1. Peer link Set-up and Maintenance
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Peer link Set-up and Maintenance
Date:
Authors:
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Jan Kruys e.a. Cisco Systems
John Doe, Some Company

2. Abstract Peer links are a basic building block of any mesh network
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Abstract
Peer links are a basic building block of any mesh network
So far we have re-used the Association of the baseline protocol
see draft D.1
We have discussed the need for a true peer link set-up protocol that is robust, fast and secure
That combination proves a tough nut to crack but we are working on it
We have not discussed how we monitor a link and terminate it in an orderly manner
That is the subject of this presentation
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

3. Month Year
doc.: IEEE yy/xxxxr0
January 2007
Taking a step back
Mesh networks are assumed to adapt to changes in environment and/or traffic demands
That implies their connections change over time
To determine who to link up with a mesh node must have some basic data about other nodes:
Mesh ID, Capabilities, protocol, etc, all data are provided in beacons and probes – overhead, but a necessary one
The peer link set-up process uses the above to find candidate peer nodes
The peer link set up process determines if a candidate becomes a real peer
Peer link set up is relative slow and costly in terms of overhead
The “assett” of a peer link merits close monitoring to avoid unnecessary re-establishment
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

4. Phases in the life of a peer link instance
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Phases in the life of a peer link instance
Set-up
Starts from nothing
Uses full EMSA handshake or abbreviated EMSA handshake
Results in a secure link or nothing…
Operation
Supports secure frame transmission
Does self-monitoring in the absence of traffic
Close
Assures orderly termination under all conditions
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

5. Peer Discovery, example
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Peer Discovery, example B B B B B B A B
Beacon/Probe Response B
Mesh ID, Capability, etc + PMK & Cipher Suite Information
A collects information about other mesh members and decides to which to peer with
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

6. (Abbreviated) Peer link set-up, example
Month Year
doc.: IEEE yy/xxxxr0
January 2007
(Abbreviated) Peer link set-up, example A B
Open(ANonce, PMKInfo, Cipher Suite Info, GTK1, MIC)
Open(BNonce, PMKInfo, Cipher Suite Info, GTK2, MIC)
Confirm(BNonce||ANonce, PMKInfo, Cipher Suite Info, MIC)
Confirm(ANonce||BNonce, PMKInfo, Cipher Suite Info, MIC)
The result is
An identifiable, bi-directional set of secure unicast “connections” between A and B (Link-ID = ANonce||BNonce)
A secure broadcast “connection” from A to B (and all MPs with which it has set-up a peer link)
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

7. Peer link Operation …is used for all frame exchanges between peers
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Peer link Operation
…is used for all frame exchanges between peers
Unicasts from A>>B and B>>A
For data transport and some management functions
Broadcasts from A>>all-peers-of-A
For some routing functions
For some management functions
Broadcasts from all-peers-of-A>>A
…Is self-monitoring to assure continuity in the absence of traffic and routing frames
Using unicast or broadcasts of “Thumbs-up” management frame
Unicast is more efficient for a small number of peers
Failure of peers to respond leads to termination of Link Operation through Peer Link Close and, eventually to a new Peer Link Set-up
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

8. Peer link Close Attempts to orderly close a peer to peer link
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Peer link Close
Attempts to orderly close a peer to peer link
By de-activation of the link instance using a secure unicast
Non-protected unicast creates an opportunity for DoS attacks
Peer responds with a Close “confirmation”
Absence of a response within “Close time out” causes A to assume that the link instance is inactive A B
Close (Link-ID, ANonce’,MIC)
Close(Link-ID, BNonce’,MIC)
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

9. High Level Peer Link Instance State Machine
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doc.: IEEE yy/xxxxr0
January 2007
High Level Peer Link Instance State Machine
Set-up
Close
Operation
Two-way CONFIRM
OPEN or CONFIRM time-out
THUMBS-UP Time out
Two-way CLOSE or CLOSE time-out
OPEN, OPEN time-out, etc
Two-way THUMBS-UP
Note: operationally, there is no need for an idle state: if there is no need to set up a link, there is no mesh, etc
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

10. Another look at Thumbs-up
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Another look at Thumbs-up
Each side sends T-up at T_up_interval and keeps a T_up _timer (> T_up_interval)
miss n in a row and you are assumed to be lost
T_up_interval can be varied with traffic density
No need to respond: can be broadcast or unicast
Unicast under a TxOP allows immediate response if desirable
Each instance is new - assures no spoofing is possible A B
Thumbs-up (Link-ID, ANonce’,MIC)
Thumbs-up (Link-ID, BNonce’,MIC)
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

11. Context for the Link Instance State Machine
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Context for the Link Instance State Machine
New Peer Discovered or Open from peer while enabled causes an new instance to be created
Set-up
Close
Operation
Two-way CONFIRM
OPEN or CONFIRM time-out
THUMBS-UP Time out
OPEN, OPEN time-out, etc
Idle
Two-way CLOSE or CLOSE time-out causes the instance to be terminated
???
out of scope for peering protocol
THUMBS-UP received
“Disable Mesh/Mesh Link ”command
The link state machine is an instance that is created by events external to it and that disappears when there is no connection
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

12. Link Process Description – Unilateral actions
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doc.: IEEE yy/xxxxr0
January 2007
Link Process Description – Unilateral actions
If a link to some MP is needed, send an Open with a new Local L.ID
The target MP is provided by Discovery or another function within the MP – that part is out of scope here.
If a secure link has been set up, each, MP may want to send probes (Thumbs-up) to the other end to make sure it is still there. A Link-_time_out timer will catch link failures in the absence of any traffic between the nodes
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

