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Networking Terms

Open Systems Interconnection (OSI) (click on image to enlarge) is a standard reference model for communication between two end users in a network. It is used as a conceptual overview in understanding networks.

The OSI Reference Model describes seven layers of related functions that are needed at each end when a message is sent from one party to another party in a network. An existing network product or program can be described in part by where it fits into this layered structure. For example, TCP/IP is usually packaged with other Internet programs as a suite of products that support communication over the Internet. This suite includes the File Transfer Protocol (FTP), Telnet, the Hypertext Transfer Protocol (HTTP), e-mail protocols, and sometimes others. Although TCP fits well into the Transport layer of OSI and IP into the Network layer, the other programs fit rather loosely (but not neatly within a layer) into the Session, Presentation, and Application layers.

Layer

Function

Other

TCP/IP

Layer 7

Application

This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

TDI

ASCII

EBCDIC

MIDI

MPEG

SMB

HTTP

SMTP

SNMP

FTP

Telnet

NFS

NTP

Layer 6

Presentation

This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems.

TDI

ASCII

EBCDIC

MIDI

MPEG

Layer 5

Session

This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.

Named Pipes

NetBIOS

SIP

SAP

SDP

Layer 4

Transport

The purpose of the Transport layer is to provide transparent transfer of data between end users, thus relieving the upper layers from any concern with providing reliable and cost-effective data transfer. The transport layer controls the reliability of a given link. Some protocols are stateful and connection oriented. This means that the session layer can keep track of the packets and retransmit those that fail.

NetBEUI

Q.931

TCP

UDP

RTP

SCTP

Layer 3

Network

The Network layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks while maintaining the quality of service requested by the Transport layer. The Network layer performs network routing, flow control, segmentation/desegmentation, and error control functions. The router operates at this layer -- sending data throughout the extended network and making the Internet possible, although there are layer 3 (or IP) switches. This is a logical addressing scheme - values are chosen by the network engineer. The addressing scheme is hierarchical

IP

ICMP

 IPsec

ARP

RIP

 OSPF

 BGP

Layer 2

Data Link

At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

Ethernet

Token Ring

FDDI

PPP

HDLC

Frame Relay

ATM

Layer 1

Physical

This layer conveys the bit stream - electrical impulse, light or radio signal through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

RS-232

 V.35/V.34

T1/T3

 nnnBASE-T

ISDN

SONET

Wireless

Networking Terms

ARP

Address Resolution Protocol is a method for finding a host's Ethernet (MAC) address from its IP address.

ASCII

ASCII (American Standard Code for Information Interchange), generally pronounced 'aski', is a character set and a character encoding based on the Roman alphabet as used in modern English and other Western European languages.

ATM

Asynchronous Transfer Mode, or ATM for short, is a cell relay network protocol which encodes data traffic into small fixed sized (53 byte) cells instead of variable sized packets as in packet-switched networks (such as the Internet Protocol or Ethernet)

BGP

The border gateway protocol (BGP) is one of the core routing protocols in the Internet. It works by maintaining a table of IP networks or 'prefixes' which designate network reachability between autonomous systems (AS). .

EBCDIC

EBCDIC (Fully, "Extended Binary Coded Decimal Interchange Code") is an 8-bit character encoding used on IBM mainframes

Ethernet

Ethernet is a frame-based computer networking technology for local area networks (LANs). It defines wiring and signaling for the physical layer, and frame formats and protocols for the media access control (MAC)/data link layer of the OSI model. Ethernet is mostly standardized as IEEE's 802.3.

FDDI

In computer networking, fiber-distributed data interface (FDDI) is a standard for data transmission in a local area network that can extend in range up to 200 km (124 miles)

FTP

The File Transfer Protocol (FTP) is a software standard for transferring computer files between machines with widely different operating systems

Frame Relay

Frame relay is an efficient data transmission technique used to send digital information quickly and cheaply to one or many destinations from one point. It can be used for voice, data, local area network (LAN), and wide area network (WAN) traffic. Each frame relay end user gets a private line to a frame relay node.

HDLC

High-Level Data Link Control (HDLC) is a bit-oriented synchronous data link Layer 2 protocol developed by the International Organization for Standardization (ISO).

HTTP

HTTP (for Hypertext Transfer Protocol) is the primary method used to convey information on the World Wide Web. The original purpose was to provide a way to publish and receive HTML pages.

ICMP

Internet Control Message Protocol. Part of TCP/IP protocol family, allows routers to send error and control messages between other routers and hosts, allowing routing information to be distributed throughout network.

IP

The Internet Protocol (IP) is a data-oriented protocol used by source and destination hosts for communicating data across a packet-switched internetwork.

IPsec

IPsec (an abbreviation of IP security) is a standard for securing Internet Protocol (IP) communications by encrypting and authenticating all IP packets.

ISDN

Integrated Services Digital Network (ISDN) is a type of telephone network system, designed to allow digital (as opposed to analog) transmission of voice and data over ordinary telephone copper wires, resulting in better quality and higher speeds. More specifically, ISDN is a set of protocols for establishing calls and then tearing them down.

MIDI

Musical Instrument Digital Interface, or MIDI, is a system designed to transmit information between electronic musical instruments. The MIDI standard was published in August 1983

MPEG

The Moving Picture Experts Group (MPEG) is a small group charged with the development of video and audio encoding standards.

NFS

Network File System (NFS) is a protocol originally developed by Sun Microsystems in 1984 and defined in RFCs 1094, 1813, (3010) and 3530, as a file system which allows a computer to access files over a network as easily as if they were on its local disks.

