ODUk container

The ODUk container consists of 15240 bytes from the OPUk container plus 3 x 14 bytes of the ODUk OH. The total container capacity is therefore:  

•15240 bytes + (14bytes x 3 row) = 15282 bytes 

The information in the ODU OH, just to recap, consists of information related to the signal path. One of the functionalities this enables is to perform a signal trace. The user can assign a signal trace of the path, which the user can then have verified at the end of path. 

Optical Transport Module (OTM-n.m, OTM-nr.m)

The OTM-n is the output from the OMS layer and is actually the signal that will be output onto the fiber. The OTM-m signal is the result of multiplexing all of the OCh payloads with the OSC signal (OOS). 

The OSC signal contains information related to:  

•The state of the clients' signals 

•Maintenance and operation functions of the OMS 

•Maintenance and operation functions of the OTS 

•General management communication between network equipment  

Putting it all together we have the visual representation below

The OTM also has a reduced version represented as OTM-nr.m where r represents reduced functionality. The primary difference between the two OTM-n.m and OTM-nr.m is that the reduced functionality version has no OSC. 

Optical Channel (OCh, OChr)

Now that the system has created all the information required and prepared it in a container of appropriate size for it to cross an OTH network and if necessary, for it to be regenerated, it is a requirement to provide an additional transparent network connection. The requirement for this transparent connection is due to the fact that to be able to direct and process client information - which is inside an OTUk remember – the system must be able to access the individual wavelength state without performing a full optical to electrical conversion. 

The way the OTH standard handles this is to use the OCh OH but instead of inserting it into the client carrier wavelength they utilize another wavelength channel altogether and this is the purpose of the OSC (optical supervisor channel) that has been mentioned in passing on several occasions. 

The OSC is carried on a frequency out with the carrier wavelength spectrum so that it does not interfere with the carrier wavelengths. Furthermore all vendor active network equipment has electrical access to this OSC channel. The OSC is the only signal, which all OTH compliant equipment can access.

Consequently if any piece of equipment on the optical path detects a client signal failure (loss of signal) it will process the corresponding OCh OH to inform the other system equipment about the state of the client wavelength. 

Note: There are two versions of the optical channel OCh & OChr.  The non-standard version is called OChr, where 'r' represents the reduced version that does not insert an OCh OH into the OSC wavelength.

Optical Channel Transport Unit (OTUk, OTUkV)

With the introduction of an overhead into each client signal as is representative of that signal only, it becomes necessary to introduce a further OH that will provide information to equipment handling regeneration. The information the equipment uses to perform this task is inserted into the OTU overhead (OTU OH). This information relates to the maintenance and operation functions to support the optical channel section. 

These functions include:  

•Functionalities of section monitoring 

•General communication channel 

•Reserved bits 

This unit also contains information that defines the use of a FEC (forward error control) as a way to improve signal quality and reliability. This unit is represented as follows: 

ODUk	OTUk
ODU1	OTU1
ODU2	OTU2
ODU3	OTU3
ODU4	OTU4

The OTU terminates at the point of assembly/disassembly and this is identical to the regeneration overhead in SDH. Note: The standard defines that the use of several types of FEC is possible though the only one standardized at the time was RS (255,239) the type of FEC used now though is based on Reed-Solomon and it is used to define the OTUk. Other possibilities of FEC are inserted into the OTUkV. 

ODUflex

ODUflex was introduced into the G.709 standards in 2009 

Two flavors of ODUflex standardization  

1.Circuit ODUflex 

 •Supports any possible client bit rate as service in circuit transport networks 

•CBR clients use a bit-sync mapping into ODUflex (239/238xthe client rate)  

2.Packet ODUflex 

•Supports variable length packet trunks for transporting packet flows using layer 0 switching 

•Theoretically can be of any size but in practice is usually set to be multiples of the lowest tributary slot size in the network  In order to support ODUflex a new ODU was created called ODU2e ODU2e Definition New Low Order (LO) tier of the hierarchy (Oct 2009) to transport “proprietary” 10G signals  

•Serves as a logical wrapper for 10GBASE-R when carried over a standardized physical layer of OTU3 or OTU4 

