Circuit-switched networks use a direct, physical connection to transmit data back and forth. Message-switched networks send entire transmissions between intermediaries. Packet-switched networks route packets through virtual circuits.
After a network grows beyond the confines of the LAN, a carrier service is required.
Carriers provide a variety of services which are connected through remote access.
carrier services Data transfer services provided by telecommunications companies, such as AT&T, Sprint, or Verizon.
remote access A direct connection to a network using regular dial-up lines. After the connection is made, the user can work on the network as if in the office.
Remote access connections are established through either a dial-up network (DUN) or virtual private network (VPN).
The advantages of a VPN are that users benefit from faster network connections, privacy, and security.
dial-up networking (DUN) A client service using regular telephone lines to connect to a network.
Virtual Private Network (VPN) An alternative to using a dial-up network connection. Is a network connection between two computers. With a VPN, a remote user can securely access the internal network from a remote location. Data in the WAN is transported through various technologies:
Circuit switching
Message switching
circuit-switched network A network that creates a direct physical connection between the sender and receiver.
message switching A technology used to route an entire message from one system to another. That message is routed through intermediate (go-between) station and does not involve a direct physical connection between the sender and receiver.
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Thursday, August 6, 2009
What is POTS?
Telecommunication systems are set along two paths, analog and digital. The most common analog communication uses Plain Old Telephone Service (POTS) provided by the phone company. Plain Old Telephone Service (POTS) One of the largest and most used networks. Also known as the phone system
POTS is provided by the Public Switched Telephone Network (PSTN). For networking, it can be in two forms:
Dial-up
Leased times
Public Switched Telephone Network (PSTN) A communication service known as the public telephone system.
Dial-up networking works well for individuals needing remote access to a network. Types of dial-up connections include:
SLIP
CSLIP
PPP
PPTP
PPPoE
Leased lines are permanent dial-up lines dedicated to full-time data transfer use.
Leased lines are often described as direct connections that are not routed through the phone company’s switching system.
Digital connections allow for faster speed to access the networks. There are several options for digital communication:
Digital data service (DDS)
ISDN
T1/T3
Digital Subscriber Line (xDSL)
digital data service (DDS) Communication lines that are dedicated, point-to-point connections. Lines transmit digital data, rather than voice calls. (p. 213)
Digital Subscriber Line (xDSL) A family of digital communications technologies. These services provide high-speed network access over the standard copper wires run into homes and offices by the telephone company.
ISDN is available in two different forms:
Basic Rate Interface (BRI)
Primary Rate Interface (PRI)
Basic Rate Interface (BRI) A form of ISDN that is typical in home use. There are two B (bearer) channels that carry data at the rate of 64 Kbps.
Primary Rate Interface (PRI) A form of ISDN that is generally used to connect a company’s telephone network. The line is divided into many channels.
T1/T3 lines transmit in full duplex, meaning both sides of the transmission can send and receive simultaneously.
To save on the cost of a full T1 line, businesses can opt for a fractional T1. fractional T1 Part rather than all of the T1 bandwidth. A business often leases this type of bandwidth. xDSL provides high speed access over standard copper wires. This range is limited, however, as shown in the table below.
POTS is provided by the Public Switched Telephone Network (PSTN). For networking, it can be in two forms:
Dial-up
Leased times
Public Switched Telephone Network (PSTN) A communication service known as the public telephone system.
Dial-up networking works well for individuals needing remote access to a network. Types of dial-up connections include:
SLIP
CSLIP
PPP
PPTP
PPPoE
Leased lines are permanent dial-up lines dedicated to full-time data transfer use.
Leased lines are often described as direct connections that are not routed through the phone company’s switching system.
Digital connections allow for faster speed to access the networks. There are several options for digital communication:
Digital data service (DDS)
ISDN
T1/T3
Digital Subscriber Line (xDSL)
digital data service (DDS) Communication lines that are dedicated, point-to-point connections. Lines transmit digital data, rather than voice calls. (p. 213)
Digital Subscriber Line (xDSL) A family of digital communications technologies. These services provide high-speed network access over the standard copper wires run into homes and offices by the telephone company.
ISDN is available in two different forms:
Basic Rate Interface (BRI)
Primary Rate Interface (PRI)
Basic Rate Interface (BRI) A form of ISDN that is typical in home use. There are two B (bearer) channels that carry data at the rate of 64 Kbps.
Primary Rate Interface (PRI) A form of ISDN that is generally used to connect a company’s telephone network. The line is divided into many channels.
T1/T3 lines transmit in full duplex, meaning both sides of the transmission can send and receive simultaneously.
To save on the cost of a full T1 line, businesses can opt for a fractional T1. fractional T1 Part rather than all of the T1 bandwidth. A business often leases this type of bandwidth. xDSL provides high speed access over standard copper wires. This range is limited, however, as shown in the table below.
Multiplexers
Multiplexers and demultiplexers are used to combine and break the high rate data stream. Multiplexing can be achieved through:
Frequency Division Multiplexing (FDU)
Time Division Multiplexing (TDM)
Statistical Time Division Multiplexing (STDM)
Wavelength Division Multiplexing (WDU)
There are two basic types of transmission types:
Asynchronous
Synchronous
asynchronous communication A form of data transmission that involves a delay of seconds, minutes, or even days. Communication does not happen instantly.
synchronous communication Communication whose bits are sent and received in a timed method. Digital systems and networks rely on this method that results in faster transmissions, but it is also more complex and more expensive.
In asynchronous transmissions, the “building blocks” are bytes delineated by start and stop bits.
In synchronous transmissions, the “building blocks” are based on frames: blocks of bits separated by equal time intervals
Frequency Division Multiplexing (FDU)
Time Division Multiplexing (TDM)
Statistical Time Division Multiplexing (STDM)
Wavelength Division Multiplexing (WDU)
There are two basic types of transmission types:
Asynchronous
Synchronous
asynchronous communication A form of data transmission that involves a delay of seconds, minutes, or even days. Communication does not happen instantly.
synchronous communication Communication whose bits are sent and received in a timed method. Digital systems and networks rely on this method that results in faster transmissions, but it is also more complex and more expensive.
In asynchronous transmissions, the “building blocks” are bytes delineated by start and stop bits.
In synchronous transmissions, the “building blocks” are based on frames: blocks of bits separated by equal time intervals
Satellite Systems
Large WANs use satellites to transfer data.
Satellites orbit the Earth in three tiers:
Geostationary earth orbit (GEO)
Medium-earth orbit (MEO)
Low-earth orbit (LEO)
geostationary earth orbit (GEO) The orbit in which satellites fly at 22,000 miles above the earth in fixed positions.
medium-earth orbit (MEO) The orbit in which satellites fly between 6,250 and 12,500 miles above Earth.
low-earth orbit (LEO) The orbit in which satellites fly between 310 and 1,240 miles above Earth.
Satellites orbit the Earth in three tiers:
Geostationary earth orbit (GEO)
Medium-earth orbit (MEO)
Low-earth orbit (LEO)
geostationary earth orbit (GEO) The orbit in which satellites fly at 22,000 miles above the earth in fixed positions.
medium-earth orbit (MEO) The orbit in which satellites fly between 6,250 and 12,500 miles above Earth.
low-earth orbit (LEO) The orbit in which satellites fly between 310 and 1,240 miles above Earth.
