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4. ROUTING PROTOCOLS. Scalability Fast route discovery and rediscovery (for reliability) Mobile user support (for seamless and efficient handover). Features for Optimal Routing in WMNs. Features for Optimal Routing in WMNs. Multiple Performance Metrics minimum hop-count  ineffective!!

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Features for optimal routing in wmns

Scalability

Fast route discovery and rediscovery (for reliability)

Mobile user support (for seamless and efficient handover)

Features for Optimal Routing in WMNs


Features for optimal routing in wmns1
Features for Optimal Routing in WMNs

  • Multiple Performance Metrics

    minimum hop-count ineffective!!

    e.g., link quality and round trip time (RTT)

  • Robustness(link failures or congestions, fault-tolerant, load balancing)

  • Adaptive Support of Both Mesh Routers and Mesh Clients(support mobility and power efficiency)


Features for optimal routing in wmns2

Flexibility

Work with/without gateways, different topologies

QoS Support

Consider routes satisfying specified criteria

Multicast

Important for some applications (e.g., emergency response)

Features for Optimal Routing in WMNs


Apply routing algorithms derived for ad hoc networks
* Apply routing algorithms derived for Ad Hoc Networks

Prelim Routing Protocols for WMNs



Overview
OVERVIEW

  • Flat

    • Reactive

      • DSR – Dynamic Source Routing

      • AODV – Ad hoc On demand Distance Vector

    • Proactive

      • FSR – Fisheye State Routing

      • FSLS – Fuzzy Sighted Link State

      • OLSR – Optimized Link State Routing Protocol

      • TBRPF – Topology Broadcast Based on Reverse Path Forwarding


Overview1
OVERVIEW

  • Hierarchical

    • CGSR – Clusterhead-Gateway Switch Routing

    • HSR – Hierarchical State Routing

    • LANMAR – Landmark Ad Hoc Routing

    • ZRP – Zone Routing Protocol


Overview2
OVERVIEW

  • Geographical Routing

    • DREAM – Distance Routing Effect Algorithm for Mobility

    • GeoCast – Geographic Addressing and Routing

    • GPSR – Greedy Perimeter Stateless Routing

    • LAR – Location-Aided Routing


Reminder ad hoc routing protocols
Reminder: Ad Hoc Routing Protocols

  • Proactive Protocols (Actively seeks for routes/paths)

    • Determine routes independent of traffic pattern

    • Traditional link-state and distance-vector routing protocols are proactive

  • Reactive Protocols (Seek for routes/paths only when required)

    • Maintain routes only if needed

  • Hierarchical Routing

    • Introduces hierarchy to the flat network

  • Geographic Position Assisted Routing

    • Why send packets North when the destination is South?


Routing protocols from ad hoc networks used for wmns
Routing Protocols from Ad Hoc Networks Used for WMNs

Dynamic Source Routing (DSR)

in Microsoft mesh networks

D.B. Johnson, D.A. Maltz, and Y.-C. Hu,

“The dynamic source routing protocol for mobile ad hoc networks (DSR),”

IETF Internet-Draft,2004.

12


Routing protocols from ad hoc networks used for wmns1
Routing Protocols from Ad Hoc Networks Used for WMNs

AODV (ad-hoc on-demand distance vector) routing

Used by many other companies

Major building block for the routing framework of IEEE

802.11s

C. E. Perkins, E. M. Belding-Royer, I. D. Chakeres, “Ad hoc On-Demand Distance Vector (AODV) Routing”, IETF Draft, Jan. 2004.

IEEE 802.11s Task Group,“Joint SEE-Mesh/Wi-Mesh proposal to 802.11

TGs overview,”IEEE Doc: 802.11-05/0567r6,2006.

13


Routing protocols from ad hoc networks used for wmns2
Routing Protocols from Ad Hoc Networks Used for WMNs

Topology broadcast based on reverse path forwarding

(TBRPF) protocol in Firetide Networks

R. Ogier, F. Templin, and M. Lewis,“Topology dissemination based on

reverse-path forwarding (TBRPF),” IETF RFC 3684, 2004.

14


4 routing protocols

Dynamic Source Routing (DSR) D. B. Johnson, D. A. Maltz, Y.-C. Hu, “Dynamic Source Routing Protocol for Mobile Ad Hoc Networks”,IETF Draft, April 2004.

  • Based on Source Routing principle!

  • On-demand

  • Route computation performed on aper-connection basis


Dynamic source routing dsr
Dynamic Source Routing (DSR)

  • Source, after route computation, appends each packet with a source-route information

  • Intermediate hosts forward packet based on source route

  • TWO PHASES: ROUTE DISCOVERY &

    ROUTE MAINTENANCE


Dynamic source routing dsr route discovery
Dynamic Source Routing (DSR):ROUTE DISCOVERY

  • When node S wants to send a packet to node D, but does not know a route to D, node S initiates a Route Discovery

  • Source node S floods (broadcasts) Route Request (RREQ) packet.

  • RREQ packet contains

    * DESTINATION ADDRESS

    * SOURCE NODE ADDRESS and

    * A UNIQUE IDENTIFICATION NUMBER.


Dynamic source routing dsr route discovery1
Dynamic Source Routing (DSR):ROUTE DISCOVERY

  • If the node is the receiver (i.e., has the correct destination address) then returns the packet to the sender

  • If the packet has already been received earlier (identified via ID) then discard the packet


Dynamic source routing dsr route discovery2
Dynamic Source Routing (DSR):ROUTE DISCOVERY

  • Each node receiving the packet checks whether

    it knows of a route to that destination.

  • If it does not, it appends/adds its own

    identifier (address) to the route record and

    forwards the RREQ packet.


Dynamic source routing dsr route discovery3
Dynamic Source Routing (DSR):ROUTE DISCOVERY

Y

Z

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N


Dynamic source routing dsr route discovery4
Dynamic Source Routing (DSR):ROUTE DISCOVERY

Y

Broadcast transmission

Z

[S]

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N

Represents transmission of RREQ

[X,Y] Represents list of identifiers appended to RREQ


Dynamic source routing dsr route discovery5
Dynamic Source Routing (DSR):ROUTE DISCOVERY

Y

Z

S

[S,E]

E

F

B

M

L

C

J

A

G

[S,C]

H

D

K

I

N

Node H receives packet RREQ from two neighbors:

Potential for collision


Dynamic source routing dsr route discovery6
Dynamic Source Routing (DSR):ROUTE DISCOVERY

Y

Z

S

E

F

[S,E,F]

B

C

M

L

J

A

G

H

D

K

[S,C,G]

I

N

Node C receives RREQ from G and H, but does not forward

it again, because node C has already forwarded RREQ once


Dynamic source routing dsr route discovery7
Dynamic Source Routing (DSR):ROUTE DISCOVERY

Y

Z

S

E

F

[S,E,F,J]

B

C

M

L

J

A

G

H

D

K

I

N

[S,C,G,K]

  • Nodes J and K both broadcast RREQ to node D

  • Since nodes J and K are hidden from each other, their transmissions

    may collide


Dynamic source routing dsr route discovery8
Dynamic Source Routing (DSR):ROUTE DISCOVERY

Y

Z

S

E

[S,E,F,J,M]

F

B

C

M

L

J

A

G

H

D

K

I

N

  • Node D does not forward RREQ, because node D is the intended

    targetof the route discovery


Route path discovery in dsr
Route/Path Discovery in DSR

  • Destination D on receiving the first RREQ, sends a

    Route Reply (RREP)

  • RREP is sent on a route obtained by reversing the

    route appended to received RREQ

  • RREP includes the route from S to D on which RREQ

    was received by node D


Route path discovery in dsr1
Route/Path Discovery in DSR

Y

Z

S

RREP [S,E,F,J,D]

E

F

B

C

M

L

J

A

G

H

D

K

I

N

Represents RREP control message


Data delivery in dsr
DATA DELIVERY IN DSR

  • Node S on receiving RREP, caches the route included in the RREP

  • When node S sends a data packet to D, the entire route is

    included in the packet header

    • hence the name Source Routing

  • Intermediate nodes use the Source Route included in a

    packet to determine to whom a packet should be forwarded


Data delivery in dsr1
Data Delivery in DSR

Y

DATA [S,E,F,J,D]

