nodes in a wide area network or between nodes on the same local area network network segment....
 protocol
Protocol (computing)

In computer science, a protocol is a convention or standard that controls or enables the connection, communication, and data transfer between computing endpoints....
 commonly used to establish a direct connection between two networking nodes
Node (networking)

In communication networks, a node is an active electronic device that is attached to a network, and is capable of sending, receiving, or forwarding information over a communications channel....
. It can provide connection authentication
Authentication

Authentication is the act of establishing or confirming something as authentic, that is, that claims made by or about the subject are true....
 and can also provide transmission encryption
Encryption

In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key ....
 privacy and compression
Compression

Compression may refer to:In physical science:*Physical compression, the result of the subjection of a material to compressive stress**Compression member, a class of structural elements, of which a column is the most common specific example...
.

PPP is used over many types of physical networks including serial cable
Serial cable

A serial cable is a cable that can be used to transfer information between two devices using serial communication, often using the RS-232 standard....
, phone line, trunk line
Trunking

Trunking is a concept in modern communications by which a communications system can provide network access to many clients by sharing a set of lines or frequencies instead of providing them individually....
, cellular telephone, specialized radio links, or fiber optic links such as SONET
Sonet

Sonet may refer to:* Sonet Records, European record label* Synchronous optical networking See also* Sonnet...
. Most Internet service provider
Internet service provider

An Internet service provider is a company that offers its customers access to the Internet. The ISP connects to its customers using a data transmission technology appropriate for delivering Internet Protocol datagrams, such as dial-up, DSL, cable modem or dedicated high-speed interconnects....
s (ISPs) use PPP for customer dial-up access
Dial-up access

Dial-up Internet Access is a form of Internet access via telephone lines. The user's computer or router uses an attached modem connected to a telephone line to dial into an Internet service provider's node to establish a modem-to-modem link, which is then used to router Internet Protocol packets between the user's equipment and hosts on the...
 to the Internet
Internet

The Internet is a global network of interconnected computers, enabling users to share information along multiple channels. Typically, a computer that connects to the Internet can access information from a vast array of available server and other computers by moving information from them to the computer's local memory....
.






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In networking
Computer network

A computer network is a group of interconnected computers. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of some types and categories and also presents the basic components of a network....
, the Point-to-Point Protocol, or PPP, is a data link
Data link layer

The Data Link Layer is layer 2 of the seven-layer OSI model of computer networking.The Data Link Layer is the protocol layer which transfers data between adjacent network nodes in a wide area network or between nodes on the same local area network network segment....
 protocol
Protocol (computing)

In computer science, a protocol is a convention or standard that controls or enables the connection, communication, and data transfer between computing endpoints....
 commonly used to establish a direct connection between two networking nodes
Node (networking)

In communication networks, a node is an active electronic device that is attached to a network, and is capable of sending, receiving, or forwarding information over a communications channel....
. It can provide connection authentication
Authentication

Authentication is the act of establishing or confirming something as authentic, that is, that claims made by or about the subject are true....
 and can also provide transmission encryption
Encryption

In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key ....
 privacy and compression
Compression

Compression may refer to:In physical science:*Physical compression, the result of the subjection of a material to compressive stress**Compression member, a class of structural elements, of which a column is the most common specific example...
.

PPP is used over many types of physical networks including serial cable
Serial cable

A serial cable is a cable that can be used to transfer information between two devices using serial communication, often using the RS-232 standard....
, phone line, trunk line
Trunking

Trunking is a concept in modern communications by which a communications system can provide network access to many clients by sharing a set of lines or frequencies instead of providing them individually....
, cellular telephone, specialized radio links, or fiber optic links such as SONET
Sonet

Sonet may refer to:* Sonet Records, European record label* Synchronous optical networking See also* Sonnet...
. Most Internet service provider
Internet service provider

