wdiff draft-ietf-mboned-ieee802-mcast-problems-00.txt draft-ietf-mboned-ieee802-mcast-problems-01.txt

MBONED WG M. McBride
Internet-Draft
Internet Area C. Perkins
Internet-Draft M. McBride
Intended status: Standards Track Huawei Informational Futurewei
Expires: July 28, August 7, 2018 January 24, D. Stanley
HPE
W. Kumari
Google
JC. Zuniga
SIGFOX
February 3, 2018

Multicast WiFi Problem Statement
draft-ietf-mboned-ieee802-mcast-problems-00 Considerations over IEEE 802 Wireless Media
draft-ietf-mboned-ieee802-mcast-problems-01

Abstract

There have been known

Well-known issues with multicast, in an 802.11
environment, which multicast have prevented the deployment of
multicast in
these wifi 802.11 [dot11], [mc-props], [mc-prob-stmt], and other
local-area wireless environments. IETF multicast experts have been
meeting together to discuss these issues and provide IEEE updates.
The mboned working group is chartered to receive regular reports on
the current state of the deployment of multicast technology, create
"practice and experience" documents that capture the experience of
those who have deployed and are deploying various multicast
technologies, and provide feedback to other relevant working groups.
As such, this
This document will gather the offers guidance on known limitations and problems of wifi with
wireless multicast. Also described are various multicast
into one problem statement document so enhancement
features that have been specified at IETF and IEEE 802 for wireless
media, as well as some operational chioces that can be taken to offer
improve the community
guidance on current limitations. performace of the network. Finally, some recommendations
are provided about the usage and combination of these features and
operational choices.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 28, August 7, 2018.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3
2. Multicast over WiFi Problems Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Identified mulitcast issues . . . . . . . . . . . . . . . . . 5
3.1. Issues at Layer 2
2.1. Low Reliability and Below . . . . . . . . . . . . . . . 5
3.1.1. Multicast reliability . . . . . . 3
2.2. Low Data Rate . . . . . . . . . . 5
3.1.2. Lower and Variable Data Rate . . . . . . . . . . . . 4
2.3. 5
3.1.3. High Interference . . . . . . . . . . . . . . . . . . 6
3.1.4. Power-save Effects on Multicast . . 4
2.4. High Power Consumption . . . . . . . . . 6
3.2. Issues at Layer 3 and Above . . . . . . . . 4
3. Common remedies to multicast over wifi problems . . . . . . . 4
4. State of the Union 7
3.2.1. IPv4 issues . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations 7
3.2.2. IPv6 issues . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations 7
3.2.3. MLD issues . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgments . . 8
3.2.4. Spurious Neighbor Discovery . . . . . . . . . . . . . 8
4. Multicast protocol optimizations . . . . . . . . 6
8. Normative References . . . . . . 9
4.1. Proxy ARP in 802.11-2012 . . . . . . . . . . . . . . 6
Authors' Addresses . . 9
4.2. IPv6 Address Registration and Proxy Neighbor Discovery . 10
4.3. Buffering to improve Power-Save . . . . . . . . . . . . . 11
4.4. IPv6 support in 802.11-2012 . . . . . . . 6

1. Introduction

Multicast over wifi has been used to low levels of success, usually
to a point . . . . . . . . 12
4.5. Conversion of being so negative that multicast over wifi is not
allowed. In addition to protocol use of broadcast/multicast for
control messages, more applications, such as push to talk in
hospitals, video in enterprises and lectures in Universities, are
streaming over wifi. And many end devices are increasingly using
wifi for their connectivity. One of the primary problems multicast
over wifi faces unicast . . . . . . . . . . . 12
4.6. Directed Multicast Service (DMS) . . . . . . . . . . . . 12
4.7. GroupCast with Retries (GCR) . . . . . . . . . . . . . . 13
5. Operational optimizations . . . . . . . . . . . . . . . . . . 14
5.1. Mitigating Problems from Spurious Neighbor Discovery . . 14
6. Multicast Considerations for Other Wireless Media . . . . . . 16
7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 16
8. Discussion Items . . . . . . . . . . . . . . . . . . . . . . 16
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
12. Informative References . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19

1. Introduction

Performance issues have been observed when multicast packet
transmissions of IETF protocols are used over IEEE 802 wireless
media. Even though enhamcements for multicast transmissions have
been designed at both IETF and IEEE 802, incompatibilities still
exist between specifications, implementations and configuration
choices.

Many IETF protocols depend on multicast/broadcast for delivery of
control messages to multiple receivers. Multicast is used for
various purposes such as neighborhood discovery, network flooding,
address resolution, as well minimizing media occupancy for the
transmission of data that is intended for multiple receivers. In
addition to protocol use of broadcast/multicast for control messages,
more applications, such as push to talk in hospitals, video in
enterprises and lectures in Universities, are streaming over wifi.
Many types of end devices are increasingly using wifi for their
connectivity.

