I have seen many questions over the years that I have been coming here, regarding T1s. DSL, SONET, DACSs and other telecom equipment. Since I am bored at work and need to do something to exercise my brain I thought I would make this FAQ (that will hopefully get stickied ) To address some of the common questions I have seen. Please feel free to ask more if you like.
Terminology
LEC - Local Exchange Carrier aka the phone company
ILEC - Incumbent Local Exchange Carrier
CLEC - Competetive Local Exchange Carrier
DACS Digital Access and Cross Connect System
SONET Synchronous optical network
BERT - Bit Error Rate Tester
What is an ILEC?
A large telephone company that has been providing local telephone service in the United States since the divestiture of the AT&T telephone monopoly in 1982.
These guys are the old fogeys on the block . With all the buyouts, mergers, Chapter 11's going on in telco right now I'm am not entirely sure who has been around since AT&T anymore. But I THINK Qwest(formerly USWest), Verizon (formally GTE) are ILEC's.
What is a CLEC?
A new local telephone company (eg, US ONE, Winstar, TCG, ICG) that is entering the local market in order to compete with the incumbent local telephone company.
There are not too many "new" ones starting up anymore, but this definition works the best.
What is the Telecom Act of 1996
This is a tricky one. I will probably massacre the full definition of what this bill was, but I will do my best. The Telecom Act of 1996 was a bill put into action by congress to de-regulate the telecommunications industry, including telco, radio, wireless and many other aspects of telecommunications. The "official" description of the bill is
Was the Telecom Act of 1996 good or bad?
This is a touchy subject. Depending on who you talk to, this bill either helped the industry or helped destroy the industry. I happen to believe its the former. I worked for a CLEC for several years, and people were migrating over at an insane rate. Fed up with lousy customer service, and ZERO competition for customers to choose from, people were surprised by what a telco company could be. I watched the change in attitude from companies such as Qwest and Verizon over the course of 2-3 years, going from "CLEC's will never amount to anything" to "Um, why did we lose 10,000 customers last quarter?" To eventually "I guess we need to change our game plan" All of a sudden ILEC's were not the only game in town. have you ever seen the "Spirit of service in action" commercial from Qwest? That whole mantra started when Qwest realized they were losing customers left and right to CLEC's.
All that being said the CLEC business model was fundamentally flawed. Even though CLEC's had access to ILEC facilities they were still customers of the ILEC's. CLEC's could not work on ILEC equipment, and still had to wait for trobule tickets to be resolved. And because CLEC's had to buy facilities from ILEC's they typically had to undersell their products in order for their service to be attractice to customers.
Eventually just like the dot com bubble, the telco bubble popped. There are still a few around (Yipes!, COVAD and XO come to mind) but its nothing compared to 2 or 3 years ago. In the end many CLEC's were bought up by LEC's. One thing the CLEC era helped in, was to prove to LEC's that you cannot get too happy sitting on your high hoarse. Given the right options people will leave LEC's in search of better service. I have dealt with telco's since then, and I can tell you its nothing like what it used to be, and I am sure it is for the better.
Today, we are slowly migrating back to the way things were. With mergers and buyouts happening on a regular basis, we will soon have no competition to choose from.
What is the difference between a bit and a byte
1.544MBps is completely different than 1.544Mbps.
MB = Megabytes
Mb = Megabits
A bit is single numerical value. It's either a 1 or a 0, that encodes a single unit of digital information. A byte is 8 bits. So when you see 1.544Mbps that is 1,544,000 bits per second. Thats a big difference from MBps.
What is a T1?
A dedicated point-to-point digital connection supporting data rates of 1.544Mbits per second. A T-1 line actually consists of 24individual channels, each of which supports 64Kbits per second. Each 64Kbit/second channel can be configured to carry voice or data traffic. Most telephone companies allow you to buy just some of these individual channels, known as fractional T-1.
What is a T3?
A dedicated point to point, high capacity digital service capable of transmitting data at speeds up to 45 Mbps. Comprised of 28 T1's.
Why do T1/T3's cost so much?
When you get T1/T3 service you are paying for an SLA. (Service level agreement)
When a T1/T3 drops it is treated differently than a DSL/phone line. T1/T3's get
worked / dispatched much quicker than normal POTS lines. Response times for T1/T3's
typically is 1-4 hours, where POTS lines have a response time of 1-4 days.
What is the difference between a DS1 and a T1?
Excellent question. Thanks to unhappy_mage for bringing it up. T1 / DS1 and T3 / DS3 are often used interchangeably. But there is a distinct difference between T1/T3 and DS1/DS3. (In the example I use T1/DS1 for simplicity. But the rule applies to T3/DS3 as well)
You can get DS1 service without a T1 line but if you have a T1 line, you've got DS1.