MODEMS
Modems are one of the most common ways for computers to connect to each other. Satellite systems are used to connect WANs across the globe. Multiplexers are a key component of WAN technology. Transmissions can be asynchronous or synchronous.
The term modem comes from the two primary tasks it performs: modulation and demodulation.
In many ways, a modem is like a language translator between the analog and digital components.
Modems have several sets of standards:
V series
Hayes-compatible (AT command set)
PC Cards
V series Standards that cover today’s modems, with speeds up to 56 Kbps.
Hayes-Compatible Standards The set of transmission signals, commands, used originally by Hayes modems for exchanging status information, such as readiness to send or receive.
PC Card standards Standards developed for personal computer cards and intended for laptop users that target a broad range of devices, including modems. Developments in the past few decades enabled modem speeds to transmit at 56 Kbps.
However, the 56K transmissions can occur downstream. The upstream, or outgoing transmission from the modem, is limited to 45 Kbps.
There are several different types of modems available:
Cable modems
ISDN modems
DSL modems
cable modem A modem that uses a cable television connection to get transmission rates that are faster than a dial-up connection.
The term modem comes from the two primary tasks it performs: modulation and demodulation.
In many ways, a modem is like a language translator between the analog and digital components.
Modems have several sets of standards:
V series
Hayes-compatible (AT command set)
PC Cards
V series Standards that cover today’s modems, with speeds up to 56 Kbps.
Hayes-Compatible Standards The set of transmission signals, commands, used originally by Hayes modems for exchanging status information, such as readiness to send or receive.
PC Card standards Standards developed for personal computer cards and intended for laptop users that target a broad range of devices, including modems. Developments in the past few decades enabled modem speeds to transmit at 56 Kbps.
However, the 56K transmissions can occur downstream. The upstream, or outgoing transmission from the modem, is limited to 45 Kbps.
There are several different types of modems available:
Cable modems
ISDN modems
DSL modems
cable modem A modem that uses a cable television connection to get transmission rates that are faster than a dial-up connection.
Security Risk of Wireless Networking
Wireless technology is somewhat more prone to security risks. Due to the fact that the signal is broadcast in a certain radius, anyone within that radius can potentially intercept that signal.
Most wireless NICs and access points have a built-in security feature, called wired encryption privacy (WEP). wired encryption privacy (WEP) A security feature that, when activated, encrypts the data prior to transmission by the NIC. At the receiving end, the data are decrypted. Most wireless NICs and access points have this security feature built in.
Most wireless NICs and access points have a built-in security feature, called wired encryption privacy (WEP). wired encryption privacy (WEP) A security feature that, when activated, encrypts the data prior to transmission by the NIC. At the receiving end, the data are decrypted. Most wireless NICs and access points have this security feature built in.
Wireless Networking
There are four types of infrared networks:
line-of-sight
scatter infrared
reflective
broadband optical telepoint
infrared A type of light beam used in wireless networks to transmit the data between devices.
Narrowband radio is similar to broadcasting from a radio station. The broadcast range is 3,000 meters (9,842 feet), and does not require line-of-sight focusing. However, because the signal is high frequency, it is subject to attenuation from steel and load-bearing walls.
narrowband radio A high-frequency transmission similar to broadcasting from a radio station. The user tunes both the transmitter and the receiver to a certain frequency.
Spread-spectrum radio broadcasts signals over a range of frequencies. This helps it avoid narrowband communication problems. The available frequencies are divided into channels, known as hops. spread-spectrum radio A transmission technology that broadcasts signals over a range of frequencies, thus providing security for the transmission.
hop One portion of a transmission’s journey between two points.
Microwave systems can be used for the following:
satellite-to-ground links
between two buildings
across large, flat, and open areas, such as bodies of water or deserts
microwave Part of the electromagnetic spectrum, and a form of radiation that can be used for short- and long-distance communications systems. A microwave system can be used to transmit data from building to building.
line-of-sight
scatter infrared
reflective
broadband optical telepoint
infrared A type of light beam used in wireless networks to transmit the data between devices.
Narrowband radio is similar to broadcasting from a radio station. The broadcast range is 3,000 meters (9,842 feet), and does not require line-of-sight focusing. However, because the signal is high frequency, it is subject to attenuation from steel and load-bearing walls.
narrowband radio A high-frequency transmission similar to broadcasting from a radio station. The user tunes both the transmitter and the receiver to a certain frequency.
Spread-spectrum radio broadcasts signals over a range of frequencies. This helps it avoid narrowband communication problems. The available frequencies are divided into channels, known as hops. spread-spectrum radio A transmission technology that broadcasts signals over a range of frequencies, thus providing security for the transmission.
hop One portion of a transmission’s journey between two points.
Microwave systems can be used for the following:
satellite-to-ground links
between two buildings
across large, flat, and open areas, such as bodies of water or deserts
microwave Part of the electromagnetic spectrum, and a form of radiation that can be used for short- and long-distance communications systems. A microwave system can be used to transmit data from building to building.
The Role of the NIC
The NIC has four primary roles:
The NIC prepares data from the computer for the network cable.
It sends the data to another computer.
It controls the flow of data between the computer and the cabling system.
It receives incoming data from the cable and translates the data into bytes that can be understood by the computer’s central processing unit (CPU).
Before data are sent over the network, a conversation between the sending and receiving NICs takes place. The following items must be determined before any transmission can begin:
maximum size of the data groups to be sent
amount of data to be sent before confirmation of receipt is given
time intervals between sending data chunks
amount of time to wait before confirmation is sent
how much data each NIC can hold before it overflows
data transmission speed
NICs act as the physical interface between the computer and the network cable.
To ensure compatibility between the computer and the network, the NIC must:
fit with the computer’s internal structure (data bus architecture).
contain the correct type of cable connector for the cabling.
The NIC performs three important functions to coordinate activities between the computer and the cabling:
Makes the physical connection to the cable
Generates the electrical signals that travel over the cable
Controls access to the cable by following specific rules
You may encounter some situations that require the use of specialized network cards. Some examples include:
wireless NICs
fiber optic NICs
programmable read-only memory (PROM)
boot-on-LAN
programmable read-only memory (PROM) A chip that contains the hardwired code to start the computer and connect the user to the network. With remote-boot PROMs, diskless workstations can join the network when they start.
boot-on-LAN The process that enables the PC to boot from a server rather than the local hard drive.
The NIC prepares data from the computer for the network cable.
It sends the data to another computer.
It controls the flow of data between the computer and the cabling system.
It receives incoming data from the cable and translates the data into bytes that can be understood by the computer’s central processing unit (CPU).
Before data are sent over the network, a conversation between the sending and receiving NICs takes place. The following items must be determined before any transmission can begin:
maximum size of the data groups to be sent
amount of data to be sent before confirmation of receipt is given
time intervals between sending data chunks
amount of time to wait before confirmation is sent
how much data each NIC can hold before it overflows
data transmission speed
NICs act as the physical interface between the computer and the network cable.
