NHD computer and networking basic part 3

Customer Care
How Cable Works

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
Objectives. 1
How Cable Works.. 2
The Headend. 2
Headend (primary Hub) 4
Fiber Node (Secondary Hub) 4
Distribution Hub. 5
Line Amplifier 5
Tap. 6
Pedestal 6
Exterior Cable Box. 6
Fiber Optics. 7
High-Speed Internet.. 9
CMTS 10
DOCSIS.. 11
Frequencies. 13
Cable Modem.. 14
Modem Installation. 15
High-speed Data Server Diagram.. 16
Detail of the cable video systems components.. 18



Introduction
This document references the way that television and Internet signals reach the cable operator, where they are processed, and then how they are distributed to Road Runner subscribers.

Objectives
At the completion of the section, you will be able to successfully do the following:
· Define telecommunications and broadband.
· Explain how television signals get from the headend to the subscriber’s home via the cable distribution system.
· Explain how the Internet signal gets to the headend.
· Define CMTS and explain its role in transferring the Internet to a subscriber’s computer.
· Describe where problems could occur throughout the cable and Internet systems.

How Cable Works
This is the meat and potatoes of our entire communication network. Understanding how data is sent and received between the Internet and the customer.

The Headend
The headend is a physical building in each divisional area that allows communication between a customer’s home and such things as the Internet, their digital phone, and cable TV.
It houses equipment such as routers, CMTS machines, DNS servers, and Gateway servers. Don’t worry…these terms will become familiar very soon!
The headend is also known as the brains of the operation and primarily does three things.
It collects, processes, and distributes data.
Often in the Internet world, the word “hub” is used to describe a central location where switches and routers communicate. The headend is often referred to as a distribution hub or a primary hub.
Antennas at a Headend
Collects
The headend collects signals from the “outside world” and pulls them into our TWC Network through our antennas, satellite dishes, and trunk-line cables.
· Broadcast or “off-air” channels (ABC, NBC, CBS, FOX, and PBS) are received through large antennas located on the ground or mounted on towers.
· TVROs (TV Receive Only) look like a satellite dish and collect satellite channels (ESPN, Discovery, MTV, HBO, etc.).
· Trunk-line cables collect data, such as Video on Demand requests and Internet website access request.
Processes
The headend processes all the signals and assigns each signal to a unique “channel”. Each “channel” acts as a home address in order to make sure that the signal (whether it be a television channel, a digital phone number, or an individual modem) reaches its destination. For example, ESPN is assigned to the signal associated with Channel 30 for a particular division.
Distributes
The distribution network branches out of the headend and consists of trunk and feeder cables that take the signal throughout the customer service area.
· Trunk cable is either strung overhead between utility poles or underground and carries the signals through large service areas. This cable is about ¾ inch in diameter. (Trunk is the main cable that runs from the headend to the neighborhoods.)
· Feeder/Distribution cable branches off into local neighborhoods, carrying the signals along alleyways on telephone poles and underground between homes to pedestals. This cable is about ½ inch in diameter. (Feeder is the secondary cable, from the trunk to the tap.)
· Along feeder and trunk lines, there are amplifiers that keep the signal at an optimal level.
· The tap breaks up the feeder system into multiple ports distributing cable to the customer’s home. The tap is either located at the pedestal, utility pole, or apartment box.
· Terminators are placed on the ports that are not being used to prevent cable theft from the tap.
· The drop system begins at the tap. The drop is connected to the tap and it routed the most direct route to the side of the customer’s home, using coaxial cable. The drop can be aerial or underground and is about ¼ inch in diameter.
· Note: Fiber optic cable, which is a cable that uses hair-thin glass fibers to transmit light beams, is usually used for both the trunk and feeder lines.

Headend (primary Hub)
· Sometimes referred to as the POP (Point Of Presence)
· Routes traffic to the backbone. (A backbone is a larger transmission line that carries data gathered from smaller lines that interconnect with it.)
· Contains IP routers and cable routers.
· Proxy servers and Local Content Servers are located here.
· The above mentioned devices are connected by a 100BaseT Ethernet Switch.



Fiber Node (Secondary Hub)
· Multiple Fiber Nodes are connected to the Headend.
· Fiber Nodes act as a junction where light signals carried by fiber are converted to RF signals to be carried by coaxial cable.



Distribution Hub
· Metal boxes located along Trunk cable.
· It can be either above ground or just under a manhole if the cable runs under ground.
· Contains forward and reverse amplifiers, and a monitoring transponder.
· A monitoring transponder is a device that allows the NOC to monitor the trunk’s performance remotely.
· Monitors signal levels in forward and reverse path.
· If performing poorly, maintenance can be dispatched to troubleshoot.
· Distribution cable feeds a street either on telephone poles or underground in urban and newer neighborhoods.

