13

PDCP
PHY
PPP
RA
SAP
SEND
SLAAC
SMI
SNAP
STA
TAP
TCP
TUN
TVL
UDP
UMTS
VC

ETSI TS 102 636-6-1 V1.1.1 (2011-03)

Packet Data Convergence Protocol
PHYsicalPoint-to-Point Protocol
Router Advertissement
Service Access Point
SEcure Neighbor Discovery
StateLess Address AutoConfiguration
Structure of Management Information
SubNetwork Access Protocol
STAtionTerminal Access Point
Transmission Control Protocol
network TUNnel
Topological Virtual Link
User Datagram Protocol
Universal Mobile Telecommunications Systems
Virtual Circuit

DUPE: Duplicated Unicast Packet Encapsulation in
Position-Based Routing VANETYe Tao ∗ , Xin Li † , Manabu Tsukada ∗ , Hiroshi Esaki ∗∗ Graduate School of Information Science and Technology, The University of Tokyo† School of Information and Communication Engineering, Beijing University of Posts and Telecommunications
4
GN6ASL in the ITS station architecture∗ {tydus,tsukada}@hongo.wide.ad.jp, hiroshi@wide.ad.jp,† leexin@bupt.edu.cn
With respect to the ITS station referencearchitecture [1], the present document only affects the layer block"Networking and Transport". As depicted in figure 1, within the layer block "Networking and Transport", the present
document introduces GN6ASL, an adaptation sub-layer for the transmission of IPv6 packets over GeoNetworking. The
other protocols depicted in figure 1 (e.g. TCP and UDP) are represented for sake of completeness in order to represent a
typical usage of the present document.

Abstract—Position-based Routing Vehicular Ad-hoc Network(PBR-VANET) is a specific type of mobile Ad-hoc network
where the nodes are present as vehicles and the routing isdecided based on node position. However, PBR-VANET routing
protocols greatly suffer from mass packet loss due to frequentchanges in topology. We discuss the requirements of the routing
protocol and propose a routing encapsulation protocol called
Duplicated Unicast Packet Encapsulation (DUPE). The protocol
is compatible with original GeoNetworking standard, and cancooperate with the existing implementations without modification
to neither GeoNetworking infrastructure nor user applications.
The protocol encapsulates GeoNetworking packet in BTP packet(a Layer 4 protocol in GeoNetworking) and duplicates theoriginal packet into different paths to reduce packet loss caused
by failure and stale paths. The evaluations on DUPE in different
scenarios show that, with reasonable latency and bandwidth
overhead achieved, packet loss in certain scenarios is eliminated,
where standard GeoNetworking protocol has packet loss of up
to 94.5% in worst case.
Index Terms—Vehicular Ad-hoc Networks, Cooperative Intelligent Transportation Systems, GeoNetworking, Routing Protocols,
Open Source Software

I. I NTRODUCTION
Road transportation is one of the most essential services forhuman mobility since ancient times. Intelligent Transportation
Systems (ITS) aim at optimization of the road traffic byrealizing safe, efficient and comfortable transportation. Withina number of research fields in ITS, Application of Cooperative
ITS includes driver assistance shortly. However, the vehicularcommunication also remains essential in autonomous driving
to support a wider perception of the other vehicles around avehicle that cannot be detected by the sensors equipped withthe vehicle.
To communicate among vehicles and roadside units,
GeoNetworking [1] is employed as one of the network protocols in the ITS Station architecture [2] standardized in ISO
and ETSI, as shown in Figure 1.
GeoNetworking employees Position-based routing VANET(PBR-VANET) to adapt high-speed movement requirement.
PBR-VANET is a type of VANET routing protocols whichuses position information of nodes to direct routing. They do
not maintain routing tables and exchange link state information
but realize the route by the position of the nodes. This typeof routing protocols performs better in high dynamic topology
while link states are frequently changing.

Basic Transport
Protocol (BTP)ETSI EN 302 636-5-1
ETSI EN 302 636-6-1

ETSI EN 302 636-4-1

Figure 1: GN6ASL in the ITS station architecture
As depicted in figure 1, the present document builds an adaptation sub-layer (GN6ASL) between the ETSI
GeoNetworking protocol [i.25] and an IPv6-compliant protocol layer and extended with mobility extensions. The
default IPv6 mobility extensions in the ETSI ITS architecture [1] (as well as in [i.19]) is the Network Mobility Basic
Support (NEMO BS) protocol [15]. The present document enables the usage of NEMO BS over the ETSI
GeoNetworking protocol [i.25].

