=Paper= {{Paper |id=Vol-2300/Paper24 |storemode=property |title=On TCP-Induced Telehaptic Packet Loss and Jitter |pdfUrl=https://ceur-ws.org/Vol-2300/Paper24.pdf |volume=Vol-2300 |authors=Vineet Gokhale,Jan Fesl |dblpUrl=https://dblp.org/rec/conf/acit4/GokhaleF18 }} ==On TCP-Induced Telehaptic Packet Loss and Jitter== https://ceur-ws.org/Vol-2300/Paper24.pdf

On TCP-Induced Telehaptic Packet Loss and Jitter
Vineet Gokhale, Jan Fesl
Institute of Applied Informatics, University of South Bohemia, CZECH REPUBLIC, emails: {vgokhale, jfesl}@prf.jcu.cz

Abstract: Telehaptic data communication (transmission telemanipulator with the feeling of touching the patient’s body
of touch signals) is known to be extremely sensitive to [1]. Telehaptic communication finds potential applications in
packet loss and jitter, the primary consequences of a wide variety of other domains as well, like telemaintenance,
network congestion. Existing studies have established the and remote disaster management to name a few.
Quality of Service (QoS) conditions that need to be Figure 1 depicts a typical telehaptic communication
guaranteed for smooth telehaptic communication. framework over a shared network. The human operator (OP),
Specifically, the telehaptic communication can tolerate no using the force, audio, and video feedback from the remote
more than 10% packet loss and 10 ms jitter. In this paper, environment, makes certain movements in an attempt to
we conduct a detailed investigation of the impact of TCP interact with and/or manipulate a remote physical object. The
cross-traffic (pre-dominant traffic on shared networks) on position and velocity signals thus generated are transmitted to
telehaptic packet loss and jitter. The important the remote environment via the forward channel. The robotic
contribution of our study is twofold. Firstly, we discover teleoperator (TOP) at the remote location utilizes these
that even during scenarios where the long term average coordinates in order to replicate OP’s movements accurately.
packet loss is comfortably below its QoS limit, the Any contact between the remote object and the TOP generates
instantaneous loss can far exceed this limit. Secondly, we forces, which are transmitted back to the OP along with audio
demonstrate that the probability of jitter QoS violation and video feedback on the backward channel. The presence of
increases with the number of concurrent TCP sources in haptic feedback has been shown to increase the immersion into
the network. These effects could potentially be harmful to the remote environment, and further improve the precision of
the telehaptic activity, thereby raising serious concerns on the telehaptic activity significantly [2].
designing efficient communication frameworks for
minimizing telehaptic packet loss and jitter on shared
networks.
Keywords: Telehaptic communication, QoS, shared
network, packet loss, jitter
I. INTRODUCTION
Everyday activities that the humans perform are largely
dependent on our sensory mechanisms that aid in learning the
physical properties of any real object such as size, shape, Fig. 1. Schematic representation of a telehaptic communication
weight, texture, hardness, smell, and so on. The touch framework depicting the signal exchange between the human
perception forms an integral part of our sensory mechanism. operator (OP) and the robotic teleoperator (TOP).
When an object is held, it exerts certain forces on the hand.
The muscles and the joints of the hand capture these forces and Naturally, such highly sensitive operations necessitate
they are then transmitted to the brain, generating a perception accurate replication of the OP’s movements by the TOP, and
map of the object. This sensory mechanism is the fundamental also timely delivery of the feedback signals to the OP. For
driving force behind the innumerous forms of seamless example, large delays in haptic feedback result in sluggish
interaction between humans and the physical world. Life perception of the patient’s body, thereby (potentially) leading
would be lot harder if one was to light a matchstick, drive a to a wrong action by the surgeon. Additionally, large telehaptic
car, or play a game of golf without the ability to feel the jitter leads to perceiving the same remote object as having
physical object. variable mass, which is absurd. Note that jitter refers to the
Haptics relates to the science behind the different variation in the packet delays. High packet losses may cause
mechanisms of perception of real objects through the sense of improper replication of the OP’s movements accurately and/or
touch. The deep research insights in this field have led to the OP being severely deprived of the feedback signals. Both these
design of elegant electro-mechanical systems that have scenarios could have catastrophic effects on the ongoing
enabled us to interact and manipulate virtual as well as remote telehaptic activity. Note that the packet loss in the network is a
objects through the feeling of touch. consequence of queue overflows during congestion. These
Telehaptic communication – the science of coding, and effects can, at times, cause irreparable damage to the patient.
subsequent transmission of haptic signals over a network – has Hence, the communication network that transfers the
witnessed rapid progress over the past decade. Such telehaptic feedback plays an instrumental role in determining
communication has been envisaged to redefine the way we the quality of the telehaptic interaction.
interact with a remote world. For example, a surgeon could Experimental studies, such as [3], have demonstrated that
perform telesurgery on a distant patient through a robotic the human perception of haptic feedback can tolerate a

