July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 1
doc.: IEEE 802.15-05-0455-00-005
Submission
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [An Architecture for Mesh Networks and Some Related Issues]Date Submitted: [15 July, 2005]Source: [Ho-In Jeon (1), Sung-Hoon Jeong (2)] Company: [Dept. Electronic Engineering, Kyung-Won University(KWU) (1), LeiiTech Inc. (2)] Address: [San 65, Bok-Jung-Dong, Sung-Nam-Shi, Kyung-Gi-Do, Republic of Korea] Voice:[ +82-31-753-2533], FAX: [+82-31-753-2532], E-Mail:[[email protected]]
Re: [This work has been supported partly by HNRC of IITA and partly by TTA]
Abstract: [This document proposes an architecture for the IEEE 802.15.5 mesh networks and some issues that need to be resolved for various applications.]
Purpose: [Final Proposal for the IEEE802.15.4a standard]
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.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 2
doc.: IEEE 802.15-05-0455-00-005
Submission
An Architecture for Mesh Networks
and Some Related Issues
Ho-In Jeon
Kyung-Won University, HNRC, TTA
Republic of Korea
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 3
doc.: IEEE 802.15-05-0455-00-005
Submission
Contents• Introduction• Definition of mesh networks• Issues of mesh networks
– Beacon Scheduling– Short Address Allocation– RTS/CTS for Collision Avoidance– Routing– Power-Saving Operation Mode
• Unsupervised Beacon Scheduling• Address Allocation• Conclusion
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 4
doc.: IEEE 802.15-05-0455-00-005
Submission
Definition of Mesh Network
• A mesh network is a PAN that employs one of two connection arrangements, full mesh topology or partial mesh topology.
• In the full mesh topology, each node is connected directly to each of the others.
• In the partial mesh topology, some nodes are connected to all the others, but some of the nodes are connected only to those other nodes with which they exchange the most data.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 5
doc.: IEEE 802.15-05-0455-00-005
Submission
Mesh Networking Topologies
STAR Cluster Tree Mesh
PAN Coordinator Coordinator End Device
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 6
doc.: IEEE 802.15-05-0455-00-005
Submission
Overview of IEEE 802.15.5
• The IEEE 802.15 Task group 5 is chartered to determine the
necessary mechanisms that must be present in the PHY and MAC
layers of WPANs to enable mesh networking.
• A mesh network is a PAN that employs one of two connection
arrangements, full mesh topology or partial mesh topology.
• In the full mesh topology, each node is connected directly to each
of the others.
• In the partial mesh topology, some nodes are connected to all the
others, but some of the nodes are connected only to those other
nodes with which they exchange the most data.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 7
doc.: IEEE 802.15-05-0455-00-005
Submission
Capabilities of Mesh Networks
• Extension of network coverage without increasing
transmit power or receive sensitivity
• Enhanced reliability via route redundancy
• Easier network configuration
• Better device battery life due to fewer retransmissions
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 8
doc.: IEEE 802.15-05-0455-00-005
Submission
Limitations of Mesh networks
• Hidden nodes
– Devices are unaware of current neighbors receiving data.
– Collisions of Beacon and Data.
– Mutual Interference Causing Beacon and Data Conflict.
• Exposed nodes
– Devices are unaware of their position relative to receiver.
– Concurrent transmission in same time period possible but
unused.
– Inefficient spatial frequency reuse.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 9
doc.: IEEE 802.15-05-0455-00-005
Submission
Issues of Mesh Networks• Beacon Scheduling for Collision Avoidance
– Reduction of Power Consumption with Beacon Network– Non-beacon-Enabled Network cannot provide a power-efficient
operational mode• Short Address Allocation Algorithms
– Savings of Address Spaces• Adoption of RTS/CTS for Data Transmission
– Deterioration of Data Throughput– Overall Delay– Exposed Node Problem
• Routing: Proactive or Reactive• Power-Efficient Operation Mode• Support of Time-Critical or Delay-Sensitive Applications
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 10
doc.: IEEE 802.15-05-0455-00-005
Submission
Mesh Example 1: Home Network
DCam.
PVR
VPhone
DTV
DAMHS/
MMRG
InternetFTTH
DTV
PVR
VPhone
Refrig.
DCam.
PC
DTV
STB
PDA
Living Room
Room #1
Room #3
Room #2
Kitchen
DoorPhone
WaterMeter
GasMeter
ZigBee/15.4802.11a/g/n/e, IEEE802.15.3
Oven
Cable, Satellite, Terrestrial
PC
AP or PNC
: IEEE802.11x, 15.3, ZigBee/15.4, 15.5 Mesh
PDA DCam.
Printer
PC
PDARoom #4
DTV
PowerMeter
Meter Reader
Phone Jack
GasOven
MicrowaveOven
DSLAM
Phone Jack
Bath-room
UtilityRoom
Washer
MeshPNC
ONU
VDSLMODEM
MeshMesh
Mesh
: IEEE1394 or UWB Connectivity
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 11
doc.: IEEE 802.15-05-0455-00-005
Submission
Mesh Example 2: Environment Management
1 2 3 4 5 N-2 NN-1
10 Km
• A scenario in which the device 1 wishes to send its sensed data to device N which is located 10 Km apart.
