Subject: [Detnet] Comment on section 5.1.1 of draft-ietf-detnet-use-cases-19.txt

From: "Venkatesan, Ganesh" <[email-masked]>
Date: Mon, 22 Oct 2018 03:24:56 +0000

Hello DetNet members:

The following comment on Section 5.1.1 of draft-ietf-detnet-use-cases-19 is based on our experience with managed Wi-Fi networks (in a wired/wireless topology) and we strongly recommended deleting the highlighted text below (from section 5.1.1). Please let me know if you have any comments or questions:

5.1.1.  Network Convergence using 6TiSCH

   Some wireless network technologies support real-time QoS, and are

   thus useful for these kinds of networks, but others do not.  For

   example WiFi is pervasive but does not provide guaranteed timing or
   delivery of packets, and thus is not useful in this context.

Comment: Recommend deleting the text in bold font above from 5.1.1

Rationale: In a managed deployment like enterprise networks, where enough Access Points (APs) are provisioned to cater to the expected traffic load, operating channels are planned to eliminate/minimize interference, admission control is enabled to eliminate congestion, the non-determinism in the gaining access to the shared medium is minimized. In such cases, packet delivery latency is well bounded.

Since we are exclusively addressing managed deployments, Wi-Fi is well-suited to meet DetNet requirements (e.g., minimize the over-the-Wi-Fi-hop latency, minimize packet error rate, provide robust security, support for IP convergence in Layer-3, provision for required throughput).

The following specifications/certifications are relevant in the context of the requirements outlined in the Use Cases described in this document:

(a)     Time Synchronization - standards based and interoperable: - IEEE802.11-2016 with IEEE802.1AS; WFA TimeSyncTM Certification

(b)     Congestion Control:  IEEE802.11-2016 Admission Control; WFA Admission Control

(c)     Security: WFA WPA2, WPA3

(d)     Interoperating with IEEE802.1Q bridges: IEEE802.11ak

(e)      Stream Reservation Protocol (part of IEEE802.1Qat) - IEEE802.11-2016

In addition, there is ongoing/planned work in the IEEE802.11 Working Group to address challenges like

(a)     dense deployment (resource limited seat speakers in theaters described in Section 2, for example) - IEEE802.11ax D3.0

(b)     Support for 802.1Qbv - IEEE802.11 Topic Interest Group on Real Time Applications; topics discussed here include support for both local and central traffic shaping in order ensure that the low latency/high reliability requirements for DetNet traffic are met while not starving non-DetNet traffic.

IEEE P802.11ax includes mechanisms, such as the use of trigger frames, that allows providing predictable scheduling in a Wi-Fi network and thereby providing guaranteed timely delivery of packets. Moreover, with the support of Orthogonal Frequency Division Multiple Access (OFDMA), multiple DetNet endpoints can be serviced simultaneously.

References:

  1.  IEEE802.11-2016: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications
  2.  IEEE802.11ak-2017: Enhancements for Transit Links Within Bridged Networks
  3.  IEEE802.11ax D3.0: Enhancements for High Efficiency WLAN (available with access to IEEE802.11 members' area)
  4.  WNG documents on RTA (18-1160r0): https://mentor.ieee.org/802.11/dcn/18/11-18-1160-00-0wng-controlling-latency-in-802-11.pptx
  5.  Wi-Fi Alliance Wireless Protected Access 2 (WPA2)
  6.  Wi-Fi Alliance Wireless Multi-Media Admission Control (WMM-AC)
  7.  Wi-Fi Alliance Wireless Protected Access 3 (WPA3)
  8.  Wi-Fi Alliance TimeSyncTM
Cheers --
ganesh