To ensure compatibility between the computer and the network, the NIC must:
fit with the computer’s internal structure (data bus architecture).
contain the correct type of cable connector for the cabling.
The NIC performs three important functions to coordinate activities between the computer and the cabling:
Makes the physical connection to the cable
Generates the electrical signals that travel over the cable
Controls access to the cable by following specific rules
You may encounter some situations that require the use of specialized network cards. Some examples include:
wireless NICs
fiber optic NICs
programmable read-only memory (PROM)
boot-on-LAN
programmable read-only memory (PROM) A chip that contains the hardwired code to start the computer and connect the user to the network. With remote-boot PROMs, diskless workstations can join the network when they start.
boot-on-LAN The process that enables the PC to boot from a server rather than the local hard drive.
Other Cable Media
Connection Hardware
10Base2 and 10Base5 cabling use special connection components, known as BNC connectors. BNC connector A hardware component used to make the connections between the cable and the computers. There are several components in the BNC family, such as:
The BNC cable connector
The BNC T connector
The BNC barrel connector
The BNC terminator
The twisting of the twisted-pair cable wire cancels out crosstalk from adjacent pairs of cable. The higher the number of twists per foot of cable, the more effectively it cancels out crosstalk.
The total number of pairs in a cable varies, depending on the purpose of the cable.
twisted-pair cable A type of cable that consists of two insulated strands of copper wire twisted around each other.
Two types of twisted-pair cable are:
unshielded twisted-pair (UTP)
shielded twisted-pair (STP)
Of the two types, UTP cable is most prevalent. Its popularity can be attributed to the fact that most buildings are prewired for telephone service.
unshielded twisted-pair (UTP) A type of twisted-pair cabling that does not have an extra shielding layer to help eliminate noise interference. However, it is highly affordable.
shielded twisted-pair (STP) A type of twisted-pair cabling that uses a woven copper-braid jacket to protect the transmitted data from outside interference.
Twisted-pair cabling uses RJ-45 connectors, which are similar to RJ-11 telephone connectors, to connect to a computer.
In a fiber optic cable, pulses of light travel down extremely thin tubes of glass or plastic to transmit data.
The signal—a light pulse—can be transmitted over many miles very quickly. fiber optic cable A type of cable made up of extremely thin tubes of glass or plastic that allow pulses of light to travel through it to transmit data
The cabling you select depends on the needs of a particular site. To determine which type of cable is best, consider the following guidelines.
The NIC is the direct link between the computer and the cable. Choose NICs carefully by identifying the computer’s bus architecture and the connector type used on the network. Specialized NICs allow connections through different media.
10Base2 and 10Base5 cabling use special connection components, known as BNC connectors. BNC connector A hardware component used to make the connections between the cable and the computers. There are several components in the BNC family, such as:
The BNC cable connector
The BNC T connector
The BNC barrel connector
The BNC terminator
The twisting of the twisted-pair cable wire cancels out crosstalk from adjacent pairs of cable. The higher the number of twists per foot of cable, the more effectively it cancels out crosstalk.
The total number of pairs in a cable varies, depending on the purpose of the cable.
twisted-pair cable A type of cable that consists of two insulated strands of copper wire twisted around each other.
Two types of twisted-pair cable are:
unshielded twisted-pair (UTP)
shielded twisted-pair (STP)
Of the two types, UTP cable is most prevalent. Its popularity can be attributed to the fact that most buildings are prewired for telephone service.
unshielded twisted-pair (UTP) A type of twisted-pair cabling that does not have an extra shielding layer to help eliminate noise interference. However, it is highly affordable.
shielded twisted-pair (STP) A type of twisted-pair cabling that uses a woven copper-braid jacket to protect the transmitted data from outside interference.
Twisted-pair cabling uses RJ-45 connectors, which are similar to RJ-11 telephone connectors, to connect to a computer.
In a fiber optic cable, pulses of light travel down extremely thin tubes of glass or plastic to transmit data.
The signal—a light pulse—can be transmitted over many miles very quickly. fiber optic cable A type of cable made up of extremely thin tubes of glass or plastic that allow pulses of light to travel through it to transmit data
The cabling you select depends on the needs of a particular site. To determine which type of cable is best, consider the following guidelines.
The NIC is the direct link between the computer and the cable. Choose NICs carefully by identifying the computer’s bus architecture and the connector type used on the network. Specialized NICs allow connections through different media.
Cable Media
The vast majority of networks are connected by some sort of cabling. The cables are the network transmission media that carry signals between computers.
Three major groups of cabling connect the majority of networks:
coaxial
twisted-pair
fiber optic
Coaxial cable consists of a core of copper wire surrounded by insulation, a braided metal shielding, and an outer cover.
shielding A layer of covering that grounds a cable and protects it from electric noise and crosstalk.
The shielding layer grounds the cable and protects it from electrical noise and crosstalk so the data are not distorted.
Coaxial cable is more resistant to interference and attenuation than twisted-pair cabling.
The farther the signal travels, the more the signal fades. Coaxial cable is more resistant to interference and attenuation than twisted-pair cabling.
noise Stray electronic signals that interfere with data transmissions along a cable and slow the transmission speed.
crosstalk Signal overflow from an adjacent wire that distorts the data signal. attenuation The process of data losing signal strength as the data are transmitted along a cable.
Three major groups of cabling connect the majority of networks:
coaxial
twisted-pair
fiber optic
Coaxial cable consists of a core of copper wire surrounded by insulation, a braided metal shielding, and an outer cover.
shielding A layer of covering that grounds a cable and protects it from electric noise and crosstalk.
The shielding layer grounds the cable and protects it from electrical noise and crosstalk so the data are not distorted.
Coaxial cable is more resistant to interference and attenuation than twisted-pair cabling.
The farther the signal travels, the more the signal fades. Coaxial cable is more resistant to interference and attenuation than twisted-pair cabling.
noise Stray electronic signals that interfere with data transmissions along a cable and slow the transmission speed.
crosstalk Signal overflow from an adjacent wire that distorts the data signal. attenuation The process of data losing signal strength as the data are transmitted along a cable.
Other Network Devices
A modem is a computer-to-computer communication device that converts digital signals from the computer to analog signals for the telephone lines. The word “modem” comes from the two operations it handles:
modulation
demodulation
modulation The process on changing the digital signal to an analog signal on the sending computer.
demodulation The process of converting the analog signal back to a digital signal on the receiving computer.
Cable is used to connect network devices. There are many types of networking cable in use today. Different types of cable have particular strengths and weaknesses, most notably in the speed at which they can transfer information.
modulation
demodulation
modulation The process on changing the digital signal to an analog signal on the sending computer.
demodulation The process of converting the analog signal back to a digital signal on the receiving computer.
Cable is used to connect network devices. There are many types of networking cable in use today. Different types of cable have particular strengths and weaknesses, most notably in the speed at which they can transfer information.
Network Devices
The hub is a central hardware component for many LANs. Hubs operate at the Physical Layer in the OSI model. Hubs contain multiple ports, and can connect to other hubs to expand the network.
