=Paper=
{{Paper
|id=Vol-1543/p7
|storemode=property
|title=Adaptive VPN Bonding Technique for Enhancing Dual-SIM Mobile Internet Access
|pdfUrl=https://ceur-ws.org/Vol-1543/p7.pdf
|volume=Vol-1543
|authors=Francesco Beritelli,Aurelio La Corte,Grazia Lo Sciuto,Corrado Rametta,Francesco Scaglione
|dblpUrl=https://dblp.org/rec/conf/system/BeritelliCSRS15
}}
==Adaptive VPN Bonding Technique for Enhancing Dual-SIM Mobile Internet Access==
https://ceur-ws.org/Vol-1543/p7.pdf
Adaptive VPN Bonding Technique for Enhancing
Dual-SIM Mobile Internet Access
Francesco Beritelli∗ , Aurelio La Corte∗ , Grazia Lo Sciuto‡ , Corrado Rametta∗ , Francesco Scaglione∗
∗ Dep. of Electrical, Electronics and Informatics Engineering, University of Catania, Italy
‡ Department of Engineering, Roma Tre University, Italy
Abstract—Mobile Internet access networks are not designed and a remote command and control and/or monitoring node. As
to support real-time data traffic because of several drawbacks to the costs/benefits balance, the proposed method on the one
concerning the wireless medium such as resource sharing, traffic hand requires a dual RF module, but on the other hand it is also
congestion, radio link coverage etc., which impact directly such true that nowadays HSPA or LTE modems have become very
parameters as delay, jitter, and packet loss rate that are strictly cheap and common and there are a lot of free and open source
connected to the quality of user experience. While in a fixed
operative systems allowing the implementation of advanced
network scenario the gap is reduced arbitrarily by an appropriate
dimensioning of the characteristics of ADSL access in terms of networking functions such as load balancing techniques, VPN
guaranteed minimum bandwidth or MCR (minimum cell rate), creation and bonding, network performance evaluation and so
in a cellular network scenario the quality of service over IP is on.
greatly reduced due to strong current limitations in terms of the The paper is structured as follows: Section II describes
requirements regarding delay and guaranteed bandwidth that the possible applications and contexts where the proposed
cannot be arbitrarily decided. The main scope of the present approach can offer considerable benefits in terms of reliability
paper is to introduce a dual USIM HSPA access point thanks to and efficiency and gives an overview on the overall system;
which it will be possible to guarantee a QoS suitable for a series Section III presents the end-to-end bandwidth measurement al-
of network-centric application such as real-time communications gorithm and the adaptive weight assignment procedure; Section
and monitoring, video surveillance, real-time sensor networks,
IV reports the performance results of a real test bed; finally,
telemedicine, vehicular and mobile sensor networks and so on.
The main idea is to exploit multiple radio access networks in in Section V conclusions are drawn.
order to enhance the available end-to-end bandwidth and the
perceived quality of experience. The scope has been reached by
combining multiple radio access with dynamic load balancing II. S CENARIO
and the VPN bond technique.
Wireless sensor networks and internet of things have be-
come very commonly used technologies enabling a large num-
I. I NTRODUCTION
ber of applications and services in everyday life. Usually the
The rapid and continuous consolidation of Mobile Inter- architecture of the above cited networks is based on a certain
net access request together with the significant increase of number of sensors and devices that communicate among them
mobile services provided by third and fourth generation (3G, and towards a critical device called sink that has the scope
HSPA, LTE) networks, have recently created the conditions of collecting data from the devices for monitoring, control,
for a considerable expansion of mobile IP applications and statistics, etc. Often the sink is designed to communicate via
services. Mobile IP networks are not designed to support real- Internet to a remote command and control position where a
time and/or time-critical traffic because of several drawbacks user can operate over the network. With this scope, the sink
concerning the wireless medium [1]: resource sharing, traffic provides the functionality of gateway with the external IP
congestion, radio link coverage etc., which impact directly world. Regarding this aspect, the gateway is equipped with
such parameters as delay, jitter, and packet losses. These are Ethernet, wifi, or 3G/4G interfaces in order to communicate
the main causes of quality degradation of numerous services with the IP world according to the applicative scenario for
over the PSTN. In recent works the authors have introduced which the ad hoc network has been conceived. In particular,
a dual streaming (or packet duplication) approach to mitigate when the sensor network or the IoT network are deployed for
the degradation of speech quality [2] in a scenario of dual-SIM command and/or control, monitoring, surveillance or similar
VoIP services over 3G-HSPA [3], [4]. use in mobile or vehicular contexts and a fixed wide area
In the present paper, the authors propose a multiple SIM network connection is not available, it is mandatory to provide
Access Point exploiting VPNs bond of two cellular radio a stable, reliable and effective wireless connection towards
access connections coupled with an adaptive load balancing the remote server in order to guarantee the required QoS
algorithm based on real time evaluation of the available end- for time-critical and real time applications (see e.g. highly
to-end bandwidth offered by two different network operators. computationally costly applications [5]–[12], or distributed
The authors propose a trivial prototype in order to evaluate services [13]).
