OBOF: A Protection Scheme for Survivable
Fiber-Wireless Broadband Access Network
Yejun Liu
1
, Lei Guo
1
and Xuetao Wei
2
1
College of Information Science and Engineering, Northeastern University, Shenyang, P. R. China
2
Department of Computer Science and Engineering, University of California - Riverside, USA
E-mail: liuyejun09@gmail.com, guolei@ise.neu.edu.cn, xwei@cs.ucr.edu
Abstract—Survivability is one of the key issues in Fiber-Wireless
(FiWi) broadband access network since huge data loss could be
caused by single segment failure. Previous schemes focus on
protecting FiWi against single segment failure by deploying
backup fibers. However, these schemes suffer from two key
problems. First, they ignore optimizing the selection of backup
ONUs, which determines the recovery delay of the traffic
interrupted by failure. Second, they underutilize the residual
capacity of segments, thus require high cost of backup fibers. In
this paper, aiming to tackle the inefficiency of previous schemes,
we propose an efficient protection scheme, called Optimizing
Backup ONUs selection and backup Fibers deployment (OBOF),
to enhance the survivability of FiWi against single segment
failure. Extensive experimental results demonstrate that our
OBOF scheme outperforms the previous schemes significantly,
especially in the scenario of higher traffic demand.
Keywords- survivability; protection; fiber-wireless broadband
access network; backup ONU; backup fiber
I. INTRODUCTION
Fiber-Wireless (FiWi) broadband access network is widely
acknowledged as a promising candidate for next generation
broadband access technology, because it integrates Passive
Optical Network (PON) with Wireless Mesh Network (WMN)
in terms of their respective merits, such as high capacity and
stable transmission from PON, as well as easy deployment and
flexibility from WMN. A typical FiWi architecture consists of
multiple segments, and each segment includes a WMN at
front-end and a PON at back-end. In each segment, the
wireless gateway is combined into Optical Network Unit
(ONU) to act as the interface between wireless front-end and
optical back-end. Therefore, besides optical functionality, each
ONU in FiWi has the wireless functionality [1]-[5].
Since FiWi carries a large amount of traffic, many traffic
flows may be interrupted by the network component failure.
Therefore, how to enhance the survivability of FiWi is a key
issue. In FiWi, the front-end is capable to self-heal from the
failure, because its mesh topology can provide alternative
routes. However, the back-end is vulnerable to the failure due
to its tree topology [6]-[8]. Thus, some works propose to
protect the back-end by means of the alternative routes in the
front-end [9]-[11]. For example, once a distribution fiber in
the back-end is broken, the traffic interrupted by this failure
can be transferred to other available distribution fibers in the
same segment by means of wireless multi-hop paths, so as to
maintain the continuously available service.
However, in the scenario of segment failure, which is
induced by feeder fiber break, Remote Node (RN) break or
simultaneous breaks of all distribution fibers in a segment, all
ONUs in this failed segment lose their connections with the
Optical Line Terminal (OLT). It is not practical to use the
wireless multi-hop paths across different segments to transfer
the interrupted traffic from the failed segment to other
available segments, because different segments may be so far
away from each other that there are no available wireless paths
among them. For this consideration, some protection schemes
are proposed to tolerate single segment failure by deploying
backup fibers among the backup ONUs in different segments
[6]-[8]. However, these protection schemes usually suffer
from two key problems. First, they ignore optimizing the
selection of backup ONUs, which determines the recovery
delay of the traffic interrupted by failure. Second, they
underutilize the residual capacity of segments, thus require
high cost of backup fibers.
In this paper, aiming to tackle the inefficiency of previous
works, we propose a new and efficient protection scheme,
called Optimizing Backup ONUs selection and backup Fibers
deployment (OBOF), to enhance the survivability of FiWi
against single segment failure. Our OBOF is composed of two
consecutive steps: in the first step, we tactically select one of
the ONUs as the backup ONU in each segment; in the second
step, we selectively deploy backup fibers among backup
ONUs, so that each segment is connected to at least one
another. We refer to the optical path traversing multiple
backup fibers as backup-optical-path. A pair of segments that
are interconnected by backup-optical-path can backup for each
other. As illustrated in Fig. 1, it is a FiWi including three
segments. We let
1
,
2
and
3
denote segment-1, segment-2 and
segment-3, respectively. We first select an ONU in each
segment and then deploy two backup fibers between
1
and
2
and between
2
and
3
, respectively. Thus,
1
,
2
and
3
can
backup for each other. In case
1
fails, its traffic interrupted by
this failure can be transferred to
2
along the backup fiber
between
1
and
2
, as well as
3
along the backup-optical-path
123
().
ss−− Thus, the amount of traffic in
1
that can be
protected by
2
and
3
depends on their available residual
capacity (i.e., the sum of residual capacity of all ONUs
in
2
and
3
).
Our contributions can be summarized as follows,
(i) In the first step of OBOF, we apply the Simulated
Annealing (SA) algorithm instead of the random method
[6][7] to optimize the selection of backup ONUs, aiming
New Trends in Optical Networks Survivability
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