Download Implementation Options for the Distribution System in the 802.11

July 2000
doc.: IEEE 802.11-00/214
Implementation Options for the
Distribution System in the
802.11 Wireless LAN Infrastructure Network
Amre El-Hoiydi,
CSEM, Switzerland
IEEE ICC 2000
Submission
Slide 1
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
IEEE 802.11
• PHY
– Frequency-Hopping / DSSS / Infra Red
• MAC
– Wireless Ethernet
• Network Architecture
– Ad Hoc Network
– Infrastructure Network
Submission
Slide 2
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Ad Hoc Network
Submission
Slide 3
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Infrastructure Network
Internet
Portal
Distribution System
Access
Point
Access
Point
Access
Point
ESS
Submission
Slide 4
BSS
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Definitions
• Basic Service Set:
• Extended Service Set:
• Distribution System:
• Access Point:
• Portal:
Submission
A wireless cell
All wireless cells
Glue between the BSS
to form the ESS
Connection DS - BSS
Connection DS - Wired LAN
Slide 5
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Distribution System
•
•
•
•
Several cells form a virtual single shared-medium
Distribution system responsible of routing frames
Distribution system transparent to LLC
Portal + Access Points = MAC Bridge between
the wired LAN and the cells
LLC
802.2
LLC
802.2
Distribution System
MAC
802.11
MAC
802.11
station
Submission
MAC
802.3
portal
access point
Slide 6
MAC
802.3
desktop
computer
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Operation: Traffic
Data frame from the station to the access point (In the FrameControl: ToDS bit is 1, FromDS bit is 0):
Frame
Address 1
Address 2
Control BSSID (=MAC AP 1) SA = MAC Station 1
Address 3
Sequ
DA = MAC Station 3 Control
Address 4
Not Used
Frame Body
0-2312 octets
FCS
Data frame from the access point to the station (In the FrameControl: ToDS bit is 0, FromDS bit is 1):
Frame
Address 1
Address 2
Address 3
Sequ
Control DA = MAC Station 3 BSSID (=MAC AP 3) SA = MAC Station 1 Control
• No direct traffic
between stations
Submission
Address 4
Not Used
Access
Point
Access
Point
Slide 7
Frame Body
0-2312 octets
FCS
Access
Point
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Operation: Roaming
Access
Point
Access
Point
Access
Point
Association request
Reassociation request
Association response
Reassociation response
1
2
• Association protocol gives to the distribution
system the necessary information to perform
the mobility management
Submission
Slide 8
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Logical Services
Internet
• Station Service
Desktop
Comp
– Authentication,
Gateway
– Encryption,
Ethernet
– MSDU Delivery
Portal
• Distribution System
Service
– Association,
integr
DSS
distrib
Distribution System Medium
DSS
AP1
distrib
assoc
SS
– Distribution (unspecified),
DSS
AP2
distrib
assoc
SS
DSS
AP3
distrib
assoc
SS
– Integration (unspecified)
SS
STA1
Submission
SS
STA2
Slide 9
SS
STA3
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Implementation Options for the
Distribution System
• Choice of a distribution transport protocol and
addressing
– LLC Type 1 (connectionless) transport, MAC addressing
or
– UDP/IP transport, IP layer addressing
• Choice of a mobility management signalling
protocol
Submission
Slide 10
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Overview of the discussed options
• MAC Layer Addressing
– Option 1: Separated Access Points and Portals
– Option 2: Joined Access Point and Portals
– Option 3: MAC Bridges
• Network Layer Addressing
– Option 4: Network Layer Addressing
Submission
Slide 11
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 1: Separated AP / Portals
LLC
802.2
LLC
802.2
assoc
distrib
MAC
802.11
MAC
802.11
station
assoc
distrib
LLC 802.2
LLC 802.2
MAC 802.3
MAC 802.3
access point
MAC
802.11
MAC
802.11
access point
station
LLC
802.2
distribution
system medium
distrib
integr
LLC 802.2
MAC
802.3
MAC
802.3
MAC 802.3
wired LAN
portal
Submission
Slide 12
desktop computer
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 1: Transport plane
• Max size of a 802.11 MSDU = 2304 Bytes
• Max size of the payload in 802.3 = 1492 Bytes
• Segmentation needed
• Connection protocol needed to avoid mixing
segments from different sources
Submission
Slide 13
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 1: Signalling
• Goal of the mobility management signalling is that
each access point or portal knows through which
access point or portal a given MAC address can be
reached.
