Transcript Document 7842872

22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Issues Outline for Mesh Using the 802.15.3b MAC]
Date Submitted: [22 March, 2005]
Source: [Dan Grossman] Company [Motorola.]
Address [111 Locke Drive Marlborough, MA USA 01752]
Voice:[+1 508 786 7527]
E-Mail:[[email protected]]
Re
: []
Abstract:[At the March 2005 Plenary, WG 3b asked the author to lead an ad-hoc activity to frame a
proposal to build upon, and extend where nececessary, the 802.15.3b MAC to operate as an ad-hoc mesh
network. This contribution attempts to outline the major issues that will need to be addressed.]
Purpose:[Starting point for discussion during the March 23, 2005 conference call]
Notice :This document has been prepared to assist the IEEE P802.15. It is offered as a basis for
discussion and is not binding on the contributing individual(s) or organization(s). The material in
this document is subject to change in form and content after further study. The contributor(s)
reserve(s) the right to add, amend or withdraw material contained herein.
Release:The contributor acknowledges and accepts that this contribution becomes the property of IEEE
and may be made publicly available by P802.15.
Submission
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
Why 802.15.3b is “Different”
Submission
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
Streams
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Supports both connection oriented data transfer (i.e., streams) and connectionless data
transfer.
– Mechanisms for connection establishment (i.e., CTRq), modification, handover and
release.
– Most extant mesh architectures assume purely connectionless data transfer at the
MAC layer.
Rate reservation needed to achieve QoS objectives for some kinds of streams.
– Capacity limits must be observed during stream establishment.
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Capacity limits of the shared medium ((link rate * number of TUs in the superframe) – overhead)
Spatial reuse
Derating for retransmission due to link error rate
DEVs might have limited frame forwarding rates.
Need for per-hop admission control and capacity-sensitive path computation.
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Changes in link throughput need to be signalled in a timely fashion to the PNC so that CTA
duration and frequency can be appropriately adjusted.
In-order delivery
At each forwarding hop, frames must wait at each for a CTA associated with that
stream.
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Latency due to arbitrary placement of CTAs will result on an average wait of ½
superframe time per hop.
– May result in end-to-end delays which are unacceptable to some applications.
Need to minimize per-hop processing, not preclude hardware based forwarding
Submission
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
TDMA mediated by PNC(s)
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MAC uses TDMA
Channel access and timing mediated by centralized Piconet Controller (PNC)
Hierarchy of child PNCs
Other meshing schemes
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Tend to use ALOHA- or CSMA-based MAC
Infrastructure (e.g., 802.11 APs) mediates access (e.g. by polling), but not timing.
Implications:
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Submission
Every DEV (especially child PNCs) must be must be able to receive beacon from a
PNC.
Need to select DEVs to become PNCs, so that coverage is achieved.
The timing of private CTAs locked to the timing of the superframe signalled from root
PNC – even if descendant PNCs cannot receive the beacon sent by the root.
Loss of a PNC is fatal. PNCs might not have time to perform handover. Need to
failover cleanly.
Number of TUs allocated to a flow will vary at different hops at different times.
Mobile DEVs need handover as they transit from in range of one PNC to another
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
Coverage
• MAC implicitly assumes that the coverage area of a
piconet (and all of its child and/or neighbor piconets)
is not larger than the nominal range of the PHY.
• Proposed 802.15.3a PHYs are short range.
• Coverage beyond a radius of several metres will
cause nodes to be hidden from each other.
• Multi-hop forwarding capability to permit end-to-end
communications between DEVs out of range of each
other
• “Orphan” DEVs that can’t see a PNC but can see
other DEVs
Submission
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
Functional Areas To Be Addressed
Submission
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
High Level Considerations
• Functional Requirements
– Beyond the IEEE P802.15-04/655 TG5 Technical
Requirements
• Functional Partitioning
• Services
– “QoS”
• Addressing and Identifiers
• Topology
– Will need different “views”
Submission
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
Mesh Organization
• Startup
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Scanning and Discovery
Partitions and “Orphans”
Selecting DEVs to become PNCs
Establishing connectivity between PNCs
Reorganizing when topology changes
PNC Failover (was “Next PNC”)
Communication between PNCs
Mesh Sublayer Protocols for startup and
reorg
Submission
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
Device Association
• How Mesh layer association relates to
MAC layer association
• Association
• Handover
• Disassociation
• Piconet services
• PNC-PNC association management
protocol
Submission
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
Forwarding
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Next-hop information
Forwarding process
ACKs
Relationship to streams
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22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
Routing
• Key decisions
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Reactive vs proactive
State-based vs flooding
Centralized vs decentralized
Link state vs distance vector
Hop-by-hop vs source
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Topology database
Metrics, constraints
Path calculation
Topology discovery
Topology update
Submission
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
Streams
• Stream Management
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Establishment
Modification
Handover
Release
Private CTA allocation
Pseudostatic CTA coordination
Admission Control
PNC-PNC stream establishment protocol
Submission
22 March 2005
doc.: IEEE 802.15-05-0199-00-003b
PHY/MAC/Mesh Interactions
• Transmit power control
• Link quality assessment
• Dynamic rate control
Interactions with
• CTA allocation
• PNC selection
• Topology/connectivity
• Routing metrics/constraints
• Path calculation
• DEV handover
• PNC failover
Submission