DMARC and MPOE an IDF

 If you ever have to pull, cut, splice, extend or punch down cables... you already know the terms DMARC, MPOE and IDF. But the terms are widely misused. Actually, in telecom there seems to be a wilderness of informal tech jargon instead of formal technical terminology. So what is the difference between these obtuse acronyms? First the definitions:

DMARC - Demarcation point. In the USA this is defined by the FCC (47 C.F.R. Part 68) as a network interface device (NID). It often contains a lightning arrest and a test jack usually RJ-11. This can be inside or outside the structure, even on the edge of a property.

MPOE - Main Point of Entry. (Sometimes just POE) I've also seen this rendered as Minimum Point of Entry. Is is the point at which a data cable enters a property. This can be anywhere inside or outside the actual structure, but is usually immediately inside a building. circuits must be extended from this point into your IDF.

As to that IDF closet (also sometimes MDF.)  that stands for Main Distribution Facility and Intermediate Distribution Facility.  These can be the same location and is a room often as small as a closet which contains all that aforementioned telecommunications equipment. I usually call it a telco closet. When used in the technical sense, the MDF is the primary telco room, and usually the DMARC and the IDF is a secondary location in the same facility.

What's the difference again? The short answer is that the MPOE is the "physical" point at which the provider's lines cross into the customer's building (or sometimes across a property line). The DMARC is the "electrical" point at which the provider's lines connect to the customers equipment. This difference is important because the hardware and support on one side belong to one party and vice versa.


How did this happen?  Think back to the Carterfone decision. Prior to the break up in 1984, AT&T owned everything. They had a total monopoly from handset to handset and everything in between. They owned the local loop, the DMARC, MPOE, cabes, poles, on-premise equipment, off-premise equipment, data centers, switches— everything. (Similar situations existed with small local phone companies as well) But even before the break up of AT&T the use of third party equipment created a need to delineate the portion of the network which was owned by the customer and the portion owned by ma bell.

The Modem (Part 2)

Let's discuss SYN-ACK. I really breezed past it yesterday and it was actually important to understanding how the modem came to be. Below is a simplified summary of the TCP 3-way handshake: (SYN, SYN-ACK, ACK) More here.

• Host A sends a TCP synchronize packet (SYN) to Host B 
• Host B receives A's synchronize packet (SYN)
• Host B sends a synchronize-acknowledgement (SYN-ACK)
• Host A receives B's synchronized-acknowledgement (SYN-ACK)
• Host A sends acknowledge (ACK)
• Host B receives acknowledgement (ACK). 
• the TCP socket connection is now established!

This whole sequence comes from the modem. That is if you tend to agree that the modem descended from the work of Jean Maurice Émile Baudot. He patented a 5-bit telegraph code in 1870. In 1874 he invented a telegraphic system of TDM (Time-Division Multiplexing.) He used synchronized clockwork-powered switches at the transmitting and receiving ends, and was able to transmit five messages simultaneously. But because the timing was controlled mechanically the telegraph operator had to enter characters at a steady 30 wpm. The receiving end was a bit more forgiving, as those signals were temporarily stored on a set of five electromagnets, before being decoded to print the corresponding character on paper tape.

If not, then for you the first modem was probably a crude device that transmitted data as audio via a loudspeaker into the earpiece of the phone. This wooden box with a speaker and a mic were formally known as an acoustic coupler. They were sensitive to external noise, and variances in the shape and size of handsets. The dialing done by modern modems now was done then by human fingers on a rotary dial. They were also wholly technologically unnecessary. But directly connecting the the phone network was illegal. Inexplicably such systems were still in use well into the 1990s for mobile use such as in Telecommunications device for the deaf (TDDs.)

It was 50 years after Baudot's work that George Stibitz invented the first relay computer in 1937. AT&T put a full scale model into production in 1940. This relay computer connected Computer in New York to a teletype at Dartmouth College in New Hampshire over a phone line. It was the first remotely accessed computer.  The computer was a "complex number computer" an early digital computer. This required an A-to-D conversion.

