Telecommunications & Networks Lab Mesh Networking Angelakis Vangelis 20 / 1 / 2005

Telecommunications & Networks LabTelecommunications & Networks LabTelecommunications & Networks LabTelecommunications & Networks Lab

Mesh NetworkingMesh Networking

Angelakis VangelisAngelakis Vangelis20 / 1 / 200520 / 1 / 2005

IntroductionIntroduction

Angelakis Vangelis 20/1/2005

In the past decade the Ad hoc Networking paradigm absorbed a lot of research effort.

Most of the work is focused on isolated military or specialized civilian application multihop ad hoc networks.

Turning ad-hoc networks into a commodity takes a few changes:

Make multihop flexible low cost last mile extensions of wired infrastructure: Turn them into MESH NETWORKS!

In the past decade the Ad hoc Networking paradigm absorbed a lot of research effort.

Most of the work is focused on isolated military or specialized civilian application multihop ad hoc networks.

Turning ad-hoc networks into a commodity takes a few changes:

Make multihop flexible low cost last mile extensions of wired infrastructure: Turn them into MESH NETWORKS!

Presentation LayoutPresentation Layout


Wireless Mobile Ad Hoc Networks (MANETs): Criticism

Wireless Mesh Networks

MANET – WMN common grounds

Standards & Committees

Research problems

Hyacinth

Routing Metrics

Locustworld

Wireless Mobile Ad Hoc Networks (MANETs): Criticism

Wireless Mesh Networks

MANET – WMN common grounds

Standards & Committees

Research problems

Hyacinth

Routing Metrics

Locustworld

Where is the ad-hoc paradigm failing?Where is the ad-hoc paradigm failing?


An ad-hoc network is a collection of mobile nodes that connect over the wireless medium without the need of any pre-deployed infrastructure.

Nodes in a MANET can dynamically self-organize into temporary and arbitrary and network topologies

+ No no pre-existing infrastructure required:Supporting Scenarios: Disaster Recovery Areas

Battlefields- Network Isolation

An ad-hoc network is a collection of mobile nodes that connect over the wireless medium without the need of any pre-deployed infrastructure.

Nodes in a MANET can dynamically self-organize into temporary and arbitrary and network topologies

+ No no pre-existing infrastructure required:Supporting Scenarios: Disaster Recovery Areas

Battlefields- Network Isolation

Where is the ad-hoc paradigm failing?Where is the ad-hoc paradigm failing?


Key Research drivers• Bluetooth (802.15.5) and 802.11 mass market deployment • IETF MANET WG standardizations• $$$ from the USA DoD

Main problem:Users want

affordable devicesInternet access

Is high quality connectivity during mobility such an important issue?

Key Research drivers• Bluetooth (802.15.5) and 802.11 mass market deployment • IETF MANET WG standardizations• $$$ from the USA DoD

Main problem:Users want

affordable devicesInternet access

Is high quality connectivity during mobility such an important issue?

Making ad-hoc networks a commodityMaking ad-hoc networks a commodity


Pass down as much research from the MANET field to a more market-viable networking paradigm.

• Relax the main constraint of MANETS:Accept the existence of infrastructure.

Wireless Mesh Networks (WMNs) are build by interconnecting internet egress points with end-user devices can act as terminals and as routers.

• Community Networks being the earliest form of Meshes, relaxed a second MANET feature:

Mesh nodes are practically stationary

Pass down as much research from the MANET field to a more market-viable networking paradigm.

• Relax the main constraint of MANETS:Accept the existence of infrastructure.

Wireless Mesh Networks (WMNs) are build by interconnecting internet egress points with end-user devices can act as terminals and as routers.

• Community Networks being the earliest form of Meshes, relaxed a second MANET feature:

Mesh nodes are practically stationary

How does this change look like?How does this change look like?


A 10-node MANET at time t0A 10-node MANET at time t0









Wired BackboneA wireless mesh network of 3 tiers

Ad-hoc – WMN, what is differentAd-hoc – WMN, what is different


The WMN concept is similar to the one of ad-hoc networks.

