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Book in glance. Basics of COMPUTER NETWORKS. Computer Engineering Faculty of Engineering Kurdistan University ( Email : ghasem.mohammadi@gmail.com). Contact information. سرفصلهاي درس. فصل 1: مفاهيم اوليه فصل 2: لايه فيزيكي فصل 3: لايه پيوند داده فصل 4: لايه شبكه فصل 5: لايه انتقال
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Book in glance Basics of COMPUTER NETWORKS Computer Engineering Faculty of Engineering Kurdistan University ( Email : ghasem.mohammadi@gmail.com)
Contact information سرفصلهاي درس • فصل 1: مفاهيم اوليه • فصل 2: لايه فيزيكي • فصل 3: لايه پيوند داده • فصل 4: لايه شبكه • فصل 5: لايه انتقال • فصل 6: لايه كاربرد • فصل 7 :كابل كشي ساخت يافته
Computer Network What’s a Computer Network? • Connecting two or more computers or other devices via a Communication media( Physical or wireless) • Categorizing networks according to size: • LAN (Local Area Network) • MAN (Metropolitan Area Network) • WAN (Wide Area Network) • Internet
Computer Network Types of Links Point-to-Point Multiple Access …
Computer Network Protocol Demultiplexing • Multiple choices at each layer FTP HTTP NV TFTP TCP UDP Network IP TCP/UDP IPX IP Type Field Protocol Field Port Number NET1 NET2 … NETn
Computer Network OSI Layers and Locations Application Presentation Session Transport Network Data Link Physical Hub Switch Host Router Host
Computer Network Network Interface Card (NIC)
Computer Network Hub (layer 1 device) Just knows bits
Computer Network Switch (layer 2 device) Knows MAC addresses
Computer Network Router (layer 3 device) Knows Logical addresses (IP and IPX)
Computer Network Twisted Pair UTP Connector STP
Computer Network Bad Good
Computer Network Connectors
Computer Network Fiber Optic Connectors
Computer Network A Fiber Optic Ring with Active repeaters
Computer Network Electromagnetic Spectrum
Computer Network Types of Propagation
Basic Modulation Types Computer Network
Computer Network Compression: • Huffman Coding • Run-length Coding • Ziv Lempel compression
Computer Network FDM (Frequency Division Multiplexing)
Computer Network WDM (Wavelength Division Multiplexing)
Computer Network TDM (Time Division Multiplexing)
Computer Network Circuit Switching
Computer Network Time Division Switch
Computer Network Packet Switching
Computer Network Message Switching
Computer Network Framing Methods Character Count Byte Stuffing Bit Stuffing
Computer Network Handling Errors
Computer Network Single bit Error Multiple bit Error
Computer Network Parity bit 0110100 1 1011010 0 One Dimensional Parity 0010110 1 1110101 1 1001011 0 1000110 1 Two Dimensional Parity
Computer Network Cyclic Redundancy Check (CRC) • Represent a (n+1)-bit message as an n-degree polynomial M(x) • E.g., 10101101 M(x) = x7 + x5 + x3 + x2 + x0 • Choose a divisor k-degree polynomial G(x) • Compute reminder R(x) of M(x)*xk / C(x), i.e., compute A(x) such that • M(x)*xk = A(x)*G(x) + R(x), where degree(R(x)) < k • Let • T(x) = M(x)*xk – R(x) = A(x)*G(x) • Then • T(x) is divisible by G(x)
Computer Network Hamming Code
Computer Network Categories of Flow Control
Computer Network Stop-and-Wait
Computer Network Sliding Window Sender/Receiver State Sender Receiver Next expected Max acceptable Max ACK received Next seqnum … … … … Sender window Receiver window Sent & Acked Sent Not Acked Received & Acked Acceptable Packet OK to Send Not Usable Not Usable
Computer Network Example of Sliding Window
Computer Network Sliding Window Go-Back-n, Damaged Frame
Computer Network Sliding window Selective-Repeat, Damaged Frame
Computer Network Media Access Control Evolution of Contention Protocols Aloha Developed in the 1970s for a packet radio network SlottedAloha Improvement: Start transmission only at fixed times (slots) CSMA = Carrier Sense Multiple Access Improvement: Start transmission only if no transmission is ongoing CSMA CD = Collision Detection Improvement: Stop ongoing transmission if a collision is detected (e.g. Ethernet) CSMA/CD
Computer Network • The Aloha Protocol • simple: if you have pkt to send, "just do it" • if pkt suffers collision, will try resending later
Computer Network • Slotted Aloha • synchronous system: time divided into slots • slot siz equals fixed packet transmission time • when pkt ready for transmission, wait until start of next slot • packets overlap completely or not at all
Computer Network • Carrier Sensing Protocols • Aloha is inefficient (and rude!): doesn't listen before talking! • Carrier Sense Multiple Access: CSMA • non-persistent CSMA: • sense (listen to) channel • if {channel sensed busy} • then wait random time; go to 1 • else transmit packet • p-persistent CSMA: • sense (listen to) channel • when {channel sensed idle} • transmit with probability p • else wait random time, go to 1
Computer Network • CSMA/CD • CSMA with collision detection(CD): • listen while talking! • stop transmitting when another pkt has collided with your pkt • wait random time before attempting to resend • worst case time to detect a collision? • performance depends (as in CSMA) on channel length