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Customer Premise Equipment

COMT 220

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Definitions

• CPE - Customer Premise Equipment– Correctly defined as “anything the

customer connects to the network”– In practice we use CPE to mean

“equipment other than simple terminals” (phones, PCs, etc.)

• We will discuss mainly voice, but the arguments apply to video and data also

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Rationale

• Placed between End-Users and CO connections

• Provide on-premise functions• Make cost-efficient use of CO connections

User

User

User

COCPE

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Different Types…

• PBX - Private Branch Exchange– Full Premise Based Switching

• Key System– Smaller System, usually non-switching– Difference to PBX often unclear

• CENTREX– PBX functionality, but implemented in

the Central Office Switch

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Switching Principles and Methods

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Cross-Point Switching“Space Division Switching

”1

1

4

4

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Three-Stage Switch

From Stallings, Voice and Data Communications.

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Time Division Switching

• Each Line Card “Samples” the inbound signal (8000 times per second, each sample is taken over 0.125 msec)

• While the cards collect the next sample (during the next 0.125 msec), the Time Slot Interchanger collects all samples and delivers them to the correct line card outputs

• The TSI must process 8000*2*(number of conversation) samples

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Time Division Switching

TSI

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PBX “Block Diagram”

PBXSwitching

System

Administration

LINES

TRUNKS

AnalogPhones

DigitalPhones

SpecialWorkstations

LocalSwitched Access

IXCSpecial Access

Private Lines

CTIMaintenance SMDR

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Packet Switching?

PBXSwitching

System

LINES

TRUNKS

AnalogPhones

DigitalPhone

DigitalPhone

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Categories of Features

• Features for the System User (Internal Customer)

• Features for the System Administrator

• Features for the Caller (External Customer)

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Handling Outbound Calls

• Call destination restrictions• Least cost route selection• Automatic redial

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Handling Inbound Calls

• Routing Calls– Attendant– Direct Inward Dialing

• Handling Unanswered Calls– Call Forwarding -- General– Call Forwarding -- Busy/No-Answer– Hunt Groups– Queuing and Message Services

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Handling Unanswered Calls

• Hunt Groups• Queuing• UCD

– Universal Call Distributor

• ACDs– Specialized PBX software for inbound

call handling

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PBX Capacity

• Traffic (usually measured in call minutes per hour)– How Many Simultaneous Calls

• Processor– Total Calling Volume– Busy Hour Call Attempts

• Physical Interfaces– Stations and Trunks

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“Programming a PBX”

• Moves, Adds, and Changes (MAC)– Establish New Service– Disconnect Service– Change Features On Existing Service

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Adding an Analog Station

• Physical Install• Assign Extension Number• Assign Class of Service and Other

Features– Often uses a template (or “Table”)

1234A

B

C

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Adding a Digital Phone

• Physical Installation• Define Feature Buttons on the

Digital Phone• Define Line Appearance Buttons• Assign Extension(s) to Line

Appearances• Assign Class of Service

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Button Assignments

A

B

C1 2 3

4 5 6

7 8 9

* 0 #1

2

3

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Button Assignments

A

B

C1 2 3

4 5 6

7 8 9

* 0 #1

2

3

Line 2

Line 1

Hold Xfer

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Extension Assignments

A

B

C1 2 3

4 5 6

7 8 9

* 0 #1

2

3

1234

5678

Hold Xfer1234

5678

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Extra Slides

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Multi-Stage Crosspoint Switching - Concept