Determining the next protocol for a packet in a protocol module using DispatchProtocolReq and EncapsulationProtocolReq.

[levy]

Use case:

• sequence of protocol headers/trailers
  e.g. Application Data, UDP, IPv4, IEEE 802.2 LLC, IEEE 802.15.4
• sequence of protocol modules
  App, Udp, Ipv4, Ieee8022Llc, Ieee802154
• dispatch decision (can be hardcoded, locally parametrizable, can depend on packet data or meta data, looked up from database, overridden by being already specified)
  App -> Udp (App)
  Udp -> Ipv4 (Udp by destination address)
  Ipv4 -> Ieee8022Llc (App, Network interface?)
  Ieee8022Llc -> Ieee802154 (Network interface)
  Ieee802154 -> NetworkInterface (Ipv4, App)

determining the next protocol for a packet in a protocol module (DispatchProtocolReq) (outgoing/incoming)

• can be unspecified
• can be hard-coded into C++ source of the module that is currently processing the packet
• can be specified by a protocol parameter on the module
• can be determined by a socket
• can be determined by the address type (e.g. Ipv4, Ipv6) of a destination address
• can be determined by one or more header fields from an incoming packet using a protocol group mapping
• can be determined by a header field directly referencing the protocol
• can be the requested transport protocol, network protocol, MAC protocol (TransportProtocolReq, NetworkProtocolReq, MacProtocolReq)
• can be the expected protocol of a network interface
• can be determined by the current packet protocol
• can be determined by from which protocol module the packet came (e.g. DispatchProtocolInd)
• can be determined by a module that created or previously processed the packet (e.g. application by EncapsulationProtocolReq)
• can be the first protocol in encapsulation protocol request (EncapsulationProtocolReq)
• can be determined by some other packet meta-data (e.g. EncapsulationProtocolReq?)

what should we do when the payload protocol is not specified in the packet (e.g. 802.15.4 or 802.11)?
this information should be attached as a meta-data to the packet by the module which knows this, so a packet dissector (or printer) can process the packet without context

documentation goes into Developer's Guide

who adds DispatchProtocolReq?

• the module who determines the next protocol
  who queries DispatchProtocolReq?
• the message dispatcher module
  who removes DispatchProtocolReq?
• the DispatchProtocolReq destination module who processes the packet

how is the EncapsulationProtocolReq used now?

• RelayInterfaceSelector appends network interface protocol into EncapsulationProtocolReq if DispatchProtocolReq is already present
• Ieee8021qTagEpdHeaderInserter removes first protocol from EncapsulationProtocolReq if present to use in DispatchProtocolReq
• Ieee8021rTagEpdHeaderInserter removes first protocol from EncapsulationProtocolReq if present to use in DispatchProtocolReq
• Ipv4 appends network interface protocol to the end of EncapsulationProtocolReq and copies first entry to DispatchProtocolReq
• StreamEncoder delays existing DispatchProtocolReq and inserts 802.1q and 802.1r protocols into EncapsulationProtocolReq depending on what tags are attached
  +? PacketTaggerBase adds EncapsulationProtocolReq with 802.1q if PcpReq is added

what are typical delayed protocol dispatch actions?

• pop protocol at the beginning of EncapsulationProtocolReq, get first protocol to where the packet must be sent to
• push protocol at the beginning of EncapsulationProtocolReq to send packet to a specific protocol first
• push protocol at the end of EncapsulationProtocolReq to send packet to a specific protocol last

fallback mechanism for next protocol:

• if InterfaceReq is added, push network interface protocol at the end of EncapsulationProtocolReq
• if L3 destination address is specified, set NetworkProtocolReq to corresponding network protocol
• pop protocol at the beginning of EncapsulationProtocolReq
• if no protocol is found, use module specific next protocol parameter
• if no protocol is specified, use module specific hard-coded next protocol
  • in applications use the protocol from TransportProtocolReq
  • in transport protocols use the protocol from NetworkProtocolReq
  • in network protocols use the protocol from MacProtocolReq
• if no protocol is hard-coded, leave DispatchProtocolReq unspecified (direct connections decide who processes the packet next)

TSN use case:
App [app] -> udp (udp app) ()
Udp [udp app] -> ipv4 (ipv4 udp app) ()
Ipv4 [ipv4 udp app] -> ethernetmac (ethernetmac ipv4 udp app) ()
StreamIdentifier [ipv4 udp app] -> ethernetmac (ethernetmac ipv4 udp app) ()
StreamEncoder [ipv4 udp app] -> ieee8021r (ethernetmac ieee8021q ieee8021r ipv4 udp app) (ethernetmac ieee8021q)
Ieee8021r [ieee8021r ipv4 udp app] -> ieee8021q (ethernetmac ieee8021q ieee8021r ipv4 udp app) (ethernetmac)
Ieee8021q [ieee8021q ieee8021r ipv4 udp app] -> ethernetmac (ethernetmac ieee8021q ieee8021r ipv4 udp app) ()
EthernetMac [ethernetmac ieee8021q ieee8021r ipv4 udp app] -> network interface (ethernetmac ieee8021q ieee8021r ipv4 udp app) ()

802.15.4 use case:
App [app] -> udp (udp app) ()
Udp [udp app] -> ipv4 (ipv4 udp app) ()
Ipv4 [ipv4 udp app] -> ieee802154 (ieee802154 ipv4 udp app) ()
Llc [ipv4 udp app] -> ieee8022llc (ieee802154 ieee8022llc ipv4 udp app) (ieee802154)
Ieee8022llc [ieee8022llc ipv4 udp app] -> ieee802154 (ieee802154 ieee8022llc ipv4 udp app) ()
Ieee802154 [ieee802154 ieee8022llc ipv4 udp app] -> network interface (ieee802154 ieee8022llc ipv4 udp app) ()