# RAET # Reliable Asynchronous Event Transport Protocol

See also

RAET Overview



OSI Layers

7: Application: Format: Data (Stack to Application interface buffering etc) 6: Presentation: Format: Data (Encrypt-Decrypt convert to machine independent format) 5: Session: Format: Data (Interhost communications. Authentication. Groups) 4: Transport: Format: Segments (Reliable delivery of Message, Transactions, Segmentation, Error checking) 3: Network: Format: Packets/Datagrams (Addressing Routing) 2: Link: Format: Frames ( Reliable per frame communications connection, Media access controller ) 1: Physical: Bits (Transceiver communication connection not reliable)

Link is hidden from Raet Network is IP host address and Udp Port Transport is Raet transactions, service kind, tail error checking, Could include header signing as part of transport reliable delivery serialization of header Session is session id key exchange for signing. Grouping is Road (like 852 channel) Presentation is Encrypt Decrypt body Serialize Deserialize Body Application is body data dictionary

Header signing spans both the Transport and Session layers.


Header ASCII Safe JSON Header termination: Empty line given by double pair of carriage return linefeed /r/n/r/n 10 13 10 13 ADAD 1010 1101 1010 1101

In json carriage return and newline characters cannot appear in a json encoded string unless they are escaped with backslash, so the 4 byte combination is illegal in valid json that does not have multi-byte unicode characters.

These means the header must be ascii safe so no multibyte utf-8 strings allowed in header.

Following Header Terminator is variable length signature block. This is binary and the length is provided in the header.

Following the signature block is the packet body or data. This may either be JSON or packed binary. The format is given in the json header

Finally is an optional tail block for error checking or encryption details

Header Fields

In UDP header

sh = source host sp = source port dh = destination host dp = destination port

In RAET Header

hk = header kind hl = header length

vn = version number

sd = Source Device ID dd = Destination Device ID cf = Corresponder Flag mf = Multicast Flag

si = Session ID ti = Transaction ID

sk = Service Kind pk = Packet Kind bf = Burst Flag (Send all Segments or Ordered packets without interleaved acks)

oi = Order Index dt = DateTime Stamp

sn = Segment Number sc = Segment Count

pf = Pending Segment Flag af = All Flag (Resent all Segments not just one)

nk = Auth header kind nl = Auth header length

bk = body kind bl = body length

tk = tail kind tl = tail length

fg = flags packed (Flags) Default '00' hex string
2 byte Hex string with bits (0, 0, af, pf, 0, bf, mf, cf) Zeros are TBD flags

Session Bootstrap

Minion sends packet with SID of Zero with public key of minions Public Private Key pair Master acks packet with SID of Zero to let minion know it received the request

Some time later Master sends packet with SID of zero that accepts the Minion



Session is important for security. Want one session opened and then multiple transactions within session.

Session ID SID sid

GUID hash to guarantee uniqueness since no guarantee of nonvolatile storage or require file storage to keep last session ID used.

Service Types or Modular Services

Four Service Types

  1. One or more maybe (unacknowledged repeat) maybe means no guarantee

  2. Exactly one at most (ack with retries) (duplicate detection idempotent)

    at most means fixed number of retries has finite probability of failing B1) finite retries B2) infinite retries with exponential back-off up to a maximum delay

  3. Exactly one of sequence at most (sequence numbered)

    Receiver requests retry of missing packet with same B1 or B2 retry type

  4. End to End (Application layer Request Response)

    This is two B sub transactions

Initially unicast messaging Eventually support for Multicast

The use case for C) is to fragment large packets as once a UDP packet exceeds the frame size its reliability goes way down So its more reliable to fragment large packets.

Better approach might be to have more modularity. Services Levels

  1. Maybe one or more
    1. Fire and forget

      no transaction either side

    2. Repeat, no ack, no dupdet

      repeat counter send side, no transaction on receive side

    3. Repeat, no Ack, dupdet

      repeat counter send side, dup detection transaction receive side

  2. More or Less Once
    1. retry finite, ack no dupdet

      retry timer send side, finite number of retires ack receive side no dupdet

  3. At most Once
    1. retry finite, ack, dupdet

      retry timer send side, finite number of retires ack receive side dupdet

  4. Exactly once
    1. ack retry

      retry timer send side, ack and duplicate detection receive side Infinite retries with exponential backoff

  5. Sequential sequence number
    1. reorder escrow
    2. Segmented packets
  6. request response to application layer

Service Features

  1. repeats
  2. ack retry transaction id
  3. sequence number duplicate detection out of order detection sequencing
  4. rep-req

Always include transaction id since multiple transactions on same port So get duplicate detection for free if keep transaction alive but if use

A) Maybe one or more B1) At Least One B2) Exactly One C) One of sequence D) End to End

A) Sender creates transaction id for number of repeats but receiver does not keep transaction alive

B1) Sender creates transaction id keeps it for retries. Receiver keeps it to send ack then kills so retry could be duplicate not detected

B2) Sender creates transaction id keeps for retries Receiver keeps tid for acks on any retires so no duplicates.

C) Sender creates TID and Sequence Number. Receiver checks for out of order sequence and can request retry.

D) Application layer sends response. So question is do we keep transaction open or have response be new transaction. No because then we need a rep-req ID so might as well use the same transaction id. Just keep alive until get response.

Little advantage to B1 vs B2 not having duplicates.

So 4 service types

  1. Maybe one or more (unacknowledged repeat)
  2. Exactly One (At most one) (ack with retry) (duplicate detection idempotent)
  3. One of Sequence (sequence numbered)
  4. End to End

Also multicast or unicast

Modular Transaction Table

Sender Side:
Transaction ID plus transaction source sender or receiver generated transaction id Repeat Counter Retry Timer Retry Counter (finite retries) Redo Timer (infinite redos with exponential backoff) Sequence number without acks (look for resend requests) Sequence with ack (wait for ack before sending next in sequence) Segmentation
Receiver Side:
Nothing just accept packet Acknowledge (can delete transaction after acknowledge) No duplicate detection Transaction timeout (keep transaction until timeout) Duplicate detection save transaction id duplicate detection timeout Request resend of missing packet in sequence Sequence reordering with escrow timeout wait escrow before requesting resend Unsegmentation (request resends of missing segment)