University of Wisconsin StoutLearning TechnologiesBryan Walhovd

Goals:

The Goal of this Module is to give you a basic understanding of a cable modem and how it operates.

This high level overview will help you understand the following: What a cable modem is. The types of interfaces that exist on the modem. Devices associated with a cable provider network. How a modem comes online. Glance into the OSI model and DOCSIS.

Future modules will provide a detailed view of each step a modem takes to come online as well as factors that limit connectivity and speed.

What is a Cable modem?

A cable modem is a broadband device used to connect to the internet over a cable companies Hybrid Fiber Coaxial Network (HFC).

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Cable modem interface A cable modem has two main interfaces that

allow operation with the cable plant and customer equipment. A coaxial cable port used to hook up to the

cable plant

A RJ45 port which is used to connect to a computer or router via an RJ45 Ethernet cable.

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In your home

Typically a modem is hooked to a router in a home or a business which allows access too the internet for multiple devices including PC’s, Phones, Printers and Gaming consoles.

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Connection

Once the cable modem is connected to the HFC plant via the Coaxial connector and your PC, your all ready to go right?

Not exactly! The modem itself has to be set up (provisioned) on the cable providers network in order for it to access the internet.

So what next?

The Cable Modem Termination System Once hooked up to the coaxial plant, the

modem connects back to the cable providers CMTS, located typically in a HeadEnd.

Image courtesy of: By Vivien Guéant [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

What does all this mean??? A Modulator Demodulator (modem)

communicates with the cable provider utilizing Radio Frequency. This communication is bi-directional as we

send and receive data from our personal devices.

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Image courtesy of: By Vivien Guéant [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

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How it works!

Downstream Lock The modem first locks onto the Downstream

frequency(s). The normal frequency range delivered from the cable provider is 54Mhz to 1000 Mhz.

Scan for Downstream Channel

Power Modem

ON

Downstream Sync Established

Upstream Lock

The CMTS then sends a UCD (Upstream Channel Descriptor) which tells the modem the Return frequency to talk back at which is typically 5Mhz to 42Mhz.

Obtain the upstream parameters

UCD acquired

Ranging and IP Once the modem has successfully locked on

downstream and upstream, it completes ranging, IP connectivity, and security.

Start Ranging

Complete Ranging and Power adjustments

IP Complete

Establish IP Connectivity

Establish TOD/TOD Established

Establish Security/ Security Established

Configuration, Registration and Baseline Privacy. Almost there!!

Transfer operational parameters and

configuration file.

Register with CMTS

Initiate and establish Baseline Privacy

Registration complete

Modem is operational!

I’m ONLINE!!

Your device can now communicate to the internet!!!

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Do all cable modems function the same? The OSI model was defined to standardize the

functions of a communication system.

A cable modem, as with most communication devices, uses the Open Systems Interconnection Model.

The OSI model breaks a communication system into different layers with the objective of interoperability between devices without requiring logic changes of hardware and software.

Open System Interconnection?Detail:

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•Each Layer is briefly described in the included diagram.

• Where do you think DOCSIS modems operate?

OSI and DOCSIS

Data Over Cable Service Interface Specification (DOCSIS) was designed to standardize high bandwidth data transfer between cable providers internationally.

DOCSIS standard changes as the consumer demand for bandwidth increases.

DOCSIS modems operate primarily at the Physical, Data Link and Network layers of the OSI model.

Quiz

Click Here to start the Quiz

What do you know about DOCSIS cable modems??

Hint: Pick the best answer!

A cable modem is a broadband device used to connect to the internet over which type of Network?

HFC Network

Fiber NetworkCoaxial Cable

Network

Wireless Network

CORRECT!!

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OSI is short for?

Open Something Interesting

Open System Interconnection

Open System Interface

Open System Internet

Try This one!

CORRECT!!

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CMTS stands for?

Cable Modem Transitional

System

Cable Modem Television system

Cable Modem Telecommunication

s System

Cable Modem Termination

System

CORRECT!!

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The first thing a modem does when hooked to the HFC network once powered on is?

Looks for its Downstream

Looks for it’s upstream

parameters

Registers with the CMTS

Accesses the internet

CORRECT!!

Great Job!! Quiz Complete

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Thank You for Completing DOCSIS Cable Modem Basics Part 1.

If you have additional questions or feedback, please click here.

Cable Modems are interesting…

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