DS1 is a digital signal level that is part of a standardized hierarchy or building blocks of digital services for TDM (Time Division Multiplexing) digital lines. A DS1 is a DS1 regardless of whether it is delivered on a T1 line, a microwave relay, a T3 line or a fiber optic carrier. So basically a T1 line is the physical copper pair which the "digital signal" (DS1) rides on. For a little more detail try this link.
I have seen you mention B8ZS/ESF and AMI/D4. Does this mean there are different types of T1's?
There are different types of T1's but the speed remains the same. B8ZS/ESF and AMI/D4 refer to line encoding and framing. I was going to make another section dedicated to this subject but I found a website that has an excellent tutorial on the inner workings of T1's. This gets fairly advanced but is extremely thorough. Click Me
What is a "smart jack?"
A smart jack is also referred to as a RJ-48x. When nothing is plugged into this smart jack
the smart jack creates a loopback back to the CO. This loopback keeps the LEC's equipment from alarming and indicating a dropped T1. When you plug in to the smart check it breaks this loop and allows for traffic to flow into whatever device you are using. i.e router, pbx, etc.
What is ATM?
This is the international standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media. I have never worked with ATM so my knowledge is limited. If anyone cares to add to this, please let me know and I will add it to the FAQ.
What is a BERT
Bit Error Rate Tester is a piece of equipment that is used to test the integrity of a circuit. There are many different models of BERT's and each is typically used for a specific function. BERT's interact with a DS-x circuit at the most basic level and can simualte different conditions on a circuit. They simulat these conditions by sending different bit patterns and reading the responses. Some of the more common patterns are QRSS, 0000, 1111, and 0101. QRSS is quasirandom. Meaning it is used to simulate live traffic. Since voice/data/video are just 1's and 0's to a T1 QRSS can randomly shoot 1's and 0's down a DS1 to see how it will react. 0000 and 1111 is all zeros and all ones respectively. These patterns are used to test the integrity of repeaters that the T1 rides across. Repeaters jobs are to "repeat" the 1's and 0's that travel accross them. By sending all ones or all zeros you are essentially stress testing the repeater. 0101 is alternating 1's and 0's. I think this is used as another QRSS type pattern but have never used it much. There are many more pattern than what I have listed, and the list gets even more confusing when you get up to the DS3 level. But I have tried to cover the most basic patterns and typically these patterns are what the LEC uses when troubleshooting a circuit problem. If you would like some more info on different test patterns check out this link
What is a demarc?
Demarc is short for Demarcation Point. This is the point where the responsibility of the LEc ends. Typically this is at the smart jack. LEC's are responsible for everything in between the smart jack and the originating point. (Commonly referred to as the A and Z location). You can pay a LEC to extend this demarc for you, which isnt a bad thing to do. When the LEC extends the demarcation point they are now responsible for everything except your CSU/DSU. Example.
Example 1. Acme Inc. orders T1 from Qwest and elects to not have the demarc extended. The techs that work for Acme Inc. extend the demarc themselves. Acme Inc is located on the 12th floor of a 12 story building. The demarc of said building is in the basement. Acme Inc's tech is now responsible for everything from the basement up to where the T1 connects to their equipment. Any problem with the cabling in between the basement and 12th floor is Acme's Inc's responsibility. If there is an accidental cable cut on the 6th floor, which drops the T1 Acme Inc. must take care of it.
Example 2. Acme Inc. orders a T1 from Qwest and elects to have Qwest extend the demarc for them, up to the 12th floor. Qwest is now responsible for the entire path of the circuit. From the CO to the 12th floor smart jack. If a cable cut occurs on the 6th floor and brings the T1 down, Acme Inc. can contact qwest and have them move the T1 to a different copper pair within the building.
IMHO Example 2 makes life a little easier at the expense of a little more money. LEC's WILL NOT TOUCH ANYTHING PAST THE DEMARC! Nothing, zilch, nadda. In fact they may actually give a little chuckle at your expense if you ask this of them.
What is a MPOE
*THANKS TO SHADE91 for the correction*
MPOE - Short for minimum point of entry, the closest practical point to where the cables of a telecommunications service carrier (i.e., a phone or cable company) cross a property line or where its wiring enters a multi-unit building. The MPOE of a multi-unit building is typically 12 inches inside the buildings foundation.
I have been on the phone with a LEC and they keep making reference to a DACS / Repeater / MUX. What are these pieces of equipment and what do they do.