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maximum packet loss and jitter of not more than 10% and 10 underutilization the network resources. The TCP source
ms, respectively. This means that the perception of the remote increases its data rate until it detects a packet loss (indicating
environment is not hampered even if at least 90% of the congestion). In response, it reduces the data rate in order to
telehaptic samples reach the OP/TOP with a jitter of no more relieve the network, and thereby achieve congestion control.
than 10 ms. These telehaptic packet loss and jitter constraints Once the source detects that the network is free, it begins to
that need to be satisfied for a seamless telehaptic activity are increase the data rate, and this cycle continues. As can be
collectively known as Quality of Service (QoS). For a smooth observed, the TCP source relies heavily on the packet loss in
telehaptic activity, the network needs to guarantee QoS- the network in order to learn the available network bandwidth.
compliance at all times. In general, QoS violations lead to In fact, the working principle of TCP is itself based on
deteriorated perception of the remote environment, as inducing packet loss in the network. This behavior naturally
explained previously. impacts the concurrent streams in the network. In addition, the
It is important to note that the work in [3] treats the packet data rate variation of TCP also introduces jitter that negatively
loss as a time-average entity. In other words, the work in [3] affects the telehaptic activity. In this work, we are interested in
averages packet losses over an entire telehaptic session; the studying whether these packet loss and jitter effects of TCP
authors discovered that when this long term average packet have any notable impact on QoS-compliance of the telehaptic
loss exceeds 10%, the users started perceiving an unacceptable stream.
deterioration in the perception of the remote environment. In this paper, we intend to study the impact of multiple TCP
Note that the long term average packet loss refers to the cross-traffic sources on a telehaptic stream. The objective of
average of the packet loss measured over the entire duration of this investigation is to gain insights into the characteristics of
the telehaptic session. It is worth noting that this work does not the instantaneous telehaptic packet loss and jitter under the
consider the characteristics of the instantaneous loss while influence of coexisting TCP cross-traffic sources. The
establishing 10% as the packet loss criteria for smooth contribution of our work is as follows.
perception. (i) We demonstrate that in a wide range of settings, even
It is important to remark that in a real world scenario the though the long term average packet loss meets the QoS
perception of remote objects (potentially) depends on the criteria, the instantaneous packet loss can be much higher.
instantaneous packet loss rather than the long term average (ii) We show that the peak telehaptic jitter can far exceed the
loss. For example, in a few network settings the instantaneous 10 ms deadline for standard network settings, and hence is
packet loss is way higher than 10% (see Figures 4 and 5) extremely prone to QoS violations.
despite its long term average value being below 10%. This The remainder of the paper is organized as follows. In
means that a vast majority of the telehaptic samples (up to 80% Section II, we discuss in brief a few prior works available in
in our simulations) do not reach the destination. As per the the literature related to the interplay between TCP and
claim in [3], this implies that even when all packets (100%) telehaptic streams. Section III describes the detailed
are lost over a certain interval, the users do not feel any simulation setup that we designed for our investigation. In
perceptual degradation. This is incorrect as no haptic feedback Section IV, we present the results of our experiments, and in
leads to improper perception of the remote world. Therefore, Section V, we state our conclusions and mention potential
the instantaneous packet loss, and not the long term average directions for future research.
loss, is a more relevant performance metric from the
standpoint of perception in any telehaptic communication. II. RELATED WORK
A telehaptic stream on a shared network, like the Internet, Only a handful of works have attempted to study the
has to contend with other cross-traffic streams that are behavior of telehaptic streams on a shared network [6, 7, 8].
concurrently being served by the network. Hence, it is crucial Although these works considered network cross-traffic in their
to study the influence of the coexisting cross-traffic streams on performance evaluation, negligible attention is paid to the TCP
the telehaptic stream in terms of instantaneous packet loss and streams that form a major component of the overall cross-
jitter. On a shared network, the telehaptic stream is guaranteed traffic. A recent work [9] conducted a comprehensive analysis
to encounter Transmission Control Protocol (TCP) traffic of the effects of a single TCP stream on the long term average
since TCP amounts to over 90% of the overall traffic [4]. TCP telehaptic packet loss as well as jitter. However, this work
provides a reliable data communication mode, and hence investigates ignores the instantaneous packet loss. As
forms the cornerstone of a wide variety of Internet services that explained earlier, the instantaneous packet loss forms a more
require reliable transfer of data, such as email, file transfer, important performance metric than the long term average
web browsing, and video streaming applications like YouTube, measure. Furthermore, this analysis confines the number of
and Netflix. concurrent TCP streams to one. Hence, the effect of multiple
For our investigation in this paper, we consider a specific TCP streams on telehaptic loss and jitter remains unexplored
flavor of TCP named TCP NewReno [5]. TCP NewReno (or in this work.
any TCP source in general) is a rate-adaptive transport layer
protocol that controls its transmission rate depending on the III. SIMULATION SETUP
congestion level in the network. The TCP source uses packet In this section, we give a detailed description of the
loss as an indicator of congestion. Based on the packet loss as experimental settings considered in our simulations. The goal
detected by the source, the data rate is adapted to match the of this section is to develop an understanding of the dynamics
available network bandwidth, and thereby eschew of interplay between TCP and telehaptic streams when the two

