We will occassionally bump in to some networking terms, so here is an initial list of some basic terms and what they mean.
Network - communication system for connecting end-systems.
End-system - anything that communicates on a network ;) Certainly computers are end-systems. Network devices such as routers and gateways are also end-systems. Some people envision a future in which nearly all consumer electronics and appliances will be end systems (refrigerator, microwave, heating system, etc).
Point-to-point network- a network in which a physical communication path exists between 2 end-systems with no other devices involved. In a point-to-point network there is no doubt where a chunk of data comes from (it can only come from one other end-system).
A point-to-point network with 3 end-systems
Multi-access network - a network in which a physical communication medium is shared among multiple end-systems. There must be some arbitration mechanism - some set of rules that all end-systems obey when transmitting data (otherwise they might all attempt to use the same physical medium at the same time).
A multi-access network with 5 end-systems
LAN - Local Area Network. A network that connects systems that are physically close (less than 1 mile). Typically LANS are high-speed multi-access networks, for example ethernet or token-ring.
WAN - Wide Area Network. A network that connects systems that are physically far apart. Also known as a "long haul network". They are typically slower than LANs and point-to-point. Often based on telephone lines and/or satellite communication.
MAN - Metropolitan Area Network. They are smaller than a WAN and larger than a LAN. Examples include our campus-wide network.
Inter-network - connection of two or more distinct (possible dissimilar) networks. Usually requires some kind of network device to facilitate the connection.
Protocol - a specification for format of exchange of information between two end-systems.
OSI Reference Model - a layered model used to describe network protocols and services. The OSI model includes 7 layers:
7. Application - highest level layer
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical - lowest level layer
Physical Layer - transmission of raw bits over a communication channel.
Data Link Layer - transmission of chunks of data (frames) between two end-systems on the same network. The Data Link layer uses the physical layer to physically send bits of data.
Network Layer - transmission of chunks of data (packets) between two end-systems on possibly different networks. The Network layer uses the Data Link layer to send data between two end-systems on the same network, some end-systems are connected to multiple networks and can forward chunks of data.
Transport Layer - transmission of chunks of data between processes on two end systems that are on possibly different networks. The Transport layer uses the Network layer to send data, in addition the destination endpoint must be able to identify and send data to the correct process.
Process - an instance of a program that is currently running.
Program - a file containing instructions that can be executed by a computer.
Session Layer - manages communication session between two processes (session creation and termination).
Presentation Layer - provides data translation/conversion so that many kinds of end-systems can exchange information (end-systems do not all need to use the same internal representation for information). Can also involve encryption/decryption or compression/decompression.
Application Layer - communication between two end-systems that deals with the specific nature of a network application. (In other words - anything not provided by any of the lower level layers).
Bridge - a network device that connects two or more networks at the Data Link layer. Forwards frames from one network to another.
Router - a network device that connects two or more networks at the Network layer. A router forwards packets between networks making decisions about what network should receive each packet.
Gateway - a network device that does some data conversion at layers higher than the Network layer. Gateways are often used to provide connection between different applications or different network layers. The picture below shows a gateway that provides for the secure connection of two networks using an insecure network:
Client/Server - a model for sharing of resources and information between processes (typically processes running on different computers connected by a network).
Server - a process that provides some service (resources or information) to another process (a client). A server accepts requests and returns responses. Servers typically are processes that are always ready (running). Examples include web servers, file servers, print servers and mail servers.
Client - a process that makes requests from a server, typically in response to user action. A client process is the process that makes the initial request, although this process may then provide some server to the peer process. A process can be both a client and server, for example, a proxy web server.