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E5122 COMMUNICATION SYSTEM

E5122 COMMUNICATION SYSTEM. EXCHANGE. T elephone exchange is a place/centre where telephone calls are connected to enable voice conversation. 3 types of exchange: Local Tandem I nternational. Local exchange-connect to the customer ( subscriber)

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E5122 COMMUNICATION SYSTEM

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  1. E5122COMMUNICATION SYSTEM

  2. EXCHANGE • Telephone exchange is a place/centre where telephone calls are connected to enable voice conversation. • 3 types of exchange: • Local • Tandem • International

  3. Local exchange-connect to the customer (subscriber) Tandem exchange- A telephone central office switch that links telco end offices together and does not connect to the customer directly International exchange-connects exchange to entire country and oversea.

  4. Switched Services: • Switched calls are dialable  (users dial a telephone number to make a connection. • People can reach anyone on public network by dialing a telephone numbers. • Charges are based  on  amount of time calls connected. • Can be used for voice/data/video/ image traffic. • Can be used with analog and digital telephone lines. • When callers hang up, network line and equipment are free to be used by another person or data device.

  5. As the number of telephones increases, so does the number of transmission lines used for calls between them, at a surprisingly large expense. Switching equipment is used to share these expensive transmission lines. A network consisting of at least one switching system (exchange) and accommodated transmission lines (optical fiber microwave) is referred to as a telephone network.

  6. 1 phone-3 phone 1 phone-Many phone 1 phone-7 phone

  7. National Exchange Hierarchy Main switching center MSC ZSC Zone switching center District switching center DSC LE Local Exchange Subscriber S

  8. Function Of Exchange • Record customer’s call meter • Monitor switching process between exchange and customer • Record customer’s request (meter termination) • Provide supervision tone such as dial and busy tone. • Control conversation quality and exchange service.

  9. Manual Switching

  10. SWITCHING NETWORK • Concentrator (Penumpu) • Distributor (Pengagih) • Expander (Pengembang) • Multiplexer

  11. CONCENTRATOR DISTRIBUTOR CONCENTRATOR

  12. CONCENTRATOR • A device that can funnel many line into few lines. • Output line will be fed into distributor. • Example: 1000 line entered concentrator and only 100 line comes out from concentrator.

  13. Concentration -- many lines funneled into a few trunks Distribution or Routing -- interconnecting trunk lines Expansion -- a few trunks expanded to many lines

  14. Line 1 Line 1 Line 2 Line 2 DISTRIBUTOR CONCENTRATOR EXPANDER Line 1000 Line 1000

  15. Distributor Expander A device between concentrator and expander. Receive output line from concentrator and fed it into expander. Receive output line from distributor. Expand the line back into source line. Example: receive 100 line from distributor and expand it back to 1000 line.

  16. MULTIPLEXER • A process where multiple analog message signals or digital data streams are combined into one signal. • The aim is to share an expensive resource. • Method of multiplexing: • TDM (Time Division Multiplexing) • FDM (Frequency Division Multiplexing)

  17. TDM FDM

  18. Line 1 Line 1 Line 2 Line 2 DEMUX MUX Line 1000 Line 1000

  19. Stored Program Control (SPC) Block Diagram Switching # 1 # 2 # 1 # 2 # n # n DTMF Scanner Driver 2 n 1 Ringer CPU Memory Control Director File

  20. Block Diagram Function • Memory-save user’s status activity in software • Control director-software that control all system • File-1)save payment data 2) prepare special schedule for other services • DTMF (Dual Tone Multi Frequency)-decodes signal produced during dialing process • Scanner-detect phone lift status and signaling from cellular line • Driver-1) connect/disconnect switch 2) provide path for tone and dial signal • CPU-control and execute stored software • Ringer-generate signal to show incoming call

  21. SPC Advantages • Maintenance and monitoring process are easier because exchange operation can be changed any time using programming • Signaling are easier and more efficient. • Additional channel doesn’t need additional signaling equipment. • Process is faster than manual method.

  22. SPC Disadvantages • Minor damage will stop exchange operation. • Need extra building and equipment (ex: air conditioning room and programming) • Need to train all workers to operate the process. • Maintenance are dependence on supplier.

  23. SIGNALLING • The information/instruction exchange between different section in a telecommunication system. • Involved section: • Caller with exchange • Exchange with exchange • Exchange with receiver

  24. a) Caller to exchange b) Exchange with receiver

  25. c) Receiver with exchange d) Tone from exchange to caller/receiver

  26. CHANNEL ASSOCIATED SIGNALING (CAS) • Voice and control signal are send in the same channel/circuit. • Can be controlled by digital or non-digital exchange. • Signaling speed is slow.

  27. (CAS) Exchange A Exchange B Traffic channel Signaling transmitter/receiver

  28. COMMON CHANNEL SIGNALING (CCS) • Voice signal and control signal are send on different channel. • Control signal will be detected and execute control duty and line switching. • Fully controlled by computer.

