1  /* 2 +  * Update dctcp alpha based on the ecn bit in the received packet. 3 +  * This procedure is called only when dctcp_ is 1. 4 +  */ 5 + void FullTcpAgent::update_dctcp_alpha(Packet *pkt) 6 + { 7 +     int ecnbit = hdr_flags::access(pkt)->ecnecho(); 8 +     int ackno = hdr_tcp::access(pkt)->ackno(); 9 +     int acked_bytes = ackno - highest_ack_; 10 + 11 +     if (acked_bytes <= 0) 12 +         acked_bytes = size_;    13 +     dctcp_total += acked_bytes;14 +     if (ecnbit) {15 +         dctcp_marked += acked_bytes;16 +     }17 + 18 +     /* Check for barrier indicating its time to recalculate alpha.19 +      * This code basically updated alpha roughly once per RTT.20 +      */21 +     if (ackno > dctcp_alpha_update_seq) {22 +         double temp_alpha;23 +         dctcp_alpha_update_seq = dctcp_maxseq;24 +         if (dctcp_total > 0) 25 +             temp_alpha = ((double) dctcp_marked) / dctcp_total;26 +         else 27 +             temp_alpha = 0.0;28 + 29 +         dctcp_alpha_ = (1 - dctcp_g_) * dctcp_alpha_ + dctcp_g_ * temp_alpha;30 +         dctcp_marked = 0;31 +         dctcp_total = 0;32 +     }33 + }