IETF protocols typically rely on network protocol layering in order
to reduce or eliminate any dependence of higher level protocols on
the specific nature of the MAC layer protocols or the physical media.
In the case of multicast transmissions, higher level protocols have
traditionally been designed as if transmitting a packet to an IP
address had the same cost in interference and network media access,
regardless of whether the destination IP address is a unicast address
or a multicast or broadcast address. This model was reasonable for
networks where the physical medium was wired, like Ethernet.
Unfortunately, for many wireless media, the costs to access the
medium can be quite different. Multicast over wifi has often been
plagued by such poor performance that it is disallowed. Some
enhancements have been designed in IETF protocols that are assumed to
work primarily over wireless media. However, these enhancements are
usually implemented in limited deployments and not widespread on most
wireless networks.

IEEE 802 wireless protocols have been designed with certain features
to support multicast traffic. For instance, lower modulations are
used to transmit multicast frames, so that these can be received by
all stations in the cell, regardless of the distance or path
attenuation from the base station or access point. However, these
lower modulation transmissions occupy the medium longer; they hamper
efficient transmission of traffic using higher order modulations to
nearby stations. For these and other reasons, IEEE 802 working
groups such as 802.11 have designed features to improve the
performance of multicast transmissions at Layer 2 [ietf_802-11]. In
addition to protocol design features, certain operational and
configuration enhancements can ameliorate the network performance
issues created by multicast traffic. as described in Section 5.

In discussing these issues over email, and in a side meeting at IETF
99, it has been generally agreed that these problems will not be
fixed anytime soon primarily because it's expensive to do so and
multicast is unreliable. A big problem is that multicast is somewhat
a second class citizen, to unicast, over wifi. There are many
protocols using multicast and there needs to be something provided in
order to make them more reliable. The problem of IPv6 neighbor
discovery saturating the wifi link is only part of the problem. Wifi
traffic classes may help. We need to determine what problem should
be solved by the IETF and what problem should be solved by the IEEE
(see Section 8). A "multicast over wifi" IETF mailing list has been
formed (mcast-wifi@ietf.org) for further discussion. This draft will
be updated according to the current state of discussion.

This Internet Draft details various problems caused by multicast
transmission over wireless networks, including high packet error
rates, no acknowledgements, and low data rate. It also explains some
enhancements that have been designed at IETF and IEEE 802, as well as
the operational choices that can be taken, to ameliorate the effects
of multicast traffic. Recommendations about how to use and combine
these enhancements are also provided.

2. Terminology

This document uses the following definitions:

AP
IEEE 802.11 Access Point.

basic rate
The "lowest common denominator" data rate at which multicast and
broadcast traffic is generally transmitted.

DTIM
Delivery Traffic Indication Map (DTIM): An information element
that advertises whether or not any associated stations have
buffered multicast or broadcast frames.

MCS
Modulation and Coding Scheme.

STA
802.11 station (e.g. handheld device).

TIM
Traffic Indication Map (TIM): An information element that
advertises whether or not any associated stations have buffered
unicast frames.

3. Identified mulitcast issues

3.1. Issues at Layer 2 and Below

In this section we describe some of the issues related to the use of
multicast transmissions over IEEE 802 wireless technologies.

3.1.1. Multicast reliability

Multicast traffic is typically much less reliable than unicast
traffic. Since multicast makes point-to-multipoint communications,
multiple acknowledgements would be needed to guarantee reception at
all recipients. Since typically there are no ACKs for multicast
packets, it is not possible for the Access Point (AP) to know whether
or not a retransmission is needed. Even in the wired Internet, this
characteristic often causes undesirably high error rates. This has
contributed to the relatively slow uptake of multicast applications
even though the protocols have long been available. The situation
for wireless links is much worse, and is quite sensitive to the
presence of background traffic. Consequently, there can be a high
packet error rate (PER) due to lack of retransmission, and because
the sender never backs off. It is not uncommon for there to be a
packet loss rate of 5% or more, which is particularly troublesome for
video and other environments where high data rates and high
reliability are required.

3.1.2. Lower and Variable Data Rate

One big difference between multicast over wired versus multicast over
wired is that transmission over wired links often occurs at a fixed
rate. Wifi, on the other hand, has a transmission rate which varies
depending upon the clients proximity to the AP. The throughput of
video flows, and the capacity of the broader wifi network, will
change and will impact the ability for QoS solutions to effectively
reserve bandwidth and provide admission control.

For wireless stations associated with an Access Points, the power
necessary for good reception can vary from station to station. For
unicast, the goal is to minimize power requirements while maximizing
the data rate to the destination. For multicast, the goal is simply
to maximize the number of receivers that will correctly receive the
multicast packet; generally the Access Point has to use a much lower
data rate at a power level high enough for even the farthest station
to receive the packet. Consequently, the data rate of a video
stream, for instance, would be constrained by the environmental
considerations of the least reliable receiver associated with the
Access Point.

