Monday, May 28, 2007
Public Safety Network
Public Safety Network
A Public Safety Network is a wireless communications network used by emergency services organizations, such as police, fire and emergency medical services, to prevent or respond to incidents that harm or endanger persons or property.
Many municipalities are turning to mobile computing and other networked applications to improve the efficiency of their workforce, including public safety personnel and first responders.
Consequently, public safety workers are increasingly being equipped with wireless laptops, handheld computers, and mobile video cameras to improve their efficiency, visibility, and ability to instantly collaborate with central command, coworkers and other agencies. Video surveillance cameras and unattended sensors are becoming important tools to extend the eyes and ears of public safety agencies.
The need to access and share this vital new flow of data and images is driving investments in a new kind of network: broadband wireless mesh networks using Wi-Fi, WiMAX, and 4.9 GHz public safety radio frequencies.
These networks are metropolitan or regional in scope, can maintain connections with highly mobile workers, deliver large amounts of low-cost bandwidth with extremely high reliability, and support real-time video, voice and data.
Wireless Network
Wireless network
While the term wireless network may technically be used to refer to any type of network that is wireless, the term is most commonly used to refer to a telecommunications network whose interconnections between nodes is implemented without the use of wires, such as a computer network (which is a type of telecommunications network). Wireless telecommunications networks are generally implemented with some type of information transmission system that uses electromagnetic waves, such as radio waves, for the carrier and this implementation usually takes place at the physical level or "layer" of the network. (For example, see the Physical Layer of the OSI Model).
Types
Wireless LAN
One type of wireless network is a wireless LAN, or Local Area Network. Similar to other wireless devices, it uses radio instead of wires to transmit data back and forth between computers on the same network as was the case for ALOHANET.
Global System for Mobile Communications (GSM)
The GSM network is divided into three major systems which are the switching system, the base station system, and the operation and support system (Global System for Mobile Communication (GSM)). The cell phone connects to the base system station which then connects to the operation and support station; it then connects to the switching station where the call is transferred where it needs to go (Global System for Mobile Communication (GSM)). This is used for cellular phones, is the most common standard and is used for a majority of cellular providers.
Personal Communications Service (PCS)
PCS is a radio band that can be used by mobile phones in North America. Sprint happened to be the first service to set up a PCS.
D-AMPS
D-AMPS, which stands for Digital Advanced Mobile Phone Service, is an upgraded version of AMPS but it is being phased out due to advancement in technology. The newer GSM networks are replacing the older system.
Wi-Fi
Wi-Fi is a commonly used wireless network in computer systems which enable connection to the internet or other machines that have Wi-Fi functionalities. Wi-Fi networks broadcast radio waves that can be picked up by Wi-Fi receivers that are attached to different computers.
Fixed Wireless Data
Fixed wireless data is a type of wireless data network that can be used to connect two or more buildings together in order to extend or share the network bandwidth without physically wiring the buildings together.
While the term wireless network may technically be used to refer to any type of network that is wireless, the term is most commonly used to refer to a telecommunications network whose interconnections between nodes is implemented without the use of wires, such as a computer network (which is a type of telecommunications network). Wireless telecommunications networks are generally implemented with some type of information transmission system that uses electromagnetic waves, such as radio waves, for the carrier and this implementation usually takes place at the physical level or "layer" of the network. (For example, see the Physical Layer of the OSI Model).
Types
Wireless LAN
One type of wireless network is a wireless LAN, or Local Area Network. Similar to other wireless devices, it uses radio instead of wires to transmit data back and forth between computers on the same network as was the case for ALOHANET.
Global System for Mobile Communications (GSM)
The GSM network is divided into three major systems which are the switching system, the base station system, and the operation and support system (Global System for Mobile Communication (GSM)). The cell phone connects to the base system station which then connects to the operation and support station; it then connects to the switching station where the call is transferred where it needs to go (Global System for Mobile Communication (GSM)). This is used for cellular phones, is the most common standard and is used for a majority of cellular providers.
Personal Communications Service (PCS)
PCS is a radio band that can be used by mobile phones in North America. Sprint happened to be the first service to set up a PCS.
D-AMPS
D-AMPS, which stands for Digital Advanced Mobile Phone Service, is an upgraded version of AMPS but it is being phased out due to advancement in technology. The newer GSM networks are replacing the older system.
Wi-Fi
Wi-Fi is a commonly used wireless network in computer systems which enable connection to the internet or other machines that have Wi-Fi functionalities. Wi-Fi networks broadcast radio waves that can be picked up by Wi-Fi receivers that are attached to different computers.
