• Serial Line Internet Protocol Meaning
• Slip Serial Line Internet Protocol
• Serial Line Internet Protocol Def

Serial Line Internet Protocol (SLIP) The SLIP is a TCP/IP protocol used for communication between two machines that are previously configured for communication with each other. For example, your Internet service provider may provide you with a SLIP connection so that the provider’s server can respond to your requests, pass them onto the.

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Point-to-Point Protocol - PPP. This protocol allows a computer to connect to the Internet with a standard dial-up telephone line and a high-speed modem and enjoy most of the benefits of a direct connection, including the ability to use graphical front ends such as a Mosaic and Netscape. Looking for Serial Line Internet Protocol? Find out information about Serial Line Internet Protocol. Software allowing the Internet Protocol, normally used on Ethernet, to be used over a serial line, e.g. An EIA-232 serial port connected to a modem. Explanation of Serial Line Internet Protocol. The Serial Line Internet Protocol (SLIP) is an encapsulation of the Internet Protocol designed to work over serial ports and modem connections. SLIP has been largely replaced by the Point-to-Point Protocol (PPP), which has more features and does not require a predefined IP address configuration.

The Serial Line Internet Protocol (also SLIP) is an encapsulation of the Internet Protocol designed to work over serial ports and router connections. It is documented in RFC1055. On personal computers, SLIP has been largely replaced by the Point-to-Point Protocol (PPP), which is better engineered, has more features and does not require its IP address configuration to be set before it is established. On microcontrollers, however, SLIP is still the preferred way of encapsulating IP packets due to its very small overhead.

Some people refer to the successful and widely used RFC1055 Serial Line Internet Protocolas 'Rick Adams' SLIP',^[1]to avoid confusion with other proposed protocols named 'SLIP'.Those other protocols include the much more complicated RFC914 appendix D Serial Line Interface Protocol.^[1]

Description[edit]

SLIP modifies a standard TCP/IPdatagram by

• appending a special 'END' byte to it, which distinguishes datagram boundaries in the byte stream,
• if the END byte occurs in the data to be sent, the two byte sequence ESC, ESC_END is sent instead,
• if the ESC byte occurs in the data, the two byte sequence ESC, ESC_ESC is sent.
• variants of the protocol may begin, as well as end, packets with END.

SLIP requires a serial port configuration of 8 databits, no parity, and either EIA hardware flow control, or CLOCAL mode (3-wire null-modem) UART operation settings.

SLIP does not provide error detection, being reliant on upper layer protocols for this. Therefore, SLIP on its own is not satisfactory over an error-prone dial-up connection. It is however still useful for testing operating systems' response capabilities under load (by looking at flood-ping statistics).

SLIP escape characters were also required on some modem connections to escape Hayes command set, allowing therefore to pass binary data through those modems that would recognize some characters as commands.

CSLIP[edit]

A version of SLIP with headercompression is called Compressed SLIP (CSLIP). The compression algorithm used in CSLIP is known as Van Jacobson TCP/IP Header Compression. CSLIP has no effect on the data payload of a packet and is independent of any compression by the serial line modem used for transmission. It reduces the Transmission Control Protocol (TCP) header from twenty bytes to seven bytes. CSLIP has no effect on User Datagram Protocol (UDP) datagrams.

See also[edit]

References[edit]

1. ^ ^abRFC1547: 'Requirements for an Internet Standard Point-to-Point Protocol'

External links[edit]

• RFC1055: Romkey, J. (June 1988). 'A Nonstandard for transmission of IP datagrams over serial lines: SLIP'.
• RFC1144: Jacobson, V. (February 1990). 'Compressing TCP/IP Headers for Low-Speed Serial Links'. — introduced the Van Jacobson TCP/IP Header Compression used by CSLIP

In computer networking, Point-to-Point Protocol (PPP) is a data link layer (layer 2) communications protocol between two routers directly without any host or any other networking in between. It can provide connection authentication, transmission encryption,^[1] and compression.

PPP is used over many types of physical networks including serial cable, phone line, trunk line, cellular telephone, specialized radio links, and fiber optic links such as SONET. Internet service providers (ISPs) have used PPP for customer dial-up access to the Internet, since IP packets cannot be transmitted over a modem line on their own, without some data link protocol.^[why?]

Two derivatives of PPP, Point-to-Point Protocol over Ethernet (PPPoE) and Point-to-Point Protocol over ATM (PPPoA), are used most commonly by ISPs to establish a digital subscriber line (DSL) Internet service connection with customers.

