1. Data and Computer Communications Chapter 11 – Asynchronous Transfer Mode

2. ATM  a streamlined packet transfer interface  similarities to packet switching transfers data in discrete chunks transfers data in discrete chunks supports multiple logical connections over a single physical interface 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. Protocol Architecture

4. Reference Model Planes  user plane provides for user information transfer, associated controls (flow control, error control) provides for user information transfer, associated controls (flow control, error control)  control plane call and connection control call and connection control  management plane plane management plane management whole system functionswhole system functions layer management layer management Resources and parameters in protocol entitiesResources and parameters in protocol entities

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

6. ATM Virtual Path Connection  virtual path connection (VPC) bundle of VCC with same end points bundle of VCC with same end points

7. Advantages of Virtual Paths  simplified network architecture  increased network performance and reliability  reduced processing  short connection setup time for new channel

8. Call Establishment Using VPs

9. Virtual Channel Connection Uses  between end users end to end user data end to end user data VPC provides overall capacity VPC provides overall capacity VCC organization done by users within the capacityVCC organization done by users within the capacity  between end user and network control signaling control signaling  between network entities network traffic management network traffic management routing routing

10. VP/VC Characteristics  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 virtual channel identifier restriction within VPC

11. Fixed vs. Variable Length Cell  # 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. Fixed vs. Variable Length Cell  # 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. What size of Fixed Length  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. What size of Fixed Length  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 Cells

16. ATM Header Fields  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. Examples  # 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. Examples  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. Examples  - 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. Summary  Asynchronous Transfer Mode (ATM)  architecture & logical connections  ATM Cell format  transmission of ATM cells