Introduction to TCP/IP: The Foundation of Modern Networking

1. CS 6027 Advanced Computer Networking Lecture 1 Lecture 1

2. Introduction and Overview • Just 50 years ago, networks were proprietary (ie. IBM, HP, DEC, etc) • Both the software (protocols or rules) and hardware used to make a network functional were proprietary. • Also, the networks’ technologies (components) were designed for a specific purpose in mind (ie. Business, manufacturing, high/low-speed, small/large capacity, etc..) • The certain applications could run on certain type networks • Larger corporations would typically have many different disjointed computer networks - company mergers caused this problem too (wasn’t perceived as a problem then) • Engineers and Scientists (or whomever) could have 3-4 terminals on his/her desk for different uses • Customer would have to go to a specific vendor for an application or network upgrade Lecture 1

3. Introduction and Overview • Back in the 70’s and early 80’s, there was a big push to make communication systems or networks “open” • “open” means “non-proprietary” - instead of the “specifications” being known only by the vendor, the specs would be be publicly known • By having publicly published specifications, all of the various vendors could design and manufacture network components that were compatible and interchangeable • Why was this a good thing ???? (Even if you were a network-component-producing company with a significant market share) Lecture 1

4. Introduction and Overview • Answer: would drive more (1) computer, (2) software application and (3) network usage - therefore, drive more revenue for all • Answer: more efficiency for businesses, government, etc.. • Also, what happened with the computer industry as it relates to OS’s ??? Lecture 1

5. Introduction and Overview • The idea behind having “open systems” is to have the ability to interconnect many different networks into a single network. • The technology that allows this is called “Internetworking” • Internetworking provides: • The Interconnection of heterogeneous (different) networks • Set of communication standards/protocols that make the interconnected heterogeneous networks interoperate (river, language scenario) • Internetworking “hides” the details of the underlying hardware and allow the network nodes to communicate independent of their physical connection (or hardware) • Internetworking can be called “internet technology” – notice to lower case “i” on internet Lecture 1

6. Introduction and Overview • Some time ago, the government realized the benefit of internet technology and funded a research project through an agency called ARPA – Advanced Research Projects Agency • Through ARPA support, the “open” system specs were realized. • These open specs were called “TCP/IP Internet Protocol Suite”, commonly called “TCP/IP” • TCP – Transmission Control Protocol – dealt with higher level issues like segmentation, reassembly and error detection. • IP – Internetworking Protocol – dealt with datagram routing • TCP/IP was heavenly sent in that: (1) previously disjointed networks WITHIN companies could now function as a single network and (2) it facilitated communications amongst geographically dispersed sites • With TCP/IP, the Internet was born. Notice the “I” on Internet – called the Global Internet • Global Internet interconnects over 170 million nodes – testimonial for TCP/IP Lecture 1

7. Introduction and Overview • Bottom Line: what makes TCP/IP so great and unique from other network protocols ??: • Network Technology Independence – independent of a particular vendor’s hardware • Universal Interconnection – any 2 computers connected to the internet can communicate – each computer has a unique internationally recognized address • End-to-End Acknowledgements – acknowledgements between the source and destination versus intermediate nodes • Application Protocol Standards – TCP/IP provides services (or software) to applications needing lower level communication services • We will cover each of these attributes in detail throughout the course • Internet uses TCP/IP Lecture 1

8. Introduction and Overview • Read more details about the history in your book (Chapter 1) • Who is responsible the Internet ?. Internet Architecture Board (IAB) • IAB coordinates the research and development in relation to the TCP/IP protocols. The organization decides which protocols are required and sets policies • Each member of the IAB chaired an Internet Task Force responsible for investigating a set of problems or issues each (there were 10 task forces) • The chairman of the IAB was called the Internet Architect Lecture 1

9. In 1989, the IAB was re-organized due to commercial usage increases The original IAB researchers were moved under the Internet Research Task Force – their focus is longer term research The Internet Engineering Task Force is more concerned about short-term issues and is mostly comprised of industry types Introduction and Overview The Internet Engineering Task Force Chairman and managers of each “working group” forms the Internet Engineering Steering Group – this group is responsible for coordination In 1992, a group called the Internet Society (ISOC) was form to encourage participation on the Internet. Lecture 1

