1. Introductory Networking Concepts Introductory Networking Concepts Rudra Dutta CSC 453 - Fall 2013

2. Copyright Fall 2013, Rudra Dutta, NCSU2 Digital Communication Digital representation of information – Reduces diverse information to same form – Allows infinite replication – Allows general purpose manipulation (computers) – Allows transmission from one computer to another Digital communication – Revolution in our times – Created digital economy – Large number of products and services seen as information

3. Copyright Fall 2013, Rudra Dutta, NCSU3 Components for Communication Nodes (computers, …) Links Communication primitive

4. Copyright Fall 2013, Rudra Dutta, NCSU4 Scalability

5. 5 Cooperation Nodes - endpoint nodes and intermediate nodes Links Communication primitive

6. Copyright Fall 2013, Rudra Dutta, NCSU6 Forwarding Performed by intermediate node – Process of copying data off one incoming link, on some outgoing link May be performed at physical layer – (Sub-bitpipe) – Utilize physical phenomena - “Switching” – Electrical circuit, etc. May be at higher layer – Bits or some organization of bits – “Forwarding” – “Routing” (ambiguity)

7. Copyright Fall 2013, Rudra Dutta, NCSU7 The Need for Sharing Taking turns “Multiplexing” – Time division, frequency division

8. Copyright Fall 2013, Rudra Dutta, NCSU8 Protocols “Rule set”, “language” Standards for communication hardware/software Common guidelines for implementations – Different implementations of same protocol – Standards bodies make protocols ITU-T, IETF, IEEE – Software manufacturers produce implementations On = “1” or “0” ?

9. Copyright Fall 2013, Rudra Dutta, NCSU9 Delay Two meanings – How fast can successive bits be put into the pipe? – How long does a bit take to traverse the pipe? Time Sender Receiver “Distance”

10. Copyright Fall 2013, Rudra Dutta, NCSU10 Throughput Total number of bits transferred, over given time – Related obviously to the transmission delay – Propagation delay often referred to simply as “delay” or “latency” – Throughput sometimes referred to as “bandwidth” – “Bandwidth-delay product” - filling the pipe

11. Copyright Fall 2013, Rudra Dutta, NCSU11 Software Protocols Syntax of a message – what fields does it contain? – in what format? Semantics of a message – what does a message mean? – for example, not-OK message means receiver got a corrupted file Actions to take on receipt of a message – for example, on receiving not-OK message, retransmit the entire file

12. Copyright Fall 2013, Rudra Dutta, NCSU12 ISO OSI reference model A set of protocols is open if – protocol details are publicly available – changes are managed by an organization whose membership and transactions are open to the public A system that implements open protocols is called an open system International Organization for Standards (ISO) prescribes a standard to connect open systems – open system interconnect (OSI) Has greatly influenced thinking on protocol stacks

13. Copyright Fall 2013, Rudra Dutta, NCSU13 The seven layers ApplicationTop level user of the system PresentationResolve platform issues (data representation, possibly encryption) SessionFull-duplex, expedited data delivery, session synchronization TransportError control, flow control, multiplex Reliability NetworkConcatenates links to form end-to-end abstraction Data Link ControlOrganizes bit transmissions into frame transmissions (LLC, MAC sublayers) PhysicalMoves bits between physically connected end-systems End-to-end Node-to-node

14. Copyright Fall 2013, Rudra Dutta, NCSU14 Peer Processes End Node Intermediate Node End Node DLC Phy DLC

15. Copyright Fall 2013, Rudra Dutta, NCSU15 Network Components Different network components function at different layers Embody service at different protocol layers Nomenclature is not very well standardized, and is changing Mixed, “layer-blurring” devices complicate matters

16. Copyright Fall 2013, Rudra Dutta, NCSU16 DLC PHY NET DLC PHY NET PHY DLC PHY NET DLC PHY NET ABCDE A B C D E Component C in this figure is a wire, or hub.

17. Copyright Fall 2013, Rudra Dutta, NCSU17 DLC PHY NET DLC PHY NET DLC PHY DLC PHY DLC PHY NET DLC PHY NET ABCDE A B C D E Computer C in this figure is a bridge. (Could be a switch, if dumb component.)