Because more robust modulation and coding schemes (MCSs) have longer
range but also lower data rate, multicast / broadcast traffic is
generally transmitted at the lowest common denominator rate, also
known as the basic rate. Depending on the specific 802.11
technology, and the configured choice for the base data rate for
multicast transmission from the Access Point, the amount of
additional interference can range from a factor of ten, to a factor
thousands for 802.11ac.

Wired multicast also affects wireless LANs when the AP extends the
wired segment; in that case, multicast / broadcast frames on the
wired LAN side are copied to WLAN. Since broadcast messages are
transmitted at the most robust MCS, many large frames are sent at a
slow rate over the air.

3.1.3. High Interference

Transmissions at a lower rate require longer occupancy of the
wireless medium and thus take away from the airtime of other
communications and degrade the overall capacity. Furthermore,
transmission at higher power, as is required to reach all multicast
clients associated to the AP, proportionately increases the area of
interference.

3.1.4. Power-save Effects on Multicast

One of the characteristics of multicast transmission is that every
station has to be configured to wake up to receive the multicast,
even though the received packet may ultimately be discarded. This
process can have a large effect on the power consumption by the
multicast receiver station.

Multicast can work poorly with the power-save mechanisms defined in
IEEE 802.11e, for the following reasons.

o Clients may be unable to stay in sleep mode due to multicast
control packets frequently waking them up.
o Both unicast and multicast traffic can be delayed by power-saving
mechanisms.

o A unicast packet is delayed until a STA wakes up and requests it.
Unicast traffic may also be delayed to improve power save,
efficiency and increase probability of aggregation.
o Multicast traffic is delayed in a wireless network if any of the
STAs in that network are power savers. All STAs associated to the
AP have to be awake at a known time to receive multicast traffic.
o Packets can also be discarded due to buffer limitations in the AP
and non-AP STA.

3.2. Issues at Layer 3 and Above

This section identifies some representative IETF protocols, and
describes possible negative effects due to performance degradation
when using multicast transmissions for control messages. Common uses
of multicast include:

o Control plane for IPv4 and IPv6
o ARP and Neighbor Discovery
o Service discovery
o Applications (video delivery, stock data etc)
o Other L3 protocols (non-IP)

3.2.1. IPv4 issues

The following list contains a few representative IPv4 protocols using
multicast.

o ARP
o DHCP
o mDNS

After initial configuration, ARP and DHCP occur much less commonly.
But service discovery can occur at any time. Apple's Bonjour
protocol, for instance, provides service discovery (for printing)
that utilizes multicast. It's the first thing operators drop. Even
if multicast snooping is utilized, many devices register at once
using Bonjour, causing serious network degradation.

3.2.2. IPv6 issues

IPv6 makes much more extensive use of multicast, including the
following:

o DHCPv6
o IPv6 Neighbor Discovery Protocol (NDP) is not very tolerant of
packet losses. In particular, the Duplicate Address Detection
(DAD) process fails when the owner of an address does not receive
the multicast DAD message from another node that wishes to own
that same address. This can result in an address being duplicated
in the subnet, breaking a basic assumption of IPv6 connectivity.
o IPv6 NDP Neighbor Solicitation (NS) messages used in DAD and
Address Lookup make use of Link-Scope multicast. In contrast to
IPv4, an IPv6 Node will typically use multiple addresses, and may
change them often for privacy reasons. This multiplies the impact
of multicast messages that are associated to the mobility of a
Node. Router advertisement (RA) messages are also periodically
multicasted over the Link.
o Neighbors may be considered lost if several consecutive packets
fail.

Address Resolution

Service Discovery

Route Discovery

Decentralized Address Assignment

Geographic routing

3.2.3. MLD issues

Multicast Listener Discovery(MLD) [RFC4541] is often used to identify
members of a multicast group that are connected to the ports of a
switch. Forwarding multicast frames into a WiFi-enabled area can use
such switch support for hardware forwarding state information.
However, since IPv6 makes heavy use of multicast, each STA with an
IPv6 address will require state on the switch for several and
possibly many multicast solicited-node addresses. Multicast
addresses that do not have forwarding state installed (perhaps due to
hardware memory limitations on the switch) cause frames to be flooded
on all ports of the switch.

3.2.4. Spurious Neighbor Discovery

On the Internet there is a "background radiation" of scanning traffic
(people scanning for vulnerable machines) and backscatter (responses
from spoofed traffic, etc). This means that routers very often
receive packets destined for machines whose IP addresses may or may
not be in use. In the cases where the IP is assigned to a host, the
router broadcasts an ARP request, gets back an ARP reply, and caches
it; then traffic can be delivered to the host. When the IP address
is not in use, the router broadcasts one (or more) ARP requests, and
never gets a reply. This means that it does not populate the ARP
cache, and the next time there is traffic for that IP address the
router will rebroadcast the ARP requests.