•Part of compromise made to enable standards progress - most commonly deployed 

•“proprietary” transparent mapping of 10GBASE-R 

•Over-clocked physical OTU2e signal remains in G.sup43 

•Can map ´10 into OPU4 (which is sized to carry 100GBASE-R) 

•Can map as ODUflex in 9´1.25G OPU3 tributary slots (up to 3´ODU2e per OPU3)  

OPU2e can carry:  

•10GBase-R 

•Transcoded FC-1200 

ODU1 and ODU2 Definition

 ODU1 Definition 

Original tier of the hierarchy to transport 2.5G signals  

•ODU1 = 2.498775Gbit/s 

•OTU1 = 2 666057Gbit/s 

 OTU1 can be used as a higher order ODU to carry lower order ODU0s  

•Divided into 2x1.25G tributary slots: 

•ODU0 maps into 1 tributary slot 

 OPU1 can carry:  

•STS-48 

•STM-16 

•FC-200 

 ODU2 Definition 

Original tier of the hierarchy to transport 10G signals  

•ODU2 = 10.037273Gbit/s 

•OTU2 = 10 709224Gbit/s 10.709224Gbit/s 

Can be used as a higher order ODU to carry lower order ODUs  

•Divided into 4´2.5G or 8´1.25G tributary slots: 

•ODU0 maps into 1 tributary slot 

•ODU1 maps into 1 2.5G or 2 1.25G tributary slot(s)  OPU2 can carry:  

•STS-192 

•STM-64 

OMS/OCh Adaptation

The bidirectional OMS/OCh adaptation (OMS/OCh_A) functions are performed by a co-located pair of sources and sink OMS/OCh adaptation functions. The OMS/OCh adaptation source (OMS/OCh_A_So) performs the following processes between its input and its output:   

•modulation of an optical carrier signal by means of a defined modulation scheme 

•wavelength (or frequency) and power allocation to the optical carrier 

•optical channel multiplexing to form an optical multiplex  

The OMS/OCh adaptation sink (OMS/OCh_A_Sk) performs the following processes between its input and its output:  

•optical channel demultiplexing according to carrier wavelength (or frequency) 

•termination of the optical carrier and recovery of the optical transport unit 

ODU0 Definition

Smallest container defined in G.709 (OTN Standard) 1.25G container size (specifically 1.244160 Gbit/s 20ppm) Established in October 2009 for transport of 1000BASE-X (Gigabit Ethernet) Sized to fit existing OTN hierarchy  

•2 into ODU1 

•8 into ODU2 

•32 into ODU3 

•80 into ODU4 

 ODU0 can carry:  

•1000Base-X (1GbE) 

•STM-1 

•STM-4 

•FC-100 

No OTU0 physical layer Only a lower order wrapper for 1000BASE X mapped into standardized physical layers 

Optical Multiplex Section Termination

The following processes are the responsibility of the optical multiplex section (OMS) trail termination, I.E the processes initiate at the point of trail termination:  

•validation of connectivity integrity 

•assessment of transmission quality 

•transmission defect detection and indication 

 As was the case with the optical channel, the optical multiplex section (OMS) consists of a pair of bidirectional but co-located optical channel termination source and sinks functions.  

•Optical multiplex section termination source: accepts the adapted information from a client layer network at its input inserts the OMS overhead and presents the characteristic information of the OMS layer network at its output.  

•Optical multiplex section termination sink: accepts the characteristic information of the OMS layer network at its input extracts the OMS overhead and presents the adapted information at its output.  

Point-to-Point with Optical Regenerator

In this topology we will consider a straightforward point-to-point topology but with a regenerator (3R) inline. What we can see happening here is that all three layers have their respective trails terminated at the regenerator. This is because the regenerator is affecting the individual signals at the highest optical channel layer. By doing 2R or 3R regeneration on the entire signal requires disturbance and manipulation of the individual client signals at the OC layer. Consequently, these changes to the client signals require subsequent changes to be made at the lower OMS and OTC layers.

In this regeneration example, we can see that the trails in all of the layers are affected by performing, 2R or 3R regeneration of the signal. Consequently, all the OCh and OMS trails sink at the regenerator and new trails are spawned and sourced again at the regenerator’s line output. 

