Legacy Telephone plant outside and inside



Outside plant is where convergence of networks has made the biggest change.
Telephone architecture is using more Fiber Optics in the Telephone plant from a total home run system of individual pairs to the Central Office to a distributed system closer to what CATV architecture is. Likewise with a fiber backbone cable companies have moved more toward the home run architecture of Telephone plant as they start developing multiple paths of fiber back to their Headend. It is the influence of Fiber optic technology that is making traditionally very different communication systems more the same in architecture.
But there is still a substantial inventory of Plain Old Telephone outside plant. A typical cable leaving Central office vault could be in the 3,000 pair size. It is typical for a cable that size leaving the telephone central office to split off at a Service Area Interface which is usually a large double door pedestal. Servicing Area Interface, SAI, or just a large enclosure could accommodate the large 3,000 pair that could have 2,400 pairs spliced through to a 2400 pair cable and dropping 600 pair for cross-connect panel where a Technician can cross-connect a pair from the 3,000 pair to a pair on the 600 pair that will split into smaller cables that are spliced through in pedestals and then terminate at a home or business.




The first point were cross-connects can be made is known as the F1 or Feeder 1.

This an example of is a high density enclosure, meaning that all combinations of function can be accomplished. Some loading can be done inside the enclosure, but if most pairs require loading, it will be done in an adjacent underground enclosure. The most practical use of the space is for addition of repeaters for lines that are not loaded.

The insulation is colored to identify (1) the tip and ring conductor of each pair and (2) each pair in the completed cable. The colors to be used in the pairs in the 25-pair group, together with the pair numbers, are shown in the following table which shows binder tape colors up to a 600-pair cable

Table 1

Group# Color of Bindings Group Pair Count
1 White-Blue 1-25
2 White-Orange 26-50
3 White-Green 51-75
4 White-Brown 76-100
5 White-Slate 101-125
6 Red-Blue 126-150
7 Red-Orange 151-175
8 Red-Green 176-200
9 Red-Brown 201-225
10 Red-slate 226-250
11 Black-Blue 251-275
12 Black-Orange 276-300
13 Black-Green 301-325
14 Black-Brown 326-350
15 Black-Slate` 351-375
16 Yellow-Blue 376-400
17 Yellow-orange 401-425
18 Yellow-Green 426-450
19 Yellow-Brown 451-475
20 Yellow-Slate 476-500
21 Violet-Blue 501-525
22 Violet-Orange 526-550
23 Violet-Green 551-575
24 Violet-Brown 576-600


The basic telephone code consists of five primary colors—white, red, black, yellow, and violet—and five secondary colors—blue, orange, green, brown, and slate. All tips will be of a primary color and all rings will be of a secondary color with binder groups following the same protocol. These binders are identified by a wraparound binder tape.

These are the colors in a standard binder unit, regardless of the binder color.

Table 2 Pair Numbers Binder Color
1-600 White
601-1200 Red
1201-1800 Black
1801-2400 Yellow
2401-3000 Violet

Notice that the only the primary color is used and is wrapped around each 600-pair group. The same color code scheme is repeated in each super-unit. Using the super-unit designation cables, up to 3,000 pairs can be managed and all pairs identified.

The hierarchy for telephone wiring would start with regular drop or station cable that would connect to the telephone. The cable would be from two to five pairs that would start with blue primary color for all of the tips and the secondary color scheme for all of the rings. For example, a two-pair cable would have a white wire with small blue dashes on it. The white indicates that it is the tip, and the blue dashes indicate that it belongs to the adjacent blue wire. The blue wire indicates that it is ring wire. This blue wire will typically have small white dashes on it to show that it belongs to the white tip wire. Some cables will not always have this extra stripping on the wire pairs, but will merely have the white tip and the blue ring twisted together.

This same order would follow with the second pair—a white again with orange dashes on it, and an orange wire with white dashes on it. Orange is the next secondary color in the two-pair cable. A five-pair cable would follow the color code for the first five pairs. A 10-pair cable would have five white tips associated with the five different secondary ring colors and five red tips with the same five secondary ring colors again.
Table 1 shows the binder scheme for a 600-pair cable. Notice that the tip and ring color scheme is used for the binder identification for each 25-pair group. Each binder group has the color coding scheme shown in Example 1 for each pair in that group. Table 1 also represents cable smaller than 600 pairs. For example, a 300-pair would go up to group 12, which would be black\orange.
Pair# Tip Ring Pair#

1 White Blue
3 ” Green
2 ” Orange
4 ” Brown
5 ” Slate

6 Red Blue
7 ” Orange
8 ” Green
9 ” Brown
10 ” Slate

11 Black Blue
12 ” Orange
13 ” Green
14 “ Brown
15 ” Slate

Pair# Tip Ring Pair#

1 White Blue
3 ” Green
2 ” Orange
4 ” Brown
5 ” Slate

6 Red Blue
7 ” Orange
8 ” Green
9 ” Brown
10 ” Slate

11 Black Blue
12 ” Orange
13 ” Green
14 “ Brown
15 ” Slate

Table 2 is a super-unit binder designation for cables from 600+ pairs up to 3,000 pairs.
Table 3 is color code for a 25 pair cable

16 Yellow Blue
17 ” Orange
18 ” Green
19 ” Brown
20 ” Slate

21 Violet Blue
22 ” Orange
23 ” Green
24 ” Brown
25 ” Slate

Inside plant

66 block




Figure 15

Premises wiring usually follows a sequence similar to Figure 15. All outside communication cables enter the building at a common point. This usually is a basement room, or a ground level wiring closet. In this case find the red number 1 it is a ground floor closet. The first point of entry is commonly called a Main Distribution Frame (MDF) but what it really is in this day and age is Point of Presence or a POP. Find the red number 2 in this Figure 15 and that is where the MDF is. Usually
I say that the number 1 location is a POP because this design has both the Incumbent Local Exchange Carrier (ILEC) which would be Qwest and then two Competitive Local Exchange Carriers (CLEC’s). The CLEC’s are XO Communications and Electric Lightwave all thee use the CLLI (Common Language Location Identifier) code to Identify this location. Just so the reader knows CLLI is commonly pronounced as “silly code”.

Location 2 Is the Customers Main Distribution frames plus a single point grounding system.


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