1. DIGITAL SWITCHING
Monday, 14 February 2016

2. TELEPHONE PCM MULTIPLEXING
Station A
Station B
The International Telecommunication Union (ITU) Telephone Standards for time slots and Frame are rigid and are implemented through timing circuits which supply:
the transmission sequence of the binary pulses
the position of each time slot
the starting of the repetition period (starting of the Frame).

3. PCM REGENERATORS
As may be desired regenerators set at regular intervals along the line from 2 to 5 Km.
The regeneration process includes:
EQUALIZATION of the signals to compensate the amplitude and phase distortions introduced by the balanced couplers
EXTRACTION and REINSERTION OF THE BIT SYNCHRONISATION, with which the coming pulses are sampled

4. OUTPUT FROM CODEC
125 µseconds exist between samples ( PCM words) which is derived as:
T= 1 𝑓 𝑠 = 1 8,000

5. MOTIVATION FOR PCM Wasted Time Gap
As speed for electronic devices increased creating ability to sample voice at high speed, it became evident that sampling at the Nyquist rate created room for multiplexing many signals in the 125 𝜇𝑠𝑒𝑐 interval.

6. BASIC FRAME GENERATION – BELL SYSTEM
In 1962, Bell Laboratories developed the system for multiplexing 24 voice channels which is commonly referred to as T1 system.

7. THE FRAMING BIT
To allow the receiver to locate the PCM samples, Bell engineers developing T1 created a special bit, called the 193rd bit or framing bit , and added it between the 24-channel frames.
The framing bit creates a repeating pattern of 1s and 0s that a receiver used to identify the 193rd bit.
The receiver used the framing bit to identify locations where PCM samples for each telephone conversation end or begin.

8. DIGITAL SIGNAL LEVEL 0 (DSO)
Twenty-four voice conversations are formatted into a PCM stream that contains an update of the PCM samples 8,000 times per second giving 192 bits.
The 24 PCM samples and the 193rd bit create a signal format known as DS1 (Digital Signal level 1).
Each PCM sample for a given voice signal constitutes a channel within the DS1 stream.
These channels are referred to as DS0 (Digital Signal level 0) channels.

9. PCM STREAM WITHOUT FRAMING BIT
192x8,000=1.536Mbps
Without the framing bit, the receiver has no means of locating and extracting the voice channels.

10. THE CHANNEL BANK (T1 SYSTEM)
On T1 trunks, a frame consists of 24 timeslots, sent every 125 µsec (1/8000 sec).
One Frame of
24×8=192 𝑏𝑖𝑡𝑠 23 1 2 3 4 5 6 7 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
8 bit
11th Channel

11. History of T1
T1 is the ubiquitous digital carrier for telecommunications in North America.
T1 was developed by Bell Laboratories to carry the DS1 signal. It was first tested in Chicago in 1961.
T1 was commercially deployed in New York City in to improve voice transmission quality and reduce cabling congestion in underground telephone ducts, where space was at a premium.

12. THE FRAMING DEMON
D1 used an alternating 1-0 pattern in the 193rd bit position.
It was therefore susceptible to framing problems arising from certain tones (1000 Hz, for example) which could mimic the alternating one-zero-one-zero Framing pattern.
Under this circumstance, a channel bank that is attempting to acquire the framing bits of a T1 signal could lock onto the false framing pattern generated by such a tone and ignore the proper 193 framing bits.
A bit sequence that mimics a framing pattern is called a framing demon.

13. DS1: ROBBED-BIT SIGNALING(1)
Instead of adding more bits to the DS1 signal to carry signaling information, D1 mode took the least significant bit of each PCM channel and reserved it for signaling bits.
As a result of robbing each PCM word of its least-significant bit and replacing it with a signaling bit, this process was given the distinctive name of robbed-bit signaling.
This signaling scheme allows only 7 bits of a DS0 channel for PCM, as the last bit is used for signaling.

14. DS1: CONSEQUENCE OF ROBBED-BIT SIGNALING
Voice (Seven Digits)
Robbed Digit
Robbed-bit technique reduced the fidelity of the transmitted voice, since voice encoding in a channel was effectively reduced from 64 kb/s (in which all 8 bits per DS0 is used) to 56 kb/s (in which only 7 bits).

15. T-CARRIER HIERARCHY

16. PCM SIGNALLING
PCM systems use in-channel signaling based in in- slot or out-slot signaling.
In-slot Signalling:
Signalling information relating to a particular channel is carried in the same time-slot as the speech.
Out-Slot Signalling:
Signalling information relating to a particular channel is carried in a time-slot that is different from that of speech.