Fig. 1. GeoNetworking in ITS Station Architecture

NOTE:

With respect to the figure 1, the scope of [i.19] includes the protocol layer IPv6 + Mobility Extensions,directly above the adaptation sub-layer specified in the present document.

Ensuring on-time delivery of packets is crucial in Intelligent
ETSI
Transportation Services. However
currently VANET routing
protocols are suffering from mass packet loss (up to 94.5%
in certain cases). Many applications are sensitive to reliablecommunication, especially the safety-related ones. In extreme
cases, humans’ life may be threatened by the non-deliveryof messages. Packet delivery ratio is the main challenge in
VANET routing protocols. A frequently loss link could render
many applications meaningless.
The rest of the paper is organized as follows. In section II,
we analyze the packet loss issue we encountered in PBRVANETs with two typical scenarios, the overtake scenario
and the shadow scenario. As results, two reasons are derived
from the scenarios. In section III we depict some efforts tosolve the issue, which is the existing routing protocols for
VANETs and an open source software of GeoNetworking.
After that, additional requirements and constraints to eachof the issues were discussed. In section IV, we discuss the
additional requirements and constraints of the routing protocol,then propose a routing encapsulation layer called DuplicatedUnicast Packet Encapsulation (DUPE) to solve the packet
loss issue. In section V, several experiments of DUPE is
conducted by the evaluation method of Combined Realistic
Evaluation Workflow (CREW) , which is proposed in [3].
All of them show a fairly promising result: we efficiently
eliminated the packet loss, with a reasonable overhead. Finally,in section VI, we summarize our contributions regards DUPE
and make a prospect to future work.

A. Adaptation to topology change
Most of the PBR-VANET routing protocols are working
based on beacons, to maintain a constant update of position
information about other nodes in the network.
In a realistic situation, the speed of vehicles can be changed
substantially due to brake or acceleration. This feature leads toa highly dynamic topology, of which the change can happen
in several hundred milliseconds. In the scenario depicted in
Figure 2 (named the overtake scenario), when a vehicle Bob
accelerates to overtake Carol, the original topology changes
along with the overtaking. But Alice may be not aware of the
topology change instantly, if there is not a dense communication between Alice and Bob. Messages from Alice to Bob
are, therefore, all lost, as Alice holds stale position information
about Bob, making Alice trying to reach Bob directly ignoring
Carol, until Alice gets the updated information about Bob.
overtake!
stale path
Bob

Alice

Bob

Carol

new path

Fig. 2. The overtake problem

B. Recover from failure path
Under real environment, the wireless communication channel can be interfered by many factors. Such as buildings,
radio noise. An example scenario is depicted in Figure 3,
which is called the shadow scenario. If the communication
channel between Alice and Bob is unstable, caused by thelong transmission range here, but not lossy enough to lose all
messages. Some sporadic messages from Bob, which carries
the position information of it, can be transmitted successfully
to Alice. Those messages make Alice choose to deliver themessage directly to Bob without considering packet loss ratio
and another alternative route. This scenario can exist in partof the route path of PBR-VANET, and result in high packet
loss ratio. Most of the PBR-VANET routing protocols cannot
perceive lossy stretches of the route, like the one between Aliceand Bob, not to mention altering them with stable ones, with
Carol relaying messages in this specific scenario. This leads
to a shadow area for Alice, in which the packet loss ratio canbe greater than 70%.
III. R ELATED WORKS
A. VANET routing protocols
Both Mobile Ad hoc Networking and Vehicular Ad hoc Networking work based on the same communication infrastruc-unexpected BEACON

unstableAlice

about 30% deliver ratio

Carolstableea
Shadow Ar

II. P ROBLEM STATEMENT
In this paper, we mainly focus on two types of reasons
which could cause packet loss on PBR-VANETs.

