High DAL Network Stack Overview for Geekfest 2024

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Overview for Geekfest '24: High-DAL UDP Stack

Context

  • We've long have DAL-E stack (LwIP) supporting development tools.
  • Customers are interested in networking usable for programs with specific needs.
  • Specifically: Multiple customers asking for high-DAL stack that does UDP and/or TSN.
    • Current potential launch customer wants UDP.





Goals

  • Protocols: at least UDP, IP, ICMP, ARP, likely IGMP.
  • APIs: sockets. Soon 653 ports.
  • High DAL (DAL-A).
  • Architecture accomodates TSN (later).
  • Eliminate need to schedule a network server in a window, and eliminate surprising latencies.
  • Later add more protocols (eg TCP).





Notes

  • UDP provides few guarantees and high DAL doesn't change that.
  • High-DAL stack not expected to replace DAL-E stack used for development.
  • Hoping to base on code from existing stack (like LwIP).





Draft Design

  • WORK IN PROGRESS!
  • A partition / RMA process that's a network client imports "libnetstack.so"
    • Each partition registers for the protocols/ports it will be using
      • (Is this static configuration at OS startup??)
    • Each partition receives only the frames for its protocols/ports
      • Relies on SoC hardware that parses/filters/classifies frames and routes them to particular queues!
      • Partition interacts with its hardware receive and transmit queues via PRL.
      • No interaction with a server needed for steady-state communication
    • libnetstack.so exports socket APIs to tasks in the partition; creates a task that handles:
      • timers
      • hardware receive queue
  • One distinguished partition, the lite-server, handles the "global" protocols and shared state -- ARP, ICMP, IGMP, ..
    • Some operations (eg, ARP request) become requests to lite-server, which performs operation and updates tables visible to all network client partitions.
    • Refactoring ordinary stack responsibilities between network-client partition and lite-server (maybe some are shared?).





Current Activities

  • Discuss: architecture/design.
  • Investigate: Are there reasonable starting points -- open-source (eg LwIP), commercial.
  • Draft: Tasks and scope.

See Higher-DAL Network Stack.





Appendix: TSN

  • TSN
    • Is a collection of IEEE Ethernet standards.
    • Aims to be a vendor-agnostic solution for deterministic Ethernet.
      • Support time-critical networking with guarantees on availability and latency. (Focus on worst case.)
      • Support sharing network with ordinary best-effort Ethernet traffic (that focuses on average performance).
    • Not vendor agnostic yet.
  • Schedule the bus bandwidth. Some classes of frames designated as scheduled (time sensitive) traffic, others designated as best-effort traffic. Switches and (TSN) end nodes receive the schedule and follow it.
  • TSN needs
    • Time synchronization (PTP)
    • Configuration (generate schedule and distribute to end nodes and switches)
    • Traffic scheduling (on end nodes and switches)
  • How possible is it to support TSN without being wedded to particular vendors?


Feature IEEE Standard Notes
Time synchronization 802.1AS-2020, IEEE 1588 .1AS is a profile of 1588. 1588 is PTP.
Scheduled traffic 802.1Qbv outbound frames. .1Q is VLANs.
Credit Based Shaper 802.1Qav Forwarding and Queuing for Time Sensitive Streams
Per-Stream Filtering and policing 802.1Qci PSFP. inbound frames
Frame preemption IEEE 802.1Qbu, 802.3br .3 is PHY/MAC
Frame replication/elimination for Reliability IEEE 802.1CB FRER
Cyclic queuing and forwarding IEEE 802.1Qch
Stream Reservation Protocol 802.1 Qcc Central Network Controller, Centralized User Configuration
MORE!
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