17. OUTSLOT SIGNALLING – E1
E1 Signaling information relating to channels is carried in a time- slot that is different from that of speech.
Also two time slots per frame are introduced for signaling and framing.
E1 was originally developed by CEPT as 30-channel system.
It has 32 time slots and one is used for frame alignment while the other is used for signaling.

18. OUTSLOT SIGNALLING – E1
Frame Synchronization
Signaling 1 2 3 4 . . . . 16 . . . 30 31
Frame
=32×8=256 𝐵𝑖𝑡𝑠
The frame is composed by 32 time slots of which 30 are reserved to the telephone channels
The first of the frame slots, identified with the index 0 (slot 0) contains frame the synchronization information .
Sixteenth (16th ) is reserved to the service signaling.

19. EXAMPLE
Q. Derive the speed in Mbps of an E1 link.

20. MULTI-FRAME STRUCTURE – E1
In the multi-frame, the frames with even order starting from the first (frame 0) have frame synchronism in the first time slot (slot 0).
In frames of odd order slot 0 contains signalling available for auxiliary services.
The alternation between ODD FRAMES and EVEN FRAMES is called ‘signalled by the alternation’ of one bit in the time slot 0.
After 6 frames starting from the one with index 0, the structure of the multi-frame repeats.

21. FRAME AND MULTIFRAME STRUCTURE OF THE CEPT PRIMARY SYSTEM

22. DIGITAL SWITCHING
ETI2506

23. BASIC SIGNAL INTO THE SWITCH

24. PRACTICAL IMPLEMENTATION
CENTRAL
CONTROL (CPU)
Address Bus, Data Bus, Control Bus

25. PRACTICAL IMPLEMENTATION
CENTRAL
CONTROL (CPU)
Address Bus, Data Bus, Control Bus

26. EXAMPLE OF DIGITAL MULTIPLEXER
ADC 0808 is one of the most commonly used Analog to Digital Converter(ADC), It consists of:
Eight-Bit Analogue-to-digital converter featuring:
impedance chopper stabilized comparator
256R voltage comparator with successive approximation register
Eight-channel Multiplexer that can directly access any of the 8-analogue channels
Micro-processor compatible logic

27. BLOCK DIAGRAM OF ADC0808

28. ANALOG CHANNEL SELECTION
Any of the analogue input channel can be selected by using the address decoder.

29. ADC 0808 PACKAGES
(a) DIP Package
The Integrated Circuit is available in two packages, i.e
Dual Inline Package (DIP) Package
(b) PLCC Package
Plastic Leaded Chip Carrier (PLCC) package.

30. NUMBERING PLAN
ETI2506
Monday, February 15, 2016

31. OBJECTIVE OF NUMBERING
Objective of Numbering Plan is to uniquely identify a subscriber who is connected to a telecommunications Network.
Initially numbering was restricted to single local exchanges with each exchange identified by its name.
With introduction of multi-exchange areas common numbering plans started evolving.
Introduction of Subscriber trunk dialling (STD) for inter city/town dialling led to the introduction of National Numbering.
Later, the development of International Subscriber Dialling led to the development of International Numbering Plans.

32. INTERNATIONAL NUMBERING PLAN
International Numbering Plan has been defined by ITU in recommendations E160-E163.
Country
Code
National Number
1-3 Digits
9-11 Digits
12 Digits Maximum

33. WORLD NUMBERING ZONES Europe North America Old USSR ME & India
South-East Asia
Central & South America
Africa
Australia

34. WORLD TELEPHONE NUMBERING PLAN

35. NATIONAL NUMBERING PLANS
Area/Trunk
Code
Exchange Code
Line Number
Area/Trunk Code identifies a particular numbering area or multi-exchange area, e.g. 20 for Nairobi or 56 for Kakamega.
Exchange Code identifies a specific exchange within a numbering area, e.g. 21, 22 for Nairobi Central.

36. GENERAL CATEGORIES OF NUMBER SCHEMES
Number Schemes can be Open, Semi-Open or Closed.
Open Number Scheme: Also known as non-uniform numbering scheme permits a wide degree of variations in the number of digits used to identify a subscriber within a country.
Semi-Open: allows the number length to differ by 1-2 digits
Closed numbering plan or uniform numbering plan has a fixed number of digits. Used in USA, Canada, France.

37. OPEN NUMBERING PLAN IN KENYA

38. SHORT CODES

39. SHORT CODES

40. NAIROBI AREA

41. NAIROBI (CONTINUED)

42. KAKAMEGA REGION

43. EXAMPLE: TO BE CARRIED OUT IN CLASS
Consider a 11-digit international number with 2-digit country code, 2-digit area code and a 7-digit subscriber number. Prefixes '0' and '00' are used for identifying national and international numbers respectively.
A few special services like fire, ambulance and police are given short subscriber numbers in the range The network is designed for remote maintenance and the maintenance exchanges are identified by the number range
Determine the number space available for subscribers and the fraction of the space lost.

