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Network Devices & Wiring Geert Jan de Groot Network Wiring • • • • • Half/full duplex Ethernet Network Wiring Autonegotiation Structured wiring Optics Half duplex • Ethernet is CSMA/CD (Carrier Sense Multiple Access/Collision Detection) • Only one station transmitting simultaniously • Listen before you transmit • Listen while you transmit Half duplex (2) • If there is a collision, both transmitters will: – – – – Jam Backoff (exponentially, randomly) Re-try sending the packet Minimal packet size: 64 bytes • Collisions are harmless! – Actually help scale / stabilize an ethernet network Full duplex • Allows transmission/reception simultaniously – Impossible on older coax media – Easy to implement on twisted pair/fiber media • No collisions • More bandwith available Copper Ethernet media • Coax (10 Mbit/sec) – now obsolete • Twisted pair – – – – – Uses pair 1-2, 3-6, 4-5, 7-8 10 Mbit/sec (10BASE-T) 100 Mbit/sec 1000 Mbit/sec (‘gigabit ethernet’) (10.000 Mbit/sec) A few words on 10BASE-T • Available everywhere today • Uses pair 1-2, 3-6 – Unshielded twisted pairs – Often miswired • Typically half-duplex – Full duplex possible • Max length 100 meters! 10BASE-T cables Normal cable Used from host to hub Crossover cable Used hub to hub or host to host Some hubs have built-in crossovers 100 Mbit copper networks • 3 standards: – 100BASE-TX <<-- Winner – 100BASE-T4 – 100VG-Anylan • Requires Category 5 (‘CAT5’) cabling – No more, no less • 100BASE-TX runs on 2 wire pairs – 1-2, 3-6, like 10BASE-T • Cheap today Faster: Gigabit Ethernet • 1000 Mbit/sec, 1000BASE-T • Still works on CAT5 cabling – Tight fit • Uses all 4 wire pairs – In both directions • About to get cheap and common – $35 SRP for a gigabit network card • Automatic crossover additional new feature Gigabit Ethernet and packet size • Faster ethernet historically kept 1500 byte packet size – Made bridging between speeds possible • Part of gigabit industry wants bigger packets – Lower overhead, hence higher performance • Bigger packets not part of standard – Unresolved issues – I believe wrong way to go Future: 10 Gigabit Ethernet • 10 Gigabit originally only on fiber • 10 Gigabit on copper currently being investigated by IEEE 802.3 standards committee Link pulses • 10BASE-T sends link pulses when idle – used to test integrity of link – link light • 100BASE-T uses faster link pulses – Automatic detection between 10 and 100 possible • Manual setting of half/full duplex – Settings must match Autonegotiation • Method to automatically select ‘best’ transmission method between link partners • Link pulse now becomes pulse train • Automatically sets speed, duplex etc Autonegotiation (2) • ‘Parallel detection’ for devices w/o autonegotiation – 10BASE-T and 100BASE-TX only – Only HDX • Autonegotiation mandatory for gigabit ethernet • Technology is mature now – Early chips had serious issues, so be aware Autonegotiation failure mode 100Mbit FDX Autonegotiation • One end set to fixed 100Mbit, Full-Duplex • Other end uses autonegotiation • What happens? Structured wiring “Everything over the same wiring” Wire Types • • • • • Category 3: 10 Mbps Category 4: 16 Mbps (for token ring) Category 5: 100 Mbps / 1000 Mbps Shielded or unshielded Advice: use Cat 5 UTP (unshielded twisted pair) • Category 6, 7 and higher marketing hype – Not official IEEE spec Structured wiring pitfalls • High installation cost – so install enough the first time • Use materials that are qualified for Cat 5 • Get guarantee from installer Fiber optics • Must use fiber between buildings – Cable length restrictions – Lightning protection • Multi mode: short hauls • Single mode: long hauls Fiber optics (2) • Different fiber diameters • Different connector types – – – – ST generally ‘older’ 10mbit stuff SC newer, generally 100mbit VF45 Others Fiber optics (3) • • • • 10BASE-F for 10Mbps ethernet 100BASE-FX for 100Mbps fast ethernet 1000BASE-SX/LX for gigabit ethernet No autonegotiation – Colours are different – HDX doesn’t make sense • Advice: run more fibers than you need, but don’t terminate them (yet) Hubs, Switches and Routers How do they work? What are the differences? Packet headers Ether IP TCP Data Edst Esrc T IPsrc IPdst Network devices may use {ether, IP} headers to do it’s job (sometimes in twisted ways) Ethernet hub Hub Ethernet hub (2) • • • • • Hub is layer 1 device Hub does not filter packets Whole hub is one collision domain Daisychaining of hubs limited Cheap • Doesn’t exist for Gigabit Ethernet Ethernet Switch Switch Ethernet Switch (2) • Switch looks at ethernet headers (layer 2) – ethernet to ethernet only • Learns what addresses are connected to which ports • If destination of packet known, the packet is only sent to the destination port Ethernet Switch (3) • Each port is a separate collision domain – no daisychain limit • Often one host per port – high performance • Security features • Dualspeed ‘hub’ includes switch Router Router Router Router (2) • Router works on IP header (layer 3) • Can use almost any underlying media – LAN or WAN • Can have several ports • Useful for long distance connections (backbone) • Must be configured – IP addresses etc. .