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The Nature of an ESS

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					May 2004

doc.: IEEE 802.11-04/0629r1

The Nature of an ESS

Darwin Engwer, Nortel Networks Bob O’Hara, Airespace
dengwer@nortelnetworks.com bob@airespace.com
Submission Slide 1 Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

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 ...

Submission

Slide 2

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

Slide 6 from [1] doc 11-04-614-00

AP + DS + Portal
HOST 802.3 network Router

Portal Distribution System

AP

AP

AP

STA

Submission

Slide 3

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

• But real world implementations (to date) look like this ...

Submission

Slide 4

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

Real World AP Devices
HOST 802.3 network Router

802.3 L2 Hub or Switch

AP Device
Portal Integration Distribution System WM Portal Integration Distribution System WM

AP Device

STA

STA

STA

Submission

Slide 5

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

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.”
Submission Slide 6 Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

Logical DS and Portal
HOST 802.3 network Router

Portal
802.3 L2 Hub or Switch

AP Device
Portal Integration Distribution System WM

Distribution System

AP Device
Portal Integration Distribution System WM

A single logical portal is indistinguishable from multiple physical portals.
STA STA STA

Submission

Slide 7

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

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.”

Submission

Slide 8

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

L2 Connectivity with a Logical DS and Portal
HOST 802.3 network Router

Portal
802.3 L2 Hub or Switch

AP Device
Portal Integration Distribution System WM

Distribution System

AP Device
Portal Integration Distribution System WM

STA

STA

STA

L2 link L2 link
Submission Slide 9 Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

Extent of the ESS
• Hence, the ESS can span all the APs in such a network.

Submission

Slide 10

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

ESS with a Logical DS and Portal
HOST 802.3 network Router

Portal
802.3 L2 Hub or Switch

AP Device
Portal Integration Distribution System WM

Distribution System

AP Device
Portal Integration Distribution System WM

STA

STA

STA

ESS L2 link
L2 ESS link
Submission Slide 11 Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

What if the network includes a router?

Submission

Slide 12

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

L2 Connectivity with a Logical DS and Portal using a Router
HOST 802.3 network Router

Portal
802.3 L2 Hub or Switch

Portal
802.3 L2 Hub or Switch

AP Device
Portal Integration Distribution System WM

Distribution System
Portal Integration Distribution System WM

AP Device

STA

STA

STA

L2 link L2 link
Submission Slide 13 Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

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 miniDS 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.
Submission Slide 14 Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

ESS with a Logical DS and Portal using a Router
• Hence, the ESS concept can apply to WLAN deployments that rely on a logical DS/ logical portal(s) construct, even when using a router.

Submission

Slide 15

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

ESS with a Logical DS and Portal using a Router
HOST 802.3 network Router

Portal
802.3 L2 Hub or Switch

Portal
802.3 L2 Hub or Switch

AP Device
Portal Integration Distribution System WM

Distribution System
Portal Integration Distribution System WM

AP Device

STA

STA

STA

ESS L2 link
L2 ESS link
Submission Slide 16 Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

ESS Summary
• BSSs with the same SSID may be part of the same ESS. • No scenarios are [necessarily] excluded.
• The 802.11-1999 definition of an ESS is somewhat broad and flexible. Therefore, TGr may need to specify and explicitly define the BSS-transition cases that are in-scope and out-of-scope.
– i.e. If TGr wants something more precise than ESS, then need to specify that.

Submission

Slide 17

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

References:

– [1] 11-04-0614-00-frfh-what-ess.ppt – [2] 11-04-0500-01-0mes-need-clarification-definition-ess-mesh.ppt

Submission

Slide 18

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace

May 2004

doc.: IEEE 802.11-04/0629r1

The End

Submission

Slide 19

Darwin Engwer, Nortel Networks; Bob O'Hara, Airespace


				
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