Chapter2

2 Teletraffic Engineering

2.1 Introduction

  • Telephone Network Dynamics

    • Many customers exist compared to available trunks.

    • Not all customers are active simultaneously.

  • Trunk Definition

    • Trunks connect Mobile Switching Centers (MSC) and are counted by voice pairs.

  • Trunk Dimensioning

    • Critical to determine the number of trunks per route based on expected usage.

    • Usage refers to the number of simultaneous calls expected over a route.

  • MSC Capacity

    • Defined as the maximum number of originating + incoming calls during peak traffic while meeting delay requirements.

    • Influenced by call types, features, equipment configuration.

    • Processing capacity, switching network limits, and directory numbers can restrict capacity.

    • Call volume is dependent on geographical area, service class mix, and time of day.

  • Supplementary Features

    • MSC must process calls while also handling features (call waiting, forwarding).

  • Key Objectives of this Chapter

    • Definitions in teletraffic engineering.

    • Numerical examples for calculating traffic.

    • Erlang and Poisson blocking formulas for calculating Grade of Service (GoS).

    • Application of traffic concepts to both wireline and wireless systems.

2.2 Service Level

  • Service Level Characteristics

    • Two areas: Delay to receive a dial tone and probability of service denial.

  • Dial-Tone Delay

    • Time a subscriber waits after lifting the handset for a dial tone.

    • High competition among users for limited dial-tone connections.

  • Service Denial

    • The probability that a trunk is unavailable affects service access.

    • Users may retry calls after receiving a busy signal.

  • Performance Measures

    • Probability of delay exceeding a set time or call denial/blockage rate (blocking probability).

2.3 Traffic Usage

  • Traffic Path Definition

    • Refers to any communication channel used for sequences of communications.

  • Key Traffic Parameters

    • Calling Rate: Number of route uses per unit time (call intensity).

    • Call Holding Time: Average duration a call occupies a traffic path.

  • Carried vs. Offered Traffic

    • Carried traffic: Volume handled by a switch.

    • Offered traffic: Volume presented to a switch (carried plus overflow).

2.4 Traffic Measurement Units

  • Traffic Intensity

    • Average simultaneous calls during a period.

    • Erlangs and CCS Measurement:

      • 1 Erlang corresponds to 36 call seconds, indicating 1 call in progress continuously.

  • Formula for Traffic Intensity

    • Calculated as total holding time of calls divided by monitoring period duration.

  • Percentage of Occupancy and Peg Count

    • Measures server occupancy and attempted call count respectively.

2.5 Call Capacity

  • Understanding Call Capacity

    • Global vs. Component views regarding service requests.

  • Global View: Treats the entire MSC as a unit capturing all request attempts for service.

  • Component View: Focuses on system subsystems, aggregating originating/terminating call metrics.

  • Call Types

    • Originating, terminating, outgoing, and intra-office calls.

  • Typical Call Mixes

    • Using standards for different traffic environments: metro, suburban, rural.

2.6 Definitions of Terms

  • Key Definitions

    • Calls Attempted: Total number of request calls, an indicator of demand.

    • Grade of Service (GoS): Reflects the ratio of successful call completions to attempts.

    • Quality of Service (QoS): Percieved satisfaction of service, influenced by delays, failures, transmission quality.

2.11 Summary

  • Covered teletraffic engineering principles for managing wireline/wireless switches.

  • Introduced calculations for designing call capacities.

  • Discussed Erlang B, Poisson blocking formulas, their applications and examples.

2.12 Problems

  • Explored various problem statements for practical applications in traffic measurements, call blockage scenarios, and average holding time calculations.