With four important differences:

1. (practically) fixed nodes => Topology changes are infrequentI. Addition of nodesII. Node failure or maintenance

2. Traffic distribution is skewed (to/from the wired network)

3. Traffic characteristics aggregated from large numbers of flows => network optimization based on profiling

4. Reactive discovery of multihop paths is not efficient for an effective backbone and not fit under (1).

The WMN concept is similar to the one of ad-hoc networks.

With four important differences:

1. (practically) fixed nodes => Topology changes are infrequentI. Addition of nodesII. Node failure or maintenance

2. Traffic distribution is skewed (to/from the wired network)

3. Traffic characteristics aggregated from large numbers of flows => network optimization based on profiling

4. Reactive discovery of multihop paths is not efficient for an effective backbone and not fit under (1).

A research decision that made a big differenceA research decision that made a big difference


Testbeds were used in WMN research from the start.

MIT Roofnet (Chambers ’02)

Proof of existence of good enough solution for civilian applications has stimulated the users’ interest to adopt this technology.

Two main solutions classes:• “off-the-shelf” community networks

- Roofnet - CUWiN- BAWUG - Seattle Wireless

• proprietary MeshNetworks, Tropos Networks, Radiant Networks, BelAir, Strix etc…

Testbeds were used in WMN research from the start.

MIT Roofnet (Chambers ’02)

Proof of existence of good enough solution for civilian applications has stimulated the users’ interest to adopt this technology.

Two main solutions classes:• “off-the-shelf” community networks

- Roofnet - CUWiN- BAWUG - Seattle Wireless

• proprietary MeshNetworks, Tropos Networks, Radiant Networks, BelAir, Strix etc…

Standards & CommitteesStandards & Committees


IEEE standards groups actively working to define specs. for wireless mesh networking techniques

Special groups established to define the requirements for mesh networking in WPANs, WLANs, and WMANs.

The following standards amendments are expected:• 802.15.5 (bluetooth - WPAN)• 802.11s (wi-fi - WLAN)• 802.16a (wi-max - WMAN)

Also 802.20 (wireless mobile broadband access -WMBA) is to support the Mesh Networking paradigm from the first spec.

(expected first draft sometime in the 2nd semester of 2006)

IEEE standards groups actively working to define specs. for wireless mesh networking techniques

Special groups established to define the requirements for mesh networking in WPANs, WLANs, and WMANs.

The following standards amendments are expected:• 802.15.5 (bluetooth - WPAN)• 802.11s (wi-fi - WLAN)• 802.16a (wi-max - WMAN)

Also 802.20 (wireless mobile broadband access -WMBA) is to support the Mesh Networking paradigm from the first spec.

(expected first draft sometime in the 2nd semester of 2006)

802.11s802.11s


The 802.11 group has set up the “TG s” to discuss proposals for a specs amendment in the 2nd quarter of ’05 and reach a final document no sooner than 2007.

“ Scope of the Project: An IEEE 802.11 Extended Service Set (ESS) Mesh is a collection of APs interconnected with wireless links that enable automatic topology learning and dynamic path configuration.

The proposed amendment shall be an extension to the IEEE 802.11 MAC. The amendment will define an architecture and protocol for providing an IEEE 802.11 ESS Mesh using the IEEE 802.11 MAC to create an IEEE 802.11 Wireless Distribution System that supports both broadcast/multicast and unicast delivery at the MAC layer using radio-aware metrics over self-configuring multi-hop topologies. An ESS Mesh is functionally equivalent to a wired ESS, with respect to the STAs relationship with the BSS and ESS.

The 802.11 group has set up the “TG s” to discuss proposals for a specs amendment in the 2nd quarter of ’05 and reach a final document no sooner than 2007.

“ Scope of the Project: An IEEE 802.11 Extended Service Set (ESS) Mesh is a collection of APs interconnected with wireless links that enable automatic topology learning and dynamic path configuration.