Line Amplifier
· Located at every 50 – 200 meters along the distribution cable.
· Boosts RF signals in forward path to ensure signal remains strong to end of line.


Tap
· A tap is attached to the distribution cable up at the telephone pole for above ground cable.
· Either a 4, 8, or 12 spigot tap
· Each spigot feeds a home.
· During an installation the cable technician is responsible for monitoring the performance from the customers modem to the tap.
· A drop cable runs from the tab to the customer’s cable box at the side of their home.

Pedestal
· If the cable is underground it attaches to a pedestal instead of a tap.


Exterior Cable Box
· The cable box is located on the outside of the customer’s home.
· The cable technician installs a splitter to the cable box and runs a dedicated coaxial cable off the splitter to the cable modem.


Fiber Optics
Fiber optic cables are used to transmit large quantities of signal upstream and downstream. They are a major part of the headend because of how much data is being transmitted. A normal cable line could not handle the capacity of what fiber optics. They are glass fibers that transmit the information via light beams.
Advantages of Fiber Optics
· Fiber optic cables have a greater bandwidth, which means they can carry more data.
· Fiber optic cables are less susceptible to interference.
· Fiber optic cables are much thinner and lighter than metal cable lines.
· Data can be transmitted digitally rather than analogically.

Disadvantages of Fiber Optic
· Fiber optic cables are more expensive to install.
· Fiber optic cables are more fragile than metal wires and are more difficult to split.

Key Terms
· Traps: A trap is a physical cylindrical device that is used to allow or disallow a cable signal. Traps are usually located next to the tap on the drop for basic services and are not accessible to customers. Some areas may use a premium trap that is located at the splitter on the side on the home or in the home next to the outlet or on the converter box. All basic levels of service use traps. Basic levels of service are Broadcast and Expanded Basic channels.
· Addressable: An “addressable” is a programmable signal that allows TWC to add or remove services, such as premium channels, PPV, digital packages, and modem provisioning from an agent’s computer to the customer’s home. This eliminates the need for TWC to physically send a technician to a customer’s home to perform these tasks.

How Cable Works – Illustrated
· Programming is sent from the network studio (1) to the satellite earth station uplink (2) to the satellite in orbit above the earth (3).
· The signal is then beamed back down to earth and received at a cable system’s earth station (4) from which it is transmitted to the headend (5), where it is processed and prepared for distribution.
· From the headend, the signal is sent along the main trunk cables (6), from which leader cables (7) branch off.
· A cable “drop” (8) connects each subscriber’s home to the feeder cable. The cable from the outlet (9) in the customer’s house is attached to the customer’s converter or TV set.

Even though this diagram shows how a customer receives cable television, the process is essentially the same for how the customer receives Internet access from the headend.
Also refer to the two graphics at the end of this document in the “Detail of the Cable Video Systems Components” section for additional insight into how cable works.

High-Speed Internet
· The Internet signal enters the headend from a point of presence (POP) via a T# (T1, T2, or T3 line) or higher speed data line leased from a phone company.
· For the high-speed Internet connection, the headend acts as the hardware/software bridge between Road Runner and the rest of the Internet.
· It contains the Cable Modem Termination System (CMTS), which is the control center on the cable modem.
· The CMTS includes servers, routers, and signal converters, and it is the focal point for everything that happens with your digital Internet packets of information being sent to and from the cable modem. It acts as a sort of telephone operator by directing incoming and outgoing signals toward their correct destinations.
· High-speed Internet is delivered to the customer’s home through the same distribution system as cable television. However, the installer must remove a high pass filter to allow a two-way signal.
· Two-way signal means that communications equipment at both ends of a cable system is able to communicate with each other.
· High-speed Internet access, digital cable services, and Video on Demand are just a few of the services that are offered by Road Runner. In order to provide these services, we must be able to accommodate a return signal from the customer’s home to the headend.
· Return signals are generated by equipment located in the customer’s home, such as Digital Cable Terminal or cable modems, which carry data back to the headend.

CMTS
CMTS is short for Cable Modem Termination System a system of devices (i.e. routers) located in the cable headend that allows cable television operators to offer high-speed Internet access to home computers. An example is shown below.

· The CMTS sends and receives digital cable modem signals on a cable network. Signals are sent upstream from a user’s cable modem then converted into IP packets.
· The CMTS directs the signals to an Internet Service Provider (ISP) for connection to the Internet.
· Downstream signals are also sent to the user’s cable modem. Cable modems cannot communicate directly with each other; they must communicate by channeling their signals through the CMTS.

DOCSIS
Developed by CableLabs and approved by the ITU (International Telecommunications Union) in March 1998, Data Over Cable Service Interface Specification (DOCSIS) is an agreed-upon industry standard that defines interface standards for cable modems and supporting equipment. The standard has evolved from version 1.0, 1.1, to 2.0.

