Auto negotiation in IEEE 802.3 based layer 2 devices: A review

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Auto negotiation in IEEE 802.3 based layer 2 devices: A review

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Abstract

Auto Negotiation is an optional yet one of the standard Plug and Play features available in almost all modern day IEEE 802.3u (Fast Ethernet) and as a mandatory feature in IEEE 802.3ab Gigabit Ethernet compliant devices. Today's Fast Ethernet devices support multiple operational modes. The Auto Negotiation protocol enables any two such devices to negotiate upon the best possible operational mode automatically. Along with an overview of the architecture and working of the Auto Negotiation arbitration protocol, typical scenarios as well as certain precautions to be taken are discussed in this paper. Applicability of this standard to fiber optic based systems, Gigabit Ethernet and IEEE 802.11
wireless networks is also discussed.

Keywords: Auto Negotiation, Auto Sensing, NWay, Parallel Detection, FLP, NLP, LCW

Introduction
The auto-negotiation standard
The arbitration control
Recent developments
Conclusion
References

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[...] LCW is a 16 bit entity containing the necessary management information that is exchanged during Auto Negotiation process. This information is represented as data pulses and encoded within FLP as shown in the fig. LCW bits directly map to the data pulses in FLP. LCW is also called as Page or FLP Burst. During Auto Negotiation a series of such LCW are transmitted by the devices supporting Auto Negotiation through FLP. The embedding of LCW in FLP is as shown in Fig FLP is just a train of NLP pulses. [...]

[...] CONCLUSION Auto Negotiation is a very useful plug and play feature for twisted pair copper based IEEE 802.3 layer two devices. It enables the link partners to negotiate their capabilities thus mitigating the risk involved in possible incompatibility of speeds and modes of operation. Moreover it makes upgrade to higher speeds/modes very easy because of plug and play nature. Also the negotiation is based upon the best possible performance and hence bandwidth efficiency is also preserved. This negotiation is automatic thus eliminating the need for manual intervention in the negotiation [...]

[...] The format of the base page is shown in Fig SELECTOR FIELD This is a 5 bit field indicating the type of IEEE 802.x system in question. Eg. The bit pattern 00001 corresponds to IEEE 802.3 Ethernet. Refer to Fig.3 & 4 for details. TECHNOLOGY ABILITY FIELD The technology ability field , which is encoded in bits D5 through D12 of the FLP burst, is shown for the IEEE 802.3 Base Page as defined in the Selector field (00001) for IEEE 802.3 Ethernet. [...]

[...] 5.2 AUTO NEGOTIATION PRIORITY RESOLUTION As mentioned in Fig item no has highest priority and item no has lowest priority.[4] This means that higher preference is given to full duplex mode and 1000 Mbps speed. This means that if both devices can support 100 BASE TX and 10 BASE T then higher preference will be given to 100 BASE TX SPECIAL CASES 6.1 INCOMPATIBLE TYPES ON BOTH ENDS: Suppose one of the link partners is a 100 BASE T4 device and the other end is a100 BASE TX device. [...]

[...] APPLICABLE DEVICES Auto Negotiation is normally applicable for IEEE 802.3 u/IEEE 802.3 ab compliant devices like network adapters, LOM (Lan On Motherboard), Layer 2 switches, bridges, etc.[5] Hubs normally support 10 Mbps only and are NOT autonegotiation enabled ARCHITECTURE The Auto Negotiation architecture consists of the following: Auto Negotiation Protocol in OSI Stack Signaling LCW (Link Code Word) or Page format 4.1 AUTO NEGOTIATION IN OSI STACK Auto Negotiation is implemented in the physical layer of transceiver as per the OSI model. [...]

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