The proposed amendment shall be an extension to the IEEE 802.11 MAC. The amendment will define an architecture and protocol for providing an IEEE 802.11 ESS Mesh using the IEEE 802.11 MAC to create an IEEE 802.11 Wireless Distribution System that supports both broadcast/multicast and unicast delivery at the MAC layer using radio-aware metrics over self-configuring multi-hop topologies. An ESS Mesh is functionally equivalent to a wired ESS, with respect to the STAs relationship with the BSS and ESS.

802.11s802.11s


The amendment shall enable interoperable formation and operation of an ESS Mesh, but shall be extensible to allow for alternative path selection metrics and/or protocols based on application requirements. A target configuration is up to 32 devices participating as AP forwarders in the ESS Mesh. However, larger configurations may also be contemplated by the standard. It is intended that the architecture defined by the amendment shall allow an ESS Mesh to interface with higher layers and to connect with other networks using higher layer protocols.

The amendment shall utilize IEEE 802.11i security mechanisms, or an extension thereof, for the purpose of securing an ESS Mesh in which all of the APs are controlled by a single logical administrative entity for security. The amendment shall allow the use of one or more IEEE 802.11 radios on each AP in the ESS Mesh.”

The amendment shall enable interoperable formation and operation of an ESS Mesh, but shall be extensible to allow for alternative path selection metrics and/or protocols based on application requirements. A target configuration is up to 32 devices participating as AP forwarders in the ESS Mesh. However, larger configurations may also be contemplated by the standard. It is intended that the architecture defined by the amendment shall allow an ESS Mesh to interface with higher layers and to connect with other networks using higher layer protocols.

The amendment shall utilize IEEE 802.11i security mechanisms, or an extension thereof, for the purpose of securing an ESS Mesh in which all of the APs are controlled by a single logical administrative entity for security. The amendment shall allow the use of one or more IEEE 802.11 radios on each AP in the ESS Mesh.”

802.16a 802.16a


802.16 is a P-MP first-mile/last-mile WMAN connection standard. (data rate up to 120Mbps @ 30miles).

A base station (BS) serves a number of subscriber stations (SS).

BS uses a broadcast channel to transmit to all SSs.

•802.16 approved in 2001 (10-66GHz operation – TDMA, TDD&FDD)

•802.16a approved in Jan. 2003 (2-11 GHz operation added -ODFM) –already obsolete and part of the 802.16-2004 doc

Stations may have direct links to each other - control can be distributed.

•WiMax forum formed later in 2003 (just like the 802.11 Wi-Fi forum) to promote IEEE standards for interoperability)

•No WiMax Forum Certified in the market yet.

802.16 is a P-MP first-mile/last-mile WMAN connection standard. (data rate up to 120Mbps @ 30miles).

A base station (BS) serves a number of subscriber stations (SS).

BS uses a broadcast channel to transmit to all SSs.

•802.16 approved in 2001 (10-66GHz operation – TDMA, TDD&FDD)

•802.16a approved in Jan. 2003 (2-11 GHz operation added -ODFM) –already obsolete and part of the 802.16-2004 doc

Stations may have direct links to each other - control can be distributed.

•WiMax forum formed later in 2003 (just like the 802.11 Wi-Fi forum) to promote IEEE standards for interoperability)

•No WiMax Forum Certified in the market yet.

Major research activity by Microsoft…Major research activity by Microsoft…


One of the most significant research efforts in the WMN field is conducted by the networking research group of Microsoft

In June Microsoft organized the “Mesh Networking Summit 2004”

Gathering most of the major players from the industry and academia community this was the first focused event on WMNs

A presentation a few days later by Victor Bahl sets the problem space and the wish list of WMNs as has been formed after that meeting…

One of the most significant research efforts in the WMN field is conducted by the networking research group of Microsoft

In June Microsoft organized the “Mesh Networking Summit 2004”

Gathering most of the major players from the industry and academia community this was the first focused event on WMNs

A presentation a few days later by Victor Bahl sets the problem space and the wish list of WMNs as has been formed after that meeting…

