EVALUATION OF MULTI-RADIO EXTENSIONS TO DSR FOR

WIRELESS MULTI-HOP NETWORKS

Saad Biaz, Bing Qi, Shaoen Wu

Dept. of Computer Science and Software Engineering, Dustan Hall 107, Auburn University, AL 36849, USA

Yiming Ji

Department of Computer Science,University of South Carolina, Hargray Building, Beaufort, SC 29909, USA

Keywords:

Multi-hop network, Dynamic Source Routing, Multi-Radio, Dynamic Source Routing with Multi-radio Ex-

tensions.

Abstract:

Performance on multi-hop networks suffers from limited throughput capacity and poor scalability problems as

the network size or density increases (Gupta and Kumar, 2000). One way to alleviate these problems is to equip

each node with multiple radios. As hardware cost drops, this approach becomes more and more appealing and

feasible. By tuning radios into non-interfering channels, the wireless spectrum can be more efﬁciently utilized,

thus enhancing the whole network performance. This work extensively evaluates Dynamic Source Routing

Protocol(DSR) (Johnson and Maltz, 1996) for multi-radio multi-hop networks. Through simulations, DSR

with multi-radio extensions exhibits an overall performance improvement for throughput, packet delivery rate

and latency.

1 INTRODUCTION

Unlike traditional wireless networks, a multi-hop net-

work is a collection of independent wireless nodes

that establish a network normally without any pre-

established infrastructure. Each node can transmit

data packets to other nodes within its radio range, and

forward packets on behalf of other nodes.

Despite their ﬂexibility and convenience to sup-

port diverse applications (Cordeiro and Agrawal,

2002), multi-hop networks are not yet widely de-

ployed since they perform poorly as the number

of nodes and/or hops increases (Gupta and Kumar,

2000). The poor performance mainly results from

the inability of a wireless radio to transmit and to

receive at the same time. Such a weakness halves

the forwarding node capacity; in addition, simultane-

ous transmissions on the same frequency channel and

the sub-optimal MAC back-off mechanisms exacer-

bate the limited capacity problem.

Many approaches have been proposed to alleviate

the capacity problem. One approach is to explore di-

rectional antennas (Ko et al., 2000; Choudhury and

Vaidya, 2002). Since directional antennas are able

to focus energy in a given direction, they have some

advantages over omni-directional antennas in multi-

hop networks, such as less interference, longer trans-

mission range and the increasing potential for spatial

reuse, etc. Such features result in higher multi-hop

capacity and better connectivity. However, replacing

omni-directional antennas with directional ones will

not fully exploit all the advantages. A number of ad-

justments are required at each layer of the networking

protocol stack to accommodate directional antennas

(e.g. broadcast problem, discovery of neighbors, etc).

Another approach consists of using multiple chan-

nels for each node. For example, the widely

deployed IEEE802.11b standard supports 3 non-

overlapping channels without interference. Users in

infrastructure-based wireless networks already suc-

cessfully exploit the multi-channel feature: differ-

ent access points are assigned to different channels

such that neighboring cells communicate on non-

overlapping channels concurrently. Such channel as-

signment results in lower interferences and higher ca-

pacity (Lee et al., 2002; Tzamaloukas and Garcia-

Luna-Aceves, 2001). However, this method cannot be

applied “as is” to multi-hop wireless networks since

neighboring nodes must communicate on the channel

with same frequency. Some researchers suggest al-

Biaz S., Qi B., Wu S. and Ji Y. (2007).

EVALUATION OF MULTI-RADIO EXTENSIONS TO DSR FOR WIRELESS MULTI-HOP NETWORKS.

In Proceedings of the Second International Conference on Wireless Information Networks and Systems, pages 65-69

DOI: 10.5220/0002147300650069

 SciTePress

lowing each node to use multiple channels following

a hopping sequence (Tyamaloukas and Garcia-Luna-

Aceves, 2000). Receiver and sender nodes will fol-

low some channel hopping sequence till they lock on

a common channel. Unfortunately, a non-negligible

switching latency (especially for off-the-shelf wire-

less network interfaces (Inc., 2004)) would negatively

impact the performance.

