1. Network Basics and Architectures Neil Tang 09/05/2008
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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
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3. Applications WWW FTP Email Instant message VoIP-based network phone
Video-on-Demand (VoD)
P2P applications
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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.
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5. Requirements Connectivity Cost-Effective Resource Sharing
Support for Common Services
Reliability
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6. Connectivity
Node: a computer or a device with Network Interface Card(s) (NIC)
Link: point-to-point and multiple access
(a)
(b)
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7. Connectivity Switched Network:
Packet Switched Network (store and forward) : Computer networks
Circuit Switched Network: Telephone network A B
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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
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9. Resource Sharing
Multiplexing
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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!
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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?).
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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
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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.
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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.
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15. Network Architecture
ISO-OSI (Open System Interconnection) Architecture
Internet Architecture
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16. OSI Model
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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.
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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: It provides a process-to-process channel.
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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.
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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, DCF
Network Layer: IP, RIP, OSPF
Transport Layer: TCP, UDP
Session Layer: TCP
Presentation Layer: SSL, TLS
Application Layer: HTTP, FTP, POP3/SMTP, Telnet
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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.
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22. Encapsulation CS440 Computer Networks Payload Payload Application Data
TCP Header
IP Header
802.3 Header
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23. Routers
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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
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