Fixed Wireless Data
Fixed wireless data is a type of wireless data network that can be used to connect two or more buildings together in order to extend or share the network bandwidth without physically wiring the buildings together.
Computer Networking
Computer networking is the engineering discipline concerned with communication between computer systems. Such communicating computer systems constitute a computer network and these networks generally involve at least two devices capable of being networked with at least one usually being a computer. The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the Internet).
Computer networking is sometimes considered a sub-discipline of telecommunications, and sometimes of computer science, information technology and computer engineering. Computer networks rely heavily upon the theoretical and practical application of these scientific and engineering disciplines.
A computer network is any set of computers or devices connected to each other. Examples of networks are the Internet, a wide area network that is the largest to ever exist, or a small home local area network (LAN) with two computers connected with standard networking cables connecting to a network interface card in each computer.
HISTORY
Before the advent of computer networks that were based upon some type of telecommunications system, communication between calculation machines and early computers was performed by human users by carrying instructions between them.
In September 1940 George Stibitz used a teletype machine to send instructions for a problem set from his Model K at Dartmouth College in New Hampshire to his Complex Number Calculator in New York and received results back by the same means. Linking output systems like teletypes to computers was an interest at the Advanced Research Projects Agency (ARPA) when, in 1962, J.C.R. Licklider was hired and developed a working group he called the "Intergalactic Network", a precursor to the ARPANet.
In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing System for distributed users of large computer systems. The same year, at MIT, a research group supported by General Electric and Bell Labs used a computer (DEC's PDP-8) to route and manage telephone connections.
Throughout the 1960s Leonard Kleinrock, Paul Baran and Donald Davies independently conceptualized and developed network systems which used datagrams or packets that could be used in a packet switched network between computer systems.
In 1969 the University of California at Los Angeles, SRI (in Stanford), University of California at Santa Barbara, and the University of Utah were connected as the beginning of the ARPANet network using 50 kbit/s circuits.
Computer networks, and the technologies needed to connect and communicate through and between them, continue to drive computer hardware, software, and peripherals industries. This expansion is mirrored by growth in the numbers and types of users of networks from the researcher to the home user.
Today, computer networks are the core of modern communication. The scope of communication has increased significantly in the past decade and this boom in communications would not have been possible without the progressively advancing computer network.
Networking Methods
Networking is a complex part of computing that makes up most of the IT Industry. Without networks, almost all communication in the world would cease to happen. It is because of networking that telephones, televisions, the internet, etc. work.
There are two (broad) types of networks in existence at the moment. These are:
Local Area Network (LAN)
A Local Area Network is a network that spans a relatively small space and provides services to a small amount of people. Depending on the amount of people that use a Local Area Network, a peer-to-peer or client-server method of networking may be used. A peer-to-peer network is where each client shares their resources with other workstations in the network. Examples of peer-to-peer networks are: Small office networks where resource use is minimal and a home network. A client-server network is where every client is connected to the server and each other. Client-server networks use servers in different capacities.
These can be classified into two types: Single-service servers, where the server performs one task such as file server, print server, etc.; while other servers can not only perform in the capacity of file servers and print servers, but they also conduct calculations and use these to provide information to clients (Web/Intranet Server).
Computers are linked via Ethernet Cable, can be joined either directly (one computer to another), or via a network hub that allows multiple connections.
Wide Area Network (WAN)
A Wide Area Network is a network where a wide variety of resources are deployed across a large domestic area or internationally. An example of this is a multinational business that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is the largest network in the world.
Wireless Networks (WLAN, WWAN)
A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transfered over sets of radio trancievers. These types of networks are beneficial when it is to costly or inconvenient to run the necessary cables. For more information, see Wireless LAN and Wireless wide area network
In order for communication to take place between computers, mediums must be used. These mediums include Protocols, Physical Routers and Ethernet, etc. This is covered by Open Systems Interconnection which comprises all the processes that make information transport
Computer networking is sometimes considered a sub-discipline of telecommunications, and sometimes of computer science, information technology and computer engineering. Computer networks rely heavily upon the theoretical and practical application of these scientific and engineering disciplines.
A computer network is any set of computers or devices connected to each other. Examples of networks are the Internet, a wide area network that is the largest to ever exist, or a small home local area network (LAN) with two computers connected with standard networking cables connecting to a network interface card in each computer.
HISTORY
Before the advent of computer networks that were based upon some type of telecommunications system, communication between calculation machines and early computers was performed by human users by carrying instructions between them.
