155.52 150.336 STS-9 STM-3 466.56 451.008 OC-12 STS-12 STM-4 622.08 601.344 OC-18 STS-18 STM-6 933.12 902.016 OC-24 STS-24 STM-8 1,244.16 1,202.688 OC-36 STS-36 STM-12 1,866.00 1,804.032 OC-48 STS-48 STM-16 2,488.32 2,405.376 OC-96 STS-96 STM-32 4,876.64 4,810.752 OC-192 STS-192 STM-64 9,953.28 9,621.504 OC-768 STS-768 STM-256 39,813.12 1,327.104 Transport Signal (STS), and in SDH, the frame is called the Synchronous Transport Module (STM). Two types of rates are important in the realm of SDH/SONET: The payload rate refers to the capacity available to carry customer content, and the data rate refers to the total capacity available for customer content as well as network management information. Table 4.3 shows the SDH/SONET signal hierarchy. You don't have to memorize all these levels, but you'll consistently encounter four or five of them in your read- ings that you should commit to memory. The following are the levels of the SDH/ SONET signal hierarchy that you need to be familiar with: OC-1-OC-1 offers about 51 Mbps and is generally used as customer access lines. Early-adopter types of customers-such as universities, airports, financial institutions, large government agencies, and ISPs-use OC-1. OC-3-OC-3 provides about 155Mbps. End users such as companies in the aerospace industry and high-tier ISPs need this extensive level. The Transport Network Infrastructure OC-12-OC-12 provides about 622Mbps. It is another capacity toward which high-tier ISPs are moving. It was originally deployed for the metro- politan area fiber rings built out across cities worldwide, although those rings are now moving to OC-48. OC-48-OC-48 offers about 2.5Gbps. This capacity has been deployed for backbone, or core, networks. Today the metropolitan area rings are moving from OC-12 to OC-48, and the backbone links are moving from OC-48 to OC-192. OC-192-OC-192 supports about 10Gbps and is being used for backbone networks. Although there are more levels in the SDH/SONET signal hierarchy, the ones discussed here are the ones for which eq