Repeaters operate at the Physical Layer of the OSI model. Essentially, repeaters allow smaller LANs to grow into larger LANs by moving transmissions from one network segment to another.
repeater A device that can be used to connect two cables and that boosts the signal before sending it along. (p. 105)
Segment A section of the network that includes the cable and nodes that are connected to a device, such as a repeater, hub, or bridge.
Bridges can be used to connect dissimilar network segments that use different methods of transferring data.
In today’s networks, it is uncommon to find bridges because switches provide “multibridge” capability.
bridge A device used to connect two network segments together. (p. 105)
switch A multiport bridge that allows several segments of a network to communicate with one another. An important function of bridges and switches is to minimize collision of data packets by creating collision domains. Bridges and switches prevent the passing of collisions from one network segment to another.
router A network device used to connect networks of different types and that forwards packets from one network to another, even those separated by great distances. A router determines the best route to use to deliver the data.
Brouters are hybrids that combine the capabilities of bridges and routers. Like bridges, they work at the Data Link Layer to transfer and filter network traffic. Like routers, they also work at the Network Layer to route packets from one network to another. brouter A network hybrid device that combines the capabilities of bridges and routers. Gateways enable dissimilar networks to communicate. Gateways operate at higher levels in the OSI model such as the Application, Presentation, and Session layers. In some cases, they operate at all seven layers. Gateway A dedicated network computer whose job is to convert data packets from one network protocol to another. Enables dissimilar networks to communicate.
Repeaters operate at the Physical Layer of the OSI model. Essentially, repeaters allow smaller LANs to grow into larger LANs by moving transmissions from one network segment to another.
repeater A device that can be used to connect two cables and that boosts the signal before sending it along. (p. 105)
Segment A section of the network that includes the cable and nodes that are connected to a device, such as a repeater, hub, or bridge.
Bridges can be used to connect dissimilar network segments that use different methods of transferring data.
In today’s networks, it is uncommon to find bridges because switches provide “multibridge” capability.
bridge A device used to connect two network segments together. (p. 105)
switch A multiport bridge that allows several segments of a network to communicate with one another. An important function of bridges and switches is to minimize collision of data packets by creating collision domains. Bridges and switches prevent the passing of collisions from one network segment to another.
router A network device used to connect networks of different types and that forwards packets from one network to another, even those separated by great distances. A router determines the best route to use to deliver the data.
Brouters are hybrids that combine the capabilities of bridges and routers. Like bridges, they work at the Data Link Layer to transfer and filter network traffic. Like routers, they also work at the Network Layer to route packets from one network to another. brouter A network hybrid device that combines the capabilities of bridges and routers. Gateways enable dissimilar networks to communicate. Gateways operate at higher levels in the OSI model such as the Application, Presentation, and Session layers. In some cases, they operate at all seven layers. Gateway A dedicated network computer whose job is to convert data packets from one network protocol to another. Enables dissimilar networks to communicate.
Protocol functions
When data are transmitted over a network, they are sent in steps. A single step includes certain actions that cannot take place at any other step. Each step has its own rules and procedures, or protocols.
There are four points to keep in mind about protocols:
There are many protocols.
Some protocols work only at particular OSI layers.
Some protocols work at multiple layers.
Protocols are consistent.
A protocol stack is a combination of protocols. Layers within the stack, which generally correspond to the OSI model, specify various protocols for handling a function or subsystem of the communication process. Each layer in the stack has its own set of rules.
protocol stack Multiple layers of protocols that work together.
The binding process is used to connect protocols, or protocol stacks, to the NIC. Protocols and NICs can be mixed and matched on an as-needed basis.
The binding order determines the sequence in which the operating system runs the protocol.
binding process The process of tying the protocols together to provide data with a route from the application level to the NIC.
binding order The sequence in which the operating system runs the protocol.
The computer industry has designated several kinds of protocol stacks as standard models. Hardware and software manufacturers can develop their products to meet any one or a combination of these protocol stacks. The most important protocol stacks include:
OSI protocol suite
Digital DECnet
Novell NetWare
AppleTalk
TCP/IP
IBM SNA
The Data Link Layer is divided into two sublayers:
Logical Link Control (LLC)
Media Access Control (MAC)
Media Access Control (MAC) The lower of two sublayers that make up the Data Link Layer. The MAC manages access to the physical network, delimits frames, and handles error control.
There are four points to keep in mind about protocols:
There are many protocols.
Some protocols work only at particular OSI layers.
Some protocols work at multiple layers.
Protocols are consistent.
A protocol stack is a combination of protocols. Layers within the stack, which generally correspond to the OSI model, specify various protocols for handling a function or subsystem of the communication process. Each layer in the stack has its own set of rules.
protocol stack Multiple layers of protocols that work together.
The binding process is used to connect protocols, or protocol stacks, to the NIC. Protocols and NICs can be mixed and matched on an as-needed basis.
The binding order determines the sequence in which the operating system runs the protocol.
binding process The process of tying the protocols together to provide data with a route from the application level to the NIC.
binding order The sequence in which the operating system runs the protocol.
The computer industry has designated several kinds of protocol stacks as standard models. Hardware and software manufacturers can develop their products to meet any one or a combination of these protocol stacks. The most important protocol stacks include:
OSI protocol suite
Digital DECnet
Novell NetWare
AppleTalk
TCP/IP
IBM SNA
The Data Link Layer is divided into two sublayers:
Logical Link Control (LLC)
Media Access Control (MAC)
Media Access Control (MAC) The lower of two sublayers that make up the Data Link Layer. The MAC manages access to the physical network, delimits frames, and handles error control.
Network Models
The birth and evolution of the Internet gave rise to yet another model. This is the TCP/IP reference model, also referred to as the Internet reference model.
The TCP/IP reference model reflects the world of internetworking.
internetworking The transfer and routing of information between and among varied workstations and networks.
Protocols are rules and procedures used to make network communications possible. Multiple protocols can be used by a NIC. Many protocols that operate in conjunction perform the various tasks needed to send and receive data.
The TCP/IP reference model reflects the world of internetworking.
internetworking The transfer and routing of information between and among varied workstations and networks.
Protocols are rules and procedures used to make network communications possible. Multiple protocols can be used by a NIC. Many protocols that operate in conjunction perform the various tasks needed to send and receive data.
Network Layers
Layer 5, the Session Layer, allows two applications on different computers to open, use, and close a connection called a session.
The Session Layer is responsible for managing this dialogue.
session A highly structured dialog between two workstations.
Layer 2, the Data Link Layer, sends data frames from the Network Layer to the Physical Layer. A data frame is like a vehicle, in which the data are the people, or cargo, who ride inside the vehicle across the network.
data frame An organized, logical structure in which data can be placed. Two other models, also layered, tend to pop up in descriptions of network architectures.
Systems Network Architecture (SNA)
Transmission Control Protocol/Internet Protocol (TCP/IP) reference model
Transmission Control Protocol/Internet Protocol (TCP/IP) reference model An Internet-related network architectural model.
SNA was originally designed around the mainframe/terminal relationship, but was later modified, in a specification known as Advanced Program to Program Communications (APPC), to include minicomputers and personal computers.