Z

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N

Packet header size grows with route length


Dsr optimization route caching
DSR Optimization: Route Caching

  • Each node caches a new route it learns by any means

  • When node S finds route [S,E,F,J,D] to node D, node

    S also learns route [S,E,F] to node F

  • When node K receives Route Request [S,C,G]destined

    for K, it learns route [K,G,C,S] to node S


Dsr optimization route caching1
DSR Optimization: Route Caching

  • When node F forwards RREP [S,E,F,J,D],

    node F learns route [F,J,D] to node D

  • When node E forwards Data [S,E,F,J,D] it learns

    route [E,F,J,D] to node D

  • A node may also learn a route when it overhears Data

    packets


Advantages of use of route caching
Advantages of Use of Route Caching

  • can speed up route discovery

  • can reduce propagation of route requests


Use of route caching
Use of Route Caching

[S,E,F,J,D]

[E,F,J,D]

S

E

[F,J,D],[F,E,S]

F

B

[J,F,E,S]

C

M

L

J

A

G

[C,S]

H

D

K

[G,C,S]

I

N

Z

[x,y,w] Represents cached route at a node

(DSR maintains the cached routes in a tree format)


Use of route caching can speed up route discovery
Use of Route Caching:Can Speed up Route Discovery

[S,E,F,J,D]

[E,F,J,D]

S

E

[F,J,D],[F,E,S]

F

B

[J,F,E,S]

C

M

L

[G,C,S]

J

A

G

[C,S]

H

D

K

[K,G,C,S]

I

N

RREP

When node Z sends a route request

for node C, node K sends back a route

reply [Z,K,G,C] to node Z using a locally

cached route

RREQ

RREQ

Z


Use of route caching can reduce propagation of route requests
Use of Route Caching:Can Reduce Propagation of Route Requests

Y

[S,E,F,J,D]

[E,F,J,D]

S

E

[F,J,D],[F,E,S]

F

B

[J,F,E,S]

C

M

L

[G,C,S]

J

A

G

[C,S]

H

D

K

[K,G,C,S]

I

N

RREP

RREQ

Z

Route Reply (RREP) from node K limits flooding of RREQ.

In general, the reduction may be less dramatic.


Dynamic source routing advantages
Dynamic Source Routing: Advantages

  • Routes maintained only between nodes who need to

    communicate

    • reduces overhead of route maintenance

  • Route caching can further reduce route discovery

    overhead

  • A single route discovery may yield many routes to the

    destination, due to intermediate nodes replying from local

    caches


Dynamic source routing disadvantages
Dynamic Source Routing: Disadvantages

  • Packet header size grows with route length

  • Flood of route requests may potentially reach all nodes

  • Care must be taken to avoid collisions between route requests propagated by neighboring nodes

    • insertion of random delays before forwarding RREQ


4 routing protocols

Ad Hoc On-Demand Distance Vector Routing (AODV) C. E. Perkins, E. M. Belding-Royer, I. D. Chakeres, “Ad hoc On-Demand Distance Vector (AODV) Routing”, IETF Draft, Jan. 2004.

  • AODV attempts to improve on DSR by maintaining routing tables at the nodes, so that data packets do not have to contain paths

  • AODV retains the desirable feature of DSR that routes are maintained only between nodes which need to communicate


4 routing protocols
AODV

  • Hop-by-hop routing as opposed to source routing

  • On-demand

  • When a source node wants to send a message to some destination

    node and does not already have a valid route to that destination,

    it initiates a Path DiscoveryProcess to locate the destination

    (as in DSR case)

  • It broadcasts the RREQ packet to its neighbors


4 routing protocols
AODV

  • RREQs are forwarded in a manner similar to DSR

  • When a node re-broadcasts a RREQ, it sets up a reverse

    path pointing towards the source

    • AODV assumes symmetric (bi-directional) links

  • When the intended destination receives a RREQ, it replies

    by sending a Route Reply (RR)

  • RR travels along the reverse path set-up when RREQ was

    forwarded


4 routing protocols
AODV

  • When RREQ propagates, routing tables are updated at intermediate nodes (for route to source of RREQ)

  • When RREP is sent by destination, routing tables updated at intermediate nodes (forroute to

    destination), and propagated back to source


4 routing protocols
AODV

  • Each node maintains its own sequence number and a broadcast ID.

  • The broadcast ID is incremented for every RREQ the node initiates


4 routing protocols
AODV

  • The node’s IP address and the broadcast ID uniquely identify a RREQ.

  • Along with its own sequence number and broadcast

    ID, the source node includes in the RREQ the most

    recent sequence number it has for the destination.


4 routing protocols
AODV

  • Intermediate nodes can reply to the RREQ only if

    they have a route to the destination whose

    corresponding Destination Sequence Number is

    greater than or equal to that contained in the RREQ.

  • During the process of forwarding the RREQ,

    intermediate nodes recording their route tables with the

    address of the neighbor from which the first copy

    of the broadcast packet is received establishing a

    reverse path.


4 routing protocols
AODV

  • If more same RREQs are received later, they are

    discarded.

  • RREP packet is sent back to the neighbors and the routing

    tables are accordingly updated.


Route requests in aodv
Route Requests in AODV

Y

Z

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N


Route requests in aodv1
Route Requests in AODV

Y

Broadcast transmission

Z

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N

Represents transmission of RREQ


Route requests in aodv2
Route Requests in AODV

Y

Z

S

E

F

B

M

L

C

J

A

G

H

D

K

I

N

Represents links on Reverse Path


Reverse path setup in aodv
Reverse Path Setup in AODV

Y

Z

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N

  • Node C receives RREQ from G and H, but does not forward

    it again, because node C has already forwarded RREQ once


Reverse path setup in aodv1
Reverse Path Setup in AODV

Y

Z

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N


Reverse path setup in aodv2
Reverse Path Setup in AODV

Y

Z

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N

  • Node D does not forward RREQ, because node D

    is the intended targetof the RREQ


Route reply in aodv
Route Reply in AODV

Y

Z

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N

Represents links on path taken by RREP


Forward path setup in aodv
Forward Path Setup in AODV

Y

Z

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N

Forward links are setup when RREP travels along

the reverse path

Represents a link on the forward path


Data delivery in aodv
Data Delivery in AODV

Y

DATA

Z

S

E

F

B

C

M

L

J

A

G

H

D

K

I

N

Routing table entries used to forward data packet.

NOTE: Route is not included in packet header as in DSR.


4 routing protocols

* Special considerations - WMN routers differ from MANET routers * Power supply * Mobility * Separation of WMN routers and clients

Routing Protocols for WMNs


Routing challenges in wmns
Routing Challenges in WMNs

Routing in WMNs is much more complicated than in Ad Hoc Networks

REASONS:

1) Network topology is variable and inconsistent (same as ad hoc networks)

2) Depending on the performance goal in routing, it may not be

possible to determine a routing path solely based on network topology

3) There may not be an optimal solution for a given routing problem

4) Routing traverses both mesh routers and mesh clients that have

different networking capabilities

56


Design principles
Design Principles

Maintaining a consistent and stable network topology

2) Performing dynamic and adaptive routing

3) Developing new routing metrics

4) Considering tradeoff between cross-layer design and single-layer solution

57


Design principles1
Design Principles

5) Deriving distributed algorithms for routing

6) Ensuring scalability in routing

7) Adaptively supporting both mesh routers and mesh clients

58


4 routing protocols

PERFORMANCE METRICS

Per-Flow Parameters:

(e.g., delay, packet loss ratio, and delay jitter and other parameters

such as hop-count, per-flow throughput, and intra-flow interference)

Per-Node Parameters:

(computational complexity and power efficiency)

Per-Link Parameters:

(e.g., link quality, channel utilization, transmission rate, and congestion)

Inter-Flow Parameters:

(e.g., inter-flow interference and fairness)

Network-Wide Parameters:

(e..g., total throughput or total delay)


Hop count per hop rtt per hop packet pair delay expected transmission count etx
* Hop-Count* Per-Hop RTT* Per-Hop Packet Pair Delay * Expected Transmission Count (ETX)

OVERVIEW OF ROUTING METRICS


4 routing protocols

* Expected Transmission on a Path (ETOP)* Expected Transmission Time (ETT)* Weighted Cumulative ETT (WCETT)* Bottleneck Link Capacity (BLC) * Expected Data Rate (EDR) * Airtime Cost Routing Metric

OVERVIEW OF ROUTING METRICS


4 routing protocols

Hop Count

* Minimum hop counting (the link quality is binary)* Simple and requires no measurementsDisadvantages:*Can lead to poor throughput * Link quality  all links do not have the same quality * Does not take packet loss or bandwidth into account * Route that minimizes hop count does not necessarily maximize the throughput


Per hop rtt
Per-Hop RTT

Measured by sending unicast probe packets between neighboring nodes

Then calculating the time spent on the probe-ack procedure

A weighted moving average is needed to get a smoother measurement, because one sample cannot really reflect the actual link status.