Due to ever decreasing hardware cost, the switch-

ing latency can be eliminated by equipping each node

with multiple radios: the radios on each node would

be tuned on multiple non-overlapping channels, thus

wireless nodes can send and receive independently

and simultaneously on multiple channels. Therefore,

with multiple radios on each node, the available spec-

trum could be more efﬁciently shared. However, after

adding one or more radios to each node in multi-hop

networks, routing data packets becomes more chal-

lenging in such scenarios. Although most well-known

multi-hop routing algorithms have been so far exten-

sively studied in case of mono radio nodes (Bouk-

erche, 2004; Broch et al., 1998), far fewer studies ex-

ist for evaluating their performance when nodes are

conﬁgured with multiple radios (Pirzada et al., 2006).

Some other research works also investigated the

multi-radio nodes effect but most of them focus on the

link-quality routing protocols and new routing metric

such as (R. Draves and Zill, 2004; Couto et al., 2003).

On the contrary, our work only extends Dynamic

Source Routing(DSR) (Johnson and Maltz, 1996) to

take advantage of multi radio feature and evaluates the

Raw performance improvement due to multi-radio in

multi-hop networks.

Extensive simulations are conducted to show that

DSR with multi-radio extensions is very efﬁcient for

high trafﬁc loads and exhibits a high delivery rate as

well as a lower latency.

The rest of the paper is organized as follows: Sec-

tion 2 brieﬂy introduces the basic DSR scheme and

describes our extensions to DSR to take advantage of

the multi-radio nodes. Section 3 outlines the simula-

tion settings. And Section 4 demonstrates and ana-

lyzes the experiment results. Finally, Section 5 con-

cludes the paper.

2 EXTENDED DYNAMIC

SOURCE ROUTING

Routing protocols for multi-hop networks are nor-

mally classiﬁed as reactive (or On demand) and

proactive (Royer and Toh, 1999) protocols. Reactive

routing protocols (e.g. AODV (Perkins and Royer,

1999), DSR (Johnson and Maltz, 1996)) create and

Source Request Destination

IP IPID

RouteRecord

Series

Figure 1: Simple RREQ Packet Format.

maintain a route between a pair source-destination

only when the source node needs to send packets

to the destination node; In contrast, proactive rout-

ing protocols (e.g. OLSR (Clausen et al., 2003),

STAR (Garcia-Luna-Aceves and Spohn, 1999)) re-

quire wireless nodes maintain routing tables for all

nodes on the network.

Broch et. al (Broch et al., 1998) evaluated multi-

ple ad hoc routing protocols and concluded that Dy-

namic Source Routing (DSR) (Johnson and Maltz,

1996) is one of the best in terms of resources con-

sumption in single radio multi-hop network. While

DSR has been extensively studied in single radio net-

works, there is no work to our knowledge that eval-

uates its performance directly over multi-radio multi-

hop networks. Thus this work extends DSR to work

with multi-radio nodes scenarios and evaluates the

performance of such extensions through extensive

simulations.

DSR (Johnson and Maltz, 1996) is a reactive rout-

ing protocol specially designed for wireless multi-hop

networks and it is based on the concept of source rout-

ing as the source node speciﬁes in the packet’s header

the sequence of nodes to reach the destination.

