The IEEE 802.11s Mesh
Networking Amendment
2011-03-14 – IEEE 802 plenary meeting – Singapore
IEEE doc. 11-11-0380-00
Dan Harkins
Guido R. Hiertz
ARUBA NETWORKS
Dee Denteneer
Kazuyuki Sakoda
PHILIPS
Guenael Strutt
POWERWAVE TECHNOLOGIES
PHILIPS
SONY
Jarkko Kneckt
NOKIA
Michael Bahr
SIEMENS AG
2
Outline
Motivation
Introduction to
802.11s
Usage scenarios
802.11s architecture
The Mesh BSS
– Mesh Discovering
– Peering
– Security
Multi hopping
– Path selection
(reactive)
– Power save
– Radio resource
management
MBSS connected to
external STAs
Wrap up
Conclusion
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Motivation for the tutorial
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Why a tutorial?
2nd recirculation Sponsor Ballot
completed March 5 with 95%
approval rate
Timeline targets approval to
forward to ExCom by July 2011
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Outline of the tutorial
• What’s new in 802.11s?
• Design principles
• Topologies of increasing complexity
Lightweight, low power nodes
Wireless
backhaul
Interworking
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Mesh network
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STA range extension
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Infrastructure networks
Peer-to-peer island
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Introduction to Mesh
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Benefit #1: it’s wireless!
Can form larger scale wireless network
without adding wired backhaul
– Networked devices go where wires cannot
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Benefit #2: it’s self-forming!
Network grows as devices are added
– Coverage is expanded with minimal
configuration
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Benefit #3: it’s self-healing!
Resilient to single point of failure
– Network continues to operate during
maintenance
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Out of service
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Out of service
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Benefit #4: it has no hierarchy!
Can deploy, extend, modify, and pullout the
wireless network easily with minimal
cost/overhead
Mesh stations can be client devices
– True ad hoc networking with relaxed range
restriction
– No (re-)configuration delays because there is
no need to define a master station or cluster
“Infrastructure” mesh stations can be
deployed, upgraded, replaced or removed
regardless of role
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Usage Scenarios
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IEEE 802.11s Mesh Usage Scenarios
1
3
5
Residential / Home
Office
Siemens-Pressebild / Siemens Press Picture
Industrial / M2M
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University Campus
Community Area
Park Area
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Smart Metering/
Smart Grid
Campus/Community/Public Access
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Public Safety/Emergency
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pictures (1)(2)(3)(4) IEEE doc 11-04/0662r16, (5) Siemens Press Picture, (6) IEEE doc 11-09-1313r5
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Backhaul Mesh
wired
LAN
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•Campus/
Community/Public
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Access
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•Office
•Industrial 5
•Smart Metering/
Smart Grid 6
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Client Mesh
wired
LAN
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•Home Networks
•Emergency/Public
Safety
•Industrial/M2M
•Smart
Metering/Smart
Grid
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5
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Mixed (backhaul & client) Mesh
wired
LAN
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•Home
Networks
•Office
•Emergency/
Public Safety
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The 802.11s architecture
Extensions required for multi-hop communications
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What has changed on the inside?
802.11 STA
802.11 Mesh STA
New Mesh Functions 3
802.1X
Peering Management
Addressing
Same frame format
Addressing + Mesh Ctrl
EDCA
EDCA reusable
PHY
No H/W change
Association
SAE
1.
2.
3.
802.1X
Needed serious improvements
(IBSS replacement, safe
disassociation, instance
management etc.)
2
SAE
EDCA
MCCA
2
1
PHY
MCCA provides much-needed determinism
SAE provides much-needed 802.11-based security
New mesh functions include routing, power management, synchronization …
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Nothing has changed from the
outside
MSDU source
MSDU destination
MSDU
MAC SAP
MPDU
Mesh
Mesh
STA 4
STA 6
Mesh
Mesh
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STA 1
Mesh
STA 5
Mesh
Mesh
Mesh
STA 2
STA 8
STA 3
Mesh
mesh BSS
(MBSS)
STA 10
Mesh
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Mesh
STA 11
Transparent forwarding to/from any 802 STA
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The Mesh BSS
Mesh Discovery
Peering
Mesh Security
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Mesh discovery
When a STA boots up, it first locates neighbor
mesh STAs
Reuse traditional mechanism in 802.11
– Passive scan (use beacon frames)
– Active scan (use Probe request/response)
Is there anybody out
there?