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traffic types share a single bottleneck link. We carry out our We now move to studying the behavior of the instantaneous
investigation using NS3 – a discrete event network simulator telehaptic packet loss for a specific value of n for which the
[10]. We use the single bottleneck network topology as shown average loss meets the telehaptic packet loss criteria. For this
in Figure 2. H 1 and H 2 are the OP and the TOP, respectively, purpose, we choose n = 10. Note, from Figure 3, that the long
of the telehaptic communication framework shown in Figure term average loss for n = 10 is approximately 10%. From
1. [S 1 , …, S n ] and [R 1 , …, R n ] are the sets of n TCP sources Figure 4, it can be seen that the instantaneous telehaptic packet
and receivers, respectively. L 1 is the bottleneck link on the loss varies rapidly between 0 and 50%. In addition to the peak
forward channel. Note that the data rate variation of TCP loss measurement of 50%, it can also be seen that the packet
influenced the queue occupancy at B 1 , the router at the ingress loss QoS criteria gets violated regularly. Although we report
of L 1 . As mentioned earlier, the TCP sources employ the instantaneous packet loss only for n = 10, we observe
NewReno congestion control scheme. For telehaptic similar behavior for other values of n as well. In short, even
communication, we leverage the protocol proposed in [8]. It though the long term average packet loss meets the QoS
can be shown that in presence of TCP NewReno sources, a criteria, the instantaneous loss can be significantly higher. This
telehaptic source employing the protocol in [8] generates confirms our conjecture that the instantaneous packet loss
packets at the rate of 250 per second. The packet scheduling at should be considered as the performance metric rather than the
the network queues is based on the standard droptail long term average packet loss.
mechanism.

Fig. 2. Single bottleneck network topology used in our simulations.
Notations: H 1 and H 2 – operator and teleoperator in telehaptic
communication, respectively; [S 1 ,..., S n ] – TCP sources; [R 1 ,..., R n ] Fig. 3. Evolution of long term average telehaptic packet loss as a
– TCP receivers; L 1 – bottleneck link; B 1 – router at the ingress of function of the number of TCP sources.
bottleneck link.
It is important to remark that even though the interval over
The propagation delay of each link is set to 5 ms, and hence which the QoS violation occurs is small (a maximum of 300
the one-way propagation delay between a source and its ms), this could potentially have severe artifacts considering the
corresponding receiver is 15 ms. The channel capacity of L 1 is scale of sensitivity that a telehaptic activity, like telesurgery,
set to 3 Mbps. The access links to L 1 have high capacities of 5 requires.
Gbps. The queue size at the B 1 is configured to 15 kB. The
TCP and the telehaptic packets have sizes 578 B and 512 B,
respectively, unless mentioned otherwise. For the purpose of
our simulations, we consider n in the range [1, 10]. However,
it is worth remarking that the observations that we make
regarding the telehaptic loss and jitter hold good for higher
values of n as well.
All sources begin the transmissions simultaneously at t = 0.
We run each simulation until t = 100 s. Throughout the
simulations, we record the packet loss and jitter encountered
by the telehaptic sources.
Fig. 4. Instantaneous telehaptic packet loss n = 10 showing
IV. RESULTS significant overshoot compared to its long term average value.
In this section, we present the results of our investigation of
telehaptic packet loss and jitter induced by the coexisting TCP
streams. We begin by reporting the packet loss, and then move
to the jitter part.
In Figure 3, we report the long term average packet loss seen
by the telehaptic source by varying n over the considered
range. It can be seen that the long term average packet loss is
an increasing function of n. However, for n < 10, the long term
average packet loss complies to the QoS limit of 10%.
However, we note that for higher n, the average loss exceeds
the QoS limit severely. For brevity, we do not report the
telehaptic packet loss in the higher n regime. Fig. 5. Variation of peak instantaneous telehaptic packet loss as a
function of the number of TCP sources in the network.

