Hello, everyone!
Today, I would like to share the novel features ot the IEEE 802.11aa amendment.
Techniques for groupcast communication.
The majority of audio/video streaming applications require a number of clients to receive similar feed at the same time. To prevent the same material being copied across the network, a multicast protocol is required.
Multicast transmission in wireless networks can take advantage of the wireless channel's inherent broadcast character, in which broadcast transmissions from an Access points are physically obtained by all other stations along the same collision domain.
Nevertheless, unlike unicast frames, multicast and broadcast frames in IEEE 802.11 networks are not secured by an acknowledgement system. As a result, traditional IEEE 802.11 layer-2 multicast transmissions are unstable and unsuitable for streaming applications.
The Direct Multicast Service (DMS) itself was established in the IEEE 802.11v amendment to partially solve this issue. DMS essentially transforms multicast streams into unicast streams. Frames intended for a multicast address are sent sequentially as unicast frames to the stations that have joined that multicast group in this way.
Figure 1: Various retransmission strategies for the GCR service
DMS offers the same degree of stability as unicast transmission services, but the bandwidth utilised grows increasingly with the number of group members. In addition to DMS, IEEE 802.11aa offers the Groupcast with Retries (GCR) service to tackle this scalability issue.
The GCR service offers new group formation procedures and administration frames, allowing a group of stations to agree on a common (non-multicast) address known as the groupcast concealment address.
Legacy stations, i.e., GCR-incapable stations, are protected by the concealing address from obtaining identical group-addressed frames.
The GCR service also provides 2 different retransmission initiatives:
GCR Block Ack (GCR-BA)
GCR Unsolicited Retry (GCR-UR)
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