624  Chapter 12  ■  Secure Communications and Network Attacks

Fiber-Optic Links

Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) are fiber-optic high-speed networking standards. SDH was standardized by the International Telecommunications Union (ITU) and SONET by the American National Standards Institute (ANSI). SDH and SONET are mostly hardware or physical layer standards defining infrastructure and line speed requirements. SDH and SONET use synchronous time-division multiplexing (TDM) to high-speed duplex communications with minimal need for control and management overhead.

These two standards have only slight variations and use the same hierarchy of bandwidth levels. The transmission service supports a foundational level of speed of 51.48 Mbps, which supports the Synchronous Transport Signals (STS) of SONET and/or the Synchronous Transport Modules (STM) of SDH. The term Optical Carrier (OC) can also be substituted for STS. The main bandwidth levels of SDH and SONET are shown in Table 12.3.

Note:The SDH service numbers are 1/3 that of SONET’s.

SDH and SONET both support mesh and ring topologies. These fiber solutions are often implemented as the backbone of a telco service and divisions or fractions of the capacity are subscribed out to customers.

Security Control Characteristics

When you’re selecting or deploying security controls for network communications, you need to evaluate numerous characteristics in light of your circumstances, capabilities, and security policy. Key characteristics are the protection of confidentiality and integrity. Since those