1 / 92

Part 4

Part 4. Local Area Networks. LANs. The trend in LANs involves use of shared transmission media or shared switching capacity to achieve high data rates over short distances. Key issues: choice of transmission medium: Coaxial used in traditional LAN.

vadin
Télécharger la présentation

Part 4

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Part 4 • Local Area Networks

  2. LANs • The trend in LANs involves use of shared transmission media or shared switching capacity to achieve high data rates over short distances. Key issues: choice of transmission medium: • Coaxial used in traditional LAN. • Twisted pair (needs efficient encoding scheme to enable high data rates over the medium). • Wireless LANs.

  3. Chapter 12:LAN Architecture & Infrastructure Business Data Communications, 7e

  4. Objectives • Define various types of LANs and list the requirements that each is intended to satisfy. • Give some representative examples of LAN Applications • Discuss the transmission media commonly used for LANs. • List the various options provided in current LAN standards, and explain why the customer should limit purchase consideration to those standards.

  5. Objectives • Technology, Design and Commercial applications of LANs are rapidly changing. • These resulted in NEW SCHEMES for High-Speed local networking. • This chapter reviews underlying technology of LANs (various types & configurations options). • Alternatives of wired LANs. • LAN Protocol architecture. • Chapter 13 & 14 have discussion of specific LAN systems • Wireless transmission will be in chapter 14.

  6. Various types of Application Areas of LANs 1. Personal Computer LANs 2. Backend Networks and Storage Area Networks 3. High-Speed Office Networks 4. Backbone LANs 5. Factory LANs

  7. 1. Personal Computer LANs • Client/server communication • mixed PCs and servers and mainframes. • Shared resources • e.g. large disc (storage) or laser printer • Peer-to-peer communication • Low cost is high priority • i.e. the data rate in this type of network is low. “the higher the data rate the higher the cost”

  8. 2. Backend & Storage Area Networks Interconnect large systems e.g. mainframes, supercomputers, and storage devices i.e. “Computer room networks”. Their typical characteristics are: • High data rate • High-speed interface • Distributed access • Limited distance • Limited number of devices

  9. Storage Area Network (SAN) Configuration In a SAN the storage devices and servers are linked directly to the network.Internet users send file request to a bank of servers connected to a SAN which supports a number of mass storage devices.

  10. 3. High-Speed Office Networks • Increased processing and transfer requirements in many graphics-intensive applications now require significantly higher transfer rates • Decreased cost of storage space leads to program and file bloat, increased need for transfer capacity • Typical office LAN runs at 1-20Mbps, high-speed alternatives run at 100+

  11. 4. Backbone Local Networks Is The Network (Channel) Interconnecting LANs. Backbone is a high-capacity LAN interconnecting lower-capacity LANs within buildings or departments. • Used instead of single-LAN strategy • Better reliability • Higher capacity • Lower cost

  12. 5. Factory Networks • Key characteristics of a factory LAN include: • High capacity • Ability to handle a variety of data traffic • Large geographic extent • High reliability • Ability to specify and control transmission delays

  13. LAN Configuration • Tiered LANs: • various equipment (generally 3 categories) is supported in an organization: • PCs & WSs • Server Farms: expensive peripherals, mass storage, applications that require large resources, databases accessible by many users. Because of this shared use, these machines may generate substantial traffic. • Mainframes: needs bulk data transfer due to their large database & scientific applications. • Evolution Scenario; and their implications for the selection and management of LANs. • Bottom up • Top down

  14. Tiered LANs • Cost of attachment to a LAN tends to increase with data rate • Alternative to connecting all devices is to have multiple tiers • Multiple advantages • Higher reliability • Greater capacity (less saturation) • Better distribution of costs based on need

  15. Tiered LAN Strategies Evolution Scenario: • Bottom-up strategy: individual departments create LANs independently, eventually a backbone brings them together • Disadvantages: suboptimization, varieties makes interconnection more difficult • Top-down strategy: management develops an organization-wide networking plan • Advantage: built-in compatibility • Disadvantage: need to be responsive and timely at the department level

  16. Tiered LAN Diagram

  17. Guided Transmission Media • Twisted Pair • Unshielded & Shielded Twisted Pair (UTP-STP) • Category 3 and 5 UTP • Coaxial Cable • Optical Fiber • Structured Cabling