AT&T built five of these complex number computers for the military. A total of 7 existed. They were used by the military to interpolate linear sequences for aiming anti-aircraft guns. It had no electronic memory, not even Baudot's simple magnets, but instead used his five-channel paper tape in a loop. Tapes had to be swapped to allow the computer to employ different mathematical functions. Post war yet different tapes allowed them to be re-purposed. (In this sense it was reprogrammable)

In 1949 Dr. George Valley of M.I.T.'s Lincoln Laboratory had recommended computerized networking  to operate our radar stations guarding the northern air approaches to the United States. Manual (i.e. human) identification, warning and control was slow compared to computers. This project was farmed out to IBM. An experimental subsector in Massachusetts was online in 1955. The SAGE (Semi-Automatic Ground Environment ) air-defense system used modems to connect their sites.  They combined analog radar signals so they could be sent from one computer to another. (Ken Olsen from MIT designed a series of transistorized computers to run the system.) It's modems were used to communicate data over the public switched telephone network or PSTN. The groundbreaking for the SAGE System was held at McChord AFB in 1957. By December of 1961 they had networked 78 SAGE radar stations and DEW Line sites.

In 1960 the Federal Communications Commission issued the Carterphone decision causing an explosion of private development.  The commercial potential was clear, by 1962, the first commercial modem was being manufactured by AT&T the Bell 103. It was the first modem with full-duplex transmission, frequency-shift keying or FSK, and had a speed of 300 bits per second or 300 bauds. in 1972, Vadic introduced the VA3400 which was capable of full duplex operation at 1200 bit per second. In 1976 AT&T came out with their own model capable of the same. Then in 1977 the Hayes modems debuted on the market and the modern era had begun...

The Carterfone Decision

It is only in the protractions of time that we realize the consequences of our actions. As we saw just days ago at the hands of FCC high mucketymuck Kevin "Bushpawn" Martin. In what can kindly be called an "interesting" re-application of the Carterfone decision, Kevy steers the course of history gently away from open access, whatever his cogent purpose may actually be. My hatred of the man is long been in evidence. I'll let The Scholars & Rogues Blog speak in his defense.

In recent months murmurs began about the fate of the white spaces. Broadcast television will switch to digital in 2009, and analog TV will cease to be. In that change, no matter how delayed or protracted and painful it may be, a large chunk of RF real estate will open up. The 700Mhz band is coveted by cell phone companies because it travels easier though walls than the currently used 2.5 GHz block. Cell phones could work indoors basically. Many parties are interested, nobody seemed to have any big ideas worth discussing here.. until Google spoke up 2 weeks ago. Google announced that they would bid $4.6 billion for a slice of the 700 MHz band to provide wireless Internet. But they attached a caveat. Access had to be open.
The policy they wish to see applied is the Carterfone decision. Blogs everwhere reference it but gloss over the event itself. It starts in 1959, Tomas Carter makes a radio phone that works with phone land lines and wireless. Ma Bell spazzes out and tells their customers they aren't allowed to use it, and if they do they will pay a penalty.

Carter, an obstinate Texan, stands up to the telephone giant and brings anti-trust proceedings against AT&T. The case is sent to the FCC. The FCC decides that the device is needed and does no harm to AT&T's existing infastructure. So in 1968 the FCC ruled that telephone networks could not forbid third-party devices to use their service. That the actions of AT&T were "unreasonable, unlawful and unreasonably discriminatory." In 1975 they expanded the idea, allowing consumers to attach any devices to a network, as long as they adhere to technical standards. More here.

But when Skype asked them to do the same thing with Voice over IP technology this Spring they hit pause. Approving that further broadens a policy that would never have been written under the current regime, yet it's the most applicable decision the commission has from which to make a decision. Google's idea of openness goes beyond even that, asking the FCC to require winning bidders to rent parts of their networks to competitors. That's not just hardware. compatibility. That's a tad bigger, but one that benefits consumers. Phone companies are claiming thsi will cause disruption and dange to their networks. yeah, that's what they said in 1959 too. It was a lie then, and a lie now.

Bidding begins in January 2008, an election year. Let the bribery begin!