DACS - Digital Access and Cross Connect System. Think of a DACS as a router for circuits. DAC's take all type of circuits, DS0, DS1, DS3 and even some Optical Carriers. Essentially this allow for the connection of circuit without any physical wiring. If a T1 is ordered from Los Angeles to Seattle, that T1 could pass through a number of DACS's along the way until it arrives at your prem. DACS basically connects one circuit to another. T1-A comes in at ones point and needs to be handed off to T1-B. The DACS performs this cross connect electronically removing the need to hardwire these connections within the CO. DACS are also known as DCS and DXS.
Repeater - There are many different repeaters but I'll stick with the ones for T1's. T1's like any communications medium have a distance limit. To overcome this limitation repeaters are put along the path of the circuit which cleans and boosts the signal as it travels the network. This is one of the reason that T1's are not as limited by distance as a DSL line.
MUX - Multiplexer/Demultiplexer. Muxing is taking in several small circuits and outputting a larger one. For example
28 T1's -> 1 T3. Demux is the opposite. Taking in a large circuit and outputting smaller ones. T3->28T1s. Muxing/Demux is at the very heart of the telco industry. Everything is built on the concept of muxing. DS0's-> Ds1'. DS1s->Ds3's etc. Once you learn how things are muxed/demuxed everything else is easy.
What is a soft loop VS a hard loop. And is there a way I can make my own hard loopback
A soft loop back is typically a loopback that is used when a LEC is testing a circuit. When a LEC test's a T1 they use a piece of eqpt. called a BERT or Bit Error Rate Tester. This device is capable of looping up the remote NIU and can pass different bit patterns to verify the integrity of the circuit.
A hard loop back is usually just a RJ-45 connector with pins 1,4 and 2,5 shorted together.
Thats all I can think of off the top of my head. If you have any questions or corrections for me please let me know.
*EDIT 07/06/2005* Added info about CLEC's, T1/DS1 Differences, ATM, BERT's, Telecom act of 96 and some minor changes*
*EDIT 07/07/2005* The post was getting way to long. So I am splitting it up between this thread and "Sonet Information" which now on page 2.
Terminology
LEC - Local Exchange Carrier aka the phone company
ILEC - Incumbent Local Exchange Carrier
CLEC - Competetive Local Exchange Carrier
DACS Digital Access and Cross Connect System
SONET Synchronous optical network
BERT - Bit Error Rate Tester
What is an ILEC?
A large telephone company that has been providing local telephone service in the United States since the divestiture of the AT&T telephone monopoly in 1982.
These guys are the old fogeys on the block . With all the buyouts, mergers, Chapter 11's going on in telco right now I'm am not entirely sure who has been around since AT&T anymore. But I THINK Qwest(formerly USWest), Verizon (formally GTE) are ILEC's.
What is a CLEC?
A new local telephone company (eg, US ONE, Winstar, TCG, ICG) that is entering the local market in order to compete with the incumbent local telephone company.
There are not too many "new" ones starting up anymore, but this definition works the best.
What is the Telecom Act of 1996
This is a tricky one. I will probably massacre the full definition of what this bill was, but I will do my best. The Telecom Act of 1996 was a bill put into action by congress to de-regulate the telecommunications industry, including telco, radio, wireless and many other aspects of telecommunications. The "official" description of the bill is
What that meant for the telco market was that ILEC's were forced in to opening up their facilities for third-party companies to use. This gave way to a surge of CLEC's. CLEC's now had the means to deliver POTS, T1,T3 and other services to customers that were normally forced to use ILEC services.An original bill to provide for a pro-competitive, de-regulatory national policy framework designed to accelerate rapidly private sector deployment of advanced telecommunications and information technologies and services to all Americans by opening all telecommunications markets to competition, and for other purposes.
Was the Telecom Act of 1996 good or bad?
This is a touchy subject. Depending on who you talk to, this bill either helped the industry or helped destroy the industry. I happen to believe its the former. I worked for a CLEC for several years, and people were migrating over at an insane rate. Fed up with lousy customer service, and ZERO competition for customers to choose from, people were surprised by what a telco company could be. I watched the change in attitude from companies such as Qwest and Verizon over the course of 2-3 years, going from "CLEC's will never amount to anything" to "Um, why did we lose 10,000 customers last quarter?" To eventually "I guess we need to change our game plan" All of a sudden ILEC's were not the only game in town. have you ever seen the "Spirit of service in action" commercial from Qwest? That whole mantra started when Qwest realized they were losing customers left and right to CLEC's.