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Having seen the instantaneous loss, we now turn towards V. CONCLUSIONS
determining the peak instantaneous telehaptic packet loss in
the simulations. Figure 5 shows the variation of the peak In this paper, we conducted an extensive investigation of the
packet loss in the considered range of n. It can indeed be interplay between TCP NewReno and telehaptic streams. We
observed that the instantaneous packet losses are substantially demonstrated that even though the long term average
higher despite the long term average packet loss complying to telehaptic packet loss satisfies the QoS criteria, the
the QoS requirement. Therefore, we demonstrate through instantaneous loss can far exceed the QoS limit of 10%.
experiments that any guarantees on the long term average Additionally, we showed that the telehaptic stream faces
packet loss do not imply any guarantees on the peak extreme jitter QoS violations for TCP packets of standard
instantaneous packet loss. This suggests that in order to ensure sizes. Hence, we conclude that it is crucial to monitor and
a seamless telehaptic activity, one must design communication control the number of TCP streams, as well as the size of TCP
frameworks that can provide QoS guarantees on the packets in order to achieve seamless telehaptic communication
instantaneous telehaptic packet loss. on a shared network.
It has been shown in the past that smaller telehaptic packets In a future version of this article, we intend to propose a
(relative to TCP packets) are less susceptible to losses [9]. telehaptic communication framework that mitigates the
Specifically, the experiments in [9] reveal that the telehaptic detrimental effects of TCP sources. Also, studying the effects
packets of size 137 B are rarely dropped by the network queues of other variants of TCP on telehaptic stream could be another
in presence of a single TCP source that transmits packets of interesting avenue for future research.
size 578 B. Hence, one potential solution for mitigating the REFERENCES
telehaptic losses is to minimize the packet sizes. The other
plausible remedy could be to design priority queueing schemes [1] R. Anderson, and M. Spong, "Bilateral control of
that can serve packets carrying crucial telehaptic data with teleoperators with time delay," IEEE Transactions on
higher precedence over other cross-traffic streams. Automatic Control, vol. 34, pp. 494–501, May 1989.
We now move to the peak telehaptic jitter measurements. [2] C. Basdogan, C. Ho, M. A. Srinivasan, and M. Slater, "An
For the packet sizes mentioned in Section III, we notice that experimental study on the role of touch in shared virtual
the peak telehaptic jitter varies in the range [2.55, 6.69] ms, environments," in ACM Transactions on Computer-Human
which satisfies the QoS constraint. Since the jitter is known to Interaction (TOCHI), vol. 7, pp. 443–460, 2000.
be heavily dependent on the TCP packet size, for concreteness [3] P. Dev, D. Harris, and D. Gutierrez, A. Shah, and S. Senger,
in exposition, we run the simulations with TCP packets of size
"End-to-end performance measurement of internet based
1042 B, which is also another standard value. In Figure 6, we
plot the peak instantaneous telehaptic jitter as a function of n. medical applications," in Proceedings of the Annual
It can be seen that the peak jitter is a non-decreasing function Symposium of the American Medical Informatics
of n. Further, for n > 5, the jitter QoS condition is severely Association, Nov 2002.
violated. This implies that higher the number of concurrent [4] S. Ryu, C. Rump, and C. Qiao, "Advances in internet
TCP streams, larger is the probability of violation of the congestion control," in IEEE Communications Surveys and
telehaptic jitter QoS violation. Tutorials, vol. 5, pp. 28–39, 2003.
Based on the analysis in [9], it is reasonable to argue that the [5] S. Floyd, A. Gurtov, and T. Henderson, "The NewReno
peak instantaneous haptic jitter increases with the number of modification to TCP’s fast recovery algorithm," 2004.
concurrent TCP streams as well as their packet sizes. For QoS [6] R. Wirz, M. Ferre, R. Marin, J. Barrio, J. M. Claver, and J.
–compliance, one needs to theoretically determine upper Ortego, "Efficient transport protocol for networked haptics
bounds for these two factors. The network administrator then
applications," in Haptics: Perception, Devices and
needs to ensure that the cross-traffic satisfies the two bounds.
Scenarios, Springer, 3–12, 2008.
This guarantees satisfaction of QoS conditions for telehaptic
jitter. [7] V. Gokhale, J. Nair, and S. Chaudhuri, "Opportunistic
adaptive haptic sampling on forward channel in telehaptic
communication," in Haptics Symposium, Apr 2016.
[8] V. Gokhale, J. Nair, and S. Chaudhuri, "Congestion control
for network-aware telehaptic communication," in ACM
Transactions on Multimedia Computing, Communications,
and Applications, vol. 13, 2017.
[9] V. Gokhale, J. Nair, and S. Chaudhuri, "Teleoperation over
a shared network: When does it work?," in International
Symposium on Haptic, Audio and Visual Environments and
Games, Oct 2017.
Fig. 6. Variation of peak instantaneous telehaptic jitter with TCP [10] "NS3 - The network simulator", 2011, online -
packets of size 1042 B. http://www.nsnam.org/.

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