NHD computer and networking basic part 2

Customer Care
Cable Modems



01 December 2007


















Copyright Notice:








The information in this document is subject to change without notice. Published by TWC Customer Care Support Delivery.
This document contains confidential and internal information and is copyrighted. All rights reserved. No part of this document may be photocopied or reproduced by any means without prior consent of TWC’s Customer Care Support Delivery.
© 2007, Time Warner Cable Customer Care Support Delivery, All Rights Reserved.
Road Runner logo and character images TM & © Warner Bros. Entertainment Inc (s07)

Table of Contents

Introduction.. 1
Overview.. 1
Objectives. 1
Cable Modem Fundamentals.. 2
Cable Modem Definition. 2
How it Works. 2
Tuner 3
Demodulator 4
Modulator 4
Modem MAC (Media Access Control) 4
Microprocessor 4
Connections. 5
Block Sync. 5
Signals. 5
Media Access Control (MAC) Address. 6
Understanding DOCSIS.. 7
Troubleshooting Cable Modems.. 9
Power Cycling the Modem.. 9
Cable Modem Rear View.. 9
Modem LED Indicators. 10
Powering-Up and Initializing the Modem & LED Descriptions. 10
Approved Cable Modem List 11
eMTA (Voice over IP) Modems. 11
eMTA Modems and UDI 13
Power Cycling a MTA Modem.. 13
Locating the Modem MTA MAC Address. 14
Helpful Cable Modem Troubleshooting Tips.. 15
Power Cycling the Modem.. 15
Asking Probing Questions. 15
Cable Routers. 17
Cable Modem Providers and WebSites.. 17
Quick Reference Guide. 17



Introduction
Overview

This module is designed to introduce various cable modems and their respective technologies to National Help Desk support personnel as they will encounter them every day throughout the course of voice and electronic customer interactions.


Objectives

Upon completion of this section, the student will be able to:
· Explain the purpose of a cable modem.
· Define the nature and advantages of a DOCSIS modem.
· Describe the connectivity requirements from the incoming broadband signal to the PC connection.
· Explain data transfer rates and download time.
· Troubleshoot cable modems issues including Power, Cable Connectivity, and PC Connectivity.
· Describe the difference between an eMTA and a standard cable modem.


Cable Modem Fundamentals
Cable Modem Definition
A cable modem is a device that enables you to hook up your PC to a local cable TV line and receive Internet data through a cable network.

How it Works
A cable modem modulates and demodulates electrical signals in a similar manner to a telephone modem. However, since coaxial cable can carry much higher wave frequencies, cable modems are far more sophisticated. Their internals can include a tuner, a bridge, a router, an encryption/decryption device, an SNMP agent and an Ethernet hub.



Tuner
The tuner connects to the cable outlet; sometimes with the addition of a splitter that separates the Internet data channel from normal CATV programming.

Since the Internet data comes through an otherwise unused cable channel, the tuner simply receives the modulated digital signal and passes it to the demodulator.

In some cases, the tuner will contain a diplexer, which allows the tuner to make use of one set of frequencies (generally between 42 and 850 MHz) for downstream traffic, and another set of frequencies (between 5 and 42 MHz) for the upstream data.
· In the past, some systems have used a cable modem tuner for downstream data and a dial-up telephone modem for upstream traffic.
· However, since the arrival of DOCSIS 1.1, cable modems have been able to send and receive data without a telephone line.
· In either case, after the tuner receives a signal, it is passed to the demodulator.


Demodulator
The most common demodulators have four functions. A quadrature amplitude modulation (QAM) demodulator takes a radio-frequency signal that has information encoded in it by varying both the amplitude and phase of the wave, and turns it into a signal of digital 1's and 0's. An error correction module then checks the received information against a known standard, so that problems in transmission can be found and fixed. In most cases, the network frames, or groups of data, are in MPEG format, so an MPEG synchronizer is used to make sure the data groups stay in line and in order.

Modulator
In cable modems that use the cable system for upstream traffic, a modulator is used to convert the digital computer network data into radio-frequency signals for transmission. This component is sometimes called a burst modulator, because of the irregular nature of most traffic between a user and the Internet, and consists of two parts:
· A section to insert information used for error correction on the receiving end
· A QAM modulator

Modem MAC (Media Access Control)
The MAC sits between the upstream and downstream portions of the cable modem, and acts as the interface between the hardware and software portions of the various network protocols. All computer network devices have MACs, but in the case of a cable modem the tasks are more complex than those of a normal network interface card. For this reason, in most cases, some of the MAC functions will be assigned to a central processing unit (CPU) -- either the CPU in the cable modem or the CPU of the user's system.