10. Introduction and Overview • Documentation of TCP/IP is placed in online repositories and made available at no charge – you will be responsible for collecting some of this documentation • The final and official TCP/IP documents start out as an Internet draft (working document) • Upon recommendation from Internet authorities, the draft may be published as a Request for Comment (RFC) • Each RFC is edited, assigned a number and made available to all interested parties. RFC’s go through maturity levels and are organized according to their requirement level • The six maturity levels are: proposed standard, draft standard, Internet standard, historic, experimental and informational • RFC’s are classified into 5 requirements levels: required, recommended, elective, limited use and not recommended • You can secure RFC’s: regular mail, e-mail, ftp or Internet (http://www.rfc-editor.org) Lecture 1

11. Introduction and Overview Lecture 1

12. Introduction and Overview • Protocols – set of rules that governs data communications – defines what is communicated, how it is communicated and when it is communicated • Protocol elements are: • Syntax – structure or format of the data (order of the bits) • Semantics – meaning of each section of bits – how to interpret the pattern of bits • Timing – deals with (1) when the data should be sent and (2) how fast it should be sent (ie. a Tx can overload a Rx and therefore data can be lost or mis-interpreted) • More clarity: the TCP/IP protocol allows one to specify data communications without understanding the details of the underlying hardware. Lecture 1

13. Why Study OSI? • Still an excellent model for conceptualizing and understanding protocol architectures • More granularity in functionality - more functional delineation • Key points: • Modular • Hierarchical (chain of command, pecking order) • Boundaries between layers (called interfaces) NOTE: the protocols or functionality with in the layer could change however, the interface remains the same – this facilitates the flexibility Lecture 1

14. OSI Reference Model ? • OSI – Open Systems Interconnection • Set of rules of how to transmit data across a network • at the lower levels of the model protocols define the electrical and physical standards • at the lower levels, the bit ordering, the transmission of the bits, and error detecting and correcting are defined • at the higher levels of the model, the protocols define the data formatting, message syntax, dialogue management, message sequences and info presentation Lecture 1

15. Advantages of Layering • Easier application development • Network can change without all programs being modified • Breaks complex tasks into subtasks • Each layer handles a specific subset of tasks • Communication occurs • between different layers on the same node or stack (INTERFACES) • between similar layers on different nodes or stacks (PEER-TO-PEER PROCESSES Lecture 1

16. Top Layer Top Layer Some Intermediate Layer Some Intermediate Layer Bottom Layer Bottom Layer OSI’s Layered Approach Example Network A Network B Actual commands invoked, presentation Facilitate the actual communications Network interfaces, raw bits How does peer-to-peer communication work ? Lecture 1

17. Open Systems Interconnection Developed by ISO (International Organization for Standardization) Contains seven layers Application Presentation Session Transport Network Data Link Physical OSI Lecture 1

18. OSI Reference Model ? • Bottom 3 layers • Bottom 3 layers responsible for getting the info to the destination • (Bottom 3 layers): at the lower levels of the model protocols define the electrical and physical standards • (Bottom 3 layers) at the lower levels, the bit ordering, the transmission of the bits, and error detecting and correcting are defined • Top 4 layers • at the higher levels of the model, the protocols define the data formatting, message syntax, dialogue management, message sequences and info presentation Lecture 1

19. Ch 2: TCP/IP and OSI Lecture 2 Lecture 2

20. OSI Physical Layer • Responsible for transmission of bits • Always implemented through hardware • Encompasses mechanical, electrical, and functional interfaces • Encoding issues: how 0’s and 1’s are converted to signals • Transport medium: Coaxial, Twisted Pair, Optical, etc.. • Transmission Rate/Data Rate – how fast to send bits • Transmission mode: transmission direction (simplex, duplex) • Physical Topology: network layout Lecture 2