44. SOLUTION Maximum possible number space 102 x 102 x 107
Due to prefixes, area codes and subscriber numbers cannot start with zero. Due to special services, the subscriber numbers cannot start with a 1. Due to maintenance, the number range starting with 9 is not available for subscribers. Hence, we have the total available number space as:
102 x 90 x 7 x 106 = 63 x 109
Fraction of Lost Space is

45. CHARGING PLAN
ETI 2506
Monday, February 15, 2016

46. WHY WE NEED A CHARGING PLAN?
Providing a telecommunication service. calls for investment in capital items as well as meeting operational expenses.
The capital cost includes that of line plant, switching systems, buildings and land.
Operating costs include staff salaries, maintenance costs, water and electricity charges and miscellaneous expenses.
A telecommunication administration receives its income from its subscribers.
A charging plan provides for recovering both the capital costs and the operating costs from subscribers.

47. CALCULATING THE COSTS
The cost of shared resources like the switching equipment is amortised among a large number of subscribers over a period of time.
The cost of dedicated resources like the telephone instrument and the subscriber line must be recovered from individual customers.
The operating costs must be worked out depending on the quantum of resources used in providing a service and the duration for which these resources are used.

48. CHARGES LEVIED ON A SUBSCRIBER
A telecommunication service can levy three categories of charges to a subscriber:
An initial charge for providing a network connection:
A. rental or leasing charge
Charges for individual calls made.

49. CHARGES TO INDIVIDUAL CALLS
Operating costs for telephone exchanges and transmission networks.
Government policy e.g. policy on subsidy of local calls by trunk/international calls, taxes or USO.
Communication regulations, e.g. CAK’s guidelines on interconnection.

50. CHARGING METHODS FOR INDIVIDUAL CALLS
Duration Independent Charging
Local calls in the fixed Networks are usually charged on a duration independent-basis.
The subscriber meter is incremented once at the start of a local call.
Duration Dependent Charging
Periodic pulse train of pulses from a common pulse generator operate the subscribers meter.
Modern exchanges store date, time and duration in seconds for the purpose of charging

51. DISTANCE-RELATED CHARGING

52. Traffic in a telecommunication network varies throughout the day.
TARIFF VARIATION
Traffic in a telecommunication network varies throughout the day.
However telephone exchange capacity is based on the estimated capacity at the busy hour.
As a result, a large part of the capacity remains idle during off-peak hours.
Most operators lower tariffs to encourage subscribers to call at off-peak hours

53. EXAMPLE OF TARIFF VARIATION SCHEME

54. At what traffic volume per day, should he move over to leased line?
EXAMPLE
A telephone administration provides leased lines at the rate of Kshs. 600 per km for a minimum rental period of 3 months. MMU, a point-to-point traffic user, has offices located 600 km apart and is confronted with the choice of using STD or leased lines.
At what traffic volume per day, should he move over to leased line?
Assume 20 working days per month and a rate of Kshs. 1 per unit recorded by the meter.
Assume that STD calls are charged at Kshs. 20 per minute.

55. x = 300 hours in 3 months = 100 Hours in a Month = 5 hours per day
SOLUTION
Cost of renting the leased line is 600 x 600 = Kshs. 360,000
Cost of STD calls per hour is 60 X 20 = Kshs.1200
Let the break-even point occur when the STD line is used for x hours in three months. Then we have
1200x = 360,000, or
x = 300 hours in 3 months = 100 Hours in a Month = 5 hours per day

56. Common Channel Signaling
ETI2506
Monday, 15 February 2016

57. TELECOMMUNICATION NETWORK SIGNALING
Exchange Hierarchy Classification
Subscriber loop signaling
Intra-exchange or register signaling
Inter-exchange or inter-register signaling.
Channel-Level Classification
In Channel Signaling
Common Channel Signaling

58. SIGNALING TECHNIQUES

59. COMMON CHANNEL SIGNALLING
SignalingTerminal
Modem

60. CCS SIGNALLING FRAME FORMAT
Information
Error
Check
Circuit
Label
Header

61. COMPARISON OF IN-CHANNEL AND COMMON-CHANNEL
Trunks are held up during signalling
Trunks are not required for signaling
Interference between Voice and Control Signals may occur
No interference since the voice and control channels are separate
Separate signaling equipment is required in each trunk hence expensive
Only one set of signaling equipment is required for a large group of trunk circuits hence economical
Can be misused by customers since it is easy to mimic voice signaling
Control channel is in-accessible to users
Signalling is relatively slow
Signalling is much faster
Speech circuit continuity is assured when signaling is received
State of speech circuit not automatically assured
It is difficult to change or add signals
There is flexibility to add or change signals