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Data Communication and Networking (((Standard Ethernet 10Base5 …

- - - - As the data packet moves
        from the lower layers (1 - 7)
        to the upper layers of the OSI model,
        headers are subtracted
      - As the data packet moves
        from the upper layers (7 - 1)
        to the lower layers of the OSI model,
        headers are added
      - .
        
        3 Network layer (data-unit = packet)
        Controls the operations of the subnet, deciding which physical path data takes
        Responsible for host-to-host routing, which is moving packets
        Encapsulating
        IP address which includes the source and destination
        Data Packet
        Logically grouped unit of information that moves between computer systems
        PACKETS (contains IP address) Routing,
        Subnet traffic control,
        Frame fragmentation,
        Logical-Physical address mapping, Subnet usage accounting.
        provides path selection, routing, and addressing
        
        Devices
        Gateway, Routers
        Routers
        Make packet forwarding decisions based on logical addresses
        
        3
        
        Network Layer
        
        Sublayers
        
        Media Access Control (MAC)
        Hexadecimal address burned on NIC cards.
        Source Address Field
        MAC frame is 48 bits long and carry the source and destination MAC addresses
        
        Unicast
        Single receiver for the packet (one to one) least significant bit is zero
        Multicast
        Multi receiver for the packet (one to one) least significant bit is one
        Broadcast
        Same network, All bits are one, in the first byte. The broadcast address in hexadecimal is FF:FF:FF:FF:FF:FF
        
        Media Access Control
        
        Controlled Access Protocols
        Token Passing
        In token passing scheme, the stations are connected logically to each other in form of ring and access of stations is governed by tokens
        Polling
        Polling process is similar to the roll-call performed in class. Just like the teacher, a controller sends a message to each node in turn
        Reservation
        In the reservation method, a station needs to make a reservation before sending data.
        
        Channelization Protocols
        Channelization is a multiple-access method in which the available bandwidth of a link is shared in time, frequency, or through code, between different stations.
        
        FDMA
        Frequency-Division Multiple Access
        Available bandwidth is divided into frequency bands.
        Each station is allocated a band to send its data.
        In other words, each band is reserved for a specific station, and it belongs to the station all the time.
        
        CDMA
        Code-Division Multiple Access
        CDMA simply means communication with different codes.
        CDMA differs from FDMA because only one channel occupies the entire bandwidth of the link.
        It differs from TDMA because all stations can send data simultaneously; there is no timesharing.
        
        TDMA
        Time-Division Multiple Access
        Stations share the bandwidth of the channel in time.
        Each station is allocated a time slot during which it can send data.
        
        Random Access Protocols
        info
        Collision Detection (CD)
        Is achieved by the hosts comparing the data on the cable to the data they are transmitting.
        If they are different then the hosts know that a collision must have occurred.
        info
        Carrier Sensing (CS)
        Each host listens to or senses the data being transmitted over the cable.
        A host will only transmit its own frames when it cannot see any data being transmitted by other hosts.
        However, now and again two hosts will attempt to transmit a frame at exactly the same time.
        This will cause a collision and the data frames will be corrupted.
        The hosts will detect that a collision has taken place and will abandon the transmission of their frames to try again later.
        
        CSMA
        Carrier Sense Multiple Access
        Ensures fewer collisions as the station is required to first sense the medium (for idle or busy) before transmitting data. If it is idle then it sends data, otherwise it waits till the channel becomes idle.
        
        CSMA/CA
        Carrier Sensing Multiple Access / Collision Avoidance
        The process of collisions detection involves sender receiving acknowledgement signals.
        If there is just one signal(its own) then the data is successfully sent but if there are two signals(its own and the one with which it has collided) then it means a collision has occurred.
        
        CSMA/CD
        Carrier Sensing Multiple Access / Collision Detection
        Is a non-deterministic network. This means that no host is guaranteed to be able to send its frame within a reasonable time (just a good probability of doing so).
        