The rate of these ARP requests is proportional to the size of the
subnets, the rate of scanning and backscatter, and how long the
router keeps state on non-responding ARPs. As it turns out, this
rate is inversely proportional to how occupied the subnet is (valid
ARPs end up in a cache, stopping the broadcasting; unused IPs never
respond, and so cause more broadcasts). Depending on the address
space in use, the time of day, how occupied the subnet is, and other
unknown factors, on the order of 2000 broadcasts per second have been
observed at the IETF NOCs.

On a wired network, there is not a huge difference amongst unicast,
multicast and broadcast traffic; but this is not true in the wireless
realm. Wireless equipment often is unable to send this amount of
broadcast and multicast traffic. Consequently, on the wireless
networks, we observe a significant amount of dropped broadcast and
multicast packets. This, in turn, means that when a host connects it
is often not able to complete DHCP, and IPv6 RAs get dropped, leading
to users being unable to use the network.

4. Multicast protocol optimizations

This section lists some optimizations that have been specified in
IEEE 802 and IETF that are aimed at reducing or eliminating the
issues discussed in Section 3.

4.1. Proxy ARP in 802.11-2012

The AP knows the MAC address and IP address for all associated STAs.
In this way, the AP acts as the central "manager" for all the 802.11
STAs in its BSS. Proxy ARP is easy to implement at the AP, and
offers the following advantages:

o Reduced broadcast traffic (transmitted at low MCS) on the wireless
medium
o STA benefits from extended power save in sleep mode, as ARP
requests for STA's IP address are handled instead by the AP.
o ARP frames are kept off the wireless medium.
o No changes are needed to STA implementation.

Here is the specification language as described in clause 10.23.13 of
[dot11-proxyarp]:

When the AP supports Proxy ARP "[...] the AP shall maintain a
Hardware Address to Internet Address mapping for each associated
station, and shall update the mapping when the Internet Address of
the associated station changes. When the IPv4 address being
resolved in the ARP request packet is used by a non-AP STA
currently associated to the BSS, the proxy ARP service shall
respond on behalf of the non-AP STA"

4.2. IPv6 Address Registration and Proxy Neighbor Discovery

As used in this section, a Low-Power Wireless Personal Area Network
(6LoWPAN) denotes a low power lossy network (LLN) that link local 802.11 doesn't necessarily support
multicast, it supports broadcast. To make make multicast over wifi
work successfully we often need
6LoWPAN Header Compression (HC) [RFC6282]. A 6TiSCH network
[I-D.ietf-6tisch-architecture] is an example of a 6LowPAN. In order
to modify control the use of IPv6 multicast over 6LoWPANs, the 6LoWPAN
Neighbor Discovery (6LoWPAN ND) [RFC6775] standard defines an address
registration mechanism that relies on a central registry to instead be
sent assess
address uniqueness, as unicast a substitute to the inefficient Duplicate
Address Detection (DAD) mechanism found in order for it the mainstream IPv6
Neighbor Discovery Protocol (NDP) [RFC4861][RFC4862].

The 6lo Working Group is now completing an update
[I-D.ietf-6lo-rfc6775-update] to successfully transmit RFC6775. The update enables the
registration to a Backbone Router [I-D.ietf-6lo-backbone-router],
which proxies for the registered addresses with useable
quality. Multicast over wifi experiences the mainstream IPv6
NDP running on a high packet error rates, no
acknowledgements, and low data rate. This draft reviews these
problems found with multicast over wifi. While this is not speed aggragating backbone. The update also
enables a
solutions draft, common workarounds proxy registration on behalf of the registered node, e.g.
by a 6LoWPAN router to some which the mobile node is attached.

The general idea behind the backbone router concept is that in a
variety of Wireless Local Area Networks (WLANs) and Wireless Personal
Area Networks (WPANs), the problems will broadcast/multicast domain should be
listed, along with
controlled, and connectivity to a particular link that provides the impact
subnet should be left to Layer-3. The model for the Backbone Router
operation is represented in Figure 1.

LLN LLN LLN

Figure 1: Backbone Link and Backbone Routers

LLN nodes can move freely from an LLN anchored at one IPv6 Backbone
Router to an LLN anchored at another Backbone Router on the same
backbone, keeping any of the workarounds.