• 1Description
• 3PPP frame
• 5Over several links
• 6Tunnels

Description[edit]

PPP is commonly used as a data link layer protocol for connection over synchronous and asynchronous circuits, where it has largely superseded the older Serial Line Internet Protocol (SLIP) and telephone company mandated standards (such as Link Access Protocol, Balanced (LAPB) in the X.25 protocol suite). The only requirement for PPP is that the circuit provided be duplex. PPP was designed to work with numerous network layer protocols, including Internet Protocol (IP), TRILL, Novell's Internetwork Packet Exchange (IPX), NBF, DECnet and AppleTalk. Like SLIP, this is a full Internet connection over telephone lines via modem. It is more reliable than SLIP because it double checks to make sure that Internet packets arrive intact.^[2] It resends any damaged packets.

Serial Line Internet Protocol Meaning

PPP was designed somewhat after the original HDLC specifications. The designers of PPP included many additional features that had been seen only in proprietary cellspacing='3'>PPP architectureIPLCPIPCPPPP encapsulationHDLC-like FramingPPPoEPPPoARS-232POSEthernetATMSONET/SDH

PPP permits multiple network layer protocols to operate on the same communication link. For every network layer protocol used, a separate Network Control Protocol (NCP) is provided in order to encapsulate and negotiate options for the multiple network layer protocols. It negotiates network-layer information, e.g. network address or compression options, after the connection has been established.

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

The following NCPs may be used with PPP:

• the Internet Protocol Control Protocol (IPCP) for the Internet Protocol, protocol code number 0x8021, RFC 1332
• the OSI Network Layer Control Protocol (OSINLCP) for the various OSI network layer protocols, protocol code number 0x8023, RFC 1377
• the AppleTalk Control Protocol (ATCP) for AppleTalk, protocol code number 0x8029, RFC 1378
• the Internetwork Packet Exchange Control Protocol (IPXCP) for the Internet Packet Exchange, protocol code number 0x802B, RFC 1552
• the DECnet Phase IV Control Protocol (DNCP) for DNA Phase IV Routing protocol (DECnet Phase IV), protocol code number 0x8027, RFC 1762
• the NetBIOS Frames Control Protocol (NBFCP) for NetBIOS Frames protocol (or NetBEUI as it was called before that), protocol code number 0x803F, RFC 2097
• the IPv6 Control Protocol (IPV6CP) for IPv6, protocol code number 0x8057, RFC 5072

Looped link detection[edit]

PPP detects looped links using a feature involving magic numbers. 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.

Configuration options[edit]

The previous section introduced the use of LCP options to meet specific WAN connection requirements. PPP may include the following LCP options:

• Authentication - Peer routers exchange authentication messages. Two authentication choices are Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP). Authentication is explained in the next section.
• Compression - Increases the effective throughput on PPP connections by reducing the amount of data in the frame that must travel across the link. The protocol decompresses the frame at its destination. See RFC 1962 for more details.
• Error detection - Identifies fault conditions. The Quality and Magic Number options help ensure a reliable, loop-free data link. The Magic Number field helps in detecting links that are in a looped-back condition. Until the Magic-Number Configuration Option has been successfully negotiated, the Magic-Number must be transmitted as zero. Magic numbers are generated randomly at each end of the connection.
• Multilink - Provides load balancing several interfaces used by PPP through Multilink PPP (see below).

PPP frame[edit]

Structure[edit]

PPP frames are variants of HDLC frames:

If both peers agree to Address field and Control field compression during LCP, then those fields are omitted. Likewise if both peers agree to Protocol field compression, then the 0x00 byte can be omitted.

The Protocol field indicates the type of payload packet: 0xC021 for LCP, 0x80xy for various NCPs, 0x0021 for IP, 0x0029 AppleTalk, 0x002B for IPX, 0x003D for Multilink, 0x003F for NetBIOS, 0x00FD for MPPC and MPPE, etc.^[3] PPP is limited, and cannot contain general Layer 3 data, unlike EtherType.

The Information field contains the PPP payload; it has a variable length with a negotiated maximum called the Maximum Transmission Unit. 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[edit]

PPP frames are encapsulated in a lower-layer protocol that provides framing and may provide other functions such as a checksum to detect transmission errors. PPP on serial links is usually encapsulated in a framing similar to HDLC, described by IETF RFC 1662.

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 (FCS) field is used for determining whether an individual frame has an error. It contains a checksum computed over the frame to provide basic protection against errors in transmission. This is a CRC 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 (2 bytes) 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 after the message has been encapsulated.

