Networking Basics

1
Networking Basics

• Terminology and ideas
• 2/10/2000

2
Upcoming

• Project proposals
• Comparison of Ubicomp-related networks
• on Tuesday (student readings)
• Good topics for research essays!

3
Tuesday Prep

• Ubicomp-relevant networks
• What are operating characteristics?
• What is availability?
• Who are the players?
• Reasons why Technology X will or will not succeed

4
Tuesday prep (contd)

• On-the-body networks
• How do they work?
• What are limitations?
• What are they good for?
• RF ID
• How does it work?
• What distinguishes different approaches
• Other neat RF ID approaches

5
Networking 101

• References
• D. E. Comer. Internetworking with TCP/IP, Volume
  1.
• Price Waterhouse Technology Forecast 1999.
• The Web
• NOTE SPEEDS and FORMATS CHANGE
• (I.e. check the current specifics)

6
2 types of networks

• Circuit-switched (connection oriented)
• dedicated point-to-point
• telephone system
• guaranteed bandwidth but wasteful
• Packet-switched (connectionless)
• information bundles contain connect info
• concurrent communication
• no bandwidth guarantee

7
Wide vs. Local Area

• WAN - long haul networks
• large distances (no limit)
• slow speed (up to 155 Mbps)
• high latency (msec to .1 sec delays)
• LAN
• short distances (buildings)
• high speed (10 Mbps to 2Gbps)
• low latency (.1 msec)

8
For ubicomp/wearables

• Proximity-based networks
• Personal Area Networks (PAN)
• Very short distances (feet)

9
An example LAN Ethernet

• Invented at PARC in early 1970s
• Standardized in 1978
• IEEE Standard 802.3
• Best-effort, broadcast bus technology using
  carrier sense multiple access (CSMA) with
  collision detection (CD)

10
CSMA/CD

• CSMA
• no central access authority
• each transmitter senses whether network is
  transmitting
• CD
• sense collisions during transmission
• if collision, then backoff policy for retransmit

11
Limited distance to LANs

• 1 kilometer for original ethernet
• Can work from first principles
• Speed of electricity in a wire
• Distance before entire packet (message) contained
  in the wire

12
Ethernet addressing

• 48-bit Ethernet address of network interface card
  (MAC)
• no 2 hardware interfaces are the same
• used as message filter

13
The Ethernet frame

• Preamble (for synchronizing)
• Source address
• Destination address
• Frame type (identifies protocol)
• Data (variable length)
• CRC

14
Ethernet capacity

• Original
• 10 Mbps (IEEE 802.3)
• Fast Ethernet
• 100 Mbps
• Gigabit Ethernet
• 1000 Mbps
• Essay Fundamental limits?

15
Other physical networks

• Token ring
• counter-rotating rings
• token controls transmission
• IBM 4-16 Mbps, FDDI
• ATM
• high-speed connection-oriented
• fiber with fixed frame-size or cell

16
Important TCP/IP abstractions

• virtual addressing
• 4 (8-bit) digits xxx.xxx.xxx.xxx or
• Address Resolution Problem (ARP)
• map from virtual network address to physical
  network address (Ethernet, ATM, FDDI, etc.)
• Domain Name Service (DNS)
• Sockets
• network connections as file I/O

17
Extensions to the IP model

• IPv4 since late 1970s
• Why is change needed?
• More address space needed
• Higher bandwidth applications
• guaranteed quality of service
• secure transmission
• support for mobility
• support for high density (Weiser)

18
Mobile IP

• each mobile unit is assigned fixed mobile host IP
  (mobile agent)
• mobile host forwards IP traffic to actual host
  (care-of address)
• Ad hoc (C K Toh in ECE)
• More details from IETF
• Good essay

19
IPv6 (IPng)

• 128 bit address space
• extensible protocol
• More details from IETF and RFCs

20
Finding more information

• Internet RFCs
• IEEE standards
• Ethernet is 802.3
• Wireless is 802.11
• 2-10 meter is 802.15

21
Tools to see what is going on

• Ping (ping -s)
• traceroute
• nslookup
• netstat
• whois
• yp

22
Transmission media

• Wires
• twisted pair
• coax
• fiber
• which is most noise immune? At what frequencies?
• Wireless
• IR, RF, satellite

