IEEE 802.11s ESS Mesh Networking - krnet.or.krB0... · BSS IBSS ESS DS #6 IEEE 802.11 WLAN Mesh –...
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KRnet 2006
IEEE 802.11s ESS Mesh NetworkingIEEE 802.11s ESS Mesh Networking
Prof. Young-Bae Ko([email protected])
Ubiquitous Networked Systems (UbiNeS) Lab(http://uns.ajou.ac.kr)
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ContentsContents
Introduction - Wireless Mesh Networks
IEEE 802.11s - IEEE Standard for Wireless LAN MeshNetwork architectureUsage modelsFunctional requirements
Mesh topology discoveryLayer 2 routing & forwarding802.11s MAC enhancementsMesh security
MAC data transport over WLAN Mesh
References
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Wireless Mesh Networks (WMN)Wireless Mesh Networks (WMN)
It is emerging as a new class of multi-hop wireless networks.One of the main constraints of mobile ad hoc networks (MANETs), “Infrastructureless”, is relaxed.For MANETs, lack of infrastructure is required, cost is not an issue, and Internet access is not a must!
WMN introduces a hierarchyin the network architecture, consisting of mesh routersand mobile clients.
Internet
Mesh Router
Mesh Router
Wi-FiNetworks
Wireless Mesh Backbone
Mesh Router with Gateway
Mesh RouterMesh Router
Wireless Mesh Clients
Mesh Router with Gateway
Mesh Router with Gateway
Mesh Router with
Gateway/Bridge
Sensor Networks
Sink Node
Sensor
Wireless Clients
Wireless Clients
Access Point
Wired Client
Wired Client
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Mesh Networking in IEEE StandardizationsMesh Networking in IEEE Standardizations
Several IEEE working groups are actively working to provide wireless mesh networking extensions to their standards.
IEEE 802.15.5 – WPAN MeshIEEE 802.16j – WMAN Mesh/RelayIEEE 802.11s – WLAN Mesh
IEEE 802.11 is the most successful WLAN standard, and continues to advance with various amendments.
802.11e for providing QoS802.11n for providing high data rates in excess of 100 Mbps…
☞ However, multi-hop connections are not regarded by any amendments.
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IEEE 802.11 WLAN IEEE 802.11 WLAN -- Network Architecture Network Architecture
Terminologies
AP (Access Point)
STA (Station)
BSS (Basic Service Set)IBSS (Independent BSS)
DS (Distribution System)WDS (Wireless DS)
ESS (Extended Service Set)
Internet
STA
STA
STASTA
STA
APAP
BSSBSS
IBSS
ESS
DS
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IEEE 802.11 WLAN Mesh IEEE 802.11 WLAN Mesh –– ““802.11s802.11s””
802.11s ESS Mesh Networking Task GroupTo extend the current IEEE 802.11 architecture and protocols forproviding the ESS mesh functionality.To define MAC and PHY layers for creating an IEEE 802.11-based WDS.
The objectivesIncreased range/coverage & flexibility in usePossibility of increased throughputReliable performanceSeamless securityPower efficient operationMultimedia transport between devicesBackward compatibility and interoperability for interworking
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802.11802.11s WLAN Mesh s WLAN Mesh -- Network Architecture Network Architecture
New TerminologiesMP (Mesh Point): Relay frames each other in a router-like hop-by-hop fashionMAP (Mesh Access Point): Mesh relaying + AP service for clientsMPP (Mesh Portal): Acting as a bridge to other networks
MP
MPP
MP
MP
STAs
802.11s Mesh links
Legacy 802.11s links
MAP
` `
`
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IEEE 802.11s IEEE 802.11s -- Architectural ModelArchitectural Model
Targeted at unmanaged WLAN Mesh networks and at enabling interoperability with low complexity.
Internet
STA
STA
STASTA
STA
Mesh PortalAP
BSS BSS
IBSS
ESS
DS
MAP
MP
MP
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Current Status of 802.11 TG Current Status of 802.11 TG ““ss””
802.11 TGs has defined the following:Scale: Target ~32 active mesh APsArchitectural model Usage models: 4 usage scenariosFunctional requirements
Two major proposals have been emerged:The one from Wi-Mesh Alliance, lead by Nortel Networks, Philips,…Another from SEEMesh, lead by Intel, TI, Samsung, Nokia, Motorola,…
→ Joint SEEMesh/Wi-Mesh proposal was presented in 2006 March meeting.→ It is expected to have an initial draft by July 2006, and a ratified 802.11s
standards by early 2008.
