Transcript On the Design of Robust and Adaptive IEEE 802.11 Multicast

On the Design of Robust and
Adaptive IEEE 802.11
Multicast Services for Video
Transmissions
Speaker: Bo-Yu Huang
Advisor: Dr. Ho-Ting Wu
Date: 2014/12/23
Outline
 Introduction
 The current trends on multicast video transmission in IEEE 802.11 WLANs.
 Adaptive Multicast Mechanism with Collision Prevention (AMM/CP)
 Simulation results
 Conclusion
 References
Introduction
 Using wireless links for video streaming has become more common.
However, real-time video streaming over wireless networks is a challenging
proposition due to the characteristics of the video data and wireless
channels.
 In wireless environments, the channel conditions change rapidly over time
due to noise, interference, multipath, and user mobility. In such context, the
transmission control schemes have to dynamically adapt the transmission
rate to the channel conditions.
Introduction(Cont.)
 In the current IEEE 802.11 standard, there are two main inter-related issues
that need to be addressed on the design of a reliable and scalable
multicast service:
 Provisioning of an efficient and scalable feedback mechanism:
 Multi-rate transmissions.
Introduction(Cont.)
 In order to enhance the performance of the multicast video service
provided by the IEEE 802.11 WLANs, we propose a novel mechanism,
referred from now on as Adaptive Multicast Mechanism with Collision
Prevention (AMM/CP).
Current trends on multicast in IEEE 802.11
 Most research efforts on multicasting in IEEE 802.11 WLANs have focused on
improving the reliability of the multicast service by integrating Automatic
Repeat-reQuest (ARQ) mechanisms into the protocol architecture.
 Leader-Based Protocol(LBP)
Leader-Based Protocol(LBP)
 This protocol assumes that one of the receivers of the multicast has been
chosen to be a leader for the purpose of supplying CTS and ACK in
response to RTS and data packets.
 [A] Base -> Receivers
Send multicast-RTS.
 [B] Receivers -> Base
Leader: if ready to receive data, send CTS.
if not ready to receive data do nothing.
Others: if ready to receive data, do nothing.
if not ready to receive data, send NCTS (Not Clear to Send).
 [C] Base -> Receivers
If a CTS was heard in slot 2, start multicast transmission.
If no CTS was heard in slot 2, back off and go to Step A.
 The next step is executed only when multicast transmission occurs in Step C.
 [D] Receivers -> Base
Leader: if packet received without error, send ACK.
if in error, send NAK.
Others: if packet received without error, do nothing.
if in error, send NAK.
 LBP uses both ACKs and NAKs from receivers as feedback to the sender. It
allows collision of an ACK with one or more NAKs to ensure that the sender
does not get a positive feedback if one or more group members receive
erroneous transmission.
 Even though the LBP address the reliability problems, it falls short on
providing a valuable solution to the adaptive channel rate adaptation
based on the changing channel conditions. To solve the rate adaption
problem, theses schemes can be used together with the ARF protocol.
 The Probing-based ARF (PARF) mechanism. PARF attempts to provide a
suitable solution to the adaptive transmission rate issue, however its
performance statistics do not defer substantially from the ones reported for
the LBP+ARF. The main drawback is that they do not provide a complete
solution to overcome the main error sources, i.e., channel access conflicts
and channel varying operating conditions.
 The IEEE Task Group aa(TGaa) has defined a new multicast service, named
Group Addressed Transmission Service (GATS). Under this new service, each
group-addressed stream may be delivered using different schemes
according to the requirements of the stations belonging to each stream.
This differentiation is done by allowing a station to request higher reliability
for one or more group addressed streams. GATS comprises two services:
Directed Multicast Service (DMS) and GroupCast with Retries (GCR).
Directed Multicast Service (DMS)
 Each multicast frame is transmitted in a unicast mode to each multicast
groupcast member. Frames transmitted to multicast addresses are
individually transmitted to each of the associated STAs belonging to the
multicast group. Those frames will be retransmitted until receiving an
acknowledgement from the AP, and they will be stopped when the
retransmission limit is achieved. Although this mechanism guarantees a
reliable transport to multicast traffic like unicast transmissions, it has large
scalability when using a high number of the multicast group
GroupCast with Retries (GCR)
 GCR is a flexible service whose main aim is to improve the delivery of
group-addressed packets.
