I will try to explain wiring of a T1/DS1 circuit end to end; since so many people have emailed me on the prior T1 wiring article and wanted more. In this article you will find references to the standards and technologies that surround a T-1/DS-1 installation. I will start with the line coming in and ending with the device. You may not have access to everything I explain, but there is a benefit in knowing the technology.
OC-Fiber Cable
Optical Carrier Fiber is how data is transmitted between Central Offices (COs). The cable itself is what runs along utility poles and is wrapped in orange when it leaves the utility pole. The type of cable used depends on distance it needs to be run. However all of the OC fiber that is used today is OSP or Outside Plant cable. The OSP cable is gel filled and resists nicks and impacts, so the 9 micron glass fibers inside do not fracture or shatter if struck with an object.
The data transmitted in this cable is what makes up the OC designation. The OC designation defines the bandwidth that can be transmitted in the cable. The speed is dependent on the optics, distance and most importantly the equipment installed at each end. Generally OC-192s are run between Central Offices in metropolitan areas, but OC-48s are run to rural areas. It all breaks down to speed (bandwidth) and capacity. A voice call requires 64kb/s of data, so when you look at the OC designations keep that in mind.
OC = SpeedsOC-1 = 51.85 mb/sOC-3 = 155.52 mb/sOC-12 = 622.08 mb/sOC-24 = 1.244 gb/sOC-48 = 2.488 gb/sOC-192 = 9.952 gb/sOC-255 = 13.21 gb/sOC-768 = 39.81 gb/s
MUX
All telephone and data communications are transmitted in serial path communications. Time slots are created in the stream and data is multiplexed into the stream and de-multiplexed on the opposite side. This is the DS in the DS designation you keep seeing; it stands for Digital Signal and is what makes up the time slots. The devices which multiplex and de-multiplex the data from the streams is called the MUX. It is also what is responsible for provisioning the Tier Service Units or T1s, T3s, etc… So an OC-3 will come into the MUX and be broken down into DS3 (T3) circuits, DS1 (T1) circuits or DS0 (POTS) lines; depending on how the MUX was configured with line cards. An OC-3 can be broken down into 3 DS-3 circuits or 1/3 of the OC-3 can be converted into 28 DS-1 circuits and each DS-1 can be broken down into 24 individual POTS lines or DS-0 circuits.
The MUX might be on your premise or it may be in an environmental vault underground. The customer is usually not allowed in the MUX, only employees of the telco are allowed in it; since you can affect many people. It is also on battery backup for at least 4 hours, so 911 calls go thru. I’ve actually seen Verizon trucks show up with generators if the power has been out for extended periods.
DS-1
Depending on your distance from the CO you may just have the 4 wires that make up the DS-1 signal coming in on POTS lines. In the end a DS-1 is 1.544 Mb/s and is a serial transmission across twisted pair, so cross talk is not a problem. Most all of the DS-1s in existence today are 4 wires, however 2 wire DS-1s can be found in older installations. The main difference is 2 wire T1s are half-duplex and 4 wire T1s are full-duplex, half-duplex T1s are a poor choice for voice communications because you can introduce echo. It is also a poor choice in data and will result in long response time, but usually problems are not as pronounced as voice calls. The line coming from the MUX to the Smart Jack or NIU is generally shielded twisted pair and is the responsibility of the telco provider. Sometimes the Smart Jack is integral with the MUX so the wire path is in the backplane of the MUX switching unit and it is assumed to be full-duplex.
Network Interface Unit / Smart Jack
The smart jack is the handoff to the customer, it is the demarcation point. The smart jack allows for remote looping of the circuit, so that they can remotely check their provisioning of the line and circuit. It is how the telco provider checks to see if it is their problem or your problem. It is where your installation job will begin once they had delivered the circuit to you…
Smart jacks come in many different shapes, sizes and styles; they can be wall mount single units or banks like the one depicted in the diagram above. If you were to order a single DS1/T1 circuit you would most likely have a 4 wire shield cable coming in from the local CO or nearest MUX into a wall mounted unit. This unit is nothing more than a box with a single line card slid into the connector, although a lot of these units do at least two or four cards/circuits. The most common line card used today is the Westell SlimJack or Adtrans DS1 card, they can be found in any telco closet or PBX room today.