Again, if this equipment is going to be OTH (G.709) compliant it must have the capability to understand, process, analyze the OTH OH, and to act accordingly. 

Optical Multiplexor Section Layer

The Optical Multiplexor Section layer will be responsible for handling the preparation, grooming, and signal equalization of client signals prior to and during the multiplexor process. The OMS layer provides the path for the transport of client signals that the transponders in the optical client layer have transformed to wavelengths in preparation for their travel through the optical multiplex section trail. 

The characteristic information that exists in the optical multiplex section layer comprises two distinct logical signals:  

1.       A data stream that represents the adapted client data stream produced by the transponders in the optical channel layer 

2.       A data stream that represents the optical multiplexor section overhead (OMS)  The Optical Multiplexor Section provides the functionality for processing and networking multi-wavelength optical signals. In OTH parlance multi-wavelength can also represent a single wavelength. 

The Optical Multiplexor Section layer capabilities include the following functionality:  

• ·       Overhead processes that ensure the integrity of the multiplexor section information that has been used to adapt the original client signal 

• ·       Processes that enable the section level  operation and management functions such as section survivability  

The process for obtaining an OMS signal consists of the following steps:  

1.       The modulation of a clients signal by the optical signal section 

2.       Allocation of a specific wavelength or frequency to the optical carrier signal 

3.       Generation of the OMS overhead 

HORIZONTAL CABLING (CABLING SUBSYSTEM 1)

Horizontal cabling includes horizontal cable, telecommunications outlet/connectors in the work area (WA), mechanical terminations and patch cords or jumpers located in a telecommunications room (TR) or telecommunications enclosure (TE) and may incorporate multi-user telecommunications outlet assemblies (MUTOAs) and consolidation points (CPs). The pathways and spaces to support horizontal cabling shall be designed and installed in accordance with the requirements of TIA-569-B.

Some networks or services require applications-specific electrical components (such as impedance matching devices). These application-specific electrical components shall not be installed as part of the horizontal cabling. When needed, such electrical components shall be placed external to the telecommunications outlet/connector. Keeping application-specific components external to the telecommunications outlet/connector will facilitate the use of the horizontal cabling for varying network and service requirements. 

A minimum of two permanent links shall be provided for each work area. The cabling should beplanned to accommodate future equipment needs, diverse user applications, ongoing maintenance, relocation and service changes. Indeed, horizontal cabling is often less accessible than backbone cabling and adding or changing horizontal cabling may cause disruption to occupants and their work once the building walls and ceilings are closed after the initial installation. The time, effort, and skills required for these subsequent changes are significant and make the choice and design layout of the horizontal cabling very important to the building occupants and to the maintenance of the telecommunications infrastructure. Therefore, it is incumbent on the designer to accommodate user needs and to reduce or eliminate the probability of requiring changes to the horizontal cabling as user requirements evolve.

Each 4-pair cable at the equipment outlet shall be terminated in an eight-position modular jack. The telecommunications outlet/connector for 100-ohm balanced twisted-pair cable shall meet the requirements of ANSI/TIA/EIA-568-B.2.

Optical fibers at the equipment outlet shall be terminated to a duplex optical fiber outlet/connector meeting the requirements of ANSI/TIA-568-C.3

Wiring for Tomorrow: Undersea Fiber Cables

The first undersea cable, which was laid for telegraph, was laid in 1851 between England and France. In 1956 the first coax cable—called transatlantic link (TAT-1)—went in. TAT-1 had the capacity to carry 35 conversations over 64Kbps channels.

The first fiber undersea cable, laid in 1988, was called TAT-8 and could support 4,000 voice channels. But undersea use of fiber didn't take off until 1994, when optical amplifiers were introduced. By the end of 1998, some 23 million miles of fiber-optic cable had been laid through out the world, by dozens of companies, at tremendous cost. By mid-1999 the total transatlantic bandwidth was 3Tbps, compared to just 100Gbps in 1998. By the end of 2001, we are likely to reach6Tbps. Between Asia and Europe, in 1997, we had bandwidth of 11Gbps; by 1999, we had 21Gbps;and by 2003, we should have 321Gbps. You can see that a great deal of spending has been done on fiber-optic cable, all over the world.

