técnicas de roteamento e atribuição de comprimento de onda em redes WDM(fribra ótica)
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técnicas de roteamento e atribuição de comprimento de onda em redes WDM(fribra ótica)

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2: Compute (K\u2212 1) routes Ri (2 \u2264 i \u2264 K) as candidate
routes, where Ri represents the ith shortest route.
3: For Ri, 2 \u2264 i \u2264 K, compute the transmission powers
pi,j (1 \u2264 j \u2264 Li) from each intermediate switch j on
Ri . Li means the number of switches on Ri. Find the
maximum transmission power Pimax = MAX(pi,j)
4: Find m such that Pmmax = MIN(Pimax) (2 \u2264 i \u2264 K),
which means the minimal of the maximum transmission
powers of all the candidate routes.
5: Select Rm as the alternate route
In this paper, we assume K = 3, i.e an alternate route is
selected from the second-shortest route and the third-shortest
In this section, we evaluate the performance of the proposed
routing by a computer simulation. We compare the proposed
routing with the fixed-alternate routing proposed in [6] which
does not consider the power constraint.
In the computer simulation, the network model in [5]
with 21 switches and 114 unidirectional fiber links [5] (shown
in figure 1) is used . In this network, every link is assumed to
be capable of carrying 8 wavelengths. Amplifiers are placed on
the links every 100km. We employ the same model of amplifier
as in [5]. The gain available at an amplifier is given by the
following function:
G(Pin, SSG) = min{SSG, (Pmax \u2212 Pin)}
where Pin is the total input power in dBm; Pmax is the max-
imum amplifier output power in dBm, and SSG is the gain in
dB, which is obtained when saturation is not occurred. We as-
sume each switch is connected with an access node ni (1 \u2264
i \u2264 21). Calls for node pair (ni, nj) (1 \u2264 i, j \u2264 21, i 6= j) are
generated according to a Poisson process with an arrival rate \u3bb.
The holding time for a call is exponentially distributed with an
average holding time h and is independent of generation and
holding times of other calls.
The blocking probability and the forced termination proba-
bility is used as performance metric. Blocking probability is
defined as a probability that a connection cannot be established
Figure 1: topology of the Italian network
due to resource contention along the desired route. Forced ter-
mination probability is defined as a probability that a connec-
tion is terminated by force due to saturation which is brought
by another new connection establishment. Figure 2 shows the
blocking probabilities and forced termination probabilities vs
traffic load \u3c1 which is defined as \u3c1 = \u3bbh.
From this figure, we can see that the forced termination
probability is drastically improved when using the proposed
routing algorithm. This is because the proposed routing avoids
occurrence of saturation along a direct route. Also we can see
that the blocking probability of proposed routing is slightly
higher than that of fixed-alternate routing. This is because
the proposed routing, even if a valid wavelength assignment
is found, blocks connection requests along the direct route
when saturation occurred.
In any communication system, we believe that it is more
important to reduce the forced termination probability than the
blocking probability because the forced termination has a more
damaging effect on users. Therefore, the proposed algorithm
can make it possible to provide high quality communication.
In this paper, we have studied the dynamic RWA problem with
power considerations in all-optical WDM networks and pro-
posed a routing algorithm that suppresses and avoids the oc-
currence of saturation. To evaluate the performance, we com-
pared the proposed routing with the fixed-alternate routing by
simulation results. It has been shown that the proposed routing
Figure 2: blocking probability and forced termination
probability versus load
algorithm significantly reduces the forced termination proba-
bility. Power constraints that we have assumed in this paper
can be more often occurred in the situation that traffic load is
heavy rather than light. Therefore, the proposal is important es-
pecially in the next generation Internet that the traffic volume
will explosively increase.
[1] B. Mukherjee, Optical Communication Networks, McGraw-Hill,
New York, 1997.
[2] H. Zang, J. P. Jue, L. Sahasrabuddhe, R. Ramamurthy,
B. Mukherjee, \u201cDynamic Lightpath Establishment in Wavelength
Routed WDM Networks,\u201d IEEE Communication Magazine, Vol.39
No.9, pp.100-107, Sep. 2001.
[3] J. Spath, \u201cDynamic routing and resource allocation in WDM
transport networks,\u201d Computer Networks 32 (2000), pp. 519-538.
[4] N. Ghani, S. Dixit, T. Wang, \u201cOn IP-over-WDM Integration,\u201d IEEE
Communication Magazine, Vol.38, No.3, pp.72-84, Mar. 2000.
[5] M.Ali, B. Ramamurthy, J. S. Deogun, \u201c Routing and Wavelength
Assignment (RWA) with Power Considerations in All-Optical
Wavelength-Routed Networks, \u201d Proc., IEEE GLOBECOM \u201999
pp.1437-43, Dec. 1999.
[6] S. Ramaurthy and B. Mukhrjee, \u201cFixed-Alternate Routing and
Wavelength Conversion in Wavelength-Routed Optical Networks,\u201d
Proc., IEEE GLOBECOM \u201998, Vol.4, pp.2295-2302, Nov.1998.
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