1. DATA COMMUNICATION (ELA…) ASYNCHRONOUS TRANSFER MODE (ATM) 1

2. ATM  a streamlined packet transfer interface  similarities to packet switching transfers data in discrete chunks supports multiple logical connections over a single physical interface  ATM uses fixed sized packets called cells  with minimal error control and flow control  data rates of 25.6Mbps to 622.08Mbps

3. P ROTOCOL A RCHITECTURE

4. R EFERENCE M ODEL P LANES  user plane provides for user information transfer, associated controls (flow control, error control)  control plane call and connection control  management plane plane management whole system functions layer management Resources and parameters in protocol entities

5. ATM L OGICAL C ONNECTIONS  virtual channel connections (VCC) analogous to virtual circuit in X.25  basic unit of switching between two end users full duplex fixed size cells  also for user-network exchange (control) network-network exchange (network mgmt & routing)

6. ATM V IRTUAL P ATH C ONNECTION  virtual path connection (VPC) bundle of VCC with same end points

7. A DVANTAGES OF V IRTUAL P ATHS  simplified network architecture  increased network performance and reliability  reduced processing  short connection setup time for new channel

8. C ALL E STABLISHMEN T U SING VP S

9. V IRTUAL C HANNEL C ONNECTION U SES  between end users end to end user data VPC provides overall capacity VCC organization done by users within the capacity  between end user and network control signaling  between network entities network traffic management routing

10. VP/VC C HARACTERISTICS  quality of service - cell loss ratio, cell delay variation  switched and semi-permanent channel connections  cell sequence integrity  traffic parameter negotiation and usage monitoring - average rate, peak rate, burstiness, and peak duration  VPC only virtual channel identifier restriction within VPC

11. F IXED VS. V ARIABLE L ENGTH C ELL  # Efficiency Consideration:  Efficiency N = Information Octets / (Information Octets + Header Octets)  Fixed Length Packets:  L = Data Field Size (Octets) in a Packet  H = Header Size (Octets)  X = Total Message Size (Octets)  # Expression for N = ? (Needs ceiling function), Nopt = ?

12. F IXED VS. V ARIABLE L ENGTH C ELL  # Variable Length Packets:  Needs an additional length field,  Hv = Additional overhead octets  H = Header Size (Octets)  X = Message Size (Octets)  # Expression for N = ? (Assume Single Cell)  # Plot of N vs. Message Size (X = 48, 96, 144, 192, 240), for fixed and variable length cells

13. W HAT SIZE OF F IXED L ENGTH  Assume that the cells are completely filled (X / L = integer)  Expression for N = ?  Packetization Delay = buffering bits until the entire packet is filled before retransmission  Expression for this delay D = ? (function of L and source data rate R)

14. W HAT SIZE OF F IXED L ENGTH  Plot of D vs. Data Field Size (L = 16, 32, 64, 128 octets) (R = 64 kbps for voice coding)  Plot of efficiency N vs. Data Field Size (16, 32, 64, 128 octets)  => 48 octet provides a trade-off between efficiency and delay

15. ATM C ELLS

16. ATM H EADER F IELDS  generic flow control  Virtual path identifier - routing  Virtual channel identifier – end to end user  payload type (3-bits, user information, congestion)  cell loss priority  header error control

17. E XAMPLES  # Consider compressed video transmission in ATM network, Cells must pass through 5 switches. The data rate is 43 Mbps.  - Transmission time of one cell through one switch?  - Assume other cells have lower priority (but non- premptive) than cell A. What is the maximum time from arrival at the first

18. E XAMPLES  Switch to the completion of transmission by the fifth for cell A? (all other delays are negligible)  - 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?

19. E XAMPLES  - what is the maximum and average variability in encountered delay (the jitter)?  # IP datagrams are segmented into ATM cells and sent over the ATM network. Loss of a cell means loss of entire IP packet.  Pc = cell loss rate  n = number of cells for a datagram  Expression for Pp = datagram loss rate?

20. S UMMARY  Asynchronous Transfer Mode (ATM)  architecture & logical connections  ATM Cell format  transmission of ATM cells