Routing of Your Phone Cable

This page will discuss the basic layout or "topology" of your cable routing.

Determining and understanding the routing of your existing cable is essential to being able to reconfigure your current wiring.
I'll add more at a latter date to cover the physical installation. In the meanwhile, I recommend that you follow this link to Low Voltage Home Pre-Wire Guide. This guide does a good job of covering the physical installation of cable in a home under construction and much of what you will find there is just as pertinent to reconfiguring your current wiring.

Basic Topologies

The term topology refers to the arrangement used in routing and connecting your cables. Each topology has its own set of advantages and disadvantages. Many installations (especially those with additions) are a "hybrid" of more than one of the basic topologies. The critical thing is to ensure that all jacks have continuity to the NID after you finish your wiring. There are three basic topologies:

Star Topology - Separate cable to each jack (also known as "home runs")
Ring Topology - All jacks on one cable that forms a "loop" with both "ends" connected at the NID
Bus Topology - All jacks on one cable that starts at the NID and terminates at the last jack location

Notes on "Floor Plan" Diagrams shown below: These diagrams are intended to represent the possible routing path of cable in the attic or basement of a hypothetical house. The cable path actually used is dependent upon the actual structure and on how and when the house was wired. Different colors are used in the diagrams to help show how the cable is routed from one location to another.

Star Topology

A star topology may be the easiest to understand. Star topology uses a separate cable to each jack. All of the cables are routed to one central location, normally in an attic, basement, garage, or other well protected but accessible location near the center of the house. If there are only a limited number of jacks required, the NID can be used as the central "hub" of the "star". Using the NID as the "hub" becomes too physically complicated if very many jacks are required. More normally, the NID is connected by a separate cable to a junction block which serves as the central "hub". If you are lucky enough to have a "pure" star topology with your current installation, Iwould encourage you to attempt to preserve it.

Star Topology Advantages

Easy to add a jack without changing to a "hybrid" the topology as long as a physical path can be identified for routing cable from the new jack location to the central "hub".
Easy to troubleshoot if wiring problems arise.
A cut or broken wire going to one jack will not normally cause problems at other jack locations.
Easiest to convert to three or more line installation.
Easiest to convert to "future" technology such as ISDN or key systems.

Star Topology Disadvantages

Initial installation may use more cable than other topologies.
Central "hub" and its connections are potential failure points if not properly installed. Fortunately, there are devices available to do this correctly.

Ring Topology

In a ring topology, all jacks are on one cable that forms a "loop", routed through the house from one jack to the next, with both "ends" connected at the NID. Each jack is connected similar to the diagram at the left. The cable comes to a jack, the sheath is removed to connect the wires to the jack, and the cable goes on to the next jack. Or the cable may in fact be cut and the wires from both sides of the cut connected to the jack. This method of wiring is often confusing to the novice, because it appears that there are two cables going to every jack.

Ring Topology Advantages

Each jack has two paths to the NID, so one cut or broken wire will not normally cause a loss of service at any jack.
Initial installation may use less cable than star topology.

Ring Topology Disadvantages

Difficult to reconfigure without changing to a "hybrid" topology.
Multiple junctions required to expand and maintain topology are potential failure points if not properly installed.
Initial installation probably uses more cable than bus topology.
May be more difficult to troubleshoot if wiring problems arise.
Difficult to convert to three or more line installation.

Bus Topology

In a bus topology, all jacks are on one cable that starts at the NID and is routed through the house from one jack to the next and terminates at the last desired jack location. All of the jacks (except the last one, which is connected at the end of the cable) are connected in the same manner as in a ring topology. This topology is probably the most prevalent in existing homes that were pre-wired during construction.

Bus Topology Advantages

Initial installation may use less cable than other topologies.
Easy to troubleshoot if wiring problems arise.
Little reason to be concerned about converting to a "hybrid" topology.
- Bus topology provides no significant advantage over a "hybrid".
- Attempting to extend from the "last" jack would probably require more cable than changing to "hybrid".

Bus Topology Disadvantages

A cut or broken wire will cause loss of service at all jacks past the break.
Difficult to convert to three or more line installation.
Adding to existing installation almost always results in a "hybrid" topology - see disadvantages of "hybrid".

Hybrid Topology

Hybrid topologies normally were initially installed as one of the basic topologies and are the result of additions. If your existing cables are a pure star topology, attempt to preserve it. If your existing cables are a ring or bus topology, you may have little choice but to convert to a hybrid. Make sure you document changes that you make for future reference when you need to add more jacks or have wiring problems.

Hybrid From Original Ring - In Wall View

Hybrid Topology Advantage

Just one - it's easy to add more jacks for one or two lines.

Hybrid Topology Disadvantage

Definitely more difficult to troubleshoot if wiring problems arise.
Impact (and location) of a cut or broken wire is difficult to determine. May cause loss of service at some or all jacks or could result in no loss of service depending on the original topology and where the break occurs.
Multiple junctions are potential failure points if not properly installed.
Very difficult to convert to three or more line installation.
Very difficult to convert to "future" technology such as ISDN or key systems.

Splices, Taps, and Junction Blocks

While trying to figure out how your existing cable is routed, be sure to identify existing splices, taps, and junction blocks. They will help you figure out the existing layout. Plan for your expansion to use or replace existing splices and taps where possible. By limiting the number of splice and tap locations, you limit the number of potential failure points. If you have wiring problems, the splices and taps are the first place to look for broken wires.

Spices and taps can be done easily using "Scotch-Lok" type crimp splice connectors or using junction blocks. To do an expansion such as shown here you'll use a bunch of crimp connectors. The additions shown for the ring or bus topologies would use 24 splice connectors. The hybrids shown would use 20 tap connectors. And you'll probably need a few extras for "the learning process"!
Junction blocks come is a wide range of shapes, sizes, and configurations. The most common junction blocks found in residential installations look similar to a surface mount screw terminal jack. Trying to use a screw terminal type junction block for the hub of a star topology leads to an unmanageable tangle of cables and is a significant potential failure point. But, screw terminal junction blocks are suitable for creating splices and taps inother topologies. Just connect wires on the screw terminal according to color. In fact, a screw terminal jack can serve dual purpose by also being used as a junction block. Just connect the wires for your new cable to the matching screw terminals and route the cable to the location for the new jack.
For a star topology, the best option is to mount a "66-block" or "110-block"and terminate each cable on it separately. "Jumper wire" is then used to make cross connects at your hub from the cable coming from the NID to the cables going to the jacks. The jumper wire can be replaced to change how the cables are connected, without having to actually change the cable connections. This greatly reduces the potential for problems caused by broken wires in the cables. More information about blocks is available at: Wiring Block Techniques and Tips.