Re: How did voice, data and TV service evolve, and how do they fit together now?
Telephone to DSL
Basic Telephony is very simple and works on very simple equipment carried by a single pair of copper wires. To talk, 48 DC volts are applied across a little dish of carbon granules. Talking vibrates the granules, generating AC at voice frequencies. The voice frequencies vibrate a speaker cone at the other end.
Original signalling was to open the circuit at the calling end, de-energizing a relay at the central location, causing a flap to drop. To signal out to a customer a hand cranked AC generator sent a signal to ring a bell. Improvements soon occurred.
Jiggling the switch hook generated DC pulses that could move relays, which became a dial to carefully time the pulses that could be processed step-by-step. Creating the requested route to a destination telephone.
The first call routing was serial. Each pulse moves the call closer to the target. This was replaced by common signalling equipment and multifrequency tone “dialing” that accepted the digits before it routed the call. The current deployment of this is to use computers to route the call as dialing is completed (signalling system seven). The call route is no longer tied to a physical path. It can go anywhere. This is what opens the door to allowing cable companies and other VOIP phones to integrate with the network & even move your number between providers. The route is not tied to a specific set of equipment. It follows a path specified by the computer.
For so many years, conversation was the only content traversing this system. The FAX machine applies picture content to a voice frequency tone that is transmitted over the network. Data sets provide similar capability for computer data. FAX started as a combination of copier technology and data set technology. It evolved into “all in one” devices. But, the FAX feature still requires an analog tel modem to send directly to a distant FAX machine. The same image can be processed as data through a computer and sent to a provider that resends it to a FAX machine.
This analog service on the local cable pair is often called Plain Old Telephone Service (POTS)
Improvements in technology led to DSL that evolves the data set into a data network device, applying the in-house LAN to the web to carry data and connect to the internet for transport beyond the local loop. The DSL transport is overlaid on the local loop cable. But, the tone will over-ride any conversation on the line. So, a filter is applied to any phone jacks that will be used for conversation. There could be multiple filters on multiple jacks or a single filter that creates a voice network and a DSL network in the house.
U-verse for internet (while retaining POTS) is similar to the two network in house wiring for DSL, with the exception that the connection from the filter to the RG(modem) should be singular and direct. Another alternative is to make the split at the VRAD and have two cable pairs come to the house. One for POTS and one for U-verse.
To add U-verse voice - (If it replaces POTS, POTS is disconnected at the NID) - It is a VOIP signal embedded in the U-verse internet signal. It is derived in the RG & dial tone is a available on the tel 1/2 jack. The house wiring is now “dry” (no tel service) To distribute throughout the house requires that the house wiring be connected to the tel 1/2 jack on the RG. This is usually done with a standard base cord (RJ-11 connectors) to the nearest wall jack.
To cover U-verse TV requires a similar “look back” at TV technology.
“standard cable” mirrors broadcast TV. It starts with analog VHF broadcast band and adds additional frequency bands, digital processing and compression techniques to stuff more channels down the COAX distribution, dropping off at individual dwellings.
The COAX delivery includes all the channels available from the provider to be individually tuned at each viewing location. This method makes possible simultaneously viewing/recording of all the channels on the COAX, providing you have sufficient equipment available to display/record it.
The total number of channels available is limited by the bandwidth of the distribution COAX — If bandwidth is not available on the COAX, another channel cannot be added. Note that HD channels consume more bandwidth than SD channels. Also, since the frequencies used are the same as broadcast, there may be frequency assignment conflicts.
The U-verse TV delivery system does not follow that broadcast/cable model. It is based on the previously described DSL model and content is applied to packets to take advantage of that technology for routing/transmission. Four channels of content are embedded in the DSL signal. Why do this? Because it is a natural evolution of the current at&t distribution plant. Because it is less expensive to reuse what exists, than it is to build new.
But, it provides only four simultaneous channels. True, but, the channels are arbitrary -assigned on the fly - selected by the customer - the bandwidth capacity is not choked by unneeded channels. The selection takes place at the head end, instead of the receiving end. The channels available for selection are not limited by the bandwidth of the delivery cable. At&t can support as many channels as they create unique numbers for - currently 10,000. Since the comm pipe does not carry every channel, it is not a limiting factor.
While four channels are not enough for every family, they provide adequate service for the vast majority. Of course, improvements in technology can increase this number in the future.
Also, the channel selection process is much faster with the U-verse model than the standard TV digital tuner.
Another advantage for the U-verse model is that it is bidirectional by design. The broadcast model applied to cable systems is by definition one way - broadcast the signal to the customers.
The U-verse system uses computer technology at various layers -
The Set Top Box (STB) converts the U-verse signal to a signal that is compatible with TV input - HDMI, Component, composite, s-video video; analog audio and analog RF (Channel 3 or 4 on COAX).
And communicates with the RG and other STBs for whole house DVR. And, communicates back to the server for just about anything. A DVR is an STB with a built in hard drive for storing recordings. With whole house DVR, the STB portion of the DVR box is just another STB.
The Residential Gateway (RG) breaks out the TV signal for the STBs and the Internet signal for computers and an analog telephone connection from the DSL input.
The VRAD connects the local loop to the network at the optical level to get back to the servers. Internet Packet(IP) technology was selected as the most efficient way to communicate & transport data across the network.
As optical fiber replaces copper in the loop it combines electrical/optical transition at the VRAD with the RG transition at the home. The fiber does have higher capacity/more bandwidth than the copper loop, but it has less development because of the low levels of deployment. As, more is deployed the electronics will be improved to surpass copper.
Just as U-verse was designed to re-use copper wire in the loop it was designed to re-use COAX cabling in the home. COAX uses HPNA technology to transform the physical COAX network into a virtual LAN. This requires high frequency components (splitters & barrel connectors)and compression fittings on the cable ends. Since the RG has only one COAX connector for both input and output, if it used for both input and output a three connector diplexer does the signal distribution - Connected to NID for incoming signal Connected to RG for combined input/output TV signal Connected to a TV or multiple TVs via a splitter Multiple splitters can cause problems).
The HPNA network is somewhat fragile. A fault anywhere in the COAX network can cause problems with the TV signal.
STBs or internet access devices can be connected cat5 to the RG. Any one leg from the RG should feed either STB or internet device, but not both. Legs can be multiplied via switches or carefully configured routers. The RG should always provide DHCP.
COAX and cat5 can co-exist. The network jack on an STB that is connected COAX can feed an internet device. Although, it is not officially supported.
Wireless internet devices have access viia the RG. The wireless can be extended.
Wireless STBs have access via a WAP. This wireless cannot be extended. The WAP must be positioned to reach the STB with a good signal. The WAP is connected to the RG via cat5 cable. The wireless receiver many be connected to the RG via cat5, but not COAX.
It is best to connect the DVR to the RG via cat5.
Cell phones may connect wi-fi to the RG for communicating data.
*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.