data communication and networking
TRANSCRIPT
Topic
OSI Reference Model
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OSI Reference ModelSimple Video Example
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5
Topic
TCP/IP Model
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8
Error Handling
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Addressing
Connection Establishment
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Connection Release
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Flow Control
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Interface and State Machine
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Agenda of TCP/IP Model
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In TCP/IP there are two main transport protocols.
Transport Protocol
TCP UDP
Reliable: if some data is lost somewhere, TCP retransmits it
Stream service: the data is delivered at destination in the order it was sent
by source (sequence guarantee)
Unit of information is a byte; grouping of data into blocks may be different
at destination than at source
In TCP (Transmission Control Protocol)
In UDP (User Datagram Protocol)
offers a datagram service to the application (unit of information is a message)
Unreliable (message may be lost)
No sequence guarantee
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Topic
LAN & WAN
share peripherals devices like printers
LAN (Local Area Network)
small geographic area
Super cheap
high-speed data network
shared access to devices
And so on ...Everything!
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•Special security measures are needed to stop the users from using programs and data that they should not have accessed to.•Network are difficult to set up and need to be maintained by skilled technicians.•If the file servers develop a serious fault, all the users are affected, rather than just one users in the case of a standalone machine. •It needs to be on all the time.
Workstations can share peripherals devices like printers. Cheaper that providing a printer for each computer.Workstations do not necessary need their own hard disk or CD-ROM drives which make them cheaper to buy than stand-alone PC.User can save their work centrally on the network’s file server. This means that they can retrieve work from any workstation on the network.They don’t need to go to the same workstation again.
Advantages Disadvantages
LAN
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network protocols like ATM, X.25, and Frame Relay
WAN (Wide Area Network)
router connects LANs to WANs
broad geographic area
high-speed data network
shared access to devices
And so on ...Everything!
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WAN (Wide Area Network)
LAN (Local Area Network)
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Topic
Network Topologies
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What is Network Topology?
• The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations. Logical topology was discussed in the Protocol chapter.
• There are several basic network topologies: star, bus, ring, mesh, and hierarchical etc.. 18
A Star topology• A star network has a central node that
connects to each of the other nodes by a single, point-to-point link. Any communication between one node and another in a star topology must pass through the central node.
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Bus Topology• In a bus topology, nodes are arranged along a single
length of twisted-pairwire, coaxial cable, or fiber-optic cable that can be extended at the ends. Using a bus topology, it is easy and inexpensive to add a node to the network, and losing a node in the network will not cause the network to fail. The main disadvantages to the bus topology are that a defective bus causes the entire network to fail. Also, providing a bus with inadequate bandwidth will degrade the performance of the network.
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•There is a limit on central cable length and number of nodes that can be connected.•Dependency on central cable in this topology has its disadvantages.If the main cable (i.e. bus ) encounters some problem, whole network breaks down. •Proper termination is required to dump signals. Use of terminators is must.•It is difficult to detect and troubleshoot fault at individual station.•It is not suitable for networks with heavy traffic.
It is easy to set-up and extend bus network.Cable length required for this topology is the least compared to other networks.Bus topology costs very less.Linear Bus network is mostly used in small networks. Good for LAN.
Advantages Disadvantages
Bus Topology
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Ring Topology• A network topology that is set up in a circular fashion in which
data travels around the ring in one direction and each device on the right acts as a repeater to keep the signal strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The network is dependent on the ability of the signal to travel around the ring.
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A mesh Topology • A mesh network design is one in which each
device is connected to every other device located on the network, like a spider web. The advantage to this design is the redundancy of the connected devices; if one link fails, it will not affect the rest of the network. The disadvantages of this design are the cost of all the required medium and limited scalability. If you add a device to a network that currently has four devices, then you must connect the new device to the four existing devices with individual cable drops.
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Hierarchical Topology• In a hierarchical topology, nodes are arranged
like an inverted tree with the root (usually the mainframe computer) as the highest level and the leaves (usually the desktop computers) as the lowest level. It is very cheap, but may have possible traffic jams at the top level.
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Hybrid Topology• In a hybrid topology, nodes are arranged in more
than one topology, which may include star, ring, and hierarchical . A hybrid topology can integrate together various computer configurations that may have special reasons for their own choice of topology. A hybrid network will allow companies to pick the advantages from several different topologies.