Another common installation is a bank of T1/DS1 cards; the unit is commonly mounted inside the MUX. The way the customer interfaces with it is a jack panel that will plug into the cage of DS1/T1 cards called the NIU, it does this with a parallel port looking connector that is prewired to the jack panel. The jack panel will have RJ-45 looking connectors called RJ-48C connectors with numbers corresponding to the line cards in the NIU/smart jack.
The RJ-48C or RJ-48X is the Demarc! The difference between an RJ-48C and an RJ-48X is; the RJ-48X has shorting blocks that short over to create a mechanical loopback at the female jack receptacle. The difference between an RJ-45 and RJ-48C is which wires are used. No matter what type of NIU / smart jack the telco installs, they will hand you off the DS1/T1 circuit thru an RJ-48C connector. So this is where you are responsible! So let’s educate ourselves on wiring.
So first let me state that if you are connecting a CSU/DSU to the RJ-48C you can use a standard network patch cable! It is straight thru cable and that is all you need, so if you are unsure TEST YOUR CABLE with the same network tester you always use. Generally you always want to use a CSU/DSU when connecting to a PBX although most PBXs do not require one; it is a good idea because the telco provider can remotely loop it and it provides a point of diagnostic. Most CSU/DSU units also allow manual looping bi-directionally to telco and to CPE.
If the equipment is not next to the smartjack then you may need to take it out of the Demarc and run it over your “house wiring”. The house wiring is nothing more than a 50-pair or 25-pair cable that runs between two locations in your building. If that is the case then you will want to wire the RJ-48C as follows and punch it down on your house wiring. The reason is the 1 and 2 pin is used for RX Ring and Tip and the TX uses the 4 and 5 pin for Ring and Tip; so when they are punched down you can use the standard USOC wiring colors. So this way the RX Ring and Tip uses the first USOC colors of white-blue/blue and the TX Ring and Tip uses the second USOC colors of white-orange/orange.
Terminology
Central Office – The physical structure that holds the signaling equipment used to switch phone calls and generally make up the exchange. (NPA – Area Code and NXX – Exchange) Many COs together make up the LATA.
LATA – (Local Access Transport Area) is a term used in telcom to represent a geographic area that was created when AT&T broke up into smaller Baby Bells. The LATA is drawn around a market and is sometimes used for billing purposes and termination of phone numbers; generally this makes up the exchange.
POTS – (Plain Old Telephone Service) is voice grade communications line that is run to most all residential and businesses since the inception of the phone.
NIU – (Network Interface Unit) is the equipment that exposes the Demarcation point to the customer.
CPE – (Customer Premise Equipment) is the equipment that is owned by the customer that connects into the telephone network.
USOC – (Universal Services Ordering Code) is the specification set forth by Bell Systems as a universal way customers could connect to the public network. These codes, adopted in part by the FCC, Part 68, Subpart F, Section 68.502, are a series of Registered Jack (RJ) wiring configurations for telephone jacks that remain in use today.
PSTN – (Public Switched Telephone Network) also known as POTS, this is the network that a PBX would interface with to place calls or your typical phone at home.
Voice Network Speed HierarchySignal Carrier Speed DS0 EquivalentsDS0 T&R Copper Pair 64 kbps 1DS1 T1 Copper Pairs 1.544 mbps 24DS3 T3 Coax 44.736 mbps 672STS-1 OC-1 Fiber 51.84 mbps 672STS-3 OC-3 Fiber 155.52 mbps 2016STS-12 OC-12 Fiber 622.08 mbps 8064STS-48 OC-48 Fiber 2488.32 mbps 32256STS-192 OC-192 Fiber 9953.28 mbps 129024This entry was postedon Monday, October 18th, 2010 at 4:44 pmand is filed under Telco.
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