2. Multicast over WiFi Problems

802.11 is IPv6 addresses they have configured.
The Backbone Routers maintain a wireless broadcast medium Binding Table of their Registered
Nodes, which works well for unicast
and has become ubiquitous in its use. With multicast, however,
problems arise over wifi. There are no ACKs for multicast packets,
for instance, so there can be serves as a high level distributed database of packet error rate (PER)
due all the LLN Nodes.
An extension to lack of retransmission and because the sender never backs off.
It Neighbor Discovery Protocol is not uncommon for there introduced to be a packet loss rate
exchange that information across the Backbone Link in the reactive
fashion of 5% which is
particularly troublesome for video and other environments where high
data rates mainstream IPv6 Neighbor Discovery.

RFC6775 and high reliability follow-on work (e.g., [I-D.ietf-6lo-ap-nd], are required. Multicast, over wifi,
is typically sent on a low date rate which makes video negatively
impacted. Wifi loses many more packets then wired due designed
to collisions
and signal loss. There are also problems because clients address the needs of LLNs, but the techniques are unable
to stay in sleep mode due likely to be
valuable on any type of link where sleeping devices are attached, or
where the use of broadcast and multicast control packets continuing operations should be
limited.

4.3. Buffering to improve Power-Save

Methods have been developed to unnecessarily help save battery life; for example, a
device might not wake up those clients which subsequently reduces
energy savings. Video is becoming when the dominant content for end
device applications, with AP receives a multicast being packet.
The AP acts on behalf of STAs in various ways. In order to improve
the most natural method power-saving feature for
applications STAs in its BSS, the AP buffers frames
for delivery to transmit video. Unfortunately, multicast, even
though it the STA at the time when the STA is a very natural choice scheduled for
reception. If an AP, for video, incurs instance, expresses a DTIM of 3 then it
will send a large penalty
over wifi.

One big difference between multicast over wired versus packet every 3 packets. But the reality is
that most AP's will send a multicast every 30 packets. For unicast
there's a TIM. But because multicast over
wired is that wired links are a fixed transmission rate. Wifi, on going to everyone, the other hand, has AP
sends a transmission rate which varies over time
depending upon the broadcast to everyone. DTIM does power management but
clients proximity can choose whether or not to wake up or not and whether or
not to drop the AP. Throughput packet. Unfortunately, without proper administrative
control, such clients may no longer be able to determine why their
multicast operations do not work.

4.4. IPv6 support in 802.11-2012

IPv6 uses Neighbor Discovery Protocol (NDP) instead of video
flows, and ARP. Every
IPv6 node subscribes to a special multicast address for this purpose.

Here is the capacity specification language from clause 10.23.13 of
[dot11-proxyarp]:

"When an IPv6 address is being resolved, the broader wifi network, will change and
will impact Proxy Neighbor
Discovery service shall respond with a Neighbor Advertisement
message [...] on behalf of an associated STA to an [ICMPv6]
Neighbor Solicitation message [...]. When MAC address mappings
change, the ability for QoS solutions AP may send unsolicited Neighbor Advertisement
Messages on behalf of a STA."

NDP may be used to effectively reserve
bandwidth and provide admission control.

The main problems associated with multicast over WiFi are as follows:

o Low Reliability request additional information

o Lower Data Rate Maximum Transmission Unit
o High interference Router Solicitation
o High Power Consumption

These points will be elaborated separately Router Advertisement, etc.

NDP messages are sent as group addressed (broadcast) frames in
802.11. Using the following
subsections.

2.1. Low Reliability

Because of proxy operation helps to keep NDP messages off the lack
wireless medium.

4.5. Conversion of acknowledgement for packets from Access Point multicast to the receivers, it unicast

It is not often possible for the Access Point to know
whether or not a retransmission transmit multicast control and data messages
by using unicast transmissions to each station individually.

4.6. Directed Multicast Service (DMS)

There are situations where more is needed. Even in the wired
Internet, this characteristic commonly causes undesirably high error
rates, contributing needed than simply converting
multicast to unicast. For these purposes, DMS enables a client to
request that the relatively slow uptake of AP transmit multicast
applications even though group addressed frames
destined to the protocols have been available requesting clients as individually addressed frames
[i.e., convert multicast to unicast]. Here are some characteristics
of DMS:

o Requires 802.11n A-MSDUs
o Individually addressed frames are acknowledged and are buffered
for
decades. power save clients
o The situation requesting STA may specify traffic characteristics for wireless links is much worse, DMS
traffic
o DMS was defined in IEEE Std 802.11v-2011
o DMS requires changes to both AP and STA implementation.

DMS is
quite sensitive to the presence of background traffic.

2.2. Low Data Rate

For wireless stations associated not currently implemented in products.

4.7. GroupCast with an Access Points, the necessary
power for good Retries (GCR)

GCR (defined in [dot11aa]) provides greater reliability by using
either unsolicited retries or a block acknowledgement mechanism. GCR
increases probability of broadcast frame reception can vary from station to station. success, but still
does not guarantee success.

