1. TCP/IPTCP/IP Dr. ClincyLecture 21 Ch 2: TCP/IP and OSI Lecture 2

2. TCP/IPTCP/IP Dr. ClincyLecture 22 OSI Open Systems Interconnection Developed by ISO (International Organization for Standardization) Contains seven layers Application Presentation Session Transport Network Data Link Physical

3. TCP/IPTCP/IP Dr. ClincyLecture 23 OSI Reference Model ? Bottom 3 layers Responsible for getting the info to the destination Top 4 layers Responsible for the creation and interpretation of the info Bottom 3 layers Responsible for getting the info to the destination Called Network Support Layers Transport Layer Links the bottom layers with the top layers Ensures what the bottom layers have transmitted is usable by the top layers Top 3 layers Responsible interoperability among unrelated software systems Called User Support Layers Your Author’s PerspectiveYour Professor’s Perspective

4. TCP/IPTCP/IP Dr. ClincyLecture 24 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

5. TCP/IPTCP/IP Dr. ClincyLecture 25 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

6. TCP/IPTCP/IP Dr. ClincyLecture 26 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 Network Layer Data Link Layer Physical Layer Actually sends the packets (groups of frames) from node to node using a routing algorithm Takes raw data (bits) and transform them into frames, error control, etc. Transmit and receive the raw data (bits)

7. TCP/IPTCP/IP Dr. ClincyLecture 27 OSI Data Link Layer

8. TCP/IPTCP/IP Dr. ClincyLecture 28 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

9. TCP/IPTCP/IP Dr. ClincyLecture 29 OSI Network Layer Transport Network Layer Data Link Layer Concerned with an error-free end-to-end flow of data Actually sends the packets (groups of frames) from node to node using a routing algorithm Takes raw data (bits) and transform them into frames

10. TCP/IPTCP/IP Dr. ClincyLecture 210 OSI Network Layer

11. TCP/IPTCP/IP Dr. ClincyLecture 211 Recap – OSI bottom 3 layers Network Data Link Physical Data Comm Layers

12. TCP/IPTCP/IP Dr. ClincyLecture 212 OSI Upper Layers Application Presentation Session Transport Peer-to-Peer Processes ….. End-to-End nodes only

13. TCP/IPTCP/IP Dr. ClincyLecture 213 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

14. TCP/IPTCP/IP Dr. ClincyLecture 214 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)

15. TCP/IPTCP/IP Dr. ClincyLecture 215 OSI Session Layer

16. TCP/IPTCP/IP Dr. ClincyLecture 216 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

17. TCP/IPTCP/IP Dr. ClincyLecture 217 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.)

18. TCP/IPTCP/IP Dr. ClincyLecture 218 Recap – Two General Objectives of Networking ? Lower Layers – getting the signal/data/info from one place to the next Upper Layers – creating and interpreting the signal, data or info

19. TCP/IPTCP/IP Dr. ClincyLecture 219 AZ BCQT 7 1 3 1 Tx Rx Intermediate Nodes What happens at the End and Intermediate Nodes ?

20. TCP/IPTCP/IP Dr. ClincyLecture 220 –between different layers on the same node or stack (INTERFACE) –between similar layers on different nodes or stacks (PEER-TO-PEER PROCESSES) Recap - OSI’s Layered Approach

21. TCP/IPTCP/IP Dr. ClincyLecture 221 An exchange using the OSI model Explain encapsulation and decapsulation

22. TCP/IPTCP/IP Dr. ClincyLecture 222 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

23. TCP/IPTCP/IP Dr. ClincyLecture 223 Summary of OSI Layers

24. TCP/IPTCP/IP Dr. ClincyLecture 224 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

25. TCP/IPTCP/IP Dr. ClincyLecture 225 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)

26. TCP/IPTCP/IP Dr. ClincyLecture 226 How TCP/IP maps to OSI ??

27. TCP/IPTCP/IP Dr. ClincyLecture 227 TCP/IP Model Explain Suite and Stack Concept Protocols for different underlying technologies – this is key SCTP

28. TCP/IPTCP/IP Dr. ClincyLecture 228 Physical addresses Physical address is also known as the link address Physical address can be different sizes (depend on the network) Unicast type physical addresses – single Rx Multicast type physical address – multiple Rxs Broadcast type physical address – all Rxs can pickup message

29. TCP/IPTCP/IP Dr. ClincyLecture 229 Physical Address Example Most local area networks use a 48-bit (6 bytes) physical address written as 12 hexadecimal digits, with every 2 bytes separated by a hyphen as shown below: 07-01-02-01-2C-4B A 6-byte (12 hexadecimal digits) physical address

30. TCP/IPTCP/IP Dr. ClincyLecture 230 IP Addresses can be either unicast, multicast or broadcast types Going from network A physical address 10 to network P physical address 95. Can’t use the physical address because different networks The network layer address contains the uniqueness we need from source to sink. Network layer address is A-P Unit at this layer - datagram Explain communications at the network layer

31. TCP/IPTCP/IP Dr. ClincyLecture 231 IP Address Example An Internet address (in IPv4) is 32 bits in length, normally written as four decimal numbers (or 4 octal numbers), with each number representing 1 byte. How many bits is a byte ? A nibble ?? The numbers are separated by a dot. Below is an example of such an address. Call “dot notation” 132.24.75.9 Example of IPv6 Address (128 bits):

32. TCP/IPTCP/IP Dr. ClincyLecture 232 Addresses in TCP/IP Application Specific Address Converts to a part address

33. TCP/IPTCP/IP Dr. ClincyLecture 233 Port addresses Addresses of sending and receiving processes (j and k) Add IP address Overhead (H2, T2) added for what ?

34. TCP/IPTCP/IP Dr. ClincyLecture 234 Port Address Example As we will see in Chapters 11 and 12, a port address is a 16-bit address represented by one decimal number as shown below. 753 A 16-bit port address

35. TCP/IPTCP/IP Dr. ClincyLecture 235 Relation- ship between Layers, Addresses, and Units in TCP/IP Signals Bits Frames Datagrams (Packets) Segments Messages

36. TCP/IPTCP/IP Dr. ClincyLecture 236 For entertainment purposes – if time permits…. If time permits (15 minutes maybe), illustrate how the US Postal System is very similar to how networking works Will help students better understand (versus memorize) networking Lower Layers – getting the signal from one place to the next Upper Layers – creating and interpreting the signal, data or info US Postal System Analogy