Bob
stablewith38
a pac0m<d<390
ket los s up m
to 70%

Fig. 3. The shadow problem

tures – IEEE 802.11 Wireless LAN. Nevertheless, comparing
to Mobile Ad hoc networks, VANETs have different resources
to be employed, different targets to be achieved, and different
problems to be solved.
The special requirements of VANET are majorly classified
into four categories: highly dynamic topology, scalability,
utilization GPS and sensors and adaption to different environments. To satisfy the requirements, many efforts have been
down to develop routing protocols for VANET. Some of theexisting protocols for MANET are adapted to VANET whilesome dedicated ones were proposed to address the special
challenges of VANET. [4] classified existing works of vehicleto-vehicle routing protocols, which includes topology based,
position based and other types.
Greedy Forwarding (GF) [5] is a simple protocol. In the
protocol, each node maintains a neighbor table by collecting
received beacons. Each neighbor table entry will time-out if
no more beacon is received over a period of time. Whena node needs to send a message to a node which is notdirectly reachable, it selects the neighbor who has the shortest
Euclidean distance towards the destination. If the neighbor is
not closer than the node itself, the algorithm fails and indicates
it comes to a local maximum. GF will fail if a concave routing
void exists between the node and destination.
Greedy Perimeter Stateless Routing (GPSR) [5] is an extended algorithm beyond GF, which could recover from local
maximum caused by a routing void. GPSR defined two working modes: one is Greedy Mode as referred above. The other isnamed perimeter mode, which is triggered when greedy mode
fails, which selects the neighbor using Right-hand Rule andhelp packet recover from local maximum.
Advanced Greedy Forwarding (AGF) [6] is an improvement
to GF. In the traditional GF protocol, the position of thedestination node in the packet is never updated. However in ahigh-speed movement scenario, during the packet traveling, thedestination node itself also travels a significant distance. AGF
could update the destination position information according topredictions by velocity given in packet. The experiment results
show a triple improvement to packet delivery ratio in certain
scenarios.
Greedy Traffic-Aware Routing (GyTAR) [7] is a junctionbased routine protocol, which means efficiently choosing
junctions which have a greater chance to meet and forward
to different nodes. Junctions are scored by equation Sj =

af (Tj ) + bg(Dj ) where Tj is the traffic density and Dj is the
distance to destination. The junction of the maximum score isselected, and the packet is forwarded to it.
Contention Based Forwarding (CBF) [8], [9] is a protocol
which does not employ neighbor information for geographicalrouting. Instead, the routing decision is made by the receiver
but not the sender. The receivers cooperate by a predefined distributed timer: the first timeout node rebroadcasts the message
which will suppress the others. CBF saves beacon consumption and also improves forwarding efficiency compared withflooding based approaches. However, it suffers from end-toend latency since a packet could only be forwarded when atimeout occurs on either receiver.
B. Multipath routing
Multipath routing is an idea to duplicate the packet and takemultiple paths for delivering. Multipath routing protocols are
discussed in Mobile ad-hoc Networks, as well as in other fields
like Wireless Sensor Networks, VoIP, and IPTV. According
to the motivation of the protocols, multipath routing protocol
could be classified into three types: reliable communication,
delay minimization, and load balancing.
Ad-hoc On-demand Multipath Distance Vector (AOMDV)[10] is an extension of AODV [11] with improved performances. When required, AOMDV selects multiple paths andensuring they are disjoint and loop-free. AOMDV can makeuse of existing information from underlying AODV protocol
to reduce probing overhead. AODV based multipath routing
protocols could not get rid of the drawback of AODV in
handling high-speed movements. Therefore, AODV could notbest fit the requirements of VANET.
Static-node-assisted Adaptive data Dissemination for
VANET (SADV) [12] is a multipath VANET routing protocol
which utilizes pre-deployed static infrastructures. In SADV, apacket is forwarded to static nodes when no vehicles on theroad could carry and forward the packet. The packet forwarded
to a static node waits until a vehicle comes and forward it.
SADV uses several different paths to forward the same packet
to ensure it is delivered in low latency. SADV could provide
multipath low latency communication. However, it relies on
pre-deployed infrastructures, which may not be practical on
all the roads.
C. GeoNetworking
GeoNetworking [1] is standardized by ETSI as a network
layer protocol as in Figure 1, integrating several position-based
routing strategies including Greedy Forwarding (GF) [5] (Alsoknown as GPSR), which chooses a directly reachable node
which is closest to the destination based on GPS location
obtained by Location Service(LS) request action, to route packets better in vehicular networks. Above the GeoNetworking,there are two different layers. One is Basic Transport Protocol(BTP) [13] which provides basic functions of the transportlayer to GeoNetworking, the other is GeoNetworking to IPv6
Adaptation Sub-Layer (GN6ASL) [14] to enable standard IPv6
over GeoNetworking. In GeoNetworking, three forwarding