The basic idea of DSR routing protocol lies in

its route discovery process. When a source node S

intends to communicate with a destination node D

whose route is unknown, the source node S initializes

a route discovery process by ﬂooding out a route re-

quest packet (RREQ) to all its neighbors (RREQ sim-

ple format is illustrated in Figure 1). On receiving a

RREQ packet, node A checks the destination address

in RREQ packet’s header: if A is the target node, it

returns a route reply packet (RREP) to the initiator

node S by following the path which is typically the

reverse of RREQ Route-Record ﬁeld. RREP will con-

tain the sequence of nodes on the path from source S

to target D; Otherwise, node A is just one intermediate

node, thus node A caches the RREQ packet, appends

its own address to the RREQ’s Route-Record ﬁeld,

and rebroadcasts the updated RREQ. Node A discards

the RREQ packet in case the same RREQ packet has

already been previously received. After the source S

receives RREP, it caches the route to send subsequent

data packets to the speciﬁc destination node.

When a node is conﬁgured with more than one

radio, radio indices are needed to make DSR aware

of the existence of multiple radios. Figure 2 shows

a simple network scenario with four nodes, in which

WINSYS 2007 - International Conference on Wireless Information Networks and Systems

S A

















Figure 2: Simple Multi-radio multi-hop network.

Source Request Destination

IP IPID

RouteRecord

Series

Source

Radio Index

Figure 3: Modiﬁed RREQ Packet Format.

every node has two independent radios (respectively

represented by a triangle and a circle). The radios on

each node are set to different non-overlapping chan-

nels such that they can independently work without

any interferences. Since each node may have one or

more radios in the multi-radio network, the route for

a given path must include the radio index information

to each hop. So on Figure 2, one possible path should

be speciﬁed as: [(S,1)-(A,2)-(B,1)-D] where 1 and 2

indicate the radio index on each node.

Therefore some slight changes should be made

to traditional single radio DSR in order to perform

properly in multi-radio scenarios: each node needs to

broadcast RREQ packets on all its radios; when an in-

termediate node gets the RREQ packets from any of

its radios, the node should append not only its own

address, but also the radio index to the route record to

indicate on which radio it recieves the RREQ packet.

As shown on Figure 3, a radio index ﬁeld is added to

DSR RREQ packet header.

Furthermore every radio within each node needs

to send out a copy of RREQ packet in multi-radio

networks. Thus many more RREQ packets will be

generated causing more RREQ packet collisions than

single radio networks, also at the same time increase

the likelihood to lose RREQ packets with good routes

information (broadcast packets are not retransmitted

when lost). In single radio multi-hop network, DSR

forwards only the ﬁrst RREQ packet and discards fur-

ther RREQ with the same request id and source ad-

dress. Here, in multi-radio network, in order to in-

crease the chances to get the shortest routes, the nodes

are required to forward RREQ packets more greedily

than single radio networks: That is the intermediate

node forwards again a RREQ packet previously seen

as long as the hop count is lower.

Table 1: Experimental Parameter.

Simulation Time 120 Seconds

Simulation Field 1500m*1500m

Propagation Mode Two-ray Ground

Trafﬁc Mode CBR

Transmission Range 250 m

Number of Connections 5,10,15,20

Packet Size 1000 bytes

Trafﬁc Interval 30 ms

Interface Queue 50

3 EVALUATION

METHODOLOGY

3.1 Experimental Set Up

The efﬁciency of DSR on a multi-radio network is

evaluated using ns-2 simulator. In our simulations,

all nodes have the same number of radios and the

radios on each node are assigned to different non-

overlapping channels. The same channel allocation

scheme is used for all wireless nodes.

The experimental multi-hop network consists of

50 nodes which are randomly positioned a ﬁeld of

1500m

. All nodes are conﬁgured with two radios

tuned to two non-interfering channel. Source node

and destination node are randomly selected to start

UDP connections. Each UDP connection sends CBR

trafﬁc with 1000 byte data packets every 30ms. To

test the effect of various trafﬁc loads, the number of

connections is varied from 5 to 20 taking values 5, 10,

15, 20. For a given set of parameters, the experiment

is repeated for 50 times with different starting time.

The performance metrics are obtained by averag-

ing the results of 50 simulation runs. DSR on single

radio network and DSR on multi-radio network are

evaluated with same simulation setting. The simula-

tion parameters are summarized in Table 1.

