Packet over SONET/SDH, abbreviated POS, is a

communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synch ...

for transmitting packets in the form of the Point to Point Protocol (PPP) over

SDH SDH may refer to: Science, medicine and technology * Serine dehydratase, an enzyme * L-sorbose 1-dehydrogenase, an enzyme * Succinate dehydrogenase, an enzyme * Shubnikov–de Haas effect * Social Determinants of Health, economic and social condit ...

SONET Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diode ...

, which are both standard protocols for communicating digital information using lasers or light emitting diodes (LEDs) over optical fibre at high line rates. POS is defined by RFC 2615 as PPP over SONET/SDH. PPP is the Point to Point Protocol that was designed as a standard method of communicating over point-to-point links. Since SONET/SDH uses point-to-point circuits, PPP is well suited for use over these links.

Scrambling Scrambling is a mountaineering term for ascending steep terrain using one's hands to assist in holds and balance.''New Oxford American Dictionary''. It is also used to describe terrain that falls between hiking and rock climbing (as a “scrambl ...

is performed during insertion of the PPP packets into the SONET/SDH frame to solve various security attacks including

denial-of-service attack In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host conne ...

s and the imitation of SONET/SDH alarms. This modification was justified as cost-effective because the scrambling algorithm was already used by the standard used to transport ATM cells over SONET/SDH. However, scrambling can optionally be disabled to allow a node to be compatible with another node that uses the now obsoleted RFC 1619 version of Packet over SONET/SDH which lacks the scrambler.

Applications of POS

The most important application of POS is to support sending of IP packets across

wide area network A wide area network (WAN) is a telecommunications network that extends over a large geographic area. Wide area networks are often established with leased telecommunication circuits. Businesses, as well as schools and government entities, u ...

s. Large amounts of traffic on the

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, p ...

are carried over POS links. POS is also one of the link layers used by the Resilient Packet Ring standard known as

IEEE The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operati ...

802.17.

History of POS

Cisco Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...

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"

POS (packet over SONET) is a double-nested abbreviation. The S represents "SONET/SDH", which itself stands for "Synchronous Optical Network/Synchronous Digital Hierarchy". Given this information, POS technically stands for "Packet over Synchronous Optical Network/Synchronous Digital Hierarchy".

Complementary Interfaces

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.

Applications of POS

History of POS

Details about the name "POS"

Complementary Interfaces

See also