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802.11s
TTA (WiFi) 2012.10.26
ETRI
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Overview
Routing
Interworking
Frame Format
MAC Enhancements
Contents
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Introduction & Background
Architectural & Usage Models in 802.11s
Framework of 802.11s Mesh Network
Topology Creation
MAC layer forwarding MAC functionality enhancements
Issues of 802.11s
Overview
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Wireless Mesh Networks?
Wireless multi-hop infra networks, where a few nodesprovide a connection to the external world (e.g., Internet)through a cable
Alternative wireless access technology, which can replacethe traditional sets of IEEE 802.11 wireless LANs
Commercialized and managed ad hoc networks, whichIntroduce a hierarchy in the network architecture withfixed, special routers and mobile, general clients
Introduction
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Many vendors have developed their own
proprietary solutions and put them on themarket, because it is flexible and more costeffective than the typical wired APs
Motorola, Tropos, Belair, PacketHop, Strix
However, though most of them are based on thecommon 802.11 MAC, these products are notinteroperable
Need for defining a standard architecture for WMNs
Motivation
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IEEE has been playing a key role in the
development of wireless mesh standards IEEE 802.11s WLAN Mesh
IEEE 802.15.5 WPAN Mesh
IEEE 802.16a/d/j WMAN Mesh
Motivation of WLAN Mesh standards Current 802.11 ad hoc mode is not sufficient for multi-hop
mesh.
Recent efforts for the advance of 802.11 standards, such
as 11e for QoS support or 11n for high data rates (>100Mbps), are still limited due to their inherent dependencyupon the wired infrastructure backbones and the last,single-hop wireless communication
WMN Standardization Efforts in IEEE 802
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Nov 2003: 802.11 ESS Mesh Study Group created
May 2004: 802.11s Task Group approved
Jan 2005: Call for 802.11s proposals issued
Mar 2006: First 802.11s Draft Spec Adopted
June 2011: Draft 12.0 July 2011: forward P802.11s to REVCOM
Sep 2011: 802.11s-2011 Standard
History of IEEE 802.11s Standardization
http://grouper.ieee.org/groups/802/11/Reports/tgs_update.htm
Mesh Networking Task Group -Task Group Acting Chair: Dee Denteneer (Philips)Vice Chair: Guido Hiertz (Philips)Technical Editor: Kazuyuki Sakoda (Sony)Secretary: Guenael Strutt (Powerwave
http://grouper.ieee.org/groups/802/11/Reports/tgs_update.htmhttp://grouper.ieee.org/groups/802/11/Reports/tgs_update.htm8/11/2019 6_ )
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The 802.11 Task Group s (TGs)
Formed in May 2004 to design mesh networks consistingof different WLAN devices performing routing at link layer(layer 2)
To be based on extensions to the current IEEE 802.11architecture and protocols:
WLAN (Layer 2) Mesh Networks
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It will provide an IEEE 802.11 Wireless DS that
supports both broadcast/multicast and unicastdelivery at the MAC layer using radio-awaremetrics over self-configuring multihoptopologies
The Objectives: Increased range/coverage & flexibility in use
Possibility of increased throughput
Reliable performance
Seamless security Power efficient operation
Multimedia transport between devices
Backward compatibility and interoperability forinterworking
IEEE 802.11s: Meshed WLAN Networks
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802.11 TGs has defined the following:
Mesh network size (scale)32 mesh nodes (up to 50)
Architectural model
Usage models: 4 usage scenarios
Originally, it was 5 usage cases including car-to-car Functional requirements
IEEE 802.11s: Major Properties
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Mesh Portal: Acting as a gateway/bridge to externalnetworks
Mesh STA (Station): Relay frames in a router-like hop-by-hop fashion
Mesh AP (Access Point): Mesh relaying functions + APservice for clients
Network Architecture
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Internal L2 behavior of WLAN Mesh is
transparent to higher layers An MBSS (Mesh Basic Service Set) appears as a single
access domain.
Mesh Basic Service Set (MBSS)
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From 11s Std.
MBSS example and Terminology
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From 11s Std.
