--- 1/draft-ietf-mboned-ieee802-mcast-problems-01.txt 2018-08-17 10:13:08.764339246 -0700 +++ 2/draft-ietf-mboned-ieee802-mcast-problems-02.txt 2018-08-17 10:13:08.808340311 -0700 @@ -1,24 +1,24 @@ Internet Area C. Perkins Internet-Draft M. McBride Intended status: Informational Futurewei -Expires: August 7, 2018 D. Stanley +Expires: February 18, 2019 D. Stanley HPE W. Kumari Google JC. Zuniga SIGFOX - February 3, 2018 + August 17, 2018 Multicast Considerations over IEEE 802 Wireless Media - draft-ietf-mboned-ieee802-mcast-problems-01 + draft-ietf-mboned-ieee802-mcast-problems-02 Abstract Well-known issues with multicast have prevented the deployment of multicast in 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 @@ -39,21 +39,21 @@ 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 August 7, 2018. + This Internet-Draft will expire on February 18, 2019. Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. 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 @@ -68,30 +68,30 @@ 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Identified mulitcast issues . . . . . . . . . . . . . . . . . 5 3.1. Issues at Layer 2 and Below . . . . . . . . . . . . . . . 5 3.1.1. Multicast reliability . . . . . . . . . . . . . . . . 5 3.1.2. Lower and Variable Data Rate . . . . . . . . . . . . 5 3.1.3. High Interference . . . . . . . . . . . . . . . . . . 6 3.1.4. Power-save Effects on Multicast . . . . . . . . . . . 6 3.2. Issues at Layer 3 and Above . . . . . . . . . . . . . . . 7 3.2.1. IPv4 issues . . . . . . . . . . . . . . . . . . . . . 7 - 3.2.2. IPv6 issues . . . . . . . . . . . . . . . . . . . . . 7 + 3.2.2. IPv6 issues . . . . . . . . . . . . . . . . . . . . . 8 3.2.3. MLD issues . . . . . . . . . . . . . . . . . . . . . 8 - 3.2.4. Spurious Neighbor Discovery . . . . . . . . . . . . . 8 + 3.2.4. Spurious Neighbor Discovery . . . . . . . . . . . . . 9 4. Multicast protocol optimizations . . . . . . . . . . . . . . 9 - 4.1. Proxy ARP in 802.11-2012 . . . . . . . . . . . . . . . . 9 + 4.1. Proxy ARP in 802.11-2012 . . . . . . . . . . . . . . . . 10 4.2. IPv6 Address Registration and Proxy Neighbor Discovery . 10 - 4.3. Buffering to improve Power-Save . . . . . . . . . . . . . 11 + 4.3. Buffering to Improve Battery Life . . . . . . . . . . . . 11 4.4. IPv6 support in 802.11-2012 . . . . . . . . . . . . . . . 12 4.5. Conversion of multicast to unicast . . . . . . . . . . . 12 - 4.6. Directed Multicast Service (DMS) . . . . . . . . . . . . 12 + 4.6. Directed Multicast Service (DMS) . . . . . . . . . . . . 13 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 @@ -155,27 +155,30 @@ 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 + This document 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. + enhancements that have been designed at IETF and IEEE 802 to + ameliorate the effects of multicast traffic. Recommendations are + also provided to implementors about how to use and combine these + enhancements. Some advice about the operational choices that can be + taken is also included. It is likely that this document will also be + considered relevant to designers of future IEEE wireless + specifications. 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 @@ -221,45 +224,50 @@ 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 + depending upon the client's 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. + known as the basic rate. The amount of additional interference + depends on the specific wireless technology. In fact backward + compatibility and multi-stream implementations mean that the maximum + unicast rates are currently up to a few Gb/s, so there can be a more + than 3 orders of magnitude difference in the transmission rate + between the basic rates to optimal unicast forwarding. Some + techinues employed to increase spectral efficiency, such as spatial + multiplexing in mimo systems, are not available with more than one + intended reciever; it is not the case that backwards compatibility is + the only factor responsible for lower multicast transmission rates. 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 @@ -385,28 +392,37 @@ 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. + On a wired network, there is not a huge difference between unicast, + multicast and broadcast traffic. Due to hardware filtering (see, + e.g., [Deri-2010]), inadvertently flooded traffic (or high amounts of + ethernet multicast) on wired networks can be quite a bit less costly, + compared to wireless cases where sleeping devices have to wake up to + process packets. Wired Ethernets tend to be switched networks, + further reducing interference from multicast. There is effectively + no collision / scheduling problem except at extremely high port + utilizations. + + This is not true in the wireless realm; wireless equipment is often + unable to send high volumes 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. @@ -491,36 +507,41 @@ An extension to the Neighbor Discovery Protocol is introduced to exchange that information across the Backbone Link in the reactive fashion of mainstream IPv6 Neighbor Discovery. RFC6775 and follow-on work (e.g., [I-D.ietf-6lo-ap-nd], are designed to address the needs of LLNs, but the techniques are likely to be valuable on any type of link where sleeping devices are