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I am here!
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I am here!
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I am here!
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Mesh discovery (cont’d)
The “Mesh profile” uniquely identifies the network
– “Mesh ID” (Information Element in mgmt. frames):
Octet string identification of the network, similar to
SSID
– Other active attribute identifiers:
the active protocol set
Mesh Profile
of STA-A
Supplemental information:
– “Connected to gate”
– “Number of mesh peerings”
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Mesh Profile
of STA-B
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Mesh Peering
A distributed, non-hierarchical, and
non-exclusive agreement to communicate
Each mesh STA manages its own peerings
with other mesh STAs
Peering Establishing Protocol
– A true peer-to-peer protocol
– Each side offers and agrees to
parameters that define the terms of the
peering and govern communication
– Two modes for secured peering (AMPE)
or unsecured peering (MPM)
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How is peering done
Capability check via profile matching
A peering has attributes that must be
agreed upon
– Each side must make an offer of attributes to
use for a potential peering
– Each side must confirm the agreed-upon
attributes that define the peering
After each side has offered and confirmed
agreement, the peering is established
Each side can initiate a peering and both
sides can initiate the peering
simultaneously
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How Peering is Done
Initiator
Responder
offer
offer
confirm
confirm
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How Peering is Done
Initiator
Responder
offer
offer
confirm
confirm
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How Peering is Done
Initiator
Initiator
offer
confirm
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offer
confirm
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Mesh Security– Simultaneous
Authentication of Equals (SAE)
Peer-to-Peer
– Non-hierarchical,
mutual authentication
Uses only a password
Resistant to attack
– Can use short, easyto-remember, weak
passwords
– Sharing a password
among mesh points
does not lessen
security
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Distributed
– No centralized server
Robust security
– Misuse-resistant
A standard RSN
authentication method
for all of 802.11
– Can be as a drop-in
replacement to
WPA(2)-PSK in BSS,
IBSS, and PBSS
networks
– Fixes well-known
security problem!
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How SAE is performed
AKM advertising support for SAE in RSN IE in beacons
and probe responses
SAE is after discovery but before peering or association
Uses 802.11 authentication frames
Simple two message exchange
– Same type of exchange used for peering
 Each side first commits to a guess of the password
 Each side then confirms its guess and verifies the peer’s guess
– Successful termination results in a PMK
– Unsuccessful termination does not leak any information
about the password
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Establishing Secure Peerings
Discovery
– Identifies peer
SAE
– Derives shared key
AMPE
– Establish peering
Subsequent traffic
is protected
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Mesh Peering: A Better Approach to
Peer-to-peer networking
Better than Bluetooth
– Easy-to-use, ad-hoc, auto-discovery
– Secure peering with short key
– High speed data transfer between
peers
Secure, direct, link establishment
– No pre-provisioning or “protected setup” necessary
– Link is directly established between
the peers without need for role
determination
– The right tool for the right job
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 No need to implement functionality of
multiple roles (e.g. STA and AP)
 Security is integrated into link
establishment
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Multi-hopping in the Mesh BSS
Path selection (reactive)
Power save
Radio resource management
Wireless Mesh network = multi-hop topology
≠ master-slave topology
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Path Selection
Determines paths from source mesh STA to destination
mesh STA in an MBSS, possibly over multiple hops
Paths are stored in forwarding information
HWMP, the Hybrid Wireless Mesh Protocol, is the
mandatory default path selection protocol
Path selection extensibility framework for use of other
path selection protocols
Active path selection protocol indicated by path
selection protocol identifier in Mesh Configuration IE
HWMP can be always configured for interoperability
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Hybrid Wireless Mesh Protocol (HWMP)
Default Routing protocol in 802.11s
Reactive path selection as basic path selection
mechanism (always available)
– path is only established if needed (on-demand)
– no path selection control traffic if no data is sent
