Autonegotiation

Auto-negotiation or auto -sensing is a procedure that the two connected Ethernet network ports (eg the network ports of a computer and as the router, hub or switch, with which it is connected, for example ) allows the maximum independent possible transmission speed and duplex mode to negotiate with each other and configure. This method is applicable only for multi-wire connections ( twisted pair cable) - but not for wireless, fiber optic or coaxial cable.

Ethernet

Autonegotiation the Ethernet (also called NWay ) works on layer 1 of the OSI model and is defined in the IEEE 802.3u standard.

Nway or N -way auto-negotiation is an older term for telecommunications. It was developed in 1994 by the company National Semiconductor to eliminate caused by the launch of Fast Ethernet/100BaseT ( 100Mbit / s) devices to incompatibilities with the formerly standard 10BaseT ( 10 Mbit / s).

Unlike the two slower versions in which a fixed configuration of speed and duplex mode was provided for Gigabit Ethernet ( 1000BaseT ) is the implementation of the mandatory auto-negotiation. Problems caused by misconfiguration, which are often the cause of poor performance in Ethernet networks, are reduced.

Link Pulse

With Ethernet over copper cable ( twisted pair cable) the collection of network nodes that are connected to active network components ( such as a hub or switch), is via voltage pulses, so-called link pulse. In 10-Mbit/s-Netzen this is realized by the NLP ( Normal Link Pulse), a periodically every 16 / - 8 ms pulse occurring.

In 100/1000 Mbit / s networks ( Fast / Gigabit Ethernet) NLP is replaced by a Fast Ethernet pulse, Fast Link Pulse ( FLP). This FLP is also sent out all 16 / -8 ms, which ensures compatibility with older network cards. These treat the FLP as a NLP and determine the existence of a connection without being able to evaluate the encoded information in the FLP.

Autonegotiation is based on pulses as they are similar to used by 10BASE- T participants in order to examine the presence of other participants. These pulses are every 16 ms (with a tolerance of 8 ms) emitted when no traffic is detected. The pulses are positive unipolar and 100 ns long. They are called in the 10BASE- T link integrity test also terminology (LIT ) pulses in the autonegotiation specification normal link pulses (NLP )

A participant detects a link failure, when 50 to 150 ms neither traffic still takes place, a pulse is detected. A receiver acknowledges a valid link with two consecutive LIT pulses.

Autonegotiation uses similar pulses. They are also positive unipolar and have a duration of 100 ns, but each is replaced by a sequence of 33 pulses. Each sequence is called fastlink pulse (FLP ) burst. The time interval between each burst is the same as between NLPs, 16 ms / - 8 ms.

Link Code Word

The 17 " odd " Pulse of an FLP bursts represent a clock signal, the 16 straight pulses contain data information. A FLC burst is therefore composed of a frame of 17 pulses with an interval of 125 microseconds. In the middle of two pulses of the frame, a further pulse to be provided, which corresponds to a logic "1", or it may be absent for a logical "0". This creates a logical word is 16 bits, which is called link code word ( LCW ). Bit 0 is the first bit and the last bit 15.

An FLP burst can not be recognized as an NLP and a 10BASE - T participants will interpret the burst as a link error.

FLP consists of clock pulses each followed by data pulses (33 pulses), which is a 16- bit data word is transmitted. If after the clock pulse does not follow any logic 0 corresponds to a value in a subsequent pulse occurs one cell value of 1

The 16 -bit data word ( LCW ) has in its basic form as the base Link Code Word defined as follows:

D0 ... D4 S0 .... S4 Selector Field ( 00001 IEEE 802.3, 00010 for IEEE 802.9 ) D5 ... D12 A0 .... A7 Technology Ability Field ( defines the possible modes of transmission of the network interface ) The following types are defined: D5 A0 10BASE- TD6 A1 10BASE T Full DuplexD7 A2 100BASE- TXD8 A3 100BASE -TX Full DuplexD9 A4 100BASE- T4D10 A5 PAUSED11 A6 asymmetric PAUSE for full-duplex VerbindungenD12 A7 reserviertD13 RF: remote fault (fault indicator) D14 AK: acknowledge (acknowledgment of a data packet ) D15 NP: Next Page (there are more data packets with manufacturer-specific data ) Base Link Code Word Definition

Both receivers of the data transmission give the Technology Ability Field their skills known and some for both parameters to best match each ( full duplex before half-duplex and high speed before lower). A receiver must receive identical times before accepting it and by setting the ACK bits in turn confirmed or acknowledged to " 1" LCW three. If the receiver detects an error or an incompatibility as it sets the RF bit to " 1". After a successful autonegotiation a LCW must wherein the RF bit to " 0" and the ACK bit is set to "1 " must be sent at least six times to complete the process.

Thus ( a Gigabit Ethernet connection) can, however, for example 1000BaseT not yet set. This is the transmission of further information in a more "word" required since the importance of the base LCWs not sufficiently expandable to permit also this configuration. For this purpose, the Next Page bit in the LCW to " 1", whereupon the next received " Word ", as well as one or more of the following unformatted "pages" to interpret differently, or to decode - namely as so-called Message page (MP) IEEE Standard 802.3, Annex 28C.

The negotiation of the transmission mode is done on both sides used to establish a priority list for the maximum possible performance:

1 (highest ) 1000BaseT - full duplex 2 1000BaseT - Half duplex 3 100BaseT2 - full duplex 4 100BaseTX - full duplex 5 100BaseT2 - Half duplex 6 100BaseT4 7 100BaseTX - Half duplex 8 10BaseT - full duplex 9 (lowest ) 10BaseT - Half duplex If there is a remote site is not in auto-negotiation mode ( disabled or not supported), the another remote location can determine the transmission speed via parallel detection. A determination of the duplex mode is not possible; thus the half-duplex mode is always selected. The other party without autonegotiation must in this case to half- duplex be set, otherwise the result is a duplex mismatch ( a page full-duplex, the other side half - duplex). Typical effect of this is indeed working, but very slow connection.

Fibre Channel

Fibre Channel ports with auto-negotiation can detect the transmission speed.

• Network protocol