I talk to local Tucson business owners every day in the business I am in. I try to asses their communication needs specifically in the areas of their "voice" (think traditional phone lines and VoIP) and "data" (think broadband internet) needs. I have thought I have seen it all. I come to find out that their are some "ethically questionable" companies locally in Tucson that are pushing "Fractionalized" T1's shared among multiple businesses as a low cost alternative to High speed broadband in areas that are under serviced….What do I mean? Well first let me give you a quick primer on a T1 in general and then I will explain a "Fractional" T1. T1 Overview and Primer T1 is a digital service made available to the public in 1983, with the break up of AT&T. Prior to 1983 T1 was only used internally by the phone companies to inter-connect Central Offices (CO's). T1's are actually a technology first developed in 1958 and used widespread by Telco's by the early 1960's. So in essence present day T1's are a "legacy" technology that is almost 40 years old and certainly archaic by today's standards. T1 operates at a baseband bit rate of 1.544 Mbps with 1.536 Mbps being available for payload data and the remaining 8 Kbps reserved for framing. Typically the T1 is comprised of 24 DS0's, 64 Kbps each. The T1 is transmitted as a Time Domain Multiplexed group of DS0's, sometimes referred to as channels or timeslots. T1 operates over special low capacitance shielded twisted pair cabling, although in some instances standard twisted pair cabling can be used if precautions are taken to avoid crosstalk. The phone company will normally terminate the T1 with an 8 pin RJ type of jack, called an RJ-48C, it looks like a large phone jack. Due to the high bandwidth (frequency) of T1, repeaters are placed along the line at about every 6000 feet. These repeaters compensate for line loss and signal distortion. The signal itself is a "return-to-zero", bipolar pulse stream. Bipolar means that the pulses deviate from the "zero" line both positively and negatively. Typically the pulses alternate in polarity, this is done for a couple of reasons; to maintain a zero Volt DC offset and to serve as a form of error detection. Should a piece of equipment receive two consecutive pulses of the same polarity (a bipolar violation), it is an indication of one or more bit errors. This alternating pulse standard is known as Alternate Mark Inversion (AMI). The 8 Kbps framing format has two common standards that are available today, the newest standard is called Extended Super Frame (ESF) and the preceding one is D4, sometimes referred to as Super Frame (SF). Both of these standards still are commonly used today. While both D4 and ESF offer ESF offers a few advantages over D4 in the form of additional error information (CRC6) and it provides a 4 Kbps channel, called a Facility Data Link (FDL), outside the 1.536 Mbps payload capacity. The FDL gives the phone company the ability to non-intrusively interrogate the customers terminating equipment for error statistics and line performance information to aid in predicting and preventing line outages and maintain the highest possible quality of service. D4 on the other hand provides for only framing synchronization. ESF has become the norm for new installation throughout the majority of North America. Due to the synchronous operation of T1 and its utilization of a return to zero, bipolar format, T1 has a "ones density" requirement. This requirement stipulates a 12 1/2 % minimum ones to zeros ratio. Another words, on average, there must be at least a single "1" for every eight "0"s. Since this is not always practical, a couple of solutions have been adopted for T1. The first is called "bit stuffing", every eighth (the LSB of each DS0) is stuffed with a "1", and this of course makes the overall bandwidth a multiple of 56Kbps. The second method is called "Bipolar Eight Zero Substitution" or B8ZS, here every series of eight consecutive zeros is substituted with four "1"s and four "0"s and two intentional bipolar violations. This technique requires the T1 line to be configured for B8ZS so as not to correct the intentional bipolar violations. A typical T1 line between two locations is comprised of two twisted pair lines, one for transmit and one for receive, running from the customer site to the central office. These pairs are usually carefully selected pairs within standard multi-pair cables already installed, repeaters are placed along the cable in required locations and powered by a simplex current (60 ma) between the two pairs. When the T1 enters the central office it is usually multiplexed up into a T3 or higher for transport to the distant location. At the other end, the serving central office demultiplexes the T1 out of the higher bandwidth service and routes it to a twisted pair cable to the customer site…..Haaaa,…Simple enough…get it?…LOL..Don't worry I barely understand it half the times. Now I will give an overview of a "Fractionalized" T1 Fractional T1 Overview and Primer A Fractional T1 is nothing more than a T1 as previously described, but with only some of the DS0s being used. The cost savings comes from the phone company's ability to allow different customers to use separate portions of the same T1. Another words as an example, customer "A" would use the first half of a T1 (DS0 #1 - #12) and customer "B" would use the second half (DS0 #13 - #24). Fractional T1 lines "look" the same as full T1 lines in the sense of termination and overall bit rate, still 1.544 Mbps. The "path" from the customer site to the point-of-presence (POP) of the carrier is a full T1. However, the customer is restricted in how many DS0s can be used to carry the data, the remaining DS0s are stuffed with all "1"s. At the POP the DS0s carrying the customer's data are multiplexed with other customers DS0s onto a full T1 and then multiplexed up to T3s and up for transport to the other location. At the other end all the required demultiplexing is done to transport the customer's DS0s to the remote location via a full T1 with the unused DS0s once again stuffed with all "1"s. At each end the terminating equipment is configured to ignore the unused DS0s and "drop" the all "1"s and only pass on the DS0s carrying the customer's data. Now why I have such a problem with this is most times the unsuspecting business owner is not aware of what the have. When I ask them they say "Oh I have a T1" with a bit of clueless arrogance in their tone that a T1 is somehow the pinnacle of technology because that is how it was sold to them from the mentioned "ethically questionable" companies. To add insult to injury, the businesses I am specifically talking about don't even have "full" T1. They have a "Fractionalized" T1 shared with 3 of their business neighbors. You see this kind of "fractionalized" T1 deployment in these local Tucson office plaza settings, such as Butterfield business park and businesses along contractor’s way. These areas have no other available Broadband service such as DSL or Cable broadband. Businesses are sold on the idea that they are getting a T1 at a smoking deal, usually in the neighborhood of $200 a month, not really understanding that they are sharing the same T1 with 3 other businesses. The going rate for a full T1 in Metro Tucson is between $380 and $800 per month. And remember a T1 is only a maximum of 1.544 Mbs of symmetrical bandwidth. So with the normal prices of a full T1, $200 a month for a fractionalized T1 does not sound like a bad deal Right? Uhh, Wrong! More to the point, you get what you pay for. If a full T1 can only ever do a maximum of 1.544 Mbs of symmetrical bandwidth what does this mean if this T1 is "fractionalized" between 4 different businesses? Do the math…Divide 4 into 1.544 Mbs and you get……DRUM ROLL Please…..a whopping 386 Kbs…Wow, for $200 a month? Does not sound like that great of a deal after all huh? Now don't get me wrong, there are some legitimate uses for a "Fractionalized" T1. An example would be if a business had a full T1 and they were "Fractionalizing" it between their data needs and their voice needs. In other words, some of the T1 bandwidth would go to service their Phone lines and the rest would go to their internet bandwidth. Now certainly this is a more legitimate deployment of a T1 but still not a "perfect solution". For a "perfect solution" I am biased to Fixed Wireless and VoIP. To learn more about this you can give me a call for a Free consultation.

Call Keith with Cox Business at 520-867-7600