Advanced Program to Program Communications (APPC) The SNA mainframe communication model was modified in a specification known as APPC to include minicomputers and personal computers.
The Session Layer is responsible for managing this dialogue.
session A highly structured dialog between two workstations.
Layer 2, the Data Link Layer, sends data frames from the Network Layer to the Physical Layer. A data frame is like a vehicle, in which the data are the people, or cargo, who ride inside the vehicle across the network.
data frame An organized, logical structure in which data can be placed. Two other models, also layered, tend to pop up in descriptions of network architectures.
Systems Network Architecture (SNA)
Transmission Control Protocol/Internet Protocol (TCP/IP) reference model
Transmission Control Protocol/Internet Protocol (TCP/IP) reference model An Internet-related network architectural model.
SNA was originally designed around the mainframe/terminal relationship, but was later modified, in a specification known as Advanced Program to Program Communications (APPC), to include minicomputers and personal computers.
Advanced Program to Program Communications (APPC) The SNA mainframe communication model was modified in a specification known as APPC to include minicomputers and personal computers.
OSI Layers
Layer Number Layer Name Description
7 Application Relates to services that directly support user applications
6 Presentation Defines the format used to exchange data among networked computers
5 Session Allows two applications on different computers to open, use, and close a connection between computers
4 Transport Ensures that data packets are delivered error-free, in sequence, and without data losses or duplications
3 Network Responsible for addressing messages and finding the best path to move data across the network
2 Data Link Sends data frames from the Network Layer to the Physical Layer
1 Physical Carries the signals to transmit the data over the cable to the network
7 Application Relates to services that directly support user applications
6 Presentation Defines the format used to exchange data among networked computers
5 Session Allows two applications on different computers to open, use, and close a connection between computers
4 Transport Ensures that data packets are delivered error-free, in sequence, and without data losses or duplications
3 Network Responsible for addressing messages and finding the best path to move data across the network
2 Data Link Sends data frames from the Network Layer to the Physical Layer
1 Physical Carries the signals to transmit the data over the cable to the network
Network Protocols
To ensure that products from various manufacturers can communicate with each other, network models have been created.
A protocol, which is part of software, is what makes a network work. The model describes what needs to be done, and the protocol performs the work.
protocol Rules that define how network devices communicate with each other and perform specific tasks. The Open Systems Interconnection (OSI) reference model consists of seven layers that define how data are sent from a computer, through the network, and into a receiving computer.
Understanding each layer and how each one interacts with other layers helps you understand how networks operate. Open Systems Interconnection (OSI) reference model An international standard that is a guide for networking. Defines how data are sent from a computer, through the network, and into a receiving computer. Also called the OSI model. The OSI model provides a description of how network hardware and software work together in a layered fashion to make communications between computers possible. Each layer includes different network activities, equipment, or protocols.
Layers are separated from each other by boundaries called interfaces.
interface The connection that provides communication between layers. It also shields neighboring layers from the details of how services are implemented.
A protocol, which is part of software, is what makes a network work. The model describes what needs to be done, and the protocol performs the work.
protocol Rules that define how network devices communicate with each other and perform specific tasks. The Open Systems Interconnection (OSI) reference model consists of seven layers that define how data are sent from a computer, through the network, and into a receiving computer.
Understanding each layer and how each one interacts with other layers helps you understand how networks operate. Open Systems Interconnection (OSI) reference model An international standard that is a guide for networking. Defines how data are sent from a computer, through the network, and into a receiving computer. Also called the OSI model. The OSI model provides a description of how network hardware and software work together in a layered fashion to make communications between computers possible. Each layer includes different network activities, equipment, or protocols.
Layers are separated from each other by boundaries called interfaces.
interface The connection that provides communication between layers. It also shields neighboring layers from the details of how services are implemented.
Transmitting Data packets
Baseband and broadband are two techniques used to transmit data packets over cable.
Bandwidth is the maximum speed at which a particular communications medium, such as cables, can transfer information. Bandwidth measurement depends on the type of signal (analog or digital) and the media used to carry the information.
Type of Signal (analog or digital) + Type of Media = Bandwidth
In an analog signal, information travels as a continuously changing wave. This signal cycles up and down in a wavelike pattern. analog A signal that travels as a continuously variable wavelike pattern.
Broadband transmissions can be divided into multiple channels separated by small bands of unused frequencies to avoid one channel interfering with the signal being transmitted on its neighbors.
Broadband is unidirectional—it moves in one direction only. To send and receive, the communications bandwidth is divided into two channels, one for each direction. broadband transmission Transmissions that rely on an analog signal, a range of frequencies, and a communications medium. Broadband signals can be divided into multiple channels separated by small bands of unused frequencies to avoid interference.
Baseband transmissions send digital signals over a single channel. Multiple transmissions can be sent through the channel simultaneously through a technique known as multiplexing.
baseband transmission Transmissions of digital signals over a single channel, typical of most current LANs. One signal at a time travels over the network cable.
multiplexing Multiple transmissions sent through a channel simultaneously and are interwoven into a single signal. Network models describe how different network devices communicate with each other. The OSI model consists of seven layers that describe the tasks a network component must handle.
Bandwidth is the maximum speed at which a particular communications medium, such as cables, can transfer information. Bandwidth measurement depends on the type of signal (analog or digital) and the media used to carry the information.
Type of Signal (analog or digital) + Type of Media = Bandwidth
In an analog signal, information travels as a continuously changing wave. This signal cycles up and down in a wavelike pattern. analog A signal that travels as a continuously variable wavelike pattern.
Broadband transmissions can be divided into multiple channels separated by small bands of unused frequencies to avoid one channel interfering with the signal being transmitted on its neighbors.
Broadband is unidirectional—it moves in one direction only. To send and receive, the communications bandwidth is divided into two channels, one for each direction. broadband transmission Transmissions that rely on an analog signal, a range of frequencies, and a communications medium. Broadband signals can be divided into multiple channels separated by small bands of unused frequencies to avoid interference.
Baseband transmissions send digital signals over a single channel. Multiple transmissions can be sent through the channel simultaneously through a technique known as multiplexing.
baseband transmission Transmissions of digital signals over a single channel, typical of most current LANs. One signal at a time travels over the network cable.
multiplexing Multiple transmissions sent through a channel simultaneously and are interwoven into a single signal. Network models describe how different network devices communicate with each other. The OSI model consists of seven layers that describe the tasks a network component must handle.
What is Packet?
Networks are very fast, but there is a limit to the amount of traffic networks can transport at one time. The solution to this problem is to break this traffic into small pieces known as data packets.
A data packet, also called a packet, is a very small part of the entire piece of data that needs to be sent.
data packet Data that consist of three parts—a header, the data itself, and a trailer.
A cyclical redundancy check (CRC) is performed at the sending and receiving computers to make sure the data packet arrived with no errors.
cyclical redundancy check (CRC) Error checking used in networks. A sending node performs a mathematical calculation on the packet and the result is attached to the packet’s trailer. The receiving node performs the same calculation on the packet it received. If the calculations differ, the CRC signals the source computer to retransmit the packet.
The job to neatly chunk, address, and deliver the information in a network is handled by the network interface card (NIC) in each computer.
