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ECE453 – Introduction to Computer Networks

ECE453 – Introduction to Computer Networks. Lecture 17 – Top – Down Approach (A Review). From the moment you type in an http link in a web browser until you get the required webpage displayed in the browser, what has exactly happened?. Application Client Server Protocol Transport layer

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ECE453 – Introduction to Computer Networks

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  1. ECE453 – Introduction to Computer Networks Lecture 17 – Top – Down Approach (A Review)

  2. From the moment you type in an http link in a web browser until you get the required webpage displayed in the browser, what has exactly happened?

  3. Application Client Server Protocol Transport layer Set up a connection Socket programming Reliable data transfer Congestion control Flow control Network layer Routing Addressing Link layer Error detection Error correction Multiple access (MAC) Addressing Physical layer GET /somedir/page.html HTTP/1.0 User-agent: Mozilla/4.0 Accept: text/html,image/gif,image/jpeg Accept-language:fr (extra carriage return, line feed) message

  4. Physical vs. Logical Communication Logical communication between processes Logical communication between end systems Logical communication between directly connected units

  5. Application Client Server Protocol DNS Aliasing vs. load distribution Email SMTP vs. POP3 vs. IMAP vs. HTTP Web File transfer Two connection flows Application protocols Push vs. pull State vs. stateless Persistent vs. non-persistent Port number Service model used Socket Programming Difference in UDP and TCP socket programming Byte order What does “accept()” do? What does “listen()” do? What does “socket()” do? What does “connect()” do? Application Layer

  6. Multiplexing/demultiplexing Error detection (checksum) Compose/decompose Reliable data transfer Stop and wait Sliding window Go back N Selective repeat Flow control Receiver’s window vs. receiver’s buffer Congestion control Slow start and AIMD Connection management Three-way handshaking Message exchange detail Connection termination Message exchange detail Transport Layer Services

  7. TCP Header 0 24 4 16 31 Source Port Destination Port Length Checksum 0 24 4 16 31 Source Port Destination Port Sequence Number Acknowledge Number HLEN Reserved Code Bits Window Checksum Urgent Pointer Options (if any) Padding

  8. The Network Layer • Routing • IP protocols • Addressing • Hierarchical addressing (5 classes) • Classless addressing (CIDR) • DHCP • NAT • IPv6 • Fragmentation • Error monitoring • ICMP

  9. DV PV LS ospfdripd bgpd UDP TCP Network layer services (routing table) Routing • Static routing • Dynamic routing • Centralized routing • Link state • The oscillation problem • Decentralized routing • Distance vector • Count to infinity problem • Good news vs. bad news • Internet routing • Hierarchical routing (what is AS? Why hierarchical routing?) • Intra-domain routing • OSPF, RIP • Inter-domain routing • BGP

  10. IP Header

  11. Link layer services Flow control RDT Error detection CRC Error correction Hamming distance and Hamming code Link layer addressing ARP Specific link layer technologies: PPP Ethernet Special features (CSMA/CD, encoding) IEEE 802.11 LANs (CSMA/CA) Multiple access protocols (MAC) ALOHA Carrier sensing 1-persistent P-persistent Non-persistent CSMA/CD Wireless LAN Link layer switching Hubs Bridges Switches Link Layer and MAC Layer Summary

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