Network Basics and Architectures Neil Tang 09/05/2008

1. Network Basics and Architectures Neil Tang09/05/2008 CS440 Computer Networks

2. Outline • Connectivity: Node, link, switched network • Resource Sharing: Multiplexing • Support for Common Services • Reliability: Failures • OSI Architecture: Functionalities of each layer • Internet Architecture: Differences and features CS440 Computer Networks

3. Applications • WWW • FTP • Email • Instant message • VoIP-based network phone • Video-on-Demand (VoD) • P2P applications CS440 Computer Networks

4. Applications Visiting a URL from a web browser: • 17 messages may be exchanged via the network. • Up to 6 messages to translate URL to IP address. • 3 messages to set up TCP connection to the web server. • 4 messages for HTTP “get” messages and responses with positive acknowledgements (ACKs). • 4 messages to tear down TCP connection. • More messages to make it happen: e.g., messages for maintaining routing tables. CS440 Computer Networks

5. Requirements • Connectivity • Cost-Effective Resource Sharing • Support for Common Services • Reliability CS440 Computer Networks

6. (a) (b) Connectivity • Node: a computer or a device with Network Interface Card(s) (NIC) • Link: point-to-point and multiple access CS440 Computer Networks

7. Connectivity Switched Network: • Packet Switched Network (store and forward) : Computer networks • Circuit Switched Network: Telephone network A B CS440 Computer Networks

8. Connectivity • Addressing: Assign a unique address to each node in the network. • Routing: The process of determining systematically how to forward messages towards the destination node is called routing. • Unicast and Multicast Routing CS440 Computer Networks

9. Resource Sharing Multiplexing CS440 Computer Networks

10. Resource Sharing Types of Multiplexing • Synchronous Time Division Multiplexing (STDM) • Frequency Division Multiplexing (FDM) Weakness: Exclusive use of certain resources for each flow is not efficient! CS440 Computer Networks

11. ■ ■ ■ Resource Sharing Statistical Multiplexing • Like STDM, the physical link is shared over time. • Unlike STDM, data is transmitted from each flow on demand rather than during a pre-determined time slot. • Large messages need to be fragmented into small-size packets. • The switch or router maintains a buffer to store incoming packets • First-In-First-Out (FIFO) basis (LIFO?). CS440 Computer Networks

12. Resource Sharing Tradeoffs and Challenges: STDM Vs. Statistical • Network Capacity: Statistical multiplexing • QoS Support: STDM • Challenges for Statistical Multiplexing: Fairness, congestion control and QoS support CS440 Computer Networks

13. Support for Common Services • The challenge is to identify the right set of common services which can satisfy the requirements of applications and hide the complexity of the network • Network provides logic channels (pipes) connecting application processes. CS440 Computer Networks

14. Reliability Types of Failures: • Bit Error: Outside forces, such as power surge, interferences, etc. • Packet Loss: Buffer overflow and software mistakes. • Link and Node Failure: Link cut and computer crash. CS440 Computer Networks

15. Network Architecture • ISO-OSI (Open System Interconnection) Architecture • Internet Architecture CS440 Computer Networks

16. OSI Model CS440 Computer Networks

17. Features of Layering • Each layer corresponds to a particular functionality, i.e., solve a particular problem. • Softwares on different layers can be developed by different companies. • Easy to modify the functionality of a particular layer. CS440 Computer Networks

18. The Functionalities of Each Layer • Physical Layer: It handles the transmissions of raw bits over physical medium. • Data Link Layer: Physical addressing,framing, multiplexing and multiple access control. • Network Layer: Addressing (logical) and routing. • Transport Layer: Itprovides a process-to-process channel. CS440 Computer Networks

19. The Functionalities of Each Layer • Session Layer: It controls the dialogues (sessions) between end users. It establishes, manages and terminates the connections between the local and remote applications. • Presentation Layer: It manages the format of data exchanged by peers. • Application Layer: It provides an interface for the user to access information on the network. CS440 Computer Networks

20. Protocols One or more protocols implements the functionalities of each layer • Physical Layer: RS-232, 10BASE-T, T1/E1 • Data Link Layer: 802.3, 802.11 DCF • Network Layer: IP, RIP, OSPF • Transport Layer: TCP, UDP • Session Layer: TCP • Presentation Layer: SSL, TLS • Application Layer: HTTP, FTP, POP3/SMTP, Telnet CS440 Computer Networks

21. Internet Architecture • Bypassing: The application is free to bypass the defined transport layers and to directly use IP or network layer. • Narrow-waisted model: IP is the focal point. It defines a common method for exchanging packets for a large variety of applications over a wide collection of networks. CS440 Computer Networks

22. Encapsulation Payload Payload Application Data TCP Header IP Header 802.3 Header CS440 Computer Networks

23. Routers CS440 Computer Networks

24. Review • Connectivity: Node, link, switched network • Resource Sharing: Multiplexing • Support for Common Services • Reliability: Failures • OSI Architecture: Functionalities of each layer • Internet Architecture: Differences and features CS440 Computer Networks