Today, Passive Optical Network (PON) system is widely prevalent for access network. The advantages of PON are low-cost and no-power due to a passive optical splitter. However, PON system has limitations of the maximum number of Optical Network Units (32 ONUs) and the maximum transmission distance (20 km) between Optical Line Terminal (OLT) and ONUs. This is because the optical power is divided at a splitter and decreases as the number of ONUs increases. Moreover, PON system is a low-security architecture in principle because all ONUs receive all signals from OLT. A malicious user can intercept all data.
To resolve these problems, we propose a secure and scalable active optical access network architecture using PLZT 10ns highspeed optical switches. By using a switch, ActiON achieve much less optical powerloss than an optical splitter for the conventional PON system. Therefore, ActiON can contain more ONUs than PON. ActiON can quadruplicate the number of subscribers (128 users) per OLT and double the maximum transmission distance (40 km) between OLT and ONUs.
In ActiON, MPCP (Multi Point Control Protocol) is adopted for compatibility with 10GE-PON (IEEE 802.3av). ActiON employs Optical Slot Switching. The bandwidth is allocated and reserved to each ONU by the slot(fixed-length time) for easy control. Therefore, it is necessary to transmit the switching control message for the slot switching.
In ActiON, there are many challenges, for examples, discovery process without broadcast and data transmission used the slot switching for the various traffic.
ActiON needs a new modified Discovery process without broadcast. First slot, called the control slot, of a cycle is used for Discovery process. This slot appears periodically, so the automatic ranging that measure the distance from OLT to ONU can be achieved by using the slot. The control slot is found out by continuous transmission of the REGISTER REQUEST messages.
TCP firendly ActiON
We focus on TCP friendly active optical access network and design the sophisticated parameter of the Cycle (the periodic time for the control of the optical switch) and the slot size in ActiON data transmission.
Figure below shows the bandwidth utilization versus the cycle. As the cycle is closer to retransmission timeout (0.2s), TCP throughput decreases greatly. Therefore, the upper bound value of the cycle for the guarantee of TCP throughput is decided at 0.14s to keep more 90 percent the bandwidth utilization.
- Kazumasa TOKUHASHI, Kou KIKUTA, Daisuke ISHII, Yutaka ARAKAWA, SatoruOKAMOTO, Naoaki YAMANAKA, “A study on optical access network with active optical switches,” IEICE Technical Report, Vol. 2008-22, pp. 49-53, August 2008.
- Kunitaka Ashizawa, Kazumasa Tokuhashi, Kou Kikuta, Daisuke Ishii, Yutaka Arakawa, Satoru Okamoto and Naoaki Yamanaka, “Parameter Design and Dynamic Slot Assignment considering TCP Throughput on Active Optical Access Network ,” IEICE Technical Report, Vol. 108, No. 476, pp. pp. 7-12, March 2009.
- Kunitaka Ashizawa, Kazumasa Tokuhashi, Kou Kikuta, Daisuke Ishii, Yutaka Arakawa, Satoru Okamoto and Naoaki Yamanaka, “Agenda of the slot allocation of Active Optical Network(ActiON)”, March 2009