attached, or where the use of broadcast and multicast operations should be limited. -4.3. Buffering to improve Power-Save +4.3. Buffering to Improve Battery Life Methods have been developed to help save battery life; for example, a device might not wake up when the AP receives a multicast packet. - The AP acts on behalf of STAs in various ways. In order to improve - the power-saving feature for STAs in its BSS, the AP buffers frames - for delivery to the STA at the time when the STA is scheduled for - reception. If an AP, for instance, expresses a DTIM of 3 then it - will send a multicast 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 is going to everyone, the AP - sends a broadcast to everyone. DTIM does power management but - clients can choose whether or not to wake up or not and whether or - not to drop the packet. Unfortunately, without proper administrative - control, such clients may no longer be able to determine why their - multicast operations do not work. + The AP acts on behalf of STAs in various ways. To enable use of the + power-saving feature for STAs in its BSS, the AP buffers frames for + delivery to the STA at the time when the STA is scheduled for + reception. If an AP, for instance, expresses a DTIM (Delivery + Traffic Indication Message) of 3 then the AP will send a multicast + packet every 3 packets. In fact, when any single wireless client + associated with an access point has 802.11 power-save mode enabled, + the access point buffers all multicast frames and sends them only + after the next DTIM beacon. + + But in practice, most AP's will send a multicast every 30 packets. + For unicast there's a TIM (Traffic Indication Message); but since + multicast is going to everyone, the AP sends a broadcast to everyone. + DTIM does power management but clients can choose whether or not to + wake up or not and whether or not to drop the 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 ARP. Every IPv6 node subscribes to a special multicast address for this purpose. Here is the specification language from clause 10.23.13 of [dot11-proxyarp]: "When an IPv6 address is being resolved, the Proxy Neighbor @@ -555,21 +576,22 @@ of DMS: o Requires 802.11n A-MSDUs o Individually addressed frames are acknowledged and are buffered for power save clients o The requesting STA may specify traffic characteristics for DMS traffic o DMS was defined in IEEE Std 802.11v-2011 o DMS requires changes to both AP and STA implementation. - DMS is not currently implemented in products. + DMS is not currently implemented in products. See [Tramarin2017] and + [Oliva2013] for more information. 4.7. GroupCast with 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 success, but still does not guarantee success. For the block acknowledgement mechanism, the AP transmits each group addressed frame as conventional group addressed transmission. @@ -763,68 +784,82 @@ 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. + [Deri-2010] + Deri, L. and J. Gasparakis, "10 Gbit Hardware Packet + Filtering Using Commodity Network Adapters", RIPE 61, + 2010, . + [dot11] P802.11, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications", March 2012. [dot11-proxyarp] P802.11, "Proxy ARP in 802.11ax", September 2015. [dot11aa] P802.11, "Part 11: Wireless LAN Medium Access Control (MAC) and 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. + Networks", draft-ietf-6lo-ap-nd-06 (work in progress), + February 2018. [I-D.ietf-6lo-backbone-router] Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo- - backbone-router-05 (work in progress), January 2018. + backbone-router-06 (work in progress), February 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. + Perkins, "Registration Extensions for 6LoWPAN Neighbor + Discovery", draft-ietf-6lo-rfc6775-update-21 (work in + progress), June 2018. [I-D.ietf-6tisch-architecture] Thubert, P., "An Architecture for IPv6 over the TSCH mode - of IEEE 802.15.4", draft-ietf-6tisch-architecture-13 (work - in progress), November 2017. + of IEEE 802.15.4", draft-ietf-6tisch-architecture-14 (work + in progress), April 2018. [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. + [Oliva2013] + de la Oliva, A., Serrano, P., Salvador, P., and A. Banchs, + "Performance evaluation of the IEEE 802.11aa multicast + mechanisms for video streaming", 2013 IEEE 14th + International Symposium on "A World of Wireless, Mobile + and Multimedia Networks" (WoWMoM) pp. 1-9, June 2013. + [RFC4541] Christensen, M., Kimball, K., and F. Solensky, "Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, . [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, . @@ -838,20 +873,26 @@ Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, DOI 10.17487/RFC6282, September 2011, . [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. Bormann, "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC 6775, DOI 10.17487/RFC6775, November 2012, . + [Tramarin2017] + Tramarin, F., Vitturi, S., and M. Luvisotto, "IEEE 802.11n + for Distributed Measurement Systems", 2017 IEEE + International Instrumentation and Measurement Technology + Conference (I2MTC) pp. 1-6, May 2017. + [uli] Pat Kinney, "LLC Proposal for 802.15.4", Nov 2015. Authors' Addresses Charles E. Perkins Futurewei Inc. 2330 Central Expressway Santa Clara, CA 95050 USA