1

Simple Efficient Extensible Mesh (SEE-

Mesh) Proposal

IEEE 802.11-05/0562r0

June 2005

This proposal can be obtained from http://www.802wirelessworld.com/.

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Current 802.11s Proposals

Short Name Person Ratio RankG 7 SEE Mesh Hidenori Aoki 83.58% 1B 31 Wi-Mesh Alliance (WiMA) Tricci So 77.16% 2K 32 Samsung SongYean CHo 76.82% 3H 9 Mesh Networks Alliance

(MNA) Guido R. Hiertz 60.62% 4J 35 Proactive Mesh Bing Zhang 53.89% 5C 6 Cooperative Protocol D. J. Shyy 52.16% 6 (merging into B:31)E 5 Hybrid Mesh Routing Hang Liu 51.03% 7 (merging into B:31)L 19 Siemens Michael Bahr 50.92% 8N 18 SNOW Mesh Jonathan Agre 48.66% 9 (merging into G:7)M 22 Common Control Channel Mathilde Benveniste 34.05% 10

I 20 Tree Based Routing (TBR) Jan Kruys 33.48% 11A 8 Mesh DCF Rui Zhao 26.02% 12F 3 Dynamic Backbone Dennis Baker 18.93% 13D 17 Intermittent Periodic

Transmit (IPT) Hiroshi Furukawa 11.98% 14O 29 Self Organizing Alexander L. Cheng 10.61% 15

Contact Jul-05Proposal #

Table from:“Proposals for TGs”, IEEE 802.11-05/0597r8

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Outline1. General Description

2. Mesh Topology Discovery and Formation Neighbor Discovery Channel Selection Link Establishment Local Link State Measurement

3. Mesh Path Selection and Forwarding Path Selection Metrics Path Selection Protocol Data Message Forwarding

4. Interworking Support

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1. General Description Device Classes

Mesh Point (MP) Mesh Access Point (MAP): MP+AP Simple Station (STA) Mesh Portal (MPP): MP+Bridge

MP

MP

MP

MPMP

MP

MAPMAP

STASTA

MPP

Bridge/Router

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2. Mesh Topology Discovery and Formation MP Boot Sequence

1) Neighbor discovery

2) Channel selection

3) Link establishment

4) Local link state measurement

5) Path selection initialization

6) AP initialization (optional – if MAP)

described in this section

described in the next section

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Each device supports one or more profiles. Each profile consists of

A Mesh ID: like SSID, e.g., “NCTU Mesh” A path selection protocol identifier: AODV, OLSR A path selection metric identifier: airtime cost

The neighbor state is one of{Neighbor, Candidate_peer, Association_pending, Subordinate_link_down, Superordinate_link_down, Subordinate_link_up, Superordinate_link_up}

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Neighbor Discovery The following is executed for each profile in the

order of user’s preference. The first match is selected. Passive (listen beacon) or Active (probe request) Scanni

ng Beacon/Probe Response frame contains:

(1) Mesh ID(2) Active Protocol ID (3) Active Metric ID(4) Peer Capacity: # of additional peer that can accommodate

If (1)~(3) are the same, State := Neighbor If, in addition, (4) > 0, State := Candidate_peer Example:

max_peer_capacity = 3C is a candidate_peerN is not

C

N A

beaconpc=1

beaconpc=0

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Channel Selection Two channel selection modes:

Simple unification mode (a) or advanced mode (b)(c).

Simple Channel Unification Protocol:1. Use the channel in the 1st profile if no neighbor is found.2. Use channel precedence indicator (CPI, a random num

ber) to coalesce disjoint graphs and support channel switching for dynamic channel selection.

beyond the scope of the proposal

(a) (b) (c)(a) (b) (c)

Figure from:“802.11 TGs Simple Efficient Extensible Mesh (SEE-Mesh) Proposal”, IEEE 802.11-05/0562r0

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Example:

A

1. MP A is turned on. No neighbor is found. It switches on channel 1 and initiates a CPI = 5. B

2. MP B is turned on. No neighbor is found. It switches on channel 2 and initiates a CPI = 8.

D

4. MP D is turned on. Find neighbor MP A and MP B. Because MP B has the higher CPI, MP C switches on channel 2 as MP B.

C

3. MP C is turned on. Find neighbor MP A. It switches on channel 1 as MP A and sets CPI to the same as MP A.

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6. MP C receives the channel cluster switch announcement and knows that it needs to switch to channel 2. It also forwards the channel cluster switch announcement.7. When the timer expires, MP A and MP C switch to channel 2 simultaneously.