• Assumptions– The RF range of each device is assumed to be 20m.– Multihop topology has been used for the propagation of data– Each device is assumed to use beacon to save power consumption. – Device 2 listens to the beacon transmitted by device 1 and decides to associate with it. Device 2
determines its beacon tramitting time slot. – Device 1 is 40m apart from device 2 which implies that device 3 cannot listen to device 1.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 12
doc.: IEEE 802.15-05-0455-00-005
Submission
A Scenario for the Operation of Mesh Network
12
3
4
5
6
78
9
• Issues to be resolved– Association and Reassociation Procedure
– Beacon Scheduling
– Short Address Allocations
– Creation and Update of Neighborhood Table
46
9
PNC
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 13
doc.: IEEE 802.15-05-0455-00-005
Submission
PNC Formation of the Mesh
1
• Device 1 first scans passively and actively, and found that there is no device that he can associate.
• So, it becomes the PNC.• Once a device becomes a PNC, it starts to transmit its beacon at the beginning of the
superframe.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 14
doc.: IEEE 802.15-05-0455-00-005
Submission
Joining of Device 2 to the Mesh
Beacon-Only Period
Active Period
1
Inactive Period
CAP
2
2
1
• Dev. 2 hears the beacon form PNC and gets associated with it.• When associated, it gets PANID, Short Address, and other informations and
determines when to send its beacon. • Dev. 1 and 2 listen to beacons of each other and store information about their
neighbir in the Neighborhood Table.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 15
doc.: IEEE 802.15-05-0455-00-005
Submission
Neighborhood Table for Mesh Node 1Device ID 2 … … …
PANID 1 … … …
Mesh neighbor
address 0x0002 … … …
RSSI(dBm) -49 … … …
BeaconTx-OffsetTime
2X maxBeaonLength
Device Information 1 … … …
• Neighborhood Table is created based on the beacon that it listens– PANID, Short Address, RSSI, PNC, Depth Information, Device
Information, and so on.
– The Device information of PNC is 0, and the device located in the 1 hop apart from the PNC has the device information of 2.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 16
doc.: IEEE 802.15-05-0455-00-005
Submission
1
2
3
Beacon-Only Period
Active Period
1
CAP
2
3
Joining of New Node 3
• Device 3 is associated with PNC after it listens to the beacons transmitted from both PNC and Dev. 2.
• The PNC assigns the PANID and Short address to Dev. 3. • Then Dev. 3 determines when to send its beacon.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 17
doc.: IEEE 802.15-05-0455-00-005
Submission
Device ID 1 2 … …
PANID 1 1 … …
Mesh Neighbor
Address 0x0001 0x0002 … …
RSSI(dBm) -49 -40 … …
BeaconTx-OffsetTime
1X
maxBeaconLength
2 X
maxBeaconLength
Device Info 0 1 … …
Neighbor Table for Mesh Node 3
• Dev. 3 stores information about its neighborhoods in the Neighborhood Table.
• Dev. 1 also updates its Neighborhood Table based on the beacon information that it hears.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 18
doc.: IEEE 802.15-05-0455-00-005
Submission
1
3
54
2
Joining of New Dev. 5 outside the Range
• Dev. 5 can listen to beacons of only Dev. 2, 3, and 4 since it is outside the RF range of Dev. 1.
• Dev. 5 decides to associate with Dev. 2 because the beacon of Dev. 2 is the first one that it hears.
• Beacon transmission time of Dev. 5 is determined by itself in the way to avoid the beacon conflict.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 19
doc.: IEEE 802.15-05-0455-00-005
Submission
Beacon-Only Period
Active Period
1
Inactive Period
CAP
2 3 4
5
Beacon Scheduling for Node 5
• Dev. 2 allocates the BeaconTxOffsetTime to Dev. 5 and send the BOP update command because Dev. 1 does not know whether Dev. 2 has allocated a BeaconTxOffseTime to Dev. 5
• When Dev. 1 receives BOP update command, it increments his BeaconTxOffsetTime register by 1.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 20
doc.: IEEE 802.15-05-0455-00-005
Submission
Octet:2 1 4/10 2 Var. Var. Var. 2
Frame
Control
Sequence
number
Addressing
Fields
Superframe
Specification
GTS
Field
Pending
Address
field
Beacon
PayloadFCS
MHR MAC payload MFR
< BeaconTxOffsetTime >
Beacon Payload for the Mesh Formation
• On receipt of BOP update command, every device increments his BeaconTxOffsetTime information in its register.
