1. 3/2/2001Hanoch Levy, CS, TAU1 Basic Communications Protocols Workshop on QoS Hanoch Levy Feb 2004

2. 3/2/2001Hanoch Levy, CS, TAU2 The objective: A talk to B, C talk to D, best performance A A B D C

3. 3/2/2001Hanoch Levy, CS, TAU3 Communications and Standards Communication networks must be based on standards!!! –Much more than any software!!! The structure of standards must be modular Thus a STANDARD and MODULAR set of communications rules must be defined.

4. 3/2/2001Hanoch Levy, CS, TAU4 The reference Model A “standard” framework for describing standard approached for delivering data over a network. Placed in different locations Want to pass data of some type, from one to another. Want this to be done good/best/ASAP. Want to do it with certain minimal quality requirements.

5. 3/2/2001Hanoch Levy, CS, TAU5 The method: A layered Model Each layer is responsible for certain tasks Each layer goes across the network Each software piece talks “horizontally” with its peer piece (on another hardware) Each software piece talks upward and downward to its parent and sibling pieces (on same hardware).

6. 3/2/2001Hanoch Levy, CS, TAU6 The principle of a layered model B B’ A C A’ C’ Each layer element: 1.Talk to its peer element 2.Carries traffic for its parent 3.Deliver traffic through its child

7. 3/2/2001Hanoch Levy, CS, TAU7 The layers : Layer 1 - Physical Deals with the physics of the media Attaches to the “iron” and understands the “iron” (cooper, fiber, ether…). Translates bits to electrical/light/radio signals and vice versa Called Modem (Modulator and Demodulator) Is responsible of transferring bits from one side to the other. When B receives a bit  transfers it to B’ Forms a BIT PIPE

8. 3/2/2001Hanoch Levy, CS, TAU8 Physical Layer: a bit pipe B B’ C A C’ A’ Physical medium (fiber, cooper, radio, pigeon) bit A bit pipe

9. 3/2/2001Hanoch Levy, CS, TAU9 Link Layer (2) Assures transferring of a packet in reliable way across a link. Uses the bit-pipe. Uses mechanism to recover from problems: –If packet does not arrive or arrive bad: –Add error detection on packet. E.g. parity bits –Add packet numbers. –Add acks (to acknowledge receipt) –Retransmit if necessary. Completed 26/3/04

10. 3/2/2001Hanoch Levy, CS, TAU10 Link Layer (layer 2): a reliable packet pipe C C’ D B D’ B’ Physical layer packet A packet pipe

11. 3/2/2001Hanoch Levy, CS, TAU11 Network Layer (3) Assures transferring of a packet in reliable way across THE NETWORK. Introduces network mechanisms : Routing, addressing Uses the link layer to transfer across a link.

12. 3/2/2001Hanoch Levy, CS, TAU12 Network Layer (layer 3): a reliable packet network pipe D D’ E C E’ C Link layer packet A packet pipe C

13. 3/2/2001Hanoch Levy, CS, TAU13 A view from above (network layer)

14. 3/2/2001Hanoch Levy, CS, TAU14 InterNetwork Layer (3.5) Arranges the delivery of a packet across many networks

15. 3/2/2001Hanoch Levy, CS, TAU15 Internet Layer (3.5)

16. 3/2/2001Hanoch Levy, CS, TAU16 Transport Layer (layer 4): a reliable communications end to end E E’ F D F’ D Link layer Data piece A packet pipe

17. 3/2/2001Hanoch Levy, CS, TAU17 Issues at Transport layer Reliable communications: -Guarantees that a packet does arrive at destination (if does not arrive – requires resend). -Acking -Numbering -Flow Control: -Can you send at your will?

18. 3/2/2001Hanoch Levy, CS, TAU18 Issues at Transport layer -Can you send at your will? -If destination is slow: destination will have its buffer full and performance degradation. Efficiency  be careful -If route is slow: sending over-traffic will just congest the network. Politeness  slow down.

19. 3/2/2001Hanoch Levy, CS, TAU19 Principles of Flow control -Use acks for each packet (receiver sends ack for each packet) -Sender uses a WINDOW (cannot send more than a “window full” of packets). If j did not arrive can send at most j-1+W. -Advanced windows: make the window size depends on speed of line. -If things go OK – increase W. -If things go slow – decrease W.

20. 3/2/2001Hanoch Levy, CS, TAU20 Application Layer (5) -Use the transport layer to ship the application.

21. 3/2/2001Hanoch Levy, CS, TAU21 Internet -Internet Layer: Internet Protocol (IP) -Takes care of passing a packet across the network to the destination (routing across networks). -Transport Control Protocol (TCP): Layer 5 protocol. -Above IP. -Creates a reliable communications path end to end.

22. 3/2/2001Hanoch Levy, CS, TAU22 Internet -UDP (Unspecified Data Protocol) -Parallel to TCP (that is, above IP) -Good news: Provides no flow control mechanism!. -Bad News: Provides no guaranteed delivery! -User’s responsibility for the packets. -Network does not control the flow of packets. -Like post service.

23. 3/2/2001Hanoch Levy, CS, TAU23 Internet : Applications: FTP -FTP: File transfer protocol -Over TCP -Want to transfer file x from A to B: -A opens a TCP connection to B. -A pushes the file, piece by piece into the TCP connection. -What does the FTP protocol needs to take care of: -Name the file. -Give list of files. -Get starting at position y, ….

24. 3/2/2001Hanoch Levy, CS, TAU24 Internet : Applications: HTTP -HTTP: Hyper Text transfer protocol -Over TCP -Used by Web browsers to get files from Web servers -A wants to get set of documents x, y, z from B: -A opens a TCP connection(s) to B. -A requests the documents (one by one, or in parallel) from B. -B sends the files over the connections. -HTTP is used for: -Naming the document -GET Command -Error codes,….

25. 3/2/2001Hanoch Levy, CS, TAU25 Internet : Applications: RTP -RTP: Real Time Protocol : -Used to transfer pieces of data at real time over the net. -Over UDP!! -Used by real time applications (voice, video) to transfer end-to-end. -Protocol defines the form of the packets. -Protocol defines the interaction (almost non is set) between sender and receiver.

26. 3/2/2001Hanoch Levy, CS, TAU26 Stack of Protocols http ftp