Download REVIEW OF SURVIVABILITY TECHNIQUES IN PASSIVE OPTICAL

REVIEW OF SURVIVABILITY TECHNIQUES IN
PASSIVE OPTICAL NETWORK
Abstract—Network survivability, reflecting the ability of a network to maintain an acceptable level of service
during and after failures, is an important requirement for Wavelength Division Multiplexing (WDM) optical
networks due to the ultrahigh capacity. The survivability is a key issue because many traffic flows may be
interrupted by the failure of network components. So dealing with network survivability is today’s demand for
seamless service. Survivable network architectures are based on Restoration and Protection.The following four
different Passive Optical Network (PON) network protection schemes are specified-Feeder fiber protection,
Optical Line Terminal (OLT) & feeder fiber protection, Full duplication, Independent duplication of feeder and
branch fibers.
Keywords-PON,Survivability
I .INTRODUCTION
The PON is a promising technology for broadband access as it can offer higher bandwidth to end
users than other alternatives such as DSL and cable TV networks. The PON is point-to-multipoint and
generally there is a single transceiver in the OLT in the central office (CO). Various Time Division
Multiplexing PON (TDMPON) technologies have been developed, including ATM PON (APON),
broadband PON (BPON), gigabit PON (GPON), and Ethernet PON (EPON). As end users demand
more bandwidth, there is the need to further increase the PON bandwidth using WDM [1]. Basically
PON has the tree topology, thus it cannot survive the failures of network components such as OLT
and Optical Network Unit (ONU). The common network failure is the link failure and double-link
failures. Compared to unicast sessions, multicast sessions suffer more seriously. Thus, survivability is
a critical issue in WDM optical networks as customers require high service availability despite
inevitable network element failures.
II. LITERATURE SURVEY
The authors of [2] proposes two self-protecting architectures for WDM-PON. The first architecture
protects against feeder fiber (FF) failures by connecting adjacent remote nodes with a fiber. The
second architecture protects against both FF failures and distribution fiber (DF) failures by duplicating
the distribution fibers. Both architectures double the wavelength requirement in order to provide
protection.
The authors of [3], proposes a protection scheme for hybrid WDM/TDM-PONs. The scheme
employs protection feeder fibers and fibers interconnecting pairs of ONUs to provide protection to
both FF and DF failures. Unlike the scheme in [2], no additional wavelengths are required for
providing protection.
In [4], a self-survivable WDM-PON architecture that can protect against FF/DF failures, remote
node (RN) failures, and failures of transmitters in the CO and ONUs is proposed. In this schemes, at
least N additional fibers need to be laid in order to protect N ONUs against FF and DF failures. This
may result in capital expenditure that is too high for the cost-sensitive access networks.
In [5], the problem of designing a survivable access network is converted to a simplex cover
problem, and it is claimed that one terminal node is protected once it is connected with some other
terminal node. However, it does not consider the capacity of each terminal node. In fact, it is possible
that the protection capacity of one terminal node is limited.
The authors of [6] propose an approach to hybrid wireless optical broadband access network ( WOBAN)
survivability that does not require the PONs to have self-protecting capability. The idea is to reroute
the traffic around the failure. Specifically, if an ONU in a segment fails, the traffic will be rerouted to
another gateway in the same segment that is connected to a live ONU. If an OLT in a segment fails,
the traffic will be rerouted to a gateway in another segment that has a live OLT. This scheme assumes
that every wireless router in one segment can find a multi-hop path to a gateway in another segment.
The authors of [7], have proposed a new and efficient protection scheme, called Optimizing Backup
ONUs selection and backup Fibers deployment (OBOF), to enhance the survivability of FiberWireless (FiWi) against single segment failure. OBOF is composed of two consecutive steps: backup
ONUs selection and backup fibers deployment. In the first step, the Simulated Annealing (SA)
algorithm is applied to select the backup ONUs with the objective of minimizing recovery delay, and
in the second step, the Enhanced Greedy Cost-Efficiency (EGCE) algorithm is proposed to deploy
backup fibers with the objective of maximizing the amount of protected traffic and minimizing the
cost.
The authors of [8], have proposed a technique protectoration, which, as its name indicates, is a
hybrid multiple-failure recovery technique that aims at combining the fast response time of protection
and the bandwidth efficiency of restoration.
In [9], a variety of redundancy options for long-reach PONs are discussed, including N+1 protection
of N OLTs and N optical amplifiers, double routed fiber cables, and optical switches for protection
switching times of <50 ms. To improve the long-reach PON’s resilience to a localized catastrophic
failure at a CO, the authors proposed to deploy dual homing of ONUs, where ONUs are connected to
two disjoint OLT. The backup OLT is used only in case of failure.
The authors of [10] propoesd a Hitless Switching Scheme in which 1+1 protection scheme and
insert an alignment delay into the shorter link such that packets sent on both working and protection
paths arrive at the destination ONU simultaneously in order to yield hitless protection switching.
The authors of [11] proposed a centralized protection switching scheme for a threestage long-reach
WDM PON with partial optical protection. The considered long-reach WDM PON uses a dual-fiber
link (i.e., one working fiber and one protection fiber) to interconnect the CO with an AWG used as a
wavelength demultiplexer at the remote node.