modes are defined based on the destination in the geographic
scope (GeoUnicast, GeoBroadcast, and GeoAnycast), otherwise, there are two forwarding modes that does not use
location information: Topological Scope Broadcast (TSB) to
broadcast the packet within a specific hop away and Single
Hop Broadcast (SHB) to broadcast the packet within the 1 hop
neighbors. Packets destine the geographic scopes are deliveredby either GF [5] or CBF [8].
All the GeoNetworking nodes send beacons in a specificinterval, and the neighbor nodes maintain its latest geographical location in the location table (LocT) from the received
beacons. Other GeoNetworking packets delivered in the network contain the location of source (SO), sender (SE) anddestination (DE); in the case that the location information in
the packet is newer than the one in the location table, thelocation table is updated. Each location table entry (LocTE)
has a lifetime counter, and the entry is removed when it isreduced to 0. When the source node does not have locationof the designation in its location table, the node triggers the
Location Service (LS) request message in order to obtain thelocation of the destination. ETSI defines the flooding based
request-reply location service to get the destination location.
D. CarGeo6: user space GeoNetworking protocol stack implementation
More than fifteen software implementations of GeoNetworking join ETSI Plugtest that provides interoperability test
opportunity every year. In our best knowledge, only the
CarGeo6 project provides GeoNetworking implementation inopen source [15].
The GeoNetworking function and the BTP function are
implemented as daemons called itsnet and btpecho,
respectively in the CarGeo6 implementation as in the Figure 4.
In source node, btpecho (client mode) sends a BTP packet
via inter-process communication to itsnet. If the destination
location is in LocT, itsnet forwards the packet to next hop
selected by GF. Otherwise, it triggers an LS request. Finally,
when the BTP echo request is forwarded to the destination,itsnet send the packet to btpecho. On the other hand,
btpecho (reflector mode) in the destination node sends a
BTP echo reply back to the source once it received a request.
The echo reply is also forwarded by GF. Thus, the reply packet
may be delivered via a different route from the request packet.

SourceIntermediate nodebtpecho

Destinationbtpecho(Client mode)(Reflector mode)

itsnetitsnet
BTP echo request

Fig. 4. Overview of CarGeo6 programs

itsnetIV. D UPLICATED U NICAST PACKET E NCAPSULATION(DUPE) FOR G EO N ETWORKING
To solve the packet loss issue caused by topology change
and failure path, here we propose the Duplicated Unicast
Packet Encapsulation (DUPE), a standard compatible drop-in
encapsulation layer to the GeoNetworking standard architecture.
A. Requirements
Besides the problem, some additional requirements to theroutine protocols besides Packet Delivery Ratio should also be
considered.
1) No changes on GeoNetworking Standards: GeoNetworking is an essential part of ETSI standard ITS stationarchitecture, which presents in the Networking and Transport
Layer. GeoNetworking includes Network Layer and Transport
Layer protocols and auxiliary facilities as depicted in Figure 1,
while interfaces for interactive with different parts were also
defined. The protocol should work according to the standard
and do not require any extensions to GeoNetworking and otherparts of ITS station architecture.
2) No changes on user applications: In GeoNetworking
standard, several interfaces between GeoNetworking infrastructures and user applications were documented. In both parts,
numbers of existing software and hardware are available, built
by different developers. Maintain the compatibility with bothpart and require no changes to user application are essential
for the protocol of being widely used.
3) Deliver packets on-time: Cooperative ITS need realtime and on-time communication with other vehicles, to realize
safety by being aware of emergencies as soon as possible. Thus
in VANET, many applications are more strict in packet delivery ratio and maximum delay. For example information about
an accident happened on a highway should be immediately
delivered to the consequential automated vehicles on the road,since not all of them could be aware of the accident from theirview. Certainly, accidents could not be expected, and vehicles
could not prepare for them. Delivering the packet on time may
save passengers’ life.
4) Moderate resource consumption: The VANETs are
essentially wireless networks and obviously have a limitation
in bandwidth. In most cases, most of the nodes should havetransit traffic which forwarded by other vehicles. Moreover,many communications may happen simultaneously causing
more transit traffic; this could burden bandwidth of a single node furthermore. Nowadays, computing devices become
more powerful. VANET devices are not an exception. However, the resources still limited towards the scalability in
specific scenarios: CPU calculation power, memory limitation,etc. Both bandwidth and resource limitation should be better
considered in the design of the protocol.
5) Utilize alternative paths: According to issue analysis,
we know the issues causing packet loss in VANETs are
stale paths and unstable paths. Nevertheless, at the sametime, several different routing paths may exist, which are less
optimal to the problematic one but more stable. We call such