Adya A, Bahl P, Padhye J, Wolman A and Zhou L,

“A multi-radio unification protocol for IEEE 802.11 wireless networks”,

Proc. IEEE BroadNets 2004

63


Per hop rtt1
Per-Hop RTT

Based on per-hop RTT, a routing protocol selects a routing path with the least sum of RTTs of all links on the path.

Per-hop RTT is able to capture

* the packet loss ratio in a link

* the traffic load

* queuing delay in two nodes on the link, and

* contention status in all neighboring nodes.

64


4 routing protocols

Per-Hop RTT

* Loss will cause RTT to increase due to ARQ * If ARQ fails, RTT is increased by some percentage* This metric is load dependent * Channel contention increases RTT


Per hop rtt2
Per-Hop RTT

Its effectiveness is constrained by two problems:

PROBLEM 1:

Per-hop RTT is too much dependent on the traffic load/queuing delay, which interferes

with the accuracy of per-hop RTT and thus, can easily lead to route instability.

If a separate queue is assigned to probe packets, then it can accurately measure the

link quality but cannot reflect the traffic load.

A solution to this problem is to adopt a link measurement

scheme !

Kim K-H and Shin KG, “On accurate measurement of link quality in

multi-hop wireless mesh networks,” Proc. ACM MOBICOM 2006

66


Per hop rtt3
Per-Hop RTT

PROBLEM 2:

Accuracy of per-hop RTT measurement totally relies on the weighted moving average scheme.

For large variations in measurements cause unreliable values for per-hop RTT

(no matter what weight is applied in the weighted moving average scheme.)

Overhead of the probe-ack procedure

REMARK:

Per-hop RTT captures per-link performance parameters, although

measurement is actually carried out at the network layer.

67


4 routing protocols

Disadvantages of Per-Hop RTT

Disadvantages: * Does not take link data rate into account. * High overhead. * Load dependent metric may cause route flaps * Need to insert probe at head of interface queue to avoid queuing delay * Not scalable - every pair needs to probe each other


Per hop packet pair delay
Per-Hop Packet Pair Delay

Measured by sending two back-to-back probe packets from a node to its neighbor

First  a small probe packet; Second  large

When the neighbor receives these two packets, it finds the delay in-between them and then sends such information back to the probing node

Since relative delay is used to measure the per-hop delay, per-hop PPD measurement is less impacted by queueing delays or traffic load in a node

Draves R, Padhye J and Zill B, “Routing in multi-radio, multi-hop wireless mesh networks,”Proc. ACM MOBICOM 2004.

69


Per hop packet pair delay1
Per-Hop Packet Pair Delay

* However, impact by traffic load still exists, because whether or

not being able to send probe packets in a link of two nodes also

depends on the queuing delays of other neighboring nodes.

EXAMPLE:

when Node A sends a probe packet to B, if A’s neighbor C is also

sending a very high traffic load to A, then A has to delay its probe to B.

Therefore, per-hop packet pair delay still has to capture

the route instability issue.

70


Per hop packet pair delay2
Per-Hop Packet Pair Delay

* Large overhead than per-hop RTT, due to the need of more probe packets

Its performance is also dependent on the weighted moving average scheme, and assumes the variation of measurements are small.

Similar to per-hop RTT, per-hop PPD only captures per-link performance parameters.

71


Expected transmission count etx
Expected Transmission Count (ETX)

ETX of a link is the expected number of transmissions before a packet is successfully delivered on a link

For a route, the ETX is the sum of the ETXs on all links

Captures the link quality and packet loss on both directions of a link

The route ETX can detect interference among links of the same route

the larger the route ETX, the more self-interference on the route.

De Couto DSJ, Aguayo D, Bicket J, and Morris R,

“A high-throughput path metric for multihop wireless routing,”

in Proc. ACM MOBICOM 2003

72


Expected transmission count etx1
Expected Transmission Count (ETX)

Every period of t seconds a node sends a broadcast probe message to all its neighbors

Each neighbor records the number of received probe messages (denoted by nw) during a period of w seconds, where w > t

Thus, the delivery ratio of sending a packet from the probing node to its neighbor is:

73


Expected transmission count etx2
Expected Transmission Count (ETX)

If a probing node embeds the information of nw from all its neighbors to the probe packet

Then each of its neighbors can derive the packet delivery ratio from the neighbor to the probing node

With the delivery ratio at both forward and reverse directions, denoted by df and dr, respectively, ETX is calculated as:

74


Advantages of expected transmission count etx
Advantages ofExpected Transmission Count (ETX)

Lower overhead because broadcast rather than unicast is applied to probe messages.

Does not measure delays, so the measurement based on probe messages are not impacted by queueing delays in a node.

75


Disadvantages of expected transmission count etx
Disadvantages of Expected Transmission Count (ETX)

Probe messages experience different packet loss ratios than unicast messages

because broadcast messages use more robust modulation and coding schemes, and thus have low transmission rates

ETX does not take into account the differences in packet size for different traffic flows and the different capacities for different links

76


Disadvantages of expected transmission count etx1
Disadvantages of Expected Transmission Count (ETX)

Estimation method in ETX may not be accurate

* It relies on the mean loss ratio;

* Wireless links usually experience bursty losses.

77


4 routing protocols

SO FAR

* ETX metric performs best in static scenarios * It is insensitive to load* RTT is most sensitive to load* Packet-Pair suffers from self-interference on multi-hop paths* Minimum hop count based routing seems to perform best in mobile scenarios* Schemes based on measurements of link quality does not converge quickly


Expected transmission on a path etop
Expected Transmission on a Path (ETOP)

* When a routing path is selected in many routing protocols, the position of a link is not considered in the routing metric

This is true if the link layer allows an infinite number of retransmissions, because a retransmitted packet has the same impact on upper layer no matter at which link retransmission happens

However, if the link layer allows only a limited number of retransmissions, end-to-end retransmission has to be carried out.

79


Expected transmission on a path etop1
Expected Transmission on a Path (ETOP)

Comparing two links, even if their ETX is the same, the one closer to

the destination can result in higher transport layer retransmissions,

i.e., this link can lead to worse performance if it would be selected.

ETOP solves the above problem by taking into account the relative

position of a link on a routing path when the routing cost of the path is

calculated.

Jakllari G, Eidenbenz S, Hengartner N, Krishnamurthy S and Faloutsos M, “Link positions matter: a non-commutative routing metric for wireless mesh networks,”Proc. IEEE INFOCOM 2008

80


Expected transmission on a path etop2
Expected Transmission on a Path (ETOP)

Consider a routing path with n links from node v0 to node vn

 its cost is denoted by Tn

For a packet to be delivered end-to-end through this routing path, the needed number of end-to-end attempts is assumed to be Yn.

In an end-to-end attempt j, the number of links that a packet has been traversed before it is dropped by the link layer is denoted as M

The number of link layer transmissions at node j is assumed to be Hj .