In [12], a multiple-stage long-reach WDM PON consisting of cascaded Arrayed waveguide gratings
(AWGs) was proposed and studied in terms of complexity, reliability, and transmission performance.
The AWG of the first stage was used as a frequency cyclic N×N wavelength router to allow for spatial
wavelength reuse and connect it to the OLT by means of N/2 working and N/2 backup feeder fibers,
whereby simultaneous upstream and downstream transmissions are realized by using two free spectral
ranges (FSRs) of the AWG.
In [13], meshed PON topologies have been examined with the goal of building resilient optical
access networks with redundant cable routes that maximize the use of existing optical fibers.
In [14], a self-protected WDMPON architecture with the idea of group protection of ONUs was
proposed to protect against any failure at the distribution fibers. Two adjacent ONUs were grouped
and their corresponding downstream and upstream wavelengths were connected to the OLT via the
same output port of the AWG at the RN. This was achieved by utilizing the periodic spectral property
of the AWG and with proper wavelength assignment.
In [15] a improved version which greatly reduced the number of optical couplers needed at the RN
by means of a novel wavelength assignment is proposed. This architectures performed protection
switching at the ONU side. This might increase the complexity at the ONUs and require the fiber
connection between two adjacent ONUs.
In [16], a novel WDM-PON architecture with protection of both the feeder fibers and distribution
fibers were proposed. Both the RN and the distribution fibers were duplicated and interconnected. The
wavelength channels for a destined ONU were copied and routed simultaneously in two different
lightpaths, one for normal operation and the other for protection purpose, to achieve lightpath
diversity. When a fiber cut occurred, the optical switch at the ONU would be triggered to redirect the
disrupted signals to the protection path.
In [17-20], centrally controlled WDM-PON survivable architectures were proposed to have all the
protection switching performed at the OLT. This could greatly facilitate the control and management
of all the protection switching and help to keep the ONUs simple.
In [21],the authors proposed a technique for WDM-PONs with ring topology where the OLT is
connected to multiple access nodes (ANs) via single or double fiber rings. Each AN comprises an
optical power splitter, to which multiple ONUs are further connected either in star or ring topologies,
protection is achieved by means of self healing rings (SHRs). Duplicated protection fiber
rings are employed to provide redundant paths, and line or path protection switching is incorporated at
both the OLT and the ANs.
In [22], a dense-WDM self-healing ring network, with a unidirectional Optical Add Drop
Multiplexer (OADM), which was based on acousto-optic switches, at each network node, is proposed.
In [23], optical filters and optical switches were employed at access nodes for wavelength dropping
and protection switching respectively.
In [23,24], an AWG add-drop filter was employed as the OADM and a loop back circuit was
implemented to provide protection switching at each access node. However, these approaches still
require two working fiber paths to support both protection as well as bidirectional transmission.
In [25], a single-fiber bi-directional self-healing optical access ring networks with bi-directional
OADM is demonstrated. The idea was to apply the same OLT architecture and alternate path
switching scheme as in [20] to achieve self-healing function in a single fiber optical access ring.
In [26, 27], an interesting protected optical starshaped ring network was proposed. The physical
network topology was star-shaped, but the logical connections of all nodes, in form of wavelength
paths, were actually in a ring topology. It was realized by the optical foldback at the AWG employed
at the OLT and the wavelength routing properties of the AWG device. Another set of backup
wavelength paths are designated for protection and can be activated by switching the fiber
connections at the designated input ports of the AWG, in case of any fiber failure. When a fiber or a
network node failed, the protection switch at the OLT would be re-configured to activate the backup
wavelength paths, so as to bypass the failed nodes or link.
Authors in [28] proposed a hybrid WDM/TDM PON architecture that utilizes a combined ring-star
based connectivity to provide shared protection against optical line terminal (OLT) failure and also
proposed an appropriate control mechanism to reduce the protection switching time. They evaluated
the availability figures of the network service per end-user subject to different failure scenarios within
the proposed network architecture along with its associated capital expenditure (CAPEX) per user.
There scheme provides a significant cost benefit over 1:1 protection scheme for achieving almost the
same value of network availability.
Authors in [29] proposed a network fault management and protection system for the ring-and-spur
long-reach passive optical network (LR-PON). They exploit an adapted, enhanced performance, and
inexpensive passive optical components in the field and electronic switches in the central office (CO).
There system allows detecting and localizing not only faulty segments but also faulty nodes. They
show that using ring duplication protection in LR-PON can save half the cost compared to full
duplication protection with relatively high reliability performance (99.972%). There system can
recover from a fault in about 0.5ms as an upper bound.
Authors in [30], proposed and experimentally investigated a novel survivable WDM/TDM PON
architecture. By using TDM rings for ONUs in the RN, the survivable protection architecture can
simultaneously protect against the distribution and feeder fiber failures as well as the fiber failures in
the ring. Error-free transmissions at BER=10^9 for downstream and upstream in either working or
protection mode were successfully demonstrated.
Authors in [31] reviewed a number of Survivability techniques together.
III. CONCLUSION
Survivability has become a very important issue in optical networks. It has gained significant
importance due to very high speed and transmission capacity provided by optical networks. A lot of
research work has been done on survivability of different types of networks. Basically two methods
are used for survivability i.e. protection and restoration. Each of these methods has certain advantages
and disadvantages which have been discussed in literature survey[31].
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