4. Bandwidth code in tor

4.1. To calculate descriptors bandwidth

The values at Bandwidth values in relays’ descriptor:

`rep_hist_bandwidth_asses that reads from bw_array_t Example:

bandwidthcapacity = max?(r 10547200, w 10536960)

In /or/router.c:

router_perform_bandwidth_test

router_build_fresh_descriptor

/* compute ri->bandwidthrate as the min of various options */
ri->bandwidthrate = get_effective_bwrate(options);
ri->bandwidthburst = get_effective_bwburst(options);
ri->bandwidthcapacity = hibernating ? 0 : rep_hist_bandwidth_assess();

router_dump_router_to_string
  (int) router->bandwidthrate,
  (int) router->bandwidthburst,
  (int) router->bandwidthcapacity,

In /or/rephist.c:

rep_hist_bandwidth_asses

commit_max

In /or/dirserv.c:

set_routerstatus_from_routerinfo

dirserv_get_credible_bandwidth_kb

measured bandwidth (by bwauths) or the self advertised bandwidth, but not any self measured bandwidth

In /or/dirvote.c:

networkstatus_compute_consensus

smartlist_add_asprintf(chunks, "w Bandwidth=%d%s%s\n",
                         rs_out.bandwidth_kb,
                         unmeasured?" Unmeasured=1":"",
                         guardfraction_str ? guardfraction_str : "");

4.2. To publish descriptor

In router.c

/** By which factor bandwidth shifts have to change to be considered large. */
#define BANDWIDTH_CHANGE_FACTOR 2

#define MAX_BANDWIDTH_CHANGE_FREQ (3*60*60)
/** How frequently will we republish our descriptor because of large (factor
 * of 2) shifts in estimated bandwidth? */

/** Maximum uptime to republish our descriptor because of large shifts in
 * estimated bandwidth. */
#define MAX_UPTIME_BANDWIDTH_CHANGE (24*60*60)

/* If the relay uptime is bigger than MAX_UPTIME_BANDWIDTH_CHANGE,
* the next regularly scheduled descriptor update (18h) will be enough */
if (get_uptime() > MAX_UPTIME_BANDWIDTH_CHANGE)

4.3. To calculate vote and consensus bandwidth

The values at Bandwidth values in relays’ descriptor:

In dirserv.c:

if (format == NS_CONTROL_PORT && rs->has_bandwidth) {
  bw_kb = rs->bandwidth_kb;
} else {
  tor_assert(desc);
  bw_kb = router_get_advertised_bandwidth_capped(desc) / 1000;
}
smartlist_add_asprintf(chunks,
                 "w Bandwidth=%d", bw_kb);

if (format == NS_V3_VOTE && vrs && vrs->has_measured_bw) {
  smartlist_add_asprintf(chunks,
                   " Measured=%d", vrs->measured_bw_kb);
}

STATIC int
measured_bw_line_apply(measured_bw_line_t *parsed_line,
                       smartlist_t *routerstatuses)
{
  vote_routerstatus_t *rs = NULL;
  if (!routerstatuses)
    return 0;

  rs = smartlist_bsearch(routerstatuses, parsed_line->node_id,
                         compare_digest_to_vote_routerstatus_entry);

  if (rs) {
    rs->has_measured_bw = 1;
    rs->measured_bw_kb = (uint32_t)parsed_line->bw_kb;
  } else {
    log_info(LD_DIRSERV, "Node ID %s not found in routerstatus list",
             parsed_line->node_hex);
  }

  return rs != NULL;
}

In dirvote.h

#define DEFAULT_MAX_UNMEASURED_BW_KB 20

4.4. Bandwidth self-test

Reasons (https://trac.torproject.org/projects/tor/ticket/22453#comment:20)

First, the reachability checks are performed, which open testing circuits. When the OR port is found reachable, it updates the descriptor (still no bandwidth test?). Then, the bandwidth test is performed, if it’s the first time.

In mainloop.c:

static int
check_for_reachability_bw_callback(time_t now, const or_options_t *options)
    [...]
    router_do_reachability_checks(1, dirport_reachability_count==0);
    [...]
    reset_bandwidth_test();
    [...]

#define MIN_BANDWIDTH_RECHECK_INTERVAL (12*60*60)
#define MAX_BANDWIDTH_RECHECK_INTERVAL (24*60*60)

In circuituse.c:

It checks there’re testing circuits, if there’re are, calls router_perform_bandwidth_test

In selftest.c:

Sends drop cells.

void
router_perform_bandwidth_test(int num_circs, time_t now)
  [...]
  log_notice(LD_OR,"Performing bandwidth self-test...done.");

4.5. Bandwidth observed

In rephist.c

/** How large are the intervals for which we track and report bandwidth use? */
#define NUM_SECS_BW_SUM_INTERVAL (24*60*60)

/** How far in the past do we remember and publish bandwidth use? */
#define NUM_SECS_BW_SUM_IS_VALID (24*60*60)

#define NUM_TOTALS (NUM_SECS_BW_SUM_IS_VALID/NUM_SECS_BW_SUM_INTERVAL)

NUM_SECS_ROLLING_MEASURE 10

rep_hist_bandwidth_assess


/** Allocate, initialize, and return a new bw_array. */
static bw_array_t *
bw_array_new(void)

  b->next_period = start + NUM_SECS_BW_SUM_INTERVAL

/** Shift the current period of b forward by one. */
STATIC void
commit_max(bw_array_t *b)

set from the begining the next_period to 1 day, so commit_max doesn’t happen until then.