L1: Introduction - Hui Chen · Identifying Nodes When networks grow, there is a need to identify...
Transcript of L1: Introduction - Hui Chen · Identifying Nodes When networks grow, there is a need to identify...
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L1: Introduction
Hui Chen, Ph.D.
Dept. of Engineering & Computer Science
Virginia State University
Petersburg, VA 23806
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Acknowledgements
� Some pictures used in this presentation were obtained from
the Internet
� The instructor used some slides the following references
� Larry L. Peterson and Bruce S. Davie, Computer Networks: A Systems
Approach, 5th Edition, Elsevier, 2011
� Andrew S. Tanenbaum, Computer Networks, 5th Edition, Prentice-
Hall, 2010
� James F. Kurose and Keith W. Ross, Computer Networking: A Top-
Down Approach, 5th Ed., Addison Wesley, 2009
� Larry L. Peterson’s (http://www.cs.princeton.edu/~llp/) Computer
Networks class web site
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Lecture Outline
� About the class
� Network building blocks
� Laying and architecture
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Course Overview by Topics� Foundation
� Layering
� Topology design
� Internet architecture
� Bandwidth and latency
� Links and simple networking� Classes of links and physical media
� Encoding
� Framing
� Error detection and correction
� Case studies
� Internetworking� Switching and bridging
� Basic internetworking
� Routing
� Implementation and performance
� Advanced internetworking� Interdomain routing
� IPv6
� End-to-End protocols� Simple demultiplexer
� Reliable byte stream
� Congestion control and resource allocation
� Network security
� Network analysis� Probabilistic modeling
� Computer simulation
� Software and applications
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Textbook
� Required textbook: Computer Networks: A Systems
Approach (5th edition), by Larry Peterson and Bruce
Davie
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� 1 Foundation
� 2 Getting Connected
� 3 Internetworking
� 4 Advanced networking
� 5 End-to-end protocols
� 6 Congestion control and resource allocation
� 7 End-to-end data
� 8 Network security
� 9 Applications
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Expectations
� Class participation
� Attendance
� Discussion
� In-class exercises
� Review after class
� Lecture nodes/slides
� Read relevant sections in the
textbook
� Assignments
� Homework
� Labs
� Project
� Presentations
� Exams and Quizzes
� Midterm
� Final
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What is the Class for?
� Focus on the designers of future products and
protocols
� To understand underlying principles of networking
� Exposure for the network administrators and
application developers
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Systems Approach
� What are the ways that a user can get connected to a larger
network? (Connectivity)
� How do we grow networks in size? (Scalability)
� What are the ways to allow different network products and
protocols to coexist on the same network? (Heterogeneity)
� How do we manager resources on the network and satisfy
requirements of different users? (Resource management and
congestion control)
� How do we keep data transmitted over networks secure?
(Network security)
� ……
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System Approach
� Building and designing networks
� Foundation: basic concepts
� Direct link network
� Nodes and links
� Grow network
� Direct link network � switched network � internetworks
� The Internet is an internetwork
� Network applications and security
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Foundation
� Topics
� Cover primarily section 1.3
� Computer network concept
� Network architecture
� Layering and Protocols
� Internet Architecture
� Reading assignment
� Chapter 1 (section 1.1, 1.2, and 1.3)
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What is a ComputerComputerComputerComputer Network?
� Built primarily from generalgeneralgeneralgeneral----purposepurposepurposepurpose programmable
hardware
� Optimized for carrying many different types of datadifferent types of datadifferent types of datadifferent types of data
� Support a wide, and ever-growing, range of
applicationsapplicationsapplicationsapplications.
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A Network Consisting of Nodes and
Links
Nodes can be indirectly connected!
Forwarding nodes (switches) Switched network
Hosts connected to the network
hosts
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Nodes and Links
� Nodes: personal computers, server computers, special-
purpose hardware …
� Links:
� Physical media
� Coax cable, optical fiber, twisted-pair network cable, wireless
(EM radiation, acoustic waves, …) …
� Connection type
� Point-to-point
� Multiple access
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Direct Link Networks
� Point-to-point networks
� Multiple access networks
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Point-to-point link
Multiple access link
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Direct Link Networks: Two Types of
Links
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Direct Link Networks: Advantage
and Disadvantages
� What are their advantage and disadvantage
between point-to-point and multiple access
networks?
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Grow Network in Size
� Direct link networks are small
� How to grow networks in size?
� Switched networks: a network of networks connected by
network switches
� A network switch (forwarding node) is a node with two or
more links
� Forward messages from one network to other networks
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Point-to-point link Point-to-point link
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Switched Networks
� Circuit-switched networks
� Carry bit-streams
� Establishes a dedicated circuit across a sequence of links between source node and destination node
� Allows the source node to send a stream of bits across this circuit to a destination node.
� e.g.: original telephone network
� Packet-switched networks
� Store-and-forward messages
� Receive: each node in a store-and-forward network first receives a complete packet over some link
� Store: stores the packet in its internal memory
� Forward: forwards the complete packet to the next node.
