Switching Technology

1. Switching Technology Circuit switching Structure and interfaces of telephone exchanges Call control Maintenance functions and fault-tolerance The principle of circuit switching Packet switching and Challenges in switching technology S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 1

2. ITU-T’s definition of switching: The establishing, on-demand, of an individual connection from a desired inlet to a desired outlet within a set of inlets and outlets for as long as is required for the transfer of information. An inlet represents a line, such as a channel(or a flow line,entering an SDL/GR macro call). Source: (Blue book Fascicle I.3 Definitions). S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 2

3. By setting up connections on demand - networks are utilized efficiently Subscriber/user/client - speech - data - video Subscriber/user/client - speech - data - video Without switching technology all subscribers would need permanent connections to all others. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 3

4. Subscriber lines and/or subscribers must have unique addresses in networks • PSTN/ISDN/GSM - E.164 conformant phone numbers • fixed length or variable length numbers • IP -addresses in the Internet • IPv4 addresses --> IPv6 - addresses • In ATM - networks: NSAP - addresses S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 4

5. There are many communication modes communication mode connection-oriented Connection less Circuit switching Packet switching Packet switching Internet PSTN ISDN X.25 Global addresses + logical channel id’s on each hop GSM Global addresses ATM ? S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 5

6. Connection set-up is needed in connection-oriented communication, so that the network can change from global addresses to local ones Set-up message [ B’s global address] Response [ hop specific logical link/channel id] B -subscriber Connection state A -subscriber E.g. speech state Unique on a hop or link - time slot (PSTN…) - logical channel (x.25) - ... Control messaging which enables setting up and tearing down connections is called signaling in telecommunications networks. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 6

7. Connections can be set up also with network management commands • Telephone networks are used to build up leased links • Frame relay is a switching technology for variable length packets that replaces leased lines - e.g. linking LANs • Also ATM can be used for establishing semi-permanent virtual connections. Nodes of the network need not support signaling in this operation model. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 7

8. Life cycles of product generations Optic switching ? Broadband switch ? IP + Servers ? ? Digital exchange SPC, analog field Coordinate exchange Direct controlled 1950 1960 1970 1980 1990 2000 2010 2020 S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 8

9. Basic structure of a digital exchange Subscriberinterface Switching Matrix Junction-line-interface Subscriber lines/ or radio links junction lines Control system S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 9

10. subscriber multiplexer V2 2/8/34M (1:1) V2 inter- face channel associated subscriber signaling V5.1 2/8/34M (1:1) V5.1 inter- face message based subscriber signaling Types of subscriber access in a local exchange Directly connected to an exchange - analog and - ISDN subscriber lines subscriber module Junction line interface Switching Matrix length of subscriber lines usually< 1km V5.2 (concentration: N:1) V5.2 inter- face message based subscriber signaling proprietary signaling RSS Local Exchange Access network S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 10

11. Functions of the subscriber interface module in a fixed network • power feed of subscriber lines • call detection (on-hook/off-hook) • receiving dialed digits • A/D conversion • traffic concentration • subscriber line testing and line statusmanagement S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 11

12. The function of the switching matrix is to connect the incoming and outgoing time slots Incoming lines Outgoing lines Switching Matrix incomingtime slots Line = 2Mbit/s link Time slot = 64kbit/s link incoming pcm, incoming tsl outgoing pcm, outgoing tsl S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 12

13. The switching matrix is based on time switches and space switches • A switching matrix can be extended without disturbing existing connections. • Extension step can be e.g. 64 PCMs. • Matrixes can be single-stage or multistage. • Due to advances in technology compared to single connection bandwidth, the trend is towards single-stage matrixes. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 13

14. 1 2 3 n 1 2 3 n 1 2 3 1 2 n 3(x) n Time switch - serial writes - addressed reads incoming frame buffer outgoing frame buffer read addresses Switching memory x rotatingwrite addresses Control memory Time slot counter Clock S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 14

15. 1 2 n 1 2 m Control memory Space switch - an example output input & & & S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 15

