UDP Reliability Layer is a user protocol that will provide connectionless reliable packet transmission.

URL Format

URL is composed of mutiple headers and might contain a payload.

Acknowledgement Header

ACK (Or NACK If URL Protocol Information : NACK Information) of the arrived message. Must not have payload.

• HT (2-bit)- Header Type.
• SQN (30-bit) - URL Message Offset for the corresponding ACK/NACK.
• MSG_ID (16-bit) - Message Identifier for the corresponding ACK/NACK.
• MAC (16-bit) - Message Authentication Code.

URL Message Initial Data Header

Indicates the start of trasmission of URL Message. Contains the size of URL Message to be sent. Payload is is required. Payload OFFSET is 0. Last header before payload.

• HT (2-bit) - Header.
• SZ (30-bit) - URL Message size.
• MSG_ID (16-bit) - Message Identifier for the corresponding segment payload.
• MAC (16-bit)- Message Authentication Code
• SEND_OPT - Send option:
  • 3:0 - Integrity Protection Algorithm.
  • 7:4 - Ciphering Algorithm.
  • 8 - Acknowledge Mode.
  • 9 - Retransmission.

URL Message Data Header

Indicates URL Segment Message. Payload is required. Last header before payload.

• HT (2-bit) - Header Type.
• OFSSET (30-bit) - URL Message Offset for the corresponding segment payload.
• MSG_ID (16-bit) - Message Identifier for the corresponding segment payload.
• MAC (16-bit) - Message Authentication Code.

URL Protocol Information : NACK Information

Indicated that there is an error in the received URL Message Segment. When present, next header is always Acknowledgement Header. Last header.

• HT (2-bit) - Header Type.
• ID (3-bit) - Infomation type.
• INFO (27-bit) - Information Label:
  • INFO = 0 - Duplicate Segment Mismatched.
  • INFO = 1 - Received Segment Overlapped.
  • INFO = 2 - Integrity Protection Failed.
  • INFO = 3 - Decryption Failed.

• When an URL message is requested to be the message size is larger than the configured URL MTU, the message will be segmented into several transmission units.
• URL Message Segment transmission size varies from channel quality and is determined during the transmission.
• In the sender the segments are transmitted sequentially every URL MESSAGE SEGMENT TX INTERVAL.
• URL Message Segment 0 is sent first, the subsequent URL Message Segments will not be sent if the URL Message Segment is ACKed.
• Every sent segment must have an ACK from receiver within URL SEGMENT TIMEOUT window.
• If the URL MESSAGE SEGMENT TIMEOUT expires without an ACK, failed segment will be transmitted again.
• Each retransmission decreases the URL Segment transmission size and increases the URL MESSAGE SEGMENT TX INTERVAL and URL MESSAGE SEGMENT TIMEOUT.
• If the total segment retransmission is equal to URL MAX MESSAGE SEGMENT RETX, the URL MESSAGE is resent from offset 0 with and with a URL Protocol Information: Sender Request INFO = Retransmit Indication.
• If the URL RETX failed URL MAX URL MSG RETX times, send function will return with an URL MESSAGE TX ERROR.