From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladimir Kondratiev Subject: TGe overview #3 Date: Mon, 2 Aug 2004 22:38:57 +0300 Sender: netdev-bounce@oss.sgi.com Message-ID: <200408022239.04871.vkondra@mail.ru> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart6500354.cgk6mvoYQD"; protocol="application/pgp-signature"; micalg=pgp-sha1 Content-Transfer-Encoding: 7bit Return-path: To: netdev@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org --nextPart6500354.cgk6mvoYQD Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline =46inally, let's review Traffic Streams. There are 2 different concepts: logical layer (admission) and completely ne= w=20 media access mechanism HCCA (Hybrid Coordinator Channel Access). Idea behind HCCA is similar to PCF (Point Coordinator Function) from old=20 802.11 standard. Hybrid Coordinator (HC), which have to be AP, decides who= =20 will talk when. Technically it is implemented as following: All time divided into contention based (EDCA TXOP's) and contention free CA= P=20 (Controlled AccessPhase). When HC want to start CAP, it simply starts it=20 after PIFS interval of idle media. PIFS is shorter then any interval betwee= n=20 EDCA frame exchange sequences, thus HC will preempt any EDCA flow at his=20 will. Then, HC can either transmit frames, or it may send Contention Free=20 Poll (CFP) frame to some STA. This frame gives to the STA "polled" TXOP, in= =20 contrast with EDCA TXOP. CFP frame provides TXOP duration. Now, admission control. For HCCA it is the only mechanism. But, admission=20 control may be activated also for 2 high priority EDCA categories. =46or EDCA it mean the following: one can't use these categories as it was= =20 described in EDCA, instead, TID should be obtained. For EDCA this mechanism= =20 used to control bandwidth allocation. But remember, EDCA is contention base= d=20 policy, without any guarantee. TID's 8-15 dedicates to TS (Traffic Streams). In order to obtain TID, STA=20 should send request to AP. Corresponded frame called ADDTS, it contain=20 traffic specification: requested bandwidth, delay, periodicity, frame size= =20 etc. AP may accept or decline this request. It may also come with counter=20 proposal with different parameters. TS may be up-stream, down-stream, or bi-direction If TS accepted by AP, AP provides schedule information. This information=20 consist of Service Interval (SI) - interval between successive Service=20 Periods (SP), during which AP serves this TS, and Start Time. Start time have the following meaning: STA may request exact timing in ADDT= S=20 request. In this case, it will be served at precise times StartTime+n*SI.=20 This used for power save: STA may identify itself as power down, but wake u= p=20 for its stream. Obvious usage is .11 phones. Here, important QoS related part is: AP admin decides upon admission control policy. For "legacy stations", that= =20 don't speak TS (stations implementing WME spec), it may provide only 2 low= =20 priority access categories. These STA will be severely impacted in=20 performance. STA have to know TGE in order to get real performance. And, STA need to kno= w=20 how to identify streams (RSVP like). One additional feature: DLP (Direct Link Protocol). Unrelated to anything=20 else. Idea is to let 2 stations to talk directly. Link establishment is=20 through AP, but later they send frames directly, reducing media time 2x. Th= is=20 is important for applications like streaming of high definition TV, for whi= ch=20 "usual" way when AP forward frames, is unacceptable. P.S. I did not covered many other stuff which is not related directly to Qo= S. --nextPart6500354.cgk6mvoYQD Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.5 (GNU/Linux) iD8DBQBBDphYqxdj7mhC6o0RAmzAAKCFDMlYn7QuujVswZshlWPTZehMMQCgpXEw 7UWwHkUzYOgsx0c61i82UpU= =QGXS -----END PGP SIGNATURE----- --nextPart6500354.cgk6mvoYQD--