In September 1940 George Stibitz used a teletype machine to send instructions for a problem set from his Model K at Dartmouth College in New Hampshire to his Complex Number Calculator in New York and received results back by the same means. Linking output systems like teletypes to computers was an interest at the Advanced Research Projects Agency (ARPA) when, in 1962, J.C.R. Licklider was hired and developed a working group he called the "Intergalactic Network", a precursor to the ARPANet.
In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing System for distributed users of large computer systems. The same year, at MIT, a research group supported by General Electric and Bell Labs used a computer (DEC's PDP-8) to route and manage telephone connections.
Throughout the 1960s Leonard Kleinrock, Paul Baran and Donald Davies independently conceptualized and developed network systems which used datagrams or packets that could be used in a packet switched network between computer systems.
In 1969 the University of California at Los Angeles, SRI (in Stanford), University of California at Santa Barbara, and the University of Utah were connected as the beginning of the ARPANet network using 50 kbit/s circuits.
Computer networks, and the technologies needed to connect and communicate through and between them, continue to drive computer hardware, software, and peripherals industries. This expansion is mirrored by growth in the numbers and types of users of networks from the researcher to the home user.
Today, computer networks are the core of modern communication. The scope of communication has increased significantly in the past decade and this boom in communications would not have been possible without the progressively advancing computer network.
Networking Methods
Networking is a complex part of computing that makes up most of the IT Industry. Without networks, almost all communication in the world would cease to happen. It is because of networking that telephones, televisions, the internet, etc. work.
There are two (broad) types of networks in existence at the moment. These are:
Local Area Network (LAN)
A Local Area Network is a network that spans a relatively small space and provides services to a small amount of people. Depending on the amount of people that use a Local Area Network, a peer-to-peer or client-server method of networking may be used. A peer-to-peer network is where each client shares their resources with other workstations in the network. Examples of peer-to-peer networks are: Small office networks where resource use is minimal and a home network. A client-server network is where every client is connected to the server and each other. Client-server networks use servers in different capacities.
These can be classified into two types: Single-service servers, where the server performs one task such as file server, print server, etc.; while other servers can not only perform in the capacity of file servers and print servers, but they also conduct calculations and use these to provide information to clients (Web/Intranet Server).
Computers are linked via Ethernet Cable, can be joined either directly (one computer to another), or via a network hub that allows multiple connections.
Wide Area Network (WAN)
A Wide Area Network is a network where a wide variety of resources are deployed across a large domestic area or internationally. An example of this is a multinational business that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is the largest network in the world.
Wireless Networks (WLAN, WWAN)
A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transfered over sets of radio trancievers. These types of networks are beneficial when it is to costly or inconvenient to run the necessary cables. For more information, see Wireless LAN and Wireless wide area network
In order for communication to take place between computers, mediums must be used. These mediums include Protocols, Physical Routers and Ethernet, etc. This is covered by Open Systems Interconnection which comprises all the processes that make information transport
Node ( Networking )
Node (networking)
A node is a device that is connected as part of a computer network. Every node must have a MAC address or Data Link Control address[1] if it is at least an OSI model layer 2 device. Nodes can be computers, personal digital assistants (PDAs), cell phones, or various other network appliances, such as routers, switches and hubs. Nodes that actively route data for the other networked devices as well as themselves are called supernodes.
In general terms, a node is a specific location in a telecommunication network. In Cable TV systems (CATV), this term has assumed a broader context and is generally associated with a Fiber Optic Node. A fiber optic node is those homes or businesses within a specific geographic area that are served from a common fiber optic receiver.
A fiber optic node is generally described in terms of the number of Homes Passed that are served by that specific fiber node.
Network node (NN):
A grouping of one or more network elements (at one or more sites) which provides network related functions, and is administered as a single entity. A single site may contain more than one network node. For the purpose of this glossary, a network node is considered synonymous with a network element, and is usually at a single site.
This restriction simplifies the definition of the network node interface (NNI) and INI, which would not apply between network elements.
A node is a device that is connected as part of a computer network. Every node must have a MAC address or Data Link Control address[1] if it is at least an OSI model layer 2 device. Nodes can be computers, personal digital assistants (PDAs), cell phones, or various other network appliances, such as routers, switches and hubs. Nodes that actively route data for the other networked devices as well as themselves are called supernodes.
In general terms, a node is a specific location in a telecommunication network. In Cable TV systems (CATV), this term has assumed a broader context and is generally associated with a Fiber Optic Node. A fiber optic node is those homes or businesses within a specific geographic area that are served from a common fiber optic receiver.
