Network Devices

1
Network Devices

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

2
Packet headers
IP
TCP
Data
Ether
Edst
Esrc
T
IPdst
IPsrc
Network devices may use ether, IP headers to do
its job (sometimes in twisted ways)
3
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)

4
Collisions (1)

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

5
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

6
Thick ethernet (10base5)
7
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

8
Thin ethernet (10base2/BNC)
9
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

10
10base-T (TP)
Hub
11
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

12
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

13
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

14
10baseT cables
Crossover cable Used hub to hub or host to host
Normal cable Used from host to hub
Some hubs have built-in crossovers
15
n-way autonegotiation

• link pulses now encoded
• carry information about senders capabilities
• full/half duplex, 10Mbps/100Mbps
• Announce your own capabilities
• Receive neighbours capabilities
• Automatically choose highest common set of
  capabilities
• Parallel detection of link pulses for backward
  compatibility

16
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

17
Ethernet Repeaters
Repeater
18
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

19
Bridges
Bridge
F
E
A
B
C
D
20
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

21
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

22
Ethernet Switch
Switch
23
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

24
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

25
Router
Router
Router
26
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.

27
Structured wiring

• Everything over the same wiring

28
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

29
Structured wiring pitfalls

• High installation cost
• so install enough the first time
• Use materials that are qualified for Cat 5
• Get guarantee from installer

30
Fiber optics

• Must use fiber between buildings
• Cable length restrictions
• Lightning protection
• Multi mode short hauls
• Single mode long hauls

31
Fiber optics (2)

• Different fiber diameters
• Different connector types
• ST generally older 10mbit stuff
• SC newer, generally 100mbit
• VF45

32
Fiber optics (3)

• 10BaseF for 10Mbps ethernet
• 100BaseFX for 100Mbps fast ethernet
• 1000BaseSX for gigabit ethernet
• Advice run more fibers than you need, but dont
  terminate them (yet)

33
Faster ethernet

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

34
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

35
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

36
Fast ethernet over fiber

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

37
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 dont buy cat6/7/whatever

38
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

39
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

40
10gbit ethernet

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