81


Expected transmission on a path etop3
Expected Transmission on a Path (ETOP)

ETOP of a routing path is the expectation of Tn

Captures the total number of link layer transmissions of a given routing path under all possible end-to-end attempts

Compared to ETX, ETOP can improve transport layer throughput, because a routing path is selected with a least number of overall link layer retransmissions.

82


Expected transmission time ett and weighted cumulative ett wcett
Expected Transmission Time (ETT) and Weighted CumulativeETT (WCETT)

Draves R, Padhye J and Zill B, “Comparisons of routing metrics for static multi-hop wireless Networks,” in Proc. ACM SigComm, 2004

  • Expected Transmission Time (ETT)

    • An extended version of ETX.

    • Based on ETX, ETT considers the impactof both packet size and link quality

    • ETT reflects the expected packettransmission time on a link.

S: packet size, B: link bandwidth.


Expected transmission time ett and weighted cumulative ett wcett1
Expected Transmission Time (ETT) and Weighted CumulativeETT (WCETT)

  • For a routing path, the expected transmission time can be thesum of ETTs of all links on the path.

  • However, ETT does not take into accountchannel diversity in WMNs using multiple radios at some nodes

  •  To resolve this issue, arouting metric called WCETT is proposed


Expected transmission time ett and weighted cumulative ett wcett2
Expected Transmission Time (ETT) and Weighted CumulativeETT (WCETT)

  • Weighted CumulativeETT (WCETT)

    given routing path.

    • First term considersthe overall expected transmission time of the routing path.

    • Second term capturesthe transmission time on the bottleneck channels.

    • In this way, WCETT takes into account thetradeoff between overall routing delay and channel diversity utilization.

n: number of hops on a routing path,

k: # of available channels for multi-radiooperation.

so

finds thebottleneck channel of a


Expected transmission time ett and weighted cumulative ett wcett3
Expected Transmission Time (ETT) and Weighted CumulativeETT (WCETT)

  • ETT enhances the performance of ETX by mapping packet size and link BW intothe transmission time.

  • However, it uses a similar estimation scheme as that of ETX, so it hassimilar problems of ETX, i.e., inaccurate estimation, bottleneck routes, etc.


Expected transmission time ett and weighted cumulative ett wcett4
Expected Transmission Time (ETT) and Weighted CumulativeETT (WCETT)

WCETT is notapplicable toWMNs based on single-radio

multi-channel operation for two reasons:

  • broadcastprobe messages cannot be sent on different

    channels of the same radio simultaneously;

    2) the channel switching time can be comparable to ETT of a link.


Bottleneck link capacity blc
Bottleneck Link Capacity (BLC)

Liu T and Liao W, “Capacity-aware routing in multi-channel multi-rate wireless mesh networks,” in Proc. IEEE ICC, 2006

  • BLC is derived based on the expected busy time (EBT) of transmitting a packet on a link.

  • EBT can be estimated by considering the packet loss rate (PLR) and transmissionmechanism in the MAC layer.

    • If RTS-CTS-Data-Ack handshake isused for packet transmission as in an IEEE 802.11 MAC,

Thandshake: Total transmission time of one RTS-CTS-Data-Ack

Ep: PLR.


Bottleneck link capacity blc1
Bottleneck Link Capacity (BLC)

  • Based on EBT, a residual capacity of a link considered as defined as theratio between the idle time and EBT.

    • Considering a path P, if the residual capacity of link i is LCi, then BLC is given by

K: Length of the routing path P

μ: fine-tuning parameter.


Bottleneck link capacity blc2
Bottleneck Link Capacity (BLC)

  • Residual capacity of the bottleneck link of a routing path

  • Dividingthe minimum residual capacity by a certain number is for penalizing a long routing path

  • Because busy time is considered in BLC, load-balancing in links has been taken intoaccount


Bottleneck link capacity blc3
Bottleneck Link Capacity (BLC)

  • However, the self-interference of a routing path is not considered, as the minimumresidual capacity is considered in BLC

    • If two routing paths have differentself-interferences, then the bottleneck link can have the same residual capacity.

    • The sameproblem applies to interference from other routing paths.


Expected data rate edr
Expected Data Rate (EDR)

  • EDR integrates the expected transmission count and expected transmission contention degree(TCD) into the same routing metric

    • TCD of a link is the time that is spent on retransmittingnon-acknowledged packets over a given period.

    • Considering link k on a routing path, if thesum of TCDs of links that interfere link k is Ik, then the the EDR of link k is

  • For EDR of a routing path, it is defined as the EDR of the bottleneck link.

Γ: maximum transmission rate of link k.


Problems of expected data rate edr
Problems of Expected Data Rate (EDR)

  • EDR integrates two closely related parameters:ETX ad TCD.

  • In fact, given the same packet length, if ETX is large, TCD is large too.

     why ETX and TCD have to be combined like an EDR equation remains a question.


Problems of expected data rate edr1
Problems of Expected Data Rate (EDR)

  • Even if the link rate is considered in the metric, it does not consider the fact that multiplerates instead of only the maximum rate are available in each link.

  • Interference range of a given link k is difficult to determine, so Ikis hard to derive.

  • EDR of a routing path cannot take into account the self-interference,

    as the EDR of abottleneck link is used as the EDR of the entire routing path.


Airtime cost routing metric
Airtime Cost Routing Metric

IEEE 802.11s Task Group, Draft, Amendment to Standard for Information Technology – Telecommunications and Information Exchange Between Systems - LAN/MAN Specific Requirements – Part 11: Wireless Medium Access Control (MAC) and physical layer (PHY) specifications: Amendment: ESS Mesh Networking, IEEE P802.11s/D1.00-2006.).

  • To identify an efficient radio-aware path among all the candidate paths,

  • A default routing metric in IEEE 802.11s draft

  • Reflectsthe amount of channel resources consumed for transmitting a frame over a particular link.


Airtime cost routing metric1
Airtime Cost Routing Metric

  • The path which has the smallest sum of airtime cost is the best path.

  • The airtime cost Ca for each link is calculated as:

Oca, Op, and Bt depend on the used transmission

technology.

Oca: channel access overhead,

Op: protocol overhead,

Bt: numberof bits in a test frame.

r and ept : bit rate in Mbit/s and frame error rate for

thetest frame size Bt, respectively.


Comparison of different routing metrics
Comparison of Different Routing Metrics

  • Many routing metrics try to capture link-layer performanceparameters by using a procedure in the network layer

  • In fact, these schemes can be enhancedby performing link-quality measurements directly in the link layer and then use such measurementsin the network layer

  • This method implies that the routingmetrics should involvecross-layer interactions





Remaining issues
Remaining Issues

  • The measurement or estimation method for a routing metric may not be accurate

  • Itmay also cause large overhead, especially for a large scale network.

  • Performance comparisons between different routing metrics need further research,although some work has been done for a few routing metrics.


Remaining issues1
Remaining Issues

  • The design of many existing routing metrics is still “ad-hoc”,

    * i.e., why theproposed routing metric can improve the network performance is not really justified;

    * usually only simulation results are used to prove the effectiveness of a routing metric.

    * the side-effect of such a design is that the effectiveness of a routing metric may belimited to a certain type of WMNs.

  • A routing metric may not be able to capture enough network parameters for a routingprotocol to optimize the network performance.


Overview of routing algorithms
OVERVIEW OF ROUTING ALGORITHMS

Hop-Count based Routing

Link Level QoS Based Routing

Interference Based Routing (IRMA)

Routing with Load Balancing

Routing Based on Residual Link Capacity

End-to-End QoS Routing

Reliability Aware Routing

Joint Channel Assignment and Routing (Layer 2.5 Routing)


Set 1 hop count based routing algorithms
SET 1:Hop-Count based Routing Algorithms

  • Light Client Management Routing (LCMR) Protocol

  • Orthogonal Rendezvous Routing (ORR) Protocol

  • HEAT Protocol


4 routing protocols

Light Client Management Routing (LCMR) ProtocolWehbi B, Mallouli W and Cavalli A, Light client management protocol for wireless mesh networks.Proc. 7th Int. Conf. on Mobile Data Management (MDM), 2006

  • End-to-end routing path from a source to a destination client consists of

    * proactive route among mesh routers and

    * reactive routes between clients and mesh routers

  • To find the best route from one client to another,

    hop-count is used as the routing metric.

