Packet over SONET (PoS) technology efficiently transports data over SONET/SDH. PoS is a flexible solution that can be used to enable a variety of transport applications. For example, some transport applications include network backbone infrastructure and data aggregation or distribution on the network edge and in the metropolitan area. Router PoS interfaces are frequently connected to add drop multiplexers (ADMs), terminating point-to-point SONET/SDH links. Direct connections over dark fiber or via dense wave-division multiplexing (DWDM) systems are also becoming increasingly popular.
PoS line cards are popular Cisco gigabit switch routers (GSRs). Other Cisco products such as the Cisco 7500 and 7200 series routers also feature PoS interfaces. The Catalyst 6500 and 8500 series enterprise switches are potential candidates for PoS interfaces in the future.
Cisco currently deploys the ONS 15190 IP Transport and the GSR 12000 Series router for PoS applications.
The current Internet Engineering Task Force (IETF) PoS specification is RFC 2615 (PPP over SONET), which makes RFC 1619 obsolete. PoS provides a method for efficiently carrying data packets in SONET/SDH frames. High-bandwidth capacity, coupled with efficient link utilization, makes PoS the preference for the core layer of data network topologies. PoS overhead, which averages about 3 percent, is significantly lower than the 15 percent average for the ATM cell tax.
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