For
unicast, the goal is to minimize power requirements while maximizing block acknowledgement mechanism, the data rate AP transmits each group
addressed frame as conventional group addressed transmission.
Retransmissions are group addressed, but hidden from non-11aa
clients. A directed block acknowledgement scheme is used to the destination. For multicast, the goal harvest
reception status from receivers; retransmissions are based upon these
responses.

GCR is simply suitable for all group sizes including medium to maximize large groups.
As the number of receivers that will correctly receive the
multicast packet. For this purpose, generally devices in the Access Point has group increases, GCR can send block
acknowledgement requests to use a much lower data rate at only a power level high enough for even small subset of the farthest station group. GCR
does require changes to receive the packet. Consequently, the data
rate of both AP and STA implementation.

GCR may introduce unacceptable latency. After sending a video stream, for instance, would be constrained by the
environmental considerations group of
data frames to the least reliable receiver
associated with the Access Point.

2.3. High Interference

As mentioned in group, the previous subsection, multicast transmission to AP has do the stations associated to an Access Point typically proceeds at following:

o unicast a
much higher power level than is required for unicat Block Ack Request (BAR) to many a subset of members.
o wait for the
receivers. High power levels directly contribute to stronger
interference. The interference due corresponding Block Ack (BA).
o retransmit any missed frames.
o resume other operations which may have been delayed.

This latency may not be acceptable for some traffic.

There are ongoing extensions in 802.11 to multicast improve GCR performance.

o BAR is sent using downlink MU-MIMO (note that downlink MU-MIMO is
already specified in 802.11-REVmc 4.3).
o BA is sent using uplink MU-MIMO (which is a .11ax feature).
o Additional 802.11ax extensions are under consideration; see
[mc-ack-mux]
o Latency may extend to
effects inhibiting packet reception at more distant stations also be reduced by simultaneously receiving BA
information from multiple clients.

5. Operational optimizations

This section lists some operational optimizations that
might even can be associated
implemented when deploying wireless IEEE 802 networks to mitigate the
issues discussed in Section 3.

5.1. Mitigating Problems from Spurious Neighbor Discovery

ARP Sponges

An ARP Sponge sits on a network and learn which IPs addresses
are actually in use. It also listen for ARP requests, and, if
it sees an ARP for an IP address which it believes is not used,
it will reply with other Access Points. Moreover, its own MAC address. This means that the use
of lower data rates implies
router now has an IP to MAC mapping, which it caches. If that
IP is later assigned to an machine (e.g using DHCP), the physical medium ARP
sponge will be occupied see this, and will stop replying for a longer time to transmit a packet than would be required at high
data rates. Thus, that address.
Gratuitous ARPs (or the level of interference due to multicast machine ARPing for its gateway) will be
not only higher, but longer
replace the sponged address in duration.

Depending on the choice router ARP table. This
technique is quite effective; but, unfortunately, the ARP
sponge daemons were not really designed for this use (the
standard one [arpsponge], was designed to deal with the
disappearance of 802.11 technology, participants from an IXP) and the configured
choice so are not
optimized for the base data this purpose. We have to run one daemon per
subnet, the tuning is tricky (the scanning rate for multicast transmission from versus the
Access Point,
population rate versus retires, etc.) and sometimes the amount of additional interference can range from a
factor of ten, daemons
just seem to stop, requiring a factor thousands for 802.11ac.

2.4. High Power Consumption

One restart of the characteristics of multicast transmission is that every
station has daemon and
causing disruption.

Router mitigations

Some routers (often those based on Linux) implement a "negative
ARP cache" daemon. Simply put, if the router does not see a
reply to an ARP it can be configured to wake up to receive the multicast,
even though cache this information
for some interval. Unfortunately, the received packet may ultimately be discarded. This
process has core routers which we
are using do not support this. When a relatively large impact on the power consumption by the
multicast receiver station.

3. Common remedies host connects to multicast over wifi problems

One common solution network
and gets an IP address, it will ARP for its default gateway
(the router). The router will update its cache with the IP to
host MAC mapping learnt from the multicast over wifi problem is request (passive ARP
learning).

Firewall unused space

The distribution of users on wireless networks / subnets
changes from meeting to convert meeting (e.g the multicast traffic into unicast. "IETF-secure" SSID was
renamed to "IETF", fewer users use "IETF-legacy", etc). This
utilization is often referred difficult to predict ahead of time, but we can
monitor the usage as
multicast attendees use the different networks. By
configuring multiple DHCP pools per subnet, and enabling them
sequentially, we can have a large subnet, but only assign
addresses from the lower portions of it. This means that we
can apply input IP access lists, which deny traffic to unicast (MC2UC). Converting the packets
upper, unused portions. This means that the router does not
attempt to unicast is
beneficial because unicast forward packets are acknowledged and retransmitted
as needed to prevent as much loss. The Access Points (AP) is also
able to provide rate limiting as needed. The drawback with this
approach is that the benefit unused portions of using multicast the
subnets, and so does not ARP for it. This method has proven to
be very effective, but is defeated.

