Other LAN Technologies

1
Other LAN Technologies
2
LAN Standards

• 802 Working Groups
• 802.3 Ethernet LANs
• 802.5 Token-Ring Networks
• 802.11 Radio LANs
• 802.12 100VG-AnyLAN

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802.5 Token-Ring Network Standard

• Championed by IBM
• Official IEEE and OSI standard, but most vendors
  follow IBM extensions to the standard
• More reliable than 802.3 Ethernet LANs
• More complex and therefore more expensive
• Lower market share than Ethernet LANs
• Mostly in firms with large IBM mainframe networks
• Tightly integrated into SNA
• Read a tutorial in token-ring networks

4
Ring Topology in Token-Ring Networks
Station C
Station B
Station B only receives frames from Station A and
only transmits frames to Station C
Frame
Ring
Ring
Frame
Station A
Station D
Station E
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Problem with Rings

• If the ring breaks, LAN stops
• Signals must go all the way around the ring, back
  to the sender
• This becomes impossible

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Use a Double Ring

• One is unused in normal operation
• If there is a break, the ring is wrapped
• Still a ring

Normal
Wrapped
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UTP and STP Wiring
Plastic Cover (Non-Shielding)
Twisted Pair
Unshielded Twisted Pair (UTP)
Twisted Pair
Outer Shield Around Bundle
Twisted Pair
Shielded Twisted Pair (STP)
Twisted Pair
Shielding Around Pair
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STP vs. UTP

• STP
• Little interference
• Thick difficult to install
• Expensive
• UTP
• Thin easy to install
• Inexpensive
• Interference is rarely a practical problem
• Does the job at a reasonable price, so dominates

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Access Units in a Ring
STP link between Access Units
Access Unit
Access Unit
Access Unit
Access Unit
STP link from Station to Access Unit
UTP Link from Station to Access Unit
Stations
Station
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Within the Access Unit

• The ring is retained
• Powered-up NICs added automatically
• Powered-off NICs bypassed automatically

Bypassed Node
Ring
NIC
NIC
NIC
Missing NIC
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Token Passing in 802.5 Token-Ring Networks
Station B may only transmit when it receives a
special frame called a token.
Station B
Token
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Ethernet (802.3) vs Token-Ring (802.5)

• Physical Layer
• Ethernet primarily uses UTP wiring
• Token-Ring Networks primarily use shielded
  twisted pair (STP) wiring
• Topology (Layout) of the Wiring
• Ethernet always uses bus (broadcast) topology
• Token-Ring always uses a ring topology
  (connectivity)
• Access Control
• (Control of When Stations May Transmit)
• Ethernet always uses CSMA/CD
• Token-Ring always uses token passing

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Ethernet (802.3) vs Token-Ring (802.5)

• Speed
• Ethernet primarily 10 Mbps (moving to 100 Mbps
  and gigabit speeds)
• Token-Ring Networks usually at 16 Mbps
• TRNs can get closer to full capacity because
  token passing is more efficient than CSMA/CD at
  high traffic loads
• Priority levels for real-time traffic (video
  teleconferencing, etc.)
• Cost
• TRN is more complex, so NICs cost much more
• TRN has low market share low vendor competition
  adds to high NIC costs
• Most firms do not find the benefits of TRNs to
  outweigh the costs

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Shared Media LANs

• Ethernet (802.3) and Token-Ring Networks (802.5)
  are Shared Media LANs
• Only one station may transmit at any moment.
• Every station hears every transmission
• Stations must wait their turn to transmit

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Congestion and Latency in Shared Media LANs
Station B is Transmitting But Must Stop Soon
Station A Must Wait to Transmit
Station C Must Wait to Transmit
Shared Media LAN
Transmission
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Congestion and Latency

• As the number of stations on a shared media LAN
  increases...
• Traffic increases, so
• Stations must wait longer to transmit
• Latency (delay) increases
• This is called congestion
• At 200-300 stations, a 10 Mbps (4-16 Mbps) shared
  media LAN becomes saturated

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100 Mbps LANs

• Reducing Congestion
• One way to decrease congestion is to increase LAN
  speed from 10 Mbps to 100 Mbps or higher
• Each transmission will be briefer, because it can
  be transmitted faster
• Therefore more stations can share the LAN before
  saturation occurs
• Only postpones the problem

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FDDI Network
FDDI Ring
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FDDI

• FDDI
• Fiber distributed data interface
• Token-ring technology (but incompatible with
  802.5)
• 100 Mbps
• Mature (1987)
• 200 km maximum diameter popular for connecting
  LANs to local internets, not to connect desktops.
• Priority levels for real-time traffic (voice,
  video)
• Expensive NICs and other equipment
• Read a tutorial in FDDI

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802.12 100VG-AnyLAN

• 100 Mbps
• Demand Priority Access Method
• Station sends high- or low-priority requests
• All high-priority requests on all repeaters
  served first
• Good for real-time applications
• Hubs (repeaters) organized as a Tree
• One is the master repeater
• Not achieving market acceptance

