quartz/content/notes/16-networks.md

title	aliases	tags	sr-due	sr-interval	sr-ease
16-networks		cosc203 lecture	2022-10-20	3	250

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 foward: 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

circuit switching

• end-end resources allocated and reserved for "call" between source and destination
• one connection is set up - reserved resources are not shared.
• 
• circuit segment is idle if not used by call
• used for e.g., telephones

network protocol

current network structure

• 
• composed of multiple subnets
• a network of networks
• not owned by one entity
• you need to connect using an ISP e.g., spark vodaphone, 2degress
• have their own network
• provice access to users
• not isolated from each other
  • connected using internet exchange point
  • or peering link?

types of ISP

• 
• tier 1
  • potentially cover multiple countries
• content provider networks e.g., google have a private network
  • often bypass tier-1, regional isps

network protocol

• a set of rules that dictate how to format, transmit and recieve data so that network devices can communicate

• like a common language for computers

• specifies a format

  • what in withing the packet
  • reciever can understand based on the format

• complex layered design

  • explicit structure allows identification of systems pieces
  • modularization eases the maintenance
  • layer
    • each implements a service
    • via its on internal layer actions
    • relying on services provided by layer below

TCP/IP reference model

• application
  • exchanges message to implement a service using the services of transport layer
• transport
  • transfers from one process to another using services of network layer
  • encapsulates application layer message, M, with transport layer-layer header H1 to create a transport-layer segment
  • Ht used by transport layer protocol to implement its service
• network
  • transferse transport-layer segment from one host to another using link layer services
• link
  • transfers datagram from host to neighboring host using network layer services
• physical

TCP/IP protocol suite

• TCP - transmission control protocol
• IP - internet protocol
• 

OSI model

• two more layers
  • presentation
  • session
• 

network performance metrics

• bandwidth - maximum rate (bits/second) a link or network can theoretically transmit

• throughput - the actual reate a link or network is transmitting

• 

• nodal delay - delay at a single router

  • propagation delay - time to send data along a link
  • transmission delay
  • processing - time to find route within router
  • queueing
  • dnodal = dproc + dqueue + dtrans + dprop

• end-to-end delay - total delay to send a packet from source to destination

• packet loss

  • queue (aka buffer) preceding link in buffer had finite capacity
  • packet arriving to full queue dropped
  • lost packet may be retransmitted by previous node, by source end system, or not at all
  • also lost due to corupted packets