Packet over SONET/SDH, abbreviated POS, is communications protocol for transmitting packets over SDH or SONET, which are both circuit switched protocols.

Applications of POS

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The most important application of POS is to support the sending of IP packets across Wide Area Networks. Much of the traffic on the Internet is carried over POS links.

POS is also one of the link layers used by the IEEE 802.17 Resilient Packet Ring standard.

History of POS

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Cisco was involved in making POS an important Wide Area Network protocol. PMC-Sierra produced an important series of early semiconductor devices which implemented POS.

Details about the name "POS"

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POS is a double nested acronym as the S in POS stands for "SONET/SDH", which itself stands for "Synchronous Optical Network/Synchronous Digital Hierarchy".

Complementary Interfaces

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The System Packet Interface series of standards from the Optical Internetworking Forum including SPI-4.2 and SPI-3 and their predecessors PL-4 and PL-3 are commonly used as the interface between packet processing devices and framer devices that implement POS. The acronym PL-4 means POS-PHY Layer 4.

External links

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• Cisco's Packet over SONET/SDH (POS) Technology Support Whitepaper (Obsolete)

Network protocols