WIRELESS MESH NETWORKSWIRELESS MESH NETWORKS

Ian F. AKYILDIZ* and Xudong WANGIan F. AKYILDIZ* and Xudong WANG

* Georgia Institute of Technology* Georgia Institute of Technology BWN (Broadband Wireless Networking) Lab &BWN (Broadband Wireless Networking) Lab &

** TeraNovi Technologies** TeraNovi Technologies

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10. STANDARDS10. STANDARDS

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Standards related to Standards related to WMNsWMNs

IEEE 802.11sIEEE 802.11s

IEEE 802.15.1IEEE 802.15.1

IEEE 802.15.4IEEE 802.15.4

IEEE 802.15.5IEEE 802.15.5

IEEE 802.16aIEEE 802.16a

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Standard Activities: Standard Activities: IEEE 802.11 Mesh NetworksIEEE 802.11 Mesh Networks

– Currently, IEEE 802.11 wireless networks can achieve a Currently, IEEE 802.11 wireless networks can achieve a peak rate of 11 Mbps (802.11b), 54 Mbps (802.11a/g), peak rate of 11 Mbps (802.11b), 54 Mbps (802.11a/g),

and 600 Mbps (802.11n draft)and 600 Mbps (802.11n draft)

– 802.11n is still under development for higher speed 802.11n is still under development for higher speed

– Researchers expect 802.11n to increase the speed ofResearchers expect 802.11n to increase the speed of Wi-Fi connections by 10 to 20 times. Wi-Fi connections by 10 to 20 times.

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IEEE 802.11 Mesh NetworksIEEE 802.11 Mesh Networks

– Protocols for 802.11 ad hoc mode are insufficient forProtocols for 802.11 ad hoc mode are insufficient for multi-hop and mesh networking, because of lack of multi-hop and mesh networking, because of lack of scalability in the MAC protocol, resulting in poor scalability in the MAC protocol, resulting in poor

network network performance. performance.

– A working group within IEEE 802.11, called 802.11s, A working group within IEEE 802.11, called 802.11s, has has

been formed recently to standardize Mesh Networksbeen formed recently to standardize Mesh Networks

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IEEE 802.11s:IEEE 802.11s:Mesh NetworkingMesh Networking

Started in May 2004Started in May 2004

802.11a/b/g were never intended to 802.11a/b/g were never intended to work multi-hopwork multi-hop

Target application: Target application: extended 802.11 coverageextended 802.11 coverage

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IEEE 802.11

– The infrastructure of each basic service set (BSS) The infrastructure of each basic service set (BSS) is connected via Ethernet LANsis connected via Ethernet LANs

– Such a fixed network architecture limits the Such a fixed network architecture limits the flexibility of network deployment and increases flexibility of network deployment and increases cost. cost.

– Thus, mobility of BSS and multihop networking are Thus, mobility of BSS and multihop networking are needed.needed.

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IEEE 802.11: IBSS Mode (Ad Hoc Networking)IBSS Mode (Ad Hoc Networking)

– Ad hoc networking has been specified in the Ad hoc networking has been specified in the independent independent basic service set (IBSS) mode. basic service set (IBSS) mode.

– Stations (STAs) can connect to each other without any Stations (STAs) can connect to each other without any central coordinator like access point (AP). central coordinator like access point (AP).

– Moreover, there is no access or connection to the distributed Moreover, there is no access or connection to the distributed system (DS). system (DS).

– STAs are totally self-contained as an ad hoc network.STAs are totally self-contained as an ad hoc network. – Such as an operation mode has been researched in the field Such as an operation mode has been researched in the field

of ad hoc networking. of ad hoc networking.

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IEEE 802.11: IBSS Mode

However, the IBSS mode is not enough for However, the IBSS mode is not enough for many interesting application scenarios many interesting application scenarios

where ad hoc networking is needed but where ad hoc networking is needed but Internet access and support of client nodes are Internet access and support of client nodes are also necessary also necessary

Both infrastructure mode and IBSS mode shall Both infrastructure mode and IBSS mode shall be integrated in a new type of multihop be integrated in a new type of multihop

networks.networks.

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IEEE 802.11s: Common Principles

The network usually includes three types of nodesThe network usually includes three types of nodes– MMesh routers, clients, and gateways.esh routers, clients, and gateways.

An ad hoc routing protocol is implemented in mesh An ad hoc routing protocol is implemented in mesh routers to work together withrouters to work together with 802.11 MAC. 802.11 MAC.

Certain radio aware functions may be included in Certain radio aware functions may be included in the routing protocol.the routing protocol.

X. Wang and A. Lim, X. Wang and A. Lim, “IEEE 802.11s Wireless Mesh Networks: “IEEE 802.11s Wireless Mesh Networks: FrameworkFramework

and Challenges,’’and Challenges,’’ Ad Hoc Networks Journal,Ad Hoc Networks Journal, vol. 6, no. 6, pp. 970- vol. 6, no. 6, pp. 970-984,984,

Aug. 2007.Aug. 2007.

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IEEE 802.11s:Common Principles

802.11 MAC driver is enhanced in mesh routers to 802.11 MAC driver is enhanced in mesh routers to improve multi-hop performance.improve multi-hop performance.

[[Typical examplesTypical examples]: ]: fine-tuning CSMA/CA parameters, fine-tuning CSMA/CA parameters, developing algorithmsdeveloping algorithms for multi-radio or directional for multi-radio or directional antennas, etc.antennas, etc.

Certain network configurations are needed to Certain network configurations are needed to support client access, Internet access, roaming, support client access, Internet access, roaming, and so on.and so on.

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Network Architecture of 802.11s:Meshed Wireless LANs

Basic ConceptBasic Concept– A meshed wireless LAN is formed via ESS mesh A meshed wireless LAN is formed via ESS mesh

networking. i.e., BSSs in the DS do not need to be networking. i.e., BSSs in the DS do not need to be connected by wired LANsconnected by wired LANs

– Instead, they are connected via mesh networking Instead, they are connected via mesh networking possibly with multiple hops in betweenpossibly with multiple hops in between

– Portals are needed to interconnect 802.11 wireless Portals are needed to interconnect 802.11 wireless LANs and wired LANs. LANs and wired LANs.

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Network Architecture of 802.11s:Meshed Wireless LANs

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STANDARDSSTANDARDS

IEEE 802.11s:Device Classes in a WLAN Mesh Network

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Network Architecture of 802.11s:Meshed Wireless LANs

Three new nodes in this architectureThree new nodes in this architecture – A mesh point (MP)A mesh point (MP) is an 802.11 entity that can is an 802.11 entity that can

support wireless LAN mesh services support wireless LAN mesh services

– A mesh access pointA mesh access point is an MP but can also work as is an MP but can also work as an access point an access point

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Network Architecture of 802.11s:Meshed Wireless LANs

– A mesh portalA mesh portal is a logical point where packets is a logical point where packets enter and exit the mesh network from and to enter and exit the mesh network from and to other parts of the system such as a traditional other parts of the system such as a traditional 802.11 LAN or from and to a non-802.11 network 802.11 LAN or from and to a non-802.11 network

– Mesh portal includes the functionality of MP. It Mesh portal includes the functionality of MP. It can be co-located with an 802.11 portalcan be co-located with an 802.11 portal

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IEEE 802.11s:Device Classes in a WLAN Mesh Network

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Network Architecture of 802.11s:Protocol Stacks

802.11s MAC is developed 802.11s MAC is developed based on existing 802.11 MAC based on existing 802.11 MAC for a MP (or the MP module in a for a MP (or the MP module in a MAP or mesh portal). MAP or mesh portal).

