11 atm


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11 atm

  1. 1. Data and Computer Communications Chapter 11 – Asynchronous Transfer Mode
  2. 2. ATM <ul><li>a streamlined packet transfer interface </li></ul><ul><li>similarities to packet switching </li></ul><ul><ul><li>transfers data in discrete chunks </li></ul></ul><ul><ul><li>supports multiple logical connections over a single physical interface </li></ul></ul><ul><li>ATM uses fixed sized packets called cells </li></ul><ul><li>with minimal error control and flow control </li></ul><ul><li>data rates of 25.6Mbps to 622.08Mbps </li></ul>
  3. 3. Protocol Architecture
  4. 4. Reference Model Planes <ul><li>user plane </li></ul><ul><ul><li>provides for user information transfer, associated controls (flow control, error control) </li></ul></ul><ul><li>control plane </li></ul><ul><ul><li>call and connection control </li></ul></ul><ul><li>management plane </li></ul><ul><ul><li>plane management </li></ul></ul><ul><ul><ul><li>whole system functions </li></ul></ul></ul><ul><ul><li>layer management </li></ul></ul><ul><ul><ul><li>Resources and parameters in protocol entities </li></ul></ul></ul>
  5. 5. ATM Logical Connections <ul><li>virtual channel connections ( VCC ) </li></ul><ul><ul><li>analogous to virtual circuit in X.25 </li></ul></ul><ul><li>basic unit of switching between two end users </li></ul><ul><ul><li>full duplex </li></ul></ul><ul><ul><li>fixed size cells </li></ul></ul><ul><li>also for </li></ul><ul><ul><li>user-network exchange (control) </li></ul></ul><ul><ul><li>network-network exchange (network mgmt & routing) </li></ul></ul>
  6. 6. ATM Virtual Path Connection <ul><li>virtual path connection ( VPC ) </li></ul><ul><ul><li>bundle of VCC with same end points </li></ul></ul>
  7. 7. Advantages of Virtual Paths <ul><li>simplified network architecture </li></ul><ul><li>increased network performance and reliability </li></ul><ul><li>reduced processing </li></ul><ul><li>short connection setup time for new channel </li></ul>
  8. 8. Call Establishment Using VPs
  9. 9. Virtual Channel Connection Uses <ul><li>between end users </li></ul><ul><ul><li>end to end user data </li></ul></ul><ul><ul><li>VPC provides overall capacity </li></ul></ul><ul><ul><ul><li>VCC organization done by users within the capacity </li></ul></ul></ul><ul><li>between end user and network </li></ul><ul><ul><li>control signaling </li></ul></ul><ul><li>between network entities </li></ul><ul><ul><li>network traffic management </li></ul></ul><ul><ul><li>routing </li></ul></ul>
  10. 10. VP/VC Characteristics <ul><li>quality of service - cell loss ratio, cell delay variation </li></ul><ul><li>switched and semi-permanent channel connections </li></ul><ul><li>cell sequence integrity </li></ul><ul><li>traffic parameter negotiation and usage monitoring - average rate, peak rate, burstiness, and peak duration </li></ul><ul><li>VPC only </li></ul><ul><ul><li>virtual channel identifier restriction within VPC </li></ul></ul>
  11. 11. Fixed vs. Variable Length Cell <ul><li># Efficiency Consideration: </li></ul><ul><li>Efficiency N = Information Octets / (Information Octets + Header Octets) </li></ul><ul><li>Fixed Length Packets: </li></ul><ul><li>L = Data Field Size (Octets) in a Packet </li></ul><ul><li>H = Header Size (Octets) </li></ul><ul><li>X = Total Message Size (Octets) </li></ul><ul><li># Expression for N = ? (Needs ceiling function), Nopt = ? </li></ul>
  12. 12. Fixed vs. Variable Length Cell <ul><li># Variable Length Packets: </li></ul><ul><li>Needs an additional length field, </li></ul><ul><li>Hv = Additional overhead octets </li></ul><ul><li>H = Header Size (Octets) </li></ul><ul><li>X = Message Size (Octets) </li></ul><ul><li># Expression for N = ? (Assume Single Cell) </li></ul><ul><li># Plot of N vs. Message Size (X = 48, 96, 144, 192, 240), for fixed and variable length cells </li></ul>
  13. 13. What size of Fixed Length <ul><li>Assume that the cells are completely filled (X / L = integer) </li></ul><ul><li>Expression for N = ? </li></ul><ul><li>Packetization Delay = buffering bits until the entire packet is filled before retransmission </li></ul><ul><li>Expression for this delay D = ? (function of L and source data rate R) </li></ul>
  14. 14. What size of Fixed Length <ul><li>Plot of D vs. Data Field Size (L = 16, 32, 64, 128 octets) ( R = 64 kbps for voice coding) </li></ul><ul><li>Plot of efficiency N vs. Data Field Size (16, 32, 64, 128 octets) </li></ul><ul><li>=> 48 octet provides a trade-off between efficiency and delay </li></ul>
  15. 15. ATM Cells
  16. 16. ATM Header Fields <ul><li>generic flow control </li></ul><ul><li>Virtual path identifier - routing </li></ul><ul><li>Virtual channel identifier – end to end user </li></ul><ul><li>payload type (3-bits, user information, congestion) </li></ul><ul><li>cell loss priority </li></ul><ul><li>header error control </li></ul>
  17. 17. Examples <ul><li># Consider compressed video transmission in ATM network, Cells must pass through 5 switches. The data rate is 43 Mbps. </li></ul><ul><li>- Transmission time of one cell through one switch? </li></ul><ul><li>- Assume other cells have lower priority (but non-premptive ) than cell A. What is the maximum time from arrival at the first </li></ul>
  18. 18. Examples <ul><li>Switch to the completion of transmission by the fifth for cell A? (all other delays are negligible) </li></ul><ul><li>- if the probability that a switch is busy is 0.6 and the average delay to wait for current transmission completion is one half a cell transmission time, what is the average time from arrival at the first Switch to the completion of transmission by the fifth for cell A? </li></ul>
  19. 19. Examples <ul><li>- what is the maximum and average variability in encountered delay ( the jitter )? </li></ul><ul><li># IP datagrams are segmented into ATM cells and sent over the ATM network. Loss of a cell means loss of entire IP packet. </li></ul><ul><li>Pc = cell loss rate </li></ul><ul><li>n = number of cells for a datagram </li></ul><ul><li>Expression for Pp = datagram loss rate? </li></ul>
  20. 20. Summary <ul><li>Asynchronous Transfer Mode (ATM) </li></ul><ul><li>architecture & logical connections </li></ul><ul><li>ATM Cell format </li></ul><ul><li>transmission of ATM cells </li></ul>