CMPE 150 Fall 2005 Lecture 18
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1 CMPE 150- Introduction to Computer Networks CMPE 150 Fall 2005 Lecture 18 Introduction to Computer Networks
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CMPE 150 Fall 2005 Lecture 18. Introduction to Computer Networks. Announcements. Midterm on 11.04. In class, closed books/notes. Homework 3 is up. Due on 11.07.05. Lab this week: discussion/review sessions for midterm. Lab next week: Layer 2. Ethernet. Today. Finish MAC. - PowerPoint PPT Presentation
Transcript of CMPE 150 Fall 2005 Lecture 18
1CMPE 150- Introduction to Computer Networks
CMPE 150
Fall 2005Lecture 18
Introduction to Computer Networks
2CMPE 150- Introduction to Computer Networks
Announcements
• Midterm on 11.04.– In class, closed books/notes.
• Homework 3 is up.– Due on 11.07.05.
• Lab this week: discussion/review sessions for midterm.
• Lab next week: – Layer 2.
– Ethernet.
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Today
• Finish MAC.
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Ethernet Cabling
• The most common kinds of Ethernet cabling.
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Ethernet Cabling (Cont’d)
• Three kinds of Ethernet cabling. • (a) 10Base5, (b) 10Base2, (c) 10Base-T.
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Ethernet Topologies
• Cable topologies. (a) Linear, (b) Spine, (c) Tree, (d) Segmented.
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Switched Ethernet
• A simple example of switched Ethernet.
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Switched Ethernet (Cont’d)
• Point-to-point connections to multi-port hub acting like switch; no collisions.
• More efficient under high traffic load: break large shared Ethernet into smaller segments.
Hub
Switch
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Fast Ethernet
• IEEE 802.3u• 100Mbps.
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Gigabit Ethernet
• (a) A two-station Ethernet. (b) A multistation Ethernet.
. IEEE 802.11z.
. All point to point.
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Gigabit Ethernet (Cont’d)
• Gigabit Ethernet cabling.
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Standardized MACs
TopologiesBus Ring
Round robin
Reservation
Contention
Token bus(802.4)Polling (802.11)
DQDB(802.6)
CSMA/CD(802.3)CSMA(802.11)
Token ring(802.5; FDDI)
Techniques
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Wireless LANs
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Wireless LANs
• 2 modes of operation:– Infrastructure mode.
– Ad hoc mode,
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Wireless LANs
• (a) Wireless networking with a base station.• (b) Ad hoc networking.
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IEEE 802.11
• IEEE standard for WLANs.• Standardizes the PHY, MAC, and LLC.– LLC is the same as Ethernet.
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The 802.11 Protocol Stack
• Part of the 802.11 protocol stack.
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IEEE 802.11 Stack (Cont’d)
• Distributed access control mechanism (DCF) based on CSMA with optional centralized control (PCF).
•
Physical Layer
DCF
PCFMAClayer
Contention-freeService (polling)
ContentionService(CSMA)
LLC
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802.11
• Distributed coordination function (DCF) uses CSMA-based protocol (e.g., ad hoc networks).
• CD does not make sense in wireless.– Hard for transmitter to distinguish its own
transmission from incoming weak signals and noise.
• Point coordination function (PCF) uses polling to grant stations their turn to transmit (e.g., cellular networks).
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Why a new MAC for wireless?
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Why a new MAC for wireless?
• The range of a single radio may not cover the entire system.
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Why a new MAC for wireless?
• (a) The hidden station problem.• (b) The exposed station problem.
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802.11 MAC
• DCF: CSMA or CSMA/CA.• PCF; uses polling (centralized round-robin)
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What’s CSMA/CA?
• CSMA with collision avoidance.• Radios are usually half-duplex.– Cannot send and listen at the same time.
– CSMA/CD not possible.
• CSMA/CA means both physical- and virtual carrier sensing.– Tries to avoid hidden terminals.
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How does CSMA/CA work?
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802.11 Fragments
• A fragment burst.
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REVIEW
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REVIEW (1)
• Introduction, overview, terminology.• The Telephone Network (PSTN or POTS).• Addressing.• Data networks.– Communication model.– System components.
• Connecting end systems:– Point-to-point (dedicated) link.– Multiple access (shared) link.– Switched point-to-point.
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REVIEW (2)
• Types of data networks:– Coverage: LAN, MAN, WAN.– Type of connection.– Topology.
• Protocols, Layering, Protocol Architecture (Stack), PDUs.
• Examples of protocol stacks.– OSI ISO.– TCP/IP.
• Protocol stack operation.– Encapsulation/de-encapsulation.– Overhead.
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REVIEW (3)
• Types of networks:– Circuit-, message-, and packet switching.
• Types of network services:– Connection versus connection-less service or
datagram versus virtual circuit.
• Physical layer (PHY).– Function.– Analog versus digital transmission.– Digitization.
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REVIEW (4)
• PHY (Cont’d).– Sampling frequency.
– Bit rate.
– Signals and Systems.• Fourier analysis.• Nyquist’s Theorem.• Shanon’s Theorem.• Bandwidth.
– Guided transmission.
– More on the PSTN.
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REVIEW (5)
• PHY (Cont’d).– More on the PSTN.• Components.• Modems.• Modulation.• Baud rate versus bit rate.• Full-, half-, and simplex transmission.• Broadband access: ADSL, Cable, Wireless LL.• Trunking.
– Mux’ing and De-mux’ing.
– Wireless transmission.
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REVIEW (6)• PHY (Cont’d).
– Wireless transmission.– Satellite.– Mobile phone system.
• DLL.– Functions.
• Framing, error-, and flow control.
– Framing.• Different framing mechanisms.• Frame fields.
– Error control.– Flow control.
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REVIEW (7)
• DLL.– Error control.• Error detection versus error correction.• Mechanisms for error detection/correction.
– Error + Flow control protocols.• Stop-and-Wait.• ARQ.• Sliding window.• Go back N• Selective repeat.
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REVIEW (8)
• DLL (Cont’d).– Window size and sequence numbers.– Bandwidth-delay product.– Example DLL protocols,
• MAC.– Why MACs?– Where is the MAC in the stack?– MACs and LANs.– Multiplexing.• FDM, TDM. Dynamic TDM.
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REVIEW (9)
• MAC (Cont’d).– Types of MACs.– Contention-based MACs.
• Aloha family.• CSMA family,
• Ethernet.– Ethernet MAC.– BEB.– Cabling.– Ethernet evolution.
• Wireless LANs.– IEEE 802.11.
