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 = Speeds
OC-1   = 51.85 mb/s
OC-3   = 155.52 mb/s
OC-12  = 622.08 mb/s
OC-24  = 1.244 gb/s
OC-48  = 2.488 gb/s
OC-192 = 9.952 gb/s
OC-255 = 13.21 gb/s
OC-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 Hierarchy

Signal   Carrier          Speed         DS0 Equivalents
DS0      T&R Copper Pair  64 kbps       1
DS1      T1 Copper Pairs  1.544 mbps    24
DS3      T3 Coax          44.736 mbps   672

STS-1    OC-1 Fiber       51.84 mbps    672
STS-3    OC-3 Fiber       155.52 mbps   2016
STS-12   OC-12 Fiber      622.08 mbps   8064
STS-48   OC-48 Fiber      2488.32 mbps  32256
STS-192  OC-192 Fiber     9953.28 mbps  129024

Usually I have a plenty of the cables on hand, but I could not find one of these in my box of tricks. I did have the EIA/TIA Serial to RJ-45 adapter, so I just needed the cable. The cable that comes supplied with Cisco equipment is a flat 8 wire telephone cable with two RJ-45 ends. The cable is called a rollover cable because Pin 1 is connected to Pin 8 on the other end and Pin 2 is connected to Pin 7 on the other end. It’ that simple!

It is sometimes called a null modem cable, because the all of the pins are reversed from side to side. The transmit is rolled over to the receive, the Ready To Send or RTS is directly connected to the Clear To Send or CTS, the Data Terminal Ready DTR is connected to the Data Set Ready or DSR, etc… All of the grounds are commonly tied together as well. This is why connecting to a Cisco device requires 9600 baud, 8 bits, No parity, 1 stop bit and no flow control. This is sometimes referred to as 9600,8,N,1.

The diagram below is how to make the rollover cable from simple Cat5 cable if you do not have the 8 wire flat Telco cable on hand that is usually gray in color. Simple crimp them down on each end of the cable as per the diagram. It does not matter which end is connected to the equipment and which end is connected to the EIA/TIA DB-9 RJ-45 connector.

Your interface with the smart jack is an RJ-48C connector, which is basically an RJ-45. When wiring the RJ-45 use the wiring spec of the TIA/EIA 568B color code. This color code is as follows…

However only Pin 1, Pin2, Pin 4 and Pin 5 are used… You only need to wire the 4 pins crimped to the RJ-45 connector. In the end the White/Blue and Blue pair of wires is your Transmit Ring and Tip and the White/Orange and Orange pair of wires is your Receive Ring and Tip. This basic wiring is what comprises a 4-wire T1 circuit with current Telco service today.

If you wanted to create a simple hardware loopback; you could simply connect Pin 1 to Pin 4 and connect Pin 2 to Pin 5. This would connect the Receive Ring with the Transmit Ring and connect the Receive Tip with the Transmit Tip. A connection like this would loop all data back to the Telco. You can fabricate a device like this with an RJ-45 connector and two wires. When you want to check your wiring you can; look at the smart jack (if you have access to it) and watch the ‘Alarm’ go off when you connect the loopback or call the Telco and have them verify the alarm is off. This is a simple way to check your T1 circuit all the way to your device.

The NANP defined how areas would be numbered as well, areas being large area or Local Area Transport Areas (LATA). All calls in the area where charged at a predefined rate and in the 80′s that changed and where split into smaller area. However the Area Code or Numbering Plan Area are the same. So the Area Code / NPA for Pittsburgh is 412 this defines the Numbering Plan Area. Inside of the NPA there are several Exchanges or Numbering Plan Exchanges these are defined as NXX. This is the BAY/229 in Bayside. The last 4 digits of a phone number are the subscriber line and again that is private data.

So looking at a number like 412-229-0123 you can tell that it is in 412 or Pittsburgh. Inside of Pittsburgh the Exchange area or NXX is 229 or Bayside and the Subscriber is 0123. Well wouldn’t it be perfect if all exchanges matched like 229 is Bayside? Well 224 is also Bayside and that doesn’t work on a phone with the number encoding. Remember the NANP was introduced in 1947 and everyone owns a phone, so area were numbered outside of the first three letters encoded to the digits on a phone. You don’t call ‘Mabel’ anymore. There is a database published that Long Distance providers subscribe to for call routing. You can find pretty up to date version that are freely searchable on the Internet, just Google ‘npa nxx’ and you will find one. You can then locate a person down to the city they live in.