{{about, PL-4, a networking protocol, the PRC missile PL-4, PL-4 (missile) PL-4 or POS-PHY Level 4 was the name of the interface that the interface SPI-4.2 is based on. It was proposed by

PMC-Sierra PMC-Sierra was a global fabless semiconductor company with offices worldwide that developed and sold semiconductor devices into the storage, communications, optical networking, printing, and embedded computing marketplaces. On January 15, 2016 ...

to the

Optical Internetworking Forum The Optical Internetworking Forum (OIF) is a prominent non-profit consortium that was founded in 1998. It promotes the development and deployment of interoperable computer networking products and services through implementation agreements (IAs) f ...

. The name means Packet Over SONET Physical layer level 4. PL-4 was developed by PMC-Sierra in conjunction with the Saturn Development Group.

Context

There are two broad categories of chip-to-chip interfaces. The first, exemplified by PCI-Express and

HyperTransport HyperTransport (HT), formerly known as Lightning Data Transport, is a technology for interconnection of computer Processor (computing), processors. It is a bidirectional Serial communication, serial/Parallel communication, parallel high-Bandwi ...

, supports reads and writes of memory addresses. The second broad category carries user packets over 1 or more channels and is exemplified by the

IEEE 802.3 IEEE 802.3 is a working group and a collection of standards defining the physical layer and data link layer's media access control (MAC) of wired Ethernet. The standards are produced by the working group of the Institute of Electrical and Electro ...

family of

Media Independent Interface The media-independent interface (MII) was originally defined as a standard interface to connect a Fast Ethernet (i.e., ) medium access control (MAC) block to a PHY chip. The MII is standardized by IEEE 802.3u and connects different types of ...

s and the Optical Internetworking Forum family of

System Packet Interface The System Packet Interface (SPI) family of Interoperability Agreements from the Optical Internetworking Forum specify chip-to-chip, channelized, packet interfaces commonly used in synchronous optical networking and Ethernet applications. A typical ...

s. Of these last two, the family of System Packet Interfaces is optimized to carry user packets from many channels. The family of System Packet Interfaces is the most important packet-oriented, chip-to-chip interface family used between devices in the

Packet over SONET Packet over SONET/SDH, abbreviated POS, is a communications protocol for transmitting packets in the form of the Point to Point Protocol (PPP) over SDH or SONET, which are both standard protocols for communicating digital information using la ...

and Optical Transport Network, which are the principal protocols used to carry the internet between cities.

Applications

PL-4 was designed to be used in systems that support

OC-192 Optical Carrier transmission rates are a standardized set of specifications of transmission bandwidth for digital signals that can be carried on Synchronous Optical Networking (SONET) fiber optic networks. Transmission rates are defined by rate o ...

SONET interfaces and is sometimes used in

10 Gigabit Ethernet 10 Gigabit Ethernet (abbreviated 10GE, 10GbE, or 10 GigE) is a group of computer networking technologies for transmitting Ethernet frames at a rate of 10 gigabits per second. It was first defined by the IEEE 802.3ae-2002 standard. Unlik ...

based systems. A typical application of PL-4 (SPI-4.2) is to connect a framer device to a network processor. It has been widely adopted by the high speed networking marketplace.

Technical details

The interface consists of (per direction): * sixteen LVDS pairs for the data path * one LVDS pair for control * one LVDS pair for clock at half of the data rate * two FIFO status lines running at 1/8 of the data rate * one status clock The clocking is Source-synchronous and operates around 700 MHz. Implementations of SPI-4.2 (PL-4) have been produced which allow somewhat higher clock rates. This is important when overhead bytes are added to incoming packets.

Trivia

The name is an

acronym An acronym is a type of abbreviation consisting of a phrase whose only pronounced elements are the initial letters or initial sounds of words inside that phrase. Acronyms are often spelled with the initial Letter (alphabet), letter of each wor ...

of an acronym of an acronym as the P in PL stands for POS-PHY and the S in POS-PHY stands for SONET ( Synchronous Optical Network).

History

PL-4 is a descendant of PL-3 which itself is a descendant of the ATM Forum UTOPIA family of standards. The UTOPIA standards were developed by the SATURN Development Group for use in ATM systems.

External links