        2 Data-link layer (data-unit = frame)
        Provides error-free transfer of data frames from one node to another over the physical layer.
        Looks for physical address to send a frame from one link to another.
        Uses the trailer of the frame for error detection
        Responsible for Node-to-node delivery of the data units
        Encapsulating
        The packet is encapsulated into a frame containing physical addresses
        
        Devices
        Gateway, Bridge, NIC,
        Level-2 Switches
        Level-2 Switches
        Make traffic routing decisions based on layer 2 addresses
        
        2
        
        Data-link layer
        
        Logical Link Control(LLC)
        It provides is a standardised interface between the network layer and the data link layer.
        In the data link layer the LLC adds its own header to the packet and the resulting structure is then passed to the MAC sublayer
        
        Logical Link Control
        
        1 Physical layer (data-unit = raw bits)
        Responsible for sending computer bits from one device to another
        Concerned with the transmission and reception of the unstructured raw bit stream over physical medium
        Encapsulating
        Data it is encoded into bits and made ready for transmission
        PHYSICAL STRUCTURE
        Data Encoding, Physical medium attachment, transmission technique(BaseBand or BroadBand), Bits and Volts
        
        Devices
        Repeaters, Hubs, Gateways
        Hub
        Provide a central point of connection for hosts
        Amplify / retime signals and send them out to all connected hosts
        They are multi-port repeaters
        
        1
        
        Physical layer
        
        4 Transport layer (data-unit = segment)
        Ensures that the messages are delivered error-free, in sequence and with no losses or duplicates
        Responsible for the end-to-end delivery of an entire message
        Encapsulating
        It adds a transport layer header which has the source and destination port address
        TCP (host-to-host, flow-control, PACKET FILTERING )
        Message segmentation,
        Message Acknowledgements,
        Message traffic control,
        Session Multiplexing
        
        Devices
        Gateways
        
        4
        
        Transport layer
        
        5 Session layer (data-unit = passed data)
        Allow session establishment between processes running on different stations
        Responsible to establish, maintain and synchronize the interaction between communicating systems
        Encapsulating
        Data It stays in the form of data with some protocol info added to it
        Sync & Send to ports (LOGICAL PORTS)
        Session establishment,
        Maintenance and termination,
        Session support, perform security, name recognition, logging etc.
        
        Devices
        Gateway
        
        5
        
        Session Layer
        
        6 Presentation layer (data-unit = formated data)
        Formats the data to be presented to the Application layer. Translator for the network
        Responsible for the formatting and delivery of information to the application layer for further processing or display
        Encapsulating
        Data It stays in the form of data with some protocol info added to it
        Syntax layer (encrypt & decrypt)
        Character code translation, data conversion, data compression, data encryption, character set translation [jpeg, ASCII GIF etc.]
        
        Devices
        Gateway
        
        6
        
        Presentation Layer
        
        7 Application layer (data-unit = received data)
        Serves as the window for users and application processes to access the network services (mail...)
        It provides user interfaces and support for services such as e-mail, shared database management and other types of distributed information services
        Encapsulating
        Data It stays in the form of data with some protocol info added to it
        End User layer
        Opens what was send/Creates what's to be sent
        Resource sharing,
        Remote file access,
        Remote printer access,
        Direct services,
        Network management
        
        Devices
        Gateway
        
        7
        
        Application Layer
- - - - Synchronous
        Each device is pre-assigned a time slot.
        Is wasteful if some devices transmit very often while others hardly transmit at all.
        Fast Transmission
        Needs a common clock signal
        May have to wait until data can be sent
        Almost all parallel transmissions are synchronous
        transmission rate = sum of the source transmission rate
      - Techniques
        
        Spread Spectrum
        In spread spectrum signals from different sources are spread over a larger bandwidth
        The goal is to prevent eavesdropping and jamming.
        If we can find a way of encoding our data into a large signal bandwidth, then we can get error free transmission under conditions where the noise is much more powerful than the signal we are using.
        
        Spreading code
        Used in the transmitter is pseudo random (PR) and has a very high bit rate.
        Produces a noise-like signal that is hard to detect
        The bandwidth allocated to each sending station needs to be, by far, larger than what is needed.
        Signals spread across the same large bandwidth do not interfere with each other as each uses a different PR code.
        Each signal can be regenerated at a receiving station if the station knows the spreading code used by the sending station
        
        Frequency Hopping
        The central idea behind a FH system is to retune the transmitter RF carrier frequency to a pseudorandomly determined frequency value. In this fashion the carrier keeps popping up a different frequencies, in a pseudorandom pattern.
        The carrier itself amy be modulated directly with the data using one of many possible schemes.
        The available radio spectrum is thus split up into a discrete number of frequency channels, which are occupied by the RF carrier pseudorandomly in time.
        Unless you know the PN code used, you have no idea where the carrier wave is likely to pop up next, therefore eavesdropping will be quite difficult.
        