Fiber technology breakthroughs are having a profound impact on service providers, and that's witnessed by the constantly changing prices for intercontinental capacity. The construction cost of 64Kbps circuits has dropped from almost US$1,500 in 1988, to US$300 in 1995, to just a couple dollars per line today. When operators purchase undersea capacity, they pay two charges. The first isa one-time charge for the bandwidth—the indefeasible right of use. The second is an ongoing operations, administration, and maintenance charge that's recurring for the maintenance vessels that service the cable, and this is typically 3% to 5% of the total purchase cost.

The economic shifts look like this for a capacity of 155Mbps: At the start of 1997, it would have costUS$20 million; in 1998, it was down to US$10 million; in early 2000, it was down to US$2 to US$3million; and in 2001, it's expected to be at US$1 million. The operations, administration, and maintenance charges have remained the same because the contracts originally called for the calculation of those charges based on the cable length as well as the bandwidth, so as you increased your bandwidth, your operations, administration, and maintenance charges increased. Those agreements were recently changed so that you are only charged the operations, administration, and maintenance costs for the length of the cable. Hence, as you expand capacity, the maintenance charge is dropped.

Coaxial Cable Connectors

Unless you have operated a 10Base-2 or 10Base-5 Ethernet network, you are probably familiar only with the coaxial connectors you have in your home for use with televisions and video equipment. Actually, a number of different types of coaxial connectors exist.

F-Series Coaxial Connectors

The coax connectors used with video equipment are referred to as F-series connectors (shown in Figure 1). The F-connector consists of a ferrule that fits over the outer jacket of the cable and is crimped in place. The center conductor is allowed to project from the connector and forms the business end of the plug. A threaded collar on the plug screws down on the jack, forming a solid connection. F-connectors are used primarily in residential installations for RG-58, RG-59, and RG-6 coaxial cables to provide CATV, security-camera, and other video services.

 
Figure 1: The F-type coaxial-cable connector

F-connectors are commonly available in one-piece and two-piece designs. In the two-piece design, the ferrule that fits over the cable jacket is a separate sleeve that you slide on before you insert the collar portion on the cable. Experience has shown us that the single-piece design is superior. Fewer parts usually means less fumbling, and the final crimped connection is both more aesthetically pleasing and more durable. However, the usability and aesthetics are largely a function of the design and brand of the two-piece product. Some two-piece designs are very well received by the CATV industry.

A cheaper F-type connector available at some retail outlets attaches to the cable by screwing the outer ferrule onto the jacket instead of crimping it in place. These are very unreliable and pull off easily. Their use in residences is not recommended, and they should never be used in commercial installations.

N-Series Coaxial Connectors

The N-connector is very similar to the F-connector but has the addition of a pin that fits over the center conductor; the N-connector is shown in Figure 2. The pin is suitable for insertion in the jack and must be used if the center conductor is stranded instead of solid. The assembly is attached to the cable by crimping it in place. A screw-on collar ensures a reliable connection with the jack. The N-type connector is used with RG-8, RJ-11U, and thicknet cables for data and video backbone applications.

 
Figure 2: The N-type coaxial connector

The BNC Connector

When coaxial cable distributes data in commercial environments, the BNC connector is often used. BNC stands for Bayonet Neill-Concelman, which describes both the method of securing the connection and its inventors. Many other expansions of this acronym exist, including British Naval Connector, Bayonet Nut Coupling, Bayonet Navy Connector, and so forth. Used with RG-6, RG-58A/U thinnet, RG-59, and RG-62 coax, the BNC utilizes a center pin, as in the N-connector, to accommodate the stranded center conductors usually found in data coax.

The BNC connector (shown in Figure 3) comes as a crimp-on or a design that screws onto the coax jacket. As with the F-connector, the screw-on type is not considered reliable and should not be used. The rigid pin that goes over the center conductor may require crimping or soldering in place. The rest of the connector assembly is applied much like an F-connector, using a crimping die made specifically for a BNC connector.

 
Figure 3: The BNC coaxial connector

To secure a connection to the jack, the BNC has a rotating collar with slots cut into it. These slots fit over combination guide and locking pins on the jack. Lining up the slots with the pins, you push as you turn the collar in the direction of the slots. The slots are shaped so that the plug is drawn into the jack, and locking notches at the end of the slot ensure positive contact with the jack. This method allows quick connection and disconnection while providing a secure match of plug and jack.