• BeaconTxOffsetTime information is always transmitted in the beacon payload to update the neighborhood table.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 21
doc.: IEEE 802.15-05-0455-00-005
Submission
New Joining of Node 6
2
4
5
6
46
1
3
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 22
doc.: IEEE 802.15-05-0455-00-005
Submission
Beacon Scheduling of Node 6
Beacon-Only Period
Active Period
1
Inactive Period
CAP
2 3 4 5
6
2
4
5
6
46
1
3
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 23
doc.: IEEE 802.15-05-0455-00-005
Submission
1
29
5
4
7
68
3
New Joining of Node 9
• Dev. 9 can listen to the beacon of Dev. 1 and is associated with it.
• Even though Dev. 9 cannot listen to Dev. 8, Dev. 8 is included in the neighborhood table of Dev. 9, because it is in the range of Dev. 8.
9
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 24
doc.: IEEE 802.15-05-0455-00-005
Submission
Device ID 1 2 3 4 5 6 7 8
PANID 1 1 1 1 1 1 1 1
Neighbor
address 0x001 0x002 0x003 0x004 0x005 0x006 0x007 0x008
RSSI(dBm) -49 -32 -59 … -69 -28 -58 -49 -57
BeaconTx OffsetTime
1X
MaxBeaconLength
2X
MaxBeaconLength
3X
MaxBeaconLength
4X
MaxBeaconLength
5X
MaxBeaconLength
6X
MaxBeaconLength
7X
MaxBeaconLength
8X
MaxBeaconLength
Device information
0 1 …1 1 2 2 2 2…
Neighborhood Table of Node 9
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 25
doc.: IEEE 802.15-05-0455-00-005
Submission
R
A B
C E F
N
Tree Link Direct Reachable
?
Beacon-Only Period
R A B C
Beacon-Only Period
R A B E F
An Example of Beacon Conflicts for Tree Topology
Occurrences of Beacon Conflicts in Tree
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 26
doc.: IEEE 802.15-05-0455-00-005
Submission
R
A B
C E F
N
Tree Link Direct Reachable
?
Beacon-Only Period
R A B C
Beacon-Only Period
R A B C E
F
1. BOP update command
Updated BeaconTxOffsetTime
BeaconTxOffsetTime can be selected based upon the updated BeaconTxOffsetTime
Beacon Conflicts and Avoidance in Tree
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 27
doc.: IEEE 802.15-05-0455-00-005
Submission
1 3 2
Unsupervised Beacon Scheduling
• Two PANs cannot listen to the other, such that they can never be associated.
• Then the Dev. 3 will never be associated when there beacon conflicts keep happening.
PAN 1 PAN 2
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 28
doc.: IEEE 802.15-05-0455-00-005
Submission
The Solution for Unsupervised Beacon
octets: 7 1
MHR fieldsCommand
frame identifier
1 3 2
1. Discovery Request
1. Discovery Request
1. Discovery Response
1. Discovery Response
1. Discovery request 1. Discovery response
octets: 7 2 1
MHR fieldsShort
address
Command
Frame Identifier
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 29
doc.: IEEE 802.15-05-0455-00-005
Submission
The Solution for Unsupervised Beacon
• When Dev. 3 cannot listen to any beacon for a given predetermined period of time, it sends, after CSMA/CA, Discovery Request command.
• Dev. 1 that received Discovery request command performs a random number generation for its new BeaconTxOffset Time where he knows empty.
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 30
doc.: IEEE 802.15-05-0455-00-005
Submission
octets: 7 1
MHR fieldsCommand
frame identifier
Command
IdentifierCommand name
0 x 01 Association request
0 x 02 Association response
0 x 03 Disassociation notification
0 x 04 Data request
0 x 05 PAN ID conflict notification
0 x 06 Orphan notification
0 x 07 Beacon request
0 x 08 Coordinator realignment
0 x 09 GTS request
0 x 10 BOP update command
0 x 11 Discovery request
0 x 12 Discovery response
0 x 13 Beacon realignment request
0 x 14 Beacon slot empty request
octets: 7 1
MHR fieldsCommand
frame identifier
< BOP update command >
< Command frame identifier >
octets: 7 1
MHR fieldsCommand
frame identifier
<Beacon realignment request command>
<Beacon slot empty request command>
The Solution for Unsupervised Beacon
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 31
doc.: IEEE 802.15-05-0455-00-005
Submission
Address Allocations
• Block addressing wastes address space
• Centralized Address allocations– May take too much time for the address
allocation.
• Distributed Address allocations– Beacon Scheduling mechanism can be used for
the address allocation
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 32
doc.: IEEE 802.15-05-0455-00-005
Submission
Conclusions
• Mesh network causes a lot of problems– Beacon conflicts
– Data Conflicts
– Address allocations
– Hidden node problems
– Delay-Sensitive Applications
– Power-saving mechanism
• Proposed some architectural solutions– Beacon scheduling
– Address allocation, if not quite in detail: next time
July 2005
Ho-In Jeon, Kyung-Won UniversitySlide 33
doc.: IEEE 802.15-05-0455-00-005
Submission
Acknowledgment
• This work has been supported partly by HNRC of IITA and partly by TTA.