        Asynchronous TDM
        Time slots are on a first-come first-served (FIFO) basis
        Is a more flexible method of TDM
        With Asynchronous TDM the length of time allocated is not fixed for each device
        Time is given to devices that have data to transmit
        This version of TDM works by tagging each frame with an identification number to note which device it belongs to
        Mouse or keyboard is a type of asynchronous transmission
        Used by the high-speed WAN telecommunication networks ATM (Asynchronous Transfer Mode)
        transmission rate < source transmission rates
      - Time-division (TDM)
        Is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern.
        digital signals
        
        Calculations:
        Frames:
        nrOfChannels * nrOfBytesToBeSennt
        Frame Rate
        nrOfFrames (nrOfBytes 8)
    - - Wavelength-division WDM
        Similar to FDM, The main difference is that signals are composed of beams of light
        *Is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light.
        This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity.*
        analog signals
        
        Calculations f * a = c
        (c= speed of light, f = frequency, a = wavelength)
    - - Sender
        Signals generated by each sending device modulate a different carrier frequency and as long as the carrier frequencies are not too close then the signals can be sent over the link at the same time.
      - Receiver
        At the receiving end the different carrier frequencies are detected and so the individual signals are re-produced.
      - . Frequency-division (FDM)
        *Is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands.
        analog signals
        
        Ex: television stations transmitted simultaneously over the same cable, (PSTN)
        Calculations: nrOfChannels * bandwith + (guardBand -1)
        (4Kh x 20signals + 20 - 1)
        guardBand is the safe distance between them
  - - - Switched Virtual-Circuit(SVC)
        A virtual circuit is created whenever it is needed and exists only for the duration of the specific exchange.
        An example of this would be the Asynchronous Transfer Mode (ATM) technology
        
        Permanent Virtual-Circuit(PVC)
        The same virtual circuit is provided between two users on a permanent basis.
        The circuit is dedicated to the specific user and always has the same route.
        An example of this is Frame-Relay which is charged on a per-bandwidth basis
        
        Virtual Circuit (VC)
        Is a means of transporting data over a packet switched computer network in such a way that it appears as though there is a dedicated physical layer link between the source and destination
        It is connection-oriented simply meaning that there is a reservation of resources like buffers, CPU, bandwidth, etc. for the time in which the newly setup VC is going to be used by a data transfer session.
        First packet goes and reserves resources for the subsequent packets which as a result follow the same path for the whole connection time. Since all the packets are going to follow the same path, a global header is required only for the first packet of the connection and other packets generally don’t require global headers.
        Since data follows a particular dedicated path, packets reach in-order to the destination. It is sure the all the packets will definitely reach to the Destination. No packet will discard due to unavailability of resources.
        From the above points, it can be concluded that Virtual Circuits are highly reliable means of transfer. Since each time a new connection has to be set up with reservation of resources and extra information handling at routers, its simply costly to implement Virtual Circuits.
        It is used by the ATM (Asynchronous Transfer Mode) Network, which is used for the Telephone calls.
        
        A single route is chosen between sender and receiver at the beginning of the session.
      - Datagram
        A self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network.
        It is connectionless service. There is no need for reservation of resources as there is no dedicated path for a connection session.
        All packets are free to go to any path on any intermediate router which is decided on the go by dynamically changing routing tables on routers. Since every packet is free to choose any path, all packets must be associated with a header with proper information about the source and the upper layer data.
        The connectionless property makes data packets reach the destination in any order, means they need not reach in the order in which they were sent.
        Datagram networks are not reliable as Virtual Circuits. The major drawback of Datagram Packet Switching is if the Buffer, CPU, and Bandwidth are available then the only Packet will be forwarded. Otherwise, Packet will discard.
        But it is always easy and cost-efficient to implement datagram networks as there is no extra headache of reserving resources and making a dedicated each time an application has to communicate.
        Its is generally used the IP network, which is used for Data services like Internet.
        Packets may take different routes and arrive out of sequence.
        
        Destination Header
        The destination address in the header of a packet in a datagram network remains the same during the entire journey of the packet
        Routing Table
        A switch in a datagram network uses a routing table that is based on the destination address.
      - Packet Switching
        Implemented at Network Layer
        Data is transmitted in variable length blocks called packets
        No physical path
        Designed for data transmission
        Do not reserve bandwidth in advance
        No bandwidth wastage
        Packets travel independently
        Packets are received out of order and assembled at the destination
        Packets contain a header with source/destination address
    - - Space-division Switches
        
        Space-division Switches
        In a space-division switch the paths in the circuit are separated from each other spatially
        Is instantaneous
        Crossbar Switch
        A crossbar switch connects n inputs to m outputs in a grid, using electronic micro-switches (transistors) at each crosspoint
        inputs * outputs = crosspoints
      - Time-division Switches
        
        Time Division Switching
        In a time-division circuit switch the slots are divided by time instead of space.
        Switching is accomplished using time-division multiplexing (TDM).
        