The NIC does the following:
Provides the source, or hardware, address of the computer.
Prepares the data from the computer for the network cable.
Sends data to another computer.
Controls the flow of data between the computer and the cabling.
Receives incoming data from another computer.
Translates electrical impulses from the cable into binary code that the computer understands.
Within the computer itself, information travels along pathways known as buses. A bus consists of multiple “lanes” (wires) set side by side. bus A data pathway that connects components in a computer using parallel cabling or wire.
Data packets travel in parallel transmission within the computer, but in serial transmission on a cable.
Data on a network move from the “multilane” computer cable to a “single-lane” network cable.
parallel transmission The orderly procession of transmitted data in computers in which groups of bits are transferred simultaneously side by side over two or more wires.
serial transmission The procession of transmitted data in which bits are sent over network cables and travel bit by bit one at a time.
A data packet, also called a packet, is a very small part of the entire piece of data that needs to be sent.
data packet Data that consist of three parts—a header, the data itself, and a trailer.
A cyclical redundancy check (CRC) is performed at the sending and receiving computers to make sure the data packet arrived with no errors.
cyclical redundancy check (CRC) Error checking used in networks. A sending node performs a mathematical calculation on the packet and the result is attached to the packet’s trailer. The receiving node performs the same calculation on the packet it received. If the calculations differ, the CRC signals the source computer to retransmit the packet.
The job to neatly chunk, address, and deliver the information in a network is handled by the network interface card (NIC) in each computer.
The NIC does the following:
Provides the source, or hardware, address of the computer.
Prepares the data from the computer for the network cable.
Sends data to another computer.
Controls the flow of data between the computer and the cabling.
Receives incoming data from another computer.
Translates electrical impulses from the cable into binary code that the computer understands.
Within the computer itself, information travels along pathways known as buses. A bus consists of multiple “lanes” (wires) set side by side. bus A data pathway that connects components in a computer using parallel cabling or wire.
Data packets travel in parallel transmission within the computer, but in serial transmission on a cable.
Data on a network move from the “multilane” computer cable to a “single-lane” network cable.
parallel transmission The orderly procession of transmitted data in computers in which groups of bits are transferred simultaneously side by side over two or more wires.
serial transmission The procession of transmitted data in which bits are sent over network cables and travel bit by bit one at a time.
Classifying Networks by Configuration
A network’s configuration describes how the types of servers and clients are used in the network.
Networks are generally divided into three broad categories based on their configuration: centralized networks, peer-to-peer networks, and client/server networks.
peer-to-peer network A network that does not require an administrator and whose computers function as both clients and servers.
client/server network A network built around one or more dedicated servers and is administered from a central location. It supports many clients and multiple computer platforms.
local area network (LAN) A network that is relatively limited in size and that usually connects computers in a small geographical area, such as in the same office building.
wide area network (WAN) A computer network that uses long-range telecommunication links to connect networked computers across long distances
A true peer-to-peer network is a LAN because it can support only a limited number of clients and peripherals, also known as nodes.
node Each piece of hardware, such as a server, client, and shared peripheral, that is connected to a network.
Some LANs make use of wireless technology to create wireless local area networks (WLANs). WLANs use media just like wired networks do, but you cannot see wireless media.
wireless local area network (WLAN) A local area network that uses either infrared (IR) light or radio frequencies (RF) to connect the clients and/or peripherals.
Most WANs use media that can very quickly transfer large amounts of data. These media include wireless connections, satellite uplinks, or specialized types of cabling, such as T1/T3 telephone-type lines or fiber optic cables.
Using these media allows the WANs to employ a large amount of bandwidth.
bandwidth Amount of data that can be transmitted in a given amount of time.
Depending on the amount of ground they cover, WANs are often categorized in subgroups or smaller clusters. These WAN subgroups include:
campus area networks (CANs)
metropolitan area networks (MANs)
home area networks (HANs)
global area networks (GANs)
storage area networks (SANs)
Networks are generally divided into three broad categories based on their configuration: centralized networks, peer-to-peer networks, and client/server networks.
peer-to-peer network A network that does not require an administrator and whose computers function as both clients and servers.
client/server network A network built around one or more dedicated servers and is administered from a central location. It supports many clients and multiple computer platforms.
local area network (LAN) A network that is relatively limited in size and that usually connects computers in a small geographical area, such as in the same office building.
wide area network (WAN) A computer network that uses long-range telecommunication links to connect networked computers across long distances
A true peer-to-peer network is a LAN because it can support only a limited number of clients and peripherals, also known as nodes.
node Each piece of hardware, such as a server, client, and shared peripheral, that is connected to a network.
Some LANs make use of wireless technology to create wireless local area networks (WLANs). WLANs use media just like wired networks do, but you cannot see wireless media.
wireless local area network (WLAN) A local area network that uses either infrared (IR) light or radio frequencies (RF) to connect the clients and/or peripherals.
Most WANs use media that can very quickly transfer large amounts of data. These media include wireless connections, satellite uplinks, or specialized types of cabling, such as T1/T3 telephone-type lines or fiber optic cables.
Using these media allows the WANs to employ a large amount of bandwidth.
bandwidth Amount of data that can be transmitted in a given amount of time.
Depending on the amount of ground they cover, WANs are often categorized in subgroups or smaller clusters. These WAN subgroups include:
campus area networks (CANs)
metropolitan area networks (MANs)
home area networks (HANs)
global area networks (GANs)
storage area networks (SANs)
Parts of Network
Networks, however, are not complete with just clients and servers. A typical network also includes peripherals, media, and data.
peripheral A device that is connected to a computer and is controlled by its microprocessor.
media Physical pieces of equipment used to transport data from one computer to another computer or peripheral device on the network. (p. 38)
data Distinct pieces of information, such as files or entries in a database.
There are different types of servers, particularly dedicated servers.
file servers
print servers
application servers
mail servers
communication servers
directory services servers
backup servers
Many backup servers use a technique called “mirroring” to protect data. Mirroring employs an array of hard drives, called Redundant Array of Inexpensive Disks (RAID).
Redundant Array of Inexpensive Disks (RAID) An array of hard drives that mirror or duplicate other drives. Should the primary hard drive fail, the second drive can be substituted for the failed drive with little or no down time.
Networks can be classified according to how servers and clients are configured, or put together. They can also be categorized by the geographic area they cover.
peripheral A device that is connected to a computer and is controlled by its microprocessor.
media Physical pieces of equipment used to transport data from one computer to another computer or peripheral device on the network. (p. 38)
data Distinct pieces of information, such as files or entries in a database.
There are different types of servers, particularly dedicated servers.
file servers
print servers
application servers
mail servers
communication servers
directory services servers
backup servers
Many backup servers use a technique called “mirroring” to protect data. Mirroring employs an array of hard drives, called Redundant Array of Inexpensive Disks (RAID).
Redundant Array of Inexpensive Disks (RAID) An array of hard drives that mirror or duplicate other drives. Should the primary hard drive fail, the second drive can be substituted for the failed drive with little or no down time.
Networks can be classified according to how servers and clients are configured, or put together. They can also be categorized by the geographic area they cover.
