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Backward Compatible or Not?

Backward Compatible or Not?. Date: 2008-07-07. Authors:. Abstract. This contribution discusses the backward compatibility issues of the IEEE 802.11 VHT works. VHT below 6 GHz PAR from 0716r0. 5.2 Scope of Proposed Standard:

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Backward Compatible or Not?

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  1. Backward Compatible or Not? Date: 2008-07-07 Authors: Junghoon Jee, ETRI

  2. Abstract This contribution discusses the backward compatibility issues of the IEEE 802.11 VHT works. Junghoon Jee, ETRI

  3. VHT below 6 GHz PAR from 0716r0 5.2 Scope of Proposed Standard: The scope of this project is to define an amendment that shall define standardized modifications to both the 802.11 physical layers (PHY) and the 802.11 Medium Access Control Layer (MAC) so that modes of operation can be enabled that are capable of supporting: o A maximum multi-STA throughput (measured at the MAC data service access point), of at least 1Gbps and a maximum single link throughput (measured at the MAC data service access point), of at least 500Mbps. o Below 6GHz carrier frequency operation excluding 2.4GHz operation andensuring backward compatibility and coexistence with legacy IEEE802.11a/n devices in the 5GHz unlicensed band. Junghoon Jee, ETRI

  4. VHT below 6 GHz 5C from 0609r3 17.5.2 Compatibility Compatibility with IEEE 802 requirements will be accomplished by keeping the MAC SAP interface the sameas the existing 802.11 standard. The proposed amendment shall introduce no 802.1 architectural changes. The MAC SAP definition shall not be altered, ensuring that all LLC and MAC interfaces are compatible to and in conformance with the IEEE 802.1 Architecture, Management and Internetworking standards. New managed objects shall be defined as necessary in a format and structure consistent with existing 802.11 managed objects. Backward compatibility and coexistence with legacy devices will be granted for the 5GHz bands. Junghoon Jee, ETRI

  5. VHT 60 GHz PAR from 0715r0 5.2 Scope of Proposed Standard: The scope of this project is to define an amendment that shall define standardized modifications to both the 802.11 physical layers (PHY) and the 802.11 Medium Access Control Layer (MAC) to enable operation in the 60 GHz frequency band (typically 57-66 GHz) capable of very high throughput. The MAC and PHY specified in this amendment: • Enable a maximum throughput of at least 1 Gbps, as measured at the MAC data service access point (SAP) • Enable fast session transfer between PHYs • Maintain the 802.11 user experience • Address coexistence with other systems in the band Junghoon Jee, ETRI

  6. VHT 60 GHz 5C from 0223r5 17.5.2 Compatibility Compatibility with IEEE 802 requirements will result from keeping the MAC SAP interface the same as for the existing 802.11 standard. The proposed amendment shall introduce no 802.1 architectural changes. The MAC SAP definition shall not be altered, ensuring that all LLC and MAC interfaces are compatible to and in conformance with the IEEE 802.1 Architecture, Management and Internetworking standards. New managed objects shall be defined as necessary in a format and structure consistent with existing 802.11 managed objects. Junghoon Jee, ETRI

  7. Impression • Both the below 6 GHz and the 60 GHz works are the amendment works for IEEE 802.11. • Only the below 6 GHz PAR and 5C are pointing out the support of the backward compatibility with legacy devices in 5 GHz bands • Rough Questions: • Backward compatibility in the IEEE 802.11 standard? • Relationship between the amendment works and the support of the backward compatibility? • The exclusion of the 2.4 GHz support means not compatible with 11b,g devices? Junghoon Jee, ETRI

  8. “Backward Compatibility” from WIKIPEDIA • Backward compatibility is a relationship between two components, rather than being an attribute of just one of them. More generally, a new component is said to be backward compatible if it providesall of the functionality of the old component. • Backward compatibility is the special case of compatibility in which the new component has a direct historical ancestral relationship with the old component. If this special relationship does not exist then it not usually spoken of as "backward" compatibility but is instead just "compatible"—a consistent interface allowing interoperability between components and products that were each developed separately. Junghoon Jee, ETRI

  9. “Backward Compatibility” from WIKIPEDIA (2) • Data does nothing in the absence of an interpreter, so the notion of compatibility does not apply to document files, it only applies to software. In the case of a program that creates document files, a new version of that program ("v2") is said to be backward compatible with the old version of the program ("v1") when it can both read and write documents that work with v1. Everything that v1 could do must also be possible with v2, including saving documents that can be read by v1. • If a newer software version cannot save files that can be read by the older version, it is not backward compatible with the older version, although it may provide an irreversible upgrade capability for the old files. --- Junghoon Jee, ETRI

  10. IEEE 802.11 Standard History Junghoon Jee, ETRI

  11. Discussion • Frequency Band and Backward Compatibility • The amendments utilizing the different frequency bands are not compatible; • IEEE 802.11b,g vs. IEEE 802.11a • IEEE 802.11n (5 GHz) vs. IEEE 802.11b,g • IEEE 802.11n (2.4 GHz) vs. IEEE 802.11a • However, 802.11a (5 GHz) uses the same core protocol as the 802.11-1997 (2.4 GHz) • Exclusion of the 2.4 GHz band in VHT • Not backward compatible with the 11b,g devices Junghoon Jee, ETRI

  12. Discussion (2) • VHT’s status in terms of operating frequency band • Backward compatible with 11a devices? • We can say ‘YES’  • Backward compatible with 11b and 11g devices? • ‘NO’ • Backward compatible with 11n devices? • Well... Only when 11n devices operate in 5 GHz band. • Another issue would be the relationship with the 802.15.3c. Junghoon Jee, ETRI

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