– on-demand path discovery mechanism
– works with arbitrary path selection metrics
Proactive path selection tree to designated mesh STAs
(can be configured at root mesh STAs)
 described later
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Path Discovery in HWMP
Path Request (PREQ)
O
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B
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C
PREQ
reverse path
PREP
forward path
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D
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O – Path Originator
T – Path Target
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Forwarding info @ “D“ after PREQ
Destination Mesh STA Address
O
Destination HWMP Sequence Number
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Next Hop Address
C
Precursor List
link metric (O-A) +
link metric (A-B) +
link metric (B-C) +
link metric (C-D)
Path Metric
Number of Hops
4
Lifetime of Forwarding Information
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<lifetime>
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Path Discovery in HWMP
Path Reply (PREP)
O
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PREQ
reverse path
PREP
forward path
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O – Path Originator
T – Path Target
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Forwarding Info @ “D” after PREP
O
T
14
2011
recipient for
forwarding
C
E
PERR forwarding,
loop prevention
(E, <lifetime>)
(C, <lifetime>)
link metric (O-A) +
link metric (A-B) +
link metric (B-C) +
link metric (C-D)
link metric (T-F) +
link metric (F-E) +
link metric (E-D)
4
3
<lifetime>
<lifetime>
Destination Mesh STA Address
loop prevention
Destination HWMP Sequence Number
Next Hop Address
Precursor List
best quality path
Path Metric
Number of Hops
timeout of unused
forwarding
information
Lifetime of Forwarding Information
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The Simplest Path Discovery
O
PREQ
PREP
T
PREP
T
… easily extensible
PREQ
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Further Features of HWMP
Path repair
– If path gets disrupted,
Path Error (PERR) is
generated at link
break and propagated
towards source mesh
STA
– Source mesh STA set
ups new path to
destination mesh STA
– PERR used for
indication of different
error conditions
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Non-forwarding mesh STA
– Is only mesh source or
mesh destination but
does not forward frames
for other mesh STAs
– Participates in HWMP,
but does not propagate
HWMP control messages
– Increases the risk of
disconnected MBSS
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Frame format
So… What do we do with this forwarding information?
2 Octets
2 Octets
6 Octets
6 Octets
6 Octets
2 Octets
6 Octets
2 Octets
4 Octets
0-7955 Octets
4 Octets
Frame
Control
Duration/ID
Address 1
Address 2
Address 3
Sequence
Control
Address 4
QoS Control
HT Control
Body
FCS
Receiver
Address
Mesh
Transmitter
Destination
Address
Address
Mesh
Source
Address
Mesh
Control
6, 12, 18, or 24
Octets
1 Octet
Mesh Flags
2 Bits
Address
Extension
Mode
1 Octet
4 Octets
0, 6, 12, or 18 Octets
Mesh Time
To Live
(TTL)
Mesh
Sequence
Number
Mesh Address Extension
6 Bits
Reserved
Mesh
Source
Address
Destination
Address
Mesh Control field provides address extension (six
addresses), TTL, & Sequence Number
Mesh Control field is encrypted as part of data
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Source
Address
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Multi-hopping in the Mesh BSS
Power save in the Mesh BSS
Wireless Mesh network = multi-hop topology
≠ master-slave topology
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Power save
Optimized power consumption for the whole
network
– Any device may operate in power save
– Power constrained devices limit forwarding and
minimize power consumption
Instant power-up
Relaxed transition to sleep
– Deep & light sleep
– Good responsiveness of the network
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Interaction between power save
and forwarding
Frames are buffered for Power save mesh
STAs
Power saving mesh STAs can limit
participation in forwarding:
– Mesh STA may limit the amount of peerings
– Mesh STA may operate in non-forwarding
mode
 Only create paths for own traffic
– Link metrics may account for power
constraints
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Power save and peerings
Each mesh peering consists of two mesh
power modes:
– Local mesh power mode, a promise to the
peer
– Peer mesh power mode, a promise by the
peer
Power modes of different mesh peerings are
independent from each other
Mesh STA may operate in Doze state (radio
off) only if no peering requires operation in
Awake state (radio on)
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Mesh power modes
Mesh STAs communicate their mesh
power mode for each link:
– Active mode
 Mesh STA available at any time
– Light sleep mode
 Monitoring peer STA beacons
 Responsible to fetch buffered data
