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Introduction

Introduction. Basic Concepts. Line configuration Topology Transmission mode Categories of networks Internetworks. Line Configuration. Two or more comm devices attached to a link Link is a physical communicating path to transfer data. Point – to – Point. Dedicated link b/w two devices

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Introduction

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  1. Introduction

  2. BasicConcepts • Line configuration • Topology • Transmission mode • Categories of networks • Internetworks

  3. Line Configuration • Two or more comm devices attached to a link • Link is a physical communicating path to transfer data

  4. Point – to – Point • Dedicated link b/w two devices • Entire capacity reserved between two devices • Normally actual path line of wire but microwaves & satellites links also possible • E.G Remote of a TV

  5. Multi Point Configuration • Also called multidrop • More than two devices share common link • Capacity of channel shared • If devices use link simultaneously • Spatially shared-in terms of space • Time shared-devices take turns

  6. Topology • Way a NW is laid out physically or logically • Two or more devices connect to a link • Two or more links form a topology • Geometrical representation of relationship of all links

  7. Possible Relationships • Peer to Peer : Devices share link equally • Ring • Mesh • Primary-Secondary :One device controls traffic & other must transmit through it • Star • Tree

  8. Mesh Topology

  9. Star Topology

  10. Tree Topology

  11. Bus Topology

  12. Ring Topology

  13. HYBRID TOPOLOGY

  14. The Internet • Loosely administered network of networks • Agreed procedures for access and intercommunication • Internetworking uses gateways, routers and firewalls • Gateways: convert data traffic from one network format to another. They link LANs to WANs and WANs to WANs

  15. An Analog signal is a continuously varying electromagnetic wave. (Clock with arm) • Have infinite values • Used in early telephone systems. • Analog signals had the drawback that they attenuate (weaken) over long distances. Needed amplifiers to boost the signals. However, amplifiers distort the signal and introduce noise. • A Digital signal is a sequence of binary voltage pulses (0’s and 1’s).It is discrete. Have limited values normally 0 & 1 • Digital transmission avoids the noise problem by encoding the analog signal into digital form. The digitized version is then sent across the network.

  16. Periodic & Nonperiodic Signal • Both analog and digital signal can take two forms • Periodic Signal : A signal which completes a pattern within a measurable time frame called Period and repeats the pattern. A sine wave is the simplest Periodic signal • The completion of one pattern is called Cycle • Period is amount of time required to complete one full cycle • Nonperiodic Signal: Also called Non-periodic which changes pattern over time. • In data comm periodic analog signal (use less bandwidth) and nonperiodic digital signals (variation in data can be represented) are used

  17. Units of Periods & Frequencies

  18. Example 1 Express a period of 100 ms in microseconds, and express the corresponding frequency in kilohertz. Solution From Table 3.1 we find the equivalent of 1 ms. We make the following substitutions: 100 ms = 100  10-3 s = 100  10-3 106ms = 105ms Now we use the inverse relationship to find the frequency, changing hertz to kilohertz 100 ms = 100  10-3 s = 10-1 s f = 1/10-1 Hz = 10  10-3 KHz = 10-2 KHz

  19. Wave Length • Wave length is another characteristic of signal moving through medium. Distance signal can travel in one period • It binds period or frequency of sine wave to the propagation speed of the medium • Frequency is in dependent of medium but wavelength depends upon both frequency and the medium • Generally used in Optical Fiber

  20. Wave Length Wave length = Propagation sp × period = Propagation / frequency Wave length is normally measured in micrometers(microns)

  21. Bandwidth • Range of frequencies contained in composite signal is its BW • The bandwidth is a property of a medium: It is the difference between the highest and the lowest frequencies that the medium can satisfactorily pass

  22. If a periodic signal is decomposed into five sine waves with frequencies of 100,300, 500, 700, and 900 Hz, what is the bandwidth? Draw the spectrum, assuming all components have a maximum amplitude of 10 V. Solution B = fh - fl = 900 - 100 = 800 Hz The spectrum has only five spikes, at 100, 300, 500, 700, and 900

  23. Bit rate & Bit Interval • Most digital signals are aperiodic thus period or frequency is not appropriate • Bit Interval is time required to send one single bit • Bit Rate is no of bits sent per second • Example: A digital signal has a bit rate of 2000 bps. What is the duration of each bit (bit interval) • Solution: The bit interval is the inverse of the bit rate Bit interval = 1/bitrate =1/ 2000 s = 0.000500 s=500microsec

  24. TRANSMISSION IMPAIRMENT • Signals travel through media, which are not perfect • The imperfection causes signal impairment • This means that the signal at the beginning of the medium is not the same as the signal at the end of the medium

  25. PERFORMANCE • In networking, we use the term Bandwidth in two contexts: • The first, bandwidth in hertz, refers to range of frequencies in a composite signal or the range of frequencies that a channel can pass • The second, bandwidth in bits per second, refers to the speed of bit transmission in a channel or link.