sub-optimal ones Alternative Paths (APs). The protocol should
select and utilize APs efficiently is also a consideration toreliable delivering.
B. Approaches
Three approaches were figured out to fix the issues andfit requirements for routing protocol. As the name of the
protocol, the approaches are: Duplicated, Unicast, Packet
Encapsulation.
1) Packet Encapsulation: In the proposal, GeoNetworking
packets (in Network Layer) are encapsulated into plain BTPB packets. BTP-B[14] is a standard transport layer protocol
defined in GeoNetworking standards, thus the DUPE packet
could be processed normally in nodes, which satisfies therequirement defined in Section IV-A1 (no changes on GeoNetworking Standards). The packets in capsules (a.k.a. payload)
are also GeoNetworking packets and could be processed either
by the original GeoNetworking protocol handler (depends
on implementation) or a separated daemon providing thesame interface (i.e. GN SAP[16]). The implementation should
provide all the functionalities of GN SAP interface, in orderto maintain the compatibility with 3rd-party user programs.
This satisfies the requirement in Section IV-A2 (no changes
on user applications).
2) Duplicate the packet: The main issue to be solvedby the protocol is packet loss. According to analysis, weknow that packet loss of VANETs could be caused by two
reasons: stale path and unstable path. Nevertheless, when theselected greedy path is stale or unstable, several alternative
paths may also exist and could be more viable comparing to
the selected ones. Thus, we decided to duplicate the packets
in such cases, to utilize alternative paths (the requirementin Section IV-A5). The duplication of packets could also
ensure that the requirement defined in Section IV-A3(on-timepacket delivery) while timeout based approaches e.g. CBF or
retransmission could increase packet latency.
3) Limited duplication using one hop GeoUnicast:
One hop GeoUnicast[1] was employed to limit the numberof duplication of a packet. The routing decisions are handled by DUPE, to bypass the routing selection in standard
GeoNetworking layer, which could result in failing routing
path. For each packet, DUPE selects several (depends on thesignificance of message, usually 2 or 3) next hop candidates
and forward the DUPE packet by encapsulating it into one
hop GeoUnicast, which means packet should directly send
to next hop. Numbers of next hops were limited by DUPE
to reduce bandwidth overhead, to meet the requirement of in
Section IV-A4 (moderate resource consumption).
C. System overview
In GeoNetworking protocol stack, DUPE works between
GeoNetworking layer and Transport layer, as depicted in Figure 5. DUPE encapsulation layer (with inner GeoNetworking
layer) is an optional layer in the protocol stack, so user
programs could either employ DUPE to achieve better packet

Original

S ource

Proposed

Intermediate 1

D estination

D UPE
BTP
GN

BTP
GN
D UPE
BTP
GN

BTP
GN

User Application

D UPE
BTP
GN

Intermediate 2

Transport Layer (BTP/GN6/etc)
GN-SAP

Encapsulated
GN Layer

D UPE
BTP
GN

DUPE-BTP
Encapsulated Layer

Fig. 6. DUPE packet flow

GN-SAP

GN-SAPGN Layer
Network Socket

MAC/PHY Layer (IEEE802.11p)

will duplicate the message to B and C. Although the message
from C to F is lost, but B will pass on the message forward in
the manner like the Figure 7(b) shows. Each node duplicatesthe message to best N next hops, here in Figure 7(b) the Nequals 2.

