What is an ESS?

1
What is an ESS?

• Jon Edney, Nokia

2
Anecdotal Definitions for ESS(I have heard
people use)

• Any group of APs having
• the same SSID and connected via a Layer 2 network
• the same SSID and connected by any network
• the same SSID

3
The Distribution System (DS)
Distribution System
AP
AP
AP
4
The BSS
DS
AP
STA
STA
5
ESS
Distribution System
AP
AP
AP
STA
STA
6
ESS
Distribution System
AP
AP
AP
MSDU
MSDU
STA
STA
THIS IS ALL 802.11 NO NON 802.11 terminations
allowed
7
What does the standard say?

• 3.25 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 layer at any station
  associated with one of those BSSs.

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More (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.

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Portal

• 3.39 portal The logical point at which medium
  access control (MAC) service data units (MSDUs)
  from a non-IEEE 802.11 local area network (LAN)
  enter the distribution system (DS) of an extended
  service set (ESS).

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Portal
HOST
Router
802.3 network
Distribution System
AP
AP
AP
STA
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SSID

• 7.3.2.1 The SSID element indicates the identity
  of an ESS or IBSS
• There is no such thing as ESSID

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Summary

• SSID does not define ESS
• Any network technology can be used for DS but
• The only terminations allowed are APs or portals
• DS must provide a tunnel for MSDUs effectively
  this means layer 2 delivery
• Connections through portal do not change when you
  roam within ESS
• If STA is required to change IP address when it
  roams then it cannot be intra-ESS roaming.
• For real networks, ESS is not a useful concept

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What to do?

• If ESS is not a useful definition was should it
  be replaced with?
• Need to define a group of APs where
• Fast transition possible between them (TGr)
• Characteristics are compatible (TGkTGr)
• Same network services are accessible through any
  AP in the group (Wien?) gt same authentication
  requirements
• The original definition of ESS which make
  transitions transparent to the link layer achieve
  some of this.
• But it is not enough any more.

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Ideas

• Define new extended identifier that includes a
  service directory and is accessible through probe
  responses.
• Have special class of SSID that is centrally
  allocated with well known capabilities and
  service support
• Have a shared token that could be used in probe
  response to validate another AP as member the
  same group.
• Tie group definition information into 802.21