MBSS example and Terminology
DS
STA 19 STA 20
STA 18
STA 13
Mesh
STA 9
STA 14STA 15 Mesh
STA 11
Mesh
STA 10
Mesh
STA 12
STA 8
Mesh
mesh
BSS 2Mesh
Gate
DS
Mesh
Gate
STA 33
STA 21
STA 22
Portal
STA 17
AP infrastructure
BSS 13
AP
Mesh
STA 1
Mesh
Gate
Mesh
STA 5
Mesh
STA 3
Mesh
STA 4
Mesh
STA 6
Mesh
STA 7
Mesh
STA 16
Mesh
STA 2
Mesh
Gate
mesh
BSS 1
Portal
Non-802.11
LAN
infrastructure
BSS 17
infrastructure
BSS 18
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MAC data plane architecture
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MAC architecture
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Residential
Inside home or a residential building High bandwidth application (e.g., multimedia content
distribution)
Office
Small to medium sized enterprise buildings
Campus/Community/Public access
Out-door deployment environment
Seamless connectivity
Public Safety Emergency sites
Military case
Usage Models
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In the digital home usage model, the primary purposes for themesh network are to create low-cost, easily deployable, high
performance wireless coverage throughout the home. The meshnetwork should help to eliminate RF dead-spots and areas oflow-quality wireless coverage throughout the home. High-bandwidth applications such as video distribution are likely to beused within a home network, thus high bandwidth performancewill be very important for residential mesh networks.
Residential Usage Case
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In the office usage model, the primary motivation for using meshnetwork technology is to create low-cost, easily deployable
wireless networks that provide reliable coverage andperformance.
WLAN Mesh networks are particularly useful in areas whereEthernet cabling does not exist or is cost prohibitive to install.Offices can reduce capital costs associated with cable installationand reduce time required for deployment. They may also benefit
from an increase in employee productivity through expandedconnectivity to key data network resources.
Office Usage Case
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Seamless connectivity over large geographic areas
Rapidly provide connectivity to locations where wired
infrastructure is not available or is cost prohibitive Lower cost / higher bandwidth alternative to traditional internet
access methods (dial up, cable, DSL, fiber)
Enable advanced applications/services through ubiquitous access& reliable connectivity
Enable location based services. Location information isparticularly important for public safety services
Campus/Community/Public Access Usage Case
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Public safety mesh networks provide wireless network access toemergency and municipal safety personnel such as fire, police,and emergency workers responding to an incident scene. Thenetwork may be used for video surveillance, tracking emergencyworkers with bio-sensors, voice and data communicationbetween emergency workers, uploading images, downloadinghazmat information, tracking air status, etc.
Public Safety Usage Case
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Military usage of mesh networks can be classified into twocategories. The first category, non-combat usage, is adequatelyrepresented by the usage cases previously described in thisdocument. The second category, combat operational usage, isdistinguished by node mobility, a heavy reliance on fullyautomated network management and, for disadvantaged nodes,e.g., dismounted troops, sensitivity to energy conservation.
Military Usage Case
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The set of services provided by the WLAN Mesh
To support the control, management, and other operation,including the transport of MSDUs between Mesh STAswithin the WLAN Mesh
Functional Requirements
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Mesh Topology Creation
Self-configuring neighbor discovery ( Mesh Peering)
Channel switching
L2 Routing
MAC address based mesh path selection and forwarding
Hybrid Wireless Mesh Protocol (HWMP)
Radio-aware metrics for routing ( Airtime link metric)
MAC Enhancement
For supporting QoS, and increasing the network throughput
Power management
Congestion control
Security
IEEE 802.11i (for link security) as basis
SAE
Key Features of 802.11s Networks
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To discover peer Mesh STA devices and theirproperties:
MSTA performs passive scanning (via periodic beacons) oractive scanning (via probe messages)
The received beacon or probe response frame contains meshrelated information
Mesh ID: name of the mesh (SSID like string)Mesh configuration element (including version and support
functions)
A discovered MSTA will become a peer MSTA after peeringprocesses by 4-way handshaking.
2-way handshaking with peering-open-frame/peering-confirm-frame exchange in each direction
Mesh Peering Mechanism
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To select single/multi-hop path(s) and to forwarddata frames across these paths between MSTAs atthe link layer
Extensible framework
A WLAN Mesh may include multiple path selection metricsand protocols for flexibility
Allow the use of vendor specific solutions
A mandatory protocol and metric for all implementations arespecified
HWMP (AODV as basis)
Airtime link metric function Only one protocol/metric will be active on a particular link at
a time
A particular mesh will have only one active protocol at a time
Mesh Path Selection and Forwarding
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A default link metric to be used by a path selectionprotocol to select the best paths
Other metrics can also be used
Its cost function is based on airtime cost (Ca),which reflects the amount of channel resourcesconsumed by transmitting the frame over aparticular link
Airtime Link Metric Function
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Unicast Cost Function based on Airtime LinkMetrics
Example
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A default path selection protocol forinteroperability
To combine the flexibility of on-demand routediscovery with extensions to enable efficientproactive routing to mesh portals.