the effectiveness of the proposed solution in terms of the With this aim the authors propose a Dual SIM 3G/4G
enhancement of both the instantaneous available bandwidth wireless access point that acts as the sink for the sensor
and connection availability between the mobile access point network and, at the same time, acts as gateway towards the IP
core network. To guarantee QoS for time critical and real time
Copyright c 2016 held by the authors. applications, the proposed device offers two main features:
47
Fig. 2. VPNs bond architecture.
Fig. 1. Scenario overview.
two connections and the perceived end-to-end bandwidth is
equal to the one offered by the best network operator. Instead,
1) a VPN bonding between the two radio access the use of the VPNs bond technique permits to enhance the
connections, thanks to which it is possible to obtain available end-to-end bandwidth also in the case of only one
a bandwidth almost equal to the sum of the two data flow from the source node, i.e. the gateway of the ad hoc
available end-to-end bandwidths; network, and the destination, i.e. the remote command and
control position.
2) a dynamic load balancing algorithm, which is a The VPNs bonding consists in unifying two or more layer
process that establishes the weights the device gives 2 connections in order to be able to assign to one data flow a
to the two different radio connections during the bandwidth ideally equal to the sum of the bandwidth offered
movement of the mobile sink/gateway on the base by single L2 connections. This technique is well known and
of the instantaneous available end-to-end bandwidth widely employed in the field of Ethernet switches where it is
offered by the two different network operators. possible to unify two or more L2 interfaces to guarantee a
larger point-to-point bandwidth in the core network.
It has been observed that in this first phase of the present In the present use case, the procedure consists in the
research the weights are established in order to maximize the creation of a VPN between each 3G/4G interface and the
cumulative bandwidth but as a future work the authors will end point of the communication, i.e. the remote server. Once
implement a more complex algorithm able to dynamically established the two VPNs it is possible to make the bonding
calculate the VPN weights based on the traffic typology (voice, of the latter in order to establish a large bandwidth connection
file transfer, best effort, etc.) and the related parameters that between source and destination nodes (see fig. 2). Usually the
directly impact on the quality of experience of the end user VPNs bond technique is coupled with a trivial load balancing
willing to use the service. algorithm that consists in assigning static and equal weights
to each L2 connection.
III. A RCHITECTURE AT A G LANCE In case of L2 switches or DSL modem/routers this ap-
proach represents a good solution because the network con-
The smart gateway proposed by the authors is based on ditions are similar for each interface and they remain almost
a well-known technique called VPNs bond, usually employed constant in time. Let us suppose that the two available con-
in the Ethernet switch and extended to the cellular domain nections provide a bandwidth equal to 2 Mbps; in such a case
to counteract some drawbacks connected to the radio access a trivial load balancer will assign weights equal to 1 to each
technology. Due to the application of VPNs bond it is possible connection and the system will provide a bandwidth equal to
to balance the data load among the available network interfaces 4 Mbps.
