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Filename: 218-usage-controller-events.txt
Title: Controller events to better understand connection/circuit usage
Author: Rob Jansen, Karsten Loesing
Created: 2013-02-06
Status: Closed
Implemented-In: 0.2.5.2-alpha
1. Overview
This proposal defines three new controller events that shall help
understand connection and circuit usage. These events are designed
to be emitted in private Tor networks only. This proposal also
defines a tweak to an existing event for the same purpose.
2. Motivation
We need to better understand connection and circuit usage in order to
better simulate Tor networks. Existing controller events are a fine
start, but we need more detailed information about per-connection
bandwidth, processed cells by circuit, and token bucket refills. This
proposal defines controller events containing the desired information.
Most of these usage data are too sensitive to be captured in the
public network, unless aggregated sufficiently. That is why we're
focusing on private Tor networks first, that is, relays that have
TestingTorNetwork set. The new controller events described in this
proposal shall all be restricted to private Tor networks. In the next
step we might define aggregate statistics to be gathered by public
relays, but that will require a new proposal.
3. Design
The proposed new event types use Tor's asynchronous event mechanism
where a controller registers for events by type and processes events
received from the Tor process.
Tor controllers can register for any of the new event types, but
events will only be emitted if the Tor process is running in
TestingTorNetwork mode.
4. Security implications
There should be no security implications from the new event types,
because they are only emitted in private Tor networks.
5. Specification
5.1. ConnID Token
Addition for section 2.4 of the control-spec (General-use tokens).
; Unique identifiers for connections or queues. Only included in
; TestingTorNetwork mode.
ConnID = 1*16 IDChar
QueueID = 1*16 IDChar
5.2. Adding an ID field to ORCONN events
The new syntax for ORCONN events is:
"650" SP "ORCONN" SP (LongName / Target) SP ORStatus
[ SP "ID=" ConnID ] [ SP "REASON=" Reason ]
[ SP "NCIRCS=" NumCircuits ] CRLF
The remaining specification of that event type stays unchanged.
5.3. Bandwidth used on an OR or DIR or EXIT connection
The syntax is:
"650" SP "CONN_BW" SP "ID=" ConnID SP "TYPE=" ConnType
SP "READ=" BytesRead SP "WRITTEN=" BytesWritten CRLF
ConnType = "OR" / "DIR" / "EXIT"
BytesRead = 1*DIGIT
BytesWritten = 1*DIGIT
Controllers MUST tolerate unrecognized connection types.
BytesWritten and BytesRead are the number of bytes written and read
by Tor since the last CONN_BW event on this connection.
These events are generated about once per second per connection; no
events are generated for connections that have not read or written.
These events are only generated if TestingTorNetwork is set.
5.4. Bandwidth used by all streams attached to a circuit
The syntax is:
"650" SP "CIRC_BW" SP "ID=" CircuitID SP "READ=" BytesRead SP
"WRITTEN=" BytesWritten CRLF
BytesRead = 1*DIGIT
BytesWritten = 1*DIGIT
BytesRead and BytesWritten are the number of bytes read and written by
all applications with streams attached to this circuit since the last
CIRC_BW event.
These events are generated about once per second per circuit; no events
are generated for circuits that had no attached stream writing or
reading.
5.5. Per-circuit cell stats
The syntax is:
"650" SP "CELL_STATS"
[ SP "ID=" CircuitID ]
[ SP "InboundQueue=" QueueID SP "InboundConn=" ConnID ]
[ SP "InboundAdded=" CellsByType ]
[ SP "InboundRemoved=" CellsByType SP
"InboundTime=" MsecByType ]
[ SP "OutboundQueue=" QueueID SP "OutboundConn=" ConnID ]
[ SP "OutboundAdded=" CellsByType ]
[ SP "OutboundRemoved=" CellsByType SP
"OutboundTime=" MsecByType ] CRLF
CellsByType, MsecByType = CellType ":" 1*DIGIT
0*( "," CellType ":" 1*DIGIT )
CellType = 1*( "a" - "z" / "0" - "9" / "_" )
Examples are:
650 CELL_STATS ID=14 OutboundQueue=19403 OutboundConn=15
OutboundAdded=create_fast:1,relay_early:2
OutboundRemoved=create_fast:1,relay_early:2
OutboundTime=create_fast:0,relay_early:0
650 CELL_STATS InboundQueue=19403 InboundConn=32
InboundAdded=relay:1,created_fast:1
InboundRemoved=relay:1,created_fast:1
InboundTime=relay:0,created_fast:0
OutboundQueue=6710 OutboundConn=18
OutboundAdded=create:1,relay_early:1
OutboundRemoved=create:1,relay_early:1
OutboundTime=create:0,relay_early:0
ID is the locally unique circuit identifier that is only included if the
circuit originates at this node.