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802.12 100VG-AnyLAN Hub Hierarchy
Repeater A
First Level Repeater
Master Repeater
Repeater B
Repeater C
Second Level Repeaters
Repeater E
Repeater D
Third Level Repeaters
High-Priority Request
Low-Priority Request
Station 1
Station 2
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100Base-X

• 100 Mbps
• Uses Normal 802.3 MAC Layer Frame
• Family of Standards
• 100Base-TX uses Cat 5 wiring (most popular to
  desk)
• 100Base-T4 uses Cat 3 and Cat 4 wiring
• 100Base-FX uses optical fiber

23
100Base-TX

• Many install 100Base-TX instead of 10Base-T Today
• Requires 100 Mbps hubs instead of 10 Mbps
• Requires 100 Mbps NICs instead of 10 Mbps
• Some hubs can also serve 10Base-T NICs, so not
  all stations have to be upgraded at once
• Uses Category 5 wiring, making upgrading easy

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Upgrading from 10Base-T to 100Base-T

• Need New Hub
• All 100Base-TX is expensive
• Often many 10Base-T hubs for client PCs
• A few 100Base-TX hubs for servers
• Need New NICs
• Only in stations with 100Base-T NICs
• Retain Old Wiring
• If Cat 5
• Avoids a major expense

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Ethernet 100Base-TX Network
100Base-TX Hub
100Base-TX Hub
50 maximum
100 m Segment Maximum
100 m Segment Maximum
- 5 UTP wiring - NICs are replaced
Station A
Station B
Station C
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Ethernet 100Base-TX Network

• The most popular 100Base-X standard, runs over
  existing 5 UTP wire of 10Base-T
• Only two segments, length 200m
• Can mix 10 Base-T and 100Base-T stations/NICs
  with hubs that take both types
• Use the same 802.3 MAC standard of 10 Base-T
• Market has chosen Ethernet 100Base-TX for
  desktop connection over FDDI and 100VG-AnyLAN
• Read classic tutorial on Fast Ethernet

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1000Base-X (Gigabit Ethernet)

• 1000 Mbps
• Usually used to link 100Base-X hubs

1000Base-X Hub
100Base-T Hubs
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1000Base-X

• Family of Standards (802.3z)
• 1000Base-LX
• Long-wave (lower frequency) laser
• 550 meters on multimode optical fiber
• 3 km on single mode fiber
• 1000Base-SX
• Short-wave ( higher frequency) laser
• 300 meters on 62.5 micron multimode fiber

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Full Duplex Ethernet

• CSMA/CD is half duplex
• Only one station may transmit at a time
• Others must wait
• Because transmission system is shared
• If station or hub connects directly to a hub,
• The access line is not shared
• Some 100Base-X and 1000Base-X hubs and NICs
  support full duplex operation
• Disable CSMA/CD
• 802.3x standard

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Shared media LANs

• Limits to Shared Media LANs
• FDDI, 100Base-X, 100VG-AnyLAN all shared media
  LANs
• Only one station can transmit at a time, causing
  latency
• Every station hears every message, so as the
  number of stations grow, the LAN saturates
• 100 Mbps speed only delays saturation

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Shared media LANs

• Shared Media Networks with Hubs (such as
  10Base-T)
• Incoming frame arrives through a single port
• Hub broadcasts frames out all ports
• Congestion on output ports

Hub
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Switched LANs

• In a switched network
• Incoming frame arrives on a single port
• Frame sent out again only on a single port--the
  one leading to the receiver
• No congestion on other ports

Switch
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Switch
With a switch, multiple stations may transmit
simultaneously no congestion as traffic grows.
Switch
Station C
Station A
Connection 1 A-C
Connection 1 A-C
Station D
Station B
Connection 2 B-D
Connection 2 B-D
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Switching in Perspective

• Switching is the wave of the future for LANs
• Congestion does not increase as the number of
  stations grows
• However,
• Today, however, switches are still more expensive
  than 10Base-T or 100Base-X hubs
• Read CISCO white paper
• discount the sales talk
• see 3COM images of switches.

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Switch connections

• paths called connections must be pre-defined
  between stations
• a fixed logical data link (logical connection) is
  established between stations before transmission
  even begins
• during the transmission, all traffic between the
  stations must pass over that data link
• unless a data link has been pre-established, two
  stations may not communicate at all
• only OSI Layer 2 (Data Link Layer) protocols are
  needed

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Ethernet Switches

• Ethernet Hubs are Half Duplex
• Most Ethernet Switches are Full Duplex
• No collisions are possible
• So two stations can both transmit to each other
  at the same time (full duplex operation)
• Requires full duplex switches
• Requires full duplex NICs
• Lowest-cost LAN switches
• Not standardized, so buyers tend to get locked
  into a single vendor

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ATM Switches

• Asynchronous Transfer Mode
• Will allow much higher speeds
• 155 Mbps to a few Gbps
• Can also be used for long-distance networking
• A single solution for both needs
• Quality of service guaranteed
• Far more expensive than Ethernet LAN switches

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ATM Switches

• standardized (others not yet)
• scalable as low as 1 Mbps to 2.4 Gbps
• can start with relative slow speeds (cheaper)
• increase the speed as needs arise
• without changing protocol

39
ATM and Ethernet

• 100Mbps and Gigabit Ethernet are outselling ATM
  for LAN usage
• High-speed Ethernet is less expensive
• Staff does not have to learn ATM technology
• Sales of NICs - Ethernet, Token Ring and ATM.

