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Networking

Internet

nut bolt view

  • billions of connected devices
    • hosts - endpoints
  • packet switches
    • forward packets
    • routers, switches
  • communication links
    • fibre, copper, radio satellite
    • transmission rate - bandwidth
  • networks
    • collection of devices, routers, link managed by organization
  • internet - networks of networks
    • interconnected ISP's
  • protocols are everywhere
    • controls sending and receiving of messages
  • internet standards
    • IETF - Internet engineering task force
      • develops and promotes voluntary Internet standards, in particular the technical standards that comprise the Internet protocol suite
    • RFC - Request for comments, produced by IETF

services view

  • infrastructure that provides services to applications
  • provides programming interfaces to distributed application

Protocols

Protocols define the

  • format
  • order of messages sent and received among network entities
  • and actions taken on message transmission,
  • receipt

Internet structure

  • network edge
    • hosts - clients
    • servers - in data centers
  • access network, physical media
    • wired, wireless communication links
  • network core
    • interconnected routers
    • network of networks

Host: sends packet of data

  • host sending function

    • take application messages
    • breaks it into small chunks, known as packets of length \(L\) bits
    • transmits packets into access network at transmission rate \(R\)

  • same things:

    • network transmission rate
    • link transmission rate
    • link capacity
    • link bandwidth

  • packet transmission delay \(d_t\)

    • time needed to transmit \(L\) bit packet into link
\[ d_t = \frac{L}{R} \frac{(\text{bit})}{(\text{bit/s})} \]
  • bit - propagates between transmitter-receiver pair
  • physical link - what lies between transmitter and receiver
  • guided media - signal propagates in solid medium
  • unguided media - signal propagates freely

guided media

  • twisted pair (TP)
    • two insulated copper wire
    • category 5 - 100 Mbps - 1Gbps Ethernet
    • category 6 - 100 Gbps Ethernet
  • coaxial cable
    • bidirectional
    • broadband
      • multiple frequency channels on cable
      • 100 Mbps per channel
  • fibre optic cable
    • 10-100 Gbps

unguided media

  • wireless radio
    • wireless LAN wifi
    • wide area - 4g
    • bluetooth
    • terrestrial microwave
    • satellite

Network core

  • packet switching and circuit switching

Circuit switching

  • end to end resources allocated to, reserve for a call between source and destination
  • dedicated resources - no sharing
  • circuit segment is idle if not used by the call
  • was used in telephone networks
Multiplexing

Multiplexing is a technique used to combine and send the multiple data streams over a single medium. The transmission medium is used to send the signal from sender to receiver. The medium can only have one signal at a time. When multiple signals share the common medium, there is a possibility of collision. Multiplexing concept is used to avoid such collisions.

  • frequency division multiplexing (FDM)
    • electromagnetic frequencies - divided into narrow bands
    • each user gets its own band
  • time division multiplexing (TDM)
    • time divided into sots
    • each call is allocated periodic slot

Packet switching

  • host breaks application layer messages into packets
  • network forward packets form one router to another
  • across links from source to destination
  • two key networks core functions
    • forwarding/switching - local action
    • routing - global action
  • store and forward
    • packet transmission delay \(L/R\) seconds
      • to transmit a \(L\) bit packet into a link at \(R\) bps
    • store and forward
      • entire packet must arrive to router before it can be transmitted
  • queuing
    • occurs because packet arrives faster than they can be transmitted
    • if arrival rate exceeds the transmission rate queuing will occur
    • packets will be in queue, waiting to be transmitted on output link
    • packets can be dropped or if memory (buffer) in router fills up
how packet delay and loss occur
  • packet queue in router buffer, waiting for their turn in transmission
  • packet loss occurs when memory to hold queued packet fills up
delay sources

delay

\[ d_{nodal} = d_{proc} + d_{queue} + d_{trans} + d_{prop} \]
  • \(d_{proc}\) - nodal processing delay
    • check bit errors
    • determine output link
    • typically less than microsecond
  • \(d_{queue}\) - queueing delay
    • time wasting at output link for transmission
    • depends on congestion level of the router
    • \(a\) - average packet arrival rate in bits per sec
    • \(L\) - packet size in bit
    • \(R\) - transmission rate in bits per sec
    • traffic intensity = \(La/R\)
      • ~ 0 - small queuing delay
      • -> 1 - large queuing delay
      • > 1 - inf queuing delay
  • \(d_{tarns}\) - transmission delay
    • \(L\) - packet size in bit
    • \(R\) - transmission rate in bits per sec
    • \(d_{trans} = L/R\)
  • \(d_{prop}\) - propagation delay
    • \(d\) - length of the physical link
    • \(s\) - propagation speed
    • \(d_{prop} = d/s\)
  • transmission delay is the amount of time required to push all the packet's bits into the wire
  • queuing delay is delays encountered by a packet between the time of insertion into the network and the time of delivery to the address
  • processing delay is the time it takes routers to process the packet header
  • propagation delay is the time duration taken for a signal to reach its destination.
throughput
  • rate - bits per second - at which data is being send form transmitter to receiver
    • instantaneous - at given point
    • average - rate over longer period of time

How is it connected

  • host connected to
    • access isp connected to
      • regional isp
        • content provider network link google
      • global isp connected by
        • ixp - internet exchange point

isp

topology it defines how the network is connected

  • bus topology
  • star topology - this is most common now
  • ring topology
  • mesh topology

Protocol, layers, service models

why layering

  • to design complex systems
  • explicit structure allows identification, relationship of system pieces
  • modularization eases maintenance and updating the system

layered protocol stack

  • application
  • presentation
  • session
  • transport
  • network
  • data link
  • physical

osi osi osi

OSI Model

  • developed by iso
  • dod - department of defense model, later renamed to tcp/ip
    • most used now
  • osi - reference model, only rules and regulations
    • tcp/ip model - follow this
    • there are other models too,
  • other network protocols are
    • netware - used by windows earlier, for file sharing
    • appletalk
  • Open system Interconnection model
  • Develop by International organization for standardization
  • Reference model
  • Describe how information from software application in one computer move through physical medium to the software application in another computer.
  • 7 layers
    • Application Layer
    • Presentation Layer
    • Session Layer
    • Transport layer
    • Network Layer
    • Data-link layer
    • Physical layer
  • upper layer (application,presentation,session,transport)
    • deals with application related issues
    • implemented only in software
  • lower layer (Network,Data-link,physical)
    • deals with data transport issue
  • Each layer is self- contained , so that the task assigned to each layer can be performed independently.

layers

APSTNDP

  • application
  • presentation
  • session
  • transport
  • network
  • data link
  • physical

NOTE:

  • every layer have some PDU - protocol data unit which is the type of data present in that layer