On-demand path selection mode
Used in intra-mesh routing for the route optimization
When a root portal is not configured or it can provide a betterpath even if root is configured.
Proactive tree building mode
If a root portal is present, a distance vector routing tree is builtTree based routing avoids unnecessary discovery flooding during
discovery and recovery
Hybrid Wireless Mesh Protocol (HWMP)
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1. Source MSTA broadcasts PREQ (path request) with thedestination and metric initialized
2. Upon receiving PREQ, MSTAs update the path to source ifsequence number is greater and offers a better metric
3. If a new path is created or the existing one is modified,PREQ is forwarded further
4. PREQ provides Destination only (DO) and Reply andForward (RF) flags
If DO=1: Only destination sends PREP (path reply) after selectingbest path
If DO=0 and RF =0: Intermediate node with path sends a unicastPREP to the source MP and does not forward PREQ
If DO=0 and RF =1: The first intermediate node with the path to thedestination sends a PREP and forwards PREQ setting DO =1 toavoid other intermediate nodes to send back PREP.
5. When source receives the PREP, it creates a path to thedestination.
HWMP: On-demand Mode
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Proactive RANN mechanism Root MSTA periodically broadcast RANN
Distribute path information for reaching the root MSTA, but theactual paths to the root can be built on-demand
(3-way handshaking)
Proactive PREQ mechanism
Root MSTA periodically broadcast PREQ To create paths between the root mesh and all mesh nodes in the
network proactively (2-way handshaking)
2 modes:
proactive PREQs on-demand PREP (no proactive PREP)
proactive PREQs proactive PREP (configured at root MSTA)
HWMP: Proactive Tree Building Mode
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1) The root MP periodically
propagates a RANNinto the network
2) Upon reception of aRANN, each MP has to
create or refresh a path to theroot through
sending a unicast PREQ to theroot MP.
3) The root MP sends a PREP
in response to each PREQ. 4) Tree path construction is
completed
Example Proactive RANN mechanism
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1) The root MP periodicallypropagates a PREQ into thenetwork
Destination Address set to all ones
The DO flag set to 1 and the RFflag set to 1
2) Upon reception of a PREQ,each MP has to create orrefresh a path to the root MP
3) The recipient MPs action
If Proactive PREP bit set to 0, MPmay send a proactive PREP if
required
If Proactive PREP bit set to 1, MPshall send a proactive PREP
4) Tree path construction iscompleted
Example Proactive PREQ mechanism
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The existing 802.11 MAC layer is being enhanced for
Supporting QoS:
EDCA(Enhanced Distributed Channel Access) specified in 802.11e,as the 802.11s basic operation mechanism
Other features of 802.11e, like HCCA, are not considered
Improving the network capacity:
Efficient handling of the two different kinds of traffic (BSS traffic &Forwarding mesh traffic)
Intra-mesh congestion control
Mesh coordinated channel access (optional)
Etc:
Mesh beacon collision avoidance (MBCA) detects and mitigatecollisions among beacon frames transmitted by other STAs within2 hops
Link specific mesh power modes defines two sleep modes (lightsleep/deep sleep) to differentiate power consumption (optional)
802.11s MAC Enhancements
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Handling BSS and mesh traffic by Mesh AP
Giving priority to mesh traffic may starve STAs
Giving priority to STAs might waste resource utilized by mesh traffic
Advanced solutions: separate radio for mesh and BSS traffic
Intra-mesh congestion control
Local congestion monitoring Congestion detection
Congestion control signaling Local rate control Only congestion control signaling is defined in the standard
Specific algorithms for local congestion monitoring, congestion detectionand local rate control are beyond the scope.
Mesh Coordinated Channel Access (MCCA)
Optional scheme based on the reservation of contention free timeslots
Lower contention (more deterministic) mechanism for improved QoSfor periodic flows
MAC Enhancements More Details
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Mesh beacon collision avoidance (MBCA) Each mesh STA shall periodically transmit beacon frames.
Neighbor offset protocol
Each mesh STA keeps track of the time base of its neighbor mesh STAs
The mesh STA adjusts beacon timing to avoid collisions among otherbeacon frames transmitted by neighboring STAs
Power save in a MBSS Active mode
The mesh STA shall be in Awake state all the time
Sleep mode
The mesh STA alternates between Awake and Doze states
Light sleep mode
The mesh STA shall listen to all the Beacon frames from its peer meshSTA
Deep sleep mode
The mesh STA may choose not to listen to the Beacons from its peer
mesh STA
MAC Enhancements More Details
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Mobility is of little concern (do not support seamlesshandover)
No mechanism for multi-channel operation
Just recommendations for multiple interfaces (no specific solutionsdefined)
One proposal called CCF (Common Channel Framework) wasadopted in the early version of the draft (before draft 1.0), but
removed from the draft
Limitations caused by the EDCA
Performance limitations in multi-hop environments
End-to-end QoS limitations
And many more More reliable and stable metric for link quality measurement and
routing?