21. Actually sends the packets (groups of frames) from node to node using a routing algorithm Network Layer Data Link Layer Takes raw data (bits) and transform them into frames, error control, etc. Transmit and receive the raw data (bits) Physical Layer OSI Data Link Layer • Responsible for error-free, reliable transmission of data • Framing, Flow control, Error control (detection/correction) • Makes use of physical address because with in the same network Lecture 2

22. OSI Data Link Layer Lecture 2

23. OSI Network Layer • Responsible for routing of messages through networks • Concerned with type of switching used (circuit v. packet) • Handles routing among different networks • NOTE: with in the same network, only the DATA LINK layer is needed – amongst multiple networks, the NETWORK LAYER is needed • No need for routing with in the same network (LAN) • Routing across “internetworks” • Makes use of logical address vs physical address because not with in same network Lecture 2

24. Concerned with an error-free end-to-end flow of data Transport Network Layer Actually sends the packets (groups of frames) from node to node using a routing algorithm Data Link Layer Takes raw data (bits) and transform them into frames OSI Network Layer Lecture 2

25. OSI Network Layer Lecture 2

26. OSI Transport Layer • Isolates messages from lower and upper layers • Breaks down message size (segmentation) (down) and performs re-assembly (up) • Monitors quality of communications channel (oversee all hops) • Selects most efficient communication service necessary for a given transmission (could change over hops) • Flow and Error control for Source and Sink Lecture 2

27. OSI Session Layer • Establishes logical connections between systems (up/down) • Manages log-ons, password exchange, log-offs (up/down) • Terminates connection at end of session (up/down) Lecture 2

28. OSI Session Layer Lecture 2

29. OSI Presentation Layer • Provides format and code conversion services • Examples • File conversion from ASCII to EBDIC • Invoking character sequences to generate bold, italics, etc on a printer • The source and sink could operate using different encoding schemes – the presentation layer makes the translations • Security • Compression Lecture 2

30. OSI Application Layer • Provides access to network for end-user (end-user being a human being or software application) • User’s capabilities are determined by what items are available on this layer (ie. remote log-in, file transfer, email service, directory service, etc.) Lecture 2

31. What happens at the End and Intermediate Nodes ? Rx Tx 7 Intermediate Nodes 3 1 1 B C Q T A Z Lecture 2

32. Recap - OSI’s Layered Approach • between different layers on the same node or stack (INTERFACE) • between similar layers on different nodes or stacks (PEER-TO-PEER PROCESSES) Lecture 2

33. An exchange using the OSI model Explain encapsulation and decapsulation Lecture 2

34. COMPLEXITY TO CONSIDER • Any particular node in an internetwork can be functioning as follows simultaneously: • Tx to other internetwork nodes • Rx from other internetwork nodes • Intermediate node to some other internetwork nodes Lecture 2

35. OSI in Action: Outgoing File Transfer • The File Transfer Program issues a command to the Application Layer • Application passes it to Presentation, which may reformat, encrypt, encode, compress, passes to Session (adds overhead) • Session requests a connection, passes to Transport (adds overhead) • Transport breaks file into chunks, adds error-checking and flow-control info, process-to-process, passes to Network (adds overhead) • Network selects the data’s route (internetworking), passes to Data Link (adds overhead) • Data Link adds error-control and flow-control info, passes to Physical (adds overhead) • Physical translates bits to signal and transmits the signal, which includes information added by each layer Lecture 2

36. OSI in Action: Incoming File Transfer • Physical receives signal and translates to bits, passes to Data Link • Data Link checks for errors and performs flow control on bits, formulates bits into some formation (frames), passes to Network • Network verifies routing (if intermediate node, determines next hop), passes to Transport • Transport checks for errors and performs flow control on the chunks, reassembles the chunks, passes to Session • Session determines if transfer is complete, may end session, passes to Presentation • Presentation may reformat, perform conversions, decode, decrypt, decompress, pass to Application layer • Application presents results to user (e.g. updates FTP program display) Lecture 2

37. US Postal System Analogy • Illustrate how the US Postal System is very similar to how networking works • Will help students better understand (versus memorize) networking Upper Layers – creating and interpreting the signal, data or info Lower Layers – getting the signal from one place to the next Lecture 2