Mesh routing protocol of a MP Mesh routing protocol of a MP (or the MP module in a MAP or (or the MP module in a MAP or mesh) is located in the MAC mesh) is located in the MAC layer. layer.

In a mesh portal, a layer 3 In a mesh portal, a layer 3 routing protocol is also needed routing protocol is also needed for path selection from the for path selection from the mesh network to external mesh network to external network or vice versanetwork or vice versa

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Topology Formation/Discovery:Discovery and Formation of Mesh Networks

When a new mesh node powers up, it mayWhen a new mesh node powers up, it may use use passive or active scanning to discover a mesh passive or active scanning to discover a mesh network. network.

In 802.11s, a new ID, calledIn 802.11s, a new ID, called mesh ID, is used to mesh ID, is used to identify a mesh network. identify a mesh network. – The mesh ID is attached in beacons and probeThe mesh ID is attached in beacons and probe response response

frames as a new IEs for passive and active scanning, frames as a new IEs for passive and active scanning, respectively.respectively.

– One of the reasons is that a mesh ID can prevent STAs One of the reasons is that a mesh ID can prevent STAs from being associatedfrom being associated withwith MPs withoutMPs without AP functionality. AP functionality.

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Topology Formation/DiscoveryDiscovery and Formation of Mesh Networks

Before a new mesh node associated with a mesh network Before a new mesh node associated with a mesh network identified by a mesh ID, itidentified by a mesh ID, it needs to check if its mesh needs to check if its mesh profile matches the established mesh network.profile matches the established mesh network.

Each mesh device must support at least one profile consisting of a mesh ID, a path selection identifier, and a path selection metric identifier.

If such mesh capability information in a mesh node matches that in the mesh network, it will start association.

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Topology Formation/Discovery:Mesh Peer Link Establishment

Once a mesh node has joined a mesh network and beforeOnce a mesh node has joined a mesh network and before it it can start sending packets, it needs to establish peer links can start sending packets, it needs to establish peer links with its neighbors. with its neighbors.

In 802.11s, stateIn 802.11s, state machines and detailed procedures have machines and detailed procedures have been specified for setting up peer links. been specified for setting up peer links.

Once thisOnce this step is completed, it is also necessary to establish step is completed, it is also necessary to establish a measure of link quality for each peera measure of link quality for each peer link. link.

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Topology Formation/Discovery:Multi-Channel Topology Formation

SSingle-channelingle-channel mode mode – A A mesh device just selectsmesh device just selects one channel during one channel during

the discovery process. the discovery process.

MMultiulti--channel channel modemode– AA mesh node needs to select mesh node needs to select multiple channels multiple channels

forfor its multiple radios or for channel switching if its multiple radios or for channel switching if single radio is supported.single radio is supported.

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Topology Formation/Discovery:Multi-Channel Topology Formation

In order to manage the topology in a multi-channel In order to manage the topology in a multi-channel mesh network, the concept of unifiedmesh network, the concept of unified channel graph channel graph (UCG) is used(UCG) is used

– In a UCG, all devices are interconnected using the In a UCG, all devices are interconnected using the commoncommon channel. channel.

– Thus, in a single-channelThus, in a single-channel mesh network, then entire mesh network, then entire network has only one UCG. network has only one UCG.

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Topology Formation/Discovery:Multi-Channel Topology Formation

– ForFor a multi-channel mesh network, the number of a multi-channel mesh network, the number of UCGs depends on a self-organization of theUCGs depends on a self-organization of the networknetwork

– In the same UCG, the channel precedence value is In the same UCG, the channel precedence value is the same for all devicesthe same for all devices

– SuchSuch a value is different in different UCGs, and is a value is different in different UCGs, and is

used for coalesce or switching the channel inused for coalesce or switching the channel in UCGsUCGs

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Topology Formation/Discovery:Multi-Channel Topology Formation

A simple channel unification protocol and a simple channel graph switching protocol were specified in IEEE 802.11s draft.

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Topology Formation/Discovery:Multi-Channel Topology Formation

– However, such mechanisms are only applicable to simple scenarios such as slow channel switching, e.g., DFS, is only needed.

– If dynamic and fast channel switching is needed, the UCG concept and its supporting procedures in the current 802.11s draft may be too insufficient to be useful.

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Routing

Previously many proprietary 802.11 Previously many proprietary 802.11 mesh networks are built using mesh networks are built using different routingdifferent routing protocols protocols

which resulted in interoperability which resulted in interoperability problemsproblems

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Routing

In 802.11s, the framework for routing is In 802.11s, the framework for routing is extensible, extensible,

which means that different routingwhich means that different routing protocols can protocols can be be

supported by following this frameworksupported by following this framework

– BBut the mandatory protocol shall beut the mandatory protocol shall be implemented implemented in order to achieve interoperability.in order to achieve interoperability.

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Routing

Routing mechanism in 802.11s handles Routing mechanism in 802.11s handles packet forwarding forpacket forwarding for MPs, MAPs, and MPs, MAPs, and associatedassociated STAs. STAs.

Unicast, multicast, and broadcast frames are Unicast, multicast, and broadcast frames are all supported in the same framework.all supported in the same framework.

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Routing

– Since routing is performed in theSince routing is performed in the MAC layer, packet MAC layer, packet forwarding is carried out viaforwarding is carried out via MACMAC addresses, addresses,

which requires the MAC header contains at least 4 which requires the MAC header contains at least 4 MAC addresses. MAC addresses.

– Compared toCompared to the previous MAC protocol, the two the previous MAC protocol, the two additional MAC addresses are for the MAC additional MAC addresses are for the MAC addresses ofaddresses of the source and the destination of an the source and the destination of an end-to-end flow.end-to-end flow.

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Routing in Current 802.11s

One mandatory routing protocol:One mandatory routing protocol:

Hybrid Wireless MeshHybrid Wireless Mesh P Protocol (HWMP)rotocol (HWMP) (hybrid of “on demand routing” and “proactive(hybrid of “on demand routing” and “proactive tree-based tree-based

routing”) routing”)

One optional routingOne optional routing protocolprotocol

based on link state routing called based on link state routing called

““radio aware optimized link state routing (RA-radio aware optimized link state routing (RA-OLSR)”OLSR)”

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Overview of Demand Routing Overview of Demand Routing ProtocolProtocol

– In HWMP, on demand routing protocolIn HWMP, on demand routing protocol is adopted is adopted for nodes that experience a changing environmentfor nodes that experience a changing environment

while proactive tree-basedwhile proactive tree-based routing protocol is an routing protocol is an efficient choice for nodes in a fixed network efficient choice for nodes in a fixed network topology topology

– Mandatory routing metric is airtime cot which Mandatory routing metric is airtime cot which measures the quality of links. measures the quality of links.

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Overview of Demand Routing Overview of Demand Routing ProtocolProtocol

– More types of metrics such as QoS parameters, traffic More types of metrics such as QoS parameters, traffic load,load, power consumption, and so on can also be power consumption, and so on can also be consideredconsidered

– However, in the same mesh, only one metric shall be However, in the same mesh, only one metric shall be used.used.

– The on-demanding routing protocol is specified based on The on-demanding routing protocol is specified based on

radio-metric AODV. radio-metric AODV.

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Overview of Proactive Overview of Proactive tree-based tree-based routingrouting

– AApplied when there is root node configured in thepplied when there is root node configured in the meshmesh

– With this root, a distance vector tree can be built With this root, a distance vector tree can be built

and maintained for other nodesand maintained for other nodes

– SuchSuch routing protocol can avoid unnecessary routing protocol can avoid unnecessary routing overhead for routing path discoveryrouting overhead for routing path discovery and and recoveryrecovery

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Routing:

HWMP

On-demand routing and tree-based routing can run On-demand routing and tree-based routing can run simultaneously.simultaneously.