Better solutions for power management?
More robust security approaches
Remaining Issues of 802.11s
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Mesh Path Selection & Forwarding Framework
Airtime Link Metric
HWMP : Hybrid Wireless Mesh Protocol
Routing
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802.11s vendor specific
Path Selection Protocol
Default: Hybrid wireless mesh protocol (HWMP)
Path Selection Metric
Default: Airtime link metric
Congestion Control Mode
Congestion control signaling protocol
Synchronization Protocol
Neighbor offset protocol
Authentication Protocol
SAE (Simultaneous Authentication of Equals)
Extensible Framework
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Assumption
Forward link and backward link have the samelink cost (Bidirectional)
Two methods Link metric request / report
Voluntarily sending link metric report to peer mesh
Action Upon reception of a link metric report, a mesh STA
updates its local link metric
Problem
Who will update the link metric (sending report)?
Link Metric Reporting
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In a single link (mesh link)
Address 1 (RA): the address of the next-hop mesh STA
Address 2 (TA): the address transmitter mesh STA
In a multi-hop mesh path
Address 3 (Mesh DA): the address of the destination mesh STA
Address 4 (Mesh SA): the address of the source mesh STA
In a end-to-end 802 communication (beyond MBSS) Address 5 (DA): the address of the destination end station
Address 6 (SA): the address of the source end station
Use of 6 Addresses
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Frame Addressing
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On receipt of an individually addressed frames, Detect duplicated frames by the pair of address 4 (Mesh SA) and
sequence number
Three cases:
Case 1) If address 3 (Mesh DA) matches own MAC address
A) If address 5, 6 dose not exist, send it to an upper layer
B) If address 5 is the proxied address, forward it
Case 2) If address 3 is known, forward it Case 3) If address 3 is unknown: three options (A, B, C)
A) Discard
B) Trigger a path discovery procedure
C) Inform the previous node (TA) that the destination is unreachable
When the received frame is forwarded, The lifetime of the forwarding information is updated
The TTL field in the frame is decremented by 1
Frame Forwarding
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Group addressed frame
It indicates multicast and broadcast frames.
On receipt of an group addressed frames, Detect duplicated frames by the pair of address 4 (Mesh SA)
and sequence number
The TTL field in the frame is decremented by 1
Set Address 2 to its own MAC address and the frame isqueued for transmission
Frame Forwarding
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A default link metric to be used by a pathselection protocol to select the best paths
Its cost function is based on airtime cost (Ca),which reflects the amount of channel resourcesconsumed by transmitting the frame over aparticular link
Cost is encoded as an unsigned integer in units of 0.01 TU.
1 TU = 1024s 1ms
Airtime Link Metric
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Combine the flexibility of on-demand path selection withextensions to enable proactive routing to the root mesh
node Proactive path allows communication to begin immediately while
an ondemand discovery finds a more optimal path
Proactive tree building mode
Periodic tree path renewal
On-demand path selection mode
A path is discovered by PREQ (Path Request) / PREP (Path Reply)exchange when the path is required
Hybrid Wireless Mesh Protocol (HWMP)
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Terminology
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Terminology
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HWMP sequence number To prevent the creation of path loops and to distinguish stale and
fresh path information
Each mesh STA keeps its own HWMP sequence number
It is included in the PREQ, PREP, PERR, and RANN elements
The HWMP sequence number in the forwarding information
It is updated whenever a mesh STA receives new information
A mesh STA increments its own HWMP sequencenumber in two circumstances: Immediately before an originator mesh STA starts a path discovery.
Immediately before a target mesh STA originates a PREP in
response to a PREQ
General Rules: HWMP Sequence Numbering
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The forwarding information (= route table entry)
When PREQ or PREP is received, the forwarding
information is updated in the following condition HWMP sequence number is greater
HWMP sequence number is same and the updated pathmetric is better than the path metric in the forwardinginformation
General Rules: Forwarding information
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1. Source MP broadcasts PREQ (path request) with thedestination and metric initialized
2. Upon receiving PREQ, MPs update the path to source ifsequence number is greater and offers a better metric
3. If a new path is created or the existing one is modified,PREQ is forwarded further.
4. PREQ provides Destination only (DO) and Reply andForward (RF) flags.
If DO=1: Only destination sends PREP (path reply) after selectingbest path.