  18. Objectives • Describe Transmission Media • Guided • Unguided

  19. Classes of Transmission Media • Guided or Conducted Media • use a conductor such as a wire or a fiber optic cable to move the signal from sender to receiver • Unguided or Wireless Media • use radio waves of different frequencies and do not need a wire or cable conductor to transmit signals

  20. Factors Affecting Quality of Data Transmission • Characteristics of Medium • Characteristics of Signal Examples: • in guided media, the medium determines the limitations or characteristics of transmission • in unguided media, the bandwidth of the signal produced by antenna is more important in determining the characteristics of transmission(e.g. omnidirectional, directional beam signals)

  21. Key Concerns in Designing Transmission System 1. Data Rate 2. Distance

  22. Design Factors for Transmission Media 1. Bandwidth: All other factors remaining constant, the greater the bandwidth of a signal, the higher the data rate that can be achieved. 2. Transmission impairments. Limit the distance a signal can travel.(Descending degree of suffering: twisted wire, coaxial, optical fiber) 3. Interference: Competing signals in overlapping frequency bands can distort or wipe out a signal. 4. Number of receivers: Each attachment introduces some attenuation and distortion, limiting distance and/or data rate. (e.g. point-to-point, shared link with multiple attachments)

  23. ELF := Extremely low Frequency VF := Voice Frequency VLF := Very Low Frequency LF := Low Frequency MF := Medium Frequency HF := High Frequency VHF := Very High Frequency UHF := Ultrahigh Frequency SHF := Superhigh Frequency EHF := Extremely High Frequency

  24. Guided Transmission Media • Transmission capacity (data rate or bandwidth)depends on: 1. Distance 2. Medium being point-to-point or multipoint • Guided media commonly used: • twisted pair wires • coaxial cables • optical fiber

  25. Thickness = 0.4-0.9 mm 5-15 cm

  26. Twisted Pair Wires • Consists of two insulated copper wires arranged in a regular spiral pattern to minimize the electromagnetic interference between adjacent pairs • Often used at customer facilities and also over distances to carry voice as well as data communications • Low frequency transmission medium

  27. Twisted Pair Wires ApplicationData Rate(bps) Digital Data Switch 64 k LAN for PC 10 M Recent Networks 100 M Long Distance Appls.(ISDN) 4+ M

  28. Transmission Characteristics • Used for transmission Analog or Digital Signals • Analog, Amplifiers required every 5-6km • Digital, Repeaters required every 2-3km • used for limited distance, Bandwidth & data rate • Susceptible to Impairments: • Interference(e.g. picks 60Hz from ac power) • Picks Impulses • Picks Noise

  29. Remedy to Interference Problem • Shielding, metallic braid or sheathing • Twisting, reduces low-frequency interference. • Different twisted length reduces crosstalk • Modified Characteristics & Applications For point-to-point analog signal, 1 MHz, For long Distance Digital, data rate up a few Mbps For short Distance, 100Mbps or1 Gbps

  30. Types of Twisted Pair • STP (shielded twisted pair) • the pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic interference • The shielded twisted pair provide better performance at lower frequencies • UTP (unshielded twisted pair) • each wire is insulated with plastic wrap, but the pair is encased in an outer covering • Voice graded twisted pair is already installed in most offices, and may be used for LAN. The data rates and distances achievable with voice-graded twisted pair are limited.

  31. EIA-568 & EIA-568-A Standard • 1991, Electronic Industries Association (EIA) published EIA-568 for STP & UTP for 1-16 Mbps • 1995, EIA-568-A for STP & UTP up to 100 Mbps

  32. Ratings of Twisted Pair • Category 3 UTP • data rates of up to 16mbps are achievable • Category 4 UTP • Cables & connecting H/W for up to 20 Mbps • Category 5 UTP • data rates of up to 100mbps are achievable • more tightly twisted (0.6-0.85 cm) than Category 3 (7.5-10 cm) cables (THE KEY DIFFERENCE) • Tighter twist makes cat 5 more expensive, but better performance • STP(Sheilded Twisted Pair) • More expensive, harder to work with

