Dynamic Wavelength and Bandwidth
Allocation Algorithms for Mitigating
Frame Reordering in NG-EPON
Wei Wang, Wei Guo, and Weisheng Hu
Abstract—The IEEE initialized a working group to study
the 100 Gb/s next-generation passive optical networks
(NG-EPON). A key technology adopted by NG-EPON is chan-
nel bonding, which enables optical network units (ONUs) to
transmit data on multiple wavelength channels simultane-
ously to achieve higher peak rates. In the upstream, ONUs
share the bandwidth of each wavelength in a time-division
multiplexing manner, and dynamic wavelength and band-
width allocation (DWBA) coordinates ONU upstream trans-
mission. If an ONU is granted transmission of data on
multiple wavelengths simultaneously, frame reordering will
occur due to simultaneous parallel transmission, which
needs to be minimized because buffer and extra processing
time are needed to restore the original frame sequence. For a
group of ONUs, DWBA can grant each ONU transmission on
either a single wavelength or multiple wavelengths without
affecting total bandwidth occupation. Since ONUs transmit-
ting on single wavelength can get rid of frame reordering,
different DWBA algorithms can result in different numbers
of ONUs suffering frame reordering. In this paper, we inves-
tigate the impacts of DWBA algorithms on frame reordering
in NG-EPON. A DWBA algorithm for mitigating frame reor-
dering without affecting bandwidth utilization is proposed.
The theoretical upper bound of a frame-reordered ONU
number with the proposed algorithm is also analyzed. The
performances (in terms of frame-reordered ONU number
and packet delay) of DWBA algorithms are evaluated
through simulations. Simulation results show that the pro-
posed algorithm can mitigate frame reordering efficiently
and reduce packet delay as well.
Index Terms—Channel bonding; DWBA; Frame reorder-
ing; NG-EPON.
I. INTRODUCTION
T
o meet the continuously increasing bandwidth de-
mand of access networks, IEEE initialized a working
group to study the next-generation Ethernet passive opti-
cal networks (NG-EPON), which can provide up to 100 Gb/s
data rate [1]. One of the most innovative features in NG-
EPON is channel bonding, which enables optical network
units (ONUs) to bundle two or four 25 Gb/s physical wave-
length channels to achieve a logical 50 Gb/s or 100 Gb/s
channel [2]. With channel bonding, ONUs are capable of
working on multiple wavelength channels simultaneously.
Through distributing frames on multiple channels , ONUs
can achieve higher peak rates [3]. All the ONUs share the
the bandwidth resources of each wavelength in the time-
division multiplexing (TDM) manner in the upstream. The
dynamic wavelength and bandwidth allocation (DWBA) in
the optical line terminal (OLT) coordinates upstream trans-
mission and grants transmission wavelengths and timeslots
to each ONU [4]. As Fig. 1 shows, ONUs can only transmit
their data frames during their dedica ted transmission grants
on each wavelength, which are arbitrated by the DWBA.
Similartoa10G-EPONONU,the100GONUtransmits
its queued frames in first-in-first-out (FIFO) order. ONU will
select its first available channel to send its earliest frame
each time. However, due to variable lengths (64–1518 bytes)
of Ethernet frames [5], later frames may finish transmission
before earlier frames after simultaneous parallel transmis-
sion. As Fig . 1 shows, for ONU n,framesb and c with shorter
lengths are completely received earlier than frame a with a
longer length. Frames sent from ONU n in the sequence of
abcde are received in the sequence of bceda at the OLT side;
hence, the frame-reordering problem occurs . T o solve this
problem, a feasible solution, similar to the widely adopted
solution in many link-aggregation scenarios such as Multi-
Link PPP [6] and channel stripping [7], is that the ONU adds
a sequence number at the head of each frame and the OLT
resequences reordered frames according to their sequence
number [8]. Besides , fragmentation mechanisms such as that
in IEEE 802.3ba [9] can solve the frame sequence problem by
fragmenting each Ethernet frame and distributing them
among multiple channels simultaneously. In addition, some
algorithms have been proposed for channel bonding, such
as the grant-awar e frame distribut er/com biner [10]and
FEC codeword [11,12]. These solutions that bond channels
in different dimensions (i.e., frame, grant, codeword) will
inevitably need complex mechanisms , certain amounts of
buffer, and some processing time (including multiplexing
delay and demultiplexing delay) [13,14]. It is necessary to
avoid the frame-reordering problem as much as possible.
Therefore, how to minimize the number of ONUs in which
frame reordering occurs under the condition of guaranteeing
bandwidth utilization needs to be studied.
For a group of ONUs, different DWBA algorithms that
allocate ONU grants in different ways may cause frame
reordering to occur in different numbers of ONUs, while
the total bandwidth occupation is the same. As Fig. 2
https://doi.org/10.1364/JOCN.10.000220
Manuscript received October 19, 2017; revised December 6, 2017;
accepted January 9, 2018; published February 23, 2018 (Doc. ID 309603).
The authors are with the State Key Laboratory of Advanced Optical
Communication Systems and Networks, Shanghai Jiao Tong University,
Shanghai 200240, China (e-mail: wangweijtu@sjtu.edu.cn).
220 J. OPT. COMMUN. NETW./VOL. 10, NO. 3/MARCH 2018 Wang et al.
1943-0620/18/030220-09 Journal © 2018 Optical Society of America