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

\[ d_t = \frac{L}{R} \frac{(\text{bit})}{(\text{bit/s})} \]

Links - physical media

• 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

\[ d_{nodal} = d_{proc} + d_{queue} + d_{trans} + d_{prop} \]

• \(d_{proc}\) - 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

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 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

Application

• use
  • provide service to user
  • software generate the data
• protocols
  • Telnet/SSH
  • FTP/SFTP/SCP
  • SMTP/POP3/IMAP
  • HTTP/HTTPS
  • BGP
  • DNS
  • SNMP
  • NetBIOS
  • NTP
  • WINS
  • RIP/RIP2/RIPRng
• pdu
  • data

Presentation

• use
  • format of the data
  • compression and decompression
  • encrypt and decrypt data
  • for translation,encryption ,compression
• pdu
  • data

Session

• use
  • maintain the session via port numbers
  • like same website on different tabs on browser
  • or different application
  • data will not get intermixed
  • used to manage , establish ,terminate session
  • it allows the communication between two processes which can be either half-duplex or full-duplex.
  • adds some checkpoints when transmitting the data in a sequence.
  • Synchronization and recovery process - if error occurs in middle of transmission, then the transmission will resume from the checkpoint.
• pdu
  • data

transport

• use
  • main responsibility, transfer the data completely
  • receives the data from the upper layer and converts them into smaller units known as segments.
  • termed as an end-to-end layer,provides a point-to-point connection between source and destination to deliver data reliably.
  • ensures that messages are transmitted in the order in which they are sent and there is no duplication of data.
  • end to end delivery of the data
  • udp and tcp protocols are used
  • flow control - don't send more data
  • congestion control - too many packets in the network
  • segmentation - dividing into packets
  • error correction
• protocols
  • TCP
  • UDP
• pdu
  • segment

Network

• use
  • manages device addressing
  • tracks the location of devices on the network.
  • determines the best path to move data from source to the destination
  • routers used in this layer
  • ip address
  • source and destination address headers are added
  • routing is done
• protocols
  • IP
  • IPv6
  • SCP
  • ARP
  • RARP
  • ICMP
  • IGMP
• pdu
  • packets

Data Link

• use
  • used for error free transfer of data frames
  • source and destination mac address is added
  • FF:FF:FF:FF:FF:FF broadcast mac address, or add mac address of the gateway
  • they keep on changing when frame is passed between routers
  • ip address in never changed
• protocols
  • Ethernet Ring
  • Token Ring
  • Frame Relay
  • ATM
  • SONET
  • SDH
  • PD H
  • CD MA
  • GSM
• pdu
  • frames

Physical

• use
  • provide physical medium through which bits are transmitted
  • connecters, cables, hub, work on this layer
• pdu
  • bit

tcp/ip model

• application
  • OSI - application, presentation, session mix
• transport
  • OSI - transport
• internet
  • OSI - network
• network access
  • OSI - data link, physical

Hardware Networking

NIC - Network Interface Card

• on pc they are connected through pic
• every nic have a mac address
• my laptop have two mac address
  • one for the ethernet nic card
  • one for the wifi nic card
• dongels which are used to connect to internet through usb
  • they also have nic card embedded and also have mordem
• when we use internet through usb mobile it also have a nic
  • embedded to it so the mac address of the mobile will be used

hub (not used anymore)

• earlier when we used to connect multiple computers together we need more nic card, because one nic card can be used to connect to another computer, but if a second computer comes in you have to purchase another nic card for it. so if network become large you cannot purchase that many cards
• hub broadcast the data
• hub shared bandwidth, i.e. if 8mbps internet speed is given to it it will distribute to all the devices, so suppose 4 devices are connected each will get 2mbps even when someone is not using it
• hub usually have 4 to 8 ports
• less no of ports

switch

• more port - 24
• learns mac address and don't broadcast the data

Note

• Unicast - one to one,
• Multicast - one to many,
• Broadcast - one to all

bridge

• software based
• less ports compared to switch

router

• does routing

repeater

• amplify the signal
• after 100m ethernet used

modem

• modulation - analog to digital
• demodulation - digital to analog

Software in networking

• cisco packet tracer
• gcna
• ping - packet internet gopher, works on icmp protocol

Packet Tracer

router

• connect router to a end device through a cable

Modes:

• usermode
• privilege mode enable disable

• configuration mode configure terminal

• ? for help whenever you want

• Ctrl+shift+6 to stop execution of a command
• show version
• show ip - show routing table
• show history - history
• show clock

connect two pc

• cross over cable is used