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Multicast Considerations over IEEE 802 Wireless Media (RFC 9119)

From https://assistivelisteningknowledgebase.org/evidence/ietf-2021-rfc9119/ · record checked 13 October 2026

  • Perkins C, McBride M, Stanley D, Kumari W, Zúñiga JC
  • Internet Engineering Task Force (IETF), RFC Editor

Standards body (IETF; an Informational RFC that represents IETF consensus but is not a standard; the authors were with Lupin Lodge, Futurewei, HPE, Google and SIGFOX)

Summary

An IETF document on the known limits of multicast over Wi-Fi and the features and network choices that can improve it.

Key findings

  • Section 2 expands AP as IEEE 802.11 Access Point, and sections 3.1 and 4.3 describe its delivery of network traffic to wireless stations. Section 3.1.1 describes multicast as point-to-multipoint communication; section 3.2 discusses multicast DNS for service discovery. These are general network mechanisms, used here as shared-path evidence for venue Wi-Fi audio.
  • Section 4.3 calls DTIM a Delivery Traffic Indication Message and says that an access point buffers multicast frames until the next DTIM beacon when an associated station uses power saving. Section 2 instead expands the same abbreviation as Delivery Traffic Indication Map; both passages describe buffered group traffic.
  • Says multicast over wireless links "is quite sensitive to the presence of background traffic", worse than on wired networks (section 3.1.1).
  • Explains that Wi-Fi multicast frames are not acknowledged, so the access point cannot tell when a resend is needed, and states that a packet loss rate of 5% or more is not uncommon.
  • States that multicast is generally sent at the slowest rate of all connected devices (the basic rate), which can be more than a thousand times slower than the best unicast rate; slower transmissions occupy more airtime and reduce the network's overall capacity.
  • Notes that when any connected device uses power-save mode, the access point holds all multicast frames until the next DTIM beacon, which delays multicast traffic.
  • Describes converting multicast to unicast over the Wi-Fi link as a mitigation, because unicast frames are acknowledged and buffered for sleeping devices; it notes there is no standardised method yet, that the access point must then track which devices subscribe to which streams, and that the approach "comes with the trade-off of sometimes sending the same packet multiple times over the Wi-Fi link".
  • Of the IEEE 802.11 features meant to help, it says Directed Multicast Service (DMS) "is not currently implemented in products" and that GroupCast with Retries (GCR) "may introduce unacceptable latency".
  • Says unicast "avoids most of the problems specific to multicast over Wi-Fi" (section 4.6.1) and that "there is not yet a standardized method" for converting multicast to unicast (section 4.6.2).

Limits

A general technical document on Wi-Fi multicast, not about audio or assistive listening; it reports no measurements of its own, and the 5% loss figure is given without a study behind it. Wi-Fi equipment and standards have changed since October 2021.

Read the original

www.rfc-editor.org/rfc/rfc9119.html

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Cited in

Cite this source

Perkins C, McBride M, Stanley D, Kumari W, Zúñiga JC. Multicast Considerations over IEEE 802 Wireless Media (RFC 9119). Internet Engineering Task Force (IETF), RFC Editor. October 2021. https://www.rfc-editor.org/rfc/rfc9119.html (accessed 13 October 2026).

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