If DO=0 and RF =0: Intermediate node with path sends a unicastPREP to the source MP and does not forward PREQ
If DO=0 and RF =1: The first intermediate node with the path tothe destination sends a PREP and forwards PREQ setting DO =1 toavoid other intermediate nodes to send back PREP.
5. When source receives the PREP, it creates a path to thedestination.
On-demand Path Selection Mode
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Proactive PREQ mechanism Root MP periodically broadcast PREQ
To create paths between the root mesh and all mesh nodes in thenetwork proactively
Proactive RANN mechanism Root MP periodically broadcast RANN
RANN is only used to disseminate path metrics to the root Reception of a RANN does not establish a path
The receiving mesh STA may initiate a PREQ/PREP exchange withthe root mesh STA to set up or update a path
Proactive Tree Building Mode
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1) The root MP periodically propagates a
PREQ into the network Destination Address set to all ones
The TO flag set to 1 and the RF flag set to 1
2) Upon reception of a PREQ, each MPhas to create or refresh a path to the
root MP 3) The recipient MPs action
If Proactive PREP bit set to 0, MP may send aproactive PREP if required
If Proactive PREP bit set to 1, MP shall send aproactive PREP
4) Tree path construction is completed
Example Proactive PREQ mechanism
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1) The root MP periodically propagates
a RANN into the network
2) Upon reception of a RANN, each MPmay create or refresh a path to the rootthrough sending a unicast PREQ to theroot MP
3) The root MP sends a PREP inresponse to each PREQ
4) Tree path (partial) is updated
Example Proactive RANN mechanism
Path Error (PERR)
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PERR is used for announcing a broken link to alltraffic sources that have an active path over this
broken link Conditions for generating a PERR
The mesh STA detects a link break to the next hop of anactive path while transmitting frames to it.
Or, the mesh STA receives a data frame with a DA for whichit has no forwarding information.
PERR Reception: Acceptance criteria
The destination in its own forwarding information is
contained in the list of unreachable destinations of the PERR And the next hop is the transmitter of the received PERR
PERR propagation
The mesh STA received a PERR from a neighbor for one or
more of its active paths
HWMP Example 1
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No Root, Destination Inside the Mesh
MP 4 wants to communicate with MP 9
1. MP 4 first checks its local forwardingtable for an active forwarding entry to MP 9
2. If no active path exists, MP 4 sends a
broadcast RREQ to discover the best pathto MP 9
3. MP 9 replies to the RREQ with a unicastRREP to establish a bi-directional path fordata forwarding
4. MP 4 begins data communication withMP 9
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HWMP Example 3
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Root Portal, Destination Outside the Mesh
MP 4 wants to communicate with X 1. MPs learns Root MP 1 through Root
Announcement messages
2. If MP 4 has no entry for X in its localforwarding table, MP 4 may immediatelyforward the message on the proactive pathtoward the Root MP 1
3. When MP 1 receives the message, if itdoes not have an active forwarding entry toX it may assume the destination is outsidethe mesh
4. Mesh Portal MP 1 forwards messages toother LAN segments according to locallyimplemented interworking
Note: No broadcast discovery requiredwhen destination is outside of the mesh
HWMP Example 4
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With Root, Destination Inside the Mesh
MP 4 wants to communicate with MP 9 1. MPs learns Root MP 1 through Root
Announcement messages
2. MP 4 first checks its local forwardingtable for an active forwarding entry to MP 9
3. If no active path exists, MP 4 mayimmediately forward the message on theproactive path toward the Root MP 1
4. When MP 1 receives the message, it flagsthe message as intra-mesh and forwardson the proactive path to MP 9
5. MP 9, receiving the message, may issue aRREQ back to MP 4 to establish a path thatis more efficient than the path via Root MP1
Default HWMP Parameters from Annex D
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PREQ propagation and retransmission
dot11MeshHWMPmaxPREQretries: 3
dot11MeshHWMPnetDiameter: 31
dot11MeshHWMPnetDiameterTraversalTime: 500 TU (0.5 sec)
dot11MeshHWMPpreqMinInterval: 100 TU (0.1 sec)
dot11MeshHWMPperrMinIntervaI: 100 TU (0.1 sec)
Path lifetime
dot11MeshHWMPactivePathTimeout: 5000 TU (5 secs)
dot11MeshHWMPactiveRootTimeout: 5000 TU (5 secs) from root
dot11MeshHWMPpathToRootTimeout: 5000 TU (5 secs) to root
Proactive mode in HWMP
dot11MeshHWMProotInterval: 2000 TU (2 secs) proactive RREQ dot11MeshHWMPrannInterval: 1000 TU (1 sec) proactive RANN
dot11MeshHWMPconfirmationInterval: 2000 TU (2 secs)
Interworking
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MBSS
Portal Behavior
Proxy Protocol
Interworking
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An MBSS (Mesh Basic Service Set) appears as asingle access domain.
