China
Africa
Explore chapters and articles related to this topic
Frequency Responses
Published in Nassir H. Sabah, Electric Circuits and Signals, 2017
Tone dialing has practically replaced pulse dialing for selecting a telephone number, as it is much faster to process. The touch-tone keypad typically has 12 buttons arranged in 3 columns and 4 rows (Figure 10.5.3). The four rows are assigned four frequencies in a low- frequency group, whereas the three columns are assigned three frequencies in a high- frequency group. Pressing the number 5, for example, generates the tones 770 Hz and 1336 Hz. Thus, only 7 tones are required for the 12 buttons.
Distribution of audio signals
Published in Michael Talbot-Smith, Audio Engineer's Reference Book, 2012
The basic objective of telephony is to provide a service to enable two customers at a distance to set up a call via the network so that both may talk to each other. The telephone system must supply the means of connecting two telephones together via signalling, switching and transmission functions. The signalling function enables the customer to interface with the telephone system and inform the telephone system which telephone the customer wishes to contact. The signalling system also informs the user of the progress that the telephone system is making in setting up the requested connection and alerting the desired distant party that someone is attempting to make contact. Switching is the mechanism to interconnect the individual telephones with each other. Transmission is the end-to-end conveyance of the voice signal at the level of loudness and intelligibility that the user originates into the telephone. To set up a connection through the network from one telephone to the other there must be a means of identifying individual telephone lines: the directory number. Thus every telephone throughout the world must have a unique number. From the directory number of the calling and the called number it must be possible for the exchange equipment to determine a route for the call via the network of telephone exchanges. When a caller lifts the handset this action signals to the exchange that the caller wishes to set up a call. The exchange signals to the caller that it is ready to receive instructions by returning the dial tone. The caller signals the desired destination telephone by dialling the directory number of the distant telephone. The exchange then decodes this directory number and translates it into routing information to set the connection up through the switches within the exchange or exchanges. When the distant telephone's status has been determined, i.e. busy or free, this is signalled back to the caller. If the distant party is free the equipment will apply a ringing signal to the called telephone to alert the telephone. When the called telephone handset is taken off the hook this signals to the exchange that the call has been answered and the ringing should be removed from the line, the line placed into the busy state as far as other callers are concerned and the call connection established for end-to-end voice communication. When the caller or the called party concludes the conversation, either will replace the telephone handset and this will signal to the exchange that the call
Assessing the impact of the 2015 introduction of increased penalties and enhanced public awareness and enforcement activities on texting while driving among adults in Ontario, Canada
Published in Traffic Injury Prevention, 2020
Christine M. Wickens, Anca R. Ialomiteanu, Steven Cook, Hayley Hamilton, Maryam Haya, Tracey Ma, Robert E. Mann, Heather Manson, André McDonald
Data were based on telephone interviews with 1,846 respondents who reported having driven in the past year. Data were derived from the 2015-2016 cycles of the Centre for Addiction and Mental Health (CAMH) Monitor, an ongoing cross-sectional telephone survey of adults aged 18+ years in Ontario, Canada. The CAMH Monitor employs random-digit-dialing (RDD) methods via Computer Assisted Telephone Interviewing. The use of a list-assisted RDD allowed for the inclusion of cellular telephones, newly listed and unlisted numbers. Each annual cycle consisted of four independent quarterly samples with approximately 750 completions each. The design employed a two-stage probability selection procedure. Within each regional stratum, a random sample of telephone numbers was selected with equal probability in the first stage of selection (i.e., households). Within households of selected telephone numbers, one respondent aged 18 years or older who could complete the interview in English was usually selected according to the last birthday method. For each calendar year, the quarterly samples were combined to provide a single annual dataset. For the purpose of our study, the two annual cycles of the survey (2015 and 2016) were merged and respondents who reported driving in the past 12 months before the survey were selected, resulting in a data set with N = 1,846 respondents.