Microprocessor
The microprocessor's job depends somewhat on whether the cable modem is designed to be part of a larger computer system or to provide Internet access with no additional computer support. In situations calling for an attached computer, the internal microprocessor still picks up much of the MAC function from the dedicated MAC module. In systems where the cable modem is the sole unit required for Internet access, the microprocessor picks up MAC slack and much more. In either case, Motorola's PowerPC processor is one of the common choices for system designers.

Connections
The cable modem is usually an external device connected to the PC’s network card using a standard Category 5 network cable or USB cable. The cable modem is then connected to the wall using a coaxial cable. Assuming the network card has been installed and the network settings in the operating system have been configured, the modem is plugged into a power outlet and begins the initialization and block sync process.


Block Sync
In order for a two-way modem to provide two-way Internet Service it must have block sync. In a nutshell block sync means the modem has “locked onto” the frequencies we transfer data on, both forward and return. Forward frequency lock is the frequency used for downloading. Return frequency lock is the frequency used for uploading. The term block sync only refers to LAN-city modems. Block sync is most commonly confirmed by a solid “cable” light on a modem.

Signals
All of the cable modems attached to a cable TV company coaxial cable line communicate with a Cable Modem Termination System (CMTS) at the local cable TV company office. All cable modems can receive from and send signals only to the CMTS, but not to other cable modems on the line.


Media Access Control (MAC) Address

Every cable modem, as well as every network adapter, has an electronic identification number built into the hardware. This number is unique from every other cable modem or network adapter. It serves to identify the physical hardware and the host that uses it from every other host on a network.



MAC: 00407B-0000531
Modem MAC address
MTA MAC: 00407B-000053
MTA MAC Address used for the VOIP service
USB MAC: 00407B-000052
This modem has a USB network adapter built in and this MAC is for the USB adapter.
CMCI MAC: 00407B-000054
Cable Modem to CPE Interface. This MAC address is not used for troubleshooting RR connection issues and is beyond the scope of this document.


Understanding DOCSIS

Developed by CableLabs and approved by the ITU in March 1998, the DOCSIS (Data Over Cable Service Interface Specification) defines interface standards for cable modems and supporting equipment. The standardization of cable modems ensures that cable modems are inter-operable, low cost, and can be easily purchased at retail stores. With certification from CableLabs, manufacturers are able to produce cable modems for retail, so consumers no longer have to depend on leased cable modems from their cable provider.


Important Note: Road Runner Divisions use many brands of cable modems. The table below illustrates only several of the most common cable modems currently in use. Most divisions will use several different brands. Some divisions use proprietary cable modems such as the Ambit and some divisions still have Legacy (non-DOCSIS) modems in use. Non-DOCSIS modems that are in use will be phased out as these divisions upgrade their plant. Non-DOCSIS modems cannot be viewed using the UDI.

Please consult your Division Matrix for the most up-to-date list of cable modems in use by a particular division.

DOCSIS modems currently in use by Time Warner divisions include, but are not limited to, DCM425, Surfboard 5100, Terayon TJ715 and the Ambit CM 60194E.







Troubleshooting Cable Modems

Power Cycling the Modem

Power cycling the modem simply means to remove power to the modem for a specified period of time, usually 60-90 seconds or longer for a Non-DOCSIS modem and 15-30 seconds for a DOCSIS modem. Power cycling clears the modem’s internal memory and clears any errors. To power cycle a modem, unplug the modem from the power source and wait a minimum of 60-90 seconds then plug the modem back into the outlet.Note: Some modems, such as the newer Voice over IP (VoIP) ready units have an internal battery which the modem uses in case of a power outage (thus having the ability to support a phone call even when the power is out, much like a traditional phone). These types of units may require a “reset” button to be pressed in order to be “power cycled”, however doing so while the customer is using it will result in a disconnect of any phone conversations. For more on voice-ready modems please refer to the eMTA modem section below.


