Speaker : Song-Ferng Wang
Advisor : Dr. Ho-Ting Wu
Date
: 2014/1/6
Outline

 Introduction
 IEEE 802.11 multicast issues
 IEEE 802.11e EDCA
 IEEE 802.11aa
 Conclusions
 References
Introduction

 Video applications are rapidly becoming the main
source of traffic in the Internet. With the presence of
IEEE 802.11 networks constantly expanding, and the
growing use of mobile devices with high
computational power and display capabilities.
Introduction

 The first IEEE 802.11 wireless LAN standards were
unable to handle efficient video transmission since
the bandwidth was too small for the demands of
video applications and they could only support a
best-effort service which is unacceptable for the QoS
restraints of video transmission
Introduction

 The multicast mechanism provided by the legacy
IEEE 802.11 is unreliable and cannot offer the
necessary QoS for transmitting video streams
 multicast communication in IEEE 802.11 wireless
LANs suffers from many problems.
IEEE 802.11 multicast
issues (1)

 the MAC layer of IEEE 802.11 networks specifies that
multicast frames can only be transmitted using the
Basic Access scheme. Therefore, it cannot use the
RTS/CTS mechanism to protect broadcasting of the
frame. means that multicast transmission is
unreliable
 issues about the scheduling and synchronization of
receiving them
IEEE 802.11 multicast
issues (2)

 IEEE 802.11 MAC specifies that multicast frames
must be transmitted using one of the bit rates
specified in the Basic Rate Set (BRS), which is a
minimum set of bit rates that must be supported by
all stations in a IEEE 802.11 wireless LAN to ensure
that they can receive control frames.
IEEE 802.11aa

 Compatibility with the relevant mechanisms defined
by IEEE 802.1AVB (802.1Qat, 802.1Qav, 802.1AS) for
multimedia stream transport.
 To allow video streams to degrade in a graceful
manner when the channel capacity is insufficient , by
enabling packet discarding without any requirement
for deep packet inspection.
IEEE 802.11aa

 The ability to prioritize between different video
transport streams that belong in the same EDCA
Access Category.
 Stream Classification Service (SCS)
 A method for mitigating the effects of overlapping
BSS environments to offer increased robustness ,
without the need for centralized management.
IEEE 802.11aa

 Improvement for the multicast/broadcast
mechanism of IEEE 802.11 in order to offer better
link reliability and low jitter characteristics.
 802.11v Directed Multicast Service
 Groupcast with Retries (GCR) Unsolicited Retries
 Groupcast with Retries (GCR) BlockAck
802.11v Directed Multicast
Service

 converts multicast traffic to unicast frames directed
to each of the group recipients in a series. The
transmission uses the normal acknowledgement
policy and will be retransmitted until it is received
correctly.
Groupcast with Retries
(GCR) Unsolicited Retries

 This mechanism allows the transmission of the
multicast frames to be repeated a number of times.
Groupcast with Retries
(GCR) BlockAck

 This method extends the BlockAck 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.

IEEE 802.11 DCF

 DCF (Distributed Coordination Function)為基本通
道存取機制，通訊台(Station, STA)利用載波偵測多重
存取/碰撞避免通訊協定(Carrier-Sense Multiple
Access/Collision Avoidance, CSMA/CA)來競爭通道
使用權。通訊台在準備傳送訊框之前，必須使用載波
偵測監測通道情況，確定通道為閒置狀態後才開始準
備傳送資料，以避免通訊台之間強行傳送訊框而發生
碰撞情況。
IEEE 802.11 DCF

IEEE 802.11e EDCA

 EDCA function in IEEE 802.11e to provide Quality of
Service for video and voice streams specifies
Access Categories (AC) with different priorities
 8 Traffic Category (TC)
 4 Access Category(AC)
IEEE 802.11e EDCA

IEEE 802.11e EDCA

Stream Classification Service
(SCS)

 The IEEE 802.11aa amendment aims to increase the
granularity of the EDCA access categories to allow
for prioritization between different video streams.
Stream Classification Service
(SCS)

Conclusions

 The IEEE 802.11aa amendment provides a
foundation for video stream transport over IEEE
802.11 wireless LANs. It provides a set of
mechanisms such as the multiple multicast policies,
the Stream Classification Service and the QLoad
information element, but the use of them is open to
the implementation. The choice of the appropriate
mechanism, depending on the situation and the
setting of its parameters, is an issue of great interest
for future research.
References

 Kostas Maraslis, Periklis Chatzimisios and Anthony
Boucouvalas,“IEEE 802.11aa: Improvements on
video transmission over Wireless LANs”,
Communications (ICC), 2012 IEEE International
Conference on Ad-hoc and Sensor Networking
Symposium, pp. 115-119, June 2012
 林佳慧，“以動態競爭視窗調整機制改善無線區域網
路IEEE 802.11e規格之效能”，碩士論文，台北科技大
學，May 2008