        Does not require crosspoints
        Each connection creates delay as packets must be stored in RAM
        TSI
        A Time Slot Interchanged must be used to implement switching
      - Circuit Switching
        Implemented at Physical Layer
        Physical path between source and destination
        Designed for voice communication
        Reserve the entire bandwidth in advance
        Dedicated connection between two devices, uses the entire capacity of a channel
        Message is received in the order sent from the source
        All packets use the same path
        Bandwidth wastage
- - - - Coaxial cable
        Carries signals of higher frequency ranges than twisted-pair.
        Has a central core conductor enclosed in an insulating sheath. The outer conductor serves as a shield and as a conductor to complete the circuit.
        Advantages
        Cheap to install compared to fiber optics,
        Wide bandwidth compared to twisted-pair,
        Suitable for operation at high frequency(cable TV), conforms to standards
        Disadvantages
        Quite bulky so its difficult to wire,
        Limited to distance when compared to fiber optic,
        Limited in number of connections,
        Optic fiber more cost-effective for long links,
        UTP more cost effective for short distances
    - - Step-index
        The density of the inner core is uniform all around, and the refraction of the light is very sharp.
        Must be kept short to avoid distortion
        
        Single-Mode Fibre
        Only one angle for rays,
        Longer propagation distance
        (>50km) and faster (>10 Gbits/s).
        Used for WAN's,
        Very expensive,
        Requires very good laser,
        Fragile due to narrow core.
        
        Graded Index
        The density of the inner core is lower towards the edge of the fiber.
        Greater bandwidth than step-index,
        Lower distortion
      - Fiber-optic cable
        Often found in Backbone networks because its wide bandwidth its cost effective.
        Transmits data signals in the form of light, a strand of silica glass fiber(thinner than a human hair acts as the core fiber).
        How it Works
        The data signals are converted to light pulses using a laser. Laser is turned ON/OFF for binary 1/0.
        Almost no attenuation or interference.
        Uses reflection to guide light, the core its surrounded by a cladding of less dense plastic which reflects the beam from the edge back in
        Advantages
        Increased capacity and bandwidth
        Light weight
        Less signal attenuation
        Immunity to electromagnetic interference
        Resistance to corrosive materials
        Disadvantages
        Difficult to install and maintain
        High cost Fragile
        Unidirectional, (ie, will need another fibre, if we need bidirectional communication)
      - Multimode Dispersion
        Light rays entering at different angles travel different distances
        (different number of reflections).
        Light from successive bits becomes mixed and dispersed over long distances causing errors in data.
        Cheap and effective for short distances (200m to 500m),
        Used in LAN's
    - - UTP
        (Unshielded twisted pair),
        Has no ground shield.
        Ground shield helps reduce signal interference from external sources
        Categories
        CAT4
        Typically used in token ring networks, CAT4 supports 16 Mbps for up to 100 m
        CAT5
        Used in Ethernet-based LANs, CAT5 contains two twisted pairs. It supports 100 Mbps for up to 100 meters
        CAT5e
        Used in Ethernet-based LANs, CAT5e contains four twisted pairs. It supports 1Gbps for 100 meters
        CAT6 Used in Ethernet-based LANs and data center networks, CAT6 contains four tightly wound twisted pairs. It supports 1Gbps for up to 100 meters and 10 Gbps for up to 50 meters.
        Advantages
        Very high installed base, cheap to install, easy to terminate
        Disadvantages
        Very noisy, limited in distance (100m), suffers from interference
      - STP
        (Shielded twisted pair),
        Has a ground shield.
        Categories
        CAT7
        Is a newer copper cable specification designed to support speeds of 10Gbps at lengths of up to 100 meters.
        To achieve this, the cable features four individually shielded pairs plus an additional cable shield to protect the signals from crosstalk and electromagnetic interference (EMI)
      - Twisted-pair cable
        Is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility.
        The twisting is used as a mechanism to reduce interference between pairs (crosstalk) and from outside sources
        Crosstalk
        Is the signal interface caused by a signal on one-pair interfering with a signal on an adjacent pair
        Advantages
        Trained personnel easily available due to shallow learning curve
        Can be used for digital or analog
        Least expensive for short distances
        Disadvantages
        Signal cannot travel long distances without repeaters
        High error rate for distances greater than 100m
        Not suitable for broadband connections
  - - - Microwaves
        It is a line of sight transmission i.e. the sending and receiving antennas need to be properly aligned with each other.
        The distance covered by the signal is directly proportional to the height of the antenna.
        Frequency Range:1GHz – 300GHz.
        These are majorly used for mobile phone communication and television distribution.
    - - Infrared
        Infrared waves are used for very short distance communication.
        They cannot penetrate through obstacles.
        This prevents interference between systems.
        Frequency Range:300GHz – 400THz.
        It is used in TV remotes, wireless mouse, keyboard, printer, etc.
    - - Radio-Waves
        Are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light.
        These are easy to generate and can penetrate through buildings.
        The sending and receiving antennas need not be aligned.
        Frequency Range:3KHz – 1GHz.
        AM and FM radios and cordless phones use Radio-Waves for transmission.
- - - - Star Topology
        All nodes are individually connected to a central connection point.
        Requires a central controller or hub
        Connection Failure
        The other devices will still be able to send data through the hub; there will be no access to the device which has the failed connection to the hub.
        ( Failure of a device does not cause system failure.)
        