Be aware that you must buy BNC connectors that match the impedance of the coaxial cable to which they are applied. Most commonly, they are available in 75 ohm and 50 ohm types, with 93 ohm as a less-used option.

Tip

With all coaxial connectors, be sure to consider the dimensions of the cable you will be using. Coaxial cables come in a variety of diameters that are a function of their transmission properties, series rating, and number of shields and jackets. Buy connectors that fit your cable.

Shielded Twisted-Pair Connectors

In the United States, the most common connectors for cables that have individually shielded pairs in addition to an overall shield are based on a pre-1990 proprietary cabling system specified by IBM. Designed originally to support Token Ring applications using a two-pair cable (shielded twisted-pair, or STP), the connector is hermaphroditic. In other words, the plug looks just like the jack, but in mirror image. Each side of the connection has a connector and a receptacle to accommodate it. Two hermaphroditic connectors are shown in Figure 1. This connector is known by a number of other names, including the STP connector, the IBM data connector, and the universal data connector.

 
Figure 1: Hermaphroditic data connectors

The original Token Ring had a maximum throughput of 4Mbps (and later 16Mbps) and was designed to run over STP cabling. The 16Mbps Token Ring used a 16MHz spectrum to achieve its throughput. Cables and connectors rated to 20MHz were required to allow the system to operate reliably, and the original STP hermaphroditic connectors were limited to a 20MHz bandwidth. Enhancements to these connectors increased the bandwidth limit to 300MHz. These higher-rated connectors (and cable) are designated as STP-A.

STP connectors are the Jeeps of the connector world. They are large, rugged, and versatile. Both the cable and connector are enormous compared to four-pair UTP and RJ-type modular plugs. They also have to be assembled and have more pieces than an Erector set. Cabling contractors used to love the STP connectors because of the premium they could charge based on the labor required to assemble and terminate them.

Darwinian theory prevailed, however, and now the STP and STP-A connectors are all but extinct—they've been crowded out by the smaller, less expensive, and easier-to-use modular jack and plug.

Crossover Cables | Modular Jacks and Plugs

One of the most frequently asked questions on wiring newsgroups and forums is "How do I make a crossover cable?" Computers that are equipped with 10Base-T or 100Base-TX network adapters can be connected "back-to-back"; this means they do not require a hub to be networked together. Back-to-back connections via crossover cables are really handy in a small or home office. Crossover cables are also used to link together two pieces of network equipment (e.g., hubs, switches, and routers) if the equipment does not have an uplink or crossover port built-in.

A crossover cable is just a patch cord that is wired to a T568A pinout scheme on one end and a T568B pinout scheme on the other end. To make a crossover cable, you will need a crimping tool, a couple of eight-position modular plugs (a.k.a. RJ-45 plugs), and the desired length of cable. Cut and crimp one side of the cable as you would normally, following whichever wiring pattern you desire, T568A or T568B. When you crimp the other end, just use the other wiring pattern.

Warning

As mentioned several times elsewhere in this book, we recommend that you buy your patch cords, either straight through or crossover, instead of making them yourself. Field-terminated patch cords can be time-consuming (i.e., expensive) to make and may result in poor system performance.

Table 1 shows the pairs that cross over. The other two pairs wire straight through.

Table 1: Crossover Pairs 

Side-One Pins	Wire Colors	Side-Two Pins
1 (Transmit +)	White/green	3 (Receive +)
2 (Transmit –)	Green	6 (Receive –)
3 (Receive +)	White/orange	1 (Transmit +)
6 (Receive –)	Orange	2 (Receive –)

Using a Single Horizontal Cable Run for Two 10Base-T Connections

Let's face it, you will sometimes fail to run enough cable to a certain room. You will need an extra workstation in an area, and you won't have enough connections. Knowing that you have a perfectly good four-pair UTP cable in the wall, and that only two of those pairs are in use, makes your mood even worse. Modular Y-adapters can come to your rescue.

