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author | David Goulet <dgoulet@torproject.org> | 2022-12-09 15:45:34 -0500 |
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committer | David Goulet <dgoulet@torproject.org> | 2022-12-09 15:45:38 -0500 |
commit | fcfeec23519e9bcbd2e9cb59f26268764824dea4 (patch) | |
tree | 171b83f01dec7027c91307beec123ffebe43bab9 /proposals/329-traffic-splitting.txt | |
parent | 1db24dddbf2203f2a465747302f133ef3ed6eed4 (diff) | |
download | torspec-fcfeec23519e9bcbd2e9cb59f26268764824dea4.tar.gz torspec-fcfeec23519e9bcbd2e9cb59f26268764824dea4.zip |
prop329: Changes after research and discussions
Series of change after discussin with mikeperry the proposal in depth.
Signed-off-by: David Goulet <dgoulet@torproject.org>
Diffstat (limited to 'proposals/329-traffic-splitting.txt')
-rw-r--r-- | proposals/329-traffic-splitting.txt | 167 |
1 files changed, 88 insertions, 79 deletions
diff --git a/proposals/329-traffic-splitting.txt b/proposals/329-traffic-splitting.txt index 9bb72be..6a0d5cb 100644 --- a/proposals/329-traffic-splitting.txt +++ b/proposals/329-traffic-splitting.txt @@ -125,15 +125,23 @@ Status: Draft 2.1. Advertising support for conflux +2.1.1 Relay + We propose a new protocol version in order to advertise support for circuit linking on the relay side: - "Relay=4" -- Relay supports an 2 byte sequence number in a RELAY cell - header used for multipath circuit which are linked with the - new RELAY_CIRCUIT_LINK relay cell command. + "Relay=5" -- Relay supports Conflux as in linking circuits together using + the new LINK, LINKED and SWITCH relay command. + +2.1.2 Onion Service + + We propose to add a new line in order to advertise conflux support in the + onion service descriptor: - XXX: Advertise this in onion service descriptor. - XXX: Onion service descriptor can advertise more than two circuits? + "conflux" SP max-num-circ NL + + The "max-num-circ" value indicate the maximum number of rendezvous + circuits that are allowed to be linked together. The next section describes how the circuits are linked together. @@ -148,29 +156,28 @@ Status: Draft All three stages of this handshake are sent on *each* circuit leg to be linked. - To save round trips, these cells SHOULD be combined with the initial - RELAY_BEGIN cell on the faster circuit leg, using Proposal 325. See - [LINKING_EXIT] and [LINKING_SERVICE] for more details on setup in each - case. + When packed cells are a reality (proposal 340), these cells SHOULD be + combined with the initial RELAY_BEGIN cell on the faster circuit leg. See + [LINKING_EXIT] and [LINKING_SERVICE] for more details on setup in each case. - There are other ways to do this linking that we have considered, but - they seem not to be significantly better than this method, especially - since we can use Proposal 325 to eliminate the RTT cost of this setup - before sending data. For those other ideas, see [ALTERNATIVE_LINKING] - and [ALTERNATIVE_RTT], in the appendix. + There are other ways to do this linking that we have considered, but they + seem not to be significantly better than this method, especially since we can + use Proposal 340 to eliminate the RTT cost of this setup before sending data. + For those other ideas, see [ALTERNATIVE_LINKING] and [ALTERNATIVE_RTT], in + the appendix. The first two parts of the handshake establish the link, and enable resumption: - 16 -- RELAY_CIRCUIT_LINK + 45 -- RELAY_CONFLUX_LINK - Sent from the OP to the exit/service in order to link - circuits together at the end point. + Sent from the OP to the exit/service in order to link circuits + together at the end point. - 17 -- RELAY_CIRCUIT_LINKED + 46 -- RELAY_CONFLUX_LINKED - Sent from the exit/service to the OP, to confirm the circuits - were linked. + Sent from the exit/service to the OP, to confirm the circuits were + linked. These cells have the following contents: @@ -201,41 +208,51 @@ Status: Draft The two sequence number fields are 0 upon initial link, but non-zero in the case of a resumption attempt (See [RESUMPTION]). - If either circuit does not receive a RELAY_CIRCUIT_LINKED response, both + If