physical and data link layers chapter 2 connecting people to information
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Physical and Data Link Layers
Chapter 2
Connecting People To InformationConnecting People To Information
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Upon completion of this chapter, you will be able to perform the following tasks:
• Identify and describe the data link sublayers and their functions
• Explain the use of MAC addresses
• Describe the topology and functionality of LANs
• Differentiate between LAN and WAN protocols
Objectives
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Physical and Data-Link Standards
• Separate physical and data link layers for LAN and WAN
Physical(bits,
signals,clocking)
Data LinkData Link(frames)(frames)
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Physical and Data-Link Standards
• Separate physical and data link layers for LAN and WAN
Physical(bits,
signals,clocking)
LAN
Data LinkData Link(frames)(frames)
Ethernet
802.3
802.5
FDDI
802.2 LLC
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Physical and Data-Link Standards
• Separate physical and data link layers for LAN and WAN
Physical(bits,
signals,clocking)
LAN WAN
Data LinkData Link(frames)(frames)
Ethernet
802.3
802.5
FDDI
802.2 LLC X.25Link
FrameRelay
ISDN
PPP
EIA-530
V.35
DialonDemand
SDLC HDLC
V.24
HSSIG.703
EIA/TIA-232
EIA/TIA-449
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LAN Data Link Sublayers
• LLC refers upward to higher-layer software functions
• MAC refers downward to lower-layer hardware functions
Media Access Control
Logical Link ControlNetworkNetworkNetworkNetwork
Data LinkData LinkData LinkData Link
PhysicalPhysical
LLCLLCLLCLLC
MACMAC
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LAN Data Link Sublayers
• LLC refers upward to higher-layer software functions
• MAC refers downward to lower-layer hardware functions
Media Access Control
Logical Link ControlNetworkNetworkNetworkNetwork
Data LinkData LinkData LinkData Link
PhysicalPhysical
LLCLLCLLCLLC
MAC FrameMAC Frame 802.2 LLC802.2 LLC802.2 LLC802.2 LLC
MACMAC
Packet or Datagram
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LLC Sublayer Functions
• Enable upper layers to gain independence over LAN media access
• Allow service access points (SAPs) from interface sublayers to upper-layer functions
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Physical and Logical Addressing
0000.0c12.3456
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MAC Address
• MAC address is burned into ROM on a network interface card
24 bits24 bits
0000.0c12. 3456
Vendor CodeVendor Code Serial NumberSerial Number
ROMROM
RAMRAM
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Finding the MAC Address
Host Y Host ZQuery
ResponseExample 1: Destination local
Router A
Example 2: Destination not local
Host Z
BroadcastBroadcast Host ZMAC ?Host ZMAC ? Host ZHost Z
Host YMAC
Host YMAC
Host ZMAC
Host ZMAC
Host Y Query
BroadcastBroadcast Host ZMAC ?Host ZMAC ? Host ZHost Z
ResponseHost YMAC
Host YMAC
Router AMAC
Router AMAC
Routing Table:Net forHost Z
Routing Table:Net forHost Z
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Written Exercise: Determining MAC Addresses
Host A0000.0c12.1111
Host B0000.0c12.2222
Host D0000.0c12.4444
Router C0000.0c12.3333
Router C0000.0c12.5555
Network Y
Network X
Common LAN Technologies
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TokenRing
Ethernet
Token Ring
FDDI
LAN Technology Overview
FDDIDual Ring
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Ethernet and IEEE 802.3
• Several framing variations exist for this common LAN technology
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Physical Layer: Ethernet/802.3
Host
10BaseT—Twisted Pair
10Base2—Thin Ethernet 10Base5—Thick Ethernet
PC MacSun Host
Hub
MAC
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The Ethernet/802.3 Interface
• Cisco router’s data link to Ethernet/802.3 uses an interface named E plus a number (for example, E0)
0800.2006.1a56
0000.0c12. 7c4d
E0
E1
0800.890c.34d50000.0c12. 83e2
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Ethernet/802.3 Operation
AA BB CC DD
D B and CApplicationPresentationSessionTransportNetworkData LinkPhysical
ApplicationPresentationSessionTransportNetworkData LinkPhysical
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Ethernet/802.3 Broadcast
DCBAApplicationApplicationPresentationSessionTransportNetworkData LinkPhysical
ApplicationApplicationPresentationSessionTransportNetworkData LinkPhysical
ApplicationApplicationPresentationSessionTransportNetworkData LinkPhysical
ApplicationApplicationPresentationSessionTransportNetworkData LinkPhysical
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Ethernet Frame Variations
Ethernet Frame
802.3 Frame
PreamblePreamble DADA SASA TypeType DataData FCSFCS8 6 6 2 4
PreamblePreamble DADA SASA LengthLength 802.2Header
and Data
802.2Header
and Data
FCSFCS8 6 6 2 4
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DSAPDSAP SSAPSSAP CTRLCTRL
AAAA AAAA CTRLCTRL OUIOUI EtherTypeEtherType
Upper Layer DataIP, AppleTalk
Upper Layer DataIP, AppleTalk
DATADATA
Ethernet Frame Variations
802.3 Frame
PreamblePreamble DADA SASA LengthLength 802.2 Headerand Data
802.2 Headerand Data FCSFCS
802.2 Frame
SNAP Frame
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Ethernet/802.3 Reliability
AA BB CC DD
Collision
AA BB CC DD
JAMJAMJAMJAM JAMJAMJAMJAM JAMJAMJAMJAM JAMJAMJAMJAM JAMJAMJAMJAMJAMJAMJAMJAM
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High-Speed Ethernet Options
• 100BaseFX
• 100BaseT4
• 100BaseTX
• 100VG-AnyLAN
Common WAN Technologies
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WAN Technology Overview
SDLC
HDLC
LAPB
PPP
X.25
Frame Relay
ISDN
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Physical Layer: WAN
(Modem)
Data Terminal EquipmentEnd of the user’s device
on the WAN link
DTEData Circuit-Terminating Equipment
End of the WAN provider’s
side of the communication facility
DCE
EIA/TIA-232V.35X.21HSSI
Others
CSU/DSU
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Data Link Layer: WAN Protocols
• SDLC—Synchronous Data Link Control
• HDLC—High-Level Data Link Control
• LAPB—Link Access Procedure, Balanced
• Frame Relay—Simplified version of HDLC framing
• PPP—Point-to-Point Protocol
• X.25—Packet level protocol (PLP)
• ISDN—Integrated Services Digital Network (data-link signaling)
(Modem)CSU/DSU
CSU/DSU
(Modem)