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KRnet 2006 IEEE 802.11s ESS Mesh Networking IEEE 802.11s ESS Mesh Networking Prof. Young-Bae Ko ([email protected]) Ubiquitous Networked Systems (UbiNeS) Lab (http://uns.ajou.ac.kr)
Transcript

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)

#2

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

#3

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

#4

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.

#5

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

#6

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

#7

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

` `

`

#8

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

#9

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.

#10

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

#11

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

#12

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

#13

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.

#14

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

#15

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.

#16

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

#17

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!

#18

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

#19

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

#20

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).

#21

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).

#22

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).

#23

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)

#24

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

#25

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

#26

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.

#27

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.

#28

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.

KRnet 2006

Thank you !Thank you !


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