Post
by 33breeze » Tue Sep 24, 2013 4:21 pm
The downstream information flows to all connected users, it is up to the individual network connection to decide whether a particular block of data
is intended for it or not. On the upstream side, information is sent from the user to the CMTS, other users do not see that data at all.
The narrower upstream bandwidth is divided into slices of time, measured in milliseconds, in which users can transmit one "burst" at a time to the Internet.
The division-by-time works well for the very short commands, queries, and addresses that form the bulk of most users' traffic back to the Internet.
A CMTS will enable as many as 1,000 users to connect to the Internet through a single 6-MHz channel.
Information Recap:
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 leasing 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 cable modem providers comply.
Important Note: *** Internet Divisions use many brands of cable modems. The bullet below illustrates only several of the most common cable modems currently in use.
Most divisions will use several different brands.
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 Ubee (Ambit) CM 60194E.
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 leasing 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 cable modem providers comply.
Important Note: Time Warner Cable Internet Divisions use many brands of cable modems. The bullet below illustrates only several of the most common cable modems currently in use. Most divisions will use several different brands.
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 Ubee (Ambit) CM 60194E.
What should the signal levels be?
When looking at cable modem RF Data table, check the following:
TX Power Level: should be between 30 – 58 dBmV (decibel millivolts)
RX Power Level: should be between -15 – +15 dBmV
RX Signal to Noise: should be not lower than 28 db
NOTE: If any of the above-mentioned levels are not within the specified guidelines,
Additional DOCSIS Signal Information
DOCSIS standards 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 Online.
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.
CABLE MODEM
A cable modem is a physical device that enables a computer to transmit data over telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A cable 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 customer without allowing any communication back, such as with the receipt of basic cable TV programming.)
Specialty Groups > Regional > Training > TV > How Cable Works
Area: All
Franchise: All Department: Customer Care
Line of Business: Cable, Digital Phone, High Speed Online
General Information
How Cable Works
Summary
References the way that television and Internet signals reach the cable operator, where they are processed, and then how they are distributed to High-Speed Online customers.
Tips
Content
THE HEADEND
HEADEND (PRIMARY HUB)
FIBER NODE (SECONDARY HUB)
DISTRIBUTION HUB
LINE AMPLIFIER
TAP
PEDESTAL
EXTERIOR CABLE BOX
FIBER OPTICS
KEY TERMS
HOW CABLE WORKS - ILLUSTRATED
HIGH-SPEED INTERNET
CMTS
DOCSIS
FREQUENCIES
CABLE MODEM
CABLE MODEM INSTALLATION
HIGH SPEED ONLINE SERVER DIAGRAM
DETAIL OF THE CABLE VIDEO SYSTEMS COMPONENTS
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. Do not 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 cable 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 strung overhead either 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 is 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.
A 100BaseT Ethernet Switch connects the above-mentioned devices.
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 customer's cable modem to the tap.
A drop cable runs from the tap 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 offers us. 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 Optics
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 cable 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 customer’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 article 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 Online Internet connection, the headend acts as the hardware/software bridge between Time Warner Cable Internet 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 Time Warner Cable. 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 Online Internet access to home computers. CMTS equipment example is shown below.
The downstream information flows to all connected users, it is up to the individual network connection to decide whether a particular block of data is intended for it or not. On the upstream side, information is sent from the user to the CMTS, other users do not see that data at all. The narrower upstream bandwidth is divided into slices of time, measured in milliseconds, in which users can transmit one "burst" at a time to the Internet. The division-by-time works well for the very short commands, queries, and addresses that form the bulk of most users' traffic back to the Internet.
A CMTS will enable as many as 1,000 users to connect to the Internet through a single 6-MHz channel.
Information Recap:
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 leasing 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 cable modem providers comply.
Important Note: Time Warner Cable Internet Divisions use many brands of cable modems. The bullet below illustrates only several of the most common cable modems currently in use. Most divisions will use several different brands.
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 Ubee (Ambit) CM 60194E.
The screen below is a portion of the AAD (Advance Agent Desktop) Tool. This screen shows that you will be able to view the customer’s cable modem signal frequencies. This is to determine whether it has the correct signal levels to communicate information from the customer’s cable modem to headend/Internet.
What should the signal levels be?
When looking at cable modem RF Data table, check the following:
TX Power Level: should be between 30 – 58 dBmV (decibel millivolts)
RX Power Level: should be between -15 – +15 dBmV
RX Signal to Noise: should be not lower than 28 db
NOTE: If any of the above-mentioned levels are not within the specified guidelines, AAD will display the field in a red indicator light instead of a green indicator light, helping you easily identify areas of concern.
Additional DOCSIS Signal Information
DOCSIS standards 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 Online.
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.
CABLE MODEM
A cable modem is a physical device that enables a computer to transmit data over telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A cable 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 customer without allowing any communication back, such as with the receipt of basic cable TV programming.)
CABLE MODEM INSTALLATION
As you can see from the diagram below, it is not difficult to hook up a cable modem to the computer. This is why we offer a self-installation kit.
When troubleshooting a customer's connectivity, you will first verify that these components are correctly connected. For example, if the cable cord were 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 cable modem to PC. This is how the cable modem and PC communicate. If the patch cable were bad, the result would be no surf. However, this is not always the reason for a no surf issue.
Cable Cord – From the wall outlet to the back of the cable modem. If the cable is out, the cable modem will have no sync.
Power Cord – From the electrical outlet to the back on the cable modem. If the electric is out, the cable modem will have no power light.
