1. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 1 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. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures, 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 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.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfstuart.kerry@philips.compatcom@ieee.org Date: 2005-05-25 Authors:

2. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 2 Abstract This presentation describes the DS, ESS, Subnet and VLAN concepts, and their inter-relation in the 802.11 environment.

3. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 3 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.

4. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 4 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.

5. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 5 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.

6. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 6 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.

7. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 7 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.

8. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 8 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

9. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 9 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.

10. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 10 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.

11. doc.: IEEE 802.11-05/0522r0 Submission July 2005 Mike Moreton, STMicroelectronicsSlide 11 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.