16. Single- processor Multi- processor Single- processor Multi- processor Most often, control systems in Exchanges are distributed Control can be Centralized Distributed Some functions centralized All functions distributed Hierarchical Non-hierarchical Pragmatic distribution S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 16

17. Internal bus (or ATM switch) An example of pragmatic distribution is the Finnish DX200 -exchange Division of loadby connections/lines and the signaling system type. Matrix control unit Centralizedfunction Signaling system specificcontrol processor Databases: subscriber- and routinginformation Statistics and charging operation andmaintenance Grouping and division by functions, replicated functions if necessary. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 17

18. Main functions of the control system are call control and charging Service switching(SSF) Incoming call control Outgoing callcontrol incoming signaling outgoing signaling Resource management Number analysis gathering charging information S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 18

19. Principles of Functional distribution in DX200 systems • The load is partitioned by dividing the incoming and outgoing line-space either statically or dynamically • e.g. replaceable 2N or N+ 1 -replication concerning signaling and call control functions • Partitioning the load dynamically for a task at a time • N+1 load partitioning • Replicating stateless services to several processors S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 19

20. Exchanges are fault tolerant Equipment and software Supervision Alarm handling Recovery faulteffectelimination Fault location • Maintenance software manages the states of devices and programs in the exchange • The critical equipment has been doubled (2N replication) • Switchovers from active to spare without disturbing calls • Fault tolerance must be taken into account always in allsoftware development • Unavailability requirement < 2…3 min/year Active Spare Separated(out-of-use) Testing S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 20

21. 80% of exchange design is software development • The size of a software load is between 3 … 10 million code lines. • A country adaptation for PSTN typically demands a work effort of ca.50 man-years. • Challenges in software design are generated by: • real-time call control • variety and nation specificity in signaling, services and features • fault tolerance • maintainability and extensibility of the software and the system S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 21

22. The junction line interface of an exchange • Main functions are: • adaptation of internal and external transmission • supervision of the condition of junction lines • E.g. external format is 2M PCM, internal 4Mbit/s TTL-logic format (in DX200) • direct SDH interfaces (e.g. 155Mbit/s ) coming to digital exchanges (available in some?) S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 22

23. PSTN/ISDN GSM Circuit switched networks are utilized also in packet transmission POP • long connection set-up time • inefficient use of resources (the call is on whether or not any packetsare transmitted) • Restricted speed (33,6 kbit/s …) • Internet calls are longer than normalcalls. Due to this fact, dimensioning ofexchanges is not the best possible. • Because of increasing traffic switchingmatrixes and routes must be enlarged. Modempole Internet POP - Point of presence of an Internet Service Provider S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 23

24. ATM-switch ATM cell VCI VPI Outgoing ATM lines incoming ATM lines ATM switching matrix virtual connections Incoming line, Incoming path, Incoming connection Outgoing line, Outgoing path, Outgoing connection virtual paths S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 24

25. Structure of a Packet Switch Outgoing lines Incoming lines Outgoing buffer Incomingbuffer Outgoing buffer Controller Outgoing buffer Outgoing buffer A problem: Constructing fast enough controllers is difficult! An example: IP-routers. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 25

26. Combined router+ATM-switch incoming lines Outgoing lines Controller Outgoing port Incoming ports Outgoing port ATM-switching matrix Outgoing port Outgoing port • The controller includes functions of routers and ATM-switch controllers. • Packet Forwarding functions are in the Incoming ports -block. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 26

27. The latest development of switching technology • Integration of router and ATM-switch.Avoiding Layer-3 per-packet forwarding operations. • loose connection-orientation (flows) in routers • setting up flows adaptively based on traffic = without an explicit set-up request • topology-based label connections • Gigabit and Terabit routers (Hw packet switching) • IP voice ==> All Services IP networks(?) S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 27

28. Challenges of Switching Technology • Packet switching • IP calls and their interworking and Interoperability with PSTN • Quality of Service in packet networks (IntServ, DiffServ, Multi Protocol Label Switching) • Third generation mobile telecommunications systems • More open software development environment S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 28