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Algorithm for Allocating Outside Optical Fiber
in Optical Access Networks
Ikuya Takahashi, Hiroshi Uno and Koichi Sano
NTT Access Network Service Systems Laboratories
1-6 Nakase, Mihama-Ku, Chiba-Shi, Chiba-Ken, 261-0023,JAPAN
TEL:+81-43-211-3375 FAX:+81-43-213-0941
E-mail: {iku, uno, sano}@ansl.ntt.co.jp
Abstract
This work details a new optical fiber allocation algorithm that enables a quick service delivery and facilityeffective allocation.
An optical access network (OAN) consists of NEs like outside fiber cable, inside fiber cable, and service
equipment. The outside optical cable has a fiber ribbon structure consisting of four or eight fibers to reduce cable size,
weight, and connection costs. Since a technology is not yet available to cut a single fiber in a fiber ribbon and connect
it to a fiber in another ribbon, the fiber ribbon has to be cut to allocate one of the fibers. However, there is no
quantitative and clear criteria for cutting fiber ribbon, the operator makes a judgment based on experience, or the
system allocates the fiber ribbon in ascending fiber-id order. This leads to delays in service delivery and inefficient use
of fiber. Therefore, an auto-allocation algorithm that takes into account all relevant information is needed for a quick
service delivery and facility-effective allocation.
The basic concept of our approach is to allocate the fiber ribbon least likely to be used in the future by
considering the fiber ribbon state throughout the cable. In other words, it is to select the cable with the most spare
ribbons and allocate one of them. Spare ribbons mean “cannot be used ribbons.” The number of “cannot be used
ribbons” depends on the number of “could be used ribbons.” The number of ribbons that will be needed in a certain
allocation area (= “could be used” number) can be calculated from the number of subscribers and the probability of
demand in the area. Since demand numbers fluctuate, a “safety rate” needs to be defined. The “safety rate” gives the
upper limit of cumulative probability of demand and determines numbers of “could be used ribbons.”
  fl  fd   ft 
i
i
(1)
i
i cable
Central
office
to next area
fl
fti 
fai
fai  Q(nsi , pi,Ti )
Q(nsi , pi,Ti)
fai  Q(nsi , pi,Ti )
Q gives x, the Cumulative probability
ns  p
nsi  pi x
Ti
e
x!
x
ft = larger number of actually or could be used fiber ribbons
fl = number of end-fiber ribbons
fd = number of dead-end fiber ribbons
fa = number of allocated fiber ribbons
p = probability of fiber demand in allocation area
ns = number of subscribers in allocation area
T = cumulative probability ( = safety rate)
i
fa
fd
Allocation area
p,ns
Figure 1. fiber-ribbon state
i
Allocation rate
The number of spare ribbons is counted by subtracting number of actually used fiber ribbons (or could be used
fiber ribbons, if it is larger than actually used ribbons) from number of available end fiber ribbons (Fig. 1). The
number of spare ribbons in target area is counted by adding up all the spare ribbons in the area (Eq. (1)). The target
area can be considered a triangle with a vertex cable. To allocate the
ribbon least likely to be needed in the future, following steps are
1.6
executed. (1) divide the triangular area into two triangles, and
Proposed algorithm
1.5
count the number of spare ribbons in each, (2) then select the area
1.4
with the most spare ribbons, (3) repeat steps (1) and (2) until last
1.3
cable, (4) finally, select the unused fiber ribbon in the last cable
Reference algorithm
1.2
and allocate one of its fibers at the demand point connected to the
1.1
fiber.


1
We simulates the proposed algorithm to evaluate the basic
0.9
 characteristic
 compared to a conventionalalgorithm and reference
Conventional algorithm
0.8
algorithm.
Figure
2
shows
the
allocation
rates
of
each
algorithm.
ns = 40

p = 0.1
The allocation rate means the number of allocated fibers normalized
0.7
T = 0.5

by the one derived from conventional algorithm. Simulation shows
0.6
0
1
2
3
4
that the proposed algorithm has an allocation rate 1.0 - 1.6 times
Number of Branched (2x)
better than that of a conventional outside fiber allocation algorithm
and more than equivalent to that of a reference one.
Figure 2. Allocation rates of each algorithm