but, for the sake of clarity, it should be highlighted that this Now, supposing that at a time t the connection number 1
technique is much more flexible if compared to the common provides a bandwidth equal to 2 Mbps whereas the connection
load balancing algorithms; in fact, the latter permit to split number 2 offers a bandwidth equal to 1 Mbps. Under this
the data connection between the source and the destination by condition, if the load balancing algorithm maintains constant
using the available connections and according to the weights weights, by using a simple round robin mechanism, the con-
assigned to each interface. In such a way, the effectiveness of nection 2 will represent a bottleneck for the system because
the mechanism is obtained only when there are more than one the overall available end-to-end bandwidth will not be equal
end-to-end connection between the sender and the receiver. to the sum of the two bandwidths but it will be equal to twice
In case there is only a data flow towards the remote server, that of the worst connection.
load balancing permits to assign the data stream to one of the In a wireless scenario characterized by the high variability
48
Fig. 4. One way delay values of the ith packet train in the SLoPS technique
Fig. 3. The prototype employed for our test bed.
IV. A DAPTIVE W EIGTH A SSIGNEMENT
of radio coverage, different traffic conditions, handover proce- The proposed algorithm can be summarized in three steps:
dures, and mobility, each radio interface equipped with the
1) Bandwidth measuremet for each available radio data
related SIM - performs according to the infrastructure and the
connection;
load conditions set by its operator. Under these conditions, a
static weights assignment would result in a drastic reduction
2) Results analysis and weight evaluation to establish
in performance where the worst connection would act as a
and set up the VPN bond parameters;
bottleneck for the whole system. With the aim of overcoming
this limit, the authors propose a mechanism of real time
3) Periodic performance evaluation to determinate the
bandwidth evaluation to establish each time and for each L2
most suitable weight for each mobile connection.
connection the weights to assign to the VPNs bond, thus
maximizing the transmission rate towards the destination node. As to the first step, i.e. the end-to-end bandwidth evalua-
In the next sections the adaptive load balancing algorithm tion, it is carried out via the Self Loading of Periodic Streams
will be described and the first performance evaluation of a (SloPS) technique [17]–[19]. The latter is based on a client-
trivial prototype will be presented. server application: the sender process runs on the multi-SIM
access point whereas the receiver process runs on a remote
host, which, in the present architecture, is the remote gathering
A. Description of the prototype node of the sensor data network.
The above mentioned architecture is suitable in case the
To prove the effectiveness of our proposal we realized mobile hot spot has to send data towards a remote sink
a prototype by using a small form factor system boards collecting sensor data; however, if the time-critical application
optimized for wireless routing and network applications, is based on the transmission from the remote host to the mobile
an ALIX2D2 board [14], equipped with a 500 MHz AMD network the upload bandwith will be taken into consideration.
Geode LX800 CPU and 256 MB DDR DRAM on board; The working principle of the Self Loading of Periodic
two USB Internet keys have been used to provide cellular Streams is very simple: it is based on the periodic transmission
connectivity and the two devices have been equipped with of packet streams from the source to the destination and on the
two SIMs of two different network operators, that we will consequent measure of the One Way Delay (OWD), which is
define as Operator 1 and Operator 2 in the following sections; the time interval between the transmission of the data packet
ZeroShell [15] and OpenVPN [16] has been used as operative and its reception at the receiver side.
system and VPN manager respectively, whereas proprietary The number of packets transmitted increases until the
scripts has been realized by using bash and python language growing one way delay; when this happens it means that the
to evaluate the available end-to-end bandwidth between the packet transmission rate is greater than the available bandwidth
couples source-destination and, consequently, to establish the provided by the radio access network. Fig. 4 shows the
weights to assign to each VPN in order to maximize the above mentioned procedure: when the transmission rate (R) is
overall performance of the prototype. compatible with the available bandwidth (A), i.e. R < A, the
For the aim of clarity, the same hardware and software one way delay shows an almost constant trend; however, when
have been employed to evaluate the performance of the the packet rate from the source to the destination is greater
standard static weights assignment procedure without using, than the available bandwidth, i.e. R > A, the one way delay
obviously, the scripts for the dynamic evaluation of the VPN increases because of the TCP congestion window mechanism.
weights. A picture of the hardware employed to realize our The measurement is obtained by the iterative sending of
prototype is shown in fig. 3. a series of K packets of L bit each of which is transmitted
during an interval of T seconds. In such a way the transmission
49
Fig. 5.