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Usage ModelsUsage Models
Residential Usage ModelTo be deployed inside home or a residential building High bandwidth application, such as multimedia content distribution
Office Usage ModelSmall to medium sized enterprise buildings
Campus/Community/Public access networking ModelOut-door deployment environmentSeamless connectivity
Public Safety ModelEmergency sites
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Functional RequirementsFunctional Requirements
PHYs
Mesh Topology Learning, Routing &
Forwarding
Medium Access Coordination
Discovery & Association
802.11 service integration Mesh Configuration & Management
Mesh Measurement
Mesh Security
Mesh Interworking with other 802 networks
LAN metaphor, 802.1 bridging support
802.11i link security based
MAC enhancements
Unmanaged, autonomic
management
Legacy 802.11 a/b/g/n
The set of services provided by the WLAN Mesh that support the control, management, and other operation, including the transport of MSDUs between Mesh Points within the WLAN Mesh.
Single-hop/multi-hop neighbor
discovery, Extensible path
selection & forwarding
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Mesh Point (MP) Boot SequenceMesh Point (MP) Boot Sequence
Neighbor discoveryActive and Passive scanning
Channel selectionSimple channel unification mode
Link establishment with neighbor MPsAuthentication Association
Local link state measurementRadio aware metrics
Path selection and forwardingExtensible path selection framework with more than one protocol
AP initialization (optional - if MAP)
Neig
hbor d
iscovery
,C
hannel s
ele
ctio
n
Lin
k e
sta
blis
hm
ent
Local lin
k s
tate
dis
covery
Path
Sele
ctio
n
(Unic
ast, M
cast,
Bcast)
Access p
oin
t in
itializ
atio
n
Discovered neighbors
Associated & authenticated
Measured
Path Forwarding Tables Initialized
AP service available
Common function
Profile-specific path initialization
Optional function
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MP MP Neighbor DiscoveryNeighbor Discovery MechanismMechanism
To discover neighbor MP devices and their properties:
A configured MP has at least one Mesh ID.
A MP performs passive scanning (via periodic beacons) or active scanning(via probe messages)
The MP attempts to maintain the discovered neighbor MP information in a table, named MP Neighbor Table.
Neighbor MAC addressOperating channel numberThe most recently observed link status and quality information
If no neighbors are detected, MP adopts the Mesh ID for its highest priority profile and remain active.
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Channel SelectionChannel Selection
Support for single & multiple channels/interfacesEach logical interface on one RF channel, belongs to one “Unified Channel Graph (UCG)”
MP specifies one of the two channel selection modes for each interface:
Simple Channel Unification mode -- enables the formation of a fully connected UCGAdvanced mode – not fully defined in the proposal
Example Unified Channel Graphs
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Mesh Path Selection and ForwardingMesh Path Selection and Forwarding
To select single-hop or multi-hop paths and to forward data frames across these paths between MPs at the link layer.
Extensible path selection frameworkA WLAN Mesh may include multiple path selection metrics and protocols for flexibility.A mandatory protocol and metric for all implementations are specified.
Hybrid Wireless Mesh Protocol (HWMP)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.
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Airtime Link Metric FunctionAirtime Link Metric Function
A default radio-aware metric to be used by a path selection protocol to identify an efficient radio-aware path.
Its cost function is based on airtime cost (Ca), which reflects the amount of channel resources consumed by transmitting the frame over a particular link.
pt
tpcaa er
BOOc−⎥⎦
⎤⎢⎣⎡ ++=
11 Parameter Description
Oca Channel access overhead (Constant)
Op Protocol overhead (Constant)
Bt Number of bits in test frame (Constant)
r Transmission bit rate for Bt
ept Error rate for Bt
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Example: Unicast Cost Function based on Example: Unicast Cost Function based on Airtime Link MetricsAirtime Link Metrics
48Mb/s, 10% PER
54Mb/s, 8% PER
12Mb/s, 10% PER
54Mb/s, 2% PER
54Mb/s, 2% PER
48Mb/s, 10% PER
This path having the minimum airtime cost is the Best!
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Hybrid Wireless Mesh Protocol (HWMP)Hybrid Wireless Mesh Protocol (HWMP)
A default mandatory path selection protocol for interoperability.
It combines the flexibility of on-demand route discovery with extensions to enable efficient proactive routing to mesh portals.
Radio Metric AODV (RM-AODV) for on-demand routing serviceUsed in intra-mesh routing for the route optimizationWhen a root portal is not configured, RM-AODV is used to discover routes to destinations in the mesh on-demand.
Tree based routing for pro-active routing serviceIf a Root portal is present, a distance vector routing tree is built and maintained.Tree based routing avoids unnecessary discovery flooding during discovery and recovery
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HWMP Example Case 1: HWMP Example Case 1: No Root Portals, No Root Portals, Destination Destination insideinside MeshMesh
Scenario: MP A (Source) wants to communicate with MP C (Destination).
