Networks

1
Networks

• Why networks?
• Impractical to connect two stations
• Limitations to number of stations that can be
  connected directly
• Distance considerations make direct connections
  infeasible
• Need to access multiple stations/services
• Any one machine may need access to many others
• Access requirements may change/expand periodically

• Network components
• Network stations
• Devices that need to communicate(computers,
  telephones, etc.)
• Network nodes
• Interface between network and station

Node
Station
Cloud
Node
Node
Station
2
Network classification schemes

• Topology star, bus, ring, mesh, hierarchical,
  hybrid
• Ownership private, public
• Purpose/transmission type VAN, PDN, ISDN, Telex
• Geography GAN, WAN, MAN, LAN, TAN
• Architecture/transfer technique
• Switched networks circuit-switched,
  packet-switched
• Broadcast networks packet radio, satellite,
  local networks
• Dedicated networks

3
Local area networking functionality

• Local and remote communication
• Mail conferencing
• Resource sharing
• Network printers CD-ROMs modems fax
  capabilities files and databases applications
• Network management
• Backup LAN monitoring problem analysis,
  diagnosis administration optimization security
• Groupware integrated LAN functionality
• Workflow automation virtual interaction
  scheduling communication

4
Local area networking approaches

• Printer-sharing networks
• Used when simple printing resources are the only
  ones required
• Zero-slot LANs
• Networked via standardized ports (e.g., serial,
  parallel ports)
• Peer-to-peer LANs
• Offers much of the full-featured functionality of
  fully-integrated LANs but server-based
  capabilities missing
• Fully integrated LANs
• Powerful network operating system server-based
  software

5
Local area networking considerations

• Types of local networks
• Circuit-switching (e.g., private branch exchange
  (PBX))
• Packet broadcasting (e.g., local area network
  (LAN))
• Differences between LANs and WANs
• Geographic scope
• Transmission WANs use switching LANs use
  broadcasting
• Media WANs use variety of media LANs typically
  use one

6
Topologies used in LANs

• Ring topology
• Unidirectional
• Stations attach to medium through repeaters
• Repeaters responsible for reception and
  transmission of data
• May be in listen, transmit, or bypass state
• Bus/tree topology
• Bidirectional or unidirectional
• Broadband is unidirectional
• Stations attach to medium through taps
• Signal balancing issue because of no repeaters
• Other
• Star, mesh, hierarchy, hybrid

7
LAN topologies basic operations

• Ring
• Repeater handles data insertion, reception,
  removal
• In listen mode
• Identifies patterns in bit stream for control
  info (e.g. address)
• Copies bit streams to attached station if
  addressed to station
• Modifies passing bits to alter control
  information
• If returning bits, removes them from medium
• In bypass mode, no delay of signal as it passes
• Bus/tree
• Station emits signal, which is propagated along
  the medium
• Stations copy information if addressed to them
• Terminators absorb signals at ends

8
LAN transmission media

• Twisted-pair
• Could be shielded or unshielded
• Usually digital signaling, could be analog
• Coaxial cable
• Transceiver interface is twisted-pair wire
• Baseband or broadband (digital or analog
  signaling)
• Optic fiber
• Can implement token ring or ethernet
• Not as expensive now as earlier
• Infrared radiation

9
Relationship between LAN medium and topology

• Certain topologies suit certain media
• Ring uses repeaters, so needs point-to-point
  links
• Broadband coax requires complex technology to be
  feasible in ring
• Bus requires convenience of tapping
• Optic fiber unsuitable due to difficulty of
  lossless taps
• Certain media suit certain topologies
• Twisted pair good for ring, bus, not tree
  (bandwidth issue)
• Broadband coax good for bus, tree, not ring (too
  complex for repeater)
• Fiber good for ring, not bus, tree (hard to tap)

10
LAN layout

• Linear layout
• Wiring follows topology, short drop cables to
  stations
• Minimizes overall wiring
• Flexibility is compromised(especially for
  growth)
• Servicing and maintenance could be difficult

• Star layout
• Topology used in wiring closet, long drop cables
  to stations
• Requires considerable wiring
• High flexibility (especially for growth)
• Easier servicing and maintenance
• Permits pre-wiring of building

11
LAN operation baseband and broadband

• Baseband and broadband transmission compared
• Baseband is digital broadband usually analog
• Baseband signal uses full spectrum broadband
  uses FDM
• Broadband uses modulation for digital data, needs
  modems
• Broadband is good as a backbone
• Baseband usable for relatively short distances
• Baseband and broadband bus
• Baseband is bidirectional broadband is
  unidirectional
• Broadband bus uses single (split) or dual cable
• Headend frequency converter on split cable
  different send/receive frequencies
• Passive headend on dual cable, same frequency for
  send/receive