        Advantages
        Less expensive than Mesh topology.
        Installation and reconfiguration is easy.
        This topology is robust and reliable.
        It is easy to detect and isolate fault in this topology.
        New devices can be easily added
        Disadvantage
        The main problem in this topology is that the whole topology is dependent on a single point called hub if the hub goes down, the whole network is dead.
        Calculations: n computers = n cables
        
        Tree Topology
        Elements are arranged like the branches of a tree.
        Is a variation of a STAR topology
        Used to organize the computers in a corporate network, or database.
        Can contain multiple hubs
        Connection failure
        Tree topologies have a significant weakness which is the central node.
        If the central node fails then the entire network goes down
        
        Advantages
        Scalable as leaf nodes can accommodate more nodes in the hierarchical chain.
        A point to point wiring to the central hub at each intermediate node of a tree topology represents a node in the bus topology
        Other hierarchical networks are not affected if one of them gets damaged
        Easier maintenance and fault finding
        Disadvantages
        Huge cabling is needed
        A lot of maintenance is needed
        Backbone forms the point of failure.
        
        Tree Topology
        
        Star Topology
        
        Mesh Topology
        Each node is connected with every other nodes via cables.
        Require the most extensive cabling
        Connection Failure
        If one connection fails, the other connections will still be working
        ( Failure of a device does not cause system failure.)
        
        Advantages
        It eliminates data traffic problems, it is the most reliable and robust topology.
        This topology maintain highest level of privacy and security.
        Its point-to-point connection gives advantage to easily find out errors and isolate it.
        Disadvantage
        It is very expensive topology.
        Because of complex connection it is very difficult to add a new device in the network.
        Calculations: n (n – 1) / 2 =
        (n stands for nr of devices)
        
        Mesh Topology
        
        Ring Topology
        Each node is connected with exactly two nodes.
        All messages travel through a ring in the same direction till the destination node receives it. It is a closed loop configuration
        Connection Failure
        The failed connection may disable the whole network unless it is a dual ring or there is a bypass mechanism.
        
        Advantages
        Ring topology is cheap to implement.
        It doesn’t get affected by high traffic or adding more nodes.
        Disadvantage
        Adding or removing a node disturb the activity of the whole network. Troubleshooting is very difficult in ring topology.
        Calculations: n computers = n cables
        
        Ring Topology
        
        Hybrid Topology
        Hybrid topology is a mixture of two or more topologies.
        It inherits the pros and cons of all using topologies in the network.
        
        Advantages
        Hybrid topologies are reliable.
        Error detection and correction is easy in such networks.
        These are effective and flexible topologies that can easily be scaled according to the size of area.
        Disadvantage
        Hybrid topology is complex in design.
        This kind of network topology is expensive.
        
        Hybrid Topology
        
        Point-to-Point
        A dedicated link between two devices.
        mesh, star, ring topology
        Advantages: much simpler
        
        Point-to-Point
      - Bus Topology
        One long cable connects all the nodes in a network.
        Requires a multipoint connection
        Connection Failure
        All transmission stops if the failure is in the bus. If the drop-line fails, only the corresponding device cannot operate.
        ( Failure of a device does not cause system failure.)
        
