July 2004
doc.: IEEE 802.11-04-614-01-frfh
What is an ESS?
Jon Edney, Nokia
Submission
Slide 1
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
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
Submission
Slide 2
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
The Distribution System (DS)
Distribution System
AP
Submission
AP
Slide 3
AP
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
The BSS
DS
AP
STA
Submission
STA
Slide 4
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
ESS
Distribution System
AP
AP
STA
STA
Submission
AP
Slide 5
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
ESS
Distribution System
AP
AP
AP
MSDU
MSDU
STA
STA
THIS IS ALL 802.11
NO NON 802.11 terminations allowed
Submission
Slide 6
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
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.
Submission
Slide 7
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
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.
Submission
Slide 8
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
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).
Submission
Slide 9
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
Portal
HOST
Router
802.3 network
Distribution System
AP
AP
AP
STA
Submission
Slide 10
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
SSID
• 7.3.2.1 “The SSID element indicates the
identity of an ESS or IBSS”
• There is no such thing as “ESSID”
Submission
Slide 11
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
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
Submission
Slide 12
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
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 (TGk+TGr)
– Same network services are accessible through any AP in the group
(Wien?) => 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.
Submission
Slide 13
Jon Edney, Nokia
July 2004
doc.: IEEE 802.11-04-614-01-frfh
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
Submission
Slide 14
Jon Edney, Nokia