Download data-link layer protocols

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Chapter 4
DATA-LINK LAYER
PROTOCOLS
Ethernet
Token Ring
FDDI
Wireless Networking
Chapter 4: DATA-LINK LAYER PROTOCOLS
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OSI MODEL AND IEEE 802.X STANDARDS
 The Institute of Electrical and Electronics Engineers (IEEE)
divides the data-link and physical layers of the Open Systems
Interconnection (OSI) model into four sublayers:
 Two IEEE data-link sublayers:
 The upper sublayer is the 802.2 or Logical Link Control (LLC)
 Operates independently from the Media Access Control (MAC)
sublayer
 Specifies the upper layer protocol carried within a frame
 The lower sublayer is the MAC sublayer.
 Defined by various 802.x standards such as IEEE 802.3, 802.5, and
802.11
Chapter 4: DATA-LINK LAYER PROTOCOLS
OSI MODEL AND IEEE 802.X STANDARDS
(CONT.)
 Two IEEE physical sublayers:
 Physical signaling
 Media specifications
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Chapter 4: DATA-LINK LAYER PROTOCOLS
FOUR IEEE SUBLAYERS
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Chapter 4: DATA-LINK LAYER PROTOCOLS
IEEE DATA-LINK AND PHYSICAL STANDARDS
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ETHERNET VERSION I AND II
 Digital Equipment Corporation, Intel, and Xerox
published the first two 10-Mbps Ethernet standards.
 Version I (also known as DIX Ethernet)
 Uses bus topology with RG-8 (thick coaxial cable)
 Uses Attachment Unit Interface (AUI) patch cables with
15-pin connectors, 50-ohm terminators, and external
transceivers
 Maximum distance per segment: 500 meters
 Maximum distance per network: 2500 meters
 Uses the 5-4-3 rule
 Adopted and renamed 10Base5 (page 157) by the IEEE
Chapter 4: DATA-LINK LAYER PROTOCOLS
ETHERNET VERSION I AND II (CONT.)
 Version II
 Uses bus topology with RG-58 (thin coaxial cable)
 Uses T-connectors, 50-ohm terminators, and internal
transceivers
 Maximum distance per segment: 185 meters
 Maximum distance per network: 925 meters
 Uses the 5-4-3 rule
 Adopted and renamed 10Base2 by the IEEE
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5-4-3 RULE
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IEEE ETHERNET STANDARDS (page 159)
 The IEEE adopted and renamed the original Ethernet
standards and then expanded them.
 All IEEE Ethernet standards are controlled by the
802.3 working group.
 10-Mbps standards: 802.3a (10Base2), 802.3e
(10Base5), 802.3i (10Base-T), and 802.3j (10BaseFP, 10Base-FB, and 10Base-FL)
 100-Mbps standards: 802.3u (100Base-X)
 1000-Mbps standards: 802.3z and 802.3ab
(1000Base-X)
Chapter 4: DATA-LINK LAYER PROTOCOLS
IEEE 10BASE-X STANDARDS
 The three primary IEEE standards for 10-Mbps
baseband networks are
 10Base5
 Physical and data-link layer standards and limitations
are identical to Ethernet version I.
 10Base2
 Physical and data-link layer standards and limitations
are identical to Ethernet version II.
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IEEE 10BASE-X STANDARDS (CONT.)
 10Base-T
 Star topology using unshielded twisted-pair (UTP)
cabling
 Two-pair UTP with RJ-45 connectors: One pair for
transmit, the other one for receive
 Supports half-duplex and full-duplex modes
 Maximum distance per segment: 100 meters
 Maximum distance per network: 500 meters (which
includes connections from workstation to hub and also
connections between hubs)
 Uses the 5-4-3 rule
Chapter 4: DATA-LINK LAYER PROTOCOLS
10BASE-T 5-4 Rule
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Chapter 4: DATA-LINK LAYER PROTOCOLS
IEEE 100BASE-X STANDARDS
 The three IEEE standards for 100-Mbps baseband
networks configured as a star topology are
 100Base-TX
 Uses the 4B5B encoding scheme over two pair




(Category 5), the same as 10Base-T
Supports half-duplex mode or full-duplex mode
Maximum distance per segment (half or full): 100
meters
Maximum distance per half-duplex network: 205
meters
Supports Class I and Class II repeaters
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IEEE 100BASE-X STANDARDS (CONT.)
 100Base-T4
 Uses the 8B/6B encoding scheme over four Category 3
(CAT3) twisted pairs
 Supports only half-duplex mode
 Maximum distance per segment: 100 meters
 Maximum distance per network: 205 meters
 Supports Class I and Class II repeaters
Chapter 4: DATA-LINK LAYER PROTOCOLS
IEEE 100BASE-X STANDARDS (CONT.)
 100Base-FX
 Uses the 4B/5B encoding scheme over fiber optic
 Supports half-duplex mode or full-duplex mode
 Maximum length of a multimode half-duplex segment: 412
meters
 Maximum length of a multimode full-duplex segment: 2
kilometers
 Maximum length of a singlemode half-duplex segment: 2
kilometers
 Maximum length of a singlemode full-duplex segment: 10+
kilometers
 Supports Class I and Class II repeaters
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CLASS I AND CLASS II REPEATERS
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IEEE 1000BASE-X STANDARDS
 The IEEE 1000Base-X standard defines Gigabit
Ethernet specifications for twisted-pair cable and
fiber optic cable.