3.2 Comparison Metrics

Average Throughput, Packet Delivery Rate, Average

End-to-end Delay, and Average Path Length are the

metrics used to evaluate DSR routing protocol on

multi-radio networks (Broch et al., 1998):

• Average Throughput measures the total number of

data bits successfully received during the unit ex-

perimental time.

• Packet Delivery Rate measures the number of

end-to-end packets successfully received over the

total number of data packets sent.

EVALUATION OF MULTI-RADIO EXTENSIONS TO DSR FOR WIRELESS MULTI-HOP NETWORKS

0.0

0.5

1.0

1.5

2.0

2.5

DSR with One Radio

DSR with Two Radios

Average Throughput (Mbps)

5 10 15 20

Number of Connections

Figure 4: Average Throughput Vs. Connections.

• Average End-to-end Delay measures the average

latency time for all successfully received data

packets.

• Average Path Length is the average number of

hops a packet took to reach its destination.

4 SIMULATION RESULTS

The simulations evaluated the impact of trafﬁc load

by varying the number of connections taking values

5, 10, 15, or 20. Promising performance results are

obtained with extended DSR for multi-radio nodes.

All plots have the number of connections on the

x-axis. Figure 4 plots the average throughput respec-

tively achieved by DSR with single radio nodes and

by extended DSR with multi-radio nodes, which il-

lustrates a signiﬁcant throughput improvement of ex-

tended DSR with the multi-radio nodes over DSR

with single-radio nodes. The average throughout im-

provement reaches up to 93% for different connec-

tions. As the number of connections increases, the

throughput enhancement is more dramatic.

The Packet Delivery Rate is plotted on Figure 5.

As illustrated, more data packets are lost as the

number of connections increases (trafﬁc load in-

creases). Losses may result from unavailable or in-

correct routes, overﬂow of the buffers, and many other

reasons. The Packet Delivery Rate for extended DSR

on the multi-radio networks is usually better than

DSR on single radio networks regardless of the num-

ber of connections.

Figure 6 plots the Average End-to-end delay re-

spectively for DSR with single radio nodes and for

extended DSR over multi-radio nodes. The delays

signiﬁcantly vary with the number of connections.

As the number of connections increase, medium con-

0.0

100

DSR with One Radio

DSR with Two Radios

Average Delivery Rate (%)

5 10 15 20

Number of Connections

Figure 5: Average Packet Delivery Rate Vs. Connections.

DSR with Two Radios

DSR with One Radio

Average Delay (seconds)

5 10 15 20

Number of Connections

Figure 6: Average Delay Vs. Connections.

tention and retransmission increase causing more de-

lay at each hop and more retransmissions. Although

the average delay for extended DSR with multi-radio

nodes is quite high for heavier trafﬁc load, it remains

dramatically lower than with DSR on single radio

nodes. On average, the delay is four times smaller.

Figure 7 plots the Average Path Length. The left-

most column indicates the average shortest hop count

that physically existed based on perfect and global

knowledge of the network topology. The middle

column and the rightmost column display the aver-

age hop length respectively taken by extended DSR

with multi-radio nodes and DSR with the single radio

nodes. Results show that extended DSR with multi-

radio nodes ﬁnds more often the existing shortest path

especially when the number of connections is high.

WINSYS 2007 - International Conference on Wireless Information Networks and Systems

DSR with Two Radios

DSR with One Radio

Shortest Hop Existed

Average Path Length

5 10 15 20

Number of Connections

Figure 7: Average Path Length Vs. Connections.

5 CONCLUSIONS AND FUTURE

WORK

This work evaluates the Dynamic Source Routing

protocol performance on a multi-radio multi-hop net-

work through extensive simulations.

