120 likes | 246 Views
Traffic Capacity issues facing the TETRA Application Developer. Richard Dewey 15 February 2000. Telecom Consultants International. Outline of presentation. TETRA tele and bearer services Mixed voice + data traffic profiles Insight from simple air interface model
E N D
Traffic Capacity issues facing the TETRA Application Developer Richard Dewey 15 February 2000
Telecom Consultants International Outline of presentation • TETRA tele and bearer services • Mixed voice + data traffic profiles • Insight from simple air interface model • Typical traffic performance results • Summary
Tele Services Supported by TETRA Clear Speech or Encrypted Speech • INDIVIDUAL CALL (POINT TO POINT) • BROADCAST (POINT TO MULTIPOINT ONE WAY) • GROUP CALL (POINT TO MULTIPOINT) • ACKNOWLEDGED GROUP CALL (POINT TO MULTIPOINT)
Bearer Services Supported by TETRA • Circuit mode unprotected data: 7.2, 14.4, 21.6, 28.8 kbits/sec • Circuit mode low protected data: 4.8, 9.6, 14.4, 19.2 kbits/sec • Circuit mode high protected data: 2.4, 4.8, 7.2, 9.6 kbits/sec • Packet connection oriented data • Packet connectionless data • Short Data Services - • 65535 Status messages (half reserved) • user defined data types • type 1: 16 bits data • type 2: 32 bits data • type 3: 64 bits data • type 4: up to 2047 bits data
Traffic performance criteria • Voice calls • T95 average, T95 maximum • access throughput, blocking probability • system throughput • Data calls • intrinsic delay • throughput
Mixed voice + data traffic profiles • Mixture of individual and group calls? • Mixture of voice and data? • Length of voice calls? • Size of data messages: packet and SDS1234 • Priorities for different voice calls?
Simple model of air interface • Control channel • grants access • allocates traffic chans • carries packet data • Traffic channels • carry circuit mode voice + data SERVERS Control Queue server Queues 1 2 3 4 Data Access
Control mechanisms for air interface • Access priority to get in to the system. • Queue priority gets in to the favoured Q. • Pre-emptive priority removes low priority active user to gain immediate service. SERVERS Control Queue server Queues 1 2 3 4 Data Access
Performance limiting factors • Control channel loading • access on the uplink • capacity on the downlink • Traffic channel loading • availability of channels
Monte Carlo simulation • Define traffic load • subscriber characteristics (individuals, groups, dispatchers, location) • traffic generated by each user • Generate traffic load • Run air interface protocol simulation • Analyse traffic runs • Plot results
Summary • Realistic traffic results only by full simulation. • Will take account of • voice + data traffic mix • voice priority mix • mix of data bearer services (SDS1234 and status). • HOWEVER priority between voice and data is “an implementation issue”. • Supplementary or extended control channels can be set up to give improved data services.