Problem space Problem space


Range and CapacityRange and CapacityInexpensive electronically steerable directional antenna or MIMO for Inexpensive electronically steerable directional antenna or MIMO for range enhancementrange enhancementMultiple frequency meshesMultiple frequency meshesMulti-radio hardware for capacity enhancement Multi-radio hardware for capacity enhancement via greater spectrum via greater spectrum utilizationutilizationNew data channel MAC with Interference management or higher New data channel MAC with Interference management or higher throughputthroughput

Multihop RoutingMultihop RoutingL2.5 L2.5 on-demand on-demand source routing with link quality based routes selectionsource routing with link quality based routes selectionRoute selection with multiple radios (multiple channels)Route selection with multiple radios (multiple channels)

Security, Privacy, and FairnessSecurity, Privacy, and FairnessGuard against malicious users (and freeloaders)Guard against malicious users (and freeloaders)EAP-TLS between MeshBoxes, PEAPv2 or EAP-TLS between clients and EAP-TLS between MeshBoxes, PEAPv2 or EAP-TLS between clients and MeshBoxesMeshBoxesPriority based admission control, Secure traceroute Priority based admission control, Secure traceroute

Self Management & Self HealingSelf Management & Self HealingMinimal human intervention - avoid network operator Minimal human intervention - avoid network operator Watchdog mechanism with data cleaning and liar detectionWatchdog mechanism with data cleaning and liar detectionOnline simulation based fault isolation and diagnosisOnline simulation based fault isolation and diagnosis

Range and CapacityRange and CapacityInexpensive electronically steerable directional antenna or MIMO for Inexpensive electronically steerable directional antenna or MIMO for range enhancementrange enhancementMultiple frequency meshesMultiple frequency meshesMulti-radio hardware for capacity enhancement Multi-radio hardware for capacity enhancement via greater spectrum via greater spectrum utilizationutilizationNew data channel MAC with Interference management or higher New data channel MAC with Interference management or higher throughputthroughput

Multihop RoutingMultihop RoutingL2.5 L2.5 on-demand on-demand source routing with link quality based routes selectionsource routing with link quality based routes selectionRoute selection with multiple radios (multiple channels)Route selection with multiple radios (multiple channels)

Security, Privacy, and FairnessSecurity, Privacy, and FairnessGuard against malicious users (and freeloaders)Guard against malicious users (and freeloaders)EAP-TLS between MeshBoxes, PEAPv2 or EAP-TLS between clients and EAP-TLS between MeshBoxes, PEAPv2 or EAP-TLS between clients and MeshBoxesMeshBoxesPriority based admission control, Secure traceroute Priority based admission control, Secure traceroute

Self Management & Self HealingSelf Management & Self HealingMinimal human intervention - avoid network operator Minimal human intervention - avoid network operator Watchdog mechanism with data cleaning and liar detectionWatchdog mechanism with data cleaning and liar detectionOnline simulation based fault isolation and diagnosisOnline simulation based fault isolation and diagnosis

Problem space II Problem space II


Smart Spectrum UtilizationSmart Spectrum Utilization Spectrum etiquettes and/or rulesSpectrum etiquettes and/or rulesAgile radios, cognitive radios, 60 GHz radio, underlay technologiesAgile radios, cognitive radios, 60 GHz radio, underlay technologiesCognitive software & applicationsCognitive software & applications

Analytical ToolsAnalytical ToolsInformation theoretic tools that predict network viability & Information theoretic tools that predict network viability & performance with practical constraints, based on experimental dataperformance with practical constraints, based on experimental data

Ease of use (Plug and play, HCI)Ease of use (Plug and play, HCI)Pleasant, hassle-free user experience Pleasant, hassle-free user experience QoS protocols to improve content deliveryQoS protocols to improve content delivery

Digital Rights Management (DRM)Digital Rights Management (DRM)Broadband access popularity related to expanded digital content.Broadband access popularity related to expanded digital content.Increase the value proposition for end-users/subscribersIncrease the value proposition for end-users/subscribers

