July 2013
doc.: IEEE 11-13/0406-05-00ak
P802.1Qbz + P802.11ak Proposed Division
of Work
Date: 2013-07-14
Authors:
Name
Affiliations
Address
Phone
email
Norman Finn
Cisco Systems
+1.408.526.4495
nfinn@cisco.com
Brian Hart
Cisco Systems
170 W Tasman Dr.
San José CA 95134 USA
170 W Tasman Dr.
San José CA 95134 USA
+1.408.525.3346
brianh@cisco.com
Submission
Slide 1
Finn and Hart, Cisco Systems
July 2013
doc.: IEEE 11-13/0406-05-00ak
Abstract
• At present, 802.1AC defines one interface to 802.11
media, the Portal.
• This document proposes that 802.1AC define three
interfaces:
• The Portal, unchanged from the current definition, providing a
single instance of the MAC service.
• The AP-DS interface, used for functions, typically bridges or
routers, co-resident with one or more APs, with a separate instance
of the MAC service for each station associated with an AP.
• The non-AP station interface, with one instance of the MAC
service for the connection to the AP, and another for each direct
connection to another non-AP station.
Submission
Slide 2
Finn and Hart, Cisco Systems
July 2013
doc.: IEEE 11-13/0406-05-00ak
The AP-DS interface
• The interface between the Access Point (AP) and Distribution System
(DS) is defined in Annex R of IEEE Std 802.11™-2011.
• R.2.2.2.4, in particular, states that the DS reflects every multicast or
broadcast back to the source station; this is exactly what must not
happen in the case of a station that is attached to a Bridge. Although
Annex R is informative, not normative, a change seems necessary.
• In general, Annex R assumes that the 3-address format is used, not the
4-address format. As discussed elsewhere, this “Subset Problem” may
be solved by use of the 4-address format, by a variant of the A-MSDU,
or by some other means.
B/R
Distribution
Portal
System (DS)
AP2
AP1
Submission
Slide 3
Finn and Hart, Cisco Systems
July 2013
doc.: IEEE 11-13/0406-05-00ak
Revised AP-DS interface
• The earlier “802.1Q changes necessary” contribution (bz-nfinn802-1Q-changes-0313-v01.pdf, or 11-13/253) outlined a
“bundle of point-to-point interfaces aka a vector” idea that the
present document will expand upon.
• The difference between this bundle of point-to-point links, an
extension of the current definitions in 802.11, and the current
definitions in 802.1, is a matter of plotting a function in polar vs.
rectilinear vs. log-log coordinates. The substance of
specifications, like the function being plotted, is the same.
• Our suggestion is that 802.11ak consider altering Annex R
(informative) to this bundle-aka-a-vector model, and that
802.1Qbz add a similar informative annex to map the 802.1Q
bridge port model to the same bundle-aka-a-vector model.
Submission
Slide 4
Finn and Hart, Cisco Systems
July 2013
doc.: IEEE 11-13/0406-05-00ak
The DS, today
Distribution
System (DS)
B/R
Portal
AP2
AP1
• What 802.11 presents to the bridge/router is a Portal, which
offers a single generic IEEE 802 MAC service to the Bridge (or
Router).
• This prevents the bridge/router from using the individual links optimally
(for accurate forwarding), because the bridge cannot access individual
links.
• Wireless (or wired) AP-AP links are the province of the DS; they are not
visible above the Portal.
• The method to be used by the DS to interconnect APs that are not
physically co-located is not specified, nor is the method by which it
accesses the wired network (the Portal is not always suitable).
Submission
Slide 5
Finn and Hart, Cisco Systems
July 2013
B/R
AP2
•
doc.: IEEE 11-13/0406-05-00ak
B/R
DS after P802.11ak
AP1
New: 802.11 AP presents to the bridge/router a bundle of MAC service
instances, which allows it to send an MSDU to any combination of ports.
•
•
•
•
Distribution
System (DS)
The bridges or routers are the DS and prevent reflection – no need for a Portal.
Broadcast distribution/reflection is what bridges/routers do for a living.
Each instance within the bundle carries only Destination Address (DA) and Source Address
(SA) – not Transmitter Address (TA) nor Receiver Address (RA).
The bundle is equivalent to presenting an MSDU, DA, SA and a vector that
identifies the combination of port(s)
•
•
•
MSDU passed from non-AP to AP MSDU to DS: RA is always the AP MAC and is discarded by
AP. AP identifies the TA to the DS by setting one bit in the vector (where the bit position is
associated with the non-AP STA)
MSDU passed from DS to AP to non-AP(s): AP sets TA as its own MAC address and the RA is
selected at the AP’s discretion to cover the bits set in the vector, as described in the next slide.