Fig. 5. GeoNetworking protocol stack and DUPE encapsulation layer
FF

delivery ratio or come to ordinary GeoNetworking packet tosave bandwidth.
The typical packet flow of DUPE is depicted in Figure 6.
Firstly, a Basic Transportation Protocol (BTP) packet (which
scope is GeoUnicast (GUC)) is generated by user application
at Source node. The packet is required to be DUPE encapsulated, so it is prepended a DUPE header and becomes DUPE
packet. DUPE processor selects two different intermediate
nodes as candidates of next hops among its neighbors, andsend the DUPE packet as payload of a BTP packet to them
one by one.
The outer BTP packet is processed by standard GeoNetworking as a regular one and eventually reaches an intermediate node. The DUPE processor on Intermediate node 1
decapsulates the packet, checks destination of the encapsulated
packet and found it should be forwarded. Therefore, theprocessor encapsulates it into a new BTP packet, sets thedestination of the outer packet to the real Destination node,and emits the packet. The DUPE processor on Intermediate
node 2 does the same thing, thus both packets from them cometo Destination node.
The DUPE processor on Destination node decapsulates thefirst packet, found the destination matches local address, andsend to the user application which should handle it. The second
packet from the other Intermediate node is dropped by the
DUPE processor to make sure user application receives only
one copy of the packet.
Figure 7 shows how DUPE works in a network with obstacles, where standard GeoNetworking comes to a failure. When
A tries to send a message to F, with standard GeoNetworking,as show in Figure 7(a), he will firstly send the message to C
to let it relay. But the obstacle between C and F makes themessage lost. When DUPE is adopted, as in Figure 7(b), A

obstacle

obstacle
C

C

H

H
E

A

E

A

G

B

G

B
D

D

(a) GeoNetworking(b) DUPE

Fig. 7. How DUPE dealing with obstacle

D. Implementation details
Because DUPE is designed as a drop-in layer, we implemented it as a separated daemon duped. Duped communicates with both sides (itsnetd and user programs)
using libgnsap provided by CarGeo6. It handles information
through the standard SAPs defined by GeoNetworking andprovides the same interfaces to the upper layer. In the duped,tasks are divided into different modules, which is shown in
Figure 8. Output module receives packet request from theuser programs, encapsulates it into BTP packet and deliverit. Input module receives BTP packet from the lower layer,
decapsulates it and notify the user program from GN SAP
interface. Deliver module duplicates the packet, select best
next hops from candidates for each ones, and then send them tolower layer. Location module handles the location information
used by different modules.
V. E VALUATION
A. Experiment setup
In this paper, we conduct the experiments within the Combined Realistic Evaluation Workflow (CREW) [3]. The workflow contains three steps: experimentation, reproduction andextension. First, the experimental evaluations are conducted inGN MGMT SAP Client

GN SAP Client

GN MGMT SAP

GN SAP

Input Module

TABLE IS IMULATOR SYSTEM CONFIGURATION

user
program

duped

Output Module

Location Module

Deliver Module

Interface Module

GN MGMT SAP Client

PacketbufferItem

Specification

Simulator
Radio Frequency
Wi-Fi Phy
Wi-Fi Mac
Receiver Gain
Propagation Delay
Propagation Loss
Node Mobility Model

NS3-DCE
5900 MHzERP-OFDM, 6 Mbps
Ad-Hoc-10 dBi
Constant
Friis
StaticGN SAP Client

B. Evaluation scenarios
itsnetd

GN SAP

GN MGMT SAP

Fig. 8. Module diagram of duped and interactive with itsnet

the real testbed, and the results are collected. Next, the sameevaluations with the same hardware environments and software
implementations are reproduced in the simulated networks. We
tune the hardware and software parameters of the simulation
environment in order to calibrate the simulator using the results
produced in the last step. Last, we extend the experiments
in different scenarios and larger networks in the calibrated
simulated environment, to produce realistic simulated results
in a low cost.
In the experiment, we make a horizontal comparison between DUPE based software stack and original CarGeo6 onesin the same environment and scenarios. On the side of thereal testbed, the programs ran on 4 ARM boxes. Mac filters
were applied to each node, to limit the neighbor that it could
communicate with adjacent nodes only, achieving an up to 3
hop topology as depicted in Figure 9. In simulation, we use alinear topology which is shown in the Figure 9: all nodes are
configured with the same Wi-Fi parameters, and kept in thesame Ad-Hoc cell; each node is in a line with 300m distanceto adjacent nodes. The wireless radio range is adjusted to 300400 meters. That means nearly all packets in 300m range canbe delivered, yet almost all packets from 400m away were
lost.