An Internet service provider is a company that offers its customers access to the Internet. The ISP connects to its customers using a data transmission technology appropriate for delivering Internet Protocol datagrams, such as dial-up, DSL, cable modem or dedicated high-speed interconnects....
s (ISPs) use PPP for customer dial-up access
Dial-up access

Dial-up Internet Access is a form of Internet access via telephone lines. The user's computer or router uses an attached modem connected to a telephone line to dial into an Internet service provider's node to establish a modem-to-modem link, which is then used to router Internet Protocol packets between the user's equipment and hosts on the...
 to the Internet
Internet

The Internet is a global network of interconnected computers, enabling users to share information along multiple channels. Typically, a computer that connects to the Internet can access information from a vast array of available server and other computers by moving information from them to the computer's local memory....
. Two encapsulated forms of PPP, Point-to-Point Protocol over Ethernet
Point-to-Point Protocol over Ethernet

PPPoE, Point-to-Point Protocol over Ethernet, is a network protocol for Encapsulation Point-to-Point Protocol frames inside Ethernet frames....
 (PPPoE) and Point-to-Point Protocol over ATM
Point-to-Point Protocol over ATM

PPPOA or PPPoA, Point-to-Point Protocol over Asynchronous Transfer Mode, is a network protocol for Encapsulation PPP frames in Asynchronous Transfer Mode AAL5....
 (PPPoA), are used by ISPs to connect Digital Subscriber Line
Digital Subscriber Line

DSL or xDSL, is a family of technologies that provides digital data transmission over the wires of a local access network. DSL originally stood for digital subscriber loop, although in recent years, the term digital subscriber line has been widely adopted as a more marketing-friendly term for ADSL, which is the most popular...
 (DSL) Internet service.

PPP is commonly used to act as a data link layer
Data link layer

The Data Link Layer is layer 2 of the seven-layer OSI model of computer networking.The Data Link Layer is the protocol layer which transfers data between adjacent network nodes in a wide area network or between nodes on the same local area network network segment....
 protocol for connection over synchronous
Synchronization

Synchronization or synchronisation is timekeeping which requires the coordination of events to operate a system in unison. The familiar Conducting of an orchestra serves to keep the orchestra in time....
 and asynchronous
Asynchrony

Asynchrony, in the general meaning, is the state of not being synchronization.* Asynchronous learning* Collaborative editing systemsIn specific terms of digital logic and physical layer of communication, an asynchronous process does not require a clock signal....
 circuits, where it has largely superseded the older, non-standard Serial Line Internet Protocol
Serial Line Internet Protocol

The Serial Line Internet Protocol is a mostly obsolete encapsulation of the Internet Protocol designed to work over serial ports and modem connections....
 (SLIP), and telephone company mandated standards (such as Link Access Protocol, Balanced
LAPB

LAPB is a data link layer Protocol in the X.25 protocol stack. LAPB is a bit-oriented protocol derived from HDLC that ensures that frames are error free and in the right sequence....
 (LAPB) in the X.25
X.25

X.25 is an ITU-T standard network layer protocol for Packet switched network wide area network communication. An X.25 WAN consists of Packet switching nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links....
 protocol suite). PPP was designed to work with numerous network layer
Network layer

The Network Layer is Layer 3 in the OSI model of computer networking. The Network Layer responds to service requests from the Transport Layer and issues service requests to the Data Link Layer....
 protocols, including Internet Protocol
Internet protocol

Internet protocol may refer to:*The Internet Protocol, a specific protocol implementation in the Internet protocol suite*The Internet protocol suite, a set of communications protocols that are used for the Internet...
 (IP), Novell's Internetwork Packet Exchange (IPX), NBF and AppleTalk
AppleTalk

AppleTalk is a proprietary protocol protocol stack developed by Apple Inc for networking computers. It was included in the original Macintosh and is now deprecated by Apple in favor of TCP/IP networking....
.

PPP is specified in RFC
Request for Comments

In computer network engineering, a request for comments is a memorandum published by the Internet Engineering Task Force describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems....
 1661.

