Network Devices • Talk about network boxes • Packet headers • Different ethernet media • Different devices • Wires • Fiberlinks • Fast ethernet / gigabit ethernet

Packet headers IP TCP Data Ether Edst Esrc T IPsrc IPdst Network devices may use {ether, IP} headers to do it’s job (sometimes in twisted ways)

Types of ethernet addresses • Use ethernet addresses to be able to filter packets in ethernet receiver hardware (performance) • 3 types of addresses: – Unicast: single host – Multicast: group of hosts – Broadcast: all hosts – (tell by lsb of first byte of address)

Collisions (1) • Ethernet is CSMA/CD (Carrier Sense Multiple Access/Collision Detection) • Listen before you transmit • Listen while you transmit

Collisions (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

Thick ethernet (10base5)

10base5 • Thick, rigid cable • Separate transceivers, AUI cable • Inflexible • Vampire clamps (unreliable) • Cables do fall off • 10base5 not used much anymore • AUI connector itself very flimsy

Thin ethernet (10base2/BNC)

10base2 (2) • Thin cable (RG58/u) and BNC connectors • Max 185 metres • “Christmas tree problem” • Very cheap • Very unreliable • Getting obsolete, even in SOHO market

10base-T (TP) Hub

10base-T (2) • Classic ethernet used coax • Classic ethernet daisychained • Phone system uses twisted pair • Phone system star shaped • 10base-T applies ‘phone culture’ to computers

10base-T (3) • Hub is layer 1 device • Individual link integrity indicators • max 100 metres • Hub does not filter packets • Whole hub is one collision domain • Daisychaining of hubs limited • Cheap

•UTP ethernet (10baseT) • Unshielded twisted pairs • Two pairs of wires – one pair transmit – one pair receive • If idle, send link pulses • Simultaneous transmit/receive possible without collisions – Full duplex operation possible

•10baseT cables Normal cable Used from host to hub Crossover cable Used hub to hub or host to host Some hubs have built-in crossovers

•n-way autonegotiation • link pulses now encoded – carry information about sender’s capabilities • full/half duplex, 10Mbps/100Mbps • Announce your own capabilities • Receive neighbour’s capabilities • Automatically choose highest common set of capabilities • Parallel detection of link pulses for backward compatibility

n-way autonegotiation • Technology is mature now – Early chips had serious issues however, so be aware • Failure scenario: – Forced full-duplex on one side – Autonegotiation on other side • Causes full-duplex/half-duplex mismatch

Repeater Ethernet Repeaters

Repeaters (2) • Layer 1 device • ‘Amplifies’ the ethernet signal • Allows for multiple ethernet segments • Does not filter packets • Whole ethernet still one collision domain • Number of repeaters on same ethernet limited

Bridges Bridge A B C D E F

Bridges (2) • Layer 2 device • Bridges look at ethernet address: – left: A, B, C – right: D, E, F • Will retransmit packet from A to D • Will not retransmit packet from A to B

Bridges (3) • Left and right are separate collision domains (less collisions) • Store-and-forward: will wait for the whole packet to arrive completely (forward delay) • Not used much these days anymore • Often used approach for dualspeed (10/100) hubs

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 – like a bridge • Cut-through forwarding – starts output as soon as headers are known

•Ethernet Switch (3) • Each port is a separate collision domain • Usually multiple ports • Often one host per port – high performance – works like a very expensive hub • Security features

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.

•Structured wiring • “Everything over the same wiring”

•Wire Types • Category 3: 10 Mbps • Category 4: 16 Mbps (for token ring) • Category 5: 100 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

Fiber optics (3) • 10BaseF for 10Mbps ethernet • 100BaseFX for 100Mbps fast ethernet • 1000BaseSX for gigabit ethernet • Advice: run more fibers than you need, but don’t terminate them (yet)

Faster ethernet • Go from 10mbit/s to 100mbit/s • 3 competing standards: – 100base-TX – 100base-T4 – 100VG-Anylan

Fast ethernet: the losers • 100base-T4 – 100 mbit over cat3, 4 wire pairs (8 wires) – One wire pair fixed in each direction, two pairs can ‘switch’ direction – Half-duplex only • 100VG-Anylan – 100mbit over cat3

Fast ethernet: the winner • 100base-TX – 100 mbit over 2 wirepairs (just like 10base-T) – Requires cat5 wiring – Can run full-duplex – Defacto standard today – Very small price difference with 10mbit-only equipment these days – Has clearly won over 100baseT4 and 100VG Anylan by now

Fast ethernet over fiber • 100base-FX for fiber • No auto-negotiation, no speed selection

Still faster: gigabit ethernet • 1 gbit/sec (100 times faster then 10mbit) • Standard for fiber well established (1000base-SX) • Standard for copper defined recently, not much equipment available yet – Will run cat5, so don’t buy cat6/7/whatever

Gigabit ethernet • Non-mature first generation products died out now – Firstgen products generally lack performance • Requires special hardware to drive it (64-bit PCI) • Generally only full-duplex operation

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

10gbit ethernet • Currently IEEE study group • Pie-in-the-sky, no products yet