Inbound and outbound refer to the direction of cell flow through the
circuit which is either to origin (inbound) or from origin (outbound).
InboundQueue and OutboundQueue are identifiers of the inbound and
outbound circuit queues of this circuit. These identifiers are only
unique per OR connection. OutboundQueue is chosen by this node and
matches InboundQueue of the next node in the circuit.
InboundConn and OutboundConn are locally unique IDs of inbound and
outbound OR connection. OutboundConn does not necessarily match
InboundConn of the next node in the circuit.
InboundQueue and InboundConn are not present if the circuit originates
at this node. OutboundQueue and OutboundConn are not present if the
circuit (currently) ends at this node.
InboundAdded and OutboundAdded are total number of cells by cell type
added to inbound and outbound queues. Only present if at least one cell
was added to a queue.
InboundRemoved and OutboundRemoved are total number of cells by
cell type processed from inbound and outbound queues. InboundTime and
OutboundTime are total waiting times in milliseconds of all processed
cells by cell type. Only present if at least one cell was removed from
a queue.
These events are generated about once per second per circuit; no
events are generated for circuits that have not added or processed any
cell. These events are only generated if TestingTorNetwork is set.
5.6. Token buckets refilled
The syntax is:
"650" SP "TB_EMPTY" SP BucketName [ SP "ID=" ConnID ] SP
"READ=" ReadBucketEmpty SP "WRITTEN=" WriteBucketEmpty SP
"LAST=" LastRefill CRLF
BucketName = "GLOBAL" / "RELAY" / "ORCONN"
ReadBucketEmpty = 1*DIGIT
WriteBucketEmpty = 1*DIGIT
LastRefill = 1*DIGIT
Examples are:
650 TB_EMPTY ORCONN ID=16 READ=0 WRITTEN=0 LAST=100
650 TB_EMPTY GLOBAL READ=93 WRITTEN=93 LAST=100
650 TB_EMPTY RELAY READ=93 WRITTEN=93 LAST=100
This event is generated when refilling a previously empty token
bucket. BucketNames "GLOBAL" and "RELAY" keywords are used for the
global or relay token buckets, BucketName "ORCONN" is used for the
token buckets of an OR connection. Controllers MUST tolerate
unrecognized bucket names.
ConnID is only included if the BucketName is "ORCONN".
If both global and relay buckets and/or the buckets of one or more OR
connections run out of tokens at the same time, multiple separate
events are generated.
ReadBucketEmpty (WriteBucketEmpty) is the time in millis that the read
(write) bucket was empty since the last refill. LastRefill is the
time in millis since the last refill.
If a bucket went negative and if refilling tokens didn't make it go
positive again, there will be multiple consecutive TB_EMPTY events for
each refill interval during which the bucket contained zero tokens or
less. In such a case, ReadBucketEmpty or WriteBucketEmpty are capped
at LastRefill in order not to report empty times more than once.
These events are only generated if TestingTorNetwork is set.
6. Compatibility
There should not be any compatibility issues with other Tor versions.
7. Implementation
Most of the implementation should be straight-forward.
8. Performance and scalability notes
Most of the new code won't be executed in normal Tor mode. Wherever
we needed new fields in existing structs, we tried hard to keep them
as small as possible. Still, we should make sure that memory
requirements won't grow significantly on busy relays.
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