142 CHINESE OPTICS LETTERS / Vol. 8, No. 2 / February 10, 2010
Extending path computation element for lightpath
restoration in wavelength-switched optical networks
Lianxing Hou (ûûûëëë,,,)
∗
, Yueming Lu (ººº²²²), Junhua Wang (ddduuu),
Yuefeng Ji (VVV¸¸¸), and Yiqiang Hua (uuurrr)
Key Laboratory of Information Photonics and Optical Communications, Ministry of Education,
Beijing University of Posts and Telecommunications, Beijing 100876, China
∗
E-mail: lancyhou@gmail.com
Received April 24, 2009
Current generalized multi-protocol label switching (GMPLS) standards do not include adequate models
for wavelength-switched optical networks (WSON) in recovery mechanisms. In this letter, GMPLS/path
computation element (PCE) extensions are applied for the restoration of the lightpaths disrupted by
collision or optical impairment. A reserved deflection routing scheme is proposed to achieve fast restoration.
It uses the expanded PCE component to compute and assign the backup paths for lightpath recovery.
Numerical results demonstrate that this scheme is effective and low cost.
OCIS co des: 060.4261, 060.4510.
doi: 10.3788/COL20100802.0142.
In transparent wavelength-switched optical networks
(WSON)
[1]
, dynamic lightpath provisioning requires
effective routing and wavelength assignment (RWA)
schemes, taking into account of both bandwidth avail-
ability and wavelength continuity constraints. However,
lightpath restoration requires a faster restoration speed
and a simpler deployment system. Toward these goals,
the centralized path computation element (PCE) has
been developed
[2]
. It is able to potentially simplify the
implementation of network nodes that may avoid com-
plex routing modules and to provide effective network
resource assignment. Thus, the path computation clients
(PCCs) can request the computation of an explicitly
routed path given a set of constraints, which are moti-
vated by mesh restoration algorithms or heuristics. Some
researchers are opposed to use PCE for restoration, since
it takes time. In our experimental setup, star topology is
applied to PCE and PCCs, and the recovery time could
be reduced to less than 50 ms.
However, the major challenge in the distributed all-
optical networks is that the current global information
on resource availability cannot be guaranteed at any par-
ticular place and time, which can lead to contentions. We
may soon have to support an increasing number of burst
traffic loads in the future such as in wavelength-routed
optical burst switched (WROBS) networks or all-optical
packed-switched (OPS) networks
[3−11]
. It is exp ected
that the connection requests will arrive at a very high
speed, while the average duration of each connection is
only several dozens or hundreds of milliseconds. One pos-
sible routing mechanism that can be used to reduce loss
or congestion due to sub-optimal path selection is deflec-
tion routing
[8]
. In this mechanism, each node maintains
several paths to a destination, with one path designated
as the primary (default). When the primary path of an
incoming connection is not available, the node deflects
the connection to any of the secondary paths. Although
deflection routing is inexpensive and simple with the
capability of high resource utilization, it may result in
optical packets looping in a multi-hop network for a long
time. Moreover, if a deflected service takes a longer
path to reach its destination, it would lead to overtime
and cause network congestion, especially at high traf-
fic loads
[9]
. To solve this problem, a deflection routing
protocol for optical burst switched (OBS) networks has
been proposed in Ref. [10], and the optical bursts might
have likely arrived out of sequence at the destination in
Ref. [11]. In addition, deflection routing is, by nature,
suboptimal b ecause it only considers the congestion of
the current switch, not the state of the links further
along the path, and may cause undesirable vibration ef-
fects. To solve these problems, Teng et al. presented
an approximate integer linear optimization scheme to
path selection with the objective of balancing the traffic
across the network links to reduce congestion and im-
prove overall performance
[12]
. However, on account of
the complex computation and huge backup route data
for each node, this scheme has become more inefficient,
resulting in an inability to handle larger non-Poisson
traffic such as link failure. While the integer linear pro-
gramming (ILP) formulation can avoid the defects men-
tioned above in WSON, and achieve high computation
efficiency and high capacity efficiency. The PCE charges
the centralized network resource assignment, while the
pre-configured cycle fast restoration scheme provides self-
adapting protection not only for on-cycle links but also
for straddling links
[13]
.
We propose the enhancement of the PCE/generalized
multi-protocol label switching (GMPLS) network archi-
tecture for the reserved deflection routing scheme to sup-
port the fast restoration of lightpaths. Unless otherwise
specified, we focus on the GMPLS-based multi-fiber net-
works that use the resource reservation protocol-traffic
engineering (RSVP-TE) signaling protocol. Wavelength
reservation is bidirectional. To ease our analysis, the
constraint called as “wavelength continuity constraint”
is considered; whereas the limited range wavelength con-
version or sparse converters in WSONs is left for further
evaluation in the future research.
1671-7694/2010/020142-04
c
° 2010 Chinese Optics Letters