A fiber optic node is generally described in terms of the number of Homes Passed that are served by that specific fiber node.
Network node (NN):
A grouping of one or more network elements (at one or more sites) which provides network related functions, and is administered as a single entity. A single site may contain more than one network node. For the purpose of this glossary, a network node is considered synonymous with a network element, and is usually at a single site.
This restriction simplifies the definition of the network node interface (NNI) and INI, which would not apply between network elements.
Computer Networking Device
Computer networking device
Computer networking devices are units that mediate data in a computer network. Computer networking devices are also called network equipment, Intermediate Systems (IS) or InterWorking Unit (IWU). Units which are the last receiver or generate data are called hosts or data terminal equipment.
List of computer networking devices
Common basic network devices:
Gateway: device sitting at a network node for interfacing with another network that uses different protocols. Works on OSI layers 4 to 7.
Router: a specialized network device that determines the next network point to which to forward a data packet toward its destination. Unlike a gateway, it cannot interface different protocols. Works on OSI layer 3.
Bridge: a device that connects multiple network segments along the data link layer. Works on OSI layer 2.
Switch: a device that allocates traffic from one network segment to certain lines (intended destination(s)) which connect the segment to another network segment. So unlike a hub a switch splits the network traffic and sends it to different destinations rather than to all systems on the network. Works on OSI layer 2.
Hub: connects multiple Ethernet segments together making them act as a single segment. When using a hub, every attached device shares the same broadcast domain and the same collision domain. Therefore, only one computer connected to the hub is able to transmit at a time. Depending on the network topology, the hub provides a basic level 1 OSI model connection among the network objects (workstations, servers, etc). It provides bandwidth which is shared among all the objects, compared to switches, which provide a dedicated connection between individual nodes. Works on OSI layer 1.
Repeater: device to amplify or regenerate digital signals received while setting them from one part of a network into another. Works on OSI layer 1.
Some hybrid network devices:
Multilayer Switch: a switch which, in addition to switching on OSI layer 2, provides functionality at higher protocol layers.
Protocol Converter: a hardware device that converts between two different types of transmissions, such as asynchronous and synchronous transmissions.
Brouter: Combine router and bridge functionality and are therefore working on OSI layers 2 and 3.
Digital media receiver: Connects a computer network to a home theatre
Hardware or software components that typically sit on the connection point of different
networks, e.g. between an internal network and an external network:
Proxy: computer network service which allows clients to make indirect network connections to other network services
Firewall: a piece of hardware or software put on the network to prevent some communications forbidden by the network policy
Network Address Translator: network service provide as hardware or software that converts internal to external network addresses and vice versa
Other hardware for establishing networks or dial-up connections:
Multiplexer: device that combines several electrical signals into a single signal
Network Card: a piece of computer hardware to allow the attached computer to communicate by network
Modem: device that modulates an analog "carrier" signal (such as sound), to encode digital information, and that also demodulates such a carrier signal to decode the transmitted information, as a computer communicating with another computer over the telephone network
ISDN terminal adapter (TA): a specialized gateway for ISDN
Line Driver: a device to increase transmission distance by amplifying the signal. Base-band networks only.
Computer networking devices are units that mediate data in a computer network. Computer networking devices are also called network equipment, Intermediate Systems (IS) or InterWorking Unit (IWU). Units which are the last receiver or generate data are called hosts or data terminal equipment.
List of computer networking devices
Common basic network devices:
Gateway: device sitting at a network node for interfacing with another network that uses different protocols. Works on OSI layers 4 to 7.
Router: a specialized network device that determines the next network point to which to forward a data packet toward its destination. Unlike a gateway, it cannot interface different protocols. Works on OSI layer 3.
Bridge: a device that connects multiple network segments along the data link layer. Works on OSI layer 2.
Switch: a device that allocates traffic from one network segment to certain lines (intended destination(s)) which connect the segment to another network segment. So unlike a hub a switch splits the network traffic and sends it to different destinations rather than to all systems on the network. Works on OSI layer 2.
Hub: connects multiple Ethernet segments together making them act as a single segment. When using a hub, every attached device shares the same broadcast domain and the same collision domain. Therefore, only one computer connected to the hub is able to transmit at a time. Depending on the network topology, the hub provides a basic level 1 OSI model connection among the network objects (workstations, servers, etc). It provides bandwidth which is shared among all the objects, compared to switches, which provide a dedicated connection between individual nodes. Works on OSI layer 1.