  26. Throughput It is the measure of how fast we can send data. It is different from BW. We may have B BW but may send only T bps Example: A network with bandwidth of 10 Mbps can pass only an average of 12,000 frames per minute with each frame carrying an average of 10,000 bits. What is the throughput of this network? Solution We can calculate the throughput as The throughput is almost one-fifth of the bandwidth in this case.

  27. Propagation Time Time required for a bit to travel from source to destination Propagation Time = Distance / Propagation Speed Example: What is the propagation time if the distance between the two points is 12,000 km? Assume the propagation speed to be 2.4 × 108 m/s in cable. Solution We can calculate the propagation time as The example shows that a bit can go over the Atlantic Ocean in only 50 ms if there is a direct cable between the source and the destination.

  28. Transmission Time Time required for transmission of all the bits. Transmission Time = Message size / Bandwidth Example: What are the propagation time and the transmission time for a 2.5-kbyte message (an e-mail) if the bandwidth of the network is 1 Gbps? Assume that the distance between the sender and the receiver is 12,000 km and that light travels at 2.4 × 108 m/s. Solution

  29. Example What are the propagation time and the transmission time for a 5-Mbyte message (an image) if the bandwidth of the network is 1 Mbps? Assume that the distance between the sender and the receiver is 12,000 km and that light travels at 2.4 × 108 m/s. Solution

  30. Latency Latency or delay is the time for a message to completely arrive at a destination from the time 1st bit left the source Latency = Propagation Time + Transmission Time +Queuing Time + Processing delay Jitter Variance in delay. More prominent in real time applications

  31. Multiplexing • When BW of a link is grater than BW requirement of devices, Link can be shared • It is technique that allows simultaneous transmission of multiple signal across single data link

  32. Dividing a link into channels • MUX: Combines n lines to 1 • DEMUX: Separates back into its components • Link refers to physical path • Channel refers to portion of link that carries transmission

  33. Categories of multiplexing

  34. FDM • Analog Technique • Applied when BW of link greater than combined BW of signals to be transmitted • Each sending device modulate different CF, which in turn combined into a composite signal for transmission • CF separated by sufficient BW to accommodate modulated signal • Channels are separated by strips of unused BW called GUARDBAND that prevent signals from overlapping • To use FDM for digital signal covert it to analog signal first

  35. WDM • WDM same as FDM except that it involves light signals • WDM is an analog multiplexing technique to combine optical signals • Designed for Fiber optic • Using Fiber optic cable for one single line wastes available bandwidth

  36. Synchronous TDM • Digital process • Each connection occupies portion of time in a link • Fig shows only multiplexing and not switching i-e source 1 to any but fixed destination

  37. Statistical TDM • Ensure no slot is wasted. Slots are not pre-assigned • Slots are dynamically allocated to improve BW • Unlike Sync TDM, total speed of input lines can be greater than capacity of path • Slots can be less than devices • Mux scan the input line until slots are filled the transmits

  38. LAN Medium • Connected directly • Signal constrained by Physical limit of media

  39. OSI Model Please DO NOT Touch Steve’s Pet Alligator

  40. Data Encapsulation • Data Encapsulation is the process of adding a header to wrap the data that flows down the OSI model. • The 5 Steps of Data Encapsulation are: 1. The Application, Presentation and Session layers create DATA from users' input. 2. The Transport layer converts the DATA to SEGMENTS 3. The NW layer converts the Segments to Packets (datagram) 4. The Data Link layer converts the PACKETS to FRAMES 5. The Physical layer converts the FRAMES to BITS.

  41. Types of Switching

  42. A Datagram Network With 4 Switches (Routers) • All packets may take different route, arrive out of order, lost or dropped in the way • These NWs are called connectionless NWs as Switch does not keep info about connection state, no setup or tear down phase

  43. A virtual Circuit Network • A virtual-circuit NW is in between a circuit-switched and datagram NW. It has some characteristics of both • It has setup, data transfer & tear down phases • Resources are allocated during setup phase as in circuit switched NW or on demand as in datagram NWs • Data are packetized & each packet carries an address (local jurisdiction only; add of next switch) in a header • All packets follow same path & implemented at data link layer • Virtual circuit NW is implemented in Datalink layer, circuit switched in Phy layer & Datagram NW in NW layer

  44. A virtual Circuit Network

  45. Single-bit error

  46. Burst error of length 5

  47. Protocols • Can not be used in real life

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