  • LCMR does not require routing functionality in clients

  • Mesh routers supporting clients take care of routing


Light client management routing lcmr protocol
Light Client Management Routing (LCMR) Protocol

  • Mesh routers need to maintain two tables:

    1. MAC and IP addresses of local clients

    2. IP addresses of remote clients as well as the

    IP addresses of remote mesh routers associated with

    remote clients


Light client management routing lcmr protocol1
Light Client Management Routing (LCMR) Protocol

  • Based on these two tables,

  • When a local client needs to set up a routing path to a remote client,

  • its associated mesh router can find out which remote mesh router is responsible for forwarding traffic to the remote client

  • Based on such information, mesh routers can then set up a routing path between them using proactive routing and hop-count metric.


Disadvantages of light client management routing lcmr protocol
Disadvantages of Light Client Management Routing (LCMR) Protocol

  • LCMR has a high overhead of maintaining the two tables on each mesh routers,

    as all clients’ IP addresses need to be collected and stored at each mesh router.


Set 1 hop count based routing protocols
SET 1: ProtocolHop-Count based Routing Protocols

  • Light Client Management Routing (LCMR) Protocol

  • Orthogonal Rendezvous Routing (ORR) Protocol

  • HEAT Protocol


4 routing protocols

Orthogonal Rendezvous Routing (ORR) Protocol ProtocolCheng B, Yuksel M and Kalyanaraman S,Orthogonal rendezvous routing protocol for wireless mesh networks. Proc. IEEE Int. Conf. on Network Protocols (ICNP), 2006.

  • Each node can define its neighbors’ directions relative to its local North.

  • Relying on such information, ORR can reduce the state information for routing, and it does not need flooding for route construction.


Orthogonal rendezvous routing orr protocol
Orthogonal Rendezvous Routing (ORR) Protocol Protocol

  • Compared to geographic routing, ORR does not need exact location of nodes.

    Idea

    In 2-D Euclidean space two orthogonal lines can have at least two intersect points with another group of two orthogonal lines,

    if these two groups of orthogonal lines have different centers.


Orthogonal rendezvous routing orr protocol1
Orthogonal Rendezvous Routing (ORR) Protocol Protocol

  • To construct routing paths, a source node sends route discovery in orthogonal directions,

    while a destination node sends route dissemination in orthogonal directions.

  • Thus, there is at least one intersect point, called rendezvous point

    where both route discovery and route dissemination messages are received.


Orthogonal rendezvous routing orr protocol2
Orthogonal Rendezvous Routing (ORR) Protocol Protocol

  • In this way a routing path is established between the source and the destination

  • Also, routing path from the source to the rendezvous point is a reactive route and

  • the remaining path to the destination is a proactive route.


Shortcomings of orthogonal rendezvous routing orr protocol
Shortcomings of Orthogonal Rendezvous Routing (ORR) Protocol Protocol

1. Direction of a node needs to be configured freely

2. Network is not really a 2-D space.

(If a 3-D space is considered, the theory for ORR may not be valid)

3. ORR may not work if the node density is high or topology change frequently happens

4. Routing path selection procedure is based on hop-count.

(However, other metrics such as link quality can be adopted to enhance the ORR).


Set 1 hop count based routing protocols1
SET 1: ProtocolHop-Count based Routing Protocols

  • Light Client Management Routing (LCMR) Protocol

  • Orthogonal Rendezvous Routing (ORR) Protocol

  • HEAT Protocol


4 routing protocols

HEAT Protocol ProtocolBaumann R, Lenders V, Heimlicher S and May M,HEAT: scalable routing in wireless mesh networks using temperature fields. Proc. IEEE Int. Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM), 2007

Anycast routing protocol HEAT considers all nodes

in a WMN as a temperature field

  • Gateways have the highest temperature

  • Temperature of a non-gateway node will be determined by hop-count to the gateways and the robustness of a routing path from this node to gateways.


Heat protocol
HEAT Protocol Protocol

Once temperatures of all nodes are determined

according to this procedure, the packets from any node

to gateways can simply follow the following method:

The node forwards the packets to its neighbor with the

highest temperature, and this neighbor will repeat the

same process until reaching gateways.


Problems of heat protocol
Problems of HEAT Protocol Protocol

  • Totally depends on the assumption that the traffic of WMNs only needs to be routed between gateways and non-gateways

  • For other scenarios, anycast routing is not supported.

  • Moreover, how to consider other routing metrics in HEAT remains an open problem


Overview of routing algorithms1
OVERVIEW OF ROUTING ALGORITHMS Protocol

Hop-Count based Routing

Link Level QoS Based Routing

Interference Based Routing (IRMA)

Routing with Load Balancing

Routing Based on Residual Link Capacity

End-to-End QoS Routing

Reliability Aware Routing

Joint Channel Assignment and Routing (Layer 2.5 Routing)


Set 2 link level qos based routing algorithms
Set 2: ProtocolLink-level QoS based Routing Algorithms

  • Link quality source routing (LQSR) protocol

  • Multi-radio LQSR (MR-LQSR) routing protocol

    - ExOR Routing Protocol

  • AODV-spanning tree (AODV-ST) protocol


4 routing protocols

Link Quality Source Routing (LQSR) Protocol ProtocolDravesR, Padhye J and Zill B,Comparisons of routing metrics for static multi-hop wireless networks. Proc. ACM SIGCOMM, 2004.

  • Based on Dynamic Source Routing (DSR)

  • Contains all basic DSR functionalities, such as

    * Route Discovery (Route Request and Route Reply messages) and

    * Route Maintenance (Route Error messages).


Link quality source routing lqsr protocol
Link Quality Source Routing (LQSR) Protocol Protocol

  • However, LQSR holds two major differences compared to DSR.

    • LQSR is implemented as layer 2.5 protocol instead of as a network layer protocol

    • LQSR supports link quality metrics.


Link quality source routing lqsr protocol1
Link Quality Source Routing (LQSR) Protocol Protocol

  • Layer 2.5 architecture brings two significant advantages.

    • On the one hand, no modification is needed for the higher layer software,

      i.e., LQSR routing protocol is transparent to higher layer software.

    • Also no modification is required for link layer software.


Link quality source routing lqsr protocol2
Link Quality Source Routing (LQSR) Protocol Protocol

  • Performance of LQSR varies based on different routing metrics and network mobility:

    • For stationary nodes in WMNs,

      the routing metric ETX, achieves the best performance


Link quality source routing lqsr protocol3
Link Quality Source Routing (LQSR) Protocol Protocol

For mobile nodes:

Minimum hop count method outperforms the three link

quality metrics, i.e., per-hop RTT, per-hop packet

pair delay, and ETX

REASON:

As the sender moves, the ETX metric cannot quickly

track the changes in the link quality.


Set 2 link level qos based routing protocols
Set 2: ProtocolLink-level QoS based Routing Protocols

  • Link quality source routing (LQSR) protocol

  • Multi-radio LQSR (MR-LQSR) routing protocol

  • ExOR Routing Protocol

  • AODV-spanning tree (AODV-ST) protocol


4 routing protocols

Multi-Radio LQSR (MR-LQSR) Routing Protocol ProtocolDraves R, Padhye J and Zill B,“Routing in multi-radio, multi-hop wireless mesh networks”, Proc. ACM MOBICOM, 2004.

  • Based on LQSR, and thus, also based on DSR

  • Major difference from LQSR is WCETT

  • To make LQSR perform well in a mesh network with multiple radios per node, WCETT is used as the routing metric in the routing protocol


Multi radio lqsr mr lqsr routing protocol
Multi-Radio LQSR (MR-LQSR) Routing Protocol Protocol

  • WCETT takes into account both link quality metric and the minimum hop-count

  • Achieves good tradeoff between delay and throughput

    because it considers channels with good quality and channel diversity in the same routing protocol


Multi radio lqsr mr lqsr routing protocol1
Multi-Radio LQSR (MR-LQSR) Routing Protocol Protocol

  • MR-LQSR assumes nodes are stationary

  • This is true for mesh routers, but obviously not applicable to mesh clients

  • Performance of MR-LQSR can also be degraded by the mobility of nodes, i.e., mesh clients.