Four control messagesFour control messages– RRoot announcement (RANN), oot announcement (RANN), – RouteRoute request (RREQ), request (RREQ), – Route reply (RREP), and Route reply (RREP), and – Route error (RERR).Route error (RERR).

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Routing:

HWMP

– Except for RERR, all controlExcept for RERR, all control messages contain three messages contain three important fields:important fields:

* Destination sequence number (DSN)* Destination sequence number (DSN) * Time-to-live* Time-to-live (TTL), and (TTL), and * Routing Metric.* Routing Metric.

– DSN and TTL can prevent the counting to infinity problem,DSN and TTL can prevent the counting to infinity problem,

– Routing metricRouting metric helps to find a better routing path than just helps to find a better routing path than just using hop countusing hop count

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Routing:

HWMP: Procedures for OProcedures for On-n-DDemand emand RRoutingouting

– A source MP broadcasts RREQ to set up aA source MP broadcasts RREQ to set up a route to a route to a destination MPdestination MP

– When an intermediateWhen an intermediate MP receives RREQ, it MP receives RREQ, it creates/updatescreates/updates a route to the source if the sequence a route to the source if the sequence number of the RREQ is greater than the previous one number of the RREQ is greater than the previous one oror the sequence number is the same but the metric is the sequence number is the same but the metric is better better

– If the intermediateIf the intermediate MP has no routeMP has no route to the destination, to the destination, it just forwards the RREQ message further. it just forwards the RREQ message further.

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Routing:

HWMP

There have differentThere have different cases depending on two flags: cases depending on two flags: destination only (DO) flag and reply and forward (RF) destination only (DO) flag and reply and forward (RF) flag. flag.

– IfIf the DO flag is set to 1the DO flag is set to 1

then the intermediate MP does nothing but just forwards then the intermediate MP does nothing but just forwards the RREQ to the next-hop MPs until the destination node. the RREQ to the next-hop MPs until the destination node.

– Once the destination node gets this message,Once the destination node gets this message, it sends a it sends a unicast RREP back to the source MP. unicast RREP back to the source MP.

– All intermediate MPs create a route to theAll intermediate MPs create a route to the destination when destination when receiving this RREP message. receiving this RREP message.

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Routing:HWMP

– If “DO flag = 0”If “DO flag = 0” and “ and “RF flag = 0”, RF flag = 0”, intermediate MP sends a unicast RREP message to intermediate MP sends a unicast RREP message to

thethe source node and does not forward RREQ. source node and does not forward RREQ.

– If “DO flag = 0” and “RF flag = 1”,If “DO flag = 0” and “RF flag = 1”, intermediate MP sends a unicast RREP message to intermediate MP sends a unicast RREP message to

the source node; additionally, itthe source node; additionally, it needs to set the RF needs to set the RF flag into 0 and then forwards the RREQ message to flag into 0 and then forwards the RREQ message to the destination node.the destination node.

Subsequent intermediate MPs will not be able to send RREP Subsequent intermediate MPs will not be able to send RREP messages to themessages to the source node. source node.

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Routing:HWMP

REMARK:REMARK:

““DO flag = 0” and “RF flag = 1”DO flag = 0” and “RF flag = 1” only when the only when the source node source node

has no valid route and wants to create a new route has no valid route and wants to create a new route to the to the

destination node. destination node.

As compared to the original AODV protocolAs compared to the original AODV protocol, t, the he above procedures have been modified for HWMP.above procedures have been modified for HWMP.

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Routing:HWMP: Procedures for Procedures for the proactive the proactive tree-based routing modetree-based routing mode

TTwo mechanismswo mechanisms: :

* Based on * Based on proactive RREQproactive RREQ

* P* Proactive RANN. roactive RANN.

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Routing:HWMP: Procedures for Procedures for the the proactive tree-based routing modeproactive tree-based routing mode

PProactive RREQ mechanismroactive RREQ mechanism– TThe roothe root MP periodically broadcasts the RREQ MP periodically broadcasts the RREQ

messages. messages.

– An MP in the mesh receivingAn MP in the mesh receiving the RREQ the RREQ

* creates/updates the path to the root, * creates/updates the path to the root,

* records the metric and hop count to the root,* records the metric and hop count to the root,

* * updates the RREQ with such information, and updates the RREQ with such information, and

* then forwards RREQ. * then forwards RREQ.

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Routing :HWMP

PProactive RANN mechanismroactive RANN mechanism– TThe root periodically floods a RANN message intohe root periodically floods a RANN message into

the network. the network.

– When an MP receives the RANN and also needs to When an MP receives the RANN and also needs to create/refresh a route tocreate/refresh a route to the root, it sends a the root, it sends a unicast RREQ message to the root. unicast RREQ message to the root.

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Routing :HWMP

– When the root receives this unicastWhen the root receives this unicast RREQ, it RREQ, it replies with a RREP to the MP. replies with a RREP to the MP.

TThe unicast RREQ forms the reverse routehe unicast RREQ forms the reverse route from from the root to the originating MP, the root to the originating MP,

while the unicast RREP creates the forward route while the unicast RREP creates the forward route fromfrom the originating MP to the root.the originating MP to the root.

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Routing:RA-OLSR

AA proactive link-state routing protocol that is developed proactive link-state routing protocol that is developed basedbased on OLSR*.on OLSR*.

* T. Clausen and P. Jacquet, “Optimized link state routing

protocol (OLSR)”, IETF RFC 3626, 2003

TTo reduce flooding overhead, severalo reduce flooding overhead, several extensions are extensions are made made

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Routing:RA-OLSR

1) O1) Only a subset of one-hop neighbors of an MP nly a subset of one-hop neighbors of an MP is is

selected to relayselected to relay control messages. control messages. –Such neighbor MPs are called multipoint relays (MPRs)Such neighbor MPs are called multipoint relays (MPRs) –MPRs areMPRs are selected such that control messages relayed by selected such that control messages relayed by them can reach all two-hop neighbors of thethem can reach all two-hop neighbors of the selecting MP. selecting MP.

–MPR selection is performed through periodic HELLO messages MPR selection is performed through periodic HELLO messages between MPs. between MPs.

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Routing:RA-OLSR

2) T2) To provide shortesto provide shortest routes, RA-OLSR routes, RA-OLSR requires requires

only partial link state information to be only partial link state information to be floodedflooded

- The minimum- The minimum set of links are the links between the set of links are the links between the MPRs MPRs

and their selectors.and their selectors.

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Routing:Support of Legacy Nodes

For packets transmitting between legacy nodes For packets transmitting between legacy nodes via the meshvia the mesh network, network,

the routing protocol inside the mesh may need the the routing protocol inside the mesh may need the source and the destination MACsource and the destination MAC addresses of a legacy addresses of a legacy node node

Thus, two additional MAC addresses are added Thus, two additional MAC addresses are added into the MACinto the MAC header header – This is the mechanism of 6-address scheme specified in 802.11sThis is the mechanism of 6-address scheme specified in 802.11s

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Routing:Support of Legacy Nodes

Other than this mechanism, the routing protocol Other than this mechanism, the routing protocol of the mesh also needs to handle legacyof the mesh also needs to handle legacy nodes. nodes. – E.g., the association of legacy nodes with a MP shall E.g., the association of legacy nodes with a MP shall

be efficiently handledbe efficiently handled such that a routing path can be such that a routing path can be found for legacy node to send packets via the mesh found for legacy node to send packets via the mesh network.network.