  33. Twisted Pair Advantages • Inexpensive and readily available • Flexible and light weight • Easy to work with and install

  34. Twisted Pair Disadvantages • Susceptibility to interference and noise • Attenuation problem • For analog, repeaters needed every 5-6km • For digital, repeaters needed every 2-3km • Relatively low bandwidth (3000Hz)

  35. Comparison of STP & UTP • Attenuation: The strength of signal falls off with distance over any transmission medium. For guided medium is exp expressed as db/distance. It causes 3 considerations: • A received signal must have sufficient strength to be picked up by receiver. • Signal to noise ration must be high enough to be received without error. • Attenuation is an increasing function of frequency.

  36. On going EIA-568-A: Twisted pair categories & Classes UTP: Unshielded twisted pair FTP: Foil twisted pair SSTP: Shielded screen twisted pair

  37. Coaxial Cable (or Coax) • Used for cable television, LANs, telephony • Has an inner conductor surrounded by a braided mesh (D = 1-2.5 cm) • Both conductors share a common center axial, hence the term “co-axial” • Used to be very popular for LANs but rarely used for LANs today.

  38. Coax Layers outer jacket (polyethylene) shield(braided wire) insulating material copper or aluminum conductor

  39. Coax Advantages • Higher bandwidth/wider range of frequencies • 400 to 600Mhz • up to 10,800 voice conversations • Because of its shielded, concentric construction model it is much less susceptible to interference than twisted pair • Compared to twisted pair coax can be used over longer distances & supports more stations • Good immunity from electromagnetic interference-similar to STP • More capacity than STP (more expensive as well)

  40. Coax Disadvantages • High attenuation rate makes it expensive over long distance, • For Analog transmission requires amplifiers every few kilometers(more with higher f) • For Digital Transmission requires repeaters every kilometer (more with higher data rate i.e. bps) • Bulky

  41. Optical Fiber/Fiber Optic • A thin filament of GLASS or other transparent material through which a signal-encoded light beam may be transmitted by means of total internal reflection. • 2-125 m (10-6 m) • [Note m/10-3 vs M/106 as scaling factor] • Optical fibers are grouped together into optical cables

  42. Schematic Diagram

  43. Fiber Optic, Physical Description • Ultrapure fiber, lowest loss, difficult to manuf. • Higher loss multi-component glass fibers, economic, good performance • Plastic fiber, even less costly, moderate high loss, used for short distances

  44. Fiber Optic Cable • Relatively new transmission medium used by telephone companies in place of long-distance trunk lines • Also used by private companies in implementing local data communications networks • Require a light source with injection laser diode (ILD) or light-emitting diodes (LED) Trunk Lines: in communications, a channel connecting two switching stations. A trunk usually carries a large number of calls at the same time.

  45. plastic jacket glass or plastic cladding fiber core Fiber Optic Layers • consists of three concentric sections

  46. Fiber Optic & its principal Operation • Light from a source enters the cylindrical glass or plastic core. • Rays at shallow angles are reflected and propagated along the fiber. • Other rays are absorbed by the surrounding material • This form of propagation refers to as step-index multi-model (refers to variety of angles that will reflect).

  47. Fiber optic multimode step-index the reflective walls of the fiber moves the light pulses to the receiver Fiber optic multimode graded-index acts to refract the light toward the center of the fiber by variations in the density Fiber optic single mode the light is guided down the center of an extremely narrow core Fiber Optic Types & Signals

  48. Light Sources in Fiber Optics • LED: light emitting diode • Cheaper, greater temp. range, longer life • ILD: Injection laser diode • LASER Principle, more efficient, higher data rate

  49. Wavelength Windows in Fiber Optics There is a relation between Wavelength, type of transmission, and achievable data rate • Light propagates best at 3 wavelength centred at: 850, 1300, 1550 nm: (nanometers) (i.e. infrared below visible light which is 400-700 nm) • Loss is lower at higher wavelengths (lower frequencies) (λ=νT, λ=ν/f ) • Local applications 100Mbps & a few km use 850 nm LED light which is the cheapest. • 1300 nm LED or laser source for higher data rates and longer distances. • 1500 nm laser source for highest data rates & longest distances.

More Related