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The Nature of an ESS

Explore the definition and implementation options of an Extended Service Set (ESS) in WLANs, including the use of logical Distribution Systems (DS) and Portals. Consider the connectivity possibilities when a router is included in the network.

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The Nature of an ESS

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  1. The Nature of an ESS Darwin Engwer, Nortel NetworksBob O’Hara, Airespace dengwer@nortelnetworks.combob@airespace.com Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  2. Further thoughts on ESS(triggered by submission 11-04-0614-00) • Doc 614 [1] cites a number quotes directly from the standard wrt the definition of an ESS. • Strictly interpreted these existing definitions constrain the implementation options as cited in doc 614 • However, other logical (abstract) views are possible, which have in fact allowed vendors to construct functional WLANs within the constraints imposed by existing definitions. • First, a diagram from doc 614 ... Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  3. AP + DS + Portal Slide 6 from [1] doc 11-04-614-00 HOST Router 802.3 network Portal Distribution System AP AP AP STA Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  4. But real world implementations (to date) look like this ... Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  5. Portal Portal Distribution System Distribution System AP AP Integration Integration WM WM Real World APs HOST Router 802.3 network 802.3 L2 Hub or Switch STA STA STA Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  6. Real World AP Review • In that common real world AP and WLAN implementation, the mini-DSs and portals in each AP combined with the 802.3 L2 network can be considered as forming a single logical Distribution System and Portal, since those logical components meet all the criteria described in 802.11-1999 Clause 5. • “5.2.2 … The IEEE 802.11 LAN architecture is specified independently of the physical characteristics of any specific implementation.” • … The DS enables mobile device support by providing the logical services necessary to handle address to destination mapping and seamless integration of multiple BSSs.” Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  7. Portal Portal Distribution System Distribution System AP AP Integration Integration WM WM Logical DS and Portal HOST Router 802.3 network Portal 802.3 L2 Hub or Switch Distribution System STA STA STA Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  8. Logical DS and Portal • There is no disagreement between the Logical DS and Portal model and the formal definitions provided in 802.11-1999 Clause 5. • Consider: “5.2.2.1 The key concept is that the ESS network appears the same to an LLC layer as an IBSS network. Stations within an ESS may communicate and mobile stations may move from one BSS to another (within the same ESS) transparently to LLC.” Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  9. Portal Portal Distribution System Distribution System AP AP Integration Integration WM WM L2 link L2 link L2 Connectivity with aLogical DS and Portal HOST Router 802.3 network Portal 802.3 L2 Hub or Switch Distribution System STA STA STA Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  10. Extent of the ESS • Hence, the ESS can span all the APs in such a network. Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  11. Portal Portal Distribution System Distribution System AP AP Integration Integration WM WM ESS with aLogical DS and Portal HOST Router 802.3 network Portal 802.3 L2 Hub or Switch Distribution System STA STA STA ESS L2 link ESS L2 link Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  12. What if the network includes a router? Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  13. Portal Portal Distribution System Distribution System AP AP Integration Integration WM WM L2 Connectivity with aLogical DS and Portal using a Router HOST Router 802.3 network Distribution System Portal Portal 802.3 L2 Hub or Switch 802.3 L2 Hub or Switch STA STA STA L2 link L2 link Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  14. L2 Connectivity thru a Distribution System that includes a Router • At first look it appears as if the two STAs on opposite sides of the router do not have L2 Connectivity. • However, the DS (or some other component in the network) can arrange this to be true. • e.g. the mini-DS in one AP can transport the MSDU to the mini-DS in the AP that is on the other side of the router. The second AP can then deliver the MSDU to the mobile STA. To the mobile STAs it appears as if they have L2 connectivity. • e.g. A consistent VLAN can be set up on both sides of the router, so that packets on that VLAN are switched across the router. In fact, this is a common deployment scenario today. Again, to the mobile STAs it appears as if they have L2 connectivity. Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  15. ESS with aLogical DS and Portal using a Router • Hence, the ESS concept can apply to WLAN deployments that rely on a logical DS, logical portal(s) construction, even when using a router. Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  16. Portal Portal Distribution System Distribution System AP AP Integration Integration WM WM ESS with aLogical DS and Portal using a Router HOST Router 802.3 network Distribution System Portal Portal 802.3 L2 Hub or Switch 802.3 L2 Hub or Switch STA STA STA ESS L2 link ESS L2 link Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  17. ESS Summary • BSSs with the same SSID may be part of the same ESS • no scenarios are [necessarily] excluded Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  18. References: • [1] 11-04-0614-00-frfh-what-ess.ppt • [2] 11-04-0500-01-0mes-need-clarification-definition-ess-mesh.ppt Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

  19. The End Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

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