        Advantages
        Provides easy installation facility.
        It require very less cable than other topologies hence not so expensive. New devices can be easily added
        Disadvantage
        Includes difficult reconnection and fault isolation.
        Signal reflection at taps can cause quality degradation.
        Calculations: n + 1 = cable links
        
        Bus Topology
        
        Multipoint
        More than two devices share a single link.
        bus topology
        Advantages: ease of installation, low cost, reliability
        
        Multipoint
      - Topology
        Computers in a network have to be connected in some logical manner.
        The layout pattern of the interconnections between computers in a network is called network topology.
        
        Topology
    - - Network
    - - Categories
        LAN
        A Local Area Network (LAN) Group of devices that share a common communications line connected within a distinct geographic area
        (EX. An Office or shop)
        MAN
        Metropolitan Area Network is designed to extend over an entire city.
        (EX. Cable TV Network)
        WAN
        A Wide Area Network is a telecommunications or computer network that extends over a large geographical distance
        (EX. The Internet)
        
        Categories
    - - Criteria/Benchmark
        Performance (Daily throughput)
        Transit time and response time.
        Depends on the number of users, type of transmission medium, hardware, software, time of day
        Reliability
        Accuracy of delivery, network reliability, frequency of failure, recovery time after a failure, robustness to catastrophe
        Security
        Network security issues include protecting data from unauthorized access, viruses.
        
        Benchmark
- - - - 2 Half-Duplex
        Both devices can send and receive, but not at the same time.
        (walkie-talkie, CB: citizens-band, etc)
    - - 3 Full Duplex
        The channel capacity is shared by both communicating devices at all times.
        (telephone line: both can talk and listen at the same time)
    - - 1 Simplex
        Only one of the devices can transmit, the other can only receive.
        (keyboard, monitor, television broadcast etc)
  - - - 3 Receiver
        The device which receives the data message
        (computer, telephone, video cameras etc.)
    - - 4 Medium
        The physical path by which a message travels from sender to receiver.
        (coaxial cable, fibre-optic cable, radio waves etc.)
    - - 2 Sender
        The device which sends the data
        (computer, workstation, telephone, video cameras etc.)
    - - Semantics
        When a protocol specifies that the address of the sender means the most recent sender and not the original source
      - Timing
        If a protocol specifies that data should be sent at 100Mbps, this is a timing issue.
      - Syntax
        When a protocol specifies that the address of the sender must occupy the first four bytes of a message
      - 5 Protocol
        Is a set of rules that govern data communications.
        (It represents an agreement between the communication devices.)
    - - 1 Message
        The information to be communicated
        (text, numbers, pictures, sound or video)
  - - - Forums
        Special-interest groups
        The Frame Relay Forum
        ATM Forum and ATM Consortium
        Internet Society and Internet Engineering Task Force
    - - Agencies
        Regulation by government agencies
        The Communications Regulator (ComReg) in Ireland
        The Federal Communications Commission (FCC) in the USA.
    - - Committees
        Body of one or more persons
        ISO
        International Standards Organisation
        ITU-T
        International Telecommunication Union
        ETSI
        European Telecommunications Standards
        ANSI
        American National Standards Institute
        IEEE
        Institute of Electrical & Electronic Engineers
        computer scientists & development of LAN
- - - - Physical layer
        No specific protocols.
        Depends on the type of network used eg. Ethernet
        
        Repeaters
        (Physical Layer 1)
        Is a network device used to regenerate or replicate a signal.
        It amplifies the analogue signal and regenerates digital signals.
        It can relay messages between networks that use different protocols or cable types
        cannot do the intelligent routing performed by bridges, switches and routers
        
        Hubs
        Regenerate and re-time network signals.
        Provide a central point of connection for hosts b.
        Amplify / retime signals and send them out to all connected hosts
        They are multi-port repeaters
        Advantages
        It creates a central connection point and increases the reliability of the network, allowing any single cable to fail without disrupting the entire network.
        The hub is used in the centre of a
        star topology.
        
        Passive
        They merely redirect the signals
        
        Active
        They take energy from a power source and regenerate network signals
      - Data-link layer
        No specific protocols.
        Depends on the type of network used eg. Ethernet.
        Data unit = frame
        
        Bridges (Physical & Data-link layers)
        A bridge forwards or filters a packet by comparing the layer 2 destination address in its address table to the packet.
        A simple bridge filters a frame, forwards a frame and extends LAN's.
        Has access to the physical address of a station on the same network
        
        Learning
        A learning bridge uses an algorithm to discover which station addresses are on which segments.
        Basically it notes the source address of frames and which segment they are coming from.
        (Builds up a table of MAC addresses and corresponding segments.)
        If it receives a frame with a particular destination MAC address it knows which segment to forward it to.
        
