Fundamentals of Networking
Analog and Digital Comparison Paper
T(X) & synchronous optical network (SONET) digital hierarchy
There are currently two infrastructure types that are in use today. The first being Plesiochronous Digital Hierarchy (PDH), which was built on the three transmission standards identified as T-carrier (North America), E- carrier (Europe), and J-carrier (Japan). These transmission standards are commonly referred to as (T-X) for North American, (E-X) for European and (J-E) for Japanese, while the second transmission being Synchronous Digital Hierarchy (SDH) or Synchronous Optical Network (SONET) (Telecom and Network Speeds website, 2011). The T-carrier digital hierarchy is comprised of five digital signal levels. The five signal levels are T-0, T-1, T-2, T-3, and T-4. T-0 represents one channel with a transmission rate at 64Kbps which is commonly used for one voice circuit as illustrated in Figure 1.
(Higgins International, 2005)
Figure 1. T-Carrier Hierarchy
The “DS” notation describes the multiplexing scheme that specifies speed, data format and various other features, whereas the “T” notation describes the physical implementation of the DS-x multiplexing scheme in a wire or cable. An example, T-0 is the cable connection that would carry a DS-0 data stream. A couple of important things to keep in mind when dealing with PDH, first, each point must be accounted for where the circuit is multiplexed. The PDH hierarchy does not allow a T-0 to a T-3 line. In order for this to occur, T-0 must pass through T-1 before jumping to a T-2 line. The reason is that the signals at each level are multiplexed differently. The same requirement goes for the opposite. A T-2 line must pass through a T-1 line before jumping to a T-0 line. The hypothetical scenario aforementioned could lead to costly equipment and installation due to the complexity for a business if they decide to go that route....