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174 lines
5.0 KiB
Markdown
174 lines
5.0 KiB
Markdown
---
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title: "16-networks"
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aliases:
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tags:
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- cosc203
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- lecture
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---
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# Types of devices
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- everything is connected
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- 
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- hosts - the end systems which run network apps
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packet swtiches - forward packets (chunks of data)
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communcation links - fiber, copper, radio, satellite
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- transmission rate: bandwidthc
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networks - collection of devices routers
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- links managed by organisation
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## internet structure
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network edge
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- hosts: clients and servers
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- servers (often in data centres)
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access networkds, physical media
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- wired inks
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- wireless communcation links
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network core
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- "backbone"
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- interconnected routers
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- network of routers
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internet is a network of networks
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## edge devices
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- sending function
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- takes app message
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- break into packers
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- transmit them
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- recieving function
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- recieve packets
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- reasseble to create app message
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# communication Medias
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## physical media
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- wired links
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- twisted pair cable (TP)
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- twist to the distance between the noisy source is roughly uniform
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- 
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- two insludate copper wires twisted together
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- one carries signal and the other is used as ground reference
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- reciever uses the different between the two
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- shielded vs unshielded
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- sheld can resits internal and external interference
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- more expensive but faster data rate
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- abt 10MBPS to 1- Gbps
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- max distance about 100 meters
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- telephone, DSL, ethernet LAN
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Coaxial cable
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- central inner conductor
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- outer conductor as a shield
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- special insulation
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- long distance at high speed
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- cable TV, ethernet LAN
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- no grouding wire because the shield protects it and the signal is more stable
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- 
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Fibre-optic cable
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- glass fibre carrying light pulses
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- high speed 10 -100 GBps
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- low error rate
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- 
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## wireless media
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- wireless radio
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- signal carried in electro magnetic spectrum
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- broadcast, half-duplex
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- propagation environment effecs
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- reflection and obstruction
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- interference/noise
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- radio link types
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- wireless LAN (WiFi)
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- wide area (e.g., 4g cellular)
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- 10's Mbps over ~10km
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- bluetooth - short distance, limited rates
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- satellite - up to 45 Mbps per channel
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# Packet and circuit switching
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- network core
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- many routers connect to subnets
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Router
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- two functions
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- forwarding
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- aka switching
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- local action: move arriving packets from routers input link to appropriate output link
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- looks at fowarding table and sends to appropriate output link depending on the header
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- 
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- routing
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- global action: determine the source-destination paths taken by packets
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- routing algorithms
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- creates fowarding tables
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packet switching
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- host break application layer messages into packets
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- network fowards packets from one router to the next, across links on path from source to destination
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- store and foward: entire packet must arrive at trouter before it can be transmitted on next link
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- packet queueing: occurs when work arrives faster than it can be serviced
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circuit switching
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- end-end resources allocated and reserved for "call" between source and destination
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- one connection is set up - reserved resources are not shared.
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- 
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- circuit segment is idle if not used by call
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- used for e.g., telephones
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# network protocol
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current network structure
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- 
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- composed of multiple subnets
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- a network of networks
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- not owned by one entity
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- you need to connect using an ISP e.g., spark vodaphone, 2degress
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- have their own network
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- provice access to users
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- not isolated from each other
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- connected using internet exchange point
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- or peering link?
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types of ISP
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- 
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- tier 1
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- potentially cover multiple countries
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- content provider networks e.g., google have a private network
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- often bypass tier-1, regional isps
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network protocol
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- a set of rules that dictate how to format, transmit and recieve data so that network devices can communicate
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- like a common language for computers
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- specifies a format
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- what in withing the packet
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- reciever can understand based on the format
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- complex layered design
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- explicit structure allows identification of systems pieces
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- modularization eases the maintenance
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- layer
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- each implements a service
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- via its on internal layer actions
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- relying on services provided by layer below
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TCP/IP reference model
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- application
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- exchanges message to implement a service using the services of transport layer
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- transport
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- transfers from one process to another using services of network layer
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- encapsulates application layer message, M, with transport layer-layer header H1 to create a transport-layer segment
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- Ht used by transport layer protocol to implement its service
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- network
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- transferse transport-layer segment from one host to another using link layer services
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- link
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- transfers datagram from host to neighboring host using network layer services
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- physical
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-
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# network performance metrics
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