Smart Spectrum UtilizationSmart Spectrum Utilization Spectrum etiquettes and/or rulesSpectrum etiquettes and/or rulesAgile radios, cognitive radios, 60 GHz radio, underlay technologiesAgile radios, cognitive radios, 60 GHz radio, underlay technologiesCognitive software & applicationsCognitive software & applications

Analytical ToolsAnalytical ToolsInformation theoretic tools that predict network viability & Information theoretic tools that predict network viability & performance with practical constraints, based on experimental dataperformance with practical constraints, based on experimental data

Ease of use (Plug and play, HCI)Ease of use (Plug and play, HCI)Pleasant, hassle-free user experience Pleasant, hassle-free user experience QoS protocols to improve content deliveryQoS protocols to improve content delivery

Digital Rights Management (DRM)Digital Rights Management (DRM)Broadband access popularity related to expanded digital content.Broadband access popularity related to expanded digital content.Increase the value proposition for end-users/subscribersIncrease the value proposition for end-users/subscribers

Capacity & ScalabilityCapacity & Scalability


Use of multiple radios per node

channel assignment (self configuration)- neighbor to interface binding - interface to channel binding

Problem Constrains:• Capacity of a radio channel within an interference zone is limited• Neighbors that need to communicate must share a common channel• # of available channels per node = # of available Wireless NICs• Fixed number of non-overlapping channels

Dynamic channel assignment depends on link load. So this problem becomes routing dependent…

Use of multiple radios per node

channel assignment (self configuration)- neighbor to interface binding - interface to channel binding

Problem Constrains:• Capacity of a radio channel within an interference zone is limited• Neighbors that need to communicate must share a common channel• # of available channels per node = # of available Wireless NICs• Fixed number of non-overlapping channels

Dynamic channel assignment depends on link load. So this problem becomes routing dependent…

HyacinthHyacinth


Distributed load balancing routing & Channel assignment

Requires (at least) 2 wireless NIC per node in order to avoid ripple effects when switching channels…

Logically each wired gateway is the root of a spanning tree and every node attempts to participate in at least one such spanning tree.

Tree construction process similar to 802.1d STP:

Each node who can reach the wired network sends an ADVERTISE packet to its neighbors that carries the cost this node has to reach the wired network.

Distributed load balancing routing & Channel assignment

Requires (at least) 2 wireless NIC per node in order to avoid ripple effects when switching channels…

Logically each wired gateway is the root of a spanning tree and every node attempts to participate in at least one such spanning tree.

Tree construction process similar to 802.1d STP:

Each node who can reach the wired network sends an ADVERTISE packet to its neighbors that carries the cost this node has to reach the wired network.

HyacinthHyacinth


“Cost” in Hyacinth is taken to be- hop count (from advertising node to wired gateway)- gateway link capacity (g/w uplink residual capacity)- path capacity (minimum path residual capacity)

Given the ADVERTISE packet each recipient chooses to JOIN the sender or ignore it.

X receiving a JOIN packet from Y - Forwards the request upward in the tree and waits for an ACCEPT message- adds Y to its children list and- Sends Y an ACCEPT message with channel and IP information

“Cost” in Hyacinth is taken to be- hop count (from advertising node to wired gateway)- gateway link capacity (g/w uplink residual capacity)- path capacity (minimum path residual capacity)

Given the ADVERTISE packet each recipient chooses to JOIN the sender or ignore it.

X receiving a JOIN packet from Y - Forwards the request upward in the tree and waits for an ACCEPT message- adds Y to its children list and- Sends Y an ACCEPT message with channel and IP information

HyacinthHyacinth


Ripple effect problemRipple effect problem

HyacinthHyacinth


Neighbor-to-interface binding

Each node is responsible to assign channels to its DOWN-NICs

To ensure relay capability to the wired medium nodes closer to it have higher priority on channel selection

Neighbor-to-interface binding

Each node is responsible to assign channels to its DOWN-NICs

To ensure relay capability to the wired medium nodes closer to it have higher priority on channel selection

HyacinthHyacinth


Interface to channel binding

To assign a channel to a DOWN-NIC a node need to be able to estimate the usage status of all channels in its interference neighborhood.