either circuit does not receive a RELAY_CONFLUX_LINKED response, both circuits MUST be closed. The third stage of the handshake exists to help the exit/service measure initial RTT, for use in [SCHEDULING]: - 18 -- RELAY_CIRCUIT_LINKED_RTT_ACK + 47 -- RELAY_CONFLUX_LINKED_ACK - Sent from the OP to the exit/service, to provide initial RTT - measurement for the exit/service. + Sent from the OP to the exit/service, to provide initial RTT + measurement for the exit/service. For timeout of the handshake, clients SHOULD use the normal SOCKS/stream timeout already in use for RELAY_BEGIN. - These three relay commands (RELAY_CIRCUIT_LINK, RELAY_CIRCUIT_LINKED, - and RELAY_CIRCUIT_LINKED_RTT_ACK) are send on *each* leg, to allow each - endpoint to measure the initial RTT of each leg. + These three relay commands are send on *each* leg, to allow each endpoint to + measure the initial RTT of each leg. + + The circuit SHOULD be closed if at least one of these conditions is met: + + - Once a LINK is received, if the next cell relay command is not a + LINKED_ACK. + - Once a LINKED_ACK is received, receiving any other command than these: + * BEGIN, DATA, END, CONNECTED, RESOLVE, RESOLVED, XON, XOFF, SWITCH + - Receiving a LINKED without a LINK. + - Receiving a LINKED_ACK without having sent a LINKED. + + XXX Must define our LINK rate limiting parameters. 2.2. Linking Circuits from OP to Exit [LINKING_EXIT] To link exit circuits, two circuits to the same exit are built. The client records the circuit build time of each. - If the circuits are being built on-demand, for immediate use, the - circuit with the lower build time SHOULD use Proposal 325 to append its - first RELAY cell to the RELAY_COMMAND_LINK, on the circuit with the - lower circuit build time. The exit MUST respond on this same leg. After - that, actual RTT measurements MUST be used to determine future - transmissions, as specified in [SCHEDULING]. + If the circuits are being built on-demand, for immediate use, the circuit + with the lower build time SHOULD use Proposal 340 to append its first RELAY + cell to the RELAY_CONFLUX_LINK, on the circuit with the lower circuit build + time. The exit MUST respond on this same leg. After that, actual RTT + measurements MUST be used to determine future transmissions, as specified in + [SCHEDULING]. - The RTT times between RELAY_COMMAND_LINK and RELAY_COMMAND_LINKED are - measured by the client, to determine each circuit RTT to determine - primary vs secondary circuit use, and for packet scheduling. Similarly, - the exit measures the RTT times between RELAY_COMMAND_LINKED and - RELAY_COMMAND_LINKED_RTT_ACK, for the same purpose. + The RTT times between RELAY_CONFLUX_LINK and RELAY_CONFLUX_LINKED are + measured by the client, to determine each circuit RTT to determine primary vs + secondary circuit use, and for packet scheduling. Similarly, the exit + measures the RTT times between RELAY_CONFLUX_LINKED and + RELAY_CONFLUX_LINKED_ACK, for the same purpose. 2.3. Linking circuits to an onion service [LINKING_SERVICE] @@ -247,9 +264,9 @@ Status: Draft meet the client at two separate rendezvous points. These introduce requests MUST be sent to the same intropoint (due to potential use of onionbalance), and SHOULD be sent back-to-back on the same intro - circuit. They MAY be combined with Proposal 325. + circuit. They MAY be combined with Proposal 340. - The first rendezvous circuit to get joined SHOULD use Proposal 325 to + The first rendezvous circuit to get joined SHOULD use Proposal 340 to append the RELAY_BEGIN command, and the service MUST answer on this circuit, until RTT can be measured. @@ -283,50 +300,42 @@ Status: Draft small. It only has to signal that a cell comes after those arriving on another circuit. - To achieve this, we add a small sequence number to the common relay - header for all relay cells on linked circuits. This sequence number is - meant to signal the number of cells sent on the *other* leg, so that - each endpoint knows how many cells are still in-flight on another leg. - It is different from the absolute sequence number used in - [LINKING_CIRCUITS] and [RESUMPTION], but can be derived from that - number, using relative arithmetic. + To achieve this, we propose a new relay command used to indicate a switch to + another leg: - Relay command [1 byte] - Recognized [2 bytes] - StreamID [2 bytes] - Digest [4 bytes] - Length [2 bytes] - > LongSeq [1 bit] # If this bit is set, use 31 bits for Seq - > Sequencing [7 or 31 bits] - Data [Remainder] + 48 -- RELAY_CONFLUX_SWITCH - The sequence number is only set for the first cell after the endpoint - switches legs. In this case, LongSeq is set to 1, and the Sequencing - field is 31 more bits. Otherwise it is a 1 byte 0 value. + Sent from the client to the exit/service when switching leg in an + already linked circuit construction. - These fields MUST be present on ALL end-to-end relay cells on each leg - that come from the endpoint, following a RELAY_CIRCUIT_LINK command. + The cell payload format is: - They are absent on 'leaky pipe' RELAY_COMMAND_DROP and - RELAY_COMMAND_PADDING_NEGOTIATED cells that come from middle relays, as - opposed to the endpoint, to support padding. + SeqNum [4 bytes] + + The "SeqNum" value is a relative sequence number which is the number of cells + that was sent on the current leg until the switch. That way, we can always + keep up with the absolute sequence number and learn how many are inflights on + the current leg. + + As an example, if on the first leg we just sent 21 cells after sending 10 + cells (for a total of 31), then the RELAY_CONFLUX_SWITCH cell contains "21" + as the SeqNum then it can compute the absolute number to be 10 + 21 which + means that the first cell coming on the new leg should be considered the 32nd + cell in the sequence for reordering. + + In the rare event that we send more than 2^31 cells (~1TB) on a single leg, + the leg should be switched in order to reset that relative sequence number to + fit within 4 bytes. + + The circuit SHOULD be closed if at least one of these conditions is met: - When an endpoint switches legs, on the first cell in a new leg, LongSeq - is set to 1, and the following 31 bits represent the *total* number of - cells sent on the *other* leg, before the switch. The receiver MUST wait - for that number of cells to arrive from the previous leg before - delivering that cell. + - The SeqNum value is below the "cwnd_min" which is currently set at 31. + - If immediately after receiving a SWITCH, another one is received. - XXX: In the rare event that we send more than 2^31 cells (~1TB) on a - single leg, do we force a switch of legs, or expand the field further? + XXX: We should define our rate limiting. - An alternative method of sequencing, that assumes that the endpoint - knows when it is going to switch, the cell before it switches, is - specified in [ALTERNATIVE_SEQUENCING]. Note that that method requires - only 1 byte for sequence number and switch signaling, but requires that - the sender know that it is planning to switch, the cell before it - switches. (This is possible with [BLEST_TOR], but [LOWRTT_TOR] can - switch based on RTT change, so it may be one cell late in that case). + - If we are NOT an exit circuit. + - If the SeqNum makes our absolute sequence number to overflow. 2.6. Resumption [RESUMPTION] @@ -636,7 +645,7 @@ Status: Draft [LINKING_CIRCUITS] may be quite noticeable. As one countermeasure, it may be possible to eliminate the third leg - (RELAY_CIRCUIT_LINKED_RTT_ACK) by computing the exit/service RTT via + (RELAY_CIRCUIT_LINKED_ACK) by computing the exit/service RTT via measuring the time between CREATED/REND_JOINED and RELAY_CIRCUIT_LINK, but this will introduce cross-component complexity into Tor's protocol that could quickly become unwieldy and fragile. @@ -774,7 +783,7 @@ A.2 Alternative Link Handshake [ALTERNATIVE_LINKING] Additionally, it is not clear that this approach actually saves us anything in terms of setup time, because we can optimize away the - linking phase using Proposal 325, to combine initial RELAY_BEGIN cells + linking phase using Proposal 340, to combine initial RELAY_BEGIN cells with RELAY_CIRCUIT_LINK. A.3. Alternative RTT measurement [ALTERNATIVE_RTT] |