COMT 2201 Managing Telecommunications Systems

COMT 2202 Managing Telecommunications Configuration Management Security Management Accounting Management Alarm Management Performance Management –This includes Traffic Engineering, or Network Design

COMT 2203 Traffic Engineering Understand the Applications a Systems is to Support Examine the Historical Amount of Resource Demand Determine the Amount of Resources Needed When a User Request for a Resource is not met, call it Blockage

COMT 2204 Examples of Resources CO Trunks for Local Calls Trunks to an IXC for Long Distance Calls Call Setup, Tone Generators, etc. in the PBX Operators (“Agents”) in a Call Center

COMT 2205 Why is “Blockage” unavoidable? Providing facilities for every user at all times is too expensive, both for companies and for carriers. Blockage will occur whenever users must share facilities. Reducing Blockage raises costs. Managing means balancing service and cost

COMT 2206 How is Blockage Measured Observe facilities during some period of time (usually an hour) Count the number of calls attempted, and the number of calls that failed. Express the result as a percentage. P.05 means 5 calls out of 100 failed. P.12 means 12 calls out of 100 failed.

COMT 2207 What is Traffic? Traffic measured the amount of information that flows over the network. For Voice Calls, we define the Average Holding Time as the information amount. Holding Time = Conversation Time + Operating Time

COMT 2208 Traffic Measurements Peg Count –Number of calls per hour. CCS (100 Call Seconds) –Sum of holding times per hour, in 100 second increments. Erlangs –Sum of holding times per hour, in 1 hour increments.

COMT 2209 Examples During one hour, we find 100 calls with average holding time of 3 minutes. –Peg Count is 100 –Sum of holding times is 300 minutes = 18,000 seconds = 180 CCS –Sum of holding times is 300 minutes = 5 hours = 5 Erlangs

COMT COMT 220 “Traffic Engineering”, or How Many Trunks Are Needed

COMT The Concept of Probability Rolling 1 dice and getting a “1” –The “Event” has a 1 in 6 chance (“probability”) –p = 1/6 = = %

COMT A Choice of Outcomes Roll a “1” or a “2” on a single dice throw –1/6 chance for “1” –1/6 chance for “2” –2/6 chance overall (1/6 + 1/6) to get “1” or “2”

COMT Two Simultaneous Events Roll a “1” on both dice simultaneously –1/6 chance that dice A has a “1” –Out of those 1/6 rolls where A has a “1”: 1/6 chance that dice B has a “1” –1/36 chance that both have a “1” (1/6 * 1/6)

COMT Probability Concepts in Telephony Check on one telephone user, once per minute.

COMT Continued… Record the number of minutes during one hour when you find the user on the phone. Say 10 minutes out of 1 hour The probability of the user being on the phone at any given time is 10/60 = 1/6.

COMT Two Users Two users, each with a probability of 1/6 of using the phone. Probability that both are using the phone is: 1/6 * 1/6 = 1/36

COMT How about Noone Using the Phone? Each user has a 5/6 probability of not using the phone. Probability of both users off the phone is: 5/6 * 5/6 = 25/36

COMT One Phone in Use? User A is on the phone (1/6), and User B is not (5/6) Probability is 1/6 * 5/6 = 5/36 User A off and User B on is also 5/36 Prob. Overall probability of one call is 10/36.

COMT Put Everything Together No Phone in Use:25/36(69%) One Phone in Use:10/36( 28%) Two Phones in Use:1/36(3%) Total Probability36/36 (as it should be)

COMT Examples With More Users Your Assignment (Practice): –Three Users –1/6 Probability for each to be on the phone –What are the chances of no, 1, 2, or 3 calls?

COMT Traffic Engineering Variables No. of Circuits Grade of Service Offered Traffic Offered Traffic = Carried Traffic + Blocked Traffic Carried Traffic = (1 - E(c,a) ) * Offered Traffic Blocked Traffic = E(c,a) * Offered Traffic [E(c,a) represents the blockage with “c” circuits and “a” Erlangs offered]

COMT Caller Choices ServerQueue First Attempt Call Connected Failed Calls Abandon Failed Calls Retry

COMT Recall Behavior Retry Attempts Add to System Congestion Traffic Engineering Corrections Must Be Made, Usually via Iterative Methods Retry Systems are Similar to Queuing Systems and Can Overload Like Queueing Systems Server First Attempt Call Connected Some Failed Calls AbandonSome Failed Calls Retry

COMT Queueing ServerQueue First AttemptCall Connected Call Enter Queue if All Servers Are Busy Average Queue Delay Replaces Blocking as the Performance Criterion

COMT Inbound Facilities, ACDs Inbound Call Center –Blocking Trunk Group on the Access Side –One or More Queues ACD IVR AG1 AG2 ACD Agent Splits Queues Blocking Trunk Group

COMT Inbound Facilities, ACDs cont… Queues and Access Trunks Interact –Queue Length Part of Call Holding Time –Access Group Blocking “Protects” Queues Traffic Engineering –Erlang B and Erlang C; Need to Iterate –Event Simulation ACD IVR AG1 AG2 ACD Agent Splits Queues Blocking Trunk Group