1. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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

2. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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).

3. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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.

4. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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

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

6. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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] A -subscriber B -subscriber Response [ hop specific logical link/channel id] Connection state 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.

7. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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.

8. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 8 Life cycles of product generations 19501960199019801970200020202010 SPC, analog field Digital exchange Broadband switch ? Optic switching ? Coordinate exchange Direct controlled IP + Servers ? ?

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

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

11. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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 status management

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

13. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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.

14. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 14 Time switch - serial writes - addressed reads 123n123n 1 2 3 n Switching memory Time slot counter 1 2 3(x) n Control memory rotating write addresses read addresses incoming frame bufferoutgoing frame buffer Clock x

15. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 15 Space switch - an example 12n 1 2 m Control memory input output & & &

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

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

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

19. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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

20. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 20 Exchanges are fault tolerant Equipment and software Supervision Alarm handling Fault location Recovery fault effect elimination 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 all software development Unavailability requirement < 2…3 min/year ActiveSpare Testing Separated (out-of-use)

21. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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

22. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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?)

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

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

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

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

27. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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(?)

28. S38.118 Principles in Telecommunications Technology s2000 RKa, (translation A.Paju) 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