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P802.1Qbz + P802.11ak Proposed Division of Work

P802.1Qbz + P802.11ak Proposed Division of Work. Authors:. Date: 2013-07 -14. Abstract. At present, 802.1AC defines one interface to 802.11 media, the Portal. This document proposes that 802.1AC define three interfaces:

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P802.1Qbz + P802.11ak Proposed Division of Work

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  1. P802.1Qbz + P802.11ak Proposed Division of Work Authors: • Date:2013-07-14 Finn and Hart, Cisco Systems

  2. 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. Finn and Hart, Cisco Systems

  3. 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 nothappen 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 DistributionSystem (DS) Portal AP2 AP1 Finn and Hart, Cisco Systems

  4. Revised AP-DS interface • The earlier “802.1Q changes necessary” contribution (bz-nfinn-802-1Q-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. Finn and Hart, Cisco Systems

  5. The DS, today B/R DistributionSystem (DS) 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). Finn and Hart, Cisco Systems

  6. DistributionSystem (DS) DS after P802.11ak B/R B/R B/R B/R AP2 AP1 • New: 802.11 AP presents to the bridge/router a bundle of MAC service instances, whichallows it to send an MSDU to any combination of ports. • 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. Finn and Hart, Cisco Systems

  7. DistributionSystem (DS) DS after P802.11ak B/R B/R B/R B/R AP2 AP1 • 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. non-AP stationemulation Finn and Hart, Cisco Systems

  8. 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-to-point 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 MSDUto a subset of stations. • For 3-address + A-MSDU stations, the vector becomes the list of stations receiving (or not receiving) the MSDUs.

  9. 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.

  10. 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 4-address format across the AP-DS interface. Finn and Hart, Cisco Systems

  11. 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. Finn and Hart, Cisco Systems

  12. Summary of standards modifications required to support 802.11ak • 11ak: • Modify the informative 802.11 Annex R to describe the bundle-of-links-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-of-links-and-a-vector model to the current Bridge Port model. Finn and Hart, Cisco Systems

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