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OSI Layer 1: Physical Layer

OSI Layer 1: Physical Layer. David Turton Conestoga College Institute of Technology & Advanced Learning http://www.conestogac.on.ca/~dturton Doon 1D17 x3610. OSI Layer 1 - Physical. Electrical connections & signaling Standard examples: Bit 0 is +2.5v Bit 1 is –2.5v

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OSI Layer 1: Physical Layer

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  1. OSI Layer 1: Physical Layer David Turton Conestoga College Institute of Technology & Advanced Learning http://www.conestogac.on.ca/~dturton Doon 1D17 x3610

  2. OSI Layer 1 - Physical • Electrical connections & signaling • Standard examples: • Bit 0 is +2.5v • Bit 1 is –2.5v • UTP standards, RJ45 pin-outs, etc. • Hardware: cable/media, hubs, repeaters

  3. Network Interface Card (NIC) Cabling or media Hub: Layer-1 device Switch: Layer-2 device Wireless networking: radio, infrared, satellite Wireless access point

  4. Coaxial Cable • Construction: • Copper core, insulation, metal shielding, insulating sheath • Good resistance to RFI & EMI interference • Older coaxial Ethernet cables: • 10base5 - Thick Ethernet (RG8) • 500M maximum length • Connector: vampire clamp & transceiver • 10base2 - Thin Ethernet (RG58) • 185M maximum length • Connector: BNC (British Naval Connector) • Coax is no longer used in networks • Mostly in cable TV (CATV) • RG-59 (ok) and RG-6 (better) grade cables RG: radio grade

  5. UTP Twisted-Pair Cable STP • 4 pairs of wires • Solid cores • Infrastructure: in walls & ceilings (don't move) • Cheaper, easier to connect, less signal attenuation • Stiffer – strains connections if used as patch cable • Max length (10/100baseT): 100M • Stranded cores • Patch cables: PC to wall jack, switch to BIX panel • More expensive, flexible (to route around desks) • Poorer electrical performance: • Max length (10/100baseT): 10-25M ? • Twists • Reduce cross-talk between pairs Foil shield Ground wire

  6. Cable Descriptorseg: 10baseT, 100baseT, 1000baseT, 10GbaseT • 10, 100, 1000 • Transmission speed in Mb/s (megabits per second) • 10 and 100 Mb/s – use 2 pair • 1,000Mb/s (1Gb/s) – uses 4 pair • 1000baseTX – 1Gb/s over 2 pair; defunct: required CAT6 • base • Baseband – one signal at a time on media • T • Twisted-pair (copper) • 100baseTX • Specific refinement of general 100baseT category

  7. Twisted-Pair gradesMHz – megahertz: millions of cycles per second • CAT 3 – 16Mb/s • 100M @ 10baseT • CAT 5 – 100MHz • 100M @ 100baseT • CAT 5e – 100MHz* • 100M @ 100baseT • <100M @ 1000baseT * • CAT 6 – 250MHz • 100M @ 1000baseT • 37-55M @ 10GbaseT • CAT 6e – 500Mhz • 100M @ 10GbaseT * Minimum CAT 5e standard is 100MHz, but manufacturers claim "tested to 350MHz"

  8. Twisted-Pair Connectors • RJ45 – networking (8 contact-points) • Shielded or unshielded • Metal jacket connects grounding wire on cable to switch/PC • Usually for solid or stranded cable … newer ones do both • Solid: v-shaped cutter • Stranded: plunge cutter • Also: • Pull-through (newer) or closed-ended (traditional) • Wire-guide insert (transition) • Note: • Use connector rated for the cable grade • CAT6 is thicker cable than CAT5e • But RJ45 external dimensions the same • Wire guides slightly offset, rather than side-by-side

  9. RJ45 Connectors Shielded RJ45 plug RJ45-to-RJ45 coupler Unshielded RJ45 plug Shielded, with strain relief Unshielded, no strain relief Unshielded RJ45 Keystone jack for wall outlet Shielded RJ45 Keystone jack

  10. BIX 100 punch-down block Mounted on a rack, RJ45 jacks on other face to connect to switch Keystone jack Punch-down tool to seat & trim wires Different cutters for 110 and Keystone Wall plate for Keystone jack