• Unsolicited-Retry: the AP retransmits a packet one or several times to
increase the probability that all the MRs in the multicast group successfully
receive the packet.
• Block-ACK mechanism: This method extends the Block Ack mechanism
specified in IEEE 802.11n for use in multicast transmissions to a group.
The AP transmits a number of multicast frames and then requests from one or
more of the recipients to acknowledge the receipt of the transmitted frames.
Frames that have not been received correctly by one or more of the receivers
can then be retransmitted.
 With the definition of the GATS, the IEEE 802.11aa offers different solutions to
the reliability problem. However, this amendment does not introduce any
improvement for the flow adaptation problem.
 In short, the IEEE 802.11aa amendment does not specify an efficient
mechanism including a rate adaptation mechanism into the multicast
service.
The AMM/CP mechanism
 In order to enhance the performance of the multicast service provided by
the IEEE 802.11 WLANs, we present a multicast mechanism for multi-rate
transmissions, called AMM/CP.
 The design of AMM/CP addresses the following three issues:
 Collision prevention
 Negative feedback for multicast packets
 Flow adaptation
Collision prevention
 It integrates the MCP mechanism, having proved effective on reducing
various orders of magnitude the multicast collision rate with respect to the
one reported by the standard multicast mechanism
Negative feedback for multicast packets
 To avoid the potential implosion of ACKs to be sent by the MRs, the
protocol makes use of NAK packets instead ACKs. Thus, an MR will only issue
a NAK in case of receiving a corrupted multicast packet.
Flow adaptation
 AMM/CP also makes use of a modified ARF mechanism. In this way, the
data transmission rate may be changed to the one offering better
guarantees given the channel conditions.
The AMM/CP mechanism(Cont.)
 In the AMM/CP mechanism, when the AP has a multicast packet to send, it
first invokes the MCP mechanism to reduce the collision probability. Once
the multicast packet is delivered, the AP senses the channel. If the AP
senses the channel busy before the timeout timer expires, it assumes that
one or more MRs have issued a NACK. In such situation, the AP should run
the rate-adaptation mechanism to check if a more robust transmission rate
should be used to retransmit the packet. On the other hand, if the waiting
period expires without having detected any activity in the channel, the
multicast packet has been successfully delivered to all MRs. In this case, the
AP runs the rate-adaptation algorithm to decide if it increases the
transmission rate of the next multicast packet.
Simulation results
 A comparison of AMM/CP and a reliable multicast service incorporating
the LBP and the ARF mechanisms( LBP+ARF mechanism ).
 The evaluation is done both in terms of QoS guarantees and QoE offered to
the end user.
 QoE is evaluated using the VQM_VFD metric and the results are converted
to the Mean Opinion Score (MOS) scale, whose values spans from 1 to 5
(1-bad, 2-poor, 3-fair, 4-good, 5-excellent).
Simulation results(Cont.)
Simulation results(Cont.)
Simulation results(Cont.)
Simulation results(Cont.)
Conclusion
 In this paper, we have evaluated our new multicast mechanism. It is able to
adapt the transmission rate of the multicast flow to the channel conditions.
The combination of collision prevention, feedback and rate adaptation
makes that our mechanism properly delivers the multicast video flow to a
group of mobile stations. We have proved it by developing a video quality
experiment for evaluating the QoS of the WLAN and the QoE perceived by
the mobile members of the multicast group.
References
 M. Santos, J. Villalon, L. Orozco-Barbosa, and L. Janowski, "On the design of
robust and adaptive IEEE 802.11 multicast services for video transmissions,"
in Proc. of WoWMoM, 2013, pp. 1-6.
 J. Kuri and S. K. Kasera, “Reliable Multicast in Multi-access Wireless LANs”.
ACM Wireless Networks”, Vol. 7(4), pp. 359-369, 2001.
Thanks for listening