Notes - Example Networks

The following are notes from Computer Networks written by Tanenbaum 5th edition.

The Internet

• Not really a network at all, vast collection of different networks that use common protocols, provide common services
• The ARPANET
• DoD wanted a command and control network that can survive nuclear war
• switching offices, small redundancy
• contract to RAND Corporation Paul Baran designed distributed fault tolerant design
• ARPA (Advanced Research Projects Agency)
• worked by issuing grants and contracts to agencies and universities
• Subnets consist of minicomputers called IMPs(Interface Message Processsors)
• connected by 56kbps transmission lines
• connect to at least two other Imps so reroute possible
• node consist of IMP and host
• host can send messages 8063 bits
• IMP breaks into packets of 1008 bits and forward them to destination
• selected BBN to contract
• Honeywell DDP-316 minicomputers
• outside of subnet software needed
• host-imp
• host-host protocol
• application software
• Hosts need software too
• Arpanet connected universities
• Arpa announced contracts to build TCP/IP on different computer platforms
• IBM, DEC, HP systems, UNIX
• TCP/IP rewritten as sockets with the 4.2 BSD release of UNIX
• DNS(Domain Name System)

NSFNET

• NSF(National Science Foundation)
• NSF funded CSNET 1981
• NSF started backbone network to connect 6 supercomputers
• given a little brother fuzzball
• LSI-11 microcomputer
• connected libraries, research labs, museums, universities
• big success
• NSF realized government cannot continue funding
• encouraged MERIT MCI IBM
• form nonprofit corporation ANS(Advanced Networks and Services)
• Awarded 4 different network operators to establish NAP(Network Access Point)
• packet has choice of backbone carriers
• 1990s countries and regions followed suit, EuropaNET EBONE
• Now WWW(World Wide Web)

Architecture of the Internet

• Changed from beginnings
• ISP(Internet service provider)
• connects to home computer user purchases internet access or connectivity
• connect to ISP with phone line
• DSL(Digital Subscriber Line) reuses telephone line for data transmission
• DSLAM(Digital Subscriber Line Access Multiplexer)
• converts between signals and packets
• Dial-up
• use telephone line
• Modem-Modulator Demodulator
• Send over Cable TV System
• Device at the home is cable modem
• Cable headend is called CMTS (Cable Modem Termination System)
• DSL and Cable access at rates small fraction of megabit/sec to multiple megabit/sec
• rates much greater than dial up due to more bandwidth
• broadband
• FTTH(Fiber to the Home)
• fiber optic transmission 45 Mbps
• Location at which customer packets arrive at ISP Network PoP(Point of Presence)
• Long distance transmission lines interconnect routers at PoP in different cities for ISP to serve users.
• ISPs connect networks to exchange traffic at IXPs(Internet exchange points)
• peer with each other
• room full of routers to forward to ISP backbone
• Small ISP may pay larger ISP for distant hosts, pay for transit
• Path of packet depends on peer choices
• AT&T/Sprint are large so do not pay for transit
• Companies that provide large content, Google Yahoo, locate computers in data centers, designed for computers, server farm
• Colocation, hosting
• Intranets-companies self interconnected all internal networks

Third Generation Mobile Phone Networks

• AMPS(Advanced Mobile Phone System)
• Deployed 1982 first generation
• Second Generation - voice in digital form offer text messaging
• GSM(Global System for Mobile Communications)
• deployed 1991 2G
• UMTS(Universal Mobile Telecommunications System)
• 3G systems provide rates of 2 Mbps for stationary, 384 kbps in moving vehicle
• WCDMA(Wideband Code Division Multiple Access)
• main 3G system deployed, 14 Mbps on downlink, 6 Mbps on uplink
• scarcity of spectrum led to cellular network design
• within a cell, users assigned channel that do not interfere with one another
• allows for good reuse of spectrum
• allows each cell to use all frequencies
• Architecture
• Air Interface
• radio communication protocol over air between mobile and base station
• CDMA
• Base Station with controller forms
• radio access network
• Controller node RNC(Radio Network Controller)
• Node B
• Mobile phone network carries traffic for radio access
• called core network
• evolved from 2G GSM system that came before it
• Connectionless/Connection Oriented
• connectionless packet independently routed, dynamic reconfigure
• potential router choking lose packets
• circuit camp comes from telephone, stable system higher quality of service
• rejected calls, busy signal
• Older mobile phones use circuit switched core
• UMTS network with legacy elements set up connections over PSTN(Public Switched Telephone Network)
• MSC(Mobile Switching Center) 
• GSMC(Gateway Switching Center)
• MGW(Media Gateway)
• GRPS(General Packet Radio Service) in GSM
• UMTS core network nodes connect directly to packet switched network
• SGSN (Serving GPRS Support Node)
• GGSN(Gateway GPRS Support Node)
• deliver data packets to and from  mobiles and interface to external packet networks like internet
• Internet protocols used to set up VoIP, change to support quality of service
• Mobility, user moves in and out of base station, handoff/handover to reroute data to new station
• soft handover is when connect before disconnect possible
• hard handover, disconnect before connection established
• HSS(Home Subscriber Server)
• knows location of each subscriber and authorization
• Sim Card
• Subscriber Identity Module defines user
• authentication of user
• 4G technologies
• LTE(Long Term evolution)
• WiMAX
• 802.16 networks

Wireless LANs: 802.11

• Laptop connected to internet easily
• WiFi 802.11
• operate in unlicensed band such as ISM bands defined by ITU-R
• made up of clients and infrastructure
• access points/base stations installed in buildings
• clients talk to each other, ad hoc networks instead of access points
• multipath fading
• signals reflected off of solid objects causing fluctuations in signals
• solve issue with path diversity
• send along multiple independent paths so at least one good signal reaches destination
• OFDM (Orthogonal Frequency Division Multiplexing)
• divides wide band spectrum into narrow slices
• CSMA(Carrier Sense Multiple Access)
• determines if transmission band is free
• ALOHA wireless network
• setup in Hawaii
• Client Mobility
• moving away between access points, cell system implemented
• Security
• WEP(Wired Equivalent Privacy)
• tried to make wireless security like wired security
• broken scheme
• WPA
• Wifi protected access
• now replaced by WPA2

RFID and Sensor Networks

• RFID(Radio frequency Identification)
• a tag that is embedded into an object or person to be tracked
• passive RFID
• no power, reflects signal
• UHF RFID (Ultra High frequency RFID)
• 902-928 Mhz
• used on shipping and driver licenses
• HF RFID(High Frequency RFID)
• 13.56 Mhz
• LF RFID (Low Frequency RFID)
• active RFID
• has power sends signal
• Readers for RFID must solve issue of multiple tags in reading range
• easy collision in return
• Security for RFID
• Sensor Network
• monitor physical world
• multihop network
• relays messages between each other, self organization before sending to data collection point

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