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Wireless LAN
Broadcast Signal
Antenna
Cluster Transceiver Receiving
Transceiver Transmitting
Hub Controller
Transceiver Receiving
Wireless LAN
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Typical 802.11 Wireless LAN Operation with Access
Points
CSMA/CAACK
Switch
UTP
Radio Link
Access Point A
Notebook
UTP
Handoff If mobile computer moves to
another access point, it switches service to that
access point
Access Point B
Client PC
Server
Large Wired LAN
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Typical 802.11 Wireless LAN Operation with
Access Points
Access Point
Industry Standard Coffee Cup
Wireless Notebook NIC
Antenna (Fan)
To Ethernet Switch
PC Card Connector
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Typical 802.11 Wireless LAN Operation with Access
Points
D-Link Wireless Access Point
Using Two Antennas Reduces Multipath Interference
(See Ch. 3)
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Typical 802.11 Wireless LAN Operation with Access
Points
Linksys Switch With Built-In Wireless Access Point
Using Two Antennas Reduces Multipath Interference
(See Ch. 3)
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Typical 802.11 Wireless LAN Operation with Access
Points

• The Wireless Station sends an 802.11 frame to a
  server via the access point
• The access point is a bridge that converts the
  802.11 frame into an 802.3 Ethernet frame and
  sends the frame to the server

802.11 Frame
802.3 Frame
Mobile Station
Access Point
Ethernet Switch
Server
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Typical 802.11 Wireless LAN Operation with Access
Points

• The server responds, sending an 802.3 frame to
  the access point
• The access point converts the 802.3 frame into an
  802.11 frame and sends the frame to the mobile
  station.

802.11 Frame
802.3 Frame
Mobile Station
Access Point
Ethernet Switch
Server
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802.11 Wireless LAN Speeds

• 802.11 2 Mbps (rare) 2.4 GHz band (limited in
  bandwidth)
• 802.11b 11 Mbps, 2.4 GHz 3
  channels/access point
• 802.11a 54 Mbps, 5 GHz (gt bandwidth than 2.4
  GHz) 11 channels/access point
• 802.11g 54 Mbps, 2.4 GHz limited
  bandwidth

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802.11 Broadcast Operation

• The Wireless Stations and Access Points Broadcast
  their Signals.
• Only one access point or wireless station may
  transmit at any moment or signals will become
  scrambled.

Wireless Station
Collision About to Occur
Access Point
Wireless Station
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CSMA/CA ACK in 802.11 Wireless LANs

• CSMA/CA (Carrier Sense Multiple Access with
  Collision Avoidance)
• Station or access point sender listens for
  traffic
• If there is no traffic, can send if there has
  been no traffic for a specified amount of time
• If the specified amount of time has not been met,
  must wait for the specified amount of time. Can
  then send if the line is still clear

50
CSMA/CA ACK in 802.11 Wireless LANs

• CSMA/CA (Carrier Sense Multiple Access with
  Collision Avoidance)
• Station or access point sender listens for
  traffic
• If there is traffic, the sender must wait until
  traffic stops
• The sender must then set a random timer and must
  wait while the timer is running
• If there is no traffic when the station or access
  point finishes the wait, it may send

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CSMA/CA ACK in 802.11 Wireless LANs

• ACK (Acknowledgement)
• Receiver immediately sends back an
  acknowledgement no waiting because ACKs have
  highest priority
• If sender does not receive the acknowledgement,
  retransmits using CSMA/CA

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Who Implements CSMA/CAACK?

• Stations (when they send)
• Access Points (when they send)

802.11 Frame
Mobile Station
Access Point
CSMA/CAACK
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Request to Send (RTS) / Clear to Send (CTS)

• There is a widely used option we should cover.
• After a station may send, its first message may
  be a Request-to-Send (RTS) message instead of a
  data message
• Only if the other party sends a Clear-to-Send
  (CTS) message does the sender begin sending data

Mobile Station
Access Point
RTS
CTS
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Ad Hoc 802.11 Networks

• Ad Hoc Mode
• There is no access point.
• Stations broadcast to one another directly
• Not scalable but can be useful for SOHO use
• NICs automatically come up in ad hoc mode

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802.11 Security

• Attackers can lurk outside your premises
• In war driving, drive around sniffing out
  unprotected wireless LANs
• In drive by hacking, eavesdrop on conversations
  or mount active attacks.

Outside Attacker
Site with 802.11 WLAN
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802.11 Security

• By default, security on 802.11 WLAN NICs and
  access points is turned off, making external
  attacks trivial
• WLAN vendors offer Wired Equivalent Privacy
  (WEP), but this is weak and easily broken.
• The 802.11 Working Group is working on a
  temporary replacement (TKIP) and longer-term
  security replacement, 802.11i
• Even if corporate access points can be secured,
  many departments create unauthorized rogue access
  points that are seldom secured.