Experimental results show a considerable im-

provement of overall performance over DSR with sin-

gle radio nodes in terms of throughput, end-to-end

delay, and packet delivery ratio. Therefore, by sim-

ply enabling Dynamic Source Routing to work with

multi-radio nodes, we can exploit the wireless spec-

trum more efﬁciently. However, DSR adopts the

shortest hop count to select the routing path, which

is quite limited and does not fully take advantage of

multi-radio feature in wireless multi-hop networks. It

would be of high interest to consider paths with min-

imal interference and higher throughput. The authors

are currently designing a metric similar to the one pro-

posed by Draves and Zill (R. Draves and Zill, 2004)

to take into account multiple criteria such as channel

conditions and radio interferences.

REFERENCES

Boukerche, A. (2004). Performance evaluation of routing

protocols for ad hoc wireless networks. Mob. Netw.

Appl., 9(4):333–342.

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

Jetcheva, J. (1998). A performance comparison of

multi-hop wireless ad hoc network routing protocols.

In Mobile Computing and Networking, pages 85–97.

Choudhury, R. and Vaidya, N. (2002). On ad hoc routing

using directional antennas.

Clausen, T., (editors), P. J., Adjih, C., Laouiti, A., Minet, P.,

Muhlethaler, P., Qayyum, A., and L.Viennot (2003).

Optimized link state routing protocol (olsr). RFC

3626. Network Working Group.

Cordeiro, C. and Agrawal, D. (2002). Mobile ad hoc net-

working.

Couto, D. D., Aguayo, D., Bicket, J., and Morris, R. (2003).

A high-throughput path metric for multi-hop wireless

routing.

Garcia-Luna-Aceves, J. J. and Spohn, M. (1999). Source-

tree routing in wireless networks. In ICNP, pages

273–282.

Gupta, P. and Kumar, P. R. (2000). The capacity of wire-

less networks. IEEE TRANSACTIONS ON INFOR-

MATION THEORY, 46:388–404.

Inc., M. I. P. (2004). Max2820, max2820a, max2821,

max2821a 2.4ghz 802.11b zero-if transceivers data

sheet rev. 04/2004. California, USA.

Johnson, D. B. and Maltz, D. A. (1996). Dynamic source

routing in ad hoc wireless networks. In Imielinski

and Korth, editors, Mobile Computing, volume 353.

Kluwer Academic Publishers.

Ko, Y.-B., Shankarkumar, V., and Vaidya, N. H. (2000).

Medium access control protocols using directional an-

tennas in ad hoc networks. In INFOCOM (1), pages

13–21.

Lee, Y., Kim, K., and Choi, Y. (2002). Optimization of

ap placement and channel assignment in wireless lans.

lcn, 00:0831.

Perkins, C. E. and Royer, E. M. (1999). Ad-hoc on-demand

distance vector routing. wmcsa, 00:90.

Pirzada, A. A., Portmann, M., and Indulska, J. (2006). Eval-

uation of multi-radio extensions to aodv for wireless

mesh networks. In MobiWac ’06: Proceedings of the

international workshop on Mobility management and

wireless access, pages 45–51, New York, NY, USA.

ACM Press.

R. Draves, J. P. and Zill, B. (2004). Routing in multi-radio,

multi-hop wireless mesh networks. In Proceedings of

the 10th annual international conference on Mobile

computing and networking, pages 114 – 128, Philadel-

phia, PA, USA.

Royer, E. and Toh, C. (1999). A review of current routing

protocols for ad-hoc mobile wireless networks.

Tyamaloukas, A. and Garcia-Luna-Aceves, J. J. (2000).

Channel-hopping multiple access. In ICC (1), pages

415–419.

Tzamaloukas, A. and Garcia-Luna-Aceves, J. J. (2001).

A receiver-initiated collision-avoidance protocol for

multi-channel networks. In INFOCOM, pages 189–

198.

EVALUATION OF MULTI-RADIO EXTENSIONS TO DSR FOR WIRELESS MULTI-HOP NETWORKS