z/VM: TCP/IP User's Guide - z/VM - IBM

Chapter 1. Introducing Computer Networks and Protocols
Computer Networks
Internet Environment
This chapter introduces the concepts of computer networks and an internet
environment. The protocols used by TCP/IP are listed by layer and then described.
Routing and addressing guidelines are also described.
A computer network is a group of connected nodes that are used for data
communication. A computer network configuration consists of data processing
devices, software, and transmission media that are linked for information
interchange.
Nodes are the functional units, located at the points of connection among the data
circuits. A node, or end point, can be a host computer, a communication controller,
a cluster controller, a video display terminal, or another peripheral device.
Computer networks can be local area networks (LANs), which provide direct
communication among data stations on the user’s local premises, or wide area
networks (WANs), which provide communication services to a geographic area
larger than that served by a LAN. Typically, WANs operate at a slower rate of
speed than LANs.
Different types of networks provide different functions. Network configurations
vary, depending on the functions required by the organization. Different
organizations implement different types of networks. The technology used by these
networks varies not only from organization to organization, but often varies within
the same company.
Networks can differ at any or all layers. At the physical layer, networks can run
over various network interfaces, such as Token-Ring, Ethernet, PC Network, Fiber
Distribution Data Interface (FDDI), and X.25. Networks can also vary in the
architectures they use to implement network strategies. Some of the more common
architectures used today are Open Systems Interconnection (OSI), Transmission
Control Protocol/Internet Protocol (TCP/IP), Systems Network Architecture (SNA),
and Integrated Services Digital Network (ISDN). Networks use different protocols
to communicate over the different physical interfaces available. In addition to these
differences, networks can use different software packages to implement various
functions.
To exchange information among these different networks, the concept of an
internet emerged.
An internet is a logical collection of networks supported by gateways, routers,
bridges, hosts, and various layers of protocols. An internet permits different
physical networks to function as a single, large virtual network, and permits
dissimilar computers to communicate with each other, regardless of their physical
connections. Processes within gateways, routers, and hosts originate and receive
packet information. Protocols specify a set of rules and formats required to
exchange these packets of information.
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