In the current draft of 802.11s, this part of In the current draft of 802.11s, this part of functionality has not been fully specifiedfunctionality has not been fully specified..

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MAC

Basic operation mechanism of 802.11s MAC is Basic operation mechanism of 802.11s MAC is

the enhanced distributed channel accessthe enhanced distributed channel access (EDCA) specified in (EDCA) specified in 802.11e. 802.11e.

Other features of 802.11e such as HCCA are not adopted intoOther features of 802.11e such as HCCA are not adopted into 802.11s.802.11s. – QoS of 802.11s in its current form is still far from QoS of 802.11s in its current form is still far from

enough for multimedia servicesenough for multimedia services

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MAC

Moreover, EDCA does not work well for mesh Moreover, EDCA does not work well for mesh networks, since its prioritizationnetworks, since its prioritization mechanism does mechanism does not perform well in a multihop mesh environment. not perform well in a multihop mesh environment.

Nevertheless,Nevertheless, the current 802.11s MAC protocol is the current 802.11s MAC protocol is built on top of EDCA with various enhancements.built on top of EDCA with various enhancements.

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MAC

Multi-Channel Operation

Multichannel operation is important to WMNs.Multichannel operation is important to WMNs.

– However,However, no mechanism has been specified in 802.11s.no mechanism has been specified in 802.11s.

– In the beginning, a proposal called In the beginning, a proposal called common channel framework common channel framework (CCF) was adopted(CCF) was adoptedinto earlier versions of the draft (before draft 1.0).into earlier versions of the draft (before draft 1.0).

– However, because of many problems thatHowever, because of many problems that were not resolved were not resolved effectively, this CCF proposal was removed from the draft effectively, this CCF proposal was removed from the draft

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MAC

Multi-Channel Operation

CCommon ommon CChannel hannel FFrameworkramework– NNodes that want to use multi-channel operation odes that want to use multi-channel operation

need to negotiate its channel inneed to negotiate its channel in the common the common channelchannel

TThe common channel is known tohe common channel is known to all nodes in all nodes in the mesh network. the mesh network.

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MAC

Multi-Channel Operation

A transmitter first sends an RTX message to request aA transmitter first sends an RTX message to request a channel. channel.

The receiver sends back a CTX to confirm the requested check. The receiver sends back a CTX to confirm the requested check.

If RTX-CTX isIf RTX-CTX is successful, then a channel is selected for these successful, then a channel is selected for these

two nodes. two nodes.

Thus, both nodes switch to theThus, both nodes switch to the selected channel and exchange selected channel and exchange

data following the data/ack procedure. data following the data/ack procedure.

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MAC

Mesh Deterministic Access

Mesh deterministic access (MDA) allows MPs to Mesh deterministic access (MDA) allows MPs to access aaccess a certain period with lower contention than certain period with lower contention than other periods without using MDA. other periods without using MDA.

– Such a period isSuch a period is called called MDA opportunity (MDAOP)MDA opportunity (MDAOP)

– Before using MDAOP to access the medium, the ownerBefore using MDAOP to access the medium, the owner of of this MDAOP, i.e., the transmitter needs to set up the this MDAOP, i.e., the transmitter needs to set up the MDAOP with its receiver.MDAOP with its receiver.

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MAC

Mesh Deterministic Access

IIn the MDA mechanism, two types of time periods are definedn the MDA mechanism, two types of time periods are defined

– RX-TX timesRX-TX times:: The neighborhood MDAOP times of an MP The neighborhood MDAOP times of an MP are the RX-TX times in which the MP and itsare the RX-TX times in which the MP and its neighbors are neighbors are either a transmitter or receiver of these MDAOPs.either a transmitter or receiver of these MDAOPs.

– NNeighboreighbor MDAOP interferingMDAOP interfering timestimes:: For a neighbor of For a neighbor of this MP, itthis MP, it also has such time periods, but to thealso has such time periods, but to the MP, these MP, these times are called neighbortimes are called neighbor MDAOP interferingMDAOP interfering times.times.

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MAC

Mesh Deterministic Access

When an intended transmitter wants to set up a When an intended transmitter wants to set up a new MDAOP to an intended receiver, it needs to new MDAOP to an intended receiver, it needs to checkcheck

* its neighbor MDAOP times, * its neighbor MDAOP times, * the TX-RX times for other frames, and * the TX-RX times for other frames, and * the* the neighbor MDAOP interfering times for the intended neighbor MDAOP interfering times for the intended

receiver. receiver.

If no overlapping occurs andIf no overlapping occurs and the MDA limit is not the MDA limit is not reached, then the transmitter sends an MDAOP reached, then the transmitter sends an MDAOP setup request to thesetup request to the receiver. receiver.

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MAC

Mesh Deterministic Access

Receiver will do the same check. Receiver will do the same check. – If the check is passed, the receiver acceptsIf the check is passed, the receiver accepts the MDAOP; the MDAOP;

OOtherwise, it rejects.therwise, it rejects.

Once the MDAOP is setup, both the transmitter and theOnce the MDAOP is setup, both the transmitter and the receiver will start to advertise their new MDAOP time inreceiver will start to advertise their new MDAOP time in the MDAOP advertisement IE. the MDAOP advertisement IE.

Both the transmitter and the receiver can initiate the Both the transmitter and the receiver can initiate the teardownteardown process to release theprocess to release the MDAOP time period. MDAOP time period. – The teardown is complete once the initiatorThe teardown is complete once the initiator is acked by the is acked by the

receiver.receiver.

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MAC

Intra-Mesh Congestion Control

An 802.11 mesh usually has multiple hops. An 802.11 mesh usually has multiple hops. – The transmissionThe transmission of one hop may impact its previous hop, of one hop may impact its previous hop,

the next hops, or any links in the neighbors.the next hops, or any links in the neighbors.– LLinks may be congested, and thus a node withinks may be congested, and thus a node with congested congested

links may receive more packets than that can be sent out.links may receive more packets than that can be sent out.

TCP can help mitigate this problem TCP can help mitigate this problem – But nBut notot effective enough in a wireless multihop effective enough in a wireless multihop

network.network.

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MAC

Intra-Mesh Congestion Control

On the other hand, contention resolution canOn the other hand, contention resolution can also also help reduce congestion. help reduce congestion. – However, in a mesh network, the contention level However, in a mesh network, the contention level

experiencedexperienced by different nodes is different, which make a by different nodes is different, which make a contention resolution protocol ineffective. contention resolution protocol ineffective.

ForFor these reasons, intra-mesh congestion control these reasons, intra-mesh congestion control is specified in 802.11s.is specified in 802.11s.– The intra-mesh congestion control is hop-by-hop scheme. The intra-mesh congestion control is hop-by-hop scheme.

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MAC

Intra-Mesh Congestion Control

Nodes in the neighbor need toNodes in the neighbor need to exchange congestion exchange congestion information and control message in order to resolve information and control message in order to resolve congestion in thecongestion in the network.network.

Thus, the scheme consists of three modules: Thus, the scheme consists of three modules:

* local congestion monitoring* local congestion monitoring * congestion* congestion control signaling, and control signaling, and * local rate control* local rate control..

62

MAC

Intra-Mesh Congestion Control

In the current draft of 802.11s, some In the current draft of 802.11s, some local congestion local congestion monitoring monitoring

schemesschemes are suggested. are suggested.

– For example, congestion can be monitored by comparing For example, congestion can be monitored by comparing the transmitting rate and the receivingthe transmitting rate and the receiving rate of packets rate of packets that need to be forwarded. that need to be forwarded.