Using 802.11n helps provide somewhat of a more reliable blunt axe, is fairly
labor intensive, and higher level of
signal-to-noise ratio in requires coordination.

Disabling/filtering ARP requests

In general, the router does not need to ARP for hosts; when a wifi environment over which multicast
(broadcast) packets can be sent. This
host connects, the router can provide higher throughput
and reliability but learn the broadcast limitations remain.

4. State of IP to MAC mapping from
the Union

In discussing these issues over email and, most recently, in a side
meeting at IETF 99, it is generally agreed ARP request sent by that these problems will
not host. This means that we should
be fixed anytime soon primarily because it's expensive able to do so disable and multicast is unreliable. The problem of v6 neighbor discovery
saturating / or filter ARP requests from the wifi link
router. Unfortunately, ARP is only a very low level / fundamental
part of the problem. A big problem IP stack, and is that often offloaded from the 802.11 multicast channel normal
control plane. While many routers can filter layer-2 traffic,
this is usually implemented as an afterthought input filter and only
given 100th of / or has
limited ability to filter output broadcast traffic. This means
that the bandwidth. Multicast is basically a second class
citizen, simple "just disable ARP or filter it outbound" seems
like a really simple (and obvious) solution, but
implementations / architectural issues make this difficult or
awkward in practice.

NAT

The broadcasts are overwhelmingly being caused by outside
scanning / backscatter traffic. This means that, if we were to unicast, over wifi. Unicast may have allocated 10mb
while Multicast will
NAT the entire (or a large portion) of the attendee networks,
there would be allocated 1mb. There are many protocols
using multicast no NAT translation entries for unused addresses,
and there needs to so the router would never ARP for them. The IETF NOC has
discussed NATing the entire (or large portions) attendee
address space, but a: elegance and b: flaming torches and
pitchfork concerns means we have not attempted this yet.

Stateful firewalls

Another obvious solution would be something provided in order to
make them more reliable. Wifi put a stateful firewall
between the wireless network and the Internet. This firewall
would block incoming traffic classes may help. We need not associated with an outbound
request. The IETF philosophy has been to
determine what problem have the network as
open as possible / honor the end-to-end principle. An attendee
on the meeting network should be solved by the IETF an Internet host, and what problem should
be solved by able to receive unsolicited requests. Unfortunately,
keeping the IEEE.

Apple's Bonjour protocol, for instance, provides service discovery
(for printing) that utilizes multicast. It's network working and stable is the first thing
operators drop. Even if multicast snooping is utilized, everyone
registers at once using Bonjour priority
and the network has serious
degradation. There is also a lot of work being developed stateful firewall may be required in order to help
save battery life such as achieve
this.

6. Multicast Considerations for Other Wireless Media

Many of the devices not waking up when receiving a
multicast packet. If an AP, causes of performance degradation described in earlier
sections are also observable for wireless media other than 802.11.

For instance, expresses a DTIM of 3 then
it problems with power save, excess media occupancy, and
poor reliability will send a multicast packet every 3 packets. But also affect 802.15.3 and 802.15.4. However,
802.15 media specifications do not include mechanisms similar to
those developed for 802.11. In fact, the reality is
that most AP's will send a multicast every 30 packets. For unicast
there's a TIM. But because multicast design philosophy for
802.15 is going to everyone, oriented towards minimality, with the AP
sends a broadcast result that many such
functions would more likely be relegated to everyone. DTIM does power management but
clients can choose operation within higher
layer protocols. This leads to wake up or not a patchwork of non-interoperable and whether
vendor-specific solutions. See [uli] for some additional discussion,
and a proposal for a task group to drop resolve similar issues, in which
the packet
or not. Then they don't know why their bonjour doesn't work. multicast problems might be considered for mitigation.

7. Recommendations

This section will provide some recommendations about the usage and
combinations of the multicast enhancements described in Section 4 and
Section 5.

(FFS)

8. Discussion Items

This section will suggest some discussion items for further
resolution.

The IETF may just need to decide that broadcast is more expensive so
multicast needs to be sent wired. For example, 802.1ak works on
ethernet and wifi. 802.1ak has been pulled into 802.1Q as of 802.1Q-2011. 802.1Q-
2011. 802.1Q-2014 can be looked at here: http://www.ieee802.org/1/pages/802.1Q-
2014.html . http://www.ieee802.org/1/
pages/802.1Q-2014.html. If we don't find a generic solution we need to establish is not found,
guidelines for multicast over wifi within the mboned wg. A multicast
over wifi IETF mailing list is formed (mcast-wifi@ietf.org) and more
discussion to should be had there. This draft will serve as the current
state of affairs.

This is not a solutions draft, but to established.