– Deep sleep mode
 Not monitoring peer STA beacons
 Not responsible for fetching buffered data
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Link-specific mesh power modes
Mesh power mode can be set dynamically
“per link”
Weak link
M3
M4
Active mode
M1
Light sleep mode
M2
Safe link
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AP
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M5
Deep sleep mode
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Power save details
Going to active mode is safe
– Transmissions cannot be missed, i.e. signaling
is done with group- and individually-addressed
frames
Going to power save is less safe
– Transmissions may be missed if peer is
assumed to be available, i.e. individuallyaddressed frames are used
The service periods maintain power saving
devices available during the individually
addressed data transmission
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Multi-hopping in the Mesh BSS
Topics in radio resource management
Wireless Mesh network = multi-hop topology
≠ master-slave topology
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Radio resource management
Main challenges:
– Hidden node problem mitigation
– Distributed management
– Minimize and localize the effect of topology dynamics
Some topics from 802.11s radio resource management
– Robust neighbor discovery
– Distributed resource reservation
– Synchronization
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Hidden node problem
Interference
STA2
STA1
STA4
STA3
MBCA  mitigates beacon collisions in 2 hop range
MCCA  enables distributed reservation access
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Mesh Beacon Collision Avoidance (MBCA)
Beacon protection from hidden nodes
– Passive scan, power management, and
distributed reservation (MCCA) rely on Beacon
frames
– Need to protect from the interference from
hidden nodes
– MBCA provides a tool for the mitigation
– MBCA reports on Beacon frames even beyond
the MBSS
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Distributed resource reservation (MCCA)
MCCA (MCF coordinated channel access) enables
allocation of deterministic channel time without
central coordinator
Deterministic channel access (i.e., TDMA type of
channel assignment) is more efficient in some
cases
OK. I am receiving traffic from
I will reserve channel for mesh
STA1 from 6am to 7am in my local
time. Please confirm if it is OK.
STA1
STA2
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AP
STA
STA
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AP
STA
STA
M
STA4
STA
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STA
mesh STA4 from 7:30am to
9:30am. Please do not interfere.
M P
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STA3
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Distributed resource reservation (MCCA)
After the negotiation process, orthogonal channel
time will be allocated for MCCAOP owner
DTIM Interval
(DTIM duration) / (MCCAOP
Periodicity)
Offset
t
MCCAOP
Duration
MCCAOP
of mesh STA k
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MCCAOP
of mesh STA n
AP
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Synchronization
802.11s defines the default synchronization method
“Neighbor Offset Synchronization”
– Do not have “global timer” in the network
– Each node runs its own TSF timer and manages
the time differences between its neighbors
– Try to minimize the impact of topology changes
Time difference to
STA1: -09:15:15
STA3: +06:27:12
Time difference to
STA2: +09:15:15
STA2
Local time: 09:27:50am
STA1
Local time: 00:12:35am
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Time difference to
STA2: -06:27:12
STA3
Local time: 03:55:02pm
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MBSS with mesh gates
connected to external STAs
Proactive path selection
Mesh gate & proxy
6-address frame format
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Proactive routing
A proactive routing functionality is necessary because
– Certain nodes are gateways to other networks and faster path
setup can be ensured
– Some nodes receive more traffic than others
Proactive routing is centered around a root node, which may (or may
not) be a mesh gate
Two methods are available:
Recall the PREQ:
•Broadcast propagation
•Unicast destination
Proactive PREQ
All reverse paths are established
with one PREQ message
– Broadcast propagation
– Broadcast destination
Forward path is established
(normally) with a PREP
– On-demand, or proactively
(configurable)
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Proactive RANN
Reuses the PREQ messages
– Unicast propagation
– Unicast destination
A Root Announcement message
provides a set of candidate
paths
Reverse path is established
(normally) with a PREP
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Forwarding
information
Proactive Path Request
Node A
C
Node C
Dest.
NH
M
Dest.
NH
M
R
R
1
R
R
1
Destination address
R
Node D
A
D
Node B
Dest.
NH
M
Dest.
NH
M
R
R
2
R
A
2
B
Next hop node
Node E
E
PREQ
Dest.
