July 2008
doc.: IEEE 802.11-08/0790r0
Backward Compatible or Not?
Date: 2008-07-07
Authors:
Name
Company
Junghoon Jee
ETRI
Minho Cheong
ETRI
Hongseok Jeon
ETRI
Changmin Park
ETRI
Yeonkwon Jeong
GSU
Yoo-Seung Song
ETRI
Chanho Yoon
ETRI
Jung Bo Son
ETRI
Sok-kyu Lee
ETRI
Submission
Address
138 Gajeongno, Yuseong-gu, Daejeon,
305-700, KOREA
138 Gajeongno, Yuseong-gu, Daejeon,
305-700, KOREA
138 Gajeongno, Yuseong-gu, Daejeon,
305-700, KOREA
138 Gajeongno, Yuseong-gu, Daejeon,
305-700, KOREA
10 Park South Building, Atlanta GA
30303, USA
138 Gajeongno, Yuseong-gu, Daejeon,
305-700, KOREA
138 Gajeongno, Yuseong-gu, Daejeon,
305-700, KOREA
138 Gajeongno, Yuseong-gu, Daejeon,
305-700, KOREA
138 Gajeongno, Yuseong-gu, Daejeon,
305-700, KOREA
Slide 1
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Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
Abstract
This contribution discusses the backward compatibility
issues of the IEEE 802.11 VHT works.
Submission
Slide 2
Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
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 and ensuring backward
compatibility and coexistence with legacy IEEE802.11a/n devices
in the 5GHz unlicensed band.
Submission
Slide 3
Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
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 same as 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.
Submission
Slide 4
Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
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
Submission
Slide 5
Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
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.
Submission
Slide 6
Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
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?
Submission
Slide 7
Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
“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 provides
all 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.
Submission
Slide 8
Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
“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. ---
Submission
Slide 9
Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
IEEE 802.11 Standard History
Standard
Release Date Op. Frequency Compatibility
802.11-1997
1997
2.4 GHz
802.11a
1999
5 GHz
with 802.11-1997
802.11b
1999
2.4 GHz
with 802.11-1997
802.11g
2003
2.4 GHz
with 802.11b
802.11-2007
2007
2.4/5 GHz
Merged 802.11a,b,d,e,g,h,i,j with
the base standard
802.11n
2009
2.4 GHz
with 802.11b,g
5 GHz
with 802.11a
Below 6 GHz
or 60 GHz
??
VHT
Submission
??
Slide 10
Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
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
Submission
Slide 11
Junghoon Jee, ETRI
July 2008
doc.: IEEE 802.11-08/0790r0
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.
Submission
Slide 12
Junghoon Jee, ETRI