The product lifecycle - upgrading: Ring, Ring, East Coast Calling

Size: px

Start display at page:

Download "The product lifecycle - upgrading: Ring, Ring, East Coast Calling"

Sharleen Little
5 years ago
Views:

1 The product lifecycle - upgrading: Ring, Ring, East Coast Calling Lecture 14: Unit 7a Disasters, Failures and other Dangerous Things Adapted from C. Hannon by L. Ball,

2 Topics Basics of Sound Telephones The telephone network Lecture slides for 7a On my course web page Primary references Course lecture text and slides 2

3 Phone Components Basic landline phones Internals of of a landline phone: components Components Microphone, amp, speaker A way to dial A ringer A way to tell if the phone is off hook What are these? Next slide 3

4 Phone Components Microphone turns the sound energy in your voice into electrical energy Speaker (opposite of microphone) Hook switch Connects and disconnects the phone from the network. It connects when you lift the handset. Duplex coil blocks the sound of your own voice from reaching your ear Ringer Frequency Generator At the telephone company, equipment detects these tones and converts into the number you have requested with the touch of the key 4

5 The telephone network starts in your house. A pair of copper wires runs from a box at the road to a box (entrance bridge) at your house. The pair of wires is connected to each phone jack in your house Along the road runs a thick cable packed with 100 or more copper pairs. Depending on where you are located, this thick cable will run directly to the phone company's switch in your area or To a box that acts as a digital concentrator that combines the signals with dozens of other voices on telephone lines 5

6 Modern Telephone Network What happens after the signal leaves the house? Digitizing and delivering Animation and more info 6

7 Changes in the telephone network Revolution 1 The computerized switch Analog to Digital communication Time Division Multiplexing Revolution 2 Out of band switching SS7 standard defined Switchboard operators. Mechanical, manual switching 7

8 Telephone exchange (switch) A system of electronic components that connects telephone calls. makes telephone calls "work" in the sense of making connections and relaying the speech information A central office is the physical building used to house equipment including telephone switches. 8

9 Simple circuit switch network Telephones are connected to switches at the local office (or exchange) switch These switches are connected to other switches which can route your phone call to other exchanges 9

10 Revolution 1: Analog and Digital Signals Analog signals Sounds and electrical signals in the real world are analog What is sound? The amplitude of these signals have continuous (nondiscrete) values Digital signals Simulate analog signals using binary (discrete) values 11

Revolution 1: Digital Signals Disadvantages You need to convert to/from analog to use numbers are turned into a voltage wave that approximates the original wave Advantages Electronics can process

11 Revolution 1: Digital Signals Disadvantages You need to convert to/from analog to use numbers are turned into a voltage wave that approximates the original wave Advantages Electronics can process faster Can be sent further and faster Groups of numbers can often be compressed by finding patterns in them Digital looks just at high vs. low Electromagnetic interference (noise) affects analog signals more, reducing quality 12

Revolution 1: Analog to Digital Conversion

get Compression (or encoding) method encoding

12 Revolution 1: Analog to Digital Conversion Some important factors are Sample rate normally, the faster the better but, the faster you sample the more digital data to get Compression (or encoding) method encoding the relative change from the last sample in each new sample 13

13 Revolution 1: Time Division Multiplexing One way using digital signals help We can send the ones and zeros that represent a sample faster than the rate at which they have to be collected This means that we can mix (or multiplex) the ones and zeros of several signals on the same single line The easiest way to do this multiplexing is by using a standard time division (or time slice) This method is called Time Division Multiplexing (or TDM) 14

14 Revolution 1: The hierarchical network Using TDM (or other methods of multiplexing) The switch connected to your phone can switch individual phone calls, while A switch between Fort Worth and some other city can switch as a group a number of calls that are all going to the same city This group of calls is sent over something called a trunk line 15

15 Revolution 2: From in-band to out-of-band switching [1] Before 1965 Telephone services (like call waiting) have to be hardwired in the switch Call setup is done on the same phone lines as the call this is called in-band switching 1965 By adding a special-purpose computer to each switch, services can now be programmed in the switch since new services can be added by only changing the software, they can be added quicker but computer power still limits what can be done Late 1960 s The switch computers are connected together over separate lines allowing them to pass call setup information without using call lines this is called out-of-band switching This allows to add extra data and commands, such as who is calling you, wait, transfer, take messages etc. 16

16 Revolution 2: From in-band to out-of-band switching [2] 1970 s US companies develop a CCS6 standard for out-of-band switching now switches from different companies can share information New components called Signal Transfer Points (or STPs) are added to the telephone network STPs are used to better route out-of-band information 1980 s The international SS7 network standard defines three types of components SSP Service Switching Point (the original telephone switch) STP Signal Transfer Point (how to route your call) SCP Service Control Point (a database for service information) 17

17 Revolution 2: The SS7 Network Overview Voice (and other service data) flow over the red lines The actual route of a call is determined by the STP based on the total network loading at the time of the call Call and service setup flow over the blue lines 18

Revolution 2: The SS7 Network Details SS7 network pairs uses primary and secondary components The secondary component is designed to listen for indications that the primary component has stopped

18 Revolution 2: The SS7 Network Details SS7 network pairs uses primary and secondary components The secondary component is designed to listen for indications that the primary component has stopped working and take over if necessary. Reliability. The intelligence for the network is primarily in the SCP These are normally large general-purpose computers running special high-availability databases SCPs handle network-wide services like Routing a 800 number to different call centers based on time-of-day Keeping base station mobile roaming databases up-to-date 19

19 Revolution 2: Intelligent Networks Advantages Can route around problems Can adapt quickly to new service and signal requirements Greater profits Disadvantages Are expensive to upgrade or replace When they do break, they really break! These are very complex systems with many possible failure points 20

20 If you want to know more Telephones How cell phones work Wikipedia Digital Analog signals 21

TELECOMMUNICATION SYSTEMS

TELECOMMUNICATION SYSTEMS By Syed Bakhtawar Shah Abid Lecturer in Computer Science 1 Public Switched Telephone Network Structure The Local Loop Trunks and Multiplexing Switching 2 Network Structure Minimize