Multi radio lqsr mr lqsr routing protocol2
Multi-Radio LQSR (MR-LQSR) Routing Protocol Protocol

  • In WMNs, multi-channel operation over a single radio is another alternative to increase the network capacity.

  • But MR-LQSR is not applicable because WCETT is limited to multi-radio mode.


Set 2 link level qos based routing protocols1
Set 2: ProtocolLink-level QoS based Routing Protocols

  • Link quality source routing (LQSR) protocol

  • Multi-radio LQSR (MR-LQSR) routing protocol

  • ExOR Routing Protocol

  • AODV-spanning tree (AODV-ST) protocol


4 routing protocols

ExOR Routing Protocol ProtocolBiswas S and Morris R, “ExOR: opportunistic multihop routing for multi-Hop wireless networks,”in Proc. ACM SIGCOMM, 2005.

* Proposed to improve throughput based on cooperative broadcasting packets from source to destination without explicitly setting up a routing path

132


Source s behavior
Source’s behavior Protocol

  • Collects enough packets of the same destination to form a batch

    • ExOR operates on batches of packets for efficiency

  • Selects a set of nodes to be candidate forwarders, and

    includes the prioritized list in the overhead of every packet


Exor routing protocol
ExOR Routing Protocol Protocol

* This priority of a forwarding node is determined by

the cost to the destination,

which is evaluated by the accumulative ETX to the destination node.

134


Exor routing protocol1
ExOR Routing Protocol Protocol

Set of nodes that are selected for forwarding packets are determined based on the packet loss ratio between the source and these nodes.

Although many nodes can receive packets from the source node, only a subset of nodes are selected as forwarding nodes

in order to reduce the overhead.

135


Forwarders behavior
Forwarders’ Behavior Protocol

  • How can a node know whether it is one of the forwarders or not?

  • Check the forwarder list in the overhead of the received packet

    • If the node finds itself in the list, buffer the packet and keep state of this batch

    • If no, discard the packet


Forwarder s behavior
Forwarder’s Behavior Protocol

Highest priority forwarding node sends its own batch of packets following the same procedure as done by the source node.

This process is repeated until 90% of packets in each batch are received by the destination node.

The remaining 10% of nodes will rely on traditional minimum hop-count routing to deliver.

137


Forwarders behavior1
Forwarders’ Behavior Protocol

  • How can a node know whether the packet it receives has also been received by a node with higher priority or not?

  • ExOR designs a “batch map” to record, for every packet in the batch, the highest-priority node known to have received that packet.


Advantages of exor routing protocol
Advantages of ExOR Routing Protocol Protocol

Most of packets are delivered without setting up routing

paths, which is similar to anycast routing.

Moreover, ExOR can improve throughput for two reasons.

It tries to use the best link to deliver packets through

cooperation of forwarding nodes.

Progress of packet forwarding can be continued even if some nodes

on a traditional path experiences bad link quality or out of order.

139


Set 2 link level qos based routing protocols2
Set 2: ProtocolLink-level QoS based Routing Protocols

  • Link quality source routing (LQSR) protocol

  • Multi-radio LQSR (MR-LQSR) routing protocol

  • ExOR Routing Protocol

  • AODV-spanning tree (AODV-ST) protocol


4 routing protocols

AODV-Spanning Tree (AODV-ST) Protocol ProtocolRamachandran K, Buddhikot MM, Chandranmenon G, Miller S, Almeroth K and Belding-Royer E,On the design and implementation of infrastructure mesh networks. Proc. IEEE WIMESH, 2005.

  • AODV ST is designed for multi-radio WMNs

  • ADOV-ST performs hybrid routing,

    i.e., for traffic inside the mesh network AODV is used

    where the spanning-tree based routing is used for traffic to/from gateways.

  • ETT is used as the routing metric


Drawbacks of aodv spanning tree aodv st protocol
Drawbacks of AODV-Spanning Tree (AODV-ST) Protocol Protocol

  • AODV may not be efficient for intra-mesh traffic

  • The WCETT proposed for multi-radio WMNs is not applicable,

    because AODV is a distance vector routing protocol


Overview of routing algorithms2
OVERVIEW OF ROUTING ALGORITHMS Protocol

Hop-Count based Routing

Link Level QoS Based Routing

Interference Based Routing (IRMA)

Routing with Load Balancing

Routing Based on Residual Link Capacity

End-to-End QoS Routing

Reliability Aware Routing

Joint Channel Assignment and Routing (Layer 2.5 Routing)


4 routing protocols

Set 3: ProtocolInterference Based Routing: IRMAWu Z, Ganu S and Raychaudhuri D,IRMA: integrated routing and MAC scheduling in multihopwireless mesh networks. Proc. IEEE WiMesh, 2006.

  • TDMA instead of CSMA/CA as MAC

  • Based on the TDMA, an integrated routing and MAC scheduling algorithm (IRMA) is derived to find a routing path for each traffic flow

  • then determine slot allocation on each link considering

    * BW allocation information

    * Link status, and

    * Topology information in the network.


Interference based routing irma
Interference based Routing: IRMA Protocol

  • A centralized scheme

  • Relies on an existing solution to collect the node, link, and topology related information of the entire network and get traffic specifications of traffic flows.

  • Such signaling can be done in a global control plane (GCP) that can be implemented in a separate dedicated channel or a dedicated time slot


Interference based routing irma1
Interference based Routing: IRMA Protocol

Two routing mechanisms defined in IRMA:

  • link scheduling with minimum-hop routing

  • link scheduling with bandwidth-aware routing (preferred)


Interference based routing irma link scheduling with minimum hop routing
Interference Based Routing: IRMA ProtocolLink Scheduling with Minimum-Hop Routing

  • A routing path is selected by shortest path using minimum hop-count.

  • Then time slots along this path are determined by the

    centralized algorithm by considering the latest flow

    information in the network.

  • may result in congested paths or links as the minimum hop-

    count routing does not consider the available BW.


Interference based routing irma link scheduling with bandwidth aware routing
Interference Based Routing: IRMA ProtocolLink Scheduling with bandwidth-aware Routing

  • Available BW on each link is factored when a routing path is selected.

  • Based on the selection, time slots are then determined for each link on the path.

  • Thus, such a scheme can not only avoid contentions in traffic flows but can also avoid bottleneck or congestedlinks.


Shortcomings of interference based routing irma
Shortcomings of Interference Based Routing: IRMA Protocol

1. Not scalable with the network size (a centralized scheme)

2. Assumes an efficient scheme to collect all control information,

which is a challenging issue for all routing protocols.

3. MAC layer is assumed to have TDMA operation, which is not the

case for many WMNs.


Overview of routing algorithms3
OVERVIEW OF ROUTING ALGORITHMS Protocol

Hop-Count based Routing

Link Level QoS Based Routing

Interference Based Routing (IRMA)

Routing with Load Balancing

Routing Based on Residual Link Capacity

End-to-End QoS Routing

Reliability Aware Routing

Scalable Routing

Joint Channel Assignment and Routing (Layer 2.5 Routing)


4 routing protocols

Set 4: ProtocolRouting with Load BalancingSong W and Fang X ,”Routing with congestion control and load balancing in wireless mesh networks,’Proc. Int. Conference on ITS Telecommunications, 2006

  • Routing is directly determined by considering network congestion

  • Given a source and its destination, a routing path is determined by using the route with the least congestion

  • If more than one paths have the same number of congested nodes, the route with minimum hop-count is selected

  • Congestion state of a link is determined by the number of retransmissions of RTS and ACK packets.