Several companies make Y-adapters that function as splitters. They take the four pairs of wire that are wired to the jack and split them off into two separate connections. The Siemon Company makes a variety of modular Y-adapters (see Figure 1) for splitting 10Base-T, Token Ring, and voice applications. This splitter will split the four-pair cable so that it will support two separate applications, provided that each application requires only two of the pairs. You must specify the type of splitter you need (voice, 10Base-T, Token Ring, etc.). Don't forget, for each horizontal cable run you will be splitting, you will need two of these adapters: one for the patch-panel side and one for the wall plate.

Figure 1: A modular Y-adapter for splitting a single four-pair cable into a cable that will support two separate applications

Warning

Many cabling professionals are reluctant to use Y-adapters because the high-speed applications such as 10Base-T Ethernet and Token Ring may interfere with one another if they are operating inside the same sheath. Certainly you should not use Y-adapters for applications such as 100Base-TX. Furthermore, Y-adapters eliminate any chance of migrating to a faster LAN system that may utilize all four pairs.

ANSI/TIA -568-C Wiring Schemes T568A and T568B

ANSI/TIA-568-C does not sanction the use of the USOC scheme. Instead, two wiring schemes are specified, both of which are suitable for either voice or high-speed LAN operation. These are designated as T568A and T568B wiring schemes.

Both T568A and T568B are universal in that all LAN systems and most voice systems can utilize either wiring sequence without system errors. After all, the electrical signal really doesn't care if it is running on pair 2 or pair 3, as long as a wire is connected to the pin it needs to use. The TIA/EIA standard specifies eight-position, eight-contact jacks and plugs and four-pair cables, fully terminated, to facilitate this universality.

The T568B wiring configuration was at one time the most commonly used scheme, especially for commercial installations; it is shown in Figure 1. The TIA/EIA adopted the T568B wiring scheme from the AT&T 258A wiring scheme.

 
Figure 1: The T568B wiring pattern

The T568A scheme (shown in Figure 10.9) is well suited to upgrades and new installations in residences because the wire-termination pattern for pairs 1 and 2 is the same as for USOC. Unless a waiver is granted, the U.S. government requires all government cabling installations to use the T568A wiring pattern. The current recommendation according to the standard is for all new installations to be wired with the T568A scheme.

 
Figure 2: The T568A wiring pattern

The wire colors and the associated pin assignments for the T568B wiring scheme look like this:

Pin	Wire Color
1	White/orange
2	Orange
3	White/green
4	Blue
5	White/blue
6	Green
7	White/brown
8	Brown

The pin assignments for the T568A wiring schemes are identical to the assignments for the T568B pattern except that wire pairs 2 and 3 are reversed. The T568A pattern looks like this:

Pin	Wire Color
1	White/green
2	Green
3	White/orange
4	Blue
5	White/blue
6	Orange
7	White/brown
8	Brown

Note that when you buy eight-position modular jacks, you may need to specify whether you want a T568A or T568B scheme because the jacks often have IDC connections on the back where you punch the pairs down in sequence from 1 to 4. The jacks have an internal PC board that takes care of all the pair splitting and proper alignment of the cable conductors with the pins in the jack. Most manufacturers now provide color-coded panels on the jacks that let you punch down either pinout scheme, eliminating the need for you to specify (and for them to stock) different jacks depending on which pinout you use.

Tip

Whichever scheme you use, T568A or T568B, you must also use that same scheme for your patch panels and follow it in any cross-connect blocks you install. Consistency is the key to a successful installation.

Be aware that modular jacks pretty much look alike even though their performance may differ dramatically. Be sure you also specify the performance level (e.g., Category 3, Category 5e, Category 6, Category 6A, etc.) when you purchase your jacks.

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Tips for Terminating UTP Connectors

Keep the following points in mind when terminating UTP connectors:

• When connecting to jacks and plugs, do not untwist UTP more than 0.5″ for Category 5e and not more than 0.375″ for Category 6.
• Always use connectors, wall plates, and patch panels that are compatible (same rating or higher) with the grade of cable used.
• To "future-proof" your installation, terminate all four pairs, even if the application requires only two of the pairs.
• Remember that the T568A wiring scheme is compatible with USOC wiring schemes that use pairs 1 and 2.
• When terminating ScTP cables, always terminate the drain wire on both ends of the connection.