An MBSS may have zero or more portalsconnected to one or more LAN segments
The IEEE 802.1D bridging protocol may be utilized to avoidbroadcast loops
Portal announcement protocol To allow mesh STAs to select the appropriate portal
A portal initiates a PANN frame at every predefined interval
Default interval: 10 seconds
A mesh STA propagates the received Portal Announcement
Example of MBSS (Mesh Basic Service Set)
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It normally appears as if all
mesh STAs in an MBSS aredirectly connected at the linklayer
Data Forwarding Behavior with Portal
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Mesh STA data forwarding behavior
If the mesh STA is not able to determine an intra-MBSS
path to the destination MAC address, the mesh STA shallassume that the destination is outside the MBSS and shallforward the message to one or more portals
If there is no portal available, the mesh STA shall discard theframe
Portal data forwarding behavior
Portals can learn the addresses of the mesh STAs and ofdevices attached to these mesh STAs
Through the receipt of path selection messages and proxy
updates
Portal Behavior
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Handling of frames that originated in the MBSS
a) A mesh STA address or a proxied address that the portal
knows is reachable through the MBSS:The portal forwards the frame to the destination mesh STA
b) An address that the portal knows is outside the MBSS:
The portal forwards the frame on the external network
c) A group address:
The portal forwards the frame on the external network as a
group addressed frame
d) An address unknown to the portal:
The portal forwards the frame on the external network
Portal Behavior
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Handling of frames that enter the MBSS
a) A mesh STA address or proxied address that the portal
knows is inside the MBSS:The portal forwards the frame to the destination mesh STA
b) A group address:
Transmit the frame within the MBSS using the forwardingprocedure for group addressed frames
c) An address that is unknown to the portal: (two options)
1) Attempt to establish a path to the destination forsubsequent delivery
2) Transmit the frame within the MBSS using the forwardingprocedure for group addressed frames
Proxy Protocol
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Proxy usage
For entities whose MAC addresses cannot be discovered
and reached using mesh services, i.e. they are not part of anMBSS
STAs that are associated with a MAP
STAs that are behind a mesh portal
Proxy Update (PU) A mesh STA generate a PU to inform a destination mesh
STA of its proxied addresses.
The destination mesh STA updates the proxy addressreported in the received PU.
Proxy Update Confirmation (PUC)
The destination mesh STA generated a PUC to inform thesender of PU that the PU has been properly received.
Frame Format
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MAC frame formats
Format of individual frame types Multi Hop Action
General Frame format
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minimal frame format, present in all frames
Mesh Control is placed in the first octets of theframe body
present only in certainframe types/subtypes
Fields & elements
Frame Control Field
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Type and subtype fields
To DS, From DS fields
indicates the presenceof Mesh Controlinformation
Frame Control Field
Mesh Control Field
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Mesh Control Field
General 6~24 octet
extended address
All Mesh Data frames andmulti-hop managementframes include Mesh ControlField
Mesh Flag field If Power Management field is
1, Power save level indicates
power save level
0 : light sleep mode
1 : deep sleep
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Beacon Information for Mesh
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Beacon frame format
Beacon frame body
Probe Request Information for Mesh
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7.2.3.8 Probe Request frame format
Probe Request frame body
Probe Response Information for Mesh
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Probe Response frame format
Probe Response frame body
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Multihop Actions
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Management Frames
Multihop Action Category
Mesh Peering Management
Mesh Link Metric
Mesh Path Selection
Mesh Interworking
Mesh Resource Coordination
Mesh Proxy Forwarding
MAC Enhancement
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EDCA & MDA , CCF
Intra mesh congestion control mesh beaconing & synchronization
power save
MAC Enhancements
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Mandatory MAC Functions
Enhanced Distributed Channel Access (EDCA)
Re-use of latest MAC enhancements from 802.11 (i.e. 802.11e)
Compatibility with legacy devices
Easy to implement, providing reasonable efficiency in simpleMesh WLAN deployments