Basic Features


PPP was designed somewhat after the original HDLC specifications. The designers of PPP included many additional features that had been seen only in various proprietary data-link protocols up to that time.

Automatic self configuration


Link Control Protocol
Link Control Protocol

In computing, the Link Control Protocol forms part of the Point-to-Point Protocol. In setting up PPP communications, both the sending and receiving devices send out LCP packet s to determine the standards of the ensuing data transmission....
 (LCP) is an integral part of PPP, and defined in the same standard specification. LCP provides automatic configuration of the interfaces at each end (such as setting datagram size, escaped characters, and magic numbers) and for selecting optional authentication. The LCP protocol runs atop PPP (with PPP protocol number 0xC021) and therefore a basic PPP connection has to be established before LCP is able to configure it.

RFC 1994 describes Challenge-handshake authentication protocol
Challenge-handshake authentication protocol

In computing, the Challenge-Handshake Authentication Protocol authentication s a user or network host to an authenticating entity. That entity may be, for example, an Internet service provider ....
 (CHAP), preferred for establishing dial-up connections with ISPs. Although deprecated, Password authentication protocol
Password authentication protocol

Password Authentication Protocol, sometimes abbreviated PAP, is a simple authentication protocol used to authenticate a user to a network access server used for example by internet service providers....
 (PAP) is often used. Another option for authentication over PPP is Extensible Authentication Protocol
Extensible Authentication Protocol

Extensible Authentication Protocol, or EAP, is a universal authentication framework frequently used in wireless LAN and Point-to-Point Protocol....
 (EAP).

After the link has been established, additional network (layer 3
Network layer

The Network Layer is Layer 3 in the OSI model of computer networking. The Network Layer responds to service requests from the Transport Layer and issues service requests to the Data Link Layer....
) configuration may take place. Most commonly, the Internet Protocol Control Protocol
Internet Protocol Control Protocol

In computer networking, Internet Protocol Control Protocol is a Network_Control_Protocol for establishing and configuring Internet Protocol over a Point-to-Point Protocol link....
 (IPCP) is available, although Internetwork Packet Exchange Control Protocol (IPXCP) and AppleTalk Control Protocol (ATCP) were once very popular. Also, Internet Protocol Version 6 Control Protocol (IPv6CP) is available, when IPv6
IPv6

Internet Protocol version 6 is the next-generation Internet layer protocol for packet -switched internetworking and the Internet. IPv4 is the dominant Internet Protocol version, and was the first to receive widespread use....
 takes the currently-de facto IPv4
IPv4

Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and it is the first version of the protocol to be widely deployed....
's position as the layer-3 protocol in the future.

Multiple network layer protocols

PPP permits multiple network layer protocols to operate on the same communication link. For every network layer protocol used, a separate Network Control Protocol
Network Control Protocol

A Network Control Protocol is a protocol that runs atop the Point-to-Point Protocol and that is used to negotiate options for a network layer protocol running atop PPP....
 (NCP) is provided in order to encapsulate and negotiate options for the multiple network layer protocols.

For example, Internet Protocol (IP) uses the IP Control Protocol (IPCP), and Internetwork Packet Exchange (IPX) uses the Novell IPX Control Protocol (IPXCP). NCPs include fields containing standardized codes to indicate the network layer protocol type that PPP encapsulates.

Looped link detection

PPP detects looped links using a feature involving magic numbers
Magic number (programming)

In computer programming, the term magic number has multiple meanings. It could refer to one or more of the following:* a constant used to identify a file format or protocol;...
. When the node sends PPP LCP messages, these messages may include a magic number. If a line is looped, the node receives an LCP message with its own magic number, instead of getting a message with the peer's magic number.

Most important features

  • Link Control Protocol initiates and terminates connections gracefully, allowing hosts to negotiate connection options. It also supports both byte- and bit-oriented encodings.
  • Network Control Protocol is used for negotiating network-layer information, e.g. network address or compression options, after the connection has been established.