Cable Modem Rear View

Below is a diagram of what the typical back panel of a cable modem looks like. Please note that this varies from model to model, and you should consult your Division Matrix for the most relevant & up-to-date modem charts (including pictures of individual modem back panels)

Common Cable Modem Connections

Modem LED Indicators

External cable modems have front panel indicator lights, called LEDs, which are used to show a modem’s current operating status, as well as for diagnostic purposes. The names and color of the lights may vary by modem manufacturers, but all external cable modems have lights that indicate similar information.


Powering-Up and Initializing the Modem & LED Descriptions

When the modem is powered-on and connected to the cable, it will begin the initialization process. The first task that the modem performs is a self-test on the inner workings of the modem. Once the modem locks onto its “downstream” carrier, it will begin the registration process with the Head-End. When the Head-End recognizes that the modem is registered with the cable system, the initialization process is complete.

Note: Below is a sample front panel LED description of the Webstar DPC2100 modem. Please consult the Division Matrix or your internal Modem Guide for a complete list of front panel & LED diagrams for other modems used by Time Warner Cable divisions.




Approved Cable Modem List

The Time Warner Cable approved modem list may be found here:

http://help.rr.com/HMSFaqs/e_rr_modems.aspx

Please note that this list changes frequently as new modems are added and end of life modems are removed.


eMTA (Voice over IP) Modems
A voice-enabled cable modem (or, an embedded multimedia terminal adapter [EMTA]) connects traditional telephones to the Time Warner Cable IP network and provides all the features of a data cable modem, including high-speed data Internet access. An EMTA provides the interface to the broadband network and performs voice compression, packetization, security and call signaling for IP communications services. Many of these modems have built in battery backups and can only be reset by using the UDI.

eMTS Modems currently in use by Time Warner Include but are not limited to the following

Modem
Model
Features
Motorola CG4500
This earlier version has been discontinued but these modems are still in use – 2 lines plus HSD.

This unit has a standby switch which deactivates HSD but not VOIP.
Motorola SBV4200
Replacement for CG4500 – 2 lines plus HSD.
Web site:
http://broadband.motorola.com/catalog/productdetail.asp?image=large&productID=208

This unit has a standby switch which deactivates HSD but not VOIP.
Motorola SBV5220
2 lines plus HSD. Integrated battery backup.
Web site:
http://broadband.motorola.com/catalog/product_documents/sbv5220%20consumer%20data%20sheet%20conversion-final-4-28-05.pdf

This unit has a standby switch which deactivates HSD but not VOIP.
Scientific Atlanta Webstar DPX2203
2 lines plus HSD. Battery backup also available for this modem.

Web site:

http://www.sciatl.com/products/consumers/userguidepdfs/webstar_userguides/2203A.pdf



Ambit U10C017
2 lines plus HSD. Deploys Q106

Web site:
http://www.ambitbroadband.com/U10C017.datasheet.pdf
Arris TM402A









With Battery Backup
2 lines plus HSD. Battery backup also available for this modem.

Web site:

http://www.arrisi.com/product_catalog/_docs/_specsheet/040806_Touchstone_Telephony_Modem_TM402A.pdf

This unit has a standby switch which deactivates HSD but not VOIP.
Arris TM402P or G
2 lines plus HSD. Integrated battery backup.

Web site:
http://www.arrisi.com/product_catalog/listers/index.asp?id=348

This unit has a standby switch which deactivates HSD but not VOIP.


eMTA Modems and UDI

The illustration below from UDI shows the cable modem and associated CPE devices of a customer with digital phone service (VOIP). Note that both the MTA and modem have their own MAC address. The modem IP address is 10.219.193.204 which is a non-routable IP because the modem only communicates within the RR network. The MTA IP is 69.202.189.212 which is a public IP address and is routable. In order for the customer to make phones calls, the IP address must be routable or they would only be able to call people on the RR network.



Power Cycling a MTA Modem
In some cases it may be necessary to power cycle or reset a MTA modem. For example, if the customer has connected a different computer to the modem, a reset would be necessary. If the customer is calling using the VOIP service, they will be disconnected once the modem is reset. You are required to call the customer back to complete your troubleshooting and ensure that the customer is online.

Locating the Modem MTA MAC Address
Every device on a network (router, modem, network card, CMTS) has a unique number or address assigned to it. This address is known as the Media Access Control or MAC address. When troubleshooting connection problems you may need to locate the modem MAC address in order to troubleshoot using the UDI. The modem MAC address is listed on a sticker usually on the bottom or back of the cable modem. The MAC address will be printed beneath a bar code. In the illustration below, there are several MAC addresses listed.


