1. Lecture 11

2. Switch Hardware Nowadays switches are very high performance computers with high hardware specifications Switches usually consist of a chassis (bus) and modules Modules are installed in the chassis Typical modules include Management modules (compulsory) Switching module (compulsory) Log and backup module Service modules (fiber, copper, wireless, Ethernet, ATM, …) Note: some modules may combine more than 1 function

3. Switch Hardware Management modules contains console for configuration It supervises and controls the switch operation Log events and configuration backups are stored in the log and backup module Contains hard disk/storage card and can also be accessed from management modules Service modules contain ports to connect to certain network type (usually a module connects to 1 type only) Switching module moves data between service modules Data between modules move through the chassis (bus)

7. Switch Hardware A pair of switching modules can be installed for more reliability (even if 1 module, it may have 2 processors) The modules can operate in one of three modes Standby mode Synchronous duplex mode Load sharing mode

8. Switch Hardware Standby mode one module active the other idle if active fails, idle takes over configuration and current state are saved periodically in storage Synchronous duplex mode modules operate in parallel and calculate switching decisions a comparator compares decisions if decisions are identical, OK, otherwise one has failed Comparator runs tests to identify faulty module then isolates it In practice one of the modules is in real control of the switch

9. Switch Hardware Load sharing mode each module handles part (half) of the load an exclusion device (ED) organizes access to resources if one fails, the other takes over with the help of ED

10. Switch Performance Switching capability is usually expressed as two values Bus capacity: maximum data rate that the bus can handle (usually very high and hence not critical) Switching capacity: maximum number of packets that can be switched between modules (expressed in Mpps) (for IP measured using 64 byte packets) Availability: a measure of the reliability of the system Availability = up time/total time up time: average time period the switch is operating down time: average time period the switch is down total time: up time + down time

11. Switch Performance For single processor system Availability (A) = MTBF/(MTBF+MTTR) MTBF: Mean Time Between Failures MTTR: Mean time To Repair Unavailability (U) = 1-A = MTTR/(MTBF+MTTR) For double processors system (MTBF) D = MTBF 2 /2MTTR

12. Switch Hardware The previous systems are centralized systems Another possibility is a distributed system where several processors (less powerful) are used Usually a processor is required to co-ordinate the operation These processors can be: Vertically decomposed: a processor is responsible of a block of hardware (e.g. switching within the module) Horizontally decomposed: a processor is responsible of certain function(s) (e.g. signaling processor, trunk setup processor … etc)

13. Switch Software Switches are so complicated that entirely hardware switches are not practical Switches need software to operate and control devices (modules) Nowadays usually a switch runs an operating system (Linux/Unix) Several programs are developed to control and monitor the switch (usually in C/C++) These programs are grouped into 4 packages

14. Switch Software Call processing software Maintenance software Database and administration software Other features software

15. Call Processing Software Responsible of call establishment, routing and monitoring Contains three levels Controller software: controls and monitors subscribers’ lines Network software: establishes and maintains the routes for the call High level software: handles the billing and call related services

16. Maintenance Software Handles the following tasks: Supervision of switch operation and available modules Monitoring of line and trunk reservations/usage Automatic line tests for remote maintenance (regular tests) Diagnostic tests (identify what is faulty) System recovery (from failures)

17. Database and Administration Software Administrative tasks include: Alarm processing Traffic recording Number changes Route changes Generation of exchange statistics Database system stores: Office statistics Billing information Software and hardware parameters (current conditions) System recovery parameters System diagnostics (tests)

18. Other Features Software Any other services not performed by the other packages Usually value added services are handled by this package