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Network Taxonomy
• There are two major ways to classify a network:– The size of the network– The transmission technology used by the
network
• There is no defined taxonomy into which all computer networks can be classified, but these two network features are acceptable for general classifications.
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Transmission Technologies
• There are two types of transmission technologies:– Broadcast– Point-to-point
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Broadcast Networks
• uses a single communications channel
• the channel is shared
• information sent from any one machine on the network is received by all other machines on the network
• each piece of data received by a computer is checked to see if it is addressed to that computer
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Broadcasting
• Broadcast networks allow data to be addressed to every machine on the network. This allows one machine to “broadcast” a message to all other machines.
• It is possible to “broadcast” to a subset of the machines on the network. This is known as “multicasting”.
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Point-to-Point
• Point-to-point networks consist of a large number of individual connections between pairs of computers.
• The data travels through the network and is directed by machines along the way.
• Although these intermediate machines look at the data to see where it is going, they do not (should not) look at the data itself.
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Point-to-Point (cont’d)
• As a general rule, point-to-point is used in larger networks while broadcasting is used in smaller, geographically localized networks. There are exceptions.
• Point-to-point is sometimes referred to as unicasting. This creates the list:– broadcasting– multicasting– unicasting
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Network Size
• We can also classify networks based on their physical size.
• Different technologies may be used based on the size of the network.
• We can determine the type of network based on the physical distance that the network covers.
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Network Size ChartInterprocessor Distance
Processors located in same
1 m Square Meter
10 m Room
100 m Building
1 km Campus
10 km City
100 km Province
1000 km Continent
10,000 km Planet
Personal Area Network
Lan Area Network
Metropolitan Area Network
Wide Area Network
The Internet
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Personal Network
• A network meant for one person.
• A personal computer network:– a wireless keyboard and mouse– a networked printer– a PDA connection
• Devices to control pacemakers
• Remote controls for car stereos
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Local Area Network (LAN)
• Usually privately-owned networks
• Confined to a building or several buildings on a campus or company location.
• Usually used to connect personal computers for data interchange and to share resources such as printers and server machines.
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LANs
• LANs are distinguished by three characteristics:– size– transmission technology– topology
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LANs - Size
• LANs are restricted in size based on the size of the campus or building.
• Knowing the size of the LAN allows the worse-case data transmission scenarios to be known ahead of time.
• This information can be used during LAN design to make decisions about the technology that will be used.
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LANs - Transmission
• LANs are usually broadcast networks that are connected by a cable that attaches all of the computers together.
• LANs can run at speeds from 10Mbps to 10Gbps depending on the technology.
• LAN delays are usually small (microseconds) and few errors (scrambled data) occur.
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LANs - Topologies
• A linear connection of computers with two distinct ends is known as a “bus network”
• One machine on the network becomes the “master” and is allowed to transmit a packet across the network.
• We have to resolve the problem of two computers wanting to be “master” at the same time.
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Bus Network Transmission
• Transmitting data on a LAN may result in two “packets” of data colliding and being “lost”.
• We can resolve this problem using the IEEE 802.3 standard known as Ethernet where if a collision is detected, the two computers just wait random amounts of time and retransmit.
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LANs – Topologies (cont’d)
• The “ring” technology is a series of computers that are connected in a circle.
• Data can travel around the ring and is picked up by the computer it is addressed to.
• We still have to deal with determining who can transmit on the ring at any given point in time.
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Ring Network Transmission
• One of the most famous ring transmission technologies is IBM’s Token Ring standard (IEEE 802.5)
• The token ring LAN can achieve speeds from 4 to 16 Mbps.
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Metropolitan Area Network (MAN)
• MANs are usually large enough to cover a city.
• Best known example – a cable TV network.
• Originally intended for TV only, it quickly became used for computer networks once the cable companies determined that there was money to be made.
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MANs - Topology
• The topology of a MAN usually results in a series of computers with a single entry point at the head end of the network.
• It is at the head end that the MAN would be connected to another network.
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Wide Area Network (WAN)
• WANs are much larger than MANs, covering a whole country or other large geographical area.
• The user computers in a WAN are called hosts.
• Host computers on various LANs are connected via a communication subnet. The subnet consists of routers and transmission lines.
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WAN – Subnet Routers
• A router is a specialized piece of switching hardware that is responsible for determining the direction that data packets should be sent.
• Routers are responsible for directing data down transmission lines from one LAN to another.
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Subnets (confusion)
• The word “subnet” also refers to network addressing.
• There is no other words to define the either the router-subnet or the addressing-subnet.
• I (and the book) will try to make it clear from context which “subnet” we are talking about.
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Subnets
• Store-and-forward or Packet-switched– The message is broken down into smaller
packets to send.– Each packet is sent out onto the network.– As a packet arrives at a router, it is stored
there until the outgoing line is free. It is then sent on it’s way.
– All the packets make take the same or different routes depending on if they are individually routed or not.
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Subnets (cont’d)
• It is possible to have a broadcast subnet.
• The best example is a satellite system, where the data is broadcast to everyone.
• With a satellite, no routing occurs at the satellite – it simply acts as a big dish to bounce signals off of.
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Wireless Networks
• Wireless networks can be divided into three main categories:– System Interconnection– Wireless LANs– Wireless WANs
• Lets take a look at these three categories…
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System Interconnection
• We can use wireless technology to interconnect our system.– wireless mouse– wireless keyboard– wireless PDA
• Bluetooth is a wireless technology that would allow all sorts of digital devices to “talk” to each other just by being close.
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Wireless LANs
• Computers and printers can connect to the network with a radio communication link.
• There is usually a (or some) central access point or base station where the radio connections are converted to wire connections.
• Computers may also be able to talk directly to one another if close enough together.
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Wireless LANs (cont’d)
• The standard is IEEE 802.11. • It works on the same frequency as 2.4
GHz portable phones and Bluetooth.• There are some compatibility issues
between 802.11 and Bluetooth that have to be worked out.
• Wireless is great for old homes you don’t want to wire and laptops that you want to be able to move around.
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Wireless WANs
• Cell phone networks are a good example of wireless WANs.
• We are on our third generation of wireless WANs – there was analog voice, digital voice, and now digital voice and data.
• Distances are much greater than LANs, but bandwidth is much lower.
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Home Networks
• Many of us have them already – multiple computers all connected.
• What about connections to phones, entertainment systems, appliances and other devices?
• How practical is a home network?
• Will people pay so that their toaster can talk to their fridge?