Exchange of a CHNL_USAGE message to all k+1-hop neighbors carrying load information on used channels.

k: interference range

A node with a loaded channel calculates the total load of other channels based on the contributed information to select a less loaded channel in its interference range.

Interface to channel binding

To assign a channel to a DOWN-NIC a node need to be able to estimate the usage status of all channels in its interference neighborhood.

Exchange of a CHNL_USAGE message to all k+1-hop neighbors carrying load information on used channels.

k: interference range

A node with a loaded channel calculates the total load of other channels based on the contributed information to select a less loaded channel in its interference range.

MetricsMetrics


Hyacinth is a higher-to-lower cross layer system

Increase in capacity is attempted by changing channels using routing and traffic load information…

The other way around is to decide on the routes based on physical channel characteristics…

Selection of routes based on existing link quality

How?Take a well studied ad-hoc routing protocol like DSR and do what we tried last year:Incorporate link information in the Route Discovery phase packet exchange.Add a metric maintenance/update mechanism.

Hyacinth is a higher-to-lower cross layer system

Increase in capacity is attempted by changing channels using routing and traffic load information…

The other way around is to decide on the routes based on physical channel characteristics…

Selection of routes based on existing link quality

How?Take a well studied ad-hoc routing protocol like DSR and do what we tried last year:Incorporate link information in the Route Discovery phase packet exchange.Add a metric maintenance/update mechanism.

Link metricsLink metrics


1. Hop count2. Per-hop RTT3. Per-hop Packet Pair Delay4. Expected Transmission Count (ETX) –MIT5. Weighted Cumulative Expected Transmission Time

(WCETT) -Microsoft

1. Hop count2. Per-hop RTT3. Per-hop Packet Pair Delay4. Expected Transmission Count (ETX) –MIT5. Weighted Cumulative Expected Transmission Time

(WCETT) -Microsoft



1. Hop count Routing goal: Minimize hop count on route.+ Simplicity

2. Per hop RTT Send a probe and get a probe ack. Routing goal: Minimize the total RTT sum.+ avoids highly loaded or lossy links- queuing delay

3. Per-hop Packet Pair Delay Send a pair of probes: A small one and then a large and measure delay between them at receiving node. Routing goal: Minimize delay+ link data rate into account- overhead

1. Hop count Routing goal: Minimize hop count on route.+ Simplicity

2. Per hop RTT Send a probe and get a probe ack. Routing goal: Minimize the total RTT sum.+ avoids highly loaded or lossy links- queuing delay

3. Per-hop Packet Pair Delay Send a pair of probes: A small one and then a large and measure delay between them at receiving node. Routing goal: Minimize delay+ link data rate into account- overhead



4. ETX

Estimate the number of retransmissions required to send unicast packets by measuring loss rate of broadcast packets.

Routing Goal: minimize sum of expected retransmissions along a route.

Broadcast every second a probe packet containing count of received probes from all neighbors in the past 10 secs and use that to calculate the probability of a correct transmission.

4. ETX

Estimate the number of retransmissions required to send unicast packets by measuring loss rate of broadcast packets.

Routing Goal: minimize sum of expected retransmissions along a route.

Broadcast every second a probe packet containing count of received probes from all neighbors in the past 10 secs and use that to calculate the probability of a correct transmission.



Eg. probability of a correct transmission

A has a packet to send to B

Packet (A->B) AND Acknowledgement (B->A) need be correct to avoid retransmission.

A received 8 probes from B in the past 10 secs B reported receiving 9 probes from A

Assuming independent losses then probability of single correct transmission is: AB BA (1-0.1) x (1-0.2)=0.72

Expected nr. of retransmissions is: 1/0.72 = 1.39

Eg. probability of a correct transmission

A has a packet to send to B

Packet (A->B) AND Acknowledgement (B->A) need be correct to avoid retransmission.