– Queue size can also be used to monitorQueue size can also be used to monitor congestion. congestion.

63

MAC

Intra-Mesh Congestion Control

– Once congestion is detected, the congested node will inform its Once congestion is detected, the congested node will inform its previous hop nodes by sending a previous hop nodes by sending a unicast Congestion Control unicast Congestion Control RequestRequest message in the mesh action frame message in the mesh action frame

– Node that receives message shall adjust its transmission rate Node that receives message shall adjust its transmission rate according to the locate rateaccording to the locate rate control algorithm. control algorithm.

– Congested node also sends a Congested node also sends a broadcast message Neighborhood broadcast message Neighborhood CongestionCongestion AnnouncementAnnouncement to all its neighbors so that neighbors to all its neighbors so that neighbors also regulate their transmission ratealso regulate their transmission rate

64

MAC

Intra-Mesh Congestion Control

Locate rate controlLocate rate control at node has not been discussed in at node has not been discussed in 802.11s so far.802.11s so far.

Although congestion control can help improve the mesh Although congestion control can help improve the mesh network performance, unfortunatelynetwork performance, unfortunately the critical part of the critical part of this mechanism such as target rate computation and local this mechanism such as target rate computation and local raterate control algorithm have not been clearly specified yet; control algorithm have not been clearly specified yet; – OOnly simple conceptual discussions arenly simple conceptual discussions are available in the draft of available in the draft of

802.11s.802.11s.

65

MAC

Power Management

Many nodes in 802.11sMany nodes in 802.11s mesh networks always work mesh networks always work in in an active statean active state since they either need to be an since they either need to be an AP or forward traffic for other nodes. AP or forward traffic for other nodes.

However, there are stillHowever, there are still other nodes that need to other nodes that need to work work in power save mode. in power save mode. – E.g., lightweightE.g., lightweight MPs or MPs that do not forward traffic MPs or MPs that do not forward traffic

for other nodes. for other nodes. – STAs associated with aSTAs associated with a MAP may also work in power MAP may also work in power

save modesave mode

66

MAC

Power Management

ATIM-window based power management ATIM-window based power management schemescheme

– AAn MP works in two states:n MP works in two states: doze or wake state.doze or wake state.

– The MP in power save mode needs to wake up The MP in power save mode needs to wake up during the ATIM windowduring the ATIM window to receive or send to receive or send control messages including beacons. control messages including beacons.

67

MAC

Power Management

The ATIM window repeats everyThe ATIM window repeats every one delivery traffic one delivery traffic indication message (DTIM) interval. indication message (DTIM) interval.

DTIM is usually equal to multipleDTIM is usually equal to multiple beacon intervals. beacon intervals.

An MP may also wake up in a scheduled time period An MP may also wake up in a scheduled time period negotiated negotiated

with otherwith other MPs. MPs.

In power save mode, packets in an MP need to be buffered In power save mode, packets in an MP need to be buffered and wait for being sent during the wake state.and wait for being sent during the wake state.

68

MAC

Power Management

To initiate the power management in a mesh, the following To initiate the power management in a mesh, the following

procedure shall be used:procedure shall be used:

– An unsynchronizingAn unsynchronizing MP shall set the values of MP shall set the values of

* DTIM* DTIM

* ATIM* ATIM windowwindow

* beacon interval,* beacon interval, and and

* power management mode. * power management mode.

- Such information is sent in beacon frames.- Such information is sent in beacon frames.

6969

Bridging functions in MPPs in a manner compatible with IEEE 802.1D.

– MPP needs to send an MPP announcement to MPP needs to send an MPP announcement to the MPs informing of its presence through IE in the MPs informing of its presence through IE in management framesmanagement frames

– On receiving a valid MPP announcement IE, MP On receiving a valid MPP announcement IE, MP checks the destination sequence number checks the destination sequence number SNSN

MAC Inter-networking

7070

– If If SN <SN < than that of a previous MPP than that of a previous MPP announcement message, the current announcement message, the current message shall be discardedmessage shall be discarded

– Otherwise, it forwards the message to Otherwise, it forwards the message to

other MPs after the portal propagation other MPs after the portal propagation delay expires and also the TTL value >0delay expires and also the TTL value >0

MAC Inter-networking

7171

– MAC address and routing metric for this MPP is stored by the MPMAC address and routing metric for this MPP is stored by the MP

– When an MP has packets to send, it first follows the data When an MP has packets to send, it first follows the data forwarding procedures as defined in the routing protocol forwarding procedures as defined in the routing protocol

– If an intra-mesh route to the destination MAC address If an intra-mesh route to the destination MAC address cannot be found, then the MP shall forward all packets cannot be found, then the MP shall forward all packets to the active MPPs in the meshto the active MPPs in the mesh

MAC Inter-networking

7272

MPP handles both egress and ingress messages

Egress Message is handled by MPP based on knowledge of– Dest. inside mesh:Dest. inside mesh: Message forwarded to the dest. Message forwarded to the dest.

node node – Dest. outside mesh:Dest. outside mesh: Message forwarded to external Message forwarded to external

networknetwork– Dest. unknown:Dest. unknown: Message forwarded to mesh + Message forwarded to mesh +

external network external network

Ingress Message received by MPP from external network– Dest. known:Dest. known: Message forwarded to the dest. node Message forwarded to the dest. node – Dest. unknown:Dest. unknown: Establish a route to dest. Or broadcast Establish a route to dest. Or broadcast

MAC Inter-networking

7373

Node mobility scenarios handled in 802.11s

Node moves from the LAN outside the mesh to another LAN outside the mesh

– No special action is needed and handled by 802.1D bridgingNo special action is needed and handled by 802.1D bridging

Node moves within the mesh network– Handled by the routing protocolHandled by the routing protocol

Node moves within the mesh network to outside the mesh– Routing protocol needs to repair path after detecting the route is Routing protocol needs to repair path after detecting the route is

changedchanged

Node moves from outside the mesh to inside the mesh– Both MPP functionality and routing protocol cooperate to build the new Both MPP functionality and routing protocol cooperate to build the new

routing pathrouting path

MAC Inter-networking

7474

MPP supports 802.1D bridging and VLAN functionality

– VLAN tag information defined in IEEE 802.1Q must be VLAN tag information defined in IEEE 802.1Q must be carriedcarriedbetween MPs and MPPsbetween MPs and MPPs

– 802.1Q defines two header formats:802.1Q defines two header formats: Ethernet-encoded Ethernet-encoded formats and SNAP-encoded headerformats and SNAP-encoded header

MAC Inter-networking

7575

802.11s Open Research Issues

Topology for Multi-Rate Operation and Physical Rate Control– Measurement is based on the Measurement is based on the current transmission current transmission

rate and transmission error rate (called the airtime rate and transmission error rate (called the airtime cost)cost)

– What packets can be sent and how they are sent are What packets can be sent and how they are sent are not specified, leading to measurement inaccuraciesnot specified, leading to measurement inaccuracies– Eg. frequency of measurement packets and their Eg. frequency of measurement packets and their

transmission rate impact the result of airtime costtransmission rate impact the result of airtime cost– The packet error rate due to transmission error does The packet error rate due to transmission error does

not actually reflect the link quality owing to MAC not actually reflect the link quality owing to MAC dependencydependency

7676

802.11s Open Research Issues

Routing Protocol– Both HWMP and RA-OLSR has several shortcomingsBoth HWMP and RA-OLSR has several shortcomings

In HWMP, the proactive tree-based routing is totally centralized and constrained by the root node – the routing protocol still routes the packets via the the routing protocol still routes the packets via the

root even when there is a short path between two MPsroot even when there is a short path between two MPs

