PME Aggregation Function (PAF) is a

computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...

ing mechanism defined in Clause 61 of the

IEEE 802.3 IEEE 802.3 is a working group and a collection 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 Institute of Electrical and Electronics Eng ...

standard, which allows one or more Physical Medium Entities (PMEs) to be combined to form a single logical

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...

link. The PAF is located in the Physical Coding Sublayer (PCS), between the Media Access Control (MAC)-

PHY PHY is an abbreviation for the physical layer of the OSI model and refers to the circuitry required to implement physical layer functions. PHY or Phy may also refer to: * Phy, the drug methadone * Phetchabun Airport (IATA code), Thailand See al ...

Rate Matching function and the Transmission Convergence (TC) sublayer. It interfaces with the PMEs across the λ-interface, and to the MAC-PHY Rate Matching function using an abstract interface. PAF is an optional function which was defined before 2007 for two IEEE 802.3 interfaces:

2BASE-TL Ethernet in the first mile (EFM) refers to using one of the Ethernet family of computer network technologies between a telecommunications company and a customer's premises. From the customer's point of view, it is their first mile, although from th ...

and

10PASS-TS Ethernet in the first mile (EFM) refers to using one of the Ethernet family of computer network technologies between a telecommunications company and a customer's premises. From the customer's point of view, it is their first mile, although from th ...

, both of which were Ethernet in the First Mile (EFM) copper physical layers.

Details

PME Aggregation function has the following characteristics: * Supports aggregation of up to 32 PMEs * Supports individual PMEs having different data rates (max 1:4 ratio) * Ensures low packet latency and preserves frame order * Scalable and resilient to PME failure * Independent of type of EFM copper PHY * Allows vendor discretionary algorithms for fragmentation PAF ''Transmit'' function works by fragmenting incoming Ethernet frames into a number of fragments, limited in size to a range between 64 and 512 Bytes. A sequential fragmentation header is prepended to each fragment, indicating if the fragment is from the start-of-packet, end-of-packet or middle of packet. A

frame check sequence A frame check sequence (FCS) is an error-detecting code added to a frame in a communication protocol. Frames are used to send payload data from a source to a destination. Purpose All frames and the bits, bytes, and fields contained within ...

(FCS) is appended to each fragment, which is then transmitted by the next available active PME in the aggregated group. The following diagram illustrates the PAF fragmentation: EFM PME Aggregation Function

PAF ''Receive'' function reassembles the original frames from the received fragments, which are buffered in a per-MAC fragment buffer. The algorithm uses the fragmentation header to make sure that the reassembled frames are in order.

History

The PME Aggregation function was first defined in IEEE

802.3ah Ethernet in the first mile (EFM) refers to using one of the Ethernet family of computer network technologies between a telecommunications company and a customer's premises. From the customer's point of view, it is their first mile, although from th ...

in 2004. The original Loop Aggregation proposal was submitted by Klaus Fosmark from now defunct First Mile Systems in 2001.http://www.ieee802.org/3/efm/public/nov01/fosmark_1_1101.pdf It was later referenced by

ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...

G.998.2 (Ethernet-based multi-pair bonding) and its ANSI equivalent NIPP-NAI T1.427.02.

Comparison

PAF algorithm and fragmentation header are very similar to MLPPP which works at layer 3 (IP). PAF is an asymmetric protocol, i.e., all information required for reassembly is contained in the fragmentation header sent with each fragment. While allowing great flexibility in Transmitter and Receiver implementations it requires an overhead consuming about 5% of the bandwidth (estimation for 2BASE-TL protocol, including 64B/65B encapsulation). PAF is optimized for the Ethernet traffic. Inverse Multiplexing for ATM (IMA) is another aggregation protocol, which unlike PAF uses fixed-size cells, sending them across multiple links in a Round-Robin fashion. IMA is optimized for ATM and in the extreme cases (short Ethernet frames) may add as much as 40% overhead due to the

AAL5 ATM Adaptation Layer 5 (AAL5) is an ATM adaptation layer used to send variable-length Packet (information technology), packets up to 65,535 Octet (computing), octets in size across an Asynchronous Transfer Mode (ATM) network. Unlike most network ...

encapsulation. ITU-T G.998.3 (Multi-pair bonding using time-division inverse multiplexing) specification, a.k.a. G.Bond/TDIM, defines a symmetric aggregation protocol, in which both sides of a point-to-point link exchange information about the aggregation, so there's no need for a separate header. G.Bond/TDIM is optimized for both

Time-Division Multiplexing Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fracti ...

and packet traffic with less than 3% overhead (estimation for Ethernet traffic, including Generic Framing Procedure (GFP) encapsulation).

References

{{Reflist

External links

Get IEEE 802.3
- "IEEE Standard for Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications", IEEE Std 802.3-2008, November 2008.
IEEE 802.3ah
- Ethernet in the First Mile Task Force archive Bonding protocols Ethernet Network protocols Physical layer protocols

Details

History

Comparison

See also

References

External links