Re: 60 GHz interface types (was: [PATCH v5 1/2] wireless: Driver for 60GHz card wil6210)

[Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>]

On Monday, November 12, 2012 11:15:56 AM Johannes Berg wrote:
> Ok, can you elaborate on the differences between PCP and AP, and their
> clients? I haven't had time to dig through the draft again

What comes to my mind: 

PBSS is new type of BSS introduced by 60g spec. Partially, it sorts out mess 
associated with IBSS; partially it helps to address 60g specifics.

PBSS is such a hybrid between ESS (infrastructure BSS) and IBSS.

PBSS can be established only with DMG (60G) stations.

PBSS features:

===Similar to IBSS===

- PBSS is ad-hoc network. Data frames use FromDS/ToDS combination 0/0
- stations communicate directly with each other.
- security: every STA implement both authenticator and supplicant roles
- STA use GAS to gather info about other STA's in the same PBSS

===Similar to ESS (infrastructure BSS)===

- there is dedicated coordination point, named PCP.
- PCP manages joining to the PBSS (association flow)
- only PCP transmits beacons. (in IBSS - every one)
- up to 254 STA may be associated with PCP (in IBSS - unlimited)
- PCP enforce uniform security policy (in IBSS each STA can enforce its own)

===Other===

- BSS type defined in beacon/probe resp etc.
- there is a protocol, called "PCP negotiation" that allows 2 STA to decide 
who will accept role of PCP, based on specific scan procedure. They compare 
"PCP factors" - something similar to P2P intents, but composed of various 
capability bits. Most importand bit is "AC powered" - if 1 STA is AC powered 
while 2-nd is battery powered, AC powered will be elected as PCP. And so on - 
idea is to elect more capable STA as PCP.
- there is no multicast in DMG network, since all data transmissions are 
directed. Due to this, if STA need to send mcast/bcast frame, it duplicates it 
for every STA within PBSS.
- there is protocol for PCP hand-off
- in 60g, P2P_GO is PCP by definition


To summarize client's POV:
- you know whether it is AP or PCP from scan results
- you associate with AP and PCP in the same way
- you set FromDS/ToDS bits differently for PCP and AP
- for PCP, you yse GAS to discover other STA's (query PCP)
- for PCP, you transmit to every STA in your PBSS directly
- for PCP, you duplicate Tx multicast frame for each STA.