Energy-saving scheme based on downstream packet scheduling in ethernet
passive optical networks
Lincong Zhang, Yejun Liu
⇑
, Lei Guo, Xiaoxue Gong
College of Information Science and Engineering, Northeastern University, Shenyang 110819, PR China
article info
Article history:
Received 16 November 2012
Revised 14 December 2012
Available online 29 January 2013
Keywords:
Ethernet passive optical networks
Packets scheduling
Hybrid sleep mode
Energy-saving scheme
abstract
With increasing network sizes, the energy consumption of Passive Optical Networks (PONs) has grown
significantly. Therefore, it is important to design effective energy-saving schemes in PONs. Generally,
energy-saving schemes have focused on sleeping the low-loaded Optical Network Units (ONUs), which
tends to bring large packet delays. Further, the traditional ONU sleep modes are not capable of sleeping
the transmitter and receiver independently, though they are not required to transmit or receive packets.
Clearly, this approach contributes to wasted energy. Thus, in this paper, we propose an Energy-Saving
scheme that is based on downstream Packet Scheduling (ESPS) in Ethernet PON (EPON). First, we design
both an algorithm and a rule for downstream packet scheduling at the inter- and intra-ONU levels,
respectively, to reduce the downstream packet delay. After that, we propose a hybrid sleep mode that
contains not only ONU deep sleep mode but also independent sleep modes for the transmitter and the
receiver. This ensures that the energy consumed by the ONUs is minimal. To realize the hybrid sleep
mode, a modified GATE control message is designed that involves 10 time points for sleep processes.
In ESPS, the 10 time points are calculated according to the allocated bandwidths in both the upstream
and the downstream. The simulation results show that ESPS outperforms traditional Upstream Centric
Scheduling (UCS) scheme in terms of energy consumption and the average delay for both real-time
and non-real-time packets downstream. The simulation results also show that the average energy con-
sumption of each ONU in larger-sized networks is less than that in smaller-sized networks; hence, our
ESPS is better suited for larger-sized networks.
Ó 2012 Elsevier Inc. All rights reserved.
1. Introduction
Recently, developing ‘‘green networks’’ has been a critical focus,
as energy saving in networks has faced unprecedented challenges
[1–3]. In particular, the ‘‘last mile’’ broadband access network
has received significant attention because energy consumption in
these networks accounts for approximately 75% of the entire net-
work [4]. As a predominant modern broadband access technology,
the Passive Optical Network (PON) has become the most feasible
and energy-efficient solution. Due to the use of optical fibers closer
to the end users in addition to the passive nature of the remote
nodes, PON consumes the smallest energy among the various ac-
cess technologies, which include Wireless Fidelity (WiFi) [5,6],
Worldwide Interoperability for Microwave Access (WiMax) [7], Fi-
ber-To-The-x (FTTx) [8], and Digital Subscriber Line (xDSL) [9].
Nevertheless, the energy consumption of PONs can be further re-
duced because the devices are not in use at all times.
In this paper, we focus on Ethernet PON (EPON), which has been
widely deployed in recent years. The devices used in the typical
Time Division Multiplex (TDM) EPON include an Optical Line Ter-
minal (OLT), a splitter and several Optical Network Units (ONUs),
which are constructed in a tree topology. In the upstream direc-
tion, the traffic from the end users is first aggregated at the ONUs
and is then sent to the OLT. All ONUs share the upstream channel
to the OLT in a time division manner. Conversely, in the down-
stream direction, the OLT broadcasts the downstream traffic to
all ONUs. The ONUs only reserve the traffic designated for them-
selves and discard the rest.
In EPON, the energy is mainly consumed by the OLT and ONUs,
where the power consumption of an OLT is 20 times of an ONU
[10]. Nevertheless, as the highest aggregate node, the OLT can
rarely be turned off because it connects the PON with the Internet.
As a result, current efforts to reduce the energy consumption in
EPON have primarily focused on ONUs. Several energy-saving mea-
sures are currently used for ONUs in EPON.
First, the power consumption of the ONUs can be reduced in
light of the hardware structure. Ref. [11] developed low-power
ONUs with integration technology, which decreased the power
consumption of the investigated ONUs from 10 W to 6 W.
1068-5200/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.yofte.2012.12.007
⇑
Corresponding author. Address: College of Information Science and Engineering,
Northeastern University, P.O. Box 365, Shenyang 110819, PR China. Fax: +86 24
83684219.
E-mail address: haveball@yeah.net (Y. Liu).
Optical Fiber Technology 19 (2013) 169–178
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