12
LAN operation medium access control (MAC)

• Carrier Sense Multiple Access w/ Collision
  Detection
• Station senses the medium if medium is busy,
  station waits
• When medium is idle, station transmits message
• If collision occurs, station transmits jamming
  signal, waits
• Token bus
• Station on logical ring controls medium when
  token received
• After specified time token passed to next station
• Station can remove itself by splicing
  predecessor, successor
• Token ring
• Station takes control of token when transmission
  required
• Converts token to start-of-packet sequence
• When message comes back, it is purged, new token
  generated

13
Network interface unit

• Unit connecting device to network
• Transceiver repeater
• Can be outboard (serial/parallel port) or inboard
• Provides multiple services
• Provides addressing, link control translates bit
  rates, makes packets provides regeneration if on
  a ring generates required signaling (baseband,
  etc.) executes MAC technique buffers data
  converts parallel to serial data
• Functions could be split between devices
• Division between medium interface and network
  services
• On a bus, transceiver attaches to medium, LAN
  coprocessor on card provides other services
• Token ring card and MAU divide services

14
LAN standards

• IEEE 802 standards project (established 1979)
• At time of initiation, 44 LAN implementations
  existed
• Committee members are vendors, users, academics
• 802 subcommittees

• 802.1 internetworking
• 802.2 logical link control
• 802.3 CSMA/CD
• 802.4 token bus
• 802.5 token ring
• 802.6 MAN-CATV, DQDB

• 802.7 broadband LAN operating specifications
• 802.8 fiber optic LAN standards
• 802.9 integrating voice/data on a LAN
• 802.11 wireless LANs
• 802.12 100BaseVG ethernet
• 802.13 100BaseX CSMA/CD ethernet

15
IEEE 802.3 CSMA/CD

• Based on Xerox Ethernet standard
• Original standard was 10Base5
• 10 Mbps baseband max segment length is 500
  meters
• Max 100 taps per segment, 2.5 meters between taps
• Multiple segments with repeaters (max five)
• Maximum four repeaters between any two stations
• Repeaters could be full (segment-repeater-segmen
  t) or half (segment-repeater-IRL-repeater-segmen
  t)
• Strictly, two of max five segments must be
  inter-repeater links (IRL) without stations
• Cable is approximately 10 mm in diameter (aka
  frozen yellow garden hose)
• Drop cables (attachment interface units) connect
  via transceiver to medium

16
IEEE 802.3 CSMA/CD

• 10Base2 (a.k.a. Cheapernet Thinnet)
• Max segment length is 185 meters max 30 taps per
  segment
• 10BaseT
• Wiring is unshielded twisted pair (UTP)
• Uses 4-pair bundles (RJ-45 connector)
• Bus located in 10BaseT hub
• 10BaseF
• Optical fibre standard
• Max segment length of 2000 meters
• 10Broad36
• Provides broadband version max segment length
  3600 meters

17
IEEE 802.4 token bus

• Physical layer specs allow for two transmission
  modes
• Broadband option supporting channels of 1, 5, and
  10 Mbps
• Headend frequency converter used on mid-split
  cable
• Carrierband option supporting a single broadband
  channel of 1, 5, or 10 Mbps
• Use of broadband makes token bus more flexible,
  more resilient than 802.3 baseband
• Could use token bus for backbones, 802.3 bus for
  subnetworks
• Token bus good in factory environment
• Process control LANs utilize this standard

18
IEEE 802.5 token ring

• Standard for shielded twisted pair at 1, 4, 16
  Mbps
• Some vendors provide UTP alternatives
• Higher data rates expected with fiber use in the
  future
• Maximum of 260 devices, 300 meters total length
• Uses star layout
• Stations connect through Multistation Access Unit
  
• Eight devices per MAU MAUs connected to form a
  ring
• MAU includes bypass capability does repeater
  function
• Token circulates on ring in free or busy state
• If busy, stations copy frame assess whether to
  keep, discard
• Transmitter removes frame on return, issues new
  token

19
802.5 vs. 802.3 (token ring vs. ethernet)

• 802.5 better than 802.3 when high utilization
• More deterministic MAC
• 802.5 more efficient MAC algorithm than CSMA/CD
• Token passing results in more predictable
  communication
• 802.5 more reliable than 802.3
• Regeneration of signals
• - 802.5 usually more expensive than 802.3
• 400 vs. 150 for interface card
• - 802.5 less established than 802.3
• Market acceptance of 802.3 is very high

20
ANSI X3T9.5 (Fiber Distributed Data Interface)

• Based on IEEE 802.5 standard data rate of 100
  Mbps
• Total distance up to 200 km up to 1,000 stations
• Used as LAN backbone as well as LAN

• Uses redundant dual ring for fault tolerance
• Rings transmit in opposite directions
• Dual-attachment (DAS) and single-attachment
  stations (SAS)
• When breaks occur, DASnearby reroute data