Repeater: device to amplify or regenerate digital signals received while setting them from one part of a network into another. Works on OSI layer 1.
Some hybrid network devices:
Multilayer Switch: a switch which, in addition to switching on OSI layer 2, provides functionality at higher protocol layers.
Protocol Converter: a hardware device that converts between two different types of transmissions, such as asynchronous and synchronous transmissions.
Brouter: Combine router and bridge functionality and are therefore working on OSI layers 2 and 3.
Digital media receiver: Connects a computer network to a home theatre
Hardware or software components that typically sit on the connection point of different
networks, e.g. between an internal network and an external network:
Proxy: computer network service which allows clients to make indirect network connections to other network services
Firewall: a piece of hardware or software put on the network to prevent some communications forbidden by the network policy
Network Address Translator: network service provide as hardware or software that converts internal to external network addresses and vice versa
Other hardware for establishing networks or dial-up connections:
Multiplexer: device that combines several electrical signals into a single signal
Network Card: a piece of computer hardware to allow the attached computer to communicate by network
Modem: device that modulates an analog "carrier" signal (such as sound), to encode digital information, and that also demodulates such a carrier signal to decode the transmitted information, as a computer communicating with another computer over the telephone network
ISDN terminal adapter (TA): a specialized gateway for ISDN
Line Driver: a device to increase transmission distance by amplifying the signal. Base-band networks only.
Classification of Computer Networks
Classification of computer networks
By network layer
Computer networks may be classified according to the network layer at which they operate according to some basic reference models that are considered to be standards in the industry such as the seven layer OSI reference model and the five layer TCP/IP model.
By scale
Computer networks may be classified according to the scale or extent of reach of the network, for example as a Personal area network (PAN), Local area network (LAN), Campus area network (CAN), Metropolitan area network (MAN), or Wide area network (WAN).
By connection method
Computer networks may be classified according to the technology that is used to connect the individual devices in the network such as HomePNA, Power line communication, Ethernet, or Wireless LAN.
By functional relationship
Computer networks may be classified according to the functional relationships which exist between the elements of the network, for example Active Networking, Client-server and Peer-to-peer (workgroup) architectures. Also, computer networks are used to send data from one to another by the hardrive
By network
Computer networks may be classified according to the network topology upon which the network is based, such as Bus network, Star network, Ring network, Mesh network, Star-bus network, Tree or Hierarchical topology network, etc.
Topology can be arranged in a Geometric Arrangement
By services provided
Computer networks may be classified according to the services which they provide, such as Storage area networks, Server farms, Process control networks, Value-added network, Wireless community network, etc.
By protocol
Computer networks may be classified according to the communications protocol that is being used on the network. See the articles on List of network protocol stacks and List of network protocols for more information.
By network layer
Computer networks may be classified according to the network layer at which they operate according to some basic reference models that are considered to be standards in the industry such as the seven layer OSI reference model and the five layer TCP/IP model.
By scale
Computer networks may be classified according to the scale or extent of reach of the network, for example as a Personal area network (PAN), Local area network (LAN), Campus area network (CAN), Metropolitan area network (MAN), or Wide area network (WAN).
By connection method
Computer networks may be classified according to the technology that is used to connect the individual devices in the network such as HomePNA, Power line communication, Ethernet, or Wireless LAN.
By functional relationship
Computer networks may be classified according to the functional relationships which exist between the elements of the network, for example Active Networking, Client-server and Peer-to-peer (workgroup) architectures. Also, computer networks are used to send data from one to another by the hardrive
By network
Computer networks may be classified according to the network topology upon which the network is based, such as Bus network, Star network, Ring network, Mesh network, Star-bus network, Tree or Hierarchical topology network, etc.
Topology can be arranged in a Geometric Arrangement
By services provided
Computer networks may be classified according to the services which they provide, such as Storage area networks, Server farms, Process control networks, Value-added network, Wireless community network, etc.
By protocol
Computer networks may be classified according to the communications protocol that is being used on the network. See the articles on List of network protocol stacks and List of network protocols for more information.
Types of Networks
Types of networks:
Below is a list of the most common types of computer networks.
A personal area network (PAN) :
A personal area network (PAN) is a computer network used for communication among computer devices (including telephones and personal digital assistants) close to one person. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink).
Personal area networks may be wired with computer buses such as USB and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.
Local Area Network (LAN):
A network that is limited to a relatively small spatial area such as a room, a single building, a ship, or an aircraft. Local area networks are sometimes called a single location network.