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5. MP A discovers a higher CPI on channel 2. It sets a channel switch wait timer and broadcasts a channel cluster switch announcement.

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Link Establishment A MP selects from its candidate_peers to establish peer

links with based on measurement of signal quality,until the maximum number of peers is established.

Use association request and association reply frame to establish the link, and use directionality field (a random number) to break two concurrent associations.

Example:A B

State of B = candidate_peer State of A = candidate_peerassoc req (dir=5)

State of B = association_pendingassoc req (dir=3)

State of A = association_pending

assoc rep (accept)

State of B = subordinate_link_down State of A = superordinate_link_down

assoc rep (reject)If dirrecv<=dirsend then reject

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Local Link State Measurement The superordinate node is responsible for measuring

the link quality. And then it sends a local link state announcement frame to the subordinate node.

The measuring parameters may be: r : current bit rate in use (modulation mode) ept : packet error rate at the current bit rate

Example:A B

State of B = subordinate_link_down State of A = superordinate_link_down

superordinatesubordinate

measuring

local link state ann.(r, ept)

State of B = subordinate_link_up State of A = superordinate_link_up

after themeasurement

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3. Mesh Path Selection and Forwarding

The framework enables flexible implementation of path selection protocols and metrics. But the following default mandatory protocol and metric must be supported for all implementations.

Path Selection Metrics Airtime Cost

Path Selection Protocols Radio Metric AODV Radio Aware OLSR (optional)

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Path Selection Metric – Airtime Cost Airtime cost reflects the amount of channel

resources (time) consumed by transmitting the frame.

pt

tpcaa er

BOOc

1

1

Parameter Value (802.11a)

Value (802.11b)

Description

Oca 75s 335s Channel access overhead

Op 110s 364s Protocol overhead

Bt 8224 8224 Number of bits in test frame

48Mb/s, 12%PER

48Mb/s, 6%PER 12Mb/s, 15%PER

36Mb/s, 5%PER

54Mb/s, 8%PER

54Mb/s, 2%PERD

S

405s

891s 1024s

435s

367s

344sD

S

(75+110+8224/48)*

(1/0.88)= 404.6 us

(75+110+8224/48)*

(1/0.88)= 404.6 us

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Path Selection Protocol – RMAODV Radio Metric Ad hoc On-Demand Distance Vector Summary of features beyond AODV:

Identify best-metric path with arbitrary path metrics Reduce flooding when maintaining multiple paths

Aggregate multiple RREQs in same message Modification to RREQ/RREP processing/forwarding rul

es Forward RREQ with better metric No route caching

Optional periodic path maintenance Allows proactive maintenance of routes to popular desti

nations (e.g. MPP)

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Example:

4

8

104

3

3C D

A

SB

RREQ(m=0)

m=3, prev=S

m=8,prev=S

m=10prev=S

Initiate RREQ

m=10,prev=S

4

8

104

3

3C D

A

SB

RREQ(m=10)

m=3, prev=S

m=8,prev=S

m=13, prev=A

Forward RREQ

Destination replies RREP

4

8

104

3

3C D

A

SB

RREP(m=13)

m=3, prev=S

m=8,prev=S

m=10,prev=S,next=D

m=13, prev=A

next=A

Forward RREQ

4

8

104

3

3C D

A

SB

RREQ(m=3)

m=3, prev=S

m=8,prev=S

m=7,prev=B,next=D

m=13, prev=A

next=A

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Example (cont.):

Forward RREQ with better metric

4

8

104

3

3C D

A

SB

RREQ(m=7)

m=3, prev=S

m=8,prev=S

m=7,prev=B,next=D

m=10, prev=A

next=A

Reply RREP with better metric

4

8

104

3

3C D

A

SB

RREP(m=10)

m=3, prev=S, next=A

m=8,prev=S

m=7,prev=B,next=D

m=10, prev=A

next=B

Forward RREQ. But the destination do notreply because the metric is no better.