AP-to-AP links are available to the DS, as they now, but on exactly the same basis as wired
links.
Submission
Slide 6
Finn and Hart, Cisco Systems
July 2013
B/R
Distribution
System (DS)
AP2
doc.: IEEE 11-13/0406-05-00ak
B/R
DS after P802.11ak
AP1
non-AP station
emulation
• Note the AP-AP link. This is not necessarily a peer-to-peer link.
(That seems to require a non-trivial amount of standardization
effort.)
• This AP-AP link could well consist of:
• One AP emulating a non-AP station, and making that link available to the
resident bridge/router/DS.
• The other AP simply behaving as described for links to non-AP stations.
• The only standardization required might be a MIB, if the TG desires.
Submission
Slide 7
Finn and Hart, Cisco Systems
doc.: IEEE 11-13/0406-05-00ak
Selecting the Receiver Address
• When transmitting, the Bridge (or router) supplies a MSDU that has only
Destination and Source addresses, and a vector indicating on which “point-topoint links” (i.e., to which stations) the MSDU is to be transmitted.
• For 3-address format stations, of course, RA == DA, and the vector can have
only all bits set (individual key) or one bit set (shared key).
• For 4 addresses stations, AP uses the full vector to pick the RA and key:
•
•
If vector has only 1 bit set, then clearly, the AP uses the unicast address of that
station as the RA, and uses that station’s key to secure the frame.
If there are multiple bits set, then the AP has a free choice:
• It can transmit the MSDU multiple times using different unicast RAs and keys.
• If all bits are set, it can transmit the MSDU once, using the broadcast RA and key.
• The AP can establish and distribute a set of multicast RAs and use the broadcast
key to distribute the MSDU to a subset of stations.
• For 3-address + A-MSDU stations, the vector becomes the list of stations
receiving (or not receiving) the MSDUs.
Submission
doc.: IEEE 11-13/0406-05-00ak
Alternatives to the 4-address format
• As discussed in 11-13/693, there are other encoding methods available
than the 4-address format.
• Any of those can be used, in place of the 4-address format mentioned,
here.
• This is the “station subsetting” problem.
Submission
July 2013
doc.: IEEE 11-13/0406-05-00ak
Existing Distribution Systems
• The bridge (or router) attached to the AP via this bundle of
point-to-point links (aka a vector) is a perfectly valid
implementation of the data transfer portion of the Distribution
System (DS).
• A DS is not required to have a portal. And now no portal is needed, in
this case.
• This does not eliminate or obsolete existing implementations of the
DS. Rather, the DS is provided with a new anti-reflection capability.
• The presence of this data transfer technique does not inhibit the DS
from performing any of its other functions.
• Note that this bundle-of-links-aka-vector model can pretty much
eliminate the difference between the 3-address format and the 4address format across the AP-DS interface.
Submission
Slide 10
Finn and Hart, Cisco Systems
July 2013
doc.: IEEE 11-13/0406-05-00ak
New non-AP station interface
• We also need a well-defined interface at the non-AP
station side.
• The differences between this and the currently-defined
interface in 802.11:
• We make it clear that the connection to the AP, and each direct
connection to a non-AP station, are presented to the upper layers as
separate instances of the standard 802.1AC ISS MAC service,
which has only two addresses, Source and Destination.
• No frame is ever echoed back to the transmitter, either
immediately or some time later, as is the current case for a non-AP
station.
Submission
Slide 11
Finn and Hart, Cisco Systems
July 2013
doc.: IEEE 11-13/0406-05-00ak
Summary of standards modifications
required to support 802.11ak
11ak:
•
•
Modify the informative 802.11 Annex R to describe the bundle-oflinks-and-a-vector model.
Add a definition of the new non-AP station interface, that does not
have frames echoed back to it.
1Qbz:
•
A Bridge (which is a function, not a chassis) can optionally use the
DS-AP interface and/or the new non-AP station interface.
1AC:
• Provide simple definitions of adaptation functions for the three
interfaces, Portal, DS-AP bundle-of-links, and new non-AP station.
Somewhere:
• Provide an informative annex specifying how to map the bundle-oflinks-and-a-vector model to the current Bridge Port model.
Submission
Slide 12
Finn and Hart, Cisco Systems