Note: For administrative purposes, large LANs are generally divided into smaller logical segments called workgroups. A workgroup is a group of computers that share a common set of resources within a LAN.
Campus Area Network (CAN):
A network that connects two or more LANs but that is limited to a specific (possibly private) geographical area such as a college campus, industrial complex, or a military base
Note: A CAN is generally limited to an area that is smaller than a Metropolitan Area Network.
Metropolitan Area Network (MAN):
A network that connects two or more Local Area Networks or CANs together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area. Multiple routers, switches & hubs are connected to create a MAN
Wide Area Networks (WAN):
A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.
Types of WANs:
1. Centralized:
A centralized WAN consists of a central computer that is connected to dumb terminals and / or other types of terminal devices.
2. Distributed:
A distributed WAN consists of two or more computers in different locations and may also include connections to dumb terminals and other types of terminal devices.
Internetwork:
Two or more networks or network segments connected using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as a router.
Note: Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.
Internet, The:
A specific internetwork, consisting of a worldwide interconnection of governmental, academic, public, and private networks based upon the Advanced Research Projects Agency Network (ARPANET) developed by ARPA of the U.S. Department of Defense – also home to the World Wide Web (WWW) and referred to as the 'Internet' with a capital 'I' to distinguish it from other generic internetworks.
Extranet:
A network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g., a company's customers may be provided access to some part of its intranet thusly creating an extranet while at the same time the customers may not be considered 'trusted' from a security standpoint).
Note: Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN, because an extranet must have at least one connection with an outside network.
Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization.
The Internet itself is not considered to be a part of the intranet or extranet, although the Internet may serve as a portal for access to portions of an extranet.
Below is a list of the most common types of computer networks.
A personal area network (PAN) :
A personal area network (PAN) is a computer network used for communication among computer devices (including telephones and personal digital assistants) close to one person. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink).
Personal area networks may be wired with computer buses such as USB and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.
Local Area Network (LAN):
A network that is limited to a relatively small spatial area such as a room, a single building, a ship, or an aircraft. Local area networks are sometimes called a single location network.
Note: For administrative purposes, large LANs are generally divided into smaller logical segments called workgroups. A workgroup is a group of computers that share a common set of resources within a LAN.
Campus Area Network (CAN):
A network that connects two or more LANs but that is limited to a specific (possibly private) geographical area such as a college campus, industrial complex, or a military base
Note: A CAN is generally limited to an area that is smaller than a Metropolitan Area Network.
Metropolitan Area Network (MAN):
A network that connects two or more Local Area Networks or CANs together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area. Multiple routers, switches & hubs are connected to create a MAN
Wide Area Networks (WAN):
A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.
Types of WANs:
1. Centralized:
A centralized WAN consists of a central computer that is connected to dumb terminals and / or other types of terminal devices.
2. Distributed:
A distributed WAN consists of two or more computers in different locations and may also include connections to dumb terminals and other types of terminal devices.
Internetwork:
Two or more networks or network segments connected using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as a router.
Note: Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.
Internet, The:
A specific internetwork, consisting of a worldwide interconnection of governmental, academic, public, and private networks based upon the Advanced Research Projects Agency Network (ARPANET) developed by ARPA of the U.S. Department of Defense – also home to the World Wide Web (WWW) and referred to as the 'Internet' with a capital 'I' to distinguish it from other generic internetworks.
Extranet:
A network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g., a company's customers may be provided access to some part of its intranet thusly creating an extranet while at the same time the customers may not be considered 'trusted' from a security standpoint).
Note: Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN, because an extranet must have at least one connection with an outside network.
Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization.
The Internet itself is not considered to be a part of the intranet or extranet, although the Internet may serve as a portal for access to portions of an extranet.
Building Computer Network
Building a computer network
A simple computer network may be constructed from two computers by adding a network adapter (Network Interface Controller (NIC)) to each computer and then connecting them together with a special cable called a crossover cable. This type of network is useful for transferring information between two computers that are not normally connected to each other by a permanent network connection or for basic home networking applications.
Alternatively, a network between two computers can be established without dedicated extra hardware by using a standard connection such as the RS-232 serial port on both computers, connecting them to each other via a special crosslinked null modem cable.
Practical networks generally consist of more than two interconnected computers and generally require special devices in addition to the Network Interface Controller that each computer needs to be equipped with.
Examples of some of these special devices are listed above under Basic Computer Network Building Blocks / networking devices.
