July 2005

Mike Moreton, STMicroelectronics

Slide 1

doc.: IEEE 802.11-05/0522r0

Submission

DS, ESS, Subnet and VLAN

Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

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Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <stuart.kerry@philips.com> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>.

Date: 2005-05-25

Name Company Address Phone email Mike Moreton STMicroelectronics Mm2004@mailsanre.net

Authors:

July 2005

Mike Moreton, STMicroelectronics

Slide 2

doc.: IEEE 802.11-05/0522r0

Submission

Abstract

This presentation describes the DS, ESS, Subnet and VLAN concepts, and their inter-relation in the 802.11 environment.

July 2005

Mike Moreton, STMicroelectronics

Slide 3

doc.: IEEE 802.11-05/0522r0

Submission

Definitions of ESS from 802.11maD1.0

• 3.45 extended service set (ESS): A set of one or more interconnected basic service sets (BSSs) and integrated local area networks (LANs) that appears as a single BSS to the logical link control (LLC) layer at any station associated with one of those BSSs.– “Appears as a single BSS” implies reachability – any STA can

send data to any other STA anywhere in the ESS using a layer 2 address.

– LLC is end-to-end (ignoring the translations when using Ethernet)

• An ESS is equivalent to a physical wired LAN. All STAs are reachable from all other STAs.

July 2005

Mike Moreton, STMicroelectronics

Slide 4

doc.: IEEE 802.11-05/0522r0

Submission

Definition of DS from 802.11maD1.0

• 3.33 distribution system (DS): A system used to interconnect a set of basic service sets (BSSs) and integrated local area networks (LANs) to create an extended service set (ESS).– A building block of the ESS

– Connects BSSes together

– Could be a LAN, but can be anything that can forward a layer 2 frame to the correct destination AP, e.g. some proprietary encapsulation and routing protocol within IP.• Whatever the technology used by the DS, the service provided by the

DS is always in terms of layer 2 addresses.

July 2005

Mike Moreton, STMicroelectronics

Slide 5

doc.: IEEE 802.11-05/0522r0

Submission

Definition of subnet

• Can’t find an official definition!

• Originally a sub-division of an IP network (identified by an IP network number), but now used interchangeably as a term for all or part of an IP network– Note: The Internet is technically not an IP network – it’s what

connects the IP networks together

• Possible definition: “A subnet is part or all of an IP Network such that all hosts may be reached directly from all other hosts without transiting an IP router.”

• Note that an IP Router is also a host, so any router must be reachable from all other hosts in the subnet.

July 2005

Mike Moreton, STMicroelectronics

Slide 6

doc.: IEEE 802.11-05/0522r0

Submission

VLAN

• A VLAN (virtual LAN) is defined as a level above the physical LAN.

• Used where you want to limit connectivity– Not all hosts on the physical LAN can talk to all other hosts on the

same physical LAN

– Sometimes the VLANs can be set-up to limit access to a particular physical location• For example, only the ethernet ports in the Accounts Department are

connected to the Accounts VLAN.

July 2005

Mike Moreton, STMicroelectronics

Slide 7

doc.: IEEE 802.11-05/0522r0

Submission

VLANs and 802.11

• 802.11 is a wireless technology, so limiting VLAN connectivity on the basis of physical location makes little sense.

• 802.11 uses 802.1X based authentication to prove entitlement to use the network, not physical location.

• The most sensible configuration for VLANs in an 802.11 environment is for all VLANs to be accessible via all APs– RADIUS authentication returns the VLAN to which the STA

should be connected by the AP

• Quite acceptable for “unusual” configurations to require extra manual configuration.

July 2005

Mike Moreton, STMicroelectronics

Slide 8

doc.: IEEE 802.11-05/0522r0

Submission

VLANs Conclusion• In an 802.11 environment, every VLAN is accessible

from every point of the physical LAN– Unless the user goes in for extensive manual configuration

• When considering reachability in an 802.11 environment can ignore VLAN– It’s only the ESS that matters.

• An AP that is not configured to allow access to all VLANs should not advertise that it is a member of the ESS

July 2005

Mike Moreton, STMicroelectronics

Slide 9

doc.: IEEE 802.11-05/0522r0

Submission

ARID• The aim of ARID (Access Router Identifier) is to determine

whether a candidate AP (for roaming to) can provide access to the STA’s current router– Potentially requires all routers connected to the subnet to be identified– With multiple subnets running on the same LAN, the problem gets even

worse.

• If the candidate AP is part of the same ESS, then reachability is guaranteed.– The current router is a host on the ESS, so access is guaranteed through

all APs (except in perverse VLAN configurations)

• So no need for ARID, if you know the identity of the ESS is the same as your current AP.

July 2005

Mike Moreton, STMicroelectronics

Slide 10

doc.: IEEE 802.11-05/0522r0

Submission

Why DS Identifier?

• From the previous discussion, what is needed is the identity of the ESS– But the TGu requirement uses “DS Identity”. Why?

• “ESSID” appears in the 1999 standard, but appears to be a misprint. (Removed in 802.11maD1.0)

• To avoid confusion “DS Identity” was used in TGu– But maybe caused more confusion than it avoided.

July 2005

Mike Moreton, STMicroelectronics

Slide 11

doc.: IEEE 802.11-05/0522r0

Submission

Is ESS Identifier in scope?

• TGr’s scope is intra-ESS handover. Isn’t an ESS identifier for inter-ESS handover, and hence out of scope?– No. Having an ESS identifier increases the speed of intra-ESS

handover, and makes no difference to the speed of inter-ESS handovers. It is hence very much in scope for TGr.

– TGr seem more open to this than in the past.

• Is it in scope for TGu, if TGr don’t do it?– It’s difficult to see how any sort of ESS Identifier or ARID can be

in scope for TGu. It’s clearly a method for speeding up intra-BSS handover, and if TGr decide not to do it, we should respect their decision.