For RA-OLSR, the overhead of control messages is too highalthough Fisheye scope mechanism is adopted

7777

802.11s Open Research Issues

Though both HWMP and RA-OLSR are specified as a routingmodule in the MAC layer, interactions with other MAC functionality are not considered

Supporting legacy nodes is still an on-going effort– Such a functionality is not specified in the HWMP, Such a functionality is not specified in the HWMP,

while the procedures in RA-OLSR incur high overhead while the procedures in RA-OLSR incur high overhead

No support for simultaneous use of multiple routing metrics

7878

802.11s Open Research Issues

Link quality measurement– 802.11s specifies a framework in which the peer-link 802.11s specifies a framework in which the peer-link

setup takes into account the link quality measurementsetup takes into account the link quality measurement

– PHY technologies support multiple rates depending on PHY technologies support multiple rates depending on the selection of different modulation and coding the selection of different modulation and coding schemesschemes

– For such multi-rate networks, the topology is very For such multi-rate networks, the topology is very sensitive tosensitive tothe transmission rate that is being used the transmission rate that is being used

– No provision for rate-dependent topology controlNo provision for rate-dependent topology control

7979

802.11s Open Research Issues

Multichannel operation– No provision for multiple channels and single No provision for multiple channels and single

radio operationradio operation

– Switching delay is considerably more than Switching delay is considerably more than packet Tx timepacket Tx time

– RTX-CTX in the common channel does not avoid RTX-CTX in the common channel does not avoid collisions from nodes of other collisions from nodes of other networks/standards in a new channelnetworks/standards in a new channel

8080

802.11s Open Research Issues

QoS Provision

– The EDCA mechanism (used in 802.11s) provides soft The EDCA mechanism (used in 802.11s) provides soft QoS onlyQoS only

– This is useful for providing priority to traffic classes, This is useful for providing priority to traffic classes, rather than actual priority to nodesrather than actual priority to nodes

8181

802.11s Open Research Issues

Congestion control– No effective way of congestion monitoring or co-No effective way of congestion monitoring or co-

working with the TCP control mechanismworking with the TCP control mechanism– The target rate computation method required 1- and 2- The target rate computation method required 1- and 2-

hop node information, no method it is specified to hop node information, no method it is specified to collect such infocollect such info

– Adjusting EDCA parameters cannot solve congestion Adjusting EDCA parameters cannot solve congestion problem as it is more effective for traffic prioritization problem as it is more effective for traffic prioritization rather than ensuring a certain traffic rate rather than ensuring a certain traffic rate

MDA mechanism for reducing contention may also raise interoperabiility issues

8282

802.11s Open Research Issues

Incorporating multiple MPPs– In the current framework of 802.11s, single MPP is In the current framework of 802.11s, single MPP is

assumedassumed

– In large scale mesh network (enterprise network) In large scale mesh network (enterprise network) multiple MPPs are needed to provide backhaul multiple MPPs are needed to provide backhaul capacity to the Internetcapacity to the Internet

– For multiple MPPs, many functionalities such as For multiple MPPs, many functionalities such as interworking and routing protocols in the current interworking and routing protocols in the current 802.11s draft need to be modified accordingly.802.11s draft need to be modified accordingly.

8383

IEEE 802.15 Mesh IEEE 802.15 Mesh NetworksNetworks

Goal: high throughput personal area networking Goal: high throughput personal area networking (PANs) (PANs)

(~10m or less) with applications in home (~10m or less) with applications in home

IEEE 802.15.3a standard is based on MultiBand IEEE 802.15.3a standard is based on MultiBand OFDM Alliance (MBOA)'s physical layer OFDM Alliance (MBOA)'s physical layer – Uses ultra wide band (UWB) to reach up to 480 MbpsUses ultra wide band (UWB) to reach up to 480 Mbps– A competing proposal of a Direct Sequence-UWB (DS-A competing proposal of a Direct Sequence-UWB (DS-

UWB) claims support for up to 1.3 GbpsUWB) claims support for up to 1.3 Gbps– WiMedia AllianceWiMedia Alliance

8484

WPAN Coordinator

Coordinator

End Device

Mesh Link

Star Link

IEEE 802.15.5:IEEE 802.15.5:High Rate Mesh NetworkHigh Rate Mesh Network

8585

High Rate (HR) Mesh NetworkHigh Rate (HR) Mesh Network

Types of nodes in 802.15.5 WPANs

Pan CoordinatorInitiates network formation

Motivation for 802.15.5– Both 802.15.1 scatternet and 802.15.4 are limited to Both 802.15.1 scatternet and 802.15.4 are limited to

tree topologies owing to their master-slave tree topologies owing to their master-slave architecturearchitecture

– Problems of poor network coverage, low reliability Problems of poor network coverage, low reliability

CoordinatorConnected to each other as a mesh network

End DeviceConnected to Coordinator in star topology

8686

High Rate (HR) Mesh High Rate (HR) Mesh NetworkNetwork

802.15.5 Mesh based WPANs target– Extending network coverage without increasing Extending network coverage without increasing

transmit power or receive sensitivitytransmit power or receive sensitivity– Enhancing reliability via route redundancyEnhancing reliability via route redundancy– Simplifying network configurationSimplifying network configuration– Increasing device battery life with better Increasing device battery life with better

transmissions and fewer retransmissionstransmissions and fewer retransmissions

802.15.5 Mesh based WPANs have PHY/MAC and routing protocol – higher layer specifications absent in 802.15 PANs

8787

High Rate (HR) Mesh High Rate (HR) Mesh NetworkNetwork

Applications

Interconnections among PCs/peripherals

Interconnections among PCs/peripherals

Multimedia Home Networkinge.g., HDTV, DVD,Interacting gaming

Standards for HR mesh networks must cover– MAC: Mobility, QoS, beacon managementMAC: Mobility, QoS, beacon management– Routing : Must balance robustness, reliability, load Routing : Must balance robustness, reliability, load

balancingbalancing– Security: Need for trusted authoritySecurity: Need for trusted authority

88

802.15 MAC Management

802.15 MAC

Frame Convergence Sublayer

(FCSL) (DME)

Device Management Entity

(DME)

88

Mesh Functions mesh routing

Enhancement for mesh

Enhancement for mesh

802.15 PHY

802.15 PHY Management

PROTOCOL STACK

8989

Low Rate Mesh PANs- Based on 802.15.4b-Applications include automation + control, monitoring, sensing location services, entertainment, among others. - Mainly tree-topology based

Low Rate Mesh NetworkLow Rate Mesh Network

Critical Requirements

Reliability Power Consumption Large Coverage

9090

UWB-Based Mesh Wireless UWB-Based Mesh Wireless PANsPANs

WiMedia Alliance WiMedia Alliance UWB ForumUWB Forum

Physical Layer: Multi-band Physical Layer: Multi-band OFDMOFDM

Physical Layer: Direct-Physical Layer: Direct-sequence UWB (DS-UWB)sequence UWB (DS-UWB)

MAC Layer: Developed by itselfMAC Layer: Developed by itself MAC Layer: Inherited from IEEE MAC Layer: Inherited from IEEE 802.15.3 – follows piconet 802.15.3 – follows piconet topologytopology

Multiple beacons possible, Multiple beacons possible, allowing multiple “groups” of allowing multiple “groups” of nodesnodes

Each piconet has 1 superframe. Each piconet has 1 superframe. Hence, only 1 beacon sent / Hence, only 1 beacon sent / superframesuperframe

UWB-Based Wireless PANs (2 Industrial Consortiums)

WiMedia Alliance more widely accepted, and also chosen by Bluetooth SIG

9191

Pros and Cons of UWB based Pros and Cons of UWB based mesh networksmesh networks

Advantages of using UWB in Mesh NetworksAdvantages of using UWB in Mesh Networks– Efficient communicationsEfficient communications– Low-power/cost requirementLow-power/cost requirement– Accurate location informationAccurate location information– High BandwidthHigh Bandwidth

* * However, these advantages have not been really However, these advantages have not been really realized yet !realized yet !