        Simple
        With the simple bridge when it is set up the MAC addresses of the stations on each LAN segment must be added into the internal table manually.
        When a new station is added, the table must be modified.
        
        Switch
        Layer 2
        It looks at MAC address to make traffic flow decisions
        
        Modular Switches
        Allows you to add expansion modules into the switches as needed, thereby delivering the best flexibility to address changing networks
        
        Fixed Configuration Switches
        Are switches with a fixed number of ports and are typically not expandable.
        
        Unmanaged Switches
        Are the most cost effective for deployment scenarios that require only basic layer 2 switching and connectivity.
        
        Smart Switches
        Are the most blurred and fastest changing.
        The general rule here is that these switches offer certain levels of Management, QoS, Security, etc. but is “lighter” in capabilities than the Managed switches
        
        Managed Switches
        Are designed to deliver the most comprehensive set of features to provide the best application experience, the highest levels of security, the most precise control and management of the network, and offer the greatest scalability in the Fixed Configuration category of Switches.
        As a result, they are usually deployed as aggregation/access switches in very large networks or as core switches in relatively smaller networks
      - Network layer (IP protocol)
        IP transports data in packets called datagrams.
        Does not keep track of the routes and has no facility for re-ordering datagrams
        
        Routers
        (Physical, Data-link & Network layers)
        They make packet forwarding decisions based on logical addresses in the header of the packets
        
        Token
        A packet travelling on one token-ring network to another token-ring network uses the services of a router
        
        Shortest Path
        Least expensive route,
        least distant route, path with the smallest number of steps
        
        Routing
        
        Static
        A static routing table contains information entered manually
        Dynamic
        A dynamic routing table is updated periodically using one of the dynamic routing protocols such as RIP, OSPF or BGP
        Routing Table
        Mask
        defines the mask applied to the IP address. In host-specific and default routing the mask is 255.255.255.255.
        In an unsubnetted network the mask is the unsubnetted mask for the class.
        Reference Count
        Is the number of users using this route at any moment.
        Destination Address
        Is a network address for network-specific routing or a host address for host-specific routing
        Use
        Is the number of packets transmitted through this router for the corresponding destination.
        Interface
        Is the name of the interface. Each interface has a unique IP address
        
        Routing Methods
        
        Next-Hop Routing
        Next hop is a routing term that refers to the next closest router a packet can go through.
        The next hop is among the series of routers that are connected together in a network and is the next possible destination for a data packet.
        
        Network Specific Routing
        Is a technique in which instead of having an entry for each and every host connected to the same physical network, it has only one entry to define the address of the network itself.
        All the hosts are connected to same network as one single entity.
        
        Host Specific Routing
        Host specific routing means to first check if the destination address is on the same network as that of source address
        
        Default Routing
        This is the method where all routers are configured to send all packets towards a single router.
        This is a very useful method for small networks or for networks with a single entry and exit point
        
        Addressing
        
        Logical (IP) addresses
        
        Port Addresses
        
        Physical (link) addresses
        The physical addresses in a network model have authority over the network (LAN or WAN).
        The size and format of these addresses vary depending on the network.
        For example, Ethernet uses a 6-byte (48-bit) physical address that is imprinted on the network interface card (NIC).
        
        Specific addresses
        
        Packetising
        
        Internetworking
        
        Internet-working
        Internetworking is "the concept of interconnecting different types of networks to build a large, global network" such that any pair of connected hosts can exchange packets.
        Internet-layer (IP protocol)
        Packets in the Internet layer are called datagrams.
        An IP a datagram is a variable-length packet (up to 65,536 bytes) consisting of two parts: header and data.
        The header identifies the sender of the datagram (source ip address) and the receiver of the datagram (destination ip address)
        Data unit=datagram
        
        IPv6 Addressing
        
        IPv4 Addressing
        An IPv4 address is a 32-bit binary address.
        Each Internet address contains four bytes (32 bits) defining two fields: netid and hostid.
        Net ID
        defines the network
        Host ID
        identifies the host on the network . determining a packet's final destination
        
