| Internet-Draft | BDP Frame Extension | March 2022 |
| Kuhn, et al. | Expires 7 September 2022 | [Page] |
This draft describes the BDP Frame extension for QUIC. It enables the exchange of information related to the path characteristics between the client and the server during a connection. This information can later be exploited when a new connection is established.¶
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This document proposes a method to exchange values between a client and the server in a interoperable manner:¶
This method applies to any resumed QUIC session: both a saved_session and a recon_session can be a 0-RTT QUIC connection or a 1-RTT QUIC connection.¶
[RFC6349] defines the BDP as follows: "Derived from Round-Trip Time (RTT) and network Bottleneck Bandwidth (BB), the Bandwidth-Delay Product (BDP) determines the Send and Received Socket buffer sizes required to achieve the maximum TCP Throughput." This document considers the BDP estimated by a server that includes all buffering along the network path. The estimated BDP estimated is related to the amount of bytes in flight and the measured path RTT.¶
A QUIC connection could use the procedure detailed in [RFC6349] to measure the BDP, but is permitted to choose another method [RFC9002] . A server might be able to utilise an other information to provide an estimate of the BDP.¶
Congestion controllers, such as CUBIC or RENO, could estimate the saved_bb and current_bb values by utilizing a combination of the cwnd/flight_size and the minimum RTT. A different method could be used to estimate the same values when using a rate-based congestion controller, such as BBR [I-D.cardwell-iccrg-bbr-congestion-control]. It is important to consider whether the methods could result in over-estimating the bottleneck bandwidth, and the preserved values there ought to be used with caution.¶
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
This section describes the use of a new Frame, the BDP Frame. The BDP Frame MUST be considered by the congestion controller and its data is not be limited by flow control limits. The server and the client MAY send multiple BDP Frames in both 1-RTT and 0-RTT connections.¶
A BDP Frame is formatted as shown in Figure 1.¶
BDP Frame {
Type (i) = 0xXXX,
Lifetime (i),
Saved BB (i),
Saved RTT (i),
Saved IP length (i),
Saved IP (...)
}
A BDP Frame contains the following fields:¶
The client can accept the transmission of BDP Frames from the server by using the enable_bdp transport extension.¶
enable_bdp (0xTBD): in the 1-RTT connection, the client indicates to the server that it wishes to receive BDP extension Frames for improving ingress of 0-RTT connection. The default value is 0. Values larger than 3 are invalid, and receipt of these values MUST be treated as a connection error of type TRANSPORT_PARAMETER_ERROR.¶
This Transport Parameter is encoded as described in Section 18 of [RFC9000].¶
With the BDP Frame extension, the client has the choice of accepting the reuse of the previous parameters or not.¶
The BDP metadata parameters are measured by the server during a previous connection. The BDP extension is protected by the mechanism that protects the exchange of the 0-RTT transport parameters. For version 1 of QUIC, the BDP extension is protected using the mechanism that already protects the "initial_max_data" parameter. This is defined in sections 4.5 to 4.7 of [RFC9001]. This provides a way for the server to verify that the parameters proposed by the client are the same as those that the server sent to the client during the previous connection.¶
The server SHOULD NOT trust the client. Indeed, even if 0-RTT packets containing the BDP Frame are encrypted, a client could modify the values within the extension and encrypt the 0-RTT packet. Authentication mechanisms might not guarantee that the values are safe. It is not an easy operation for a client to modify authenticated or encrypted data without this being detected by a server. Modification could be realized by malicious clients. One way to avoid this is for a server to also store the saved_rtt and saved_bb parameters.¶
The authors would like to thank Gabriel Montenegro, Patrick McManus, Ian Swett, Igor Lubashev, Robin Marx, Roland Bless and Franklin Simo for their fruitful comments on earlier versions of this document.¶
TBD: Text is required to register the BDP Frame and the enable_bdp transport parameter. Parameters are registered using the procedure defined in [RFC9000].¶