Disadvantage Disadvantage – Communication range is rather shortCommunication range is rather short

9292

WiMedia UWB

Standards published by the European association for standardizing information and communication systems (ECMA)

WiMedia Alliance (December 2005). - ECMA-368 is a standard on UWB MAC and physical layer technologies

- ECMA-369 is a standard for the interface between MAC and physical layers specified in ECMA-368

9393

WiMedia UWB

Overview of WiMedia UWB Physical Layer (ECMA-368)

- 3.1–10.6 GHz unlicensed frequency bands- Data rates of 53.3/80/106.7/160/200/320/400/480 Mbps.- UWB spectrum is divided into 14 bands, each with b/w of 512 MHz.

9494

WiMedia UWB

OFDM symbol structure- In each band there are 110 subcarriers (100 data subcarriers and 10 guard subcarriers) to transmit information and 12 pilot subcarriers for coherent detection - The data is coded by convolution codes and spread by time-frequency codes (TFC)

9595

WiMedia UWB

TFC code Types: – Time-frequency interleaving (TFI) : Coded data is Time-frequency interleaving (TFI) : Coded data is

interleaved over 3 Tx bandsinterleaved over 3 Tx bands– Fixed-frequency interleaving (FFI): Coded data sent Fixed-frequency interleaving (FFI): Coded data sent

over the same bandover the same band

WiMedia UWB MAC – Superframe consists of 256 medium access slots for a Superframe consists of 256 medium access slots for a

total of 65536 total of 65536 μμss

9696

WiMedia UWB Superframe structure

Beacon Period (BP)

Data Transmission Period

Reservation Period Prioritized Contention Access

Beacon Period (BP) has multiple beacon slots– BP can be further extended to support variable BP can be further extended to support variable

number of nodes in rangenumber of nodes in range

9797

WiMedia UWB

Nodes periodically send BP occupancy IE (BPOIE) in each beacon– Allows nodes within two hops to uniquely occupy the Allows nodes within two hops to uniquely occupy the

beacon slotsbeacon slots– Reduces beacon collisionsReduces beacon collisions– Based on a multi-beacon BP, beacon groups can be Based on a multi-beacon BP, beacon groups can be

easily merged as an extended beacon groupeasily merged as an extended beacon group

9898

WiMedia UWB

Data transmission types– prioritized contention access (PCA)prioritized contention access (PCA)– reservation via distributed reservation protocol (DRP)reservation via distributed reservation protocol (DRP)

PCA Features– Similar to IEEE 802.11e EDCASimilar to IEEE 802.11e EDCA– Used for non-real-time trafficUsed for non-real-time traffic– Any medium access slots that are not reserved by DRP Any medium access slots that are not reserved by DRP

can be used for PCAcan be used for PCA

9999

WiMedia UWB Types of DRP Reservations

– Alien BP: Reserves medium access slots to protect Alien BP: Reserves medium access slots to protect alien BPsalien BPs

– Hard: Reserves medium access slots for reservation Hard: Reserves medium access slots for reservation owner and target onlyowner and target only

– Soft: Permits PCA, but reservation owner has priority Soft: Permits PCA, but reservation owner has priority accessaccess

– Private: Reservation owner and target may use by Private: Reservation owner and target may use by other access schemes that are not specified by other access schemes that are not specified by WiMedia MACWiMedia MAC

– PCA: Reserves medium access slots exclusively for PCAPCA: Reserves medium access slots exclusively for PCA

100100

Open Research Issues Standards have not kept pace with technological progress

- Both IEEE 802.15.5 and WiMedia specifications of the MAC protocol for wireless mesh PANs are far from being completed

Proposed standards protocols lack thorough evaluation

- For both high/low rate wireless mesh PANs, routing protocols are alltree-based without validating their utility for mesh networks

802.15.5 will only be a recommended practice rather than a mandatory standard

- Possible interoperability issues

101101

Open Research Issues For WiMedia UWB, the DRP module (handles resource allocation in a distributed network) does not consider multiple hops

For both 802.15.5 and WiMedia Alliance, there is no provision for cross-layer design between MAC and routing

Multichannel operation not yet incorporated in the standards

102102

IEEE 802.15.1 BluetoothIEEE 802.15.1 Bluetooth Low data rate (<1 Mbps) PAN technologyLow data rate (<1 Mbps) PAN technology Targets wire replacementTargets wire replacement Piconets formed by master-slave(s)Piconets formed by master-slave(s) Has provisions for multi-hop scatternets Has provisions for multi-hop scatternets

with several masters and slaveswith several masters and slaves

Single SlaveSingle Slave(Point-to-point)(Point-to-point)

Multi-SlaveMulti-Slave(Point-to-multipoint)(Point-to-multipoint)

MasterMaster

SlaveSlave

Master/SlaveMaster/Slave Multi-SlaveMulti-Slave(Point-to-multipoint)(Point-to-multipoint)

103

Bluetooth is not a popular wireless Bluetooth is not a popular wireless mesh network platform due to:mesh network platform due to:– Low bandwidth Low bandwidth – Limited hardware support for Limited hardware support for

scatternetsscatternets– Need for more distributed network Need for more distributed network

architecture supportarchitecture support

Open Research Issues

104104

IEEE 802.15.4 ZigbeeIEEE 802.15.4 Zigbee Lower data rate PAN (250,40,20kbps)Lower data rate PAN (250,40,20kbps) Multi-months – years lifetime on small batteriesMulti-months – years lifetime on small batteries Supports star topology and peer-to-peer multihop Supports star topology and peer-to-peer multihop

mesh topology mesh topology – One coordinator responsible for setting up the One coordinator responsible for setting up the

networknetwork

Full Function DeviceFull Function Device

Reduced FunctionReduced Function DeviceDevice

105105

IEEE 802.16a WiMaxIEEE 802.16a WiMax

April 2003April 2003 Enhances the original 802.16 standardEnhances the original 802.16 standard Original IEEE 802.16 specifies only point to Original IEEE 802.16 specifies only point to

multipoint functionality – great for gateway to multipoint functionality – great for gateway to internet linksinternet links

The extensions specifies user-user links using:The extensions specifies user-user links using:– either centralized schedules, or either centralized schedules, or – distributed schedules.distributed schedules.

106106

IEEE 802.16a WMAN featuresIEEE 802.16a WMAN features– ““mesh mode” in addition to the mesh mode” in addition to the

point-to-multipoint (PMP) mode point-to-multipoint (PMP) mode defined in IEEE 802.16. defined in IEEE 802.16.

– Operating in the licensed and Operating in the licensed and unlicensed lower frequencies of unlicensed lower frequencies of 2–11 GHz, allowing non-line-of-2–11 GHz, allowing non-line-of-sight (NLO) communications, sight (NLO) communications, spanning up to 50 km range.spanning up to 50 km range.

– Supporting Supporting multihopmultihop communications.communications.

