CPE 426 Computer Networks Week 1 Introduction Review
- Slides: 80
CPE 426 Computer Networks Week 1: Introduction Review 1: Data Communications
Course Outlines n n ดใน Sheet สามารถ Download ได n http: //cpe. rsu. ac. th/ut
TOPICS n 1. Communication/NW Model n n 2. Communication Protocols OSI and TCP/IP n n Ch. 5. 1 -5. 5 Ch. 1. 1 -1. 10 3. Communication/NW Topology n Ch. 13. 8
TOPICS n 4. Signal/Power/Loss n n 5. Data Coding(Line Coding) n n Ch. 6. 1 -6. 10 Ch. 6. 11 -6. 20 6. Trasmission Media/Noise/Channel Capacity n Ch. 7. 1 -7. 10 & 7. 20 -7. 22
TOPICS n 7. Multiplexing & DSL n n 8. Asynchronous Communication n n Ch. 11. 1 -11. 3 & 12. 1 -12. 7 Ch. 9. 1 -9. 8 9. Synchronous Communication n Ch. 9. 9 -9. 13
TOPICS n 10. Flow Control/Error Control/ARQ n n 11. Circuit vs Packet Switching NW n n Ch. 8. 12 -8. 15 Ch. 3. 1 -3. 5 % 13. 1 -13. 5 ALSO Reference From CPE 326 (Stalling Book)
การสอสาร Entity ประกอบดวย 2 Destination Sender = Source ������������� Transmitter Receiver ������ DATA Signal = ������ Transmission Medium DATA
Data comm. Model ม 5 สวน Destination Sender = Source ������������� Transmitter Receiver ������ DATA ABC… Signal = ������ 01011… File: ABCD… Data Coding/Compression (ASCII, EBCDIC/ZIP) 010110001101…. Transmission Medium Wire/Wireless Loss and Noise Line Coding/Modulation Plus Multiplexing DATA 01011… Plus Error Decodine/Demodulation Demultiplexing ABC… ADC…
ASCII Code n American Standard Code for Information Interchange n ASCII includes definitions for 128 characters: 33 are non-printing control characters (now mostly obsolete) that affect how text and space is processed; 94 are printable characters, and the space is considered an invisible graphic. The most commonly used character encoding on the World Wide Web was US-ASCII until December 2007, when it was surpassed by UTF-8
Simplex บางครงเรยก Source Tx Destination Rx 4 -wire Duplex Rx Destination Tx Source Transmission Medium
Duplex Source Tx Destination Rx Transmission Medium Rx Destination Tx Source Half-Duplex Destination Source Tx/Rx Destination Tx/Rx Transmission Medium Full-Duplex Source
วธแกคอ Share Medium และทำ Multiple Access Control n ใน LAN จะใช Topology 3 แบบทสำคญ n Bus (และ Tree), Ring, Star Multiple Access = MA hub
วธแกคอ Share Medium และทำ Multiple Access Control n ใน WAN มกจะเปน Partial Mesh Medium จดไดวาเปน Statistical Time Division Multiplexing แบบหนง n C A Intermediate Node = Switching/Routing Node D B End Node E H G F
LAN vs WAN Technologies n LAN มกจะใชการ Share Medium แบบ Contention ดงนนจะตองมขบวนการควบคมการทำ Multiple Access n n Bus, Ring, Star WAN จะ Share Medium เชนกน แตมกจะใชวธของ Synchronous Multiplexing (TDM) ใน Circuit Switching Networkหรอ Statistical Multiplexing (ใชใน Packet Switching Network) n n Topology ทเหมาะสมคอ Partial Mesh Network และมกจะเปน Internetworking Technologies มกจะถกใชในการเชอมตอระหวาง ผาน WAN Network n ทนยมคอ Internet (IP Network) LAN
Protocol Architecture (Protocol Stack) n n Protocol Architecture ทเปนมาตรฐานมสองอน 7 Layer OSI Reference Model ของ ISO n n ปจจบนไมไดใชงานจรง แตใชเปน Reference TCP/IP Protocol Suite (ม 5 ชน n n การสอสารเกอบจะทงหมด มาตรฐานของ Internet )
7 Layer OSI Reference Model
OSI Environment
TCP/IP Protocol Architecture n n n Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET) Used by the global Internet No official model but a working one. n Application layer n Host to host or transport layer n Internet layer n Network access layer n Physical layer
TCP/IP Protocol Architecture Application INTERNET Transport Layer Internet Layer Network Access Physical
Physical Layer n n n Physical interface between data transmission device (e. g. computer) and transmission medium or network Characteristics of transmission medium Signal levels Data rates etc.