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Topic
Network Technologies
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•Under heavy use there can be a delay•Data packets can get lost or become corrupted•Protocols are needed for a reliable transfer•Not so good for some types data streams (e.g. real-time video streams can lose frames due to the way packets arrive out of sequence)
SecurityBandwidth used to full potentialDevices of different speeds can communicateNot affected by line failure (redirects signal)Availability – no waiting for a direct connection to become availableDuring a crisis or disaster, when the public telephone network might stop working, e-mails and texts can still be sent via packet switching
Advantages Disadvantages
Packet Switching
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•Inefficient – the equipment may be unused for a lot of the call; if no data is being sent, the dedicated line still remains open.•It takes a relatively long time to set up the circuit.•During a crisis or disaster, the network may become unstable or unavailable.•It was primarily developed for voice traffic rather than data traffic.
Circuit is dedicated to the call – no interference, no sharingGuaranteed the full bandwidth for the duration of the callGuaranteed quality of service
Advantages Disadvantages
Circuit Switching
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What is Frame Relay?Frame Relay is a packet switching technology for connecting network points in Wide Area Networks (WAN). It
is a connection oriented data service and establishes a virtual circuit between two end points. Data transfer is done in packets of data known as frames. These frames are variable in packet size and more efficient due to flexible transfers. Frame Relay was originally introduced for ISDN interfaces though it is currently used over a variety of other network interfaces as well.
In Frame Relay, connections are called as ‘Ports’. All the points which need to connect to the frame relay network needs to have a port. Every port has a unique Address. A frame is made of two parts which can be called as ‘actual data’ and the ‘frame relay header’. Frame architecture is same as defined for LAP-D (Link Access Procedures on the D channel) which has a variable length for information field. These frames are sent over Virtual Connections.
Frame Relay can create multiple redundant connections among various routers, without having multiple physical links. Since frame relay is not specific for media, and provides means to buffer speed variations, it has the possibility to create a good interconnect medium between different types of network points with different speeds. 31
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What is ATM?ATM is a network switching technology that uses a cell based methodology to quantize data. ATM data
communication consists of fixed size cells of 53 bytes. An ATM cell contains a 5 byte header and 48 bytes of ATM payload. This smaller size, fixed-length cells are good for transmitting voice, image and video data as the delay is minimized.
ATM is a connection oriented protocol and therefore a virtual circuit should be established between sending and receiving points. It establishes a fixed route between two points when the data transfer starts.
ATM is designed to be convenient for hardware implementation and therefore processing and switching have become faster. Bit rates on ATM networks can go up to 10 Gbps. ATM is a core protocol used over the SONET/SDH backbone of the ISDN.
ATM provides a good quality of service in networks where different types of information such as data, voice, and are supported. With ATM, each of these information types can pass through a single network connection.
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Topic
Transmission Medium
There are two main types of transmission medium
Transmission Medium
Guided (Wired)
Unguided (Wireless)
Bandwidth
higher bandwidth gives higher data rate
Transmission impairments
e.g.. attenuation
Interference
Number of receivers in guided media
more receivers introduces more attenuation
Design Factors
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Transmission Characteristics of Guided Media
Frequency Range
Frequency Range
Typical Attenuation
Typical Attenuation
Typical DelayTypical Delay Repeater Spacing
Repeater Spacing
Twisted pair (with loading)Twisted pair (with loading)
0 to 3.5 kHz0 to 3.5 kHz 0.2 dB/km @ 1 kHz0.2 dB/km @ 1 kHz
50 µs/km50 µs/km 2 km2 km
Twisted pairs (multi-pair cables)
Twisted pairs (multi-pair cables)
0 to 1 MHz0 to 1 MHz 0.7 dB/km @ 1 kHz0.7 dB/km @ 1 kHz
5 µs/km5 µs/km 2 km2 km
Coaxial cableCoaxial cable 0 to 500 MHz0 to 500 MHz 7 dB/km @ 10 MHz7 dB/km @ 10 MHz
4 µs/km4 µs/km 1 to 9 km1 to 9 km
Optical fiberOptical fiber 186 to 370 THz186 to 370 THz 0.2 to 0.5 dB/km0.2 to 0.5 dB/km
5 µs/km5 µs/km 40 km40 km
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Twisted Pair
• analog – needs amplifiers every 5km to 6km
• digital– can use either analog or digital signals– needs a repeater every 2-3km
• limited distance• limited bandwidth (1MHz)• limited data rate (100MHz)• susceptible to interference and noise 36
Coaxial Cable
• superior frequency characteristics to TP• performance limited by attenuation & noise• analog signals
– amplifiers every few km– closer if higher frequency– up to 500MHz
• digital signals– repeater every 1km– closer for higher data rates 37
Optical Fiber
• greater capacity– data rates of hundreds of Gbps
• smaller size & weight• lower attenuation• electromagnetic isolation• greater repeater spacing
– 10s of km at least 38
network protocols like ATM, X.25, and Frame Relay
WAN (Wide Area Network)
router connects LANs to WANs
broad geographic area
high-speed data network
shared access to devices
And so on ...Everything!
