From: Henrik Austad <haus...@cisco.com> Describe the overall design behind the TSN standard, the TSN-driver, requirements to userspace and new functionality introduced.
Cc: "David S. Miller" <da...@davemloft.net> Signed-off-by: Henrik Austad <haus...@cisco.com> --- Documentation/TSN/tsn.txt | 147 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 147 insertions(+) create mode 100644 Documentation/TSN/tsn.txt Index: linux/Documentation/TSN/tsn.txt =================================================================== --- /dev/null +++ linux/Documentation/TSN/tsn.txt @@ -0,0 +1,188 @@ + Time Sensitive Networking (TSN) + ------------------------------- + +[work in progress] + +1. Motivation +============= + +TSN is a set of open standards, formerly known as 'AVB' (Audio/Video +Bridging). It was renamed to TSN to better reflect that it can do much +more than just media transport. + +TSN is a way to create reliable streams across a network without loss of +frames due to congestion in the network. By using gPTP (a specialized +IEEE-1588v2 PTP profile), the time can be synchronized with sub-us +granularity across all the connected devices in the AVB domain. + +2. Intro to AVB/TSN +=================== + +The original standards were written with Audio/Video in mind, so the +initial standards refer to this as 'AVB'. In later standards, this has +changed to TSN, and AVB now refers to a service you can add on top of +TSN. Hopefully it will not be too confusing. + +In this document, we refer to the infrastructure part as TSN and AVB to +the ALSA/V4L2 shim which can be added on top of TSN to provide a +media-service. + +TSN operates with 'streams', and one stream can contain pretty much +whatever you like. Currently, only media has been defined properly +though, which is why you only have media-subtypes for the +avtp_subtype-field. + +For a media-setup, one stream can contain multiple channels, all going +to the same destination. A destination can be a single Listener +(singlecast) or a group of Listeners (multicast). + +2.1 Endpoints + +A TSN 'endpoint' is where a stream either originates or ends -what +others would call sources (Talkers) and sinks (Listeners). Looking back +at pre-TSN when this was called AVB, these names make a bit more sense. + +Common for both types, they need to be PTPv2 capable, i.e. you need to +timestamp gPTP frames upon ingress/egress to improve the accuracy of +PTP. + +2.1.1 Talkers + +Hardware requirements: +- Multiple Tx-queues +- Credit based shaper on at least one of the queues for pacing the + frames onto the network +- VLAN capable + +2.1.2 Listener + +A Listener does not have the same requirements as a Talker as it cannot +control the pace of the incoming frames anyway. It is beneficial if the +NIC understands VLANs and has a few Rx-queues so that you can steer all +TSN-frames to a dedicated queue. + +2.2 Bridges + +What TSN calls switches that are TSN-capable. They must be able to +prioritize TSN-streams, have the credit-based shaper available for that +class, support SRP, support gPTP and so on. + +2.3 Relevant standards + +* IEEE 802.1BA-2011 Audio Video Bridging (AVB) Systems + +* IEEE 802.1Q-2011 sec 34 and 35 + + What is referred to as: + IEEE 802.1Qav (Forwarding and Queueing for Time-sensitive Streams) + IEEE 802.1Qat (Stream Registration protocol) + +* IEEE 802.1AS gPTP + + A PTPv2 profile (from IEEE 1588) tailored for this domain. Notable + changes include the requirement that all nodes in the network must be + gPTP capable (i.e. no traversing non-PTP entities), and it allows + traffic over a wider range of medium that what "pure" PTPv2 allows. + +* IEEE 1722 AVTP Layer 2 Transport Protocol for Time-Sensitive + Applications in Bridged Local Area Networks + +* IEEE 1722.1 Device Discovery, Connection Management and Control for 1722 + + What allows AVB (TSN) devices to handle discovery, enumeration and + control, basically let you connect 2 devices from a 3rd + + In this (in the scope of the Linux kernel TSN driver) must be done + purely from userspace as we do not want the kernel to suddenly attach + to a remote system without the user's knowledge. This is further + reflected in how the attributes for the link is managed via ConfigFS. + + +3. Overview and/or design of the TSN-driver +=========================================== + +The driver handles the shifting of data for TSN-streams. Anything else +is left for userspace to handle. This includes stream reservation (using +some sort of MSRP client), negotiating multicast addresses, finding the +value of the different attributes and connect application(s) to the +exposed devices (currently we only have an ALSA-device). + + /--------------------\ + | | + | Media application | + | | + \--------------------/ + | | + +----------+ +----+ + | | + | | + +------------+ | + | ALSA | | + +------------+ | + | | + | | + +------------+ +--------------+ + | avb_alsa | | tsn_configfs | + | (tsn-shim) | +--------------+ + +------------+ | + | | + | | + +------+ | + | | + | | + +------------+ | + | tsn_core |<--------+ + +------------+ + | + | + +------------+ + | tsn_net | + +------------+ + | + | + +------------+ + | network | + | subsystem | + +------------+ + | + | + ... + + +3.1 Terms and concepts + +TSN uses the concept of streams and shims. + +- A shim is a thin wrapper that binds TSN to another subsystem (or + directly to userspace). avb_alsa is an example of such a shim. + +- A stream is the only data TSN cares about. What the data inside the + stream represents, is left for the associated shim to handle. TSN will + verify the headers up to the protocol specific header and then pass it + along to the shim. + +Note: currently, only the data-unit part is implemented, the control +part, in which 1722.1 (discovery and enumeration) is part, is not +handled. + +3.2 Userspace requirements + +(msrp-client, "tsnctl"-tool + +4. Creating a new link from userspace +===================================== + +[coming] + + +5. Creating a new shim +====================== + +shim_ops +[coming] + + +6. Other resources: +=================== + +https://en.wikipedia.org/wiki/Audio_Video_Bridging
