- What are SONET and T1
- The Development of SONET
- Role of ANSI and Key Standards documents
- The Network and Services Integration Forum (NSIF)
- SONET and T1
- Features of SONET and T1
- Synchronous Networks
- SONET Timing
- Payloads and Envelopes
- Optical Fiber—The Bedrock for SONET
- Typical SONET Topology
- Present Transport Systems and SONET
- Clarification of Terms
SONET and T1
While the primary focus of this book is on SONET, we devote considerable coverage to T1 technology. With this in mind, we will use this section to introduce T1 and compare the T1 and SONET technologies.
Comparison of SONET and T1
Figure 11 shows the placement of T1 and SONET in a communications network. Currently, several configurations exist in commercial systems. SONET may operate end-to-end or it may act as the transport system within the network carrying T1 traffic through the network between customer premises equipment (CPEs). Of course, in some networks SONET has not been implemented so T1/T3 may operate within the network. Another widely used placement is the installation of fractional T1 (FT1) at the CPE switch, which then multiplexes user payloads into a T1 or T3 transport frame. As you can see from Figure 11, SONET can operate end-to-end or can function as a backbone technology, operating within the network.
Figure 11 T1 and SONET.
Figure 12 shows the relationship of the Open System Interconnection Model (OSI) layers to the layers of T1 and SONET. The first observation is that T1 and SONET operate at the physical layer of the OSI Model. As such, they are concerned with the physical generation of the signals at a transmitting machine and their correct reception and detection at a receiving machine. While this statement may imply that these technologies are rather simple, we shall see that the opposite is true, especially regarding SONET.
Figure 12 Comparison of the layers in regard to OSI.
The layers operating above the physical layer are quite varied. Some products run the Internet protocols in these layers, others run SS7, still others run vendor-specific protocols, such as IBM's Systems Network Architecture (SNA). Later chapters explore the relationships of these layers and SONET.