Technical Product Manual - DCT1900Configuration Directions, Traffic Capacity of the SystemConfig-DCT1900/R8/mw/ 5-1© 2000-2005CHAPTER 5Traffic Capacity of the SystemThe traffic capacity of the DCT1900 system is mainly determined by the RE and in exceptionalcases also by the Base Stations. The RE can handle a maximum of 60 simultaneous calls, and asingle Base Station has a capacity of 8 simultaneous calls.5.1 Traffic Capacity of the Radio ExchangeThe traffic capacity of the RE is determined by:z Total traffic (Erlang)z The GOS accepted by the customer.z The number of speech circuits available, with a limit of 60.Erlang is a measurement of telphone traffic. One Erlang is equal to one full hour of use, or 60 x 60= 3,600 seconds of phone conversation. You convert CCS (hundred call seconds) into Erlangs bydividing by 36.The GOS is the probability that a call cannot be made because of congestion in the system. Thecustomer has to indicate which GOS is acceptable. A GOS of 1%, or 0.01, means an average of 1blocked call in every 100 calls.SPU and SLU boards provide for 8 speech circuits. When a total of 8 SPU and SLU boards areinstalled, then 64 circuits are available, of which only 60 can be used simultaneously, as theDCT1900 system can handle only a maximum of 60 simultaneous calls.The two parameters mentioned above (GOS and number of speech circuits) and the total amountof traffic (Erlang) that is required are related to each other. Table 5–1 below shows how theseparameters are related for certain values. This table is used to calculate from a given GOS andErlang value the number of SPUs/SLUs needed. The Erlang value is the total traffic generated byall Portable Telephone users (including visiting Portable Telephone users) in the coverage area ofthe system.Table 5–1 Erlang Table–B values for given GOS and Number of Speech CircuitsGOS (GOS)Number ofSPUs/SLUsSpeechcircuits 2%(1/50)1%(1/100)0.5%(1/200)0.1%(1/1000)1 8 3.6 3.2 2.7 2.12 16 9.8 8.9 8.1 6.73 24 16.6 15.3 14.2 12.24 32 23.8 22.1 20.6 18.25 40 31.0 29.0 27.3 24.56 48 38.4 36.1 34.2 30.97 56 45.9 43.3 41.2 37.58 60 49.7 46.9 44.8 40.8