PPP frame






















Name Number of bytes Description
Protocol 1 or 2 setting of protocol in data field
Information variable (0 or more) datagram
Padding variable (0 or more) optional padding


The Protocol field indicates the kind of payload packet (e.g. LCP, NCP, IP, IPX, AppleTalk, etc.).

The Information field contains the PPP payload; it has a variable length with a negotiated maximum called the Maximum Transmission Unit
Maximum transmission unit

In computer networking, the term Maximum Transmission Unit refers to the size of the largest packet that a given layer of a communications protocol can pass onwards....
. By default the maximum is 1500 octets. It might be padded on transmission; if the information for a particular protocol can be padded, that protocol must allow information to be distinguished from padding.

Encapsulation

PPP frames are encapsulated in a lower-layer protocol that provides framing and may provide other functions such as a checksum
Checksum

A checksum or hash sum is a fixed-size data computed from an arbitrary block of digital data for the purpose of error detection that may have been introduced during its telecommunications or computer storage....
 to detect transmission errors. PPP on serial links is usually encapsulated in a framing similar to HDLC, described by IETF RFC 1662.










































Name Number of bytes Description
Flag 1 indicates frame's begin or end
Address 1 broadcast address
Control 1 control byte
Protocol 1 or 2 setting of protocol in information field
Information variable (0 or more) datagram
Padding variable (0 or more) optional padding
FCS 2 (or 4) error check sum


The Flag field is present when PPP with HDLC-like framing is used.

The Address and Control fields always have the value hex FF (for "all stations") and hex 03 (for "unnumbered information"), and can be omitted whenever PPP LCP Address-and-Control-Field-Compression (ACFC) is negotiated.

The Frame Check Sequence
Frame Check Sequence

A frame check sequence refers to the extra checksum characters added to a Frame in a Communications protocol for error detection and correction....
 (FCS) field is used to determine whether an individual frame has an error. It contains a checksum
Checksum

A checksum or hash sum is a fixed-size data computed from an arbitrary block of digital data for the purpose of error detection that may have been introduced during its telecommunications or computer storage....
 computed over the frame to provide basic protection against errors in transmission. This is a CRC
Cyclic redundancy check

A cyclic redundancy check is a type of function that takes as input a data stream of any length, and produces as output a value of a certain space, commonly a 32-bit integer....
 code similar to the one used for other layer two protocol error protection schemes such as the one used in Ethernet. According to RFC 1662, it can be either 16 bits (2bytes) or 32 bits (4 bytes) in size (default is 16 bits - Polynomial x16 + x12 + x5 + 1).

The FCS is calculated over the Address, Control, Protocol, Information and Padding fields.

Although these are not standard applications, PPP is also used over broadband
Broadband

The term broadband can have different meanings in different contexts. The term's meaning has undergone substantial shifts....
 connections. RFC 2516 describes Point-to-Point Protocol over Ethernet
Point-to-Point Protocol over Ethernet

PPPoE, Point-to-Point Protocol over Ethernet, is a network protocol for Encapsulation Point-to-Point Protocol frames inside Ethernet frames....
 (PPPoE), a method for transmitting PPP over Ethernet
Ethernet

Ethernet is a family of Data frame-based computer networking technologies for local area networks . The name comes from the physical concept of the Luminiferous aether....
 that is sometimes used with DSL
Digital Subscriber Line

DSL or xDSL, is a family of technologies that provides digital data transmission over the wires of a local access network. DSL originally stood for digital subscriber loop, although in recent years, the term digital subscriber line has been widely adopted as a more marketing-friendly term for ADSL, which is the most popular...
. RFC 2364 describes Point-to-Point Protocol over ATM
Point-to-Point Protocol over ATM

PPPOA or PPPoA, Point-to-Point Protocol over Asynchronous Transfer Mode, is a network protocol for Encapsulation PPP frames in Asynchronous Transfer Mode AAL5....
 (PPPoA), a method for transmitting PPP over ATM
Asynchronous Transfer Mode

Asynchronous Transfer Mode is an electronic digital data transmission technology. ATM is implemented as a network protocol and was first developed in the mid 1980s....
 Adaptation Layer 5 (AAL5), which is also sometimes used with DSL.

