U On Wed, Nov 27, 2019 at 11:16 PM Xuan k <kxuan...@gmail.com> wrote:
> Hi Ekr, > > Thanks for your help. > > I have another question about the "message_seq" in section "6. Example of > Handshake with Timeout and Retransmission". > Could you please explain it? > > In the secion 6, the Client send message_seq = 0 in Record 0 and > message_seq = 2,3,4 in Record 2. > > Why message_seq = 1 is skipped by Client? > It's a typo in the example. The Certificate should be 1. I think the ClientHello in the figure should begin with message_seq=1. The > message_seq = 0 is used by the first ClientHello which is the one without > cookies. > I agree in principle, but that's not this example, because, as you can see, there is no HRR. Rather, this needs to remove +cookie. -Ekr > Thanks, > Zhai Zhaoxuan > > On 11/28/19 5:37 AM, Eric Rescorla wrote: > > > > On Tue, Nov 26, 2019 at 10:05 PM Xuan k <kxuan...@gmail.com> wrote: > >> Hi all, >> >> I'm trying to implement a DTLS1.3 library for embedded devices. But It >> seems something weird about retransmissions and ACKs. >> >> In the section "5.2. DTLS Handshake Message Format": >> >> The first message each side transmits in each association always has >> message_seq = 0. Whenever a new message is generated, the >> message_seq value is incremented by one. When a message is >> retransmitted, the old *message_seq value is re-used*, i.e., not >> incremented. From the perspective of the DTLS record layer, the >> retransmission is a new record. This record will have a *new* >> * DTLSPlaintext.sequence_number* value. >> >> >> In the section "7. ACK Message", the ACK message use the record_numbers >> (corresponds to *DTLSPlaintext.sequence_number*). >> >> For my understanding, the "message_seq" belongs to "Handshake" and the >> "sequence_number" or "record_numbers" belongs to >> record layer. >> > > Yes. > > The retransmission detection is done by "Handshake" using "message_seq", >> but the "acknowledge" is done by "record layer" using "record_numbers". >> It is so weird. >> > > Hmm... I don't think that this is particularly weird. This is, for > instance, how QUIC stream acknowledgement and retransmission works. > > > The retransmission, retransmission detection and acknowledge should be >> done in handshake process, but we need the record layer passing the >> record_numebrs to the handshake process. >> >> Since a new "sequence_number" is used for retransmission, we have to >> maintain a "record_numbers" to "message_seq" map with dynamic size. >> Each retransmission attempt creates a new relationship between a new >> "record_numbers" to an old "message_seq". >> > > Yes, that's how it works in NSS. > > > Since ACK is only used with Handshake messages, is it possible that we use >> "message_seq" in ACK messages? >> > Or we use *old* "sequence_number" for retransmission, >> > > Both of these give you strictly less information about the network. One of > the cool innovations in QUIC is to label each packet separately so you can > determine whether an ACK is an ACK of the original packet or a retransmit. > We are trying to inherit tha there > > -Ekr > > so we do not need maintain the dynamic map. And if replay detection is >> implemented, the retransmitted >> record can be dropped by record layer (by replay detection), the >> "Handshake Protocol" do not need to do retransmission detection. >> >> Thanks >> Zhai Zhaoxuan >> _______________________________________________ >> TLS mailing list >> TLS@ietf.org >> https://www.ietf.org/mailman/listinfo/tls >> >
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