diff options
| author | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2008-09-04 07:30:19 +0200 |
|---|---|---|
| committer | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2008-09-04 07:45:43 +0200 |
| commit | a3cbdde8e9c38b66b4f13ac5d6ff1939ded0ff20 (patch) | |
| tree | 8e66f40579776dbc07fdacb206c4d56e1b351e86 /net/dccp/ccids/ccid3.h | |
| parent | 53ac9570c8145710aaed9e1eb850c2e991a4ebc1 (diff) | |
dccp ccid-3: Preventing Oscillations
This implements [RFC 3448, 4.5], which performs congestion avoidance behaviour
by reducing the transmit rate as the queueing delay (measured in terms of
long-term RTT) increases.
Oscillation can be turned on/off via a module option (do_osc_prev) and via sysfs
(using mode 0644), the default is off.
Overflow analysis:
------------------
* oscillation prevention is done after update_x(), so that t_ipi <= 64000;
* hence the multiplication "t_ipi * sqrt(R_sample)" needs 64 bits;
* done using u64 for sqrt_sample and explicit typecast of t_ipi;
* the divisor, R_sqmean, is non-zero because oscillation prevention is first
called when receiving the second feedback packet, and tfrc_scaled_rtt() > 0.
A detailed discussion of the algorithm (with plots) is on
http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/ccid3/sender_notes/oscillation_prevention/
The algorithm has negative side effects:
* when allowing to decrease t_ipi (leads to a large RTT) and
* when using it during slow-start;
both uses are therefore disabled.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Diffstat (limited to 'net/dccp/ccids/ccid3.h')
| -rw-r--r-- | net/dccp/ccids/ccid3.h | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/net/dccp/ccids/ccid3.h b/net/dccp/ccids/ccid3.h index 342235c57bf..af6e1bf937d 100644 --- a/net/dccp/ccids/ccid3.h +++ b/net/dccp/ccids/ccid3.h @@ -47,8 +47,8 @@ /* Two seconds as per RFC 3448 4.2 */ #define TFRC_INITIAL_TIMEOUT (2 * USEC_PER_SEC) -/* Parameter t_mbi from [RFC 3448, 4.3]: backoff interval in seconds */ -#define TFRC_T_MBI 64 +/* Maximum backoff interval t_mbi (RFC 3448, 4.3) */ +#define TFRC_T_MBI (64 * USEC_PER_SEC) /* * The t_delta parameter (RFC 3448, 4.6): delays of less than %USEC_PER_MSEC are @@ -76,6 +76,7 @@ enum ccid3_options { * @x_recv - Receive rate in 64 * bytes per second * @x_calc - Calculated rate in bytes per second * @rtt - Estimate of current round trip time in usecs + * @r_sqmean - Estimate of long-term RTT (RFC 3448, 4.5) * @p - Current loss event rate (0-1) scaled by 1000000 * @s - Packet size in bytes * @t_rto - Nofeedback Timer setting in usecs @@ -94,6 +95,7 @@ struct ccid3_hc_tx_sock { u64 x_recv; u32 x_calc; u32 rtt; + u16 r_sqmean; u32 p; u32 t_rto; u32 t_ipi; |