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A Terminology

Most definitions below are taken from [2].

Abbreviation for acknowledgement.

A response sent by the receiver to indicate a successful reception of information.

(Address Resolution Protocol) The TCP/IP protocol used to dynamically bind a high-level IP address to a low-level physical address.

A packet delivery system that delivers a copy of a given packet to all hosts that attach to the same network.

A small, integer value computed from a sequence of bytes by treating them as integers and computing the sum. A checksum is used to detect errors that result when a sequence of bytes is transmitted from one machine to another. Typically, protocol software computes a checksum an appends it to a packet when transmitting. Upon reception, the protocol software verifies the contents of the packets by recomputing the checksum and comparing to the value sent. Many TCP/IP protocols use a 16-bit checksum computed witch one's complement arithmetic, with all integer fields in the packet stored in network byte order.

(Checksum Redundancy Avoidance) A way to eliminate the checksum calculation if it is possible, e.g. when the packet has only travelled over a local network.

(Cyclic Redundancy Check) A small, integer value computed from a sequence of bytes used to detect errors that result when the sequence of bytes is transmitted from one machine to another.

Flow control
Control of the rate at which hosts or routers inject packets into a network or internet, usually to avoid congestion.

Any end-user computer system that connects to a network. Hosts range in size from personal computers to supercomputers.

(Internet Control Message Protocol) An integral part of the Internet Protocol that handles error and control messages. Specifically routers and hosts use ICMP to send reports of problems about datagrams back to the original source that sent the datagram.

Physically, a collection of packet switching networks interconnected by routers along with TCP/IP protocols that allow them to function logically as a single, large, virtual network. When written in upper case, Intern refers specifically to the global Internet.

The collection of networks and routers that spans the world, and uses TCP/IP protocol to form a single, cooperative network.

(Internet Protocol) The TCP/IP standard protocol that defines the IP datagram as the unit of information passed across an internet and provides the basis for connectionless, best-effort packet delivery service.

IP address
A 32-bit address assigned to each host that participates in an internet. IP addresses are the abstraction of physical hardware address just as an internet is an abstraction of physical networks.To make routing efficient IP addresses are divided into a network potion and a host portion.

IP datagram
The basic unit of information passed across a TCP/IP internet.An It contains source and destination address along with data.

(Internet Protocol -the Next Generation) A term applied to all the activities surrounding the specification and standardization of the next version of IP, IPv6.

Used loosely to refer to any small block of data sent across a packet switching network.


The abstraction that TCP/IP transport protocols use to distinguish among multiple destinations within a given host computer. TCP/IP protocols identify ports using small positive integers. Usually, the operating system allows an application program to specify which port it wants to use. Some ports are reserved for standard services (e.g. electronic mail).

A formal description of message formats and the rules two or more machines must follow to exchange those messages. Protocols can describe low-level details of machine to machine interfaces, or high-level exchange between application programs.

Pseudo header
Source and destination IP address information sent in the IP header, but included in a TCP or UDP checksum.

The operation an application performs on a TCP to force data to be sent immediately. A bit in the segment header marks pushed data.

The process of collecting all the fragments of an IP datagram and using them to create a copy of the original datagram. The ultimate destination performs reassembly.

(Request For Comments) The name of a series of notes that contain surveys, measurements, ideas, techniques, and observations, as well as proposed and accepted TCP/IP protocol standards.

In general, a route is the path that network traffic takes from its source to its destination. In TCP/IP internet, each IP datagram is routed independently; routes can change dynamically.

A special purpose, dedicated computer that attaches to two or more networks and forwards packets from one to the other. A router uses the destination address on a datagram to choose a next-hop to which is forwards the datagram.

The unit of transfer sent from TCP on one machine to TCP on another. Each segment contains part of a stream of bytes being sent between the machines as well as additional fields that identify the current position in the stream and a checksum to ensure validity of received data.


Sliding window
Characteristic of protocols that allow a sender to transmit more than one packet of data before receiving an acknowledgement. After receiving an acknowledgement for the first packet sent, the sender ``slides'' the packet window and sends another. The number of outstanding packets or bytes is known as the window size; increasing the widow size improves throughput.

(SYNchronizing segment) The first segment sent by the TCP protocol, it is used to synchronize the two ends of a connection in preparation for opening a connection.

(Transmission Control Protocol) The TCP/IP standard transport level protocol that provides the reliable, full duplex, stream service on which many application protocols depend. TCP allows a process on one machine to send a stream of data to a process on another. TCP is connection-oriented in the sense that before transmitting data, participants must establish a connection. All data travel in TCP segments, which each travel across the Internet in an IP datagram. The entire protocol suite is often referred to as TCP/IP because TCP and IP are the two fundamental protocols.

(User Datagram Protocol) The TCP/IP standard protocol that allows an application program on one machine to send a datagram to an application on another. UDP uses Internet Protocol to deliver datagrams. Conceptually, the important difference between UDP datagrams and IP datagrams is that UDP includes a protocol port number, allowing sender to distinguish among multiple application programs on a given remote machine. In practice, UDP also includes an optional checksum over the data being sent. UDP use unlike TCP unreliable data transfer.

next up previous contents
Next: B The Test Setup Up: Implementing a High Performance Previous: References

Peter Kjellerstedt
Thu Jun 5 00:52:23 MET DST 1997