PPP line activation and phases

The phases of the Point to Point Protocol according to RFC 1661 are listed below:
  • Link Dead. This phase occurs when the link fails, or one side has been told not to connect (e.g. a user has finished his or her dialup connection.)
  • Link Establishment Phase. This phase is where Link Control Protocol negotiation is attempted. If successful, control goes either to the authentication phase or the Network-Layer Protocol phase, depending on whether authentication is desired.
  • Authentication Phase. This phase is optional. It allows the sides to authenticate each other before a connection is established. If successful, control goes to the network-layer protocol phase.
  • Network-Layer Protocol Phase. This phase is where each desired protocols' Network Control Protocol
    Network Control Protocol

    A Network Control Protocol is a protocol that runs atop the Point-to-Point Protocol and that is used to negotiate options for a network layer protocol running atop PPP....
    s are invoked. For example, IPCP
    Internet Protocol Control Protocol

    In computer networking, Internet Protocol Control Protocol is a Network_Control_Protocol for establishing and configuring Internet Protocol over a Point-to-Point Protocol link....
     is used to establish IP service over the line. Data transport for all protocols which are successfully started with their network control protocols also occurs in this phase. Closing down of network protocols also occur in this phase.
  • Link Termination Phase. This phase closes down this connection. This can happen if there is an authentication failure, if there are so many checksum errors that the two parties to the link decide to tear down the link automatically, if the link suddenly fails, or if the user decides to hang up his connection. This phase tries to close everything down as gracefully as possible depending on the circumstances.


Multiclass PPP

MP's monotonically increasing sequence numbering (contiguous numbers are needed for all fragments of a packet) does not allow suspension of the sending of a sequence of fragments of one packet in order to send another packet. The obvious approach to providing more than one level of suspension with PPP Multilink is to run Multilink multiple times over one link. Multilink as it is defined provides no way for more than one instance to be active. Each class runs a separate copy of the mechanism defined i.e. uses a separate sequence number space and reassembly buffer. See RFC 2686...

Other features

Numerous documents on PPP have been published through the RFC process since July 1990, including various authentication, encryption, and compression methods, and the use of PPP in conjunction with other network protocols.

RFC 2615 is also used in Packet over SONET/SDH
Packet over SONET/SDH

Packet over SONET/SDH, abbreviated POS, is a communications protocol for transmitting Packet in the form of the Point to Point Protocol over Synchronous_optical_networking or SONET, which are both standard protocols for communicating digital information using lasers or light emitting diodes over optical fibre at high line rates....
 (PoS) transmissions.

PPTP is a form of PPP between two hosts via GRE
Generic Routing Encapsulation

Generic Routing Encapsulation is a tunneling protocol developed by Cisco Systems that can Encapsulation a wide variety of network layer Protocol packet types inside IP tunnels, creating a virtual Point-to-point to Cisco routers at remote points over an Internet Protocol internetwork....
. It is often used to set up a VPN, with optional encryption (MPPE) or compression (MPPC
Microsoft Point-to-Point Compression

Microsoft Point-to-Point Compression is a streaming data compression algorithm based on an implementation of Lempel-Ziv using a sliding window buffer....
).

RFCs

PPP is defined in RFC 1661 (The Point-to-Point Protocol, July 1994). RFC 1547 (Requirements for an Internet Standard Point-to-Point Protocol, December 1993) provides historical information about the need for PPP and its development. A series of related RFCs have been written to define how a variety of network control protocols-including TCP/IP, DECnet
DECnet

DECnet is a suite of network protocols created by Digital Equipment Corporation, originally released in 1975 in order to connect two PDP-11 minicomputers....
, AppleTalk
AppleTalk

AppleTalk is a proprietary protocol protocol stack developed by Apple Inc for networking computers. It was included in the original Macintosh and is now deprecated by Apple in favor of TCP/IP networking....
, IPX
IPX

Internetwork Packet Exchange is the OSI model Network layer Protocol_ in the IPX/SPX protocol stack.The IPX/SPX protocol stack is supported by Novell, Inc.'s NetWare network operating system....
, and others-work with PPP.

