1. 1 ATM Switching: An Overview Carey Williamson Department of Computer Science University of Calgary

2. 2 Introduction l ATM switches are central to the operation of ATM networks l Lots of research on ATM switch design in the last 10 years l This presentation: an overview of the basic components and functionality common to all ATM switching systems

3. 3 ATM Switch Components l Input ports l Output ports l Switch fabric l Buffering l VPI / VCI table l Control unit

4. 4 Generic ATM Switch Output Ports Switch Fabric Input Ports Control Unit VPI VCI

5. 5 Switch Ports l Provide the physical connection to other ATM entities l Dedicated point-to-point links l Each port (or card) is for a particular type of interface and particular data rate (e.g., OC-3, DS-3, JPEG, Ethernet,T1,...) l N inputs, N outputs

6. 6 Switch Fabric l Defines the interconnection between the input ports and the output ports l Distinguishing characteristic of different types of ATM switches (e.g., shared memory, banyan, Benes, hypercube,...) l Affects performance (cell delay, cell loss)

7. 7 Buffering l Some switches are bufferless l Some switches are buffered l Buffers provide physical storage (i.e., memory) to hold cells that cannot yet be sent on their desired output ports l Uses RAM, DRAM, or FIFO...

8. 8 Buffering (Cont’d) l Buffering can be located at the input ports, at the output ports, internal to the switch fabric, or any combination l Buffers are usually limited in size: –e.g., 100 cells per port –e.g., 4096 cells per port l Buffer size and location affects performance

9. 9 VPI / VCI Table l Physical memory that is used to keep track of how to map cells of different VC’s from input ports to output ports l Translation table: 14151512 3271042233 Port VPI VCI INPUTOUTPUT

10. 10 VPI / VCI Table (Cont’d) l Entries initialized during call setup l Lookup done for each data cell l Determines “routing tag” to be used for switch fabric

11. 11 Control Unit l Controls entire operation of switch l Cell switching l Signalling (UNI and NNI) l Call Admission Control (CAC) l Usage Parameter Control (UPC) l Accounting statistics

12. 12 ATM Switch Functionality l Cell switching –also known as “label switching” or “label multiplexing” –cell with VPI = a and VCI = b on input port c is sent out with VPI = d and VCI = e on output port f –uses VPI / VCI table –simple fast harware switching (for data cells)

13. 13 ATM Switch Functionality l Signalling –participate in UNI signalling protocol (edge switches) –participate in NNI signalling protocol (core switches) –connection setup and teardown –update VPI / VCI table

14. 14 ATM Switch Functionality l Call Admission Control (CAC) –makes decision to accept / reject new call –considers traffic descriptor (TD) and QOS requested by the new call (e.g., PCR, SCR, CLR, CDV) –considers available resources, and (potential) impact on the QOS of existing calls –many different approaches proposed

15. 15 ATM Switch Functionality l Usage Parameter Control (UPC) –mechanism to monitor incoming traffic flows on a VPI / VCI basis –check for conformance to traffic descriptor –e.g., leaky bucket, dual leaky bucket –can provide “traffic shaping” –tags or discards non-conforming cells

16. 16 ATM Switch Functionality l Accounting –statistics accumulation –simple counters (e.g., per port) –statistics are reported to network management station (e.g., Newbridge 4602)

17. 17 Summary l ATM switches form the very heart of ATM networks l Basic components and functionality are common to all switches l Switches from different vendors differ in the details (e.g., switch fabric, buffering, control software, etc.)