private function depthHandler(array $json)
    {
        $symbol = $json['s'];
        if ($json['u'] <= $this->info[$symbol]['firstUpdate']) {
            return;
        }

        foreach ($json['b'] as $bid) {
            $this->depthCache[$symbol]['bids'][$bid[0]] = $bid[1];
            if ($bid[1] == "0.00000000") {
                unset($this->depthCache[$symbol]['bids'][$bid[0]]);
            }

        }
        foreach ($json['a'] as $ask) {
            $this->depthCache[$symbol]['asks'][$ask[0]] = $ask[1];
            if ($ask[1] == "0.00000000") {
                unset($this->depthCache[$symbol]['asks'][$ask[0]]);
            }

        }
    }