IEEE 802.16a WiMaxIEEE 802.16a WiMaxpoint-to-multipointpoint-to-multipoint

mesh-modemesh-mode

107

WiMAX Positioning: WiMAX Positioning: Capacity and MobilityCapacity and Mobility

Wireless Technology Positioning

Systems Beyond 3G

>2010

Mobility / Range

Data rates

10 Mbps0.1

IEEE802.16d

1 100

IEEE802.16e

WLAN(IEEE 802.11x)

GSMGPRS

DECT

Bluetooth

EDGE

Fix

ed

Walk

Veh

icle

Indoor

Pedestrian

High Speed

VehicularRural

Personal Area

VehicularUrban

Fixed urban

Nomadic

WiMAX for wireless-DSL

with limited mobility

Flash-OFDM

UMTS

HSDPA

108

MAP OF WIRELESS MAP OF WIRELESS SYSTEMSSYSTEMS

109

More Than 250 Operator Trials and Deployments More Than 250 Operator Trials and Deployments in 65+ Countries!in 65+ Countries!

Source: Intel, the WiMAX Forum* Other names and brands may be claimed as the property of others

110

WiMAX: New Broadband Last MileWiMAX: New Broadband Last Mile

  Wi-Fi Wi-Fi for the last one hundred feet (300 ft) for the last one hundred feet (300 ft)

WiMAX (Worldwide Interoperability for Microwave WiMAX (Worldwide Interoperability for Microwave Access)Access)

for the last mile (30 miles)for the last mile (30 miles)

111

WiMAX ARCHITECTUREWiMAX ARCHITECTURE

  

112

WiMAX ArchitectureWiMAX Architecture

1. A WiMAX Tower (similar in concept to a cell-phone tower; a single (similar in concept to a cell-phone tower; a single WiMAX tower can provide coverage to a very large WiMAX tower can provide coverage to a very large area -- as big as 3,000 square miles (~8,000 sq.km). area -- as big as 3,000 square miles (~8,000 sq.km).

2. A WiMAX Receiver The receiver and antenna could be a small box or PCMCIA card, or they could be built into a laptop the way WiFi access is today.

113

WiMAX TOWERWiMAX TOWER

114

WiMAX RECEIVERWiMAX RECEIVER

115

Fixed WiMAXFixed WiMAX

IEEE 802.16dIEEE 802.16d 1BS – thousands of users1BS – thousands of users < 50km coverage< 50km coverage < 75Mbps< 75Mbps

116

Fixed WiMAX Fixed WiMAX ArchitectureArchitecture

117

Mobile WiMAXMobile WiMAX

IEEE 802.16eIEEE 802.16e 2-3km coverage (optimal)2-3km coverage (optimal) High speed hand overHigh speed hand over

(< 50ms latencies)(< 50ms latencies) Ensures performance at Ensures performance at

vehicular speeds greater vehicular speeds greater than 120km/hthan 120km/h

< 30Mbps for downlink< 30Mbps for downlink < 15Mbps for uplink< 15Mbps for uplink

118

Two Forms of Wireless ServiceTwo Forms of Wireless Service

1. Non-Line-of-Sight Service:1. Non-Line-of-Sight Service:

* Lower frequency range – 2 GHz to 11 GHz * Lower frequency range – 2 GHz to 11 GHz

2. Line-of-Sight Service2. Line-of-Sight Service::

119

WiMAX FactsWiMAX Facts Ideal for the "last-mile" problem that plagues many neighborhoods Ideal for the "last-mile" problem that plagues many neighborhoods

that are too remote to receive Internet access via cable or DSL.that are too remote to receive Internet access via cable or DSL.

In areas with cable or DSL access, WiMAX will provide consumers In areas with cable or DSL access, WiMAX will provide consumers

with an additional — and possibly cheaper — alternative (less than with an additional — and possibly cheaper — alternative (less than

$50).$50).

Uplink and the downlink up to 75 MbpsUplink and the downlink up to 75 Mbps

120

WiMAX FactsWiMAX Facts

Up to 50 km (31 miles) Up to 50 km (31 miles)

This should not be taken to mean that users 50 km away This should not be taken to mean that users 50 km away without line of sight will always have connectivity.without line of sight will always have connectivity.

Practical limits from real world tests seem to be around 3 to 5 Practical limits from real world tests seem to be around 3 to 5

miles. miles.

If the density of users and thus the demand for bandwidth If the density of users and thus the demand for bandwidth are high, the range will be determined by the demand for BW. are high, the range will be determined by the demand for BW.

121

802.16 Standards History802.16 Standards History

802.16a(Jan 2003)

• Extension for 2-11 GHz: Targeted for non-line-of-sight, Point-to-Multi-Point applications like “last mile” broadband access

802.16(Dec 2001)

• Original fixed wireless broadband air Interface for 10 – 66 GHz: Line-of-sight only, Point-to-Multi-Point applications

802.16c(2002)

802.16 AmendmentWiMAX System Profiles

10 - 66 GHz

802.16REVd (802.16-2004)

(Oct 2004)

• Adds WiMAX System Profiles and Errata for 2-11 GHz

802.16e(802.16-2005)

(Dec 2005)

• MAC/PHY Enhancements to support subscribers moving at vehicular speeds

122

IEEE 802.16 SpecificationsIEEE 802.16 Specifications 802.16a802.16a

Uses the licensed frequencies from 2 to 11 GHzUses the licensed frequencies from 2 to 11 GHz

Supports Mesh networkSupports Mesh network 802.16b 802.16b

Increase spectrum to 5 and 6 GHzIncrease spectrum to 5 and 6 GHz

Provides QoS( for real time voice and video service)Provides QoS( for real time voice and video service) 802.16c 802.16c

Represents a 10 to 66GHzRepresents a 10 to 66GHz 802.16d 802.16d

Improvement and fixes for 802.16a Improvement and fixes for 802.16a 802.16e802.16e

Addresses on MobileAddresses on Mobile

Enable high-speed signal handoffs necessary for communications with Enable high-speed signal handoffs necessary for communications with users users

moving at vehicular speedsmoving at vehicular speeds

123

RESEARCH CHALLENGESRESEARCH CHALLENGES

* Limited Radio Spectrum Much of the radio spectrum is already

allocated by governments or used for other purposes

by carriers.

124

RESEARCH CHALLENGESRESEARCH CHALLENGES

* High Cost The cost of deploying WiMAX towers is considerably

high when the service is offered on higher radio

frequencies because the line-of-sight requirements of WiMAX necessitate the installation of additional antennas

to cover the same service area.

125

RESEARCH CHALLENGESRESEARCH CHALLENGES

* Incomplete Network Architecture IEEE 802.16e standard only addresses PHY and MAC layers, leaving it to the WiMAX Forum to tackle issues such as call control, session management, security, the network architecture, roaming, etc.

126126

Open Research IssuesOpen Research Issues

A group within 802.16, the Mesh Ad Hoc committee is A group within 802.16, the Mesh Ad Hoc committee is investigating ways to improve the performance of mesh investigating ways to improve the performance of mesh networking.networking.

Following issues are yet to be fully considered in specifying the Following issues are yet to be fully considered in specifying the 802.16 mesh MAC protocol802.16 mesh MAC protocol – Avoiding hidden terminal collisionsAvoiding hidden terminal collisions– Selection of linksSelection of links– SynchronizationSynchronization– Power versus data rate tradeoffsPower versus data rate tradeoffs– Greater routing-MAC interdependenceGreater routing-MAC interdependence

127

IEEE 802.16jIEEE 802.16j

Mobile multihop relay (MMR) based on Mobile multihop relay (MMR) based on relaying stationsrelaying stations

A more practical multihop networking A more practical multihop networking mode than mesh modemode than mesh mode

Features Features – Improve network capacityImprove network capacity– Extend coverageExtend coverage– Support mobile stationsSupport mobile stations

128

IEEE 802.16j Network IEEE 802.16j Network ArchitectureArchitecture