Introduction to Computer Networks CMPE 150 Fall 2005 Lecture 18 CMPE 150 Introduction to Computer Networks 1 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 CMPE 150 Introduction to Computer Networks 2 Today Finish MAC CMPE 150 Introduction to Computer Networks 3 Ethernet Cabling The most common kinds of Ethernet cabling CMPE 150 Introduction to Computer Networks 4 Ethernet Cabling Cont d Three kinds of Ethernet cabling a 10Base5 b 10Base2 c 10Base T CMPE 150 Introduction to Computer Networks 5 Ethernet Topologies Cable topologies a Linear b Spine c Tree d Segmented CMPE 150 Introduction to Computer Networks 6 Switched Ethernet A simple example of switched Ethernet CMPE 150 Introduction to Computer Networks 7 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 Switch Hub CMPE 150 Introduction to Computer Networks 8 Fast Ethernet IEEE 802 3u 100Mbps CMPE 150 Introduction to Computer Networks 9 Gigabit Ethernet IEEE 802 11z All point to point a A two station Ethernet b A multistation Ethernet CMPE 150 Introduction to Computer Networks 10 Gigabit Ethernet Cont d Gigabit Ethernet cabling CMPE 150 Introduction to Computer Networks 11 Standardized MACs Techniques Round robin Reservation Contention Bus Topologies Ring Token bus 802 4 Polling 802 11 DQDB 802 6 Token ring 802 5 FDDI CSMA CD 802 3 CSMA 802 11 CMPE 150 Introduction to Computer Networks 12 Wireless LANs CMPE 150 Introduction to Computer Networks 13 Wireless LANs 2 modes of operation Infrastructure mode Ad hoc mode CMPE 150 Introduction to Computer Networks 14 Wireless LANs a Wireless networking with a base station b Ad hoc networking CMPE 150 Introduction to Computer Networks 15 IEEE 802 11 IEEE standard for WLANs Standardizes the PHY MAC and LLC LLC is the same as Ethernet CMPE 150 Introduction to Computer Networks 16 The 802 11 Protocol Stack Part of the 802 11 protocol stack CMPE 150 Introduction to Computer Networks 17 IEEE 802 11 Stack Cont d Distributed access control mechanism DCF based on CSMA with optional centralized control PCF MAC layer LLC PCF DCF Physical Layer CMPE 150 Introduction to Computer Networks Contention free Service polling Contention Service CSMA 18 802 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 CMPE 150 Introduction to Computer Networks 19 Why a new MAC for wireless CMPE 150 Introduction to Computer Networks 20 Why a new MAC for wireless The range of a single radio may not cover the entire system CMPE 150 Introduction to Computer Networks 21 Why a new MAC for wireless a The hidden station problem b The exposed station problem CMPE 150 Introduction to Computer Networks 22 802 11 MAC DCF CSMA or CSMA CA PCF uses polling centralized round robin CMPE 150 Introduction to Computer Networks 23 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 CMPE 150 Introduction to Computer Networks 24 How does CSMA CA work CMPE 150 Introduction to Computer Networks 25 802 11 Fragments A fragment burst CMPE 150 Introduction to Computer Networks 26 REVIEW CMPE 150 Introduction to Computer Networks 27 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 CMPE 150 Introduction to Computer Networks 28 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 CMPE 150 Introduction to Computer Networks 29 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 CMPE 150 Introduction to Computer Networks 30 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 CMPE 150 Introduction to Computer Networks 31 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 CMPE 150 Introduction to Computer Networks 32 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 CMPE 150 Introduction to Computer Networks 33 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 CMPE 150 Introduction to Computer Networks 34 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 CMPE 150 Introduction to Computer Networks 35 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 CMPE 150 Introduction to Computer Networks 36
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