© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Introduction to VoIP Allocating Bandwidth for Voice and Data Traffic
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Outline Overview Sources of Traffic Statistics Network Objectives for Voice and Data Meeting the Current Network Objective Traffic Theory Busy Hour Erlangs Traffic Probability Assumptions Traffic Calculations Call Density Matrix Bandwidth Calculations Summary Lesson Self-Check
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Sources of Traffic Statistics Voice traffic statistics –PSTN carrier –PBX CDR –Telephone bills Data network statistics –Network management systems –Sniffers –show interface commands –Router-based accounting
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Network Objectives Data network –Throughput –Delay Voice network –Grade of service
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Meeting Objectives Are the delay and throughput acceptable on the data network? Are you achieving grade of service on the voice network?
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Network Demand
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Traffic Offered A = C * T Where: –A is the offered load. –C is the number of calls. –T is the average holding time of a call.
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Busy Hour
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Erlangs The amount of traffic a trunk can handle in one hour. Equals: 60 call minutes 3600 call seconds 36 centum call seconds (CCS)
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Assumptions Potential sources Traffic arrival characteristics Lost calls
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Traffic Calculations
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Call Density
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v VoIP Bandwidth CodecCodec SpeedSample SizeFrame RelayFrame Relay with CRTP Ethernet Bits per Second Bytes Bits per Second G.71164, ,26766,13379,467 G.71164, ,40067,20087,200 G.726r3232, ,26734,13347,467 G.726r3232, ,40035,20055,200 G726r2424, ,80026,40041,400 G.726r2424, ,40027,20047,200 G.726r1616, ,20017,60027,600 G.726r1616, ,40019,20039,200 G.72816, ,20017,60027,600 G.72816, ,40019,20039,200 G , ,600 G ,40011,20031,200 G.723r , ,913 G.723r , ,525 G.723r , ,985 G.723r , ,670
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Bandwidth
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Practice Item: Bandwidth Calculation Traffic statistics and requirements: 50 concurrent calls during busy hour G.729 using 20-byte sample size Frame Relay with CRTP 10 percent call-processing overhead 30 percent bandwidth savings using VAD 2-Mbps data requirement
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Summary Voice traffic statistics and data network statistics are among the sources of traffic statistics. The network objective for voice is measured in grade of service. To meet the current network objective, delay and throughput must be acceptable on the data network and grade of service must be achieved on the voice network. The equation A = C * T is used to calculate traffic flow. Call volume should be measured during the busiest hour. Erlangs help determine trunk requirements.
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Summary (Cont.) Three traffic probability assumptions to consider when determining the number of required trunks involve potential sources, traffic arrival characteristics, and lost calls. Traffic calculations can be used to determine the number of physical trunks required to meet grade of service. A call density matrix helps determine the number of trunks. Bandwidth required does not equal link speed.
© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v