� e.g.: Internet
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Identifying Nodes
� When networks grow, there is a need to identify and
differentiate different nodes and to forward
messages to a or a set of nodes
� Addressing and routing
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Addressing and Routing
� Address: byte-string that identifies a node
� Usually unique
� Routing: process of finding ways to forward messages
to the destination nodes based on its address
� Type of addresses
� Unicast: node-specific
� Broadcast: all nodes on the network
� Multicast: some subset of nodes on the network
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Multiplexing
� A system resource is shared among multiple users
� Examples:
� Time-division multiplexing (TDM)
� Frequency-division multiplexing (FDM)
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Static and Statistical Multiplexing
� Static Multiplexing
� Examples: TDM and FDM
� Limitations
� If one flow does not have any data to send, its share of physical link (time quantum or frequency) remains idle
� The maximum number of flows is fixed and known ahead of time
� Statistical Multiplexing
� On-demand time-division
� Schedule link on a per-packet basis
� Packages from different sources interleaved on link
� Buffer packets that are contending for the link
� Congestion: Buffer (queue) overflow
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An Example of Multiplexing
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Statistical Multiplexing: Challenges
� Fairly allocating link capacity to different flows
� Dealing with congestion
� Ensuring quality of service
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Inter-Process Communication
� Turn host-to-host connectivity into process-to-process communication
� Fill gap between what applications expect and what the underlying technology
provides.
� What should a network provide?
� What should an application provide?
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Examples of IPC Abstractions
� Request/reply-based
� Distributed file systems
� Web access
� Stream-based
� Video: sequence of
frames
� Video application
� On-demand video
� Video conference
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Things can go wrong!
� Network failures:
� Bit-level errors (electrical interference, e.g., lightning)
� Packet-level errors (congestion)
� Link and node failures (cable is cut, computers crashes)
� Other related issues
� Messages/packets are delayed
� Messages/packets are delivered out of order
� Third parties eavesdrop
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Protocols
� Well-defined procedure that runs on multiple parties
� A set of rules and conventions
� Two interface
� Service interface: operations on this protocol
� Peer-to-peer interface: message exchanged with peer
� Building blocks for a network architecture
� Term “protocol” is overloaded
� Specification of peer-to-peer interface
� Module that implements this interface
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Layered Architecture
� Network Architecture
� A structured set of protocols that implement the exchange of
information between computers/parties
� Use abstractionsabstractionsabstractionsabstractions to hide complexity
� Abstraction naturally leads to layering
� Alternative abstractions at each layer
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Service and Peer Interfaces
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Example of Protocol Machinery
� Most peer-to-peer communication is indirect
� Peer-to-peer is directly only at hardware level
Layers
Service are grouped in a hierarchy of layers, which provide service interfaceLayer N protocols only use services provided by layer N-1
Layer N protocols only provide services to layer N+1Q: does layer N needs to know the inner-working of layer N-1 or layer N+1?
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Encapsulation and Multiplexing/Demultiplexing
� Header can have demultiplexing key
header
payload
header
payload
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OSI (Open System Interconnection) Architecture
� Defined by ISO. Used as a reference model
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OSI: Physical Layer (Layer 1)
� Converts bits into physical signals such as electrical,
optical, acoustic signals …
� Transmits these signals over the hardware
communication medium such as twisted pair cable,
coaxial cable, fiber optics, open/free space, water …
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OSI: Data Link Layer (Layer 2)
� Reliably transfers data frames over a link
� Performs synchronization, error control, and flow
control
� Example: Point-to-Point Protocol (PPP)
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OSI: Network Layer (Layer 3)
� Moves packets inside the network
� Performs routing, addressing, switching, congestion
control
� Example: Internet Protocol (IP)
010…
010…
010…010…
010…
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OSI: Transportation Layer (Layer 4)
� Controls delivery of data between hosts
� Connection management, error control, flow control,
multiplexing
� Example: Transmission Control Protocol (TCP) and
User Datagram Protocol (UDP)
010…
010…
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OSI: Session Layer (Layer 5)
� Support dialog between application programs
� Session management, synchronization
� Example: Remote-Procedure-Call (RPC)
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OSI: Presentation Layer (Layer 6)
� Data conversion into application format
� Encryption and decryption
� Example: Secure Sockets Layer (SSL)
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OSI: Application Layer (Layer 7)
� Provides network access to application programs
� Application specific
� Example: File Transfer, Electronic Mail
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Internet (TCP/IP) Architecture
� Defined Internet Engineering Task Force (IETF)
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OSI and Internet Architectures
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Key Characteristics of Internet
Architecture
� Layering is not strict
� Hourglass design with IP as focal point
� Protocol specification + 1 (preferable 2)
representative implementation
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Application
Transport
Network
Data Link
Physical
Medium
Data Link
Physical
Application
Transport
Network
Data Link
Physical
Data Link
Physical
Network Network
Radio
Often we need to implement a function across multiple layers.
The Layered Reference Model
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Summary
� What is a computer network?
� Basic requirements
� General purpose
� Cost-effective network sharing
� Fair network link allocation
� Robust connectivity
� Layered architecture
� Question:
� How is the performance (see next lecture)?
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Additional Reading Assignment
� Leonard Kleinrock, An Early History of Internet, IEEE
Communications Magazine, Vol. 48, No. 8, pp. 26-36,
Available:
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&ar
number=5534584
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