All that being said the CLEC business model was fundamentally flawed. Even though CLEC's had access to ILEC facilities they were still customers of the ILEC's. CLEC's could not work on ILEC equipment, and still had to wait for trobule tickets to be resolved. And because CLEC's had to buy facilities from ILEC's they typically had to undersell their products in order for their service to be attractice to customers.
Eventually just like the dot com bubble, the telco bubble popped. There are still a few around (Yipes!, COVAD and XO come to mind) but its nothing compared to 2 or 3 years ago. In the end many CLEC's were bought up by LEC's. One thing the CLEC era helped in, was to prove to LEC's that you cannot get too happy sitting on your high hoarse. Given the right options people will leave LEC's in search of better service. I have dealt with telco's since then, and I can tell you its nothing like what it used to be, and I am sure it is for the better.
Today, we are slowly migrating back to the way things were. With mergers and buyouts happening on a regular basis, we will soon have no competition to choose from.
What is the difference between a bit and a byte
1.544MBps is completely different than 1.544Mbps.
MB = Megabytes
Mb = Megabits
A bit is single numerical value. It's either a 1 or a 0, that encodes a single unit of digital information. A byte is 8 bits. So when you see 1.544Mbps that is 1,544,000 bits per second. Thats a big difference from MBps.
What is a T1?
A dedicated point-to-point digital connection supporting data rates of 1.544Mbits per second. A T-1 line actually consists of 24individual channels, each of which supports 64Kbits per second. Each 64Kbit/second channel can be configured to carry voice or data traffic. Most telephone companies allow you to buy just some of these individual channels, known as fractional T-1.
What is a T3?
A dedicated point to point, high capacity digital service capable of transmitting data at speeds up to 45 Mbps. Comprised of 28 T1's.
Why do T1/T3's cost so much?
When you get T1/T3 service you are paying for an SLA. (Service level agreement)
When a T1/T3 drops it is treated differently than a DSL/phone line. T1/T3's get
worked / dispatched much quicker than normal POTS lines. Response times for T1/T3's
typically is 1-4 hours, where POTS lines have a response time of 1-4 days.
What is the difference between a DS1 and a T1?
Excellent question. Thanks to unhappy_mage for bringing it up. T1 / DS1 and T3 / DS3 are often used interchangeably. But there is a distinct difference between T1/T3 and DS1/DS3. (In the example I use T1/DS1 for simplicity. But the rule applies to T3/DS3 as well)
You can get DS1 service without a T1 line but if you have a T1 line, you've got DS1.
DS1 is a digital signal level that is part of a standardized hierarchy or building blocks of digital services for TDM (Time Division Multiplexing) digital lines. A DS1 is a DS1 regardless of whether it is delivered on a T1 line, a microwave relay, a T3 line or a fiber optic carrier. So basically a T1 line is the physical copper pair which the "digital signal" (DS1) rides on. For a little more detail try this link.
I have seen you mention B8ZS/ESF and AMI/D4. Does this mean there are different types of T1's?
There are different types of T1's but the speed remains the same. B8ZS/ESF and AMI/D4 refer to line encoding and framing. I was going to make another section dedicated to this subject but I found a website that has an excellent tutorial on the inner workings of T1's. This gets fairly advanced but is extremely thorough. Click Me
What is a "smart jack?"
A smart jack is also referred to as a RJ-48x. When nothing is plugged into this smart jack
the smart jack creates a loopback back to the CO. This loopback keeps the LEC's equipment from alarming and indicating a dropped T1. When you plug in to the smart check it breaks this loop and allows for traffic to flow into whatever device you are using. i.e router, pbx, etc.
What is ATM?
This is the international standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media. I have never worked with ATM so my knowledge is limited. If anyone cares to add to this, please let me know and I will add it to the FAQ.
What is a BERT
Bit Error Rate Tester is a piece of equipment that is used to test the integrity of a circuit. There are many different models of BERT's and each is typically used for a specific function. BERT's interact with a DS-x circuit at the most basic level and can simualte different conditions on a circuit. They simulat these conditions by sending different bit patterns and reading the responses. Some of the more common patterns are QRSS, 0000, 1111, and 0101. QRSS is quasirandom. Meaning it is used to simulate live traffic. Since voice/data/video are just 1's and 0's to a T1 QRSS can randomly shoot 1's and 0's down a DS1 to see how it will react. 0000 and 1111 is all zeros and all ones respectively. These patterns are used to test the integrity of repeaters that the T1 rides across. Repeaters jobs are to "repeat" the 1's and 0's that travel accross them. By sending all ones or all zeros you are essentially stress testing the repeater. 0101 is alternating 1's and 0's. I think this is used as another QRSS type pattern but have never used it much. There are many more pattern than what I have listed, and the list gets even more confusing when you get up to the DS3 level. But I have tried to cover the most basic patterns and typically these patterns are what the LEC uses when troubleshooting a circuit problem. If you would like some more info on different test patterns check out this link
What is a demarc?
