Network Basics and Architectures Neil Tang 09/05/2008 CS440 Computer Networks

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

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

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

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

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

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

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

Resource Sharing Multiplexing CS440 Computer Networks

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

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

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

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

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

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

OSI Model CS440 Computer Networks

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

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: It provides a process-to-process channel. CS440 Computer Networks

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

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

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

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

Routers CS440 Computer Networks

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