  11. Fire Rating(UL – Underwriters Laboratories) • Concerns: • Conducting fire through building & noxious fumes • UL1581 - General purpose: • Enclosed in walls or conduit (pipe) • UL910 - Plenum: • Horizontal in free-flowing air • Ducts, suspended ceilings • UL1666 - Riser: • Vertical in free-flowing air • Between floors

  12. RFI & EMIfibre-optic is immune, though expensive • RFI • Radio Frequency Interference • Short-wave, CB radios, microwaves • EMI • Electromagnetic Induction • Machinery, trucks/loaders, florescent lights • Both induce current (noise) in metal wires • Create errors in signals • Force re-transmissions, increasing traffic load

  13. STP vs UTPshielded or unshielded? • UTP • Unshielded twisted pair • Usually OK, but not around machinery • STP • Shielded twisted-pair • Metal foil inside plastic casing, sometimes around wire pairs • Grounded at one end (OK), or both ends (better) • Reduces or eliminates RFI & EMI • Ground loop - different grounds at ends • Creates a voltage in shield • Can heat wire and interfere with signal • Shield not grounded • It becomes an antenna

  14. Ground Loop Situation Switch in office here Cables are 60M long Buried in conduit, in tunnel across roadway, run beside machinery, 10Mb/s required now Used CAT 5E STP, direct-burial grade Grounds are likely to be at different potential Will cause voltage in shield  Causing interference Grounded one end, at switch or camera IP cameras here

  15. UTP/STP pin-out logicTerminating vs Communication Equipment • DTE – Data Terminating Equipment • Signal ends here, is not passed on • Hosts: computers, servers, printers & routers • DCE – Data Communication Equipment • Pass signals from one DTE device to another • Switches, hubs For 10baseT & 100baseT: • Pins 1 & 2 on DTE are transmit • Pins 1 & 2 on DCE are receive • I talk  you hear • Pins 3 & 6 on DTE are receive • Pins 3 & 6 on DCE are transmit • You talk  I hear receive green T568B transmit orange blue brown 1 2 3 4 5 6 7 8 It's almost as if the 3-6 pair is split to keep the other pairs away from each other

  16. MDI-X switch portsExtending networks by daisy-chaining switches • MDI - Medium Dependent Interface • Network interface on a PC • MDI-X • Network interface on a switch • Transmit/receive pins reversed • PC-to-switch connections • Use straight-through cables • Pin 1  pin1, pin 2  pin 2, etc. • Switch-to-switch extensions? • Use dedicated MDI-x or switched MDI/MDI-x port • Use a crossover cable( ): 13, 26, etc. • Most switches today detect & switch MDI-X to MDI • Can use a straight-through cable between switches 3rd floor PCs 2nd floor PCs 1st floor PCs servers

  17. Wiring Patterns • Straight-through: 11, 22, etc. • To connect DTE to DCE • Computer to switch • Crossover • To connect similar devices: • DTEDTE (computer to computer) • DCEDCE (switch to switch) • Rolled cable • Connect network port to serial port • Computer to router’s console port • Loopback • Connect your input pins to your output pins • To test your network card

  18. Wiring Standards • 568A & 568B • Pick a standard...and stay with it • Either will work • Patch cables are usually 568B • Same standard both ends: • Straight-through cable • 568A one end, 568B other: • 10/100baseT crossover oranges split around blues receive green T568B greens split around blues transmit orange blue brown 1 2 3 4 5 6 7 8

  19. Cross-Over Cablesused between similar devices:switch-to-switch, PC-to-PC, router-to-router • 10/100baseT – 2 pair used • 1  3 • 2  6 • 3  1 • 4  4 (unused) • 5  5 (unused) • 6  2 • 7  7 (unused) • 8  8 (unused) • 1000baseT – all 4 pair used • 1  3 • 2  6 • 3  1 • 4  7 • 5  8 • 6  2 • 7  4 • 8  5 • Or just use straight-through • And rely on auto-sense MDI/MDI-X

  20. Rollover Cable • Used to connect to serial console port on Cisco routers • So can use HyperTerminal to talk to it. • Use same 568A or 568B pin-out on both ends • Like a straight-though cable • Just have the tab up on one end, down on t’other

  21. Hardware Loopback10/100baseT simulation • PC sees own output as input • Used to test network card • When NIC has hardware diagnostics • RJ45 jack wired one pin to another • 1-3, 2-6