1. MP A first checks its local layer-2 forwarding table for route entry of C.
2. If entry does not exist, A broadcasts a RREQ to discover the best path to C.
3. C replies back to A with a RREPforming bidirectional link for data forwarding.
4. A starts data communication with C.
EEDD
CC
AABB
AF AG
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HWMP Example Case 2: HWMP Example Case 2: No Root Portals,No Root Portals,Destination Destination outsideoutside MeshMesh
3. If no RREP is received, A assumes X is outside the mesh and sends messagesdestined to X to mesh portal B for interworking.
4. Mesh portal B forwards messages to other LAN segments according to locally implemented interworking protocol.
1. MP A checks its local forwarding table for an active forwarding entry to X.
2. If entry does not exist, A broadcasts a RREQfor finding the best path to X.
EEDD
CC
AABB
AF AG
X
Scenario: MP A (Source) wants to communicate with MP X (Destination).
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HWMP Example Case 3: HWMP Example Case 3: With Root Portals, With Root Portals, Destination Destination insideinside MeshMesh
1. MP A checks its local forwarding table for route entry of C.
2. If no entry exists, A may directly send the messageon the proactive path towards the root portal B.
3. When B receives the message, it flags message as “intra-mesh” and forwards it to C using proactive route.
4. When C receives the message, it may issue RREQ to A for finding the best on-demand intra-mesh MP-to-MP path.
5. A and C may use the best on-demand path for data delivery.
BEEDD
CC
AA
AGAF
Scenario: MP A (Source) wants to communicate with MP C (Destination).
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HWMP Example Case 4: HWMP Example Case 4: WithWith Root portals, Root portals, Destination Destination outsideoutside MeshMesh
3. When B receives the message and it does not have an active forwarding entry to X, it may assume the destination is outside the mesh and forward the message to other LAN segments according to locally implemented interworking.
2. If no entry exists, A may directly send the message on the proactive path towards the root portal B.
1. MP A checks its local forwarding table for route entry of X.
EEDD
CC
AABB
AF AG
X
Scenario: MP A (Source) wants to communicate with MP X (Destination).
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An optional path selection protocolA unified, extensible proactive routing frameworkBased on the two link-state routing protocols:
OLSR (Optimal Link State Routing)FSR (Fish eye state routing) -- optional
Utilization of radio-aware metrics in forwarding path calculation
RA-OLSR, proactively maintains link-state for routing Suitable for usage models with low mobility and multimedia services
Radio Aware OLSR (RARadio Aware OLSR (RA--OLSR)OLSR)
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The existing 802.11 MAC layer is being enhanced to support mesh services.
EDCA (Enhanced Distributed Channel Access) as a basis for the 802.11s media access mechanism:
Re-use of latest MAC enhancement in 802.11eCompatible with legacy WLAN devices
Other MAC Enhancements for MeshCommon Channel Framework (optional)Mesh deterministic access (optional)
802.11802.11s MAC Enhancements s MAC Enhancements
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Traffic Management Traffic Management ---- Congestion ControlCongestion Control
Engineering traffic to avoid congestion within a multi-hop wireless mesh network is a challenge.
Heterogeneous link capacities along the path of a flow Traffic aggregation: Multi-hop flows sharing intermediate links
Extensions to the QoS mechanisms defined in 802.11e are being considered to support hop-by-hop congestion control.
Intra-mesh congestion control mechanism Local congestion monitoringCongestion control signalingLocal rate control
High capacity linkLow capacity linkFlow
2
1
7
6
3
4
5
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Mesh Security Mesh Security
Basically, the 802.11s group intends to take advantage of security mechanisms specified in 802.11i (completed in 2004).
However, extensions will be necessary because 802.11i provides only one-hop link security.
Multi-hop or end-to-end security is required.Association/authentication among neighboring MPs/MAPs is needed.
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MAC Data Transport over a WLAN MeshMAC Data Transport over a WLAN Mesh
WLAN Mesh is transparent to higher layers.Internal layer 2 behavior of WLAN Mesh is hidden from higher-layer protocols under the MAC-SAP.
MAC SAP
MeshPoint
MeshPoint
MeshPoint
MeshPoint
MeshPoint
MSDU Source
MSDU DestMSDU (e.g. ARP, DHCP, IP, etc)
MPDU
MSDU source may be:• Endpoint application• Higher-layer protocol
(802.1D, IP, etc.), e.g. at Mesh Portal
• Etc.
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ReferencesReferences
1) R. Bruno, M. Conti and E. Gregori, “Mesh Networks: Commodity Multihop Ad Hoc Networks,” in IEEE Communications Magazine, March 2005.
2) I. F. Akyildiz, X. Wang and W. Wang, “Wireless mesh networks: a survey,” in Computer Networks Journal (Elsevier), March 2005.
3) Joint SEE-Mesh/Wi-Mesh Proposal to IEEE 802.11 TGs, Feb. 2006.