Packet-over-SONET is a high-speed method of transporting IP traffic between two points. This
technology combines the Point-to-Point Protocol (PPP) with Synchronous Optical Network (SONET)
and Synchronous Digital Hierarchy (SDH) interfaces.
SONET is an octet-synchronous multiplex scheme defined by the American National Standards Institute
(ANSI) standard (T1.1051988) for optical digital transmission at hierarchical rates from 51.840 Mbps
to 2.5 Gbps (Synchronous Transport Signal, STS-1 to STS-48) and greater. SDH is an equivalent
international standard for optical digital transmission at hierarchical rates from 155.520 Mbps
(Synchronous Transfer Mode-1 [STM-1]) to 2.5 Gbps (STM-16) and greater.
SONET specifications have been defined for single-mode fiber and multimode fiber. The POS SPAs on
the Cisco 7600 series router allow transmission over both single-mode and multimode fiber at various
optical carrier rates.
SONET/SDH transmission rates are integral multiples of 51.840 Mbps. The following transmission
multiples are currently specified and used on the POS SPAs on the Cisco 7600 series router:
• OC-3c/STM-1—155.520 Mbps
• OC-12c/STM-4—622.080 Mbps
• OC-48—2.488 Gbps
• OC-192c/STM-64—9.953 Gbps