        Address Classes
        A
        if the first bit is zero is of class A
        ( 0xxx xxxx.hostid.hostid.hostid)
        (2^7) Class A networks and (2^24-2) nodes ,
        default subnet mask 255.0.0.0
        B
        if the second bit is zero is of class B
        ( 10xx xxxx.xxxx xxxx .hostid.hostid)
        (2^14) Class B networks and (2^16-2) nodes,
        default subnet mask 255.255.0.0
        C
        if the third bit is zero is of class C
        ( 110x xxxx.xxxx xxxx.xxxx xxxx.hostid )
        (2^21) Class C networks and (2^8-2) nodes,
        default subnet mask 255.255.255.0
        D
        if forth bit is zero is of class D
        ( 1110 xxxx.xxxx xxxx.xxxx xxxx.xxxx xxxx ),
        Multicast address no netid or hostid
        E
        if all 4 bits are one than is of class E
        ( 1111 xxxx.xxxx xxxx.xxxx xxxx.xxxx xxxx ),
        reserved class no netid or hostid
        
        Subnetting
        a network is divided into smaller subnetworks with each subnetwork (or subnet) having its own subnetwork address
        
        Three-Level Addressing
        Now when the datagram arrives at the router the interpretation of the IP address changes.
        The router examines the third byte to determine which subnetwork to forward the datagram to.
        The routing of the IP datagram now involves three steps: delivery to the site, delivery to the subnetwork and delivery to the host.
        
        Masking
        Is a process that extracts the address of the physical network from an IP address.
        The part of the mask containing 0s defines the hostid.
        
        Supernetting
        several networks are combined to create a supernetwork
        
        Fragmentation
      - Transport layer
        (TCP-UDP)
        
        Gateways (all layers)
        A Gateway is a special type of Router that acts as a protocol convertor and operates in
        all 5 layers
        of the TCP/IP model.
      - TCP/IP
        
        Virtual Lan's
        The whole idea of Virtual LAN (VLAN) technology is to divide a LAN into logical, instead of physical, segments.
        Each VLAN is a workgroup in an organisation. If a person moves workgroup there is no need to change physical connections
        Characteristics
        Vendors use different characteristics such as: Switch port numbers MAC addresses IP addresses IP multicast addresses or a combination of two or more of the above
      - Application layer
        (TCP/IP)
        Data unit = message
- - - - 1 Pulse Amplitude Modulation (PAM)
        Takes the original analog information, samples it at equal intervals and generates a series of pulses based on the result of the sampling.
        
        2 Pulse Code Modulation (PCM)
        Quantitise the PAM signal,
        Quantitisation is the process of assigning integral values to the PAM pulses
        analog-to-digital conversion
        
        Sampling
        analog-to-digital conversion
        digital-to-analog conversion
        Sampling Rate
        Is the number of samples taken per second.
        To ensure accurate reproduction of an analog signal the sampling rate should be at least twice the highest frequency in the analog signal.
        Sampling Rate >= 2 * Freq(max.)
      - Line Coding
        Is the code used for data transmission of a digital signal over a transmission line. Bits to electric pulse
      - Digital
        An electrical signal that is converted into a pattern of bits.
        Only a limited number of values
        
        Digital signals are more resilient against noise than analog signals.
    - - Frequency
        Refers to the number of cycles per second.
        Unit of Frequency is the Hertz
        
        Formula
        six periods in 1 sec = 6Hz**
        As frequency increases
        As frequency increases the period decreases
      - Wavelength
        Is the distance, measured in metres, for one cycle as it travels through a medium eg. the air
        Frequency and wavelength are inversely related
        
        Frequency x Wavelength = speed
        Propagation Speed
        Air or Space = 300,000 km/s
        Cat5e TP cable = 200, 000 km/s
        Optical fibre = 222,000 km/s
        As wavelength Decreases
        As wavelength decreases, frequency increases
      - Bandwidth in hertz (analogue)
        Is the difference between the
        highest and the lowest frequencies contained in that signal.
        
        Bandwidth in bps (digital)
        Bandwidth in bits per second, refers to the speed of bit, transmission in a channel or link.
      - Period
        Refers to the amount of time, in seconds, a signal needs to complete one cycle.
        Unit of Period is the Time/Second
        
        Formula period = 1/6s
      - Analog
        Is a continuous signal that contains time-varying quantities.
        Infinite number of values in a range
        
        Sine Wave
        Is periodic and continuous
    - - Signal
  - - - Serial
        If 8 bits are sent together, they will travel on the same line, one after another
        
        Synchronous
        We send bits one after another without start/stop bits or gaps.
        It is the responsibility of the receiver to group the bits.
        Does not have: a start bit, stop bit, gaps between bytes
        
        Asynchronous
        We send 1 start bit (logic 0) at the beginning and 1 or more stop bits (logic 1s) at the end of each byte.
        There may be a gap of variable duration between each byte.
        Gap time between bytes is variable
    - - Parallel
        If 8 bits are sent together, we need eight lines.
        Signals may interfere with each other