Network Access Layer n n n Exchange of data between end system and network Destination address provision Invoking services like priority ปกตมาตรฐานของ TCP/IP จะไมครอบคลมถง Layer 1 -2 ทวไปเรานำ TCP/IP เปน WAN และวางบน LAN คอ Ethernet
Internet Layer (IP) n n Systems may be attached to different networks Routing functions across multiple networks Implemented in end systems and routers คอ IP Protocol n มการทำงานแบบ Datagram
Transport Layer (TCP) n n n Reliable delivery of data Ordering of delivery ทสำคญม 2 Protocol n TCP = Transport Control Protocol n n n Connection Oriented Guarantee Delivery UDP = User Datagram Protocol n n Connectionless Best Effort
Application Layer n n Support for user applications e. g. http, SMPT
TCP/IP VS OSI Application Software NOS = Window NIC + Driver Physical Link
Addressing ใน TCP/IP n n n TCP Port หรอ UDP Port = 16 Bit IP Address, IPv 4 = 32 Bit หมายเลขเครอง และหมายเลข Network Physical Hardware Address n ถาใช TCP/IP บน Ethernet LAN อนนคอ Address ของ NIC หรอ MAC Address = 48 Bit
PDU = Protocol Data Unit TCP Segment IP Packet / IP Datagram Frame
Protocol ทสำคญของ TCP/IP
Standard n LAN: n n n WAN n n IEEE 802 Ethernet IEEE 802. 3 มยอยอกหลายตว WLAN IEEE 802. 11, 802. 11 b, 802. 11 g, 802. 11 n, 802. 11 i PAN-Bluetooth IEEE 802. 15 www. ieee. org มหลายตว (ITU) TCP/IP n n ทสำคญมกจะถกดแลโดย RFC = Request for Comments มมากกวา 4000 RFCs อนใหมจะแทนอนเกา (Obsolete) OSI
Summary Physical Layer n Physical Layer จะสลบซบซอนทสด ปกตจะเกยวกบไฟฟาสอสาร n n กำหนด Medium, Signal, Coding, Connector รวมถงกระบวนการ การสอสารจะถกจำกดจาก Layer น n Bit Rate/Baud Rate ~ Power, Noise, Distortion, Interference, Cross Talk n n ทสำคญ ขดจำกดตาม SNR และ Eb/No Channel Capacity
Line Coding n n n การสง Pulse เพอทจะแทน Data แตละบต n Pulse 2 ระดบ = Binary Signal n M-ary Signal จะใช M ระดบ ขอควรคำนง n Average DC เปนศนยหรอไม n Signal Transition มากเพยงพอ NRZ, AMI, Pseudoternary, Manchester, Differential Manchester และ อนๆ n อาจจะรวมกบการทำ Scrambling n HDB 3, B 8 ZS
FDM vs TDM
Statistical TDM Frame Formats
ADSL Channel Configuration
Mode ของการสงขอมล Digital n n Timing problems require a mechanism to synchronize the transmitter and receiver Two solutions n n Asynchronous Synchronous
Asynchronous (diagram)
Data Communications Interfacing (DTE-DCE Concept)
Mechanical Specification
Electrical Specification n n n Digital signals Values interpreted as data or control, depending on circuit Less than -3 v is binary 1, more than +3 v is binary 0 (NRZ-L) Signal rate < 20 kbps Distance <15 m For control, Less than-3 v is off, +3 v is on
Null Modem: DTE to DTE n n RS-232 -C Null Modem Cable (for Terminal/PC with 25 pin Connector) RS-232 -C Null Modem Cable (for Terminal/PC with 9 -pin Connector)
Null Modem
Summary Null Modem Simple Null Modem without Handshaking Null Modem With Loop-Back Handshaking Null Modem With Partial Handshaking Null Modem With Full Handshaking
Synchronous - Bit Level n n n Block of data transmitted without start or stop bits Clocks must be synchronized Can use separate clock line n n n Good over short distances Subject to impairments Embed clock signal in data n n Manchester encoding Carrier frequency (analog)
Synchronous - Block Level n n Need to indicate start and end of block Use preamble and postamble n n n e. g. series of SYN (hex 16) characters e. g. block of 1111 patterns ending in 11111110 More efficient (lower overhead) than async
Synchronous (diagram)
Simple Switched Network
Simple Switched Network BLOCKING
Simple Switched Network B D Finish
Example Modem Huahin Chiang Mai เครอขายโทรศพท Bangkok Modem Koraj
Packet Switched Network
Advantages n Line efficiency n n n Data rate conversion n n Each station เชอมตอกบ ดวยความเรวทตวเองกำหนด Queue Local Node Packets are accepted even when network is busy โดยเกบไวใน Queue n n แตละ Link สามารถจะ Share กนได Packets ทเขามาแตละ Node จะถกเขา เพอสงออกไป Delivery may slow down = Delay Priorities can be used
สรป Packet Switching Network n 2 Concepts กำหนดการทำงานใน Network(L 3) n n n Datagram Virtual Circuit 2 Concepts กำหนดการเชอมตอกบผใชภายน อก (ปกตจะอยใน L 4) n n Connection Oriented Connectionless
การทำงานของ Datagram n n n Each packet treated independently Packets can take any practical route Packets may arrive out of order Packets may go missing Up to receiver(ปลายทาง) to re-order packets and recover from missing packets สรปแลว การทำงานของ Network ประเภทนจะไม Guarantee การสงขอมล
Datagram Diagram
Virtual Circuit n n n Preplanned route established before any packets sent เสนทางจะถกกำหนดในชวงการ Connection Call request and call accept packets establish connection (handshake) กำหนด Connection ดวยตวเลข คอ VC Number Each packet contains a virtual circuit identifier instead of destination address No routing decisions required for each packet ดจาก VC # กเพยงพอ Clear request to drop circuit เมอจบ Not a dedicated path แตมองจากผใชเหมอน Circuit Switching
Virtual Circuit Diagram
End of Review Part I n n End of Review Part I Next Week n n n LAN and LAN Technologies Internet Concept ยงไมมการบาน
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