4

8

104

3

3C D

A

SB

RREQ(m=8)

m=3, prev=S, next=A

m=8,prev=S

m=7,prev=B,next=D

m=10, prev=A

next=B

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Data Message Forwarding MSDU Ordering

Mesh E2E Sequence Number Use a buffer to re-order the frame Use a timer to avoid indefinitely waiting

Eliminates possibility of infinite loops Mesh TTL

FrameCtrl

DurAddr

1Addr

2Addr

3SeqCtrl

Addr4

QoSCtrl

MeshCtrl

Body FCS

MAC Header

Mesh E2ESeq

MeshTTL

2 2 6 6 6 2 6 2 3 4

0 7 8 23

new field

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Translation between four-address frames and three-address frames

ToDS

1

1

0

FromDS

1

0

1

Addr1

RA

BSSID

DA

Addr2

TA

SA

BSSID

Addr3

DA

DA

SA

Addr4

SA

N/A

N/A

Frames in Mesh

Frames to AP in BSS

Frames from AP in BSS

MP

MPMP

MAP

STA STA

Four-address frames

Three-address frames

19The Mesh is considered a broadcast LAN.

4. Interworking Support

H

CF

EA

B

D

GX

Y

MPPs are expected to support: Transparent forwarding (broadcast LAN) Bridge learning (overhearing of packets) Support for bridge-to-bridge communications (e.g. allow

ing MPPs to participate in Spanning Tree Protocol)

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Key Decisions in Packet Forwarding Determine if the destination is inside or outside

the Mesh: first ask all MPPs For the destination inside the Mesh,

Use Mesh path selection For the destination outside the Mesh,

Forward to all MPPs, until the right MPP is found Identify the right MPP and deliver packets via unicast

Is the destination inside or outside

the Mesh? Which MPP(s) should forward

the packet?

What is the pathto the

destination?inside

outside

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Example:

When A wants to send data to X, A multicasta portal update request message to all MPPs.

C

G

A

H

BX Y

AForwarding table of G

AForwarding table of H

G and H have no information of X in their forwarding tables. So their do not respond.

When X replies (e.g. TCP-ACK),G and A learn that information.

C

G

A

H

BX Y

X AForwarding table of G

AForwarding table of H

C

G

A

H

BX Y

Forwarding table of GForwarding table of H

When a timeout expires, A floods the data packet to all MPPs. MPPs forward it to the whole LAN.

C

G

A

H

BX Y

AForwarding table of G

AForwarding table of H

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Example (cont.):

When B wants to send data to X, B multicasta portal update request message to all MPPs.

C

G

A

H

BX Y

X AForwarding table of G

AForwarding table of H

Because G knows where X is, it replies a portal update response message to B.

C

G

A

H

BX Y

X A,BForwarding table of G

A,BForwarding table of H

So B can send the data packet to X via G.

C

G

A

H

BX Y

X A,BForwarding table of G

A,BForwarding table of H

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Example (cont.):

When C wants to send data to A, C multicasta portal update request message to all MPPs.

C

G

A

H

BX Y

X A,BForwarding table of G

A,BForwarding table of H

G and H know A is in the Mesh, they reply portal update response messages to C.

C

G

A

H

BX Y

X A,B,CForwarding table of G

A,B,CForwarding table of H

Since C knows A is in the Mesh, it initiates a RREQ to find the path.

C

G

A

H

BX Y

X A,B,CForwarding table of G

A,B,CForwarding table of H

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Conclusion The SEE-Mesh proposal provides a simple,

efficient and extensible solution for wireless mesh networks.

It just specifies a framework which provides all the common features of the target applications.

It is flexible to extend for future enhancements. Channel selection modes Path selection protocols Path selection metrics