A simple computer network may be constructed from two computers by adding a network adapter (Network Interface Controller (NIC)) to each computer and then connecting them together with a special cable called a crossover cable. This type of network is useful for transferring information between two computers that are not normally connected to each other by a permanent network connection or for basic home networking applications.
Alternatively, a network between two computers can be established without dedicated extra hardware by using a standard connection such as the RS-232 serial port on both computers, connecting them to each other via a special crosslinked null modem cable.
Practical networks generally consist of more than two interconnected computers and generally require special devices in addition to the Network Interface Controller that each computer needs to be equipped with.
Examples of some of these special devices are listed above under Basic Computer Network Building Blocks / networking devices.
Transmission Errors
Transmission Errors
It is virtually impossible to send any signal, analog or digital, over a distance without any distortion even in the most perfect conditions due to:
1. Delay Distortion
Signals of varying frequencies travel at different speeds along the medium. The speed of travel of a signal is highest at the center of the bandwidth of the medium and lower at both the ends. Therefore, at the receiving end, signals with different frequencies in the given medium will arrive at different times causing delay error.
2. Attenuation
As a signal travels through a medium, its signal strength decreases.
3. Noise
A signal travels as an electromagnetic signal through any medium. Electromagnetic energy that gets inserted somewhere during transmission is called noise.
Many attempts have been made to detect and rectify the transmission errors. Error detection schemes:
Vertical Redundancy Check (VRC) or Parity Check
Longitudinal Redundancy Check (LRC)
Cyclic Redundancy Check (CRC)
Error correction schemes:
1. stop-and-wait
2. go-back-n
3. sliding-window
It is virtually impossible to send any signal, analog or digital, over a distance without any distortion even in the most perfect conditions due to:
1. Delay Distortion
Signals of varying frequencies travel at different speeds along the medium. The speed of travel of a signal is highest at the center of the bandwidth of the medium and lower at both the ends. Therefore, at the receiving end, signals with different frequencies in the given medium will arrive at different times causing delay error.
2. Attenuation
As a signal travels through a medium, its signal strength decreases.
3. Noise
A signal travels as an electromagnetic signal through any medium. Electromagnetic energy that gets inserted somewhere during transmission is called noise.
Many attempts have been made to detect and rectify the transmission errors. Error detection schemes:
Vertical Redundancy Check (VRC) or Parity Check
Longitudinal Redundancy Check (LRC)
Cyclic Redundancy Check (CRC)
Error correction schemes:
1. stop-and-wait
2. go-back-n
3. sliding-window
Modes of data Transmission
Modes Of Data Transmission
Digital data can be transmitted in a number of ways:
1. Parallel and serial communication
2. Synchronous, iso-synchronous and asynchronous communication
3. Simplex, half-duplex and full-duplex communication
Digital data can be transmitted in a number of ways:
1. Parallel and serial communication
2. Synchronous, iso-synchronous and asynchronous communication
3. Simplex, half-duplex and full-duplex communication
Communication Techniques
Communication Techniques
Data is transmitted in the form of electrical signals. The electrical signals are of two types viz., analog and digital. Similarly, data can also be either analog or digital. Based on them, data communication may be of following types:
1. Analog data, analog transmission
e.g.: transmission of voice signals over telephone line
2. Analog data, digital transmission
e.g.: transmission of voice signal after digitization using PCM, delta modulation or adaptive delta modulation
3. Digital data, analog transmission
e.g.: communication using modem
4. Digital data, digital transmission
e.g.: most of present day communication
Data is transmitted in the form of electrical signals. The electrical signals are of two types viz., analog and digital. Similarly, data can also be either analog or digital. Based on them, data communication may be of following types:
1. Analog data, analog transmission
e.g.: transmission of voice signals over telephone line
2. Analog data, digital transmission
e.g.: transmission of voice signal after digitization using PCM, delta modulation or adaptive delta modulation
3. Digital data, analog transmission
e.g.: communication using modem
4. Digital data, digital transmission
e.g.: most of present day communication
Regulatory Agencies
Regulatory Agencies
These are government appointed agencies like Federal Communications Commission (FCC).
These are government appointed agencies like Federal Communications Commission (FCC).
Forums
Forums
University students, user groups, industry representatives and experts come together and set up forums to address various issues and concerns of data communication technology and come up with standards for the day's need. Some of the well-known forums are:
1. The Internet Society(ISOC)
2. Internet Engineering Task Force (IETF)
3. Frame Relay Forum
4. ATM Forum
5. ATM Consortium
University students, user groups, industry representatives and experts come together and set up forums to address various issues and concerns of data communication technology and come up with standards for the day's need. Some of the well-known forums are:
1. The Internet Society(ISOC)
2. Internet Engineering Task Force (IETF)
3. Frame Relay Forum
4. ATM Forum
5. ATM Consortium
Standards Organizations
Standards Organizations
Various standards organizations for data communication exist today.
