Sunday, May 20, 2012

Goodbye Landlines.... Hello Fixed LTE

I've been buried with final exams and travel the past few weeks and have not had a chance to post. Lots of things have been happening though.

With all of the Facebook IPO hype and the Verizon Wireless' data cap announcement you may have missed something potentially much bigger. Back on May 2, Verizon Wireless put out a news release titled HomeFusion Broadband From Verizon Now Available Nationwide on America's HomeFusion Broadband From Verizon Now Available Nationwide on America's Largest 4G LTE Network

It's about putting an antenna on your house that will replace those copper telephone wires with 4G LTE wireless. Now, Verizon's 4G LTE network currently covers approximately two-thirds of the U.S. population and 230 markets and this new product is designed to deliver both data and voice services for these people in these markets. LTE has been pitched initially as a mobile product but works great using fixed antennas attached to a home or business.

Here's how this new fixed antenna Verizon 4G LTE product works. Verizon techs come out to your home and install a cylinder-shaped 4G LTE antenna (see picture). This antenna picks up an LTE signal and transmits it to a broadband router in the home. That broadband router can have up to 4 wired and 20 wireless WiFi connections.

Verizon is saying that, in a fully loaded real world environment, users should experience average data rates between 5 and 12 Mbps downstream and and between 2 and 5 Mbps upstream. That's some pretty good bandwidth. Pricing ranges from $60 (10 GB cap) to $120 (30 GB cap) per month. If users go over the cap, they'll pay an extra $10 per GB.

Here's where it gets really interesting. Back on April 19, Verizon announced they would stop selling DSL as an option to customers who live in FiOS territory. Today I heard (unconfirmed) Verizon will stop using DSL range extenders. These range extenders are being used to get DSL signal out long distances. DSL sure sounds like it is going away soon.

Is 4G LTE the next step? Will fixed 4G LTE replace those old copper landlines that voice and DSL run on? Two thirds of the U.S. population is covered by 4G LTE...... I've written about it in the past...... I've always thought so and right now I'm thinking it's all going to happen a lot quicker than I ever imagined.

Wednesday, May 2, 2012

Data Transmission on T1 Carriers - Part 2

In Part 1of this topic I described how a T1 carrier is used to transmit data. Data transmission by nature is "bursty" meaning large amounts of information are typically transmitted and then followed by relatively quiet transmission periods. This can cause transmission problems for T-carrier systems since they rely on timing synchronization. Let's take a look how this potential problem is avoided.

T-1 lines that are not constantly active (having binary 1’s) will have timing problems because actual pulses are also used for signal synchronization by the receiver. To add synchronization on “quiet” T-1 lines a technique called Bipolar with Zero Substitution (B8ZS) has been developed. B8ZS adds pulses by substituting 8 zero bit groups with one of two specific 8 bit codes.

B8ZS Substitution with Most Previous “1” Pulse a Positive Going Pulse
When the transmitter gets a string of eight zeroes and the most previous “1” pulse was a positive going pulse the following 8 bit pulse sequence is substituted for the eight zero sequence.

B8ZS Substitution with Most Previous “1” Pulse a Positive Going Pulse

Notice there is a bi-polar polarity discrepancy in this substituted pulse sequence. Pulses 5 and 7 are sequential “1” pulses and are both negative going – they do not alter in polarity. 

B8ZS Substitution with Most Previous “1” Pulse a Negative Going Pulse
When the transmitter gets a string of eight zeroes and the most previous “1” pulse was a negative going pulse the following 8 bit pulse sequence is substituted for the eight zero sequence.

B8ZS Substitution with Most Previous “1” Pulse a Negative Going Pulse

Notice there is also a bi-polar polarity discrepancy in this substituted pulse sequence. Again pulses 5 and 7 are sequential “1” pulses. In this case they are both positive going and do not alter in polarity.
T-1 receivers can detect both of these bi-polar polarity discrepancies and substitute strings of 8 zeroes whenever one is detected.