---

When working with ScTP wiring, the drain wire makes contact with the cable shield along its entire length; this provides a ground path for EMI energy that is collected by the foil shield. When terminating ScTP, the drain wire within the cable is connected to a metal shield on the jack. This must be done at both ends of the cable. If left floating or if connected only on one end, instead of providing a barrier to EMI the cable shield becomes a very effective antenna for both emitting and receiving stray signals.

In a cable installation that utilizes ScTP, the plugs, patch cords, and patch panels must be shielded as well.

USOC Wiring Scheme

The Bell Telephone Universal Service Order Code (USOC) wiring scheme is simple and easy to terminate in up to an eight-position connector; this wiring scheme is shown in Figure 1. The first pair is always terminated on the center two positions. Pair 2 is split and terminated on each side of pair 1. Pair 3 is split and terminated on each side of pair 2. Pair 4 continues the pattern; it is split and terminated on either side of pair 3. This pattern is always the same regardless of the number of contacts you populate. You start in the center and work your way to the outside, stopping when you reach the maximum number of contacts in the connector.

 
Figure 1: The Universal Service Order Code (USOC) wiring scheme

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Tip and Ring Colors

When looking at wiring schemes for modular plugs and jacks, you may see the letters T and R used, as in Figure 1. The T identifies the tip color, and the R identifies the ring color. In a four-pair cable, the cable pairs are coded in a standard color coding, which is on the insulation of the individual wires. In a four-pair cable, the tip is the wire that is predominantly white, and the ring identifies the wire that is a predominantly solid color.

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The wire colors and associated pin assignments for USOC look like this:

Pin	Wire Color
1	White/brown
2	White/green
3	White/orange
4	Blue
5	White/blue
6	Orange
7	Green
8	Brown

Warning

Do not use the USOC wiring scheme for systems that will support data transmission.

USOC is used for analog and digital voice systems but should never be used for data installations. Splitting the pairs can cause a number of transmission problems when used at frequencies greater than those employed by voice systems. These problems include excessive crosstalk, impedance mismatches, and unacceptable signal-delay differential.

Solid- vs. Stranded-Conductor Cables

UTP and ScTP cables have either solid copper conductors or conductors made of several tiny strands of copper. Solid conductors are very stable geometrically and, therefore, electrically superior, but they will break if flexed very often. Stranded conductors are very flexible and resistant to bend-fatigue breaks, but their cross-sectional geometry changes as they are moved, and this can contribute to electrical anomalies. Stranded cables also have a higher attenuation (signal loss) than solid-conductor cables.

Note

Solid-conductor cables are usually used in backbone and horizontal cabling where, once installed, there won't be much movement. Stranded-conductor cables are used in patch cords, where their flexibility is desirable and their typically short lengths mitigate transmission problems.

The differences in conductors mean a difference in IDC types. You have to be careful when you purchase plugs, wall plates, and patch panels because they won't work interchangeably with solid- and stranded-core cables—the blade designs are different.

Warning

Using the wrong type of cable/connector combination can be a major source of intermittent connection errors after your system is running.

With a solid-conductor IDC, you are usually forcing the conductor between two blades that form a V-shaped notch. The blades slice through the plastic and into the copper conductor, gripping it and holding it in place. This makes a very reliable electrical contact. If you force a stranded conductor into this same opening, contact may still be made. But, because one of the features of a stranded design is that the individual copper filaments can move (this provides the flexibility), they will sort of mush into an elongated shape in the V. Electrical contact may still be made, but the grip on the conductor is not secure and often becomes loose over time.

The blade design of IDC connectors intended for stranded-core conductors is such that forcing a solid-core conductor onto the IDC connector can break the conductor or fail to make contact entirely. Broken conductors can be especially problematic because the two halves of the break can be close enough together that contact is made when the temperature is warm, but the conductor may contract enough to cause an open condition when cold.

Some manufacturers of plugs advertise that their IDC connectors are universal and may be used with either solid or stranded conductors. Try them if you like, but if you have problems, switch to a plug specifically for the type of cable you are using.

Jacks and termination blocks are almost exclusively solid-conductor devices. You should never punch down on a 66, 110, or modular jack with stranded conductors.