1 hop

2 hop

d=300mNode 03 hop

d=300mNode 1d=300mNode 2

Node 3

Node N

m
00

<4

<R
0m

30

Fig. 9. Topology of 300m distance (achieved by mac filter)

The detailed system configuration of the simulator is depicted in Table I.

In the experiment, we vary node distances, packet sizes,
and number of hops. We define Neighbor distance (ND) as
the distance between adjacent nodes, Terminal Distance (TD)as the distance between destination and source nodes.
The first experiment we conducted is different ND and TDs.
We measure 1000 round trip packets of btpecho between thefirst and last nodes, with fixed ND = 300 m and TD varied
from 300 to 3000 meters.
The second experiment is about the shadow problem which
is described in Section II-B. The ND is fixed to 100 meters,with varied TDs to make the shadow problem happen between
different hops. The Network topology of the experiment is
depicted in Figure 10.
Shad

190m

A

rea

ow A

Shad

rea

ow A

190m

B

C

D

E

F

Fig. 10. Chain of shadow areas in 190 meter tests

C. Evaluation results
In the experiments, we evaluate the packet delivery fromend to end. These three metrics are considered, prioritizedfrom top to bottom.
1) Packet delivery ratio (PDR): PDR is the basic metricto measure the quality of a network link. Packet delivery is
the most important requirement in VANETs even rather thanlatency. Thus, it is the most direct evaluation metric to measure
the quality of DUPE.
Figure 11 shows the comparison of PDR of DUPE and
CarGeo6 under different ND and TDs. It suggests that DUPE
can persist high PDR while CarGeo6 is unstable in long
distance.
Especially, when the TD is 190 meters, which leads to a
scenario conducting the shadow problem, as we have discussed
in Section II-B. Remind the topology (Figure 10) we use inthis scenario. When A sends a message to F, it will firstly
let C to relay the message, then C chooses E to relay themessage to F. The Shadow Area seriously affects the PDRof messages from A to C, and messages from C to E. The

Packet Delivery Ratio (%)

and get rid of packet loss caused by congestion or wirelessinterference. Transmission cost of program p (T Cp ) is given
by Equation 1, where Ti refers to GeoNetworking packet
transmitted on node i, N Tp refers to total transmitted packets
of program p, and N Dp denotes number of packet successfully
delivered.
∑
N Tpi∈N odesp Ti
T Cp =
=
(1)
N dp
N Dp

100
80
60
40
20
0

Original ND=100
Original ND=190
0

100

200

Proposed ND=100
Proposed ND=190

300

400

500

600

700

800

900 1000

Terminal Distance(m)Fig. 11. Comparison of Packet Delivery Ratio in 100 meters and the shadow
scenariosuperimposition of packet losses results in about 5.5% of PDR,
when the terminal distance is greater than 780 meters in this
scenario. Meanwhile, the PDR of DUPE remains constantly
high in contrast.
2) Round-trip time (RTT): RTT is also an important
metric in network communication. In VANET, the maximum
latency is more important because of the on-time delivery
constraint from the applications.

Round-Trip Time (ms)25

Original ND=100
Original ND=300

Proposed ND=100
Proposed ND=300

20
15
10
5
0

0

100

200

300

400

500

600

700

800

900 1000

Terminal Distance(m)Fig. 12. Minimum-average-maximum round-trip Time

Figure 12 shows the minimum-average-max round trip timeof DUPE in different ND and TD.
When N D = 300 m, both average and maximum RTTs
show a tendency of linear growth on hop count. However,both of them are slower than the original CarGeo6 becauseof additional packet processing. When N D = 100 m, bothaverage and maximum RTTs are notably higher than same
T D of N D = 300 m. This is possibly due to additional
packet processing and interference caused by multiple timetransmissions. A deeper profiling and analysis should be done
to locate the specific reasons leads to extra latency. Although
DUPE introduced some overhead in packet processing, themaximum RTT is reasonable: around 22 miliseconds in 1000m experiment.
3) Transmission cost (TC): TC denotes totally how many
packets are transmitted to deliver one packet of data successfully from end to end, includes lost ones and unused ones.
Reduce transmission cost could save bandwidth consumption