• What access point correspond to what MAC
address ?
• It is proposed to use a dynamic route resolution
protocol similar to the Ethernet Address Resolution
Protocol (ARP, RCF826)
Submission
Slide 14
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 1: Route Resolution
Submission
Slide 15
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 1: Handover
Submission
Slide 16
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 2: Joined AP / Portals
LLC
802.2
LLC
802.2
assoc
MAC
802.11
integr
integr
distrib
MAC
802.11
MAC
802.11
distrib
LLC
LLC
MAC 802.3
station
assoc
MAC
802.11
MAC 802.3
access point /
portal
access point /
portal
station
LLC
802.2
wired LAN and
distribution system
medium
Submission
Slide 17
MAC
802.3
desktop
computer
Amre
El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 2 versus Option 1
• The mobility management signalling protocol is
identical as in option 1
• Having the portal functions in the access points
prevents the need of forwarding over the
distribution medium the traffic to/from the wired
LAN
Submission
Slide 18
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 3: MAC Bridge
• If the MSDU maximum size in 802.11 is reduced
from 2304 to 1476, each access point can be a
filtering bridge
• The access point will forward into the cell the
frames destined to associated stations
• No need of mobility management signalling
• Association protocol is sufficient to give enough
information for the filtering task
Submission
Slide 19
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 3: Network Architecture
LLC
802.2
LLC
802.2
assoc
integr
integr
assoc
MAC
802.11
MAC
802.11
station
MAC
802.3
MAC
802.3
MAC
802.11
MAC
802.11
Access Point
MAC Bridge
Access Point
MAC Bridge
station
LLC
802.2
wired LAN
MAC
802.3
desktop
computer
Submission
Slide 20
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 4: Network Layer Addressing
LLC
802.2
LLC
802.2
assoc
distrib
MAC
802.11
assoc
distrib
UDP/IP
MAC
802.11
station
UDP/IP
LLC 802.2
LLC 802.2
MAC 802.3
MAC 802.3
access point
subnet 192.168.120.0
station
subnet 172.16.100.0
subnet
192.168.121.0
distribution system medium
LLC
802.2
distrib
integr
MAC
802.3
UDP/IP
IP
Router
LLC 802.2
MAC
802.3
MAC 802.3
subnet 192.168.122.0
portal
Submission
MAC
802.11
access point
IP
Router
subnet 172.16.100.0
MAC
802.11
Slide 21
wired LAN
desktop computer
Amre El-Hoiydi, CSEM
subnet 172.16.100.0
July 2000
doc.: IEEE 802.11-00/214
Option 4: Signalling
• Access points not linked through a broadcast
medium anymore
• RoutingRequest and RoutingIndication messages
cannot be broadcast anymore
• It is proposed to use a dynamic address
resolution protocol similar to the Address
Resolution Protocol over ATM (ARP over ATM,
RCF2225)
• Each access point must be given the IP address
of the server
Submission
Slide 22
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 4: Route Resolution
Submission
Slide 23
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Option 4: Handover
Submission
Slide 24
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Summary
Option
Addressing Comments
1
Separated AP /
Portal
MAC
2
Joined AP / Portal
MAC
3
MAC Bridge
MAC
4
Network Layer
Addressing
Submission
IP
Routing resolution signalling uses
broadcast messages
- Wired LAN traffic repeated
Routing resolution signalling uses
broadcast messages
+ Wired LAN traffic not repeated
+ No signalling
- Maximum 802.11 MSDU size not standard
Solution used today in the industry
Routing resolution signalling uses a central
server
+ Flexibility in backbone network
architecture
- Transmission delay can be high
Slide 25
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Standardisation
• 802.11 TGf Task Group has started the work on IAPP
• One IAPP proposal made in 1996
– Uses IP layer addressing
– Transmission of unsolicited “announce” messages
• Schedule
– May 2000, fist meeting held
– July 2000, proposals
– Sept 2000, first draft
Submission
Slide 26
Amre El-Hoiydi, CSEM
July 2000
doc.: IEEE 802.11-00/214
Conclusion
• MAC bridge solution simple but limited
• Should be augmented with a network layer IAPP
• Remaining points to study
• impact of lost messages
• impact of crossed handover messages (RoutingIndication)
• comparison between schemes based on requests or on
unsolicited messages
Submission
Slide 27
Amre El-Hoiydi, CSEM