Countryside route of the test bed.
rate is equal to R = L/T [bit/s]. Each packet of the series 3) The iterative process ends when (Rmax −Rmin ) < w,
has a timestamp to indicate when the data packet has been where w indicates the value depending on the pre-
created and sent to the receiver node. Once the destination node cision of the bandwidth evaluation procedure (obvi-
receives the packets stream it compares the arrival time (Ai ) ously, the greater the w the less accurate evaluation
and the sending time (Si ) of the packets in order to calculate but, at the same time, the faster the convergence
the one way delay of the ith stream, i.e. Di = Ai Si . period required by the algorithm).
The sender and the receiver communicate according to
the client-server paradigm in order to establish the available The above mentioned algorithm runs for each radio access
bandwidth. When the one way delay at the destination side connection and converges to the actually available end-to-end
increases, in fact, the receiver process notifies the sender that bandwidth. When the process ends, the bandwidth values are
behaves as follows: communicated to the adaptive load balancing process that
updates the VPNs bond weights as follows:
a If R(i) < A, the source process will send the a the VPN weight of the worst connection is set equal
following packets stream at R(i + 1) > R(i); to 1;
b If R(i) > A, the source process will send the b the VPN weight of the best connection is set equal
following packets stream at R(i + 1) < R(i); to Abetter /Aworst ;
Furthermore, the rate of the stream (i + 1) is established as in case the bandwidth offered by one of the two operators is
follows [10]: equal to 0, e.g. because of a lack of radio coverage, the whole
traffic is routed to the active connection.
1) Two start parameters, Rmin ed Rmax , are initial-
ized equal to zero and equal to the ideal maximum V. P ERFORMANCE EVALUATION
throughput provided by the connection Rmax ;
In the above sections some problems have been illustrated
o If R(i) < A then Rmin = R(i); that arise when a mobile wireless sensor networks have to be
o If R(i) > A then Rmax = R(i); connected to a remote command and control server by using
the public 3G or 4G radio network.
2) R(i + 1) = (Rmax − Rmin )/2; In order to overcome such drawbacks as connection inter-
ruption, lack of bandwidth, delay in performance, jitter and
50
Fig. 6. Throughput comparison Single operators and static bond.
Fig. 8. Static scheme vs. Adaptive scheme.
first part of the test bed the two network operators have similar
performances in terms of available end-to-end bandwidth; in
the second part the Operator 2 performs better that the Operator
1.
When the first case appears both static and adaptive
bonding perform well outperforming the performance of the
two single operators; static and adaptive approaches show
almost the same behavior. When the second case appears, the
performance of the static bonding mechanism is drastically
worse than the proposed adaptive approach and, furthermore,
the VPNs bonding provides an end-to-end bandwidth lower
than the one offered by the best single network operator, in
such a case the Operator 2.
More in detail, during the sink movement the network
Fig. 7. Throughput comparison Single operators and adaptive bond. operator 2 delivers better performance respect with the network
operator 1. In such a case, the VPNs bond and the static load
balancing algorithm does not perform as expected and the
packet loss rate not compatible with time critical applications, dual SIM gateway behaves similarly to the worst of the two
a smart dual SIM sink/gateway based on multiple radio ac- network operators (the throughput should be double the worst
cess, VPN bonding and adaptive load balancing between the connection but the overhead due to the establishment of the two
available connections is proposed. VPNs, i.e. the overhead related to the establishment of SSH
The present section will prove the effectiveness of the tunnel among the two radio network interfaces and the remote
proposed solution showing the results obtained during our test server, drastically reduces the effective available bandwidth.);
bed. We performed two campaigns of simulation, the first has in fact, the load balancing algorithm splits into two equal flows
been realized in a countryside scenario as shown in fig. 5, the original one, assigning to each connection the amount of
the second has been realized by moving the prototype in an data to transmit equal to the available bandwidth offered by
urban scenario as shown in fig. 10; for each test bed 15 data the worst operator, the latter representing, the bottleneck of the
transfers from the mobile sink/gateway to the remote C2 have system. In such a case, the VPN bond coupled with the static
been performed; during the test bed it has been evaluated: load balancing does not offer any performance enhancement
because of the incorrect assignment of bond weights.