NTP

The Network Time Protocol (NTP) is a protocol for synchronising the clocks of computer systems over packet-switched, variable-latency data networks. NTP is a purely UDP/IP protocol, not TCP/IP. It is designed particularly to resist the effects of variable latency.

Named Pipes

In computing, a named pipe (also FIFO for its behaviour) is an extension to the classical pipe concept on Unix and Unix-like systems, and is one of the methods of interprocess communication.

NetBEUI

NetBEUI (pronounced net-booey) is an acronym for NetBIOS Extended User Interface. It is an enhanced version of the NetBIOS protocol used by network operating systems such as LAN Manager, LAN Server, Windows for Workgroups, Windows 95 and Windows NT

NetBIOS

Network Basic Input/Output System. Program that allows applications on different computers to communicate within a LAN. Created by IBM for its early PC Network, adopted by Microsoft, is now de facto industry standard.

OSPF

Open Shortest Path First (OSPF) is a link-state, hierarchical Interior Gateway Protocol (IGP) routing algorithm. The well known Dijkstra's algorithm is used to calculate the shortest path tree. It uses cost as its routing metric. A link state database is constructed of the network topology which is identical on all routers.

PPP

IPoint-to-Point Protocol. For communication between two computers using serial interface, typically a personal computer connected by phone line to a server. Most commonly used for dial-up Internet access to transmit IP packets between workstation or PC and an ISP. Part of Layer 2 Tunneling Protocol; core part of Microsoft's secure remote access solution for Windows 2000 and beyond. Protocol that provides router-to-router and host-to-network connections over both synchronous and asynchronous circuits.

PPPoE

Point-to-Point Protocol over Ethernet. PPP form when used by some ISPs for DSL and cable modem authentication. Supported by bridging functions. Specification for connecting multiple computer users on an Ethernet LAN to a remote site through common CPEs or modems. Can be used to have an office or MTU users share a common DSL, cable modem or wireless connection to the Internet. Combines PPP with Ethernet, which supports multiple users in a LAN. PPP information is encapsulated within an Ethernet frame.

PPTP

Point-to-Point Tunneling Protocol. Allows corporations to extend their own corporate network through private "tunnels" over public Internet. Effectively, using a WAN as a single large LAN, company no longer needs to lease its own lines for wide-area communication but can securely use the public networks.

RIP

The Routing Information Protocol (RIP) is one of the most commonly used Interior Gateway Protocols on internal networks (and to a lesser extent, the internet), which helps routers dynamically adapt to changes of network connections by communicating information about which networks each router can reach and how far away those networks are.

RS-232

RS-232 (also referred to as EIA RS-232C or V.24) is a standard for serial binary data interchange between a DTE (Data Terminal Equipment) and a DCE (Data Communication Equipment). It is commonly used in personal computer serial ports.

RTP

The Real-time Transport Protocol (or RTP) was developed by the Audio-Video Transport Working Group of the IETF and published in 1996 as RFC 1889

SAP

The Session Announcement Protocol (SAP) is a protocol for broadcasting multicast session information.A SAP listening application can listen to the well-known SAP multicast address and construct a guide of all advertised multicast sessions. SAP was published by the IETF as RFC 2974

SCTP

SCTP, or Stream Control Transmission Protocol is a new transport layer protocol (2000) defined by the IETF. The protocol is defined in RFC 2960, and an introductory text is provided by RFC 3286

SDP

SDP, or Session Description Protocol, is a format for describing streaming media initialization parameters. It has been published by the IETF as RFC 2327.

SIP

Session Initiation Protocol (SIP) is an IETF proposed standard for setting up sessions between one or more clients. It is currently (2004) the leading signaling protocol for Voice over IP, gradually replacing H.323 in this role.

SMB

The Server Message Block (SMB) is an equivalent implementation of a network file system under Microsoft Windows.

SMTP

Simple Mail Transfer Protocol (SMTP) is the de facto standard for email transmission across the Internet. SMTP is a relatively simple, text-based protocol, where one or more recipients of a message are specified (and in most cases verified to exist) and then the message text is transferred. It is quite easy to test a SMTP server using the telnet program.

SNMP

The Simple Network Management Protocol (SNMP) forms part of the internet protocol suite as defined by the Internet Engineering Task Force. The protocol can support monitoring of network-attached devices for any conditions that warrant administrative attention.

SONET

SONET (standing for Synchronous Optical Networking) is a standard for communicating digital information over optical fiber. It was developed to replace the PDH system for transporting large amounts of telephone and data traffic. It is defined by GR-253-CORE from Telcordia. The more recent Synchronous Digital Hierarchy (SDH) standard built on the experience of the development of SONET. Both SDH and SONET are widely used today; SONET in the U.S. and Canada, SDH in the rest of the world.

T1/T3

In telecommunications, T-carrier is the generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America and Japan. The most common legacy of this whole system is the line rate designations. A "T1" now seems to mean any data circuit that runs at the original 1.544 Mbit/s line rate, T3 is used to refer to any circuit that runs at 45 Mbps

TCP

Transmission Control Protocol (TCP) is a connection-oriented, reliable delivery byte-stream transport layer communication protocol, currently documented in IETF RFC 793.  It does the task of the transport layer in the simplified OSI model of computer networks. In the Internet protocol suite, TCP is the intermediate layer between the Internet Protocol below it, and an application above it. Applications most often need reliable pipe-like connections to each other, whereas the Internet Protocol does not provide such streams, but rather only unreliable packets.