  22. Fibre-Optic Cables • Immune to RFI & EMI • Glass or plastic core, refractive cladding • 1 to 40km without repeaters • Expensive & difficult to install • Cut/polish ends exactly square, no splinters • Switch port or transceiver converts back to copper • Kink, sharp turn … it's broken • SMF – single-mode fibre-optic cable • High speed, long distance, one signal • MMF – multi-mode fibre-optic cable • Multiple signals • High speed, high bandwidth, medium distance

  23. Fibre-Optic Connectors Newer, smaller More connections in same space Transmit & receive fibres are in one connector Pre-terminated ends – easy to use Older, but Popular ST (straight tip) BNC-like connections Easy to connect Most popular MT-RJ • LC • Becoming more popular • fibre-channel to SANs • Gig Ethernet switches SC (square connector) Latch connector

  24. Physical Topologies Main LAN topologies: bus star ring

  25. Bus Topology • Common with coaxial cables • Max network length: 185M without repeaters • Cable goes from T-connector on one device • To T-connector on next device

  26. Bus Topology • All computers see all traffic • Only 1 message on network at a time • Only read in stuff addressed to them • Can modify interface to "sniff" traffic & snoop on others • Difficult to troubleshoot • Continuous line end-to-end • Need terminators (resistors) to stop "echo" • A break takes whole network down. • Not scalable • Break network to add/move a computer • Limits: number of devices, total cable length, bandwidth, collision/resend, etc.

  27. Star Topology • Devices connect to a central hub or switch • Using twisted-pair cables • Easier to troubleshoot: • One computer down: • Check hub port, cable, computer • All computers down • Check hub (single point of failure) • Scalable: • Just plug in another computer • Can daisy-chain additional hubs • Up to 100M host-to-hub • Hub is a repeater Hub Max 100M

  28. Ring Topology • Each computer connected to 2 neighbours • 2 cables per computer: ring in/ring out • Everyone "sees" everything… • No contention: • Can attain full rated speed • Adds, moves & cable faults • Take whole network down • Harder to troubleshoot • Common in WANs, not LANs • SONET has a backup ring to bypass faults

  29. Mesh Topology • Every device connects to every other device • n(n-1)/2 connections • Very fault-tolerant • Very expensive • Difficult to manage/maintain • Internet • Modified or hybrid mesh 4 hosts  6 connections Add one … 5 hosts  10 connections 6 hosts  15 connections

  30. Point-to-Point • Direct connection between two devices • Common on WAN links • Physical connection between routers • Logical connection in connection-oriented protocols (Frame Relay) WAN link between routers Cable/DSL/modem to ISP's router Ethernet, serial, parallel, wireless

  31. Point-to-Multipoint • One device to multiple devices • Dedicated connection to each remote device • Connections are all part of same network • Structure of Internet • Also as network backbone

  32. Hybrid Topologies • Combination of two or more topologies • Examples: • Star-bus: star configuration using a hub • Hubs have a shared bus between all the ports. • Star-ring: star configuration on a token-ring network • Point-to-point bridge connecting two star LAN segments

  33. Key point: TCO • Network's going to be there for 10 years or more • Ensure it is scalable • Computers will be added • Computers will be moved • Faster switches, faster PCs will be added • Cables are in walls & ceilings • Costly to replace or upgrade • Pray for dropped ceilings! • Ensure cables are rated for future speeds • And connectors…

  34. RepeaterHub  a multi-port repeater • Interprets and regenerates signals before they’re unintelligible • Voltage (signal strength) diminishes over distance (attenuation) • Interference induces noise (waveform damage) in signal • Doesn't just amplify the signal • That would not repair the waveform 10base2: 185M UTP: 100M Repeater Initial signal: +2.5v – bit 0 -2.5v – bit 1 Still readable, but just Regenerated: +2.5v – bit 0 -2.5v – bit 1

  35. Layer-1 Devices:Hubs & Repeaters

  36. Layer-1 Devices:Hubs & Repeaters • Used to extend LAN distance • Regenerate & forward signals, indiscriminately • They have an internal bus • All ports are connected together • Only one transmission is allowed at one time • 8 hosts on 10baseT or 10base2: • Average 1.2Mb/s per host • Can interpret between media • Convert from coax to UTP to fibre

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