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Wireless Transmission
Frequecies
2GHz to 40GHz
30MHz to 1GHz
3 x 1011 to 2 x 1014
microwavehighly directionalpoint to pointsatellite
omnidirectionalbroadcast radio
Infraredlocal
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Antennas
• electrical conductor used to radiate or collect electromagnetic energy
• transmission antenna– radio frequency energy from transmitter– converted to electromagnetic energy byy antenna– radiated into surrounding environment
• reception antenna– electromagnetic energy impinging on antenna– converted to radio frequency electrical energy– fed to receiver
• same antenna is often used for both purposes41
Radiation Pattern
• power radiated in all directions• not same performance in all directions– as seen in a radiation pattern diagram
• an isotropic antenna is a (theoretical) point in space– radiates in all directions equally– with a spherical radiation pattern
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Terrestrial Microwave
• used for long haul telecommunications• and short point-to-point links• requires fewer repeaters but line of sight• use a parabolic dish to focus a narrow beam onto a
receiver antenna• 1-40GHz frequencies• higher frequencies give higher data rates• main source of loss is attenuation– distance, rainfall
• also interference43
Satellite Microwave• satellite is relay station• receives on one frequency, amplifies or repeats
signal and transmits on another frequency– eg. uplink 5.925-6.425 GHz & downlink 3.7-4.2 GHz
• typically requires geo-stationary orbit– height of 35,784km– spaced at least 3-4° apart
• typical uses– television– long distance telephone– private business networks– global positioning
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Satellite Point to Point Link
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Satellite Broadcast Link
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Broadcast Radio
• radio is 3kHz to 300GHz• use broadcast radio, 30MHz - 1GHz, for:– FM radio– UHF and VHF television
• is omnidirectional• still need line of sight• suffers from multipath interference– reflections from land, water, other objects
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Infrared
• modulate noncoherent infrared light• end line of sight (or reflection)• are blocked by walls• no licenses required• typical uses– TV remote control– IRD port
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Wireless PropagationGround Wave
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Wireless PropagationSky Wave
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Wireless PropagationLine of Sight
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Topic
Communication
Connections between devices may be classified into three categories
Simplex. This is a unidirectional connection, i.e., data can only travel in onedirection. Simplex connections are useful in situations where a device onlyreceives or only sends data (e.g., a printer).
Half-duplex. This is a bidirectional connection, with the restriction that data cantravel in one direction at a time.
Full-duplex. This is a bidirectional connection in which data can travel in bothdirections at once. A full-duplex connection is equivalent to two simplexconnections in opposite directions.
Topic
Network Units
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Topic
Switching Technologies
•Switch will save the entire packet to the buffer and check it for errors or other problems before sending.•If the packet has an error, it is discarded.•Entire packet is processed•Packets are filtered
• Bad packets are filtered
A packet switch where the switch starts forwarding that frame (or packet) before the whole frame has been received, normally as soon as the destination address is processed. This technique reduces latency through the switch, but decreases reliabilityReads only part of the packet
The addresses header Packet is forwarded accordingly
Bad packets are not filtered
Cut throughSwtich
Straight andForward Switch
Bus Topology
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Topic
Network Connectors
Hubs are Layer-1 devices that physically connect network devices together
for communication. Hubs can also be referred to as repeaters.
Hubs provide no intelligent forwarding whatsoever. Hubs are incapable of
processing either Layer-2 or Layer-3 information, and thus cannot make
decisions based on hardware or logical addressing.
Multilayer switching is a generic term, referring to any switch thatforwards traffic at layers higher than Layer-2. Thus, a Layer-3 switch isconsidered a multilayer switch, as it forwards frames at Layer-2 and packetsat Layer-3.A Layer-4 switch provides the same functionality as a Layer-3 switch, butwill additionally examine and cache Transport-layer application flowinformation, such as the TCP or UDP port.
Layer-3 routing is the process of forwarding a packet from one network toanother network, based on the Network-layer header. Routers build routingtables to perform forwarding decisions, which contain the following:• The destination network and subnet mask• The next hop router to get to the destination network• Routing metrics and Administrative Distance
A switch is defined as a device that allows a LAN to be segmented.
-The segments will operate under the same protocol
Improve the network performance and reliability Better manage the network in general.
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1 OSI Reference Model
2 TCP/IP Model
3 LAN and WAN
4 Network Topologies
5 Network Technologies
Topics list covered in the assignment
Huh, Finally Done!
6 Transmission Medium
7 Communication
8 Network Units
9 Switching Technologies
10 Network Connectors
QUESTIONS
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THANK YOU!