They are broadly classified into three categories:
1. Standards ,Creation and Committees.
2. Forums
3. Regulatory Agencies
Standards Creation Committees
Some important organizations in this category are:
International Organization for Standardization (ISO; also known as International Standards Organization)
A multinational standards body
International Telecommunications Union - Telecommunication Standards Sector (ITU-T)
Previously, CCITT. Developed under United Nations for national standards.
American National Standards Institute (ANSI)
An affiliate of ITU-T
Institute of Electrical and Electronic Engineers (IEEE)
Largest professional engineering body in the world. Oversees the development and adoption of international electrical and electronic standards.
Electronic Industries Alliance (EIA; formerly Electronic Industries Association)
Aligned with ANSI. Focuses public awareness and lobbying for standards.
Various standards organizations for data communication exist today.
They are broadly classified into three categories:
1. Standards ,Creation and Committees.
2. Forums
3. Regulatory Agencies
Standards Creation Committees
Some important organizations in this category are:
International Organization for Standardization (ISO; also known as International Standards Organization)
A multinational standards body
International Telecommunications Union - Telecommunication Standards Sector (ITU-T)
Previously, CCITT. Developed under United Nations for national standards.
American National Standards Institute (ANSI)
An affiliate of ITU-T
Institute of Electrical and Electronic Engineers (IEEE)
Largest professional engineering body in the world. Oversees the development and adoption of international electrical and electronic standards.
Electronic Industries Alliance (EIA; formerly Electronic Industries Association)
Aligned with ANSI. Focuses public awareness and lobbying for standards.
Protocols
Protocols
A protocol is a set of rules and conventions about the communication in the network. A protocol mainly defines the following:
1. Syntax: Defines the structure or format of data.
2. Semantics: Defines the interpretation of data being sent.
3. Timing: Refers to an agreement between a sender and a receiver about the transmission.
A protocol is a set of rules and conventions about the communication in the network. A protocol mainly defines the following:
1. Syntax: Defines the structure or format of data.
2. Semantics: Defines the interpretation of data being sent.
3. Timing: Refers to an agreement between a sender and a receiver about the transmission.
Basics
Basics
A computer network may be described as the interconnection of two or more computers that may share files and folders, applications, or resources like printers, scanners, web-cams etc. Internet is also a type of computer network which connects all the computers of the world having Internet facility on them
A computer network may be described as the interconnection of two or more computers that may share files and folders, applications, or resources like printers, scanners, web-cams etc. Internet is also a type of computer network which connects all the computers of the world having Internet facility on them
Computer Network
A computer network.
A computer network is multiple computers connected together using a telecommunication system for the purpose of communicating and sharing resources.
Experts in the field of networking debate whether two computers that are connected together using some form of communications medium constitute a network. Therefore, some works state that a network requires three connected computers.
For example, "Telecommunications: Glossary of Telecommunication Terms"states that a computer network is "A network of data processing nodes that are interconnected for the purpose of data communication", the term "network" being defined in the same document as "An interconnection of three or more communicating entities". A computer connected to a non-computing device (e.g., networked to a printer via an Ethernet link) may also represent a computer network, although this article does not address this configuration.
This article uses the definition which requires two or more computers to be connected together to form a network. Therefore, this does not include intranets, due to their not needing to be connected via two or more computers.The same basic functions are generally present in this case as with larger numbers of connected computers.
A computer network is multiple computers connected together using a telecommunication system for the purpose of communicating and sharing resources.
Experts in the field of networking debate whether two computers that are connected together using some form of communications medium constitute a network. Therefore, some works state that a network requires three connected computers.
For example, "Telecommunications: Glossary of Telecommunication Terms"states that a computer network is "A network of data processing nodes that are interconnected for the purpose of data communication", the term "network" being defined in the same document as "An interconnection of three or more communicating entities". A computer connected to a non-computing device (e.g., networked to a printer via an Ethernet link) may also represent a computer network, although this article does not address this configuration.
This article uses the definition which requires two or more computers to be connected together to form a network. Therefore, this does not include intranets, due to their not needing to be connected via two or more computers.The same basic functions are generally present in this case as with larger numbers of connected computers.
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