Line activation and phases[edit]

Link Dead

This phase occurs when the link fails, or one side has been told to disconnect (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 Protocols are invoked. For example, IPCP is used in establishing 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 decide to tear down the link automatically, if the link suddenly fails, or if the user decides to hang up a connection.

Over several links[edit]

Multilink PPP[edit]

Multilink PPP (also referred to as MLPPP, MP, MPPP, MLP, or Multilink) provides a method for spreading traffic across multiple distinct PPP connections. It is defined in RFC 1990. It can be used, for example, to connect a home computer to an Internet Service Provider using two traditional 56k modems, or to connect a company through two leased lines.

On a single PPP line frames cannot arrive out of order, but this is possible when the frames are divided among multiple PPP connections. Therefore, Multilink PPP must number the fragments so they can be put in the right order again when they arrive.

Multilink PPP is an example of a link aggregation technology. Cisco IOS Release 11.1 and later supports Multilink PPP.

Multiclass PPP[edit]

With PPP, one cannot establish several simultaneous distinct PPP connections over a single link.

That's not possible with Multilink PPP either. Multilink PPP uses contiguous numbers for all the fragments of a packet, and as a consequence it is not possible to suspend the sending of a sequence of fragments of one packet in order to send another packet. This prevents from running Multilink PPP multiple times on the same links.

Multiclass PPP is a kind of Multilink PPP where each 'class' of traffic uses a separate sequence number space and reassembly buffer. Multiclass PPP is defined in RFC 2686

Tunnels[edit]

Slip Serial Line Internet Protocol

Derived protocols[edit]

PPTP (Point-to-Point Tunneling Protocol) is a form of PPP between two hosts via GRE using encryption (MPPE) and compression (MPPC).

As a layer 2 protocol between both ends of a tunnel[edit]

Many protocols can be used to tunnel data over IP networks. Some of them, like SSL, SSH, or L2TP create virtual network interfaces and give the impression of a direct physical connections between the tunnel endpoints. On a Linux host for example, these interfaces would be called tun0 or ppp0.

As there are only two endpoints on a tunnel, the tunnel is a point-to-point connection and PPP is a natural choice as a data link layer protocol between the virtual network interfaces. PPP can assign IP addresses to these virtual interfaces, and these IP addresses can be used, for example, to route between the networks on both sides of the tunnel.

IPsec in tunneling mode does not create virtual physical interfaces at the end of the tunnel, since the tunnel is handled directly by the TCP/IP stack. L2TP can be used to provide these interfaces, this technique is called L2TP/IPsec. In this case too, PPP provides IP addresses to the extremities of the tunnel.

IETF standards[edit]

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, AppleTalk, IPX, and others-work with PPP.

• RFC 1332, The PPP Internet Protocol Control Protocol (IPCP)
• RFC 1661, Standard 51, The Point-to-Point Protocol (PPP)
• RFC 1662, Standard 51, PPP in HDLC-like Framing
• RFC 1962, PPP Compression Control Protocol (CCP)
• RFC 1963, PPP Serial Data transport Protocol
• RFC 1990, The PPP Multilink Protocol (MP)
• RFC 1994, PPP Challenge Handshake Authentication Protocol (CHAP)
• RFC 2153, Informational, PPP Vendor Extensions
• RFC 2284, PPP Extensible Authentication Protocol (EAP)
• RFC 2364, PPP over ATM
• RFC 2516, PPP over Ethernet
• RFC 2615, PPP over SONET/SDH
• RFC 2686, The Multi-Class Extension to Multi-Link PPP
• 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
• RFC 6361, PPP Transparent Interconnection of Lots of Links (TRILL) Protocol Control Protocol

See also[edit]

• Link Access Procedure for Modems (LAPM)
• Multiprotocol Encapsulation (MPE) for MPEG transport stream
• Point-to-Point Protocol daemon (PPPD)
• Unidirectional Lightweight Encapsulation (ULE) for MPEG transport stream

References[edit]

1. ^RFC1968
2. ^ ^abStevens 1994, p. 26-27, sec 2.6: 'PPP: Point-to-Point Protocol'
3. ^'Point-to-Point (PPP) Protocol Field Assignments'. IANA. Retrieved 3 September 2015.

• William Richard Stevens (2016) [1994]. TCP/IP Illustrated [TCP/IP详解]. 卷一：协议 (Volume 1: The Protocols) (1st ed.). Pearson Education Asia Ltd., 人民邮电出版社 (China Posts & Telecommunications Press). ISBN978-7-115-40132-8.

Serial Line Internet Protocol Def