CLASSIFICATION OF COMPUTER NETWORKS-2011

Computer Networking PrinciplesICS 216

Classification of computer networks


• There is no generally accepted taxonomy into which all computer networks fit

• Two dimensions stand out: transmission technology and scale


Transmission technology dimension


• There are broadly two types of transmission technologies Broadcast links Point to point links

Broadcast networks

Broadcast networks

• Broadcast systems have a single communication channel that is shared by all the machines on the network.

• Packets sent by any machine are received by all others.

Broadcast networks

• An address field within the packet specifies for whom it is intended.

• Upon receiving a packet, a machine checks the address field. If the packet is intended for some other machine it is ignored.

Broadcast networks

• Broadcast systems generally also allow the possibility of addressing a packet to all destinations by using a special code in the address field.

• When a packet with this code is transmitted, it is received and processed by every machine on the network.

• This mode of operation is called broadcasting

Broadcast networks

• Some broadcast systems also support transmission to a subset of the machines, something known as multicasting.

• May be achieved by reserving one bit for multicasting with the remaining n-1 bits address bits holding the group number

• Each machine can subscribe to any or all of the groups• When a packet is sent to a certain group, it is delivered to

all machines subscribing to the group

Point-to-point networks

Point to point Networks

• Point to point networks consist of many connections between individual machines

• The network contains numerous cables or leased telephone lines which link individual computers indirectly via intermediate computers.

Point to point networks

• If two individual computers that do not share a cable nevertheless wish to communicate, they must do this indirectly via intermediate machines

• Often multiple routes of different lengths are possible


• Point-to-point transmission with one sender and one receiver is often called unicasting


• A general rule: Smaller geographically localized networks tend to use

broadcasting Larger networks tend to use point-to-point

classification of computer networks

Scale dimension


• An alternative criterion for classifying networks is their scale

• These can be divided into Local Area networks (LAN) Wide area networks (WAN) Metropolitan area networks (MAN) Internetworks


Classification of computer networks by scale

Local area networks

Local area networks

• LANS are usually privately owned. The owning organization usually owns all the attached devices.

• They are widely used to connect Personal computers and workstations in offices to share resources and exchange information

• The management responsibilities of a LAN are carried out solely by the owning organization

Local area networks

• LANs can be distinguished from other kinds of networks by their Size Transmission technology Topology

Local area networks

• Size A LAN covers a small geographical area A LAN is usually the interconnection of a collection of

computer systems in a single building or a cluster of buildings

Network is usually up to a few kilometers in size In TCP/IP networking, a LAN is often but not

always implemented as a single IP subnet. Cost low (thousands of dollars).

Local area networks

• Transmission technology A cable to which all machines are attached and can

transmit The internal data rates of LANs are typically high

(10Mbps-10 Gbps).

Local area networks

• Topology: Various topologies are possible for broadcast LANS Bus Ring

Local area networks

Two broadcast networks (a) Bus (b) Ring

Local area networks

• Characteristics

• Geographical scope?

• Ownership?

• Transmission Technology?

Metropolitan area networks


• A MAN covers a medium-size geographic region (e.g. entire town or city). A MAN is larger than a LAN and smaller than a WAN

and is constrained to a defined geographical area.

• A MAN may be controlled by an organization, or by a Telecommunications provider or may be a regional resource.


• Best known example of a MAN is the cable television network

• This type of network is based on high bandwidth copper wire and/or fiber optic cabling installed in towns and cities for the transmission of television programming and other services directly to peoples homes over distances of up to 50 kilometers .


• A number of television channels collected at a central location (called a headend) is distributed to subscribers within a community by means of a network of optical fibers and/or coaxial cables.


• With the increased use of internet, cable TV systems are now offering two way internet services in the unused part of the spectrum.

• Both the TV signals and internet are being fed into the headend for subsequent distribution into peoples homes.


Metropolitan area network based on cable TV


• Characteristics

• Geographical scope?

• Ownership?

• Transmission Technology?

Wide area networks

Wide area networks

• A WAN covers a large geographical area (e.g a country or continent).

• Typically a WAN is a geographically-dispersed collection of LANs.

• Connects multiple LANs to one another over great geographic distances, the size of a country or continent.

• The type of WAN can be Enterprise wide Private network (leased circuits) or simply use Public carrier networks.

Wide area networks

• Most organizations do not build their own WANs by laying cables, building Microwave towers or sending up satellites.

• Instead most organizations lease circuits from Public communication providers and use those to transmit their data.

• They require crossing of public right-of-ways. Hence WANs depend on telecommunication providers for actual data transmission when communicating computers are located in different sites.

Wide area networks

• WAN circuits come in all Types and sizes but typically span hundreds or thousands of miles and provide data transmission rates from 56Kbps to 10Gbps.

• The speed available on a WAN varies depending on the cost of the connections (which increases with distance) and may be low

Wide area networks

• WANs operate using an interconnection of routers which can "choose" the most appropriate path for data to take to reach a network node

Wide area networks

Relationship between hosts and subnet

Wide area networks

• The network consists of a collection of user machines (hosts) connected to a communication subnet.

• The subnet, typically owned and operated by a telephone company or internet service provider, consists of a number of inter connected switching nodes (or routers).

• The transmission lines interconnecting routers can be made of copper wire or optical fiber or even radio links

Wide area networks

• The job of the subnet is to carry messages from source host to destination host.

• A transmission is routed through these internal nodes to the specified destination device. These nodes are not concerned with the content of the data but the moving data from node to node until they reach destination.

• Traditionally WANs have been implemented using one of two technologies: Circuit switching and packet switching. More recently we have Frame relay and ATM networks

• The Speed of data transmission over a WAN is usually slower than the speed of data transmission over a LAN

Wide area networks

Sending from source host to destination host

Internetworks

Internetworks

• An internetwork is a collection of networks that are interconnected together

• People connected to one type of network often want to communicate with people attached to a different one. This requires incompatible networks to be connected. E.g. LAN and WAN or LAN and LAN

• Internetworking means connecting different types of networks that use different technologies such as Ethernet, ATM, FDDI.

Internetworks

• An internetwork is therefore a logical network built around multiple separate physical networks.

• These different networks are connected, sometimes by means of machines called gateways to make connections and provide the necessary translation in terms of both hardware and software

Internetworks

• A common form of internet is a collection of LANs connected by a WAN

LAN-WAN-LAN• The world wide Internet is the most widely used

interconnection of networks to which a large number of networks are connected.

• The Internet is an internetwork of widely used networks.

Internetworks

• While Internet is a specific world-wide connection of networks, internet is a generic term.

Internetworks

• Additional Reading/Assignment:

• Personal Area Network

• Storage Area Network

• System Area Network

• Intranet/Extranet

References

• Local Area networks by Behrouz A. Forouzan Chapter 1

Questions?

Documents

CLASSIFICATION OF COMPUTER NETWORKS-2011