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Network Hardware

Tananbaum Ch1.2

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Outline

• Network taxonomy

• Network software

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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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Local Area Networks

• Two broadcast networks(a) Bus(b) Ring

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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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MAN based on cable

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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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Wide Area Networks

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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?

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Internetworks

• A collection of interconnected networks is called an internetwork or internet.

• Connections are usually made through gateways that can provide the translation between the two different technologies.

• An internetwork is formed when distinct networks are connected.