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the UDP service cannot deliver SDUs that are larger than 65467 bytes [#fmtuudp]_
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the UDP service does not guarantee the delivery of SDUs (losses can occur and SDUs can arrive out-of-sequence)
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the UDP service will not deliver a corrupted SDU to the destination
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The User Datagram Protocol
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The User Datagram Protocol (UDP) is defined in :rfc:`768`. It provides an unreliable connectionless transport service on top of the unreliable network layer connectionless service. The main characteristics of the UDP service are :
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This limitation is due to the fact that the network layer cannot transport packets that are larger than 64 KBytes. As UDP does not include any segmentation/reassembly mechanism, it cannot split a SDU before sending it. The UDP header consumes 8 bytes and the IPv6 header 60. With IPv4, the IPv4 header only consumes 20 bytes and thus the maximum UDP payload size is 65507 bytes.
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UDP Header Format
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UDP uses a single segment format shown in the figure below.
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