13. Basic Peer Link Set-up- Responder
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Basic Peer Link Set-up- Responder
Case
Current State
Received Content
Action 1
Idle
Triggered by external event
New L.ID = Active L.ID
state = Open 2
Open
Open (Active L.ID = Peer L.ID)
Process other variables 3
Open (Active L.ID = Peer L.ID +Peer Local L.ID)
Process other variables, state = Confirm 4
Time-out
Drop Active L.ID state = Idle 5
Confirm
Confirm (Active L.ID = Peer L.ID +Peer Local L.ID) 6
Process other variables, state =Monitor 7
Drop L.ID & Peer ID state = Idle
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

14. Basic Link Monitor & Close - Responder
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Basic Link Monitor & Close - Responder
Case
Current State
Content
Action 1
Monitor
Any with invalid MIC
Ignore 2
Probe (Active L.ID = Peer L.ID +Peer Local L.ID)
Restart protective link probe timer 3
Close (Active L.ID = Peer L.ID +Peer Local L.ID) or Close_time_ out
Send Close, state = Close 4
Anything else
Close
Close (Active L.ID = Peer L.ID +Peer Local L.ID) or Close_ time_out
State = Idle
Open (new Peer L.ID)
New L.ID = Active L.ID
Set Local L.ID, state = Open
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

15. Adding Security January 2007 Sync Link IDs Perform 802.1X exchange
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Adding Security
Parameters external to the Link Process determine the security details of the Set-up phase
Abbreviated EMSA handshake
Set-up
Close
Operation
Two-way CONFIRM
OPEN or CONFIRM time-out
THUMBS-UP Time out
OPEN, OPEN time-out, etc
Sync Link IDs and GTKs
Validate possession of PMK
Sync Link IDs
Validate possession of PMK (4-way hsk)
Sync Link IDs
Validate possession of PMK
Perform 802.1X exchange
Perform MKD exchange
Full 802.1X handshake
EMSA “get key” handshake
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

16. Peer Link Set-up with Full EMSA handshake
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Peer Link Set-up with Full EMSA handshake
Case
Current Link State
Content
Action 3a
Open/c
Active L.ID = Peer L.ID +Peer Local L.ID, Authenticate: start 802.1X exchange, etc)
Process other variables, if authentication complete: state = Confirm, send Confirm
(802.1X exchange and first 2 of 4-way handshake) 5a
Confirm
Confirm (Active L.ID = Peer L.ID +Local L.ID) **)
Process other variables 6a
Confirm (Active L.ID = Peer L.ID + Local L.ID …MIC) **)
Process other variables, state =Monitor
**) Ideally these two should look like the last two of the 4way handshake
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

17. Peer Link Set-up with Abbr. EMSA handshake
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Peer Link Set-up with Abbr. EMSA handshake
Case
Current Link State
Content
Action 3b
Open
(Active L.ID = Peer L.ID +Peer Local L.ID… GTK, MIC, etc)
Process other variables, if GTK is ok: state = Confirm, send Confirm 5a
Confirm
Confirm (Active L.ID = Peer L.ID +Local L.ID)
Process other variables 6a
Confirm (Active L.ID = Peer L.ID + Local L.ID …MIC)
Process other variables, state =Monitor
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

18. Impact on the draft January 2007 Re-sequence to improve accessibility:
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doc.: IEEE yy/xxxxr0
January 2007
Impact on the draft
Re-sequence to improve accessibility:
A11.1 Mesh Intro
Mesh Membership / Mesh ID
Channel Selection
Default Mesh metric
Default Wireless Mesh Routing Protocol
Default Mesh Security (EMSA = Efficient Mesh Security Architecture)
Extensibility
A11.2 Interworking
A11.3 Peer Link Control Procedures
Discovery
Set-up – invokes EMSA security
Monitor
Close
A11.4 [Route] Selection and Forwarding
A11.5 HWMP
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

19. The bigger picture: Mesh Services
Month Year
doc.: IEEE yy/xxxxr0
January 2007
The bigger picture: Mesh Services
Discovery
Allows MPs to find others MPs and their roles
Peer Link Control
Uses information provided by the Discovery Service
Allows MPs to set up, maintain and close secure links between MPs that are considered neighbours according to some criteria
Transport
Gets the bits across a link between two neighbour MPs that have joined the mesh (using the Formation Service)
Routing
Creates routes to destinations inside or outside the mesh – uses the Transport Service
Forwarding
Delivers bits across the mesh using the Transport Service
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

20. Relationships of Mesh Services
Month Year
doc.: IEEE yy/xxxxr0
January 2007
Relationships of Mesh Services
Mesh MAC User (LLC)
Forwarding Service
Routing Service
Layer Management
Transport Service
Peer Link Control
Discovery Service
Basic MAC Services
Jan Kruys e.a. Cisco Systems
John Doe, Some Company

21. Month Year
doc.: IEEE yy/xxxxr0
January 2007
Summary
Mesh Link processes cover three phases: set-up, monitor and close
Adding security does not change this – EMSA (full and abbrev.) can be incorporated into the set-up phase
The three possible cases: full 802.1X, MKD key pull and abbreviated handshake can be performed as part of the peer link open/confirm process
By separating out link monitor and link close, the whole process can be made more easily understood and the state machine simplified
The context in which this process operates can be mapped to the infamous/abstract MLME interface
With a bit of restructuring, the mesh part of the Amendment can be made easier to understand and apply.
Jan Kruys e.a. Cisco Systems
John Doe, Some Company