NH
M
R
D
2
reverse path
forward path is created as in reactive method
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• on-demand (only when needed)
• immediately (proactive)
• configured at root mesh STA
R – Root
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Proactive Root Annoucement
R
A
G
B
E
D
F
C
RANN
candidate path
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M
M
AP
STA
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No forwarding information
affected
R – Root
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Unicast Path Request
T
A
O
B
E
D
F
C
PREQ
reverse path
PREP
forward path
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L
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P
AP
STA
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AP
STA
STA
M
O – Path Originator
T – Path Target
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STA
PREP method is
unchanged
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Proxy
STAs that are outside the MBSS are reached
through a proxy Mesh STA (gate)
Proxy information is carried through PREQs
and PREPs
– The originator STA does not know whether the
target is inside or outside the MBSS until the
PREP is received
Proxy information can also be communicated
via Proxy Updates
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Path Request with Proxy info
Node O
Dest.
Proxy
T
P
Intermediate nodes don’t
need to know about
external addresses
O
Node O
Dest.
NH
M
P
A
7
A
P
B
In the example, the reverse
path has already been
created
P
AP
STA
STA
E
D
reverse path
PREP
forward path
STA
M
M
M
F
C
PREQ
L
STA
T
AP
STA
STA
M P
STA
O – Path Originator
T – Path Target
P – Mesh Proxy
62
End to end 802 communication
SA
mesh SA
link
STA 33
Portal
Gate
Mesh
TA
mesh
link
STA 1
802.x LAN
Mesh
STA 4
RA
Mesh
mesh
link
STA 6
mesh DA
mesh
link
Mesh
DA
Gate
STA 2
mesh path
end to end 802 communication
Transmitter
Address
Mesh
STA 6
Mesh
STA 4
STA
L
STA
P
AP
STA
STA
M
M
M
AP
STA
STA
M P
STA
Mesh
Destination
Address
Mesh
STA 2
Mesh Source
Address
Mesh
STA 1
link
STA 22
infrastructure BSS
mesh BSS (MBSS)
Receiver
Address
AP
STA 17
Destination
Address
Source
Address
STA 22
STA 33
63
Wrap Up
64
û
The big
picture …
û
802.3
J
Gate C
Gatel B
Mesh STA C
Mesh STA B
802.3
Gate D
Internet
router
Mesh STA D
Mesh STA Y
Mesh STA E
SS B
Portal E
AP L
BSS
L
Mesh STA Y
SS A
A
B
Gate A
Mesh STA G
Mesh STA F
Mesh STA A
Mesh BSS
802.16
Mesh STA K
Mesh STA J
AP K
E
Mesh STA U
D
BSS K
Mesh STA W
Mesh STA V
802.11s Mesh Link (forwarding, may be part of a mesh path)
802.11s Mesh Link (non-forwarding)
P
AP
STA
STA
M
M
802.11 link within Basic Service Set (BSS)
STA
L
STA
Link released after transitioning to new location
AP
STA
STA
M
M P
STA
C
BSS
M
B
Mesh STA H
BS C
AP M
65
One broadcast domain
The 802.11s
mesh
appears as a
single,
logical
broadcast
domain
Support for
spanning
tree
guarantees
loop free
connectivity
with external
networks
û
AP
STA
STA
M
M
802.3
Mesh STA Y
SS B
Portal E
AP L
BSS
L
SS A
A
Mesh STA G
BS C
Mesh STA F
Mesh STA A
Mesh BSS
Mesh STA K
Mesh STA J
AP K
E
Mesh STA U
STA
STA
C
BSS
M
B
Gate A
802.16
AP M
B
Mesh STA H
D
BSS K
Mesh STA V
M P
Mesh STA E
