Types of devices

everything is connected
hosts - the end systems which run network apps

packet swtiches - forward packets (chunks of data) communcation links - fiber, copper, radio, satellite - transmission rate: bandwidthc networks - collection of devices routers

links managed by organisation

internet structure

network edge

hosts: clients and servers
- servers (often in data centres)

access networkds, physical media

wired inks
wireless communcation links

network core

"backbone"
interconnected routers
network of routers

internet is a network of networks

edge devices

sending function
- takes app message
- break into packers
- transmit them
recieving function
- recieve packets
- reasseble to create app message

communication Medias

physical media

wired links
twisted pair cable (TP) - twist to the distance between the noisy source is roughly uniform
- two insludate copper wires twisted together
- one carries signal and the other is used as ground reference
- reciever uses the different between the two
- shielded vs unshielded
  - sheld can resits internal and external interference
  - more expensive but faster data rate
- abt 10MBPS to 1- Gbps
- max distance about 100 meters
- telephone, DSL, ethernet LAN

Coaxial cable

central inner conductor
outer conductor as a shield
special insulation
long distance at high speed
cable TV, ethernet LAN
no grouding wire because the shield protects it and the signal is more stable

Fibre-optic cable

glass fibre carrying light pulses
high speed 10 -100 GBps
low error rate

wireless media

wireless radio
- signal carried in electro magnetic spectrum
- broadcast, half-duplex
- propagation environment effecs
  - reflection and obstruction
  - interference/noise
radio link types
- wireless LAN (WiFi)
- wide area (e.g., 4g cellular)
- 10's Mbps over ~10km
- bluetooth - short distance, limited rates
- satellite - up to 45 Mbps per channel

Packet and circuit switching

network core
- many routers connect to subnets
Router
- two functions
- forwarding
  - aka switching
  - local action: move arriving packets from routers input link to appropriate output link
  - looks at fowarding table and sends to appropriate output link depending on the header
- routing
  - global action: determine the source-destination paths taken by packets
  - routing algorithms
  - creates fowarding tables

packet switching

host break application layer messages into packets
network fowards packets from one router to the next, across links on path from source to destination

store and fowards: entire packet must arrive at trouter before it can be transmitted on next link packet queueing: occurs when work arrives faster than it can be serviced

network protocol

network performance metrics

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