Demarc is short for Demarcation Point. This is the point where the responsibility of the LEc ends. Typically this is at the smart jack. LEC's are responsible for everything in between the smart jack and the originating point. (Commonly referred to as the A and Z location). You can pay a LEC to extend this demarc for you, which isnt a bad thing to do. When the LEC extends the demarcation point they are now responsible for everything except your CSU/DSU. Example.
Example 1. Acme Inc. orders T1 from Qwest and elects to not have the demarc extended. The techs that work for Acme Inc. extend the demarc themselves. Acme Inc is located on the 12th floor of a 12 story building. The demarc of said building is in the basement. Acme Inc's tech is now responsible for everything from the basement up to where the T1 connects to their equipment. Any problem with the cabling in between the basement and 12th floor is Acme's Inc's responsibility. If there is an accidental cable cut on the 6th floor, which drops the T1 Acme Inc. must take care of it.
Example 2. Acme Inc. orders a T1 from Qwest and elects to have Qwest extend the demarc for them, up to the 12th floor. Qwest is now responsible for the entire path of the circuit. From the CO to the 12th floor smart jack. If a cable cut occurs on the 6th floor and brings the T1 down, Acme Inc. can contact qwest and have them move the T1 to a different copper pair within the building.
IMHO Example 2 makes life a little easier at the expense of a little more money. LEC's WILL NOT TOUCH ANYTHING PAST THE DEMARC! Nothing, zilch, nadda. In fact they may actually give a little chuckle at your expense if you ask this of them.
What is a MPOE
*THANKS TO SHADE91 for the correction*
MPOE - Short for minimum point of entry, the closest practical point to where the cables of a telecommunications service carrier (i.e., a phone or cable company) cross a property line or where its wiring enters a multi-unit building. The MPOE of a multi-unit building is typically 12 inches inside the buildings foundation.
I have been on the phone with a LEC and they keep making reference to a DACS / Repeater / MUX. What are these pieces of equipment and what do they do.
DACS - Digital Access and Cross Connect System. Think of a DACS as a router for circuits. DAC's take all type of circuits, DS0, DS1, DS3 and even some Optical Carriers. Essentially this allow for the connection of circuit without any physical wiring. If a T1 is ordered from Los Angeles to Seattle, that T1 could pass through a number of DACS's along the way until it arrives at your prem. DACS basically connects one circuit to another. T1-A comes in at ones point and needs to be handed off to T1-B. The DACS performs this cross connect electronically removing the need to hardwire these connections within the CO. DACS are also known as DCS and DXS.
Repeater - There are many different repeaters but I'll stick with the ones for T1's. T1's like any communications medium have a distance limit. To overcome this limitation repeaters are put along the path of the circuit which cleans and boosts the signal as it travels the network. This is one of the reason that T1's are not as limited by distance as a DSL line.
MUX - Multiplexer/Demultiplexer. Muxing is taking in several small circuits and outputting a larger one. For example
28 T1's -> 1 T3. Demux is the opposite. Taking in a large circuit and outputting smaller ones. T3->28T1s. Muxing/Demux is at the very heart of the telco industry. Everything is built on the concept of muxing. DS0's-> Ds1'. DS1s->Ds3's etc. Once you learn how things are muxed/demuxed everything else is easy.
What is a soft loop VS a hard loop. And is there a way I can make my own hard loopback
A soft loop back is typically a loopback that is used when a LEC is testing a circuit. When a LEC test's a T1 they use a piece of eqpt. called a BERT or Bit Error Rate Tester. This device is capable of looping up the remote NIU and can pass different bit patterns to verify the integrity of the circuit.
A hard loop back is usually just a RJ-45 connector with pins 1,4 and 2,5 shorted together.
- thanks digilink!A loopback cable is very simple to build. A T1 operates on pins 1,2,4, and 5 on a RJ-45 plug. Pins 1 and 2 are the transmit pair, 4 and 5 are the receive pair. Just short pins 1 and 4 together and 2 and 5 and voila you have a loopback plug. I usually take some cross connect wire or use a piece of ethernet cable to make mine.
Thats all I can think of off the top of my head. If you have any questions or corrections for me please let me know.
*EDIT 07/06/2005* Added info about CLEC's, T1/DS1 Differences, ATM, BERT's, Telecom act of 96 and some minor changes*
*EDIT 07/07/2005* The post was getting way to long. So I am splitting it up between this thread and "Sonet Information" which now on page 2.