Mesh STA Y
Mesh STA W
AP
Internet
router
Mesh STA D
STA
M
Mesh STA C
Gate D
STA
L
P
J
Gate C
Gatel B
Mesh STA B
–  Gates
B&C
blocked
STA
û
802.3
66
Transparent integration
Via Gate
D, 802.3
station J
integrates
transparently
with the
802.11s
mesh
û
Mesh STA C
802.3
Gate D
Mesh STA Y
SS B
BSS
L
A
Mesh STA G
BS C
STA
Mesh BSS
Mesh STA K
STA
STA
M
Mesh STA F
Mesh STA A
Mesh STA J
AP
M P
STA
C
BSS
M
B
Gate A
802.16
AP M
B
Mesh STA H
STA
M
M
Portal E
AP L
SS A
L
AP
Mesh STA E
Mesh STA Y
AP K
E
D
BSS K
Mesh STA V
STA
Internet
router
Mesh STA D
Mesh STA W
P
J
Gate C
Gatel B
Mesh STA B
Mesh STA U
STA
û
802.3
67
Works as Distribution System
Medium
The 802.11
concept relies
on a central AP
that forms a
Basic Service
Set (BSS)
Interconnected
by 802.11s &
802.3, stations
can transition
to and from
APs K, L & M
within BSSs K,
L & M,
respectively
STA
AP
STA
STA
M
M
M
û
802.3
J
Gate C
Gatel B
Mesh STA C
Mesh STA B
802.3
Gate D
Internet
router
Mesh STA D
Mesh STA Y
SS B
Mesh STA E
Portal E
AP L
BSS
L
Mesh STA Y
SS A
A
Mesh STA G
BS C
Mesh STA F
Mesh STA A
Mesh BSS
Mesh STA K
Mesh STA J
AP K
E
Mesh STA U
D
BSS K
Mesh STA W
Mesh STA V
AP
STA
STA
M P
STA
C
BSS
M
B
Gate A
802.16
AP M
B
Mesh STA H
STA
L
P
û
68
Mobility within the Mesh
û
802.11s
enables a
mobile Mesh
STA Y to
establish a
new mesh link
to Mesh STA C
and to release
mesh links to
Mesh STAs A
and H
û
802.3
J
Gate C
Gatel B
Mesh STA C
Mesh STA B
802.3
Gate D
Mesh STA Y
SS B
Mesh STA E
BSS
L
SS A
A
Mesh STA G
BS C
Mesh STA F
Mesh STA A
Mesh BSS
AP K
E
Mesh STA U
D
BSS K
Mesh STA W
Mesh STA V
STA
L
AP
STA
STA
M
M
AP
STA
STA
M
M P
STA
C
BSS
M
B
Gate A
802.16
AP M
B
Mesh STA H
Mesh STA K
P
Portal E
AP L
Mesh STA Y
Mesh STA J
STA
Internet
router
Mesh STA D
69
Mesh Networking
û
Owing to its
mesh
capabilities,
Mesh STA U
connects
simultaneously
to the printer
Mesh STA W,
the storage
device Mesh
STA V and
maintains
internet
connectivity via
Mesh STA J.
P
AP
STA
STA
M
M
AP
802.3
Internet
router
Mesh STA D
Mesh STA Y
SS B
Mesh STA E
Portal E
AP L
BSS
L
Mesh STA Y
SS A
A
Mesh STA G
BS C
Mesh STA F
Mesh STA A
Mesh BSS
Mesh STA K
Mesh STA J
AP K
E
Mesh STA U
D
BSS K
Mesh STA W
Mesh STA V
STA
C
BSS
M
B
Gate A
802.16
AP M
B
Mesh STA H
STA
M P
Mesh STA C
Gate D
STA
M
J
Gate C
Gatel B
Mesh STA B
STA
L
STA
û
802.3
However, as a non-forwarding
mesh device, it does not
interconnect Mesh STAs W, V and
J.
70
Transient Network
802.11s
mesh
integrates
with
other 802
networks
(802.3,
802.16
etc.)
û
Mesh STA C
802.3
Gate D
Mesh STA Y
SS B
AP
STA
STA
M
M
Portal E
AP L
BSS
L
SS A
A
Mesh STA G
BS C
Mesh STA F
Mesh STA A
Mesh BSS
Mesh STA K
Mesh STA J
AP K
E
Mesh STA U
AP
STA
M P
STA
C
BSS
M
B
Gate A
802.16
AP M
B
Mesh STA H
STA
M
Mesh STA E
Mesh STA Y
STA
L
Internet
router
Mesh STA D
D
BSS K
Mesh STA V
P
J
Gate C
Gatel B
Mesh STA B
Mesh STA W
STA
û
802.3
71
Conclusion
Transparent
integration of other
802 networks
Minimal manual
configuration
needed
No change to
802.11 hardware
– All-software
solution
STA
L
STA
P
AP
STA
STA
M
M
AP
STA
STA
M
M P
STA
Opens up new
markets
– Standardized range
extension
– Collaborative
networks
Truly ad hoc
Solves old
problems
– Peer-to-peer
– Authentication