Deliver Cable TV over DSL & T1 [The Future of CATV Part 2] Page 2 of 2
Radiant Communications Company ~ 5001 Hadley Road ~ South Plainfield, NJ 07080
Call: 1-800-969-3427 ~ Web Site: www.rccfiber.com
Let’s Talk Technology. Before we get into the nuts and bolts of how this works, let’s define a
few terms:
1. T1 – This is the Bread and Butter, Plain Vanilla circuit that’s been around since 1956.
Imagine that! It’s a digital circuit. That means that the electrical pulses on the wire
conform to an “On-Off” code as the input signal changes. Data is a series of voltage
changes within a set time period. OK, that’s the tekkie stuff. It operates at 1.544
Megabits per Second which we’ll call Mbps from now on. A T-1 is full-duplex with a
dedicated link each for data transmission [Tx] and data reception [Rx].
T1s are used to connect PBXs [Telephone Switches] together and to connect routers.
2. DSL – This is the TLA [Three Letter Acronym] for Digital Subscriber Line. It’s been
with us since the 1980’s but only in the last 5-10 years have the standards and products
been adequate for the TELCOs to invest in adding to their Central Offices and rolling out
DSL. Like any technology, it’s had its fits and starts and it has certain physical
limitations that makes it expensive to deploy system wide. It works by using an external
input [your data] to change a signal operating on COPPER WIRE at a frequency far
away from to telephony signals. Your existing phone line is used to carry both your
phone traffic and the DSL frequency. Just like a radio tuned to a particular station, the
DSL modem is configured to listen and talk on these “above telephony” frequencies
DSL comes in many flavors to meet the needs of a wide variety of consumers.
a. ADSL – Asymmetric Digital Subscriber Line. This is the most common
residential and small business line. Asymmetric means that transmitting from
your office is slower than receiving. The circuit is lopsided. ADSL was created
because bandwidth is a precious commodity and most subscribers are Internet
surfers, wanting more data coming in than they send out.
ADSL speeds are typically sold at either 768Kilobits per second [Kbps]
downstream [your “receive rate”] and 128 Kbps upstream [your “transmit rate”].
Or, for power users, you can buy 1.5Mbps Down and 256Kbps upstream.
b. SDSL – Symmetric Digital Subscriber Line. An SDSL circuit has the same
transmission and reception bandwidth.
3. IP – Internet Protocol. IP is a set of rules that governs the management of packets of
data over a physical infrastructure like Ethernet, SONET or ATM. When we say Video
over IP, we mean that we’re going to input Video at Baseband [Video & Stereo Audio]
and digitize it then we’re going to compress that digital signal. We’ll then PACKETIZE
the digital signal [break it up into little snippets] and when we packetize, we look up the
rules [IP] and do the following:
a. Add a packet for origination address
b. Add a packet for destination address
c. Add a packet defining the type of data in the packet
d. Add a packet coding the priority the originator wants the network to set
e. And some more tekkie stuff only the engineers understand.
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