Network Components
Networks consist of client and server computers. Servers can be dedicated or nondedicated servers.
All networks are made up of the same basic components.
The most important of these are clients and servers.
client A network computer that requests, or orders, information from a server.
server Computers that work behind-the-scenes to provide (serve) shared resources to network users, or clients.
Client computers are desktop machines with local storage and processing power.
A thin client is a network computer with no local storage. It processes information independently, but relies on servers for applications, data storage, and administration.
thin client A network computer that has no local storage and relies on servers for applications, data storage, and administration
Servers are categorized as either nondedicated servers or dedicated servers, depending on the type of work they do.
A nondedicated server can be used for everyday tasks such as e-mail or word processing.
A dedicated server functions only as a server. It is not used as a client or workstation. It is dedicated to one purpose—being a server.
nondedicated server A server that provides many different services to its client computers, such as file retrieval, printing, and e-mailing.
dedicated server A server that provides a specific type of resource to its clients, such as just printing.
All networks are made up of the same basic components.
The most important of these are clients and servers.
client A network computer that requests, or orders, information from a server.
server Computers that work behind-the-scenes to provide (serve) shared resources to network users, or clients.
Client computers are desktop machines with local storage and processing power.
A thin client is a network computer with no local storage. It processes information independently, but relies on servers for applications, data storage, and administration.
thin client A network computer that has no local storage and relies on servers for applications, data storage, and administration
Servers are categorized as either nondedicated servers or dedicated servers, depending on the type of work they do.
A nondedicated server can be used for everyday tasks such as e-mail or word processing.
A dedicated server functions only as a server. It is not used as a client or workstation. It is dedicated to one purpose—being a server.
nondedicated server A server that provides many different services to its client computers, such as file retrieval, printing, and e-mailing.
dedicated server A server that provides a specific type of resource to its clients, such as just printing.
Career Paths tied to networking
There are many careers tied to networks and networking.
*network administrator
*network engineer
network administrator Trained individual responsible for installing computers and their operating systems and managing networks on a daily basis.
network engineer Highly trained individual responsible for connecting computers to the network and connecting networks to networks.
network architect Highly trained individual who oversees the construction, maintenance, and expansion of a company’s network.
network support technician Individual with specialized technical knowledge to troubleshoot the many problems that arise in network usage.
outsourcing To hire an outside company to handle various information technology (IT) services, such as technical support
*network administrator
*network engineer
network administrator Trained individual responsible for installing computers and their operating systems and managing networks on a daily basis.
network engineer Highly trained individual responsible for connecting computers to the network and connecting networks to networks.
network architect Highly trained individual who oversees the construction, maintenance, and expansion of a company’s network.
network support technician Individual with specialized technical knowledge to troubleshoot the many problems that arise in network usage.
outsourcing To hire an outside company to handle various information technology (IT) services, such as technical support
What is Arpanet?
The U.S. Department of Defense established ARPANET. ARPANET linked computers around the country and provided a data highway for military communications.
ARPANET The Advanced Research Projects Agency Network created in the 1960s made it possible for military and university computers to communicate long distances and to share files through an interconnected network.
Networks have become a part of everyday life. The original Internet was primarily a text-based network.
Tim Berners-Lee developed the World Wide Web, using a graphic user interface (GUI) with hyperlinks to access information on the Internet.
hyperlink Text or image that “links” the user to another document when clicked
Although the Web is only one part of the Internet, most users think they are the same thing.
The Internet is hardware connected together to create a network.
The Web includes software (browsers) that send information along the Internet’s hardware.
ARPANET The Advanced Research Projects Agency Network created in the 1960s made it possible for military and university computers to communicate long distances and to share files through an interconnected network.
Networks have become a part of everyday life. The original Internet was primarily a text-based network.
Tim Berners-Lee developed the World Wide Web, using a graphic user interface (GUI) with hyperlinks to access information on the Internet.
hyperlink Text or image that “links” the user to another document when clicked
Although the Web is only one part of the Internet, most users think they are the same thing.
The Internet is hardware connected together to create a network.
The Web includes software (browsers) that send information along the Internet’s hardware.
What is throughput?
Throughput is the capacity to handle network traffic. A measure for network data transfer performance.
The first computers could only perform one task at a time. Within a few years, computers were able to multitask and timeshare, which increased the computer’s productivity.
multitask A computer’s ability to work on more than one job at a time. The processor can turn its attention from one job to another if one is held up waiting for input or output.
timesharing In the early days of computers, the concept of running multiple jobs at the same time. The idea of switching the computer’s processing from one task to another and incorporating a main, or host, computer
Timesharing allowed for direct human/machine interaction through terminals.
Terminals used with timesharing computers were known as dumb terminals.
terminal A device with a keyboard and a monitor that connects directly to a mainframe through a communications link or cable. The terminal requests information from the mainframe computer.
dumb terminal Computers consisting of keyboards for input and screens for output. They are wired directly to the host computer and have little or no processing power of their own.
The first computers could only perform one task at a time. Within a few years, computers were able to multitask and timeshare, which increased the computer’s productivity.
multitask A computer’s ability to work on more than one job at a time. The processor can turn its attention from one job to another if one is held up waiting for input or output.
timesharing In the early days of computers, the concept of running multiple jobs at the same time. The idea of switching the computer’s processing from one task to another and incorporating a main, or host, computer
Timesharing allowed for direct human/machine interaction through terminals.
Terminals used with timesharing computers were known as dumb terminals.
terminal A device with a keyboard and a monitor that connects directly to a mainframe through a communications link or cable. The terminal requests information from the mainframe computer.
dumb terminal Computers consisting of keyboards for input and screens for output. They are wired directly to the host computer and have little or no processing power of their own.
What is network?
network A system of two or more computer systems connected together so they can share and exchange data.
file sharing Sharing files between computers; the act of making files on one computer accessible to others on a network.
resource Software or hardware, such as a hard drive, printer, or scanner, that can be shared over a network.
Sharing resources, such as a printer, provides many benefits.
synchronous communication When people talk to each other at the same time.
asynchronous communication A form of data transmission that involves a delay of seconds, minutes, or even days. Communication does not happen instantly.
reliable network A dependable network that user’s trust to work.
scalable network A network that the hardware or software can grow (scale) up or down to meet an organization’s needs.
redundant network Networks that duplicate data and/or resources to minimize down time and losses in the event of a disaster
file sharing Sharing files between computers; the act of making files on one computer accessible to others on a network.
resource Software or hardware, such as a hard drive, printer, or scanner, that can be shared over a network.
Sharing resources, such as a printer, provides many benefits.
synchronous communication When people talk to each other at the same time.
asynchronous communication A form of data transmission that involves a delay of seconds, minutes, or even days. Communication does not happen instantly.
reliable network A dependable network that user’s trust to work.
scalable network A network that the hardware or software can grow (scale) up or down to meet an organization’s needs.
redundant network Networks that duplicate data and/or resources to minimize down time and losses in the event of a disaster
Monday, July 6, 2009
Applications of wireless technology
Applications of wireless technology
Source: wikipedia.org
Security systems
Wireless technology may supplement or replace hard wired implementations in security systems for homes or office buildings.
