Re: [quicwg/base-drafts] Updated spinbit text (#2564)

[Lars Eggert <[e-mail]>]

larseggert requested changes on this pull request.



> @@ -3932,6 +3938,58 @@ version-independent.  The remaining fields are specific to the selected QUIC
 version.  See {{QUIC-INVARIANTS}} for details on how packets from different
 versions of QUIC are interpreted.
 
+### Latency Spin Bit {#spin-bit}
+
+The latency spin bit enables passive latency monitoring from observation points
+on the network path throughout the duration of a connection. The spin bit is
+only present in the short packet header, since it is possible to measure the
+initial RTT of a connection by observing the handshake. Therefore, the spin bit
+is available after version negotiation and connection establishment are
+completed. On-path measurement and use of the latency spin bit is further
+discussed in {{QUIC-MANAGEABILITY}}.
+
+The spin bit is an OPTIONAL feature of QUIC. A QUIC stack that chooses to
+support the spin bit MUST implement it as specified in this document.

document -> section

> +The latency spin bit enables passive latency monitoring from observation points
+on the network path throughout the duration of a connection. The spin bit is
+only present in the short packet header, since it is possible to measure the
+initial RTT of a connection by observing the handshake. Therefore, the spin bit
+is available after version negotiation and connection establishment are
+completed. On-path measurement and use of the latency spin bit is further
+discussed in {{QUIC-MANAGEABILITY}}.
+
+The spin bit is an OPTIONAL feature of QUIC. A QUIC stack that chooses to
+support the spin bit MUST implement it as specified in this document.
+
+Each endpoint unilaterally decides if the spin bit is enabled or disabled for a
+connection. Implementations MUST allow administrators of clients and servers
+to disable the spin bit either globally or on a per-connection basis. Even when
+the spin bit is not disabled by the administrator implementations MUST disable
+the spin bit on a randomly chosen fraction of connections. The random selection

on a randomly chosen fraction of connections -> for a given connection with a certain likelihood

> +only present in the short packet header, since it is possible to measure the
+initial RTT of a connection by observing the handshake. Therefore, the spin bit
+is available after version negotiation and connection establishment are
+completed. On-path measurement and use of the latency spin bit is further
+discussed in {{QUIC-MANAGEABILITY}}.
+
+The spin bit is an OPTIONAL feature of QUIC. A QUIC stack that chooses to
+support the spin bit MUST implement it as specified in this document.
+
+Each endpoint unilaterally decides if the spin bit is enabled or disabled for a
+connection. Implementations MUST allow administrators of clients and servers
+to disable the spin bit either globally or on a per-connection basis. Even when
+the spin bit is not disabled by the administrator implementations MUST disable
+the spin bit on a randomly chosen fraction of connections. The random selection
+process SHOULD be designed such that on average the spin bit is disabled for at
+least one eighth of network paths. The selection process should be externally

Is it 1/8th of *paths*? I thought it was supposed to be 1/8th of *connections*? (Related to @mirjak's comment below.)

> +to disable the spin bit either globally or on a per-connection basis. Even when
+the spin bit is not disabled by the administrator implementations MUST disable
+the spin bit on a randomly chosen fraction of connections. The random selection
+process SHOULD be designed such that on average the spin bit is disabled for at
+least one eighth of network paths. The selection process should be externally
+unpredictable but consistent for any given combination of source and destination
+address and port. The selection process performed at the beginning of the
+connection SHOULD be applied for all paths used by the connection.
+
+In case multiple connections share the same five-tuple, i.e. same source and
+destination IP address and UDP port the setting of the spin bit needs to be
+coordinated across all connections to ensure a clear signal to any on path
+measurement point, however that might not be feasible.
+
+When the spin bit is disabled, endpoints MAY set the spin bit to any value, and
+MUST accept any incoming value. It is RECOMMENDED that they set the spin bit to

accept -> ignore

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