Switching Technology Circuit switching Structure and interfaces of

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 S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 1

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). S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 2

By setting up connections on demand networks are utilized efficiently Subscriber/user/client - speech - data Without - video Subscriber/user/client - speech - data - video switching technology all subscribers would need permanent connections to all others. S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 3

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 – IPv 4 addresses --> IPv 6 - addresses • In ATM - networks: NSAP - addresses S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 4

There are many communication modes communication mode connection-oriented Circuit switching PSTN GSM ISDN Connection less Packet switching X. 25 Global addresses + logical channel id’s on each hop Packet switching Internet Global addresses ATM ? S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 5

Connection set-up is needed in connectionoriented 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 A -subscriber Connection state E. g. speech state Control messaging which enables setting up and tearing down connections is called signaling in telecommunications networks. S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) Unique on a hop or link - time slot (PSTN…) - logical channel (x. 25) -. . . 6

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 semipermanent virtual connections. Nodes of the network need not support signaling in this operation model. S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 7

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 S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 2010 2020 8

Basic structure of a digital exchange Subscriber interface Subscriber lines/ or radio links Switching Matrix Control system S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) Junctionlineinterface junction lines 9

Types of subscriber access in a local exchange subscriber module V 2 (1: 1) 2/8/34 M channel associated subscriber signaling length of subscriber lines usually< 1 km V 5. 1 (1: 1) 2/8/34 M message based subscriber signaling V 5. 2 (concentration: N: 1) message based subscriber signaling RSS V 2 interface Junction line interface Directly connected to an exchange - analog and - ISDN subscriber lines subscriber multiplexer Switching Matrix V 5. 1 interface V 5. 2 interface proprietary signaling Access network S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) Local Exchange 10

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 S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 11

The function of the switching matrix is to connect the incoming and outgoing time slots Incoming lines Switching Matrix Outgoing lines incoming time slots Line = 2 Mbit/s link Time slot = 64 kbit/s link incoming pcm, incoming tsl outgoing pcm, outgoing tsl S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 12

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. S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 13

Time switch - serial writes - addressed reads incoming frame buffer 1 2 3 rotating write addresses n 1 2 3 Switching memory outgoing frame buffer 1 2 3 x n Clock Time slot counter S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) n read addresses 1 2 3(x) Control memory n 14

Space switch - an example output input 1 1 2 n & 2 & m & Control memory S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 15

Most often, control systems in Exchanges are distributed Control can be Centralized Hierarchical Singleprocessor Multiprocessor Distributed Non-hierarchical Singleprocessor Multiprocessor Some functions centralized All functions distributed Pragmatic distribution S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 16

An example of pragmatic distribution is the Finnish DX 200 -exchange Division of load by connections/lines and the signaling system type. Signaling system specific Matrix control unit control processor Centralized function Internal bus (or ATM switch) Databases: subscriber- and routing information Statistics and charging operation and maintenance Grouping and division by functions, replicated functions if necessary. S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 17

Main functions of the control system are call control and charging Service switching(SSF) Incoming call control Outgoing call control incoming signaling outgoing signaling Resource management Number analysis gathering charging information S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 18

Principles of Functional distribution in DX 200 systems • The load is partitioned by dividing the incoming and outgoing line-space either statically or dynamically – e. g. replaceable 2 N 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 S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 19

Exchanges are fault tolerant Equipment and software Supervision Active Alarm handling Spare Recovery fault effect elimination Fault location • Maintenance software manages the states of devices and programs in the exchange • The critical equipment has been doubled (2 N replication) • Switchovers from active to spare without disturbing calls Separated (out-of-use) Testing • Fault tolerance must be taken into account always in all software development • Unavailability requirement < 2… 3 min/year S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 20

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 S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 21

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 2 M PCM, internal 4 Mbit/s TTL-logic format (in DX 200) • direct SDH interfaces (e. g. 155 Mbit/s ) coming to digital exchanges (available in some? ) S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 22

Circuit switched networks are utilized also in packet transmission PSTN/ISDN GSM Modem pole POP • 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 POP - Point of presence of an Internet Service Provider • 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. S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 23

ATM-switch VCI VPI ATM cell 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 S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 24

Structure of a Packet Switch Outgoing lines Incoming lines Outgoing buffer Incoming buffer Outgoing buffer Controller Outgoing buffer A problem: Constructing fast enough controllers is difficult! An example: IP-routers. S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 25

Combined router+ATM-switch incoming lines Outgoing lines Controller Incoming ports Outgoing port ATMswitching matrix Outgoing port • The controller includes functions of routers and ATM-switch controllers. • Packet Forwarding functions are in the Incoming ports -block. S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 26

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(? ) S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 27

Challenges of Switching Technology • Packet switching – IP calls and their interworking and Interoperability with PSTN – Quality of Service in packet networks (Int. Serv, Diff. Serv, Multi Protocol Label Switching) • Third generation mobile telecommunications systems • More open software development environment S 38. 118 Principles in Telecommunications Technology s 2000 RKa, (translation A. Paju) 28