A received 8 probes from B in the past 10 secs B reported receiving 9 probes from A

Assuming independent losses then probability of single correct transmission is: AB BA (1-0.1) x (1-0.2)=0.72

Expected nr. of retransmissions is: 1/0.72 = 1.39



ETX pros and cons

+ Probing overhead is small

+ no delays measured so no self-interference

-broadcasts sent at 1Mbps 802.11b and 6 Mbps 802.11g so loss rate will be less than that of unicast traffic rate

-no link load or throughput correlation

ETX pros and cons

+ Probing overhead is small

+ no delays measured so no self-interference

-broadcasts sent at 1Mbps 802.11b and 6 Mbps 802.11g so loss rate will be less than that of unicast traffic rate

-no link load or throughput correlation



5. WCETT –the first multi-radio metricWith ETX in mind WCETT is a path metric taking into account the time it would take for a packet of some fixed size S to go over each link of the path.Routing Goal: WCETT minimization

Assume ETT is known.ETT can bebased on the ETX calculated previously

ETT = ETX x S / B

Forgetting multi-ratio, for an n-hop path

5. WCETT –the first multi-radio metricWith ETX in mind WCETT is a path metric taking into account the time it would take for a packet of some fixed size S to go over each link of the path.Routing Goal: WCETT minimization

Assume ETT is known.ETT can bebased on the ETX calculated previously

ETT = ETX x S / B

Forgetting multi-ratio, for an n-hop path

n

iiETTWCETT

1



Assume that two co-channel hops on a path always interfere with eachother , then defining Xj to be the sum of transmission times on a channel j, for each channel k in the system

one can argue that the total path throughput will be dominated by the bottleneck channel so

Actual metric:

Assume that two co-channel hops on a path always interfere with eachother , then defining Xj to be the sum of transmission times on a channel j, for each channel k in the system

one can argue that the total path throughput will be dominated by the bottleneck channel so

Actual metric:

ij ETTXHop i on channel j

)max( jXWCETT

)max()1(1

j

n

ii XETTWCETT



From a design viewpoint WCETT achieves 3 goals:

• Takes loss rate & bandwidth into account (ETT definition)

• Is increasing over the path length

• Accounts for throughput reduction due to co-channel interference of links on a path.

From a design viewpoint WCETT achieves 3 goals:

• Takes loss rate & bandwidth into account (ETT definition)

• Is increasing over the path length

• Accounts for throughput reduction due to co-channel interference of links on a path.

)max()1(1

j

n

ii XETTWCETT

locustworldlocustworld


A diverse sellable mesh-in-a-box solution

Linux modified kernel –boot-from-cd and ready to play

Meshing operation based on a good mingling of known protocols

A diverse sellable mesh-in-a-box solution

Linux modified kernel –boot-from-cd and ready to play

Meshing operation based on a good mingling of known protocols



The software boots, it then allocates itself an address, typically in the 10.x.x.x range. Initially the allocated address is random.

Then, it attempts to find an internet gateway, first probing 192.168.1.1/255.255.128.0 and then using a DHCP client on the Ethernet interface to try to sign on to a gateway. If no gateway can be found, the software considers that it has only wireless links and is a repeater-cell.

The cell starts an internal dns server and transparent web proxy on port 80 and 8080, a dhcp server is also started an a random class C network is picked in the range 192.168.128.0/255.255.128.0

Clients connecting to the dhcp cell are pointed to the wireless interface for default gateway and dns server. The dns server running on the repeater always returns the address of the gateway, no matter what domain name is resolved.

At this point, the node still cannot serve clients, but it will sign them on.

Meanwhile, an AODV module is loaded and the node then finds neighbour cells in its local range by sending/receiving UDP packets to the broadcast address.

The software boots, it then allocates itself an address, typically in the 10.x.x.x range. Initially the allocated address is random.

Then, it attempts to find an internet gateway, first probing 192.168.1.1/255.255.128.0 and then using a DHCP client on the Ethernet interface to try to sign on to a gateway. If no gateway can be found, the software considers that it has only wireless links and is a repeater-cell.