MAC: 00407B-0000531
Modem MAC address
MTA MAC: 00407B-000053
MTA MAC Address used for the VOIP service
USB MAC: 00407B-000052
This modem has a USB network adapter built in and this MAC is for the USB adapter.
CMCI MAC: 00407B-000054
Cable Modem to CPE Interface. This MAC address is not used for troubleshooting RR connection issues and is beyond the scope of this document.


Helpful Cable Modem Troubleshooting Tips
Most cable modem problems are tier 1 issues. The following information will give you a better understanding of how cable modems work and will aid to your troubleshooting skills.

Power Cycling the Modem
Power cycling the modem simply means to remove power to the modem for a specified period of time, usually 30 seconds or longer. Power cycling clears the modem’s internal memory and clears any errors. To power cycle a modem, unplug the modem from the power source and wait a minimum of 30 seconds then plug the modem back into the outlet. This should always be the first step when the modem appears off line.


Asking Probing Questions
· Is the customer’s cable TV working? If the cable TV is not working, the cable modem probably isn’t either. Possible causes could be an outage, downed drop wire or other plant issue.
· Is the electrical outlet for the cable modem switched? Check that the wall light switch or power strip switch is turned on.
· Is the modem switch off or is the Stand By switch on? Some modems have an on/off switch or a stand by switch. If the Stand By switch is on, all the modem lights will be off.
· Is the coaxial cable connected and tight? A Loose coaxial connection is often the cause of intermittent bloc sync.
· Has the customer switched computers? If so, the modem must be reset to clear its memory. If the memory is not cleared the customer will be unable to connect to the Internet with any computer.

This is why. The cable modem is a “bridge” between the customer’s computer and the RR network. Cable modems have a “Bridging Table” which records the MAC addresses of all devices that have communicated with the modem. The bridging table consists of two parts or sides, Ethernet and CATV. The Ethernet side records the modem MAC address and the MAC address of any other device that the modem has “learned” from the customer side of the modem. The CATV side records the MAC addresses of all the devices that the modem has “learned” going out to the Internet, routers, switches, etc.

In the illustration below, the customer has switched computers without resetting the modem. The Ethernet side of the bridging table shows the MAC address of the modem and the MAC address of each computer. The modem restricts each connection (computer) to one IP address unless the customer has multiple IP service. Since the modem has “learned” two MAC addresses, the connection is closed and the customer will be unable to connect to the network. Resetting (power cycling) the cable modem will clear the memory and the customer will be able to connect to the Internet.


· Has the customer moved the cable modem outlet? If so, the modem may not be able to achieve bloc sync.

This is why. There are numerous possible reasons why a cable modem may not work if it has been moved to a different location:

· Broken or damaged coaxial cable or connectors.

· High Pass Filter. Some divisions use high pass filters to prevent Ingress (electrical noise) from being introduced into the cable system. Generally, the line to the cable modem is unfiltered and if the modem is filtered, it may not get a strong enough signal to achieve block sync.

· Signal loss. Each time the coaxial cable is split there is 3-5 db signal loss. Most of the time this isn’t a problem but if the customer has a long drop wire and/or many splitters in their line or older coaxial cable (RG-59) the modem may not achieve block sync when moved to a different location.




Cable Routers

Cable routers are cable modems (DOCSIS and Non-DOCSIS) that have routers built into the modem. These modems are used for business class customers. The advantage of these routers is that they support many different configurations and meet the needs of commercial customers. Modems currently deployed are Ambit, Cisco and Zyxel. Various models from these manufactures are in use. Please consult the Division Matrix to see which cable routers a customer may have within a specific Time Warner Cable division.


Cable Modem Providers and WebSites

Quick Reference Guide

Scientific Atlanta Cable Modems
http://www.sciatl.com/products/consumers/new_cablemodems.htm
RCA Cable Modems
http://www.rca.com/product/viewproductcategory/0,,CI305,00.html
Motorola Cable Modems
http://broadband.motorola.com/noflash/cablemodems.html
Toshiba Cable Modems
http://www.toshiba.com/taisnpd/
Ambit Cable Modems
http://www.ambitbroadband.com/broadband/
Arris Cable Modems
http://www.arrisi.com/products_solutions/product_families/Touchstone/cable_modems.asp