- the throughput for each cellular operator; Fig. 7 indicates the results obtained by the proposed
cellular bonding prototype with the use of the adaptive load
- the throughput obtained by using the dual SIMs balancing algorithm in order to counteract the drawbacks
VPNs bonding with static weights assignment; related to the variability of the end-to-end bandwidth offered
by each radio operator during the movement of the mobile
- the throughput obtained by using the bond of the two sink/gateway. The mobile sink/gateway was moved following
VPNs coupled with the adaptive weights assignment the same route. It clearly appears that the cellular bonding
and load balancing. almost always outperforms the best cellular operator; however,
when this does not happen it is due to the convergence time
In fig. 6 and fig. 7, referring to the static and the adaptive of the adaptive weights algorithms. Also, this case highlights
weights assignment respectively in the extra-urban scenario, it that the final end-to-end bandwidth is not equal to the sum of
is possible to notice that two different conditions appear: in the all bandwidths because of the presence of the overhead due to
51
Fig. 10.
Urban route of the test bed.
weights assignment respectively in the urban scenario, it is
possible to notice that three different conditions appear: in the
first part of the test bed one of the two operator goes down
because of lack of radio coverage or network congestion; in
the second phase Operator 1 and Operator 2 have almost the
same performance, and the same condition appear at the end
of the test bed; in the third phase of the test bed Operator 1
performs better than Operator 2.
When the first condition appear, the use of the VPNs
bond technique and the use of two or more network accesses
guarantees a seamless connectivity between the source and the
destination if compared to the use of only one radio interface.
More in detail when one of the two operators goes down the
VPNs bond performs as the only working operator and the
prototype behaves every time like a common single stream
device equipped with the USIM belonging to the best network
operator, i.e. the operator offering the best connectivity at the
Fig. 9. Average end-to-end bandwidth comparison.
given time.
Static and adaptive approaches behaves in the same manner
and the performance delivered by the VPN bond coupled with
the implementation of the VPNs and their bonding.
the static load balancing between the two available connections
In the fig. 8 the behaviour of static and dynamic weights
is satisfactory in the above mentioned scenarios; however,
is presented, whereas in the fig. 9 the average end-to-end
when the performances of the two radio access networks are
bandwidths of the two schemes and of the single operators
different the adaptive scheme appropriately adjust the weights
are compared. As we can see, the VPNs bond with adaptive
assigned to the VPNs (see fig. 13) and it outperforms the static
weights assignment outperforms the static assignment scheme
one as shown in fig. 14. Finally, when the available bandwidth
by almost 60% showing the effectiveness of the proposed solu-
offered by each operator is almost equal, the adaptive scheme
tion in vehicular applications such as telemedicine, telemetry,
converges to the static one assigning the same weight to
remote command and control, etc...
the two connections and the two approaches show equal
In fig. 11 and fig. 12, referring to the static and the adaptive
52
Fig. 11. Throughput comparison Static scheme.
Fig. 13. Weights assigned to each VPN by the Adaptive scheme.
Fig. 12. Throughput comparison Adaptive scheme.
Fig. 14. Static scheme vs. Adaptive scheme.
performance. Under this condition, the dynamic assignment of the weight
to each connection of the VPN bonding plays a key role in
exploiting the best connection available at the given time.
VI. C ONCLUSION Performance evaluation of the prototype shows the effective-
The present paper proposes a dynamic VPNs bonding and ness of our approach in terms of instantaneous throughput.
load balancing techniques between two or more available radio Considering the future work, the authors of the present paper
access connections. are currently working on a device that is able to calculate the
dynamic weights of the load balancing algorithm based on the
kind of data traffic the sink/gateway has to transmit or receive
The approach is based on a smart gateway and the typical from the remote command and control station.
scenario is based on the following applications: mobile wire-
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