  • RFC 1661, Standard 51, The Point-to-Point Protocol (PPP)
  • RFC 1662, Standard 51, PPP in HDLC-like Framing
  • RFC 1994, PPP Challenge Handshake Authentication Protocol (CHAP)
  • RFC 2153, Informational, PPP Vendor Extensions
  • RFC 2687, Proposed Standard, PPP in a Real-time Oriented HDLC-like Framing
  • RFC 5072, IP Version 6 over PPP
    • RFC 5172, Negotiation for IPv6 Datagram Compression Using IPv6 Control Protocol


Other VPN Protocols

  • IPsec
    IPsec

    Internet Protocol Security is a Protocol suite for securing Internet Protocol communications by authentication and encryption each packet #Example: IP packets of a data stream....
  • L2F Layer 2 Forwarding Protocol
    Layer 2 Forwarding Protocol

    L2F, or Layer 2 Forwarding, is a tunneling protocol developed by Cisco Systems, Inc. to establish Virtual Private Network connections over the Internet....
  • L2TP Layer 2 Tunneling Protocol
  • PLIP Parallel Line Internet Protocol
    Parallel Line Internet Protocol

    The Parallel Line Internet Protocol is an encapsulation of the Internet Protocol designed to work overa personal computer parallel port via a laplink cable, sometimes called a'laplink' cable....
  • PPTP Point-to-Point Tunneling Protocol
    Point-to-point tunneling protocol

    The Point-to-Point Tunneling Protocol is a method for implementing virtual private networks. PPTP does not provide confidentiality or encryption; It relies on the protocol being tunneled to provide privacy....
  • PPP Point-to-Point Protocol
    Point-to-Point Protocol

    In Computer network, the Point-to-Point Protocol, or PPP, is a Data Link Layer Protocol commonly used to establish a direct connection between two Node ....
  • SLIP Serial Line Internet Protocol
    Serial Line Internet Protocol

    The Serial Line Internet Protocol is a mostly obsolete encapsulation of the Internet Protocol designed to work over serial ports and modem connections....


See also


  • Extensible Authentication Protocol
    Extensible Authentication Protocol

    Extensible Authentication Protocol, or EAP, is a universal authentication framework frequently used in wireless LAN and Point-to-Point Protocol....
  • Hayes command set
    Hayes command set

    The Hayes command set is a specific command language originally developed for the Hayes Microcomputer Products Smartmodem 300 baud modem. The command set consists of a series of short text strings which combine together to produce complete commands for operations such as dialing, hanging up, and changing the parameters of the connection....
  • Link Access Procedure for Modems (LAPM)
  • RADIUS
    RADIUS

    Remote Authentication Dial In User Service is a networking protocol that provides centralized access, authorization and accounting management for people or computers to connect and use a network service....
  • Diameter
  • PPPoA
  • PPPoE
  • point-to-Point Protocol daemon
  • PPPoX
    PPPoX

    PPPoX designates a family of encapsulating communications protocols implementing Point-to-Point Protocol.Specific implementations:* Point-to-Point Protocol over Ethernet...
  • Multiprotocol Encapsulation
    Multiprotocol Encapsulation

    Multiprotocol Encapsulation, or MPE for short, is a Data link layer protocol definedby DVB which has been published as part of ETSI EN 301 192....
     (MPE) for MPEG transport stream
  • Unidirectional Lightweight Encapsulation
    Unidirectional Lightweight Encapsulation

    The Unidirectional Lightweight Encapsulation is a Data link layer protocol for the transportation of network layer packets over MPEG-2 Transport Streams....
     (ULE) for MPEG transport stream