new proposal 168

i2p2www/spec/proposals/168-tunnel-bandwidth.rst

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+===================================
+Tunnel Bandwidth Parameters
+===================================
+.. meta::
+    :author: zzz
+    :created: 2024-07-31
+    :thread: http://zzz.i2p/topics/3652
+    :lastupdated: 2024-07-31
+    :status: Open
+    :target: 0.9.65
+
+.. contents::
+
+
+
+Overview
+========
+
+As we have increased the performance of the network over the last several years
+with new protocols, encryption types, and congestion control improvements,
+faster applications such as video streaming are becoming possible.
+These applications require high bandwidth at each hop in their client tunnels.
+
+Participating routers, however, do not have any information about how much
+bandwidth a tunnel will use when they get a tunnel build message.
+They can only accept or reject a tunnel based on the current total bandwidth
+used by all participating tunnels and the total bandwidth limit for participating tunnels.
+
+Requesting routers also do not have any information on how much bandwidth
+is available at each hop.
+
+This proposal addresses the issue by adding bandwidth parameters to
+the tunnel build request and reply messages.
+
+
+
+Design
+======
+
+Add bandwidth parameters to the ECIES tunnel build messages [Tunnel-Creation-ECIES]_
+in the tunnel build options mapping field. Use short parameter names since the space available
+for the options field is limited.
+Tunnel build messages are fixed-size so this does not increase the
+size of the messages.
+
+
+
+Specification
+=============
+
+Update the ECIES tunnel build message specification [Tunnel-Creation-ECIES]_
+as follows:
+
+For both long and short ECIES build messages:
+
+Build Request Options
+---------------------------
+
+The following two options may be set in the tunnel build options mapping field.
+A requesting router may include either or both.
+
+- m := minimum bandwidth required for this tunnel (KBps positive integer as a string)
+- r := requested bandwidth for this tunnel (KBps positive integer as a string)
+
+The participating router should reject the tunnel if "m" is specified and it cannot
+provide at least that much bandwidth.
+
+
+Build Reply Option
+---------------------------
+
+The following option may be set in the tunnel build reply options mapping field.
+
+- b := bandwidth available for this tunnel (KBps positive integer as a string)
+
+The participating router should include this if either "m" or "r" was specified
+in the build request. The value should be at least that of the "m" value if specified,
+but may be less or more than the "r" value if specified.
+
+The participating router should attempt to reserve and provide at least this
+much bandwidth for the tunnel, however this is not guaranteed.
+Routers cannot predict conditions 10 minutes into the future, and
+participating traffic is lower-priority than a router's own traffic and tunnels.
+
+Routers may also over-allocate available bandwidth if necessary.
+
+
+
+
+Implementation Notes
+=====================
+
+Bandwidth parameters are as seen at the participating routers at the tunnel layer,
+i.e. the number of fixed-size 1 KB tunnel messages per second.
+Transport (NTCP2 or SSU2) overhead is not included.
+
+This bandwidth may be much more or less than the bandwidth seen at the client.
+Tunnel messages contain substantial overhead, including overhead from higher layers
+including ratchet and streaming. Intermittent small messages such as streaming acks
+will be expanded to 1 KB each.
+However, gzip compression at the I2CP layer may substantially reduce bandwidth.
+
+
+
+
+Security Analysis
+=================
+
+Client fingerprinting based on requests.
+
+Avoid over-allocation ddos.
+
+
+
+
+Compatibility
+===============
+
+No issues. All known implementations currently ignore the mapping field in build messages,
+and correctly skip over a non-empty options field.
+
+
+Migration
+=========
+
+Implementations may add support at any time, no coordination is needed.
+
+
+
+References
+==========
+
+.. [Tunnel-Creation-ECIES]
+    {{ spec_url('tunnel-creation-ecies') }}