18. Copyright Fall 2013, Rudra Dutta, NCSU18 DLC PHY NET DLC PHY NET DLC PHY DLC PHY DLC PHY NET DLC PHY NET ABCDE Computer C in this figure is a router, or switch A B CD E DLC PHY NET

19. Copyright Fall 2013, Rudra Dutta, NCSU19 DLC PHY NET DLC PHY NET DLC PHY DLC PHY DLC PHY NET DLC PHY NET AB C DE Computer C in this figure is a router, or switch Computers A, B, D, E are hosts A B CD E DLC PHY NET TxP APP TxP APP TxP APP TxP APP

20. Copyright Fall 2013, Rudra Dutta, NCSU20 Physical Layer Communication Digital – concept – Information can be analog or digital EM waves – analog by definition Analog EM signal can be made to transfer digital data Thus we could (and usually do) have: “Digital interpretation of analog signal representing digital representation of analog data” 010100…

21. Copyright Fall 2013, Rudra Dutta, NCSU21 Propagation Media Guided – Twisted pair – Coax cable – Optical fiber Unguided – Radio (semi-guided follow curvature of earth) – Radio bounced off ionosphere – Fiberless optical (wireless optical) – Communication satellites

22. Copyright Fall 2013, Rudra Dutta, NCSU22 Communication in the EM Spectrum

23. Copyright Fall 2013, Rudra Dutta, NCSU23 Modulation A “carrier” wave exists on the medium – Own amplitude, frequency, phase – Base energy pattern – no information – Analog, of course A “signal” needs to be transmitted – Time varying; analog, or digital The value of the signal from instant to instant is used to change the energy pattern of the carrier

24. Copyright Fall 2013, Rudra Dutta, NCSU24 The Issue of Bitrate Consider simple AM (ASK) – Transmit one of two distinct amplitudes (voltages)  transmission of one bit How soon after can we transmit another bit? – How fast can transmitter change its state? – How fast can receiver recognize line state? – Appears to limit bit rate, but - Does not have to be just two states – Why not transmit one of four distinct amplitudes? – Why not more?  No limit to bit rate ?!  Limited by noise 10 00011011

25. Logical Link, Medium Access Copyright Fall 2013, Rudra Dutta, NCSU25

26. Copyright Fall 2013, Rudra Dutta, NCSU26 Layers in a Router/Switch DLC PHY NET DLC PHY DLC PHY NET ARD DLC PHY NET Forwarding

27. Copyright Fall 2013, Rudra Dutta, NCSU27 Software Router Operation Some of L2 and all of L3 protocols are software processes Exchange of data requires IPC, and blocking Buffering may be employed between layers – Almost certainly at higher than the bitpipe layer Forwarding

28. Copyright Fall 2013, Rudra Dutta, NCSU28 Buffering at L3 Operation of L3 itself may require buffering data – Store-and-forward Input-buffer-process-buffer-output cycle – May fall behind Discard data  loss DLC PHY NET DLC PHY DLC PHY NET ARD DLC PHY NET Forwarding

29. Copyright Fall 2013, Rudra Dutta, NCSU29 Overlay Networking Operation of L3 can be performed by L7 – Overlay forwarding – integrate with application logic Receive-process-decide-output cycle – May fall behind Discard data  loss DLC PHY NET DLC PHY DLC PHY NET AD DLC PHY NET L7 “NET” TRANSPORT Forwarding Host TRANSPORT APP APPLICATION

30. Copyright Fall 2013, Rudra Dutta, NCSU30 Transport Layer First end-to-end layer Functions – Endpoint abstraction Multiplexing on a host – “Ports”

31. Copyright Fall 2013, Rudra Dutta, NCSU31 Communication Endpoints

32. Copyright Fall 2013, Rudra Dutta, NCSU32 Endpoint Access Transport software built in two parts – Host specific part - multiplexes network layer, global context – Application specific part - maintains flow state and provides network Also provides access point for higher layers (sockets)

33. Summary Necessary to move bits Break down complex functionality – networking stack Form packets of bits – PDU Inject packets, forward packets, receive packets API - socket Copyright Fall 2013, Rudra Dutta, NCSU33