  • If the congestion exceeds a threshold, the congestion weight on this link increases


4 routing protocols

Routing with Load Balancing: CAR ProtocolLiu T and Liao W,Capacity-aware routing in multi-channel multi-rate wireless mesh networks. Proc. IEEE ICC, 2006.

  • A capacity-aware routing (CAR) protocol is proposed to balance load among links and channels in a multi-radio WMN

  • CAR assumes channel assignment on radios lasts long time and can be static.

  • With static channels on each radio in the network, CAR determines the BLC in a reactive manner for each traffic flow.


Routing with load balancing car
Routing with Load Balancing: CAR Protocol

  • Transmissions start on a routing path that is determined according to the best BLC metric.

  • However, this path can be switched to a new one if the source finds the new path has a higher BLC value.


Routing with load balancing car1
Routing with Load Balancing: CAR Protocol

  • Due to the bottlenecked link capacity in routing, CAR improves throughput and delay performance.

  • CAR may not achieve optimal performance because the path selection on different flows affect each other but is not coordinated among such flows.


Overview of routing algorithms4
OVERVIEW OF ROUTING ALGORITHMS Protocol

Hop-Count based Routing

Link Level QoS Based Routing

Interference Based Routing (IRMA)

Routing with Load Balancing

Routing Based on Residual Link Capacity

End-to-End QoS Routing

Reliability Aware Routing

Scalable Routing

Joint Channel Assignment and Routing (Layer 2.5 Routing)


4 routing protocols

Set 5: ProtocolRouting Based on Residual Link CapacityRaniwala A, Gopalan K and Chiueh T ,”Centralized channel assignment and routing algorithms formulti-channel wireless mesh networks,” ACM Mobile Computing and Communications Review, 2005.

  • An alternative scheme to consider link capacity in routing is to get the information of residual link capacity

  • A protocol called Hyacinth is developed to perform routing and channel assignment for a multi-channel WMN.


Routing based on residual link capacity
Routing Based on Residual Link Capacity Protocol

  • Hyacinth considers traffic from/to gateways in WMNs and thus uses tree-based routing for such traffic.

  • Each node advertises its costs of its path from/to the gateway

  • Based on such information, a neighbor that finds a lower value in the cost will leave its old parent node and selects the new node as the new parent node.


Routing based on residual link capacity1
Routing Based on Residual Link Capacity Protocol

  • With such a procedure, all nodes in the network build up routing paths to the gateway like a spanning tree

  • To reflect the cost of a path,

    residual capacity of a link the routing metric.

  • Links are selected which have the largest available capacity


Overview of routing algorithms5
OVERVIEW OF ROUTING ALGORITHMS Protocol

Hop-Count based Routing

Link Level QoS Based Routing

Interference Based Routing (IRMA)

Routing with Load Balancing

Routing Based on Residual Link Capacity

End-to-End QoS Routing

Reliability Aware Routing

Scalable Routing

Joint Channel Assignment and Routing (Layer 2.5 Routing)


Set 6 end to end qos routing
Set 6: ProtocolEnd-to-End QoS Routing

  • Quality Aware Routing Protocol

  • Ring Mesh Routing Protocol


4 routing protocols

Quality Aware Routing Protocol ProtocolKoksal CE and Balakrishnan H,”Quality-aware routing metrics for time-varying wireless mesh networks,”IEEE Journal on Selected Areas in Communications, 2006.

  • End-to-end QoS can be considered in a routing protocol by ensuring end-to-end packet loss rate, delay, or bandwidth.

  • End-to-end packet loss rate is ensured

    where both ETX and ENT are used as routing metrics

  • ENT is used to determine what routing paths can be used


Quality aware routing protocol
Quality Aware Routing Protocol Protocol

  • Allowed packet loss rate in a link is given

  • Based on this packet loss threshold and the measurement of the

    link, a positive number δ used by ENT is derived.

  • With δ and an existing probe scheme, ENT of each link is determined.


Quality aware routing protocol1
Quality Aware Routing Protocol Protocol

  • ENT is then compared with the maximum number of transmissions of a packet before it is discarded at the link layer

  • If ENT is larger than the link-layer value, the routing cost of the link will become ∞

  • Otherwise, ETX is used for the routing cost of the link


Quality aware routing protocol2
Quality Aware Routing Protocol Protocol

  • As a result, all links that do not satisfy packet loss requirement will be excluded from routing paths

  • After this step, routing path selection is performed by just choosing a path with smallest routing cost

  • One critical issue:

    How to determine the allowed packet loss rate of a link

    given the threshold of end-to-end packet loss requirement?


  • Set 6 end to end qos routing1
    Set 6: ProtocolEnd-to-End QoS Routing

    • Quality Aware Routing Protocol

    • Ring Mesh Routing Protocol


    4 routing protocols

    RingMesh Routing Protocol ProtocolLin D, Moh T and Moh M,”A delay-bounded multi-channel routing protocol for wireless mesh networks using multiple token rings: extended summary,”Proc. 31st IEEE Conference on Local Computer Networks (LCN), 2006.

    • End-to-end delay

    • RingMesh is developed based on a token ring

      protocol proposed for wireless LANs


    Ringmesh routing protocol
    RingMesh Routing Protocol Protocol

    • Multiple token rings are created and organized from the gateway to all other nodes like a spanning tree scheme

    • Different channels are used in neighboring rings

    • First ring containing the gateway is called a root ring

    • Next ring connected to the root ring is a child ring.


    Ringmesh routing protocol1
    RingMesh Routing Protocol Protocol

    • These two rings share a common node which is called a pseudo gateway

    • Following this process, other child rings are connected together all the way to the root ring

    • For a node in the network, which ring it can join depends on the delay from it to the gateway:

    • the node joins a ring that can satisfy the end-to-end delay requirement.


    Shortcomings of ringmesh routing protocol
    Shortcomings of RingMesh Routing Protocol Protocol

    • How to form multiple rings to support multiple gateways to improve the delay performance is not addressed?

    • It is also unknown what happens if no ring can be joined by a node

    • No mechanism is also available to determine the delay from a node to the gateway, which is not a trivial task

    • Thus, end-to-end delay aware routing is still a challenging research topic


    Overview of routing algorithms6
    OVERVIEW OF ROUTING ALGORITHMS Protocol

    Hop-Count based Routing

    Link Level QoS Based Routing

    Interference Based Routing (IRMA)

    Routing with Load Balancing

    Routing Based on Residual Link Capacity

    End-to-End QoS Routing

    Reliability Aware Routing

    Scalable Routing

    Joint Channel Assignment and Routing (Layer 2.5 Routing)


    4 routing protocols

    Set 7: ProtocolResilient Opportunistic Mesh Routing (ROMER) ProtocolYuan Y, Yang H,Wong SHY, Lu S and Arbaugh W,”ROMER: resilient opportunistic mesh routing for wireless mesh networks,”Proc. IEEE WIMESH, 2005

    • ROMER creates forwarding mesh on the fly for each packet

    • ROMER assumes that there is an existing scheme that can find the minimum cost from each mesh router to the gateway

    • Then the credit is determined while a packet is forwarded on the fly


    Resilient opportunistic mesh routing romer protocol
    Resilient Opportunistic Mesh Routing (ROMER) protocol Protocol

    • When a packet is to be delivered from a mesh router, e.g., Node S, to the gateway, the source mesh router needs to set a credit cost.

    • If the minimum cost from S to the gateway is Cmin,S and the credit cost is Ccredit,S,

      then S has a budget cost of Cmin,S + Ccredit,S to the gateway.

    • When the packet is sent to the next mesh router, e.g., node A, the budget is reduced by the cost of the traversed link clinkSA


    Resilient opportunistic mesh routing romer protocol1
    Resilient Opportunistic Mesh Routing (ROMER) protocol Protocol

    • At mesh router A, the needed credit is computed according to the requirement of

      Ccredit,A + Cmin,A + ClinkSA <=Cmin,S + Ccredit,S,

      i.e., the remaining credit at mesh router A is

      Ccredit,A = Cmin,S + Ccredit,S − Cmin,A − ClinkSA.