Cable modem manufacturers are able to produce cable modems for retail that will function on any MSO (Multiple System Operators) network by being DOCSIS compliant.

Prior to this development, consumers were dependent upon the MSOs to provide a cable modem that would operate with their own specific network. Now, the consumers are able to purchase their own cable modem instead of lease one from their cable provider because all cable modems are interchangeable from one service provider to another. This is thanks to the DOCSIS standardization to which all modem providers comply.

The screen below is a portion of the UDI (Universal Diagnostic Interface) Tool. You will learn how to use UDI at a later date. However, this screen shows that you will be able to view the customer’s cable modem signal frequencies.


DOCSIS – Continued
DOCSIS specifies downstream traffic transfer rates between 27 and 36 Mbps over a radio frequency (RF) path in the 50 MHz to 750+ MHz range, and upstream traffic transfer rates between 320 Kbps and 10 Mbps over a RF path between 5 and 42 MHz.
· Because data over cable travels on the same cable lines to multiple customers before being branched out to individual homes, individuals will see transfer rates drop as more users gain access.
· This is why cable companies add amplifiers along cable lines to amplify signal strength in order to stay within the DOCSIS-specific upstream and downstream standards.

Other devices that recognize and support the DOCSIS standard include HDTVs and Web-enabled set-top boxes for regular televisions.

Frequencies
Cable signals are transmitted through radio frequencies at different levels for different product lines, such as cable TV, digital phone, and high-speed data.
These signals must stay within a certain range in order for the cable modem and the headend to communicate. If the signal is too high or too low, it will fall into ranges that the cable modem and headend cannot process.


For more information on which frequencies the RF Spectrum uses, refer to the following websites:
· http://www.newamerica.net/templets/ssl_forms/download/spectrum_front.pdf
· http://www.newamerica.net/templets/ssl_forms/download/spectrum_back.pdf

Cable Modem
A modem is a physical device that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms.
A cable modem is designed to operate over cable TV lines. Because the coaxial cable used by cable TV provides much greater bandwidth than telephone lines, a cable modem can be used to achieve extremely fast access to the Internet.

There are a number of technical difficulties, however. One is that the cable TV infrastructure is designed to broadcast TV signals in just one direction – from the cable TV company to people’s homes.

The Internet is a two-way system (hence the term 2-Way) where data flows both from the servers at the headend to the customer (client) and from the customer (client) to the servers. (1-Way only communicates data to the client without allowing any communication back, such as with the receipt of basic cable TV programming.)


Modem Installation
As you can see from the diagram below, it is not difficult to hook up a cable modem to the computer. This why we offer a self-installation kit.

When troubleshooting a client’s connectivity, you will first verify that these components are correctly connected. For example, if the cable cord was not completely screwed into the back of the cable modem, there would be intermittent connectivity or slow speed issues.
· Patch Cable – Ethernet or USB from the modem to PC. This is how the modem and PC communicate. If the patch cable is bad, the result would be no surf. But this is not always the reason for a no surf issue.
· Cable Cord – From the wall outlet to the back of the modem. If the cable is out, the modem will have no sync.
· Power Cord – From the electrical outlet to the back on the modem. If the electric is out, the modem will have no power light.

High-speed Data Server Diagram
The diagram on the following page is an example of how some of our main servers at the headend communicate together to make our network function properly.
· Cable Modem – DOCSIS 2.0 or higher in the customer’s home. Is assigned a private 10.x.x.x IP address which is static.
· DHCP/pLDAP – Dynamic Host Configuration Protocol / DORA process (Discover, Offer, Request and Acknowledge) offering a public dynamic IP address to surf the Internet. Example 68.x.x.x or 67.x.x.x etc.
· BPS – Broadband Provisioning System – manages modem configuration, Registration authentication for our products, and provisioning
· UDI – Universal Diagnostics Interface – modem information (flap, blade, CPE, status, speeds, quarantines) and testing (URL, Ping, Traceroute)
· Billing –product codes, payments, charges and sending the product codes to BPS and UDI for HSI services.
· CA - Computer Associates – Security Services (Anti-Virus, Parental Control, Anti-Spyware). Must register using a road runner email account.
· Email Server – username and password availability and authentication
· Personal Home Page– to create a free 5 mb web space for are residential customer’s. Must register using their master email account.
· RR.com & Help.rr.com – our HSI customer web site for webmail access, troubleshooting and product information in additional to are premium services.

High-speed Data Server Diagram – Continued
This diagram is just an example of how servers communicate. It could be slightly different dependent on which products are used by the client.



Detail of the cable video systems components

CUSTOMER’S HOME CABLE LINES ALONG THE PATH THE HEADEND