Transmission cost

128

Original ND=100
Original ND=300

64

Proposed ND=100
Proposed ND=300

32
16
8
4
2
1

0

100

200

300

400

500

600

700

800

900 1000

Terminal Distance(m)Fig. 13. Transmission cost of DUPE and CarGeo6

Figure 13 shows TC of DUPE compare with CarGeo6, in
100 meter experiments, with different TD.
In the experiments, we evaluate T CDU P E divided by
T CCarGeo6 , which means how many times of overhead DUPE
is committed over the original CarGeo6.
In N D = 300 m experiments, the TC of DUPE and
CarGeo6 are almost the same, suggests the transmission of
DUPE in this scenario is minimal. The reason is the nodes
are sparse, and each one could only connect to two neighbors:
receive from one of them, and send to another.
While in N D = 100 m, the results varies by T D. WhenT D = 100 m, which means only two vehicles in the test, TC
is also the same. The reason is as same as N D = 300 m.
When T D = 300 m, DUPE is high because of backward
propagations, which means to forward packets to the node
which is farther than the node itself. If backward propagation
is disabled, the overhead could be reduced to around 2 times.
When T D >= 400 m, the PDR reduces, which means
many transmissions is wasted because of packet loss. Thus,
the overhead reduced again to less than 2, suggests it coulddeliver packet more efficiently.
VI. C ONCLUSION AND FUTURE WORKITS is a technique to realize safe, efficient and comfortable
driving experiences. VANET is a technique for direct intervehicular communication, which is essential for ITS. However
current a widely deployed VANET standard, which is GeoNetworking, faces the serious packet loss problem in dynamic
topology. The packet loss problem must be solved because it
could render safety related applications completely useless.
In this paper, we proposed the Duplicated Unicast Packet
Encapsulation (DUPE) protocol to enable reliable real-timecommunication among vehicles for VANETs.

DUPE was evaluated on CREW, suggesting that packet
loss in different scenarios can be successfully eliminated,
especially in the shadow problem and the overtake problem.
The main features of DUPE are:
1) Reliable
Experiments about DUPE shows it eliminated packet loss
in both the shadow scenario and the Overtake scenario.
Among them, CREW evaluation indicates in the worse
case of the shadow scenario, could increase end to end
Packet delivery Ratio from 5.5% to nearly 100%. These
two simple and typical scenarios are likely to happen
in the real VANETs. Generally, DUPE could increase
the packet delivery ratio (PDR), leads to a more reliablecommunication channel.
2) Independent
DUPE is designed to maintain independence in different
sense: DUPE does not require modifications on GeoNetworking infrastructures; DUPE does not require modifications on user applications; DUPE does not require digitalmaps present on Nodes.
3) Efficient
DUPE has a reasonable processing and duplicated transmission overhead. In short distance and dense traffic situations, DUPE performed well which means overhead
is moderate. In long distance or sparse traffic scenarios,
DUPE has a large duplication overhead; however DUPE
could drastically increase PDR which makes most sense.
Due to time limitation of the master course, not all works
were included in the paper. In the future, several directions
are considered, while some of them are working in progress.
From the experiments and analysis, we know packet transmission cost of DUPE could be high in certain scenarios. To
reduce Transmission Cost, mechanisms such as single hop
broadcasting or adaptive duplication count could be considered. Such techniques may adjust according to communication
distance and traffic density, to balance PDR with transmission
overhead.
Currently, middleboxes (i.e. the nodes which did not run
duped) could not be detected. For this issue, we need to
introduce some mechanism to detect the middlebox. A reactive
method could make sense because the status of “running” or“not-running” duped on a node may not change frequently.
Another method of combining it with Multiple Hop Broadcast(MHB) is also considerable.
In this work, we start the DUPE based on GeoNetworking
and GF algorithm, yet actually, it could be considered in any
other beacon based position routing protocols. In the future,
we could adapt DUPE to other protocols. Moreover, if theunderlying protocol could provide more information e.g. speed
and heading information of vehicles or digital maps, moreadvanced routing selection could be employed in DUPE.
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