Chapter 5: Modeling Detailed Operations

Chapter 5: Modeling Detailed Operations
• Model 5-1: A call center system
• Multiple Types of Entities
• Balking, three-way decisions, expressions, queue priorities
• Model 5-2: The enhanced call center system
• Nonstationary arrival process
• Data structure of ARENA
• Model 5-3: The call center model with output
performance measures
• Run conditions, model size and speed, costing
• Model 5-4: An (s, S) inventory simulation
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 1
A Simple Call Center Model
• Single telephone number, 26 trunk lines
• Technical support: 8 tech support employees
• Sales information: four salespersons
• Order-status inquiry: computer system
• Goal
• Evaluate current service
• Try to improve service w/o
too much operating cost
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 2

Call Arrivals
• Calls arrive from 8 AM until 6 PM ~expo(0.857)
• Every caller needs a phone line to enter the process
• If all 26 lines busy, caller gets busy signal and leaves
• Calls get recording asking … UNIF(0.1, 0.6) min
• Technical support (76%)
• Sales information (16%)
• Order-status inquiry (8%)
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 3
Technical Support Calls
• Calls get 2nd recording asking … UNIF(0.1, 0.5) min
• Product type 1 support (25%)
• Product type 2 support (34%)
• Product type 3 support (41%)
• 8 tech support employees: two qualified for type
1, three for type 2, and three for type 3.
• If no qualified tech-support person is available,
call waits in electronic queue
• All tech support conversations ~ TRIA (3, 6, 18)
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 4

Sales Calls and Order-Status Calls
• Sales call goes to one of the four salespersons
• If salespersons are busy, call waits in electronic queue
• All sales conversations ~ TRIA (4, 15, 45)
• Order status calls handled by computer system
• No service employee and no capacity limit
• Time for “conversation” ~ TRIA (2, 3, 4)
• After call, 15% take option to talk to a salesperson
• Have lower priority than incoming sales calls
• Conversation durations ~ TRIA (2,3,4)
no
resource
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 5
Daily Operation
• Accept calls from 8 AM until 6 PM
• Some staff available until 7 PM
• Incoming calls shut out after 6 PM
• But all calls that entered before 6 PM are answered
• Performance Measures
• Number of call rejections (balking, getting busy signals)
• Time waiting on line for service, by customer type
• Number of calls waiting for service, by customer type
• Total time on the line, by customer type
• Personnel utilization
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 6

Initial Process Flow Chart
Check
Phone Line
Ask Call Type
Ask Product Type
Technical Support
Sales
Computer
Talk to Sales
entity types
resource types
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 7
Problems Need to be Solved
• 紀 錄 打 不 進 來 的 電 話 次 數 Record
• 全 程 占 用 trunk line, 中 間 步 驟 須 使 用 其 他 資 源 , 流 程
結 束 時 才 釋 放 出 trunk line
Seize, Release
• 收 集 不 同 類 型 顧 客 的 服 務 績 效
entity type
• Order status calls 的 優 先 權 次 於 Sales calls
Attribute: Priority
• 阻 止 六 點 以 後 的 電 話 進 入 系 統
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 9

I. Create and Direct Arrivals
1
2
3
4
1. Creates arrivals
2. If all lines are busy, record rejected call
3. 顧 客 聽 取 歡 迎 使 用 的 錄 音
4. Directs to appropriate type of service
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 9
Create and Direct Arrivals
• Create phone calls
• 目 前 不 分 顧 客 類 型
• Max Arrivals
– MaxCalls=999999 (variable)
• Decide module – 2 way by
condition
• MR: number of resource units
• NR: number of busy units
• If NRMR, calls are rejected.
• If NR

Seize Module
• Seize + Release (advanced process panel)
• 相 當 於 Process, 但 是 提 供 較 有 彈 性 的 流 程 建 構
• 顧 客 先 seize trunk line, 流 程 中 使 用 其 他 資 源 進 行 服 務 , 結 束
流 程 前 才 release trunk line。
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 10
Placing an Entity in a Storage
• Entering Store module allows the animation showing the
number of calls in the initial recording delay.
• The default option in Unstore module removes an entity
from the storage it resides.
• 若 不 需 動 畫 顯 示 聽 取 錄 音 的 人 數 , 可 刪 除 Store 與 Unstore
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 12

Directs to Appropriate Type of Service
• N-way by Chance: 76%, 16% (8%)
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 13
Stop Arrivals after 6 PM
• 獨 立 的 系 統 管 理 流 程 , 於 6PM 停 止 接 受 電 話 進 入 系 統
• Create a virtual entity that arrives at time=600 (6PM).
• Changes MaxCalls from 999999 to 1.
• No more phone calls arrive after 6PM.
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 14

2.Technical Support Calls Process Flow
1
2
4
3
1. Change entity type and picture
2. Store and Unstore modules for animation
3. Decide module determines product type
4. Request tech support service
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 15
Service Process for Technical Calls
• Expressions (Advanced
Process panel)
• Store mathematical formula,
use constants, variables,
attributes, system variables,
random distributions
• Can not be reassigned
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 16

3. Sales and Order Status Calls Process Flow
• Change entity type and picture
• Delay module from Blocks Panel
• Same as Store+Delay+Unstore
from Advanced Process panel
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 17
Setting Priority for Order Status Call
1. If order status calls require sales person, change
priority to 1.
2. Process Sales Call.Queue
與 sales call 的 顧 客 一 起 排 隊 等 候
1
2
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 18

Shared Queue
• 兩 種 顧 客 在 各 自 的 流 程 中 , 排 隊 等 候 相 同 的 資 源 提 供 服 務
• 須 勾 選 在 Process Sales Call.Queue 的 Shared 選 項
• Queue 的 服 務 順 序 可 依 照 顧 客 Attribute Name 的 高 低 安 排
• Default priority for sales calls is 0. ( 最 優 先 )
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 19
Release Module
• Seize + Release (advanced process panel)
• 顧 客 在 入 流 程 時 seize trunk line, 在 流 程 中 使 用 其 他 資 源 進 行
服 務 , 流 程 結 束 前 才 release trunk line。
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 20

Simulation Setup for Model 5-1
• Run simulation until after 6PM and the system is empty.
• Replication Length: Infinite
• Termination Condition
• TNOW >= 600 (after 6PM)
• Total WIP == 0 (system is empty)
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 21
Output for Model 5-1
• Long wait time for Type 1 tech calls
• Too many rejected calls
Simulation with Arena Chapter 5 –Modeling Detailed Operations part 1 Slide 22