The cell starts an internal dns server and transparent web proxy on port 80 and 8080, a dhcp server is also started an a random class C network is picked in the range 192.168.128.0/255.255.128.0

Clients connecting to the dhcp cell are pointed to the wireless interface for default gateway and dns server. The dns server running on the repeater always returns the address of the gateway, no matter what domain name is resolved.

At this point, the node still cannot serve clients, but it will sign them on.

Meanwhile, an AODV module is loaded and the node then finds neighbour cells in its local range by sending/receiving UDP packets to the broadcast address.



Any cells within the mesh which are gateways, periodically broadcast a route to a bogus address which implies an internet gateway. This route is repeated outwards in a “ring” fashion as per the AODV protocol.

Any cell without a gateway receiving this address then attempts to establish a compressed encrypted IP-tunnel VPN via the “vtund” package.

This IP tunnel could be over multiple hops to the destination gateway, AODV handles the optimised routing between linked cells.

The cell then switches all its outbound dns and ip traffic to go via this VPN gateway link. The DHCP configuration is also updated to now serve the remote gateway address as a dns server (gateway nodes run a real dns proxy) – Any clients who signed on before the link was found will forward traffic to the local cell which will proxy it via http proxy etc, any clients signing on after a gateway is found will receive the remote gateway details and will have full IP routing.

Any client signing directly on to a cell which has a local internet gateway will go directly via that gateway.

Generally, all “end user” clients, eg non-mesh are routed via standard NAT

Any cells within the mesh which are gateways, periodically broadcast a route to a bogus address which implies an internet gateway. This route is repeated outwards in a “ring” fashion as per the AODV protocol.

Any cell without a gateway receiving this address then attempts to establish a compressed encrypted IP-tunnel VPN via the “vtund” package.

This IP tunnel could be over multiple hops to the destination gateway, AODV handles the optimised routing between linked cells.

The cell then switches all its outbound dns and ip traffic to go via this VPN gateway link. The DHCP configuration is also updated to now serve the remote gateway address as a dns server (gateway nodes run a real dns proxy) – Any clients who signed on before the link was found will forward traffic to the local cell which will proxy it via http proxy etc, any clients signing on after a gateway is found will receive the remote gateway details and will have full IP routing.

Any client signing directly on to a cell which has a local internet gateway will go directly via that gateway.

Generally, all “end user” clients, eg non-mesh are routed via standard NAT

Further Reading & Some PointersFurther Reading & Some Pointers

TNL - Mobile Computing Group Angelakis Vangelis 21/10/2003

Jinyang Li, et.al., Capacity of Ad Hoc Wireless Networks, (MobiCom '01), Rome, July 2001.

B. A. Chambers; ``The Grid Roofnet: a Rooftop Ad Hoc Wireless Network''; MS Thesis, Dept of Electrical Engg and Computer Science, MIT.

Hyacinth: An IEEE 802.11-based Multi-channel Wireless Mesh Network http://www.ecsl.cs.sunysb.edu/multichannel/

R. Bruno, M. Conti, E. Gregori Mesh Networks: Commodity Multi-hop Ad-Hoc Networks

R. Draves, et. al. Comparison of Routing Metrics for Static Multi-Hop Wireless Networks ACM SIGCOMM, Portland, OR, August 2004.

R. Draves, et. al. Routing in Multi-radio, Multi-hop Wireless Mesh NetworksACM MobiCom, Philadelphia, PA, September 2004.

http://research.microsoft.com/mesh/papers/metrics.pdf

Further Reading & Some PointersFurther Reading & Some Pointers

TNL - Mobile Computing Group Angelakis Vangelis 21/10/2003

http://research.microsoft.com/mesh

• Roofnet

• Seattle Wireless

• Locust World

• Kingsbride Link

• Mesh Networks Inc

• FireTide Inc.

• Strix Networks Inc

• Telabria Inc

• Tropos Inc

• Cowave Inc

Documents

Telecommunications & Networks Lab Mesh Networking Angelakis Vangelis 20 / 1 / 2005