23
Wired media

• Copper cable twisted pair
• shielded (STP) or not (UTP)
• category levels
• performance characteristics
• e.g., Category 5 is 100MHz up to 100 meters

24
Digital Subscriber Line (DSL)

• Leverages off installed twisted pair base
• Many varieties
• difference in downstream/upstream, distance
  covered, permanent connections, shared voice
• ISDN DSL (IDSL), HDSL, SDSL, ADSL, RADSL, VDSL

25
Some specifics (take w/ grain of salt)

• ISDN 128K 128K 18k feet
• HDSL 1.544M 1.544M 12k feet
• SDSL 1.544M 1.544M 10k feet
• ADSL 8M 1M 12k feet
• RADSL 7M 1M 18k feet
• VDSL 51.84M 2.3M 1k feet

26
Coaxial cable

• What cable TV uses
• For data, can transmit 10Mbps downstream and
  2Mbps upstream

27
Fiber

• Send information via light and not electrical
  impulse
• Many advantages over copper
• Rated by OC-levels (SONET)
• OC-1 51.84 Mbps
• OC-192 ? 10 Gbps
• Wave Division Multiplexing up to 1.28Tbps

28
What about wireless?

• General issues
• Categories
• Wireless LAN (near range, high b/w)
• Wireless telephony (long range, low b/w)
• Wide area data (long range, high b/w)
• Paging (long range, very low b/w)
• Satellite (long range, very low b/w)

29
General issues

• Frequency spectrum
• where the action is limited
• Capacity and Frequency bandwidth
• Shannon bps delta f (1 S/N)
• Sampling rates
• Nyquist

30
Wireless LAN

• Wireless Ethernet (IEEE 802.11)
• InfraRed (not regulated)
• Three major RF frequency bands
• 900 MHz (902 - 928)
• 2.4 MHz (2.4000 - 2.4835)
• 5.8 MHz (5.7250 - 5.825)
• Industrial Scientific Medical (ISM) bands

31
How is RF transmitted?

• Spread spectrum
• across a range of frequencies
• Frequency hopping
• signal jumps between frequency channels
• Direct sequence
• signal spread over all channels

32
More info on wireless LANs

• See Web for vendors
• Essays
• Where is this heading? What are limits?
• RF vs. Infrared

33
Wireless telephony

• Late 1970s - first analog systems
• Cellular
• AMPS is North American standard
• Digital cellular
• greater capacity
• smaller handsets with longer battery life

34
Wide Area Data

• Circuit-switched data
• analog phone with modem (9.6 - 14.4 Kbps)
• pay while connected
• must initiate connection
• Cellular Digital Packet Data (CDPD)
• obvious advantages over circuit-switched
• 19.2 Kbps

35
How digital cellular works

• 2.5 techniques
• Time Division Multiple Access (TDMA)
• freq channels split into 6 time intervals
• compatible with AMPS
• data rates up to 9.6 Kbps

36
GSM

• Global System for Mobile Comms
• TDMA with 8 time slots
• European standard, moving to N. America
  (Powertel)
• incompatible with AMPS
• Data rates 9.6 Kbps, but much greater possible
  (see Web)

37
CDMA

• Code Division Multiple Access
• An example of spread spectrum
• greater capacity than TDMA

38
Tricks for digital voice/audio

• Never send silence
• Compress
• Send at higher rate than real time
• Time compress with SOLA
• Up to 300 words per minute

39
Specialized Mobile Radio

• initial analog radio dispatch
• push to talk
• Motorola made digital
• added for telephony, paging and packet-switched
  data
• Nextel is example

40
Other packet-switched

• Mobitex
• Originated in Europe
• In U.S. as BellSouth Mobile Data
• 8 Kbps
• What Palm VII will use
• ARDIS
• Metricom

41
Up and coming

• GPRS
• 128kbps compatible with current equipment
• 384kbps Edge
• 3Gs
• Up to 2 Mbps
• Some estimates of 5 years

42
Some more essay topics

• What wireless services are available in Atlanta?
• Research the Georgia Tech BellSouth cellular
  infrastructure
• We should be able to get GSM-3rd generation
  high-speed data, but how?