 Uses the 8B/10T encoding scheme
 Supports full-duplex mode only
 Maximum length of UTP segment: 100 meters
 Maximum length of multimode fiber segment: 220+
meters
 Maximum length of singlemode fiber segment: 5000
meters
Chapter 4: DATA-LINK LAYER PROTOCOLS
FOUR ETHERNET FRAME TYPES
 There are four different Ethernet frame types:
 Version II
 Ethernet 802.3
 IEEE 802.3
 IEEE 802.3 SNAP
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Chapter 4: DATA-LINK LAYER PROTOCOLS
VERSION II FRAME
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ETHERNET 802.3 FRAME
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IEEE 802.3 FRAME
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IEEE 802.3 SNAP FRAME
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MAC ADDRESSES (page 162)
Media Access Control: Is the mechanism that
enables multiple computers to use the same
network medium without conflicting
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CARRIER SENSE MULTIPLE ACCESS WITH
COLLISION DETECTION (CSMA/CD)
Phase
Description
Carrier sense
A computer listens to the network before
transmitting.
Multiple access
When the network is clear, the computer
transmits the packet.
Collision detection
The computer checks for signs of a
collision. If one occurs, it retransmits the
packet.
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CARRIER SENSE MULTIPLE ACCESS WITH
COLLISION DETECTION (CSMA/CD)
 All half-duplex implementations of Ethernet use the
CSMA/CD channel access method.
 Carrier Sense
 A device that wants to transmit must first listen to the
channel to see if it is in use.
 If the channel is busy, the device must wait.
 If the channel is idle, the device can transmit a frame.
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CARRIER SENSE MULTIPLE ACCESS WITH
COLLISION DETECTION (CSMA/CD) (CONT.)
 Multiple Access
CSMA
 All devices on the network contend for access to the
channel.
 Collision Detection
 When two or more devices transmit at the same time,
their signals collide.
 Devices detect collisions when they receive a different
frequency on their receive pair.
 Devices must immediately stop transmitting data and
send out a jamming signal and then back off for a
random interval before trying again.
Chapter 4: DATA-LINK LAYER PROTOCOLS
COLLISIONS
Collision
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Contention
 Collisions are also called signal quality errors.
 They are normal on Ethernet networks.
 The frequency of collisions increases as network
traffic increases.
 Late collisions are a sign of a serious problem.
Do Exercise 4-2 (Page 194)
Chapter 4: DATA-LINK LAYER PROTOCOLS
TOKEN RING
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Token Ring Network
 Token Ring was originally developed by IBM, and then it was
adopted by the IEEE and renamed 802.5.
 Star wired ring topology
 Operates at either 4 Mbps or 16 Mbps
 Token-passing channel access method (Next Slide)
 Uses Multistation Access Units (MAUs) to connect nodes to the
network
 You can connect MAUs together, using RI (Ring In) and RO (Out)
ports to form a larger ring.
 Can use both shielded and unshielded twisted-pair cable
Chapter 4: DATA-LINK LAYER PROTOCOLS
TOKEN Passing
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Token Passing
 A token frame circulates continuously around the
network.
 Only the computer holding the token can transmit
data.
 The transmitting system is responsible for removing
the data from the ring.
Chapter 4: DATA-LINK LAYER PROTOCOLS
TOKEN RING FRAMES
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Chapter 4: DATA-LINK LAYER PROTOCOLS
FDDI (Fiber Distributed Data Interface )
 Developed by the American National Standards Institute
(ANSI)
 Uses dual ring topology
 The primary ring serves as a data path.
 The secondary ring provides fault tolerance.
 Has a 100-Mbps transmission rate over fiber optic cabling
 Uses the token passing channel access method
 Supports early token release
 Uses single attachment station (SAS) or dual attachment
station (DAS) FDDI
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FDDI (Fiber Distributed Data Interface )
 Supports both:
 Singlemode cable (600 Km segments)
 Multimode cable (100 Km segments &
500 Workstations) This is the industry
standard for fiber optic LANs.
Chapter 4: DATA-LINK LAYER PROTOCOLS
SAS AND DAS DEVICES
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Chapter 4: DATA-LINK LAYER PROTOCOLS
RING WRAP (page 185)
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FDDI FRAMES
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WIRELESS LANS
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Wireless LANs
 IEEE standard 802.11 defines the specifications for wireless
LANs (WLANs).
 Support various transmission rates, depending on the standard
 802.11b supports up to 11 Mbps.
 802.11a and 802.11g support up to 54 Mbps.
 Support ad hoc or infrastructure topologies
 Use three different signaling methods: Direct Sequence Spread
Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS),
and infrared
 Use the Carrier Sense Multiple Access with Collision Avoidance
(CSMA/CA) channel access method
Chapter 4: DATA-LINK LAYER PROTOCOLS
AD HOC WLAN
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INFRASTRUCTURE WIRELESS
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SUMMARY
 DIX and IEEE 802.3 define physical and data-link
layer standards and functions for Ethernet networks
using CSMA/CD over coaxial, twisted-pair, or fiber
optic cabling.
 IBM and IEEE 802.5 define physical and data-link
layer standards and functions for a token passing
ring topology.
 FDDI defines the physical and data-link layer
standards for a token-passing, fiber optic ring
topology.
 WLANs can either be ad hoc or infrastructure.