Optional MAC Enhancements Mesh Deterministic Access (MDA)
Reservation-based deterministic mechanism
Common Channel Framework (CCF)
Multi-channel operation mechanism
Intra-mesh Congestion Control
Power Management
Enhanced Distributed Channel Access (EDCA)
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MAC QoS enhancement introduced by 802.11eproviding prioritized back-off
Used as baseline by 802.11s
Mesh Deterministic Access (MDA)
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MAC enhancement based on a reservation protocol
QoS support in large scale distributed Mesh networks
Synchronized operation Reduced contention (two-hop clearing)
Distributed scheduling
MDAOP Protocol
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Setup Request
Unicast from a transmitter to a receiver using MDAOP Setup RequestInformation Element (IE)
Setup Reply
Unicast from a receiver of Setup Request IE to the sender using theMDAOP Setup Reply IE (Accept or Reject, possibly with reasons andalternate suggestions)
MDAOP advertisements
MDAOP and other known busy times (e.g. HCCA, Beacons, etc.) can bebroadcast using MDAOP Advertisements IEs
MDAOP teardown
Either transmitter or receiver may indicate a teardown at any time bytransmitting an MDAOP Set Teardown IE
MDAOP Operation
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Nodes that own an MDAOP Access the channel using MDA parameters for CWMin,
CWMax, and AIFSN
Send traffic for one TXOP
Use the same retransmit rules as common EDCA
Relinquish any remaining MDAOP time by sending CF-Endor QoS-Poll to self with zero duration
Nodes that defer during a known MDAOP Set NAV to the end of the MDAOP
Shorten the NAV if CF-End or QoS-Poll with zero durationreceived
Common Channel Framework (CCF)
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Used for negotiating other channels for dataexchange
Provides means for using orthogonal frequencychannels
Entities periodically switch to common channel
CCF Protocol
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Simple RTX/CTX protocol
Using RTX, the transmitter suggests a destination channel
The receiver accepts/declines the suggested channel using CTX
After a successful RTX/CTX exchange, the transmitter and receiverswitch to the destination channel
Switching is limited to channels with little activity
Existing medium access schemes are reused(i.e.EDCA) To devices that do not implement CCF, the common channel
appears as a conventional single channel
Common channel can also be used for normal data transmission
CCF Operation
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Channel Coordination Window (CCW)
Defined for CCF-enabled MPs to tune into the common channel
Channel Utilization Vector (U) of each MP gets reset Allows MPs marking other channels unavailable based on RTX/CTX
exchanges
CCW repetition period P
CCF-enabled MPs initiate transmissions that end before P
MPs may stay tuned to the common channel beyond CCW
Intra-mesh congestion control
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Mesh characteristics
Heterogeneous link capacities along the path of a flow Traffic aggregation with multi-hop flows sharing intermediate links
Some issues with the 11/11e MAC for mesh Nodes blindly transmit as many packets as possible, regardless of
how many reach the destination
Results in throughput degradation and performance inefficiency
Intra-mesh congestion control
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Local congestion monitoring
Each node actively monitors local channel utilization
If congestion detected, notifies previous-hop neighbors and/or theneighborhood
Congestion control signaling
Congestion Control Request (unicast)
Congestion Control Response (unicast)
Neighborhood Congestion Announcement (broadcast)
Local rate control
Each node that receives either a unicast or broadcast congestionnotification message should adjust its traffic generation rateaccordingly
Rate control (and signaling) on per-AC basis e.g., data traffic ratemay be adjusted without affecting voice traffic
Example: MAPs may adjust BSS EDCA parameters to alleviatecongestion due to associated stations
Mesh beaconing and synchronization
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Necessity of synchronization MCCA, MBCA, and power save mode require time synchronization
between 1-hop neighborhood Neighbor Offset Protocol
Default synchronization protocol
It keeps track of the time base of its neighbor mesh STAs
TBTT: Target Beacon Transmission Time
Mesh Beacon Collision Avoidance (MBCA)mechanism It detects and mitigates collisions among Beacon frames
transmitted by other STAs on the same channel within 2 hop range
Beacon timing element that indicates TBTT of neighbors is containedin the beacon frame
Each mesh STA can know TBTT within 2 hop range
Power Management in Mesh
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Reuses existing mechanisms defined for BSS/IBSSwith some modifications ATIM window and ATIM frames with some new rules