Television remote control
Modern televisions use wireless (generally infrared) remote control units. Now radio waves are also used.
Cellular telephony (phones and modems)
Perhaps the best known example of wireless technology is the cellular telephone and modems. These instruments use radio waves to enable the operator to make phone calls from many locations world-wide. They can be used anywhere that there is a cellular telephone site to house the equipment that is required to transmit and receive the signal that is used to transfer both voice and data to and from these instruments.
WiFi
Main article: Wi-Fi
Wi-Fi (for wireless fidelity) is a wireless LAN technology that enables laptop PC’s, PDA’s, and other devices to connect easily to the internet. Technically known as IEEE 802.11 b,g,n, Wi-Fi is faster and less expensive than standard Ethernet and other common wire-based LAN technologies. Several Wi-Fi hot spots have been popular over the past few years. Some businesses charge customers a monthly fee for service, while others have begun offering it for free in an effort to increase the sales of their goods.[5]
Wireless energy transfer
Main article: Wireless energy transfer
Wireless energy transfer is a process whereby electrical energy is transmitted from a power source to an electrical load that does not have a built-in power source, without the use of interconnecting wires.
[edit] Computer Interface Devices
Answering the call of customers frustrated with cord clutter, many manufactures of computer peripherals turned to wireless technology to satisfy their consumer base. Originally these units used bulky, highly limited transceivers to mediate between a computer and a keyboard and mouse, however more recent generations have used small, high quality devices, some even incorporating Bluetooth. These systems have become so ubiquitous that some users have begun complaining about a lack of wired peripherals.[who?] Wireless devices tend to have a slightly slower response time than there wired counterparts, however the gap is decreasing. Initial concerns about the security of wireless keyboards have also been addressed with the maturation of the technology.
Many scientists have complained that wireless technology interferes with their experiments, forcing them to use less optimal peripherals because the optimum one is not available in a wired version.[who?] This has become especially prevalent among scientists who use trackballs as the number of models in production steadily decreases.
Source: wikipedia.org
Wireless Communincation
Wireless communication is the transfer of info. over a distance without the use of electrical conductors or "wires".[1] The distances involved may be short (a few meters as in television remote control) or long (thousands or millions of kilometers for radio communications). When the context is clear, the term is often shortened to "wireless". Wireless communication is generally considered to be a branch of telecommunications.
It encompasses various types of fixed, mobile, and portable two way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, garage door openers and or garage doors, wireless computer mice, keyboards and headsets, satellite television and cordless telephones.
Source:wikipedia.org
It encompasses various types of fixed, mobile, and portable two way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, garage door openers and or garage doors, wireless computer mice, keyboards and headsets, satellite television and cordless telephones.
Source:wikipedia.org
Some hybrid network devices:
Some hybrid network devices:
Source:wikipedia.org
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.
Bridge Router(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.
Source:wikipedia.org
Sunday, July 5, 2009
What are Network Devices?
Common basic networking devices:
source:wikipedia.org
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.
source:wikipedia.org
Network Topology
A network consists of multiple computers connected using some type of interface, each having one or more interface devices such as a Network Interface Card (NIC) and/or a serial device for PPP networking. Each computer is supported by network software that provides the server or client functionality. The hardware used to transmit data across the network is called the media. It may include copper cable, fiber optic, or wireless transmission. The standard cabling used for the purposes of this document is 10Base-T category 5 ethernet cable. This is twisted copper cabling which appears at the surface to look similar to TV coaxial cable. It is terminated on each end by a connector that looks much like a phone connector. Its maximum segment length is 100 meters.
Network Categories
There are two main types of network categories which are:
Server based
Peer-to-peer
In a server based network, there are computers set up to be primary providers of services such as file service or mail service. The computers providing the service are are called servers and the computers that request and use the service are called client computers.
In a peer-to-peer network, various computers on the network can act both as clients and servers. For instance, many Microsoft Windows based computers will allow file and print sharing. These computers can act both as a client and a server and are also referred to as peers. Many networks are combination peer-to-peer and server based networks. The network operating system uses a network data protocol to communicate on the network to other computers. The network operating system supports the applications on that computer. A Network Operating System (NOS) includes Windows NT, Novell Netware, Linux, Unix and others.
Three Network Topologies
The network topology describes the method used to do the physical wiring of the network. The main ones are bus, star, and ring.
Source:www.comptechdoc.org
Network Categories
There are two main types of network categories which are:
Server based
Peer-to-peer
In a server based network, there are computers set up to be primary providers of services such as file service or mail service. The computers providing the service are are called servers and the computers that request and use the service are called client computers.
In a peer-to-peer network, various computers on the network can act both as clients and servers. For instance, many Microsoft Windows based computers will allow file and print sharing. These computers can act both as a client and a server and are also referred to as peers. Many networks are combination peer-to-peer and server based networks. The network operating system uses a network data protocol to communicate on the network to other computers. The network operating system supports the applications on that computer. A Network Operating System (NOS) includes Windows NT, Novell Netware, Linux, Unix and others.
Three Network Topologies
The network topology describes the method used to do the physical wiring of the network. The main ones are bus, star, and ring.
Source:www.comptechdoc.org
What is Network Topology?
Network topology is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially the physical (real) and logical (virtual) interconnections between nodes.[1][2] A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN will have one or more links to one or more other nodes in the network and the mapping of these links and nodes onto a graph results in a geometrical shape that determines the physical topology of the network. Likewise, the mapping of the flow of data between the nodes in the network determines the logical topology of the network. The physical and logical topologies might be identical in any particular network but they also may be different.
Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. LAN Network Topology is, therefore, technically a part of graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical.
Source: Wikipedia.org
Networks
LAN - Local Area Network
Source:compnetworking.about.com
A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.
In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.
WAN - Wide Area Network
As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth.
A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.
A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.
LAN, WAN and Home Networking
Residences typically employ one LAN and connect to the Internet WAN via an Internet Service Provider (ISP) using a broadband modem. The ISP provides a WAN IP address to the modem, and all of the computers on the home network use LAN (so-called private) IP addresses. All computers on the home LAN can communicate directly with each other but must go through a central gateway, typically a broadband router, to reach the ISP.
Other Types of Area Networks
While LAN and WAN are by far the most popular network types mentioned, you may also commonly see references to these others:
•Wireless Local Area Network - a LAN based on WiFi wireless network technology
•Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation.
•Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus.
•Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel.
•System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.
Source:compnetworking.about.com
Types of Network
One way to categorize the different types of computer network designs is by their scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network. Common examples of area network types are:
•LAN - Local Area Network
•WLAN - Wireless Local Area Network
•WAN - Wide Area Network
•MAN - Metropolitan Area Network
•SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network
•CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
•PAN - Personal Area Network
•DAN - Desk Area Network
LAN and WAN were the original categories of area networks, while the others have gradually emerged over many years of technology evolution.
Note that these network types are a separate concept from network topologies such as bus, ring and star.
source:compnetworking.about.com
What is Computer Network?
Network- is a set of interconnected computers that shares resources such information
and printers.
and printers.
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