To provide an idea going forward, perhaps a reliable registration to
Layer-2 multicast groups and a reliable multicast operation at
Layer-2 could provide a generic solution. There is no need to
support 2^24 groups to get solicited node multicast working: it is
possible to simply select a number of trailing bits that make sense
for a given network size to limit the amount of unwanted deliveries
to reasonable levels. We need to
encourage IEEE 802.1 802.1, 802.11, and 802.11 802.15 should be
encouraged to revisit L2 multicast issues. In particular, Wi-Fi
provides a broadcast service, not a multicast one.
In fact one; at the PHY level,
all frames are broadcast at the PHY level unless we beamform.
What comes with unicast is except in very unusual cases in which
special beamforming transmitters are used. Unicast offers the property
advantage of being much faster (2 orders of magnitude) and much more
reliable (L2 ARQ).

5. IANA Considerations

None

9. Security Considerations

None

7. Acknowledgments

The following people

This document does not introduce any security mechanisms, and does
not have contributed information affect existing security mechanisms.

10. IANA Considerations

This document does not specify any IANA actions.

11. Acknowledgements

This document has benefitted from discussions with the following
people, in alphabetical order: Pascal Thubert

12. Informative References

[arpsponge]
Arien Vijn, Steven Bakker, "Arp Sponge", March 2015.

[dot11] P802.11, "Part 11: Wireless LAN Medium Access Control
(MAC) and discussion Physical Layer (PHY) Specifications", March
2012.

[dot11-proxyarp]
P802.11, "Proxy ARP in
the meetings 802.11ax", September 2015.

[dot11aa] P802.11, "Part 11: Wireless LAN Medium Access Control
(MAC) and on the list which proved helpful Physical Layer (PHY) Specifications Amendment 2:
MAC Enhancements for Robust Audio Video Streaming", March
2012.

[I-D.ietf-6lo-ap-nd]
Thubert, P., Sarikaya, B., and M. Sethi, "Address
Protected Neighbor Discovery for Low-power and Lossy
Networks", draft-ietf-6lo-ap-nd-05 (work in progress),
January 2018.

[I-D.ietf-6lo-backbone-router]
Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
backbone-router-05 (work in progress), January 2018.

[I-D.ietf-6lo-rfc6775-update]
Thubert, P., Nordmark, E., Chakrabarti, S., and C.
Perkins, "An Update to 6LoWPAN ND", draft-ietf-6lo-
rfc6775-update-11 (work in progress), December 2017.

[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the development TSCH mode
of the latest version this IEEE 802.15.4", draft-ietf-6tisch-architecture-13 (work
in progress), November 2017.

[ietf_802-11]
Dorothy Stanley, "IEEE 802.11 multicast capabilities", Nov
2015.

[mc-ack-mux]
Yusuke Tanaka et al., "Multiplexing of Acknowledgements
for Multicast Transmission", July 2015.

[mc-prob-stmt]
Mikael Abrahamsson and Adrian Stephens, "Multicast on
802.11", March 2015.

[mc-props]
Adrian Stephens, "IEEE 802.11 multicast properties", March
2015.

[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Draft:

Dave Taht, Donald Eastlake, Pascal Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.

[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.

[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.

[RFC6282] Hui, J., Ed. and P. Thubert, Juan Carlos Zuniga,
Mikael Abrahamsson, Diego Dujovne, David Schinazi, Stig Venaas,
Stuart Cheshire, Lorenzo, Greg Shephard, Mark Hamilton

8. Normative References

[RFC2119] Bradner, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.

[RFC6775] Shelby, Z., Ed., Chakrabarti, S., "Key words Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for use in RFCs to Indicate
Requirement Levels", BCP 14, IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 2119, 6775, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. 10.17487/RFC6775, November 2012,
<https://www.rfc-editor.org/info/rfc6775>.

[uli] Pat Kinney, "LLC Proposal for 802.15.4", Nov 2015.

Authors' Addresses

Mike McBride
Huawei

Charles E. Perkins
Futurewei Inc.
2330 Central Expressway
Santa Clara Clara, CA 95055 95050
USA

Phone: +1-408-330-4586
Email: michael.mcbride@huawei.com
Charlie Perkins
Huawei charliep@computer.org

Mike McBride
Futurewei Inc.
2330 Central Expressway
Santa Clara Clara, CA 95055
USA

Email: charlie.perkins@huawei.com michael.mcbride@huawei.com

Dorothy Stanley
Hewlett Packard Enterprise
2000 North Naperville Rd.
Naperville, IL 60566
USA

Phone: +1 630 979 1572
Email: dstanley@arubanetworks.com

Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
USA

Email: warren@kumari.net
Juan Carlos Zuniga
SIGFOX
425 rue Jean Rostand
Labege 31670
France

Email: j.c.zuniga@ieee.org