TIM IE in beacon frame and PS-poll frame
APSD mechanism
Uses reduced beaconing frequency
Possibility of beaconing only at DTIM timing
Efficient sharing of Mesh beaconing responsibility
Provides efficient Power Save mode advertising Indicated in beacon frames
Indication by PS bit in Frame Control field
Defines mechanisms to allow MPs being awake onlyfor the portion of time required for actual reception Efficient use of more data bit and EOSP
ATIM-based Sleep-wake Operation
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Announcement Traffic Indication Message (ATIM)
Guaranteed window of awake time after periodic Delivery Traffic
Indication Message (DTIM) beacons DTIM interval defined as a multiple of beacon intervals
Globally unique to the mesh
Control communication transferred during ATIM window
Indicating pending traffic, change in PS state or re-instating stopped
flows
Remain awake time after ATIM window dependant on controlcommunication exchanged during ATIM window
Power Management in Mesh
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Two different power states
Awake: the mesh STA is able to transmit or receive frames and isoperating at full power
Doze: the mesh STA is not able to transmit or receive and consumesvery low power
Three power modes:
Active mode
The mesh STA shall be in Awake state all the time Power save mode (optional)
The mesh STA alternates between Awake and Doze states
Light sleep mode
The mesh STA shall listen to all the Beacon frames from its peer mesh STA
Deep sleep mode
The mesh STA may choose not to listen to the Beacons from its peer meshSTA
Link specific power modes
A mesh STA has its own power mode for each peering
An Example of Power Mode (PM) Use
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References
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2010.03 TTA WG7041
2011.12 TTAK.KO-06.0252/R1
2006 IEEE 802.11s Tutorial, IEEE 802 Plenary
2011 IEEE Std 802.11s-2011, Amendment 10: MeshNetworking
2011 IEEE P802.11 Task Group S Meeting Report
Thank you
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Q&A
Thank you
-
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WMN Examples: RoofNet
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97
MIT campus,USA80 Roofnet nodesinstalled
http://pdos.csail.mit.edu/roofnet
WMN Examples: SFNet
http://pdos.csail.mit.edu/roofnet/media/634u-internal.jpghttp://pdos.csail.mit.edu/roofnet/media/.cache/87e5e2fb64b45cba36276981a6acdb06.jpg8/11/2019 6_ )
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98
San Fancisco, CAEarthlink, Google1mi2(2.7km2) area
15000 residents25 wireless routers5 gateways
Suman Sarkar, Hong-Hsu Yen, Sudhir Dixit, Biswanath Mukherjee,
Hybrid Wireless-Optical Broadbad Access Network (WOBAN), IEEE Journal in Commmunications, 2008
WMN Examples : WiMesh Testbed @ KAIST
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Currently, 60 fixed meshnodes in north-side
(CHiPs, UndergraduateDormitory Region )
15 mobile mesh nodes
(tested in south-side)
* MP
1.2km
1.35kmCHiPs
Undergraduate
Dormitory Region
ONFIDENTI L
WMN Examples :
u-City
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, /,
,
,CCTV
Creawave (enaruTNT)
RF
STP x 2
RF
STP x 2
WMN Examples :
FUN Beach
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FUN Beach
Firetide
Mesh Network , CCTV, Public InternetService, PDA
http://www.jejukipa.or.kr/module?module.seq=15
MESH 6201 MESH 6202 MESH Link : 5GHz
1
2
3
45
6
7
8 9
10
11
12 13
14
21
15 16
17
19
20
22
23
24
18
1
MESH 6201 MESH 6202 MESH Link : 5GHz
1
2
3
45
6
7
8 9
10
11
12 13
14
21
15 16
17
19
20
22
23
24
18
1
WMN Examples : u-
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u-
Firetide
,3,, USN/, Network CCTV,
Node9
570m
170m
160m270m
170m
320m420m
550m
940m
150m
350m
415m
620m
629m
320m
300m
1
3
4
5
6
7
8
9
1
11
12
13
14
15
16
17
18
19
2
Firetide HotPort 62 2 Outdoor node : 18 Point
Firetide HotPort 61 2 Indoor node : 4 Point
Firetide HotPoint46 Outdoor AP : 1 Point
Firetide HotPoint45 Indoor AP : 1 Point
http://www.jejukipa.or.kr/module?module.seq=15
WMN Examples :
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Mesh
Nortel AP7220
http://www.texcell-netcom.co.kr/support/technology
()
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()
PDA,
-
WiFi
-
(u-Highway)
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-Car PC Navi ,,-Radio
-,
-~31km, 2-10
-CCTV, , ,
(I-Port)
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I-Port
, , WiFi PTT
-OWS2400 11
MWS7PDA, ,WiFi PTT,
-, Mesh.MWS100
NIA-USN
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(NIA)
5
-, , , , ,
NIA
-USNMesh , U-City.
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3
12
-
-Mesh
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3 4
YMCA
1 2
34
1 2
(,) & < >
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46Km
U-ShelterDIDIPTV, ,
(
)
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-
- 24Km2
- 20
- 2
-
-
- ,
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