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a few clarifications to the spec

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still not done at the end


svn:r195
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Roger Dingledine 2003-03-18 07:21:31 +00:00
parent eaf60d09a6
commit 12d956f7f3
1 changed files with 35 additions and 29 deletions
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tor-spec.txt
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@ -355,10 +355,10 @@ which reveals the downstream node.
the payload. Create a half-open circuit with this ACI, and
begin queueing CREATE cells for this circuit.
Otherwise, we have a half-open circuit. If the total
payload length of the CREATE cells for this circuit is at
least equal to the onion length in the first cell (minus
4), then process the onion.
Otherwise, we have a half-open circuit. If the total payload
length of the CREATE cells for this circuit is at exactly equal
to the onion length specified in the first cell (minus 4), then
process the onion. If it is more, then tear down the circuit.
2. Once we have a complete onion, decrypt the first 128 bytes
of the onion with this OR's RSA private key, and extract
@ -483,44 +483,50 @@ which reveals the downstream node.
As discussed above in section 2.1, ORs and OPs negotiate a maximum
bandwidth upon startup. The communicants only read up to that
number of bytes per second on average, though they may smooth the
number of bytes read over a 10-second window.
[???? more detail? -NM]
number of bytes per second on average, though they may use mechanisms
to handle spikes (eg token buckets).
Communicants rely on TCP flow control to prevent the bandwidth
from being exceeded.
Communicants rely on TCP's default flow control to push back when they
stop reading, so nodes that don't obey this bandwidth limit can't do
too much damage.
6.2. Link padding
On every cell connection, every ????/bandwidth seconds, if less
than MIN(bandwidth/(100*128), 10) cells are waiting to be sent
along a connection, nodes add a single padding cell to the cells
they will send along the connection.
Currently nodes are not required to do any sort of link padding or
dummy traffic. Because strong attacks exist even with link padding,
and because link padding greatly increases the bandwidth requirements
for running a node, we plan to leave out link padding until this
tradeoff is better understood.
6.3. Circuit flow control
To control a circuit's bandwidth usage, each node keeps track of
how many cells it is allowed to send to the next hop in the circuit
before queueing cells. This 'window' value is initially set to
1000 cells in each direction. Each edge node on a circuit sends a
SENDME cell (with length=100) every time it has received 100 cells
on the circuit. When a node receives a SENDME cell for a circuit,
it increases the circuit's window in the corresponding by the value
of the cell's length field, and (if not an edge node) passes an
equivalent SENDME cell to the next node in the circuit.
how many data cells it is allowed to send to the next hop in the
circuit. This 'window' value is initially set to 1000 data cells
in each direction (cells that are not data cells do not affect
the window). Each edge node on a circuit sends a SENDME cell
(with length=100) every time it has received 100 data cells on the
circuit. When a node receives a SENDME cell for a circuit, it increases
the circuit's window in the corresponding direction (that is, for
sending data cells back in the direction from which the sendme arrived)
by the value of the cell's length field. If it's not an edge node,
it passes an equivalent SENDME cell to the next node in the circuit.
If a window value ever reaches 0, the OR queues cells for the
corresponding circuit and direction until it receives an
appropriate SENDME cell.
If the window value reaches 0 at the edge of a circuit, the OR stops
reading from the edge connections. (It may finish processing what
it's already read, and queue those cells for when a SENDME cell
arrives.) Otherwise (when not at the edge of a circuit), if the
window value is 0 and a data cell arrives, the node must tear down
the circuit.
6.4. Topic flow control
Edge nodes use TOPIC_SENDME data cells to implement end-to-end flow
control for individual connections across circuits. As with
circuit flow control, edge nodes begin with a window of cells (500)
per topic, and increment the window by a fixed value (50) upon
receiving a TOPIC_SENDME cell. Edge nodes create and additional
TOPIC_SENDME cells when [????] -NM
control for individual connections across circuits. As with circuit
flow control, edge nodes begin with a window of cells (500) per
topic, and increment the window by a fixed value (50) upon receiving
a TOPIC_SENDME data cell. Edge nodes initiate TOPIC_SENDME data
cells when
7. Directories and routers