    • If the ratio of the remaining credit over the initial credit Ccredit,S is less than a threshold, e.g., (Cmin,A / Cmin,S)2,

      then the packet at mesh router A shall be discarded;


    Resilient opportunistic mesh routing romer protocol2
    Resilient Opportunistic Mesh Routing (ROMER) protocol Protocol

    • Otherwise, mesh router A forwards the packet according to a randomized opportunistic forwarding scheme.

    • The above process is repeated until the packet is delivered to the gateway


    Resilient opportunistic mesh routing romer protocol3
    Resilient Opportunistic Mesh Routing (ROMER) protocol Protocol

    • Finally, when multiple intermediate routers receive the same packet from a mesh router and

      all have enough credit to forward the packet,

      they need to follow a randomized opportunistic forwarding scheme to forward packets.


    Resilient opportunistic mesh routing romer protocol4
    Resilient Opportunistic Mesh Routing (ROMER) protocol Protocol

    • Probability that each intermediate router can forward a packet depends on the quality of the link to the parent router


    Resilient opportunistic mesh routing romer protocol5
    Resilient Opportunistic Mesh Routing (ROMER) protocol Protocol

    Intermediate router with the best link quality forwards the packet with probability 1,

    while other intermediate routers forward the packet with a probability of (Rl /Rmax),

    where Rl is the current rate of the considered link and Rmax is the current rate at the best link.


    Drawbacks of resilient opportunistic mesh routing romer protocol
    Drawbacks of Resilient Opportunistic Mesh Routing (ROMER) Protocol

    • ROMER has to rely on an existing scheme to find out the minimum cost from each mesh router to the gateway

    • What type of cost is the best for ROMER and how to dynamically update the cost to best serve ROMER remain open questions !


    Overview of routing algorithms7
    OVERVIEW OF ROUTING ALGORITHMS Protocol

    Hop-Count based Routing

    Link Level QoS Based Routing

    Interference Based Routing (IRMA)

    Routing with Load Balancing

    Routing Based on Residual Link Capacity

    End-to-End QoS Routing

    Reliability Aware Routing

    Joint Channel Assignment and Routing (Layer 2.5 Routing)


    Multichannel protocols
    Multichannel Protocols Protocol

    • Multi-channel operation is widely adopted in WMNs to improve network capacity

    • Single-channel routing protocols may be run in each of the

      channels of the WMN

      • Easy design but not optimal, and does not guarantee availability of spectrum in the

        routes

    • Multi-channel routing protocols are better suited


    Multichannel protocols1
    Multichannel Protocols Protocol

    • Two types of multi-channel routing protocols

      • Type 1: Consider the impact of multi-channel operation such as link

        quality, interference, packet loss, bandwidth

      • Type 2: Conduct close routing/MAC cross-layer design such as joint

        channel allocation and routing


    Multichannel protocols2
    Multichannel Protocols Protocol

    • Most existing protocols are of type 1

      • As an example, in MQ-LSR ignores the close relationship between

        traffic distribution and channel allocation by assuming different

        radios are assigned non-overlapping channels

      • It also incorrectly assumes that the channel assignment changes

        relatively infrequent, leading to the necessity of joint channel-route

        assignment


    4 routing protocols

    Joint Channel Assignment and Routing ProtocolAlicherry M, Bhatia R and Li L, “Joint channel assignment and routing for throughput optimization in multi-radio wireless mesh networks,”in Proc. ACM MobiCom, 2005

    For infrastructure WMNs (IWMNs)

    Assumption:

    Aggregated traffic load at mesh routers and channels assigned to

    each router is not changing frequently

    Channels assigned to radios on a node are determined together with routing paths

    with an objective to obtain interference-free link schedule and achieve maximum throughput.

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    4 routing protocols

    Joint Channel Assignment and Routing ProtocolTang J, Xue G and Zhang W, “Interference-aware topology control and QoS routing in multichannel wireless mesh networks,”ACM MobiHoc, 2005.

    Assumes the channel assignment can be static in WMNs

    Goal:mathematical formulation of the joint design between

    channel assignment and routing

    However, no actual protocol is proposed

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    4 routing protocols

    Distributed Joint Channel and Routing Protocol ProtocolAvallone S and Akyildiz, IF and Ventre G, “A channel and rate assignment algorithm and a layer-2.5 forwarding paradigm for multi-radio wireless mesh neetworks,” IEEE/ACM Transactions on Networking, 2009

    It takes into account the number of flows that are possible to route on each link

    Amount of flows is obtained from a solution to the joint channel assignment and routing problem

    185


    Distributed joint channel and routing protocol
    Distributed Joint Channel and Routing Protocol Protocol

    Objective

    Enable every router to utilize each of its links in proportion to their assigned flow rates

    Routing protocol only requires a partial knowledge of the network topology and does not make use of a destination-based routing table

    Hence, the name Layer-2.5 (L2.5) given to the routing protocol.

    186


    Layer 2 5 routing algorithm
    Layer-2.5 Routing Algorithm Protocol

    • Each mesh router is configured with the set of pre-

      computed flow rates associated with its links

    • Packets are forwarded using such information (rather

      than routed using routing tables)

      • Layer-2 information are used, hence the name

    • Each mesh router attempts to keep the utilization of

      the outgoing links proportional to their pre-computed

      flow rates


    Channel assignment routing
    Channel Assignment & Routing Protocol

    * An approximate solution:

    • Determine pre-computed flow rates

      A pre-computed flow rate is determined for every link based on the

      given optimization objective

    • Determine the channel assignment

      Channels are assigned to radios in the attempt to make such

      pre-computed flow rates schedulable

    • Adjust the pre-computed flow rates

      The pre-computed flow rates may be adjusted in order to obtain a set

      of schedulable flow rates given the computed channel assignment


    Open research issues
    Open Research Issues Protocol

    Performance Benchmark

    Large number of routing metrics and routing protocols available for WMNs.

    Considering routing protocols for other multi-hop wireless networks, the number is much bigger

    Confusion about which routing metric and what type of routing protocols can provide the best performance => benchmark to investigate and compare different routing metrics and protocols.

    189


    Open research issues1
    Open Research Issues Protocol

    It is expected to include theoretical analysis of performance bound, practical consideration of protocol design, and performance evaluation either through simulations or testbeds.

    In [1], a comparative study is carried out for different routing strategies for WMNs.

    Some design guidelines are provided in [2] for multihop wireless networks.

    However, such work is still far from providing a benchmark of selecting routing metrics and protocols.

    [1] Wellons J, Dai L, Xue Y and Cui Y, “Predictive or oblivious: a comparative study of Routing strategies for wireless mesh networks under uncertain demand," Proc. IEEE SECON, 2008

    [2] Yang Y and Wang J, “Design guidelines for routing metrics in multihop wireless networks,”

    Proc. IEEE INFOCOM, 2008.

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    Open research issues2
    Open Research Issues Protocol

    New routing metrics

    How to integrate multiple routing metrics into the same routing protocol is another challenging issue.

    191


    Open research issues3
    Open Research Issues Protocol

    Scalable routing

    This is a critical requirement by WMNs, achieved by few routing protocols so far.

    Hierarchical routing protocols can only partially solve this problem due to their complexity and difficulty of management.

    Geographic routing needs GPS or similar  cost, complexity. Additional traffic by inquiry of destination position.

    Scalability is also related to MAC protocols. Thus, an eventual scalable routing protocol must be closely integrated with the MAC protocol.

    192


    Open research issues4
    Open Research Issues Protocol

    Network coding and routing

    Can potentially improve the performance of WMNs

    E.g., research to apply network coding to WMNs [1], [2],

    Benefits of network coding to a multichannel WMN in [2]

    However, as network coding is still in an early phase of being applicable to a practical networking protocol, integrating network coding with routing is still a new and challenging research direction

    [1] Omiwade O, Zheng R and Hua C, “Practical localized network coding in wireless mesh networks,”

    Proc. of IEEE SECON, 2008

    [2] Zhang X and Li B, “On the benefits of network coding in multi-channel wireless networks,”

    Proc. of IEEE SECON, 2008

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