  29. CCS Exchange A Exchange B Traffic channel Signaling line Signaling transmitter/receiver

  30. Traffic Engineering – Traffic Intensity • Holding Time - the length of time that a resource is being held (the duration of a phone call) • Traffic volume - for an interval is the sum of all the traffic holding times for that interval • Traffic intensity = traffic volume / time interval which is a measure of demand • Erlangs - describe traffic intensity in terms of the number of hours of resource time required per hour of elapsed time

  31. TRAFFIC UNITS • The international dimensionless unit of telephone traffic is called the Erlang after A. K. Erlang (1878 –1929) a Danish scientist. • Defined as one circuit occupied for one hour. • 1 Erlang= 1 Call–hour / hour • 1 Erlang= one circuit busy 100% of the time • 1 Erlang= two circuits busy 50% of the time • Traffic of one Erlang refers to a single resource being in continuous use, or two channels being at fifty percent use, and so on.

  32. 1 hour of continuous use of one channel = 1 Erlang • 1 Erlang = 1 hour (60 minutes) of traffic • 1 Erlang= 1 call last for 1 hour or 2 calls with an average call duration of 30 minutes • 2 E =2 telephone operators who are both busy all the time • 0.5 E =a radio channel that is occupied for 30 minutes during an hour • 10 erlangs =300 two-minute calls in an hour

  33. A = CH / TErlangs The traffic intensity offered by each user is: A= Traffic intensity H=The average holding time of a call C=The average number of call requested/hour T=1 hour / 60 minutes / 3,600 seconds

  34. Example 1 • A call established at 1am between a mobile and MSC. Assuming a continuous connection and data transfer rate at 30 kbit/s, determine the traffic intensity if the call is terminated at 1.50am. Solution: C=1 call H=50 minutes Traffic intensity (A) = CH/T = (1 call)*(50 mins)/(60 min) = 0.833 E Note, traffic intensity has nothing to do with the data rate, only the holding time is taken into account.

  35. Example 2 • Consider a PSTN which receives 240 calls/hr. Each call lasts an average of 5 minutes. What is the outgoing traffic intensity to the public network. Solution C = 240 calls H = 5 minutes A = CH/T = (240 calls x 5 min) / 60 min = 20 E

  36. Example 3 • Find traffic intensity for a system if 60 calls are received in one hour, each call lasting 5 minutes Solution C=60 calls H=5 minutes A = CH/T A = 60 x 5 / 60 = 5 E

  37. Example 4 • If a group of user made 30 calls in one hour, and each call had an average call duration of 5 minutes, find traffic intensity. A = CH/T = (30 x 5) / 60 = 2.5 E

  38. Example 5 • A system received 120 outgoing calls with duration of 2 minutes and 200 incoming calls with duration of 3 minutes. Find outgoing traffic, incoming traffic and total traffic. Solution Incoming traffic, Ain= 200 calls x 3 min / 60 min = 10 E Outgoing traffic, Aout= 120 calls x 2 min / 60 min = 4 E Total traffic = Aout + Ain = 14 E

  39. Grade of Service (GOS), B • How to compare the quality of services provides by different service providers? • What is the probability of not being able to make a call? • What is the probability of waiting before a call is connected? • All these can be explained by the Grade of Service (GOS)

  40. When a user attempts to make a telephone call, the routing equipment handling the call has to determine whether to accept the call, reroute the call to alternative equipment, or reject the call entirely. • Rejected calls occur as a result of heavy traffic loads (congestion) on the system and can result in the call either being delayed or lost. • If a call is delayed, the user simply has to wait for the traffic to decrease, however if a call is lost then it is removed from the system. • The Grade of Service is one aspect of the quality a customer can expect to experience when making a telephone call.

  41. B = Number of calls lost Number of calls offered B = Traffic lost Traffic offered Grade Of Service, B is used to observe and measure how many calls are offered, carried and lost in the system. The lower this number, the higher the GOS.

  42. For example, if GOS = 0.05, one call in 20 will be blocked during the busiest hour because of insufficient capacity • For GOS = 0.02. This means that two users of the circuit group out of a hundred will encounter a call refusal during the busy hour.

  43. Example 6 • 1200 calls are offered to a channel and 6 calls are lost. Duration of a call is 3 minutes. Find: • Offered traffic, A • Carried traffic • Lost traffic • GOS, B • Congestion time

  44. A = CH/T = (1200 x 3) / 60 = 60 E • Carried traffic = [(1200-6) x 3] / 60 = 59.7 E • Lost traffic = (6 x 3) / 60 = 0.3 E • B = Lost traffic / Offered traffic = 6/1200 = 0.005 • Congestion time = B x 1 hours (second) = 0.005 x 60 x 60 = 18 seconds

  45. Call Intensity • Call intensity, λ which is the mean number of calls offered per time unit, and mean service time s. • The offered traffic is equal to: λ = A / s A=Traffic intensity s= Average holding time for a call

  46. Example 7 • Given traffic intensity of 90 E and holding time for a call is 3 minutes. Find call intensity. λ = A / s = (90 x 60) / 3 = 1800 call

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