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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 13, Iss. 26 — Dec. 26, 2005
  • pp: 10457–10468
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Dynamic lightpath provisioning with signal quality guarantees in survivable translucent optical networks

Yong Ouyang, Qingji Zeng, and Wei Wei  »View Author Affiliations


Optics Express, Vol. 13, Issue 26, pp. 10457-10468 (2005)
http://dx.doi.org/10.1364/OPEX.13.010457


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Abstract

This paper studies the problem of signal-quality-guaranteed lightpath provisioning in survivable translucent optical networks under dynamic traffic. A new protection scheme, called regeneration-segment protection (RSP), is proposed. Provisioning approaches with shared path protection and shared RSP are presented. Two main signal quality constraints are integrated with the provisioning problem. Different regenerator placement strategies for working path and protection path are employed. Joint path selection method is used to select the “optimal” working-protection pair. With the above considerations, survivable lightpath provisioning with signal-quality-guarantees is achieved in a cost-effective manner. Results show that in a moderate-size network, RSP has less blocking probability than path protection when the network load is low or modest. Besides, RSP obtains better performance in terms of recovery time than path protection in all network scenarios.

© 2005 Optical Society of America

1. Introduction

This paper is devoted to study lightpath provisioning with signal-quality-guarantees in translucent optical networks under dynamic traffic. To the best of our knowledge, no prior work has been done on this issue. We first propose a new protection scheme called regeneration-segment protection (RSP). We show that RSP has advantages over path protection scheme. Then, we present provisioning approaches with path protection and RSP. In order to provide signal-quality-guaranteed lightpaths, we integrate two main signal quality constraints into the provisioning problem. In order to utilize resources efficiently, we employ different regenerator placement strategies to minimize the number of regenerators utilized on working paths, and maximize sharing of regenerators on protection paths, respectively. Besides, we use joint path selection method to select the working-protection pair with the minimum cost sum among multiple candidate working-protection pairs. In the simulations results, we can see that in a moderate-size network, RSP has less blocking probability than path protection when the network load is low or moderate. In addition, RSP obtains better performance in terms of recovery time than path protection in all network scenarios.

The rest of the paper is organized as follows. Section 2 provides the network model. The new protection scheme is introduced in Section 3. Section 4 presents optical signal quality constraints considered in this paper. Section 5 describes the details of provisioning approaches with path protection and RSP. The numerical results are presented and discussed in Section 6. Section 7 concludes the paper.

2. Network model

Figure 1(a) shows the node architecture considered in this paper. It mainly consists of a PXC fabric and a shared regenerator bank. The former provides wavelength switching functionality, while the latter contains a number of optical-electronic-optical (OEO) based regenerators. The regenerators are equipped with tunable transmitters, and hence can provide signal regeneration and wavelength translation functionality simultaneously. The number of regenerators at a node is fixed, but this number may vary from one node to another. Some hub nodes may have a larger number of regenerators, while some do not have any.

Fig. 1. Network model

3. Regeneration-segment protection

Segment protection has been widely studied before. It divides a working path into several segments and protects each segment with a backup path. It is a promising scheme due to the features of high resource efficiency and short protection-switching time [8

8 . J. Cao , L. Guo , H. Yu , and L. Li , “ Dynamic segment shared protection algorithm for reliable wavelength-division-multiplexing mesh networks ,” Opt. Express. 13 , 3087 – 3095 ( 2005 ). [CrossRef] [PubMed]

]. RSP is a special form of traditional segment protection. In traditional segment protection, a segment means any subpath that consists of a sequence of links. However, in RSP, a segment refers to a RS which is a particular subpath that terminates between two neighboring transceivers. Fig. 2 illustrates the concept of RSP. Purposely, we explain it in comparison with path protection. As shown in Fig. 2(a), the working path is a translucent lightpath which contains three RSs. Path protection provides an end-to-end protection path from the source node (node 1) to the destination node (node 8). When a failure occurs, the working path is replaced by the protection path. However, in RSP, as shown in Fig. 2(b), each RS on the working path is protected by a particular protection path. When a failure occurs, only the affected RS performs protection switching and the other unaffected RSs are oblivious to the failure. We can easily see that, for transparent lightpaths, RSP is just the same as path protection.

Fig. 2. Illustration of path protection and regeneration-segment protection

4. Signal quality constraints

4.1 Optical signal-to-noise ratio

OSNR is a major contributor to bit-error-rate (BER). OSNR at the receiver can not exceed a threshold, OSNRmin, dependent on the required BER and transmitter-receiver technology, such as forward-error-correction (FEC). Let OSNRb represent the received OSNR at node b of RS (a,b). OSNR constraint can be described as:

OSNRbOSNRmin
(1)

With an intermediated parameter, Q-factor, the relationship of BER and OSNRmin is given by [10

10 . Alcatel’s White Contribution COM 15-33-E: Electrical (BER, Q-factor, el. SNR) and Optical (OSNR, OCR) System Performance Parameters for G.DSN ITU-T SG 15 Contribution, ( 2000 ).

]:

BER(Q)(12π)·(exp(Q22)Q)
(2)
OSNRmin=(1+r)(1+r)2(1r)2·BeBo·Q2
(3)

Where r is the extinction ratio of the transmitted optical signal, which is defined as the ratio of the mean peak powers in “0” and “1” bits at the transmitter, Be is the electrical bandwidth (typically, Be = 0.75 × B, B is the digital bit rate of the signal) and Bo is the optical bandwidth for OSNR measurement (a typical value of Bo is 12.6Hz or 0.1nm for a given optical spectrum analyzer)). For example, for a BER of 1.0 × 10-16, we have Q = 8.0. Let B = 10Gb/s, r = 0.15 and assume FEC bring a gain of 5dB on OSNR. We get OSNRmin to be 20.67dB without FEC, and 15.67dB with FEC. Moreover, if we set a system margin of 3 dB to allow other impairments such as nonlinear effects, we can get the requirement of OSNRmin to be 23.67dB without FEC, and 18.67dB with FEC.

PASE(k,j)=2nsp(k,j)·(G(k,j)1)·h·v·Bo
(4)

Where nsp(k,j) is the spontaneous emission factor, G(k,j) is the small-signal gain, h is the Planck constant, ν is the optical frequency, and Bo is the optical bandwidth.

Assume the loss in a span can be exactly compensated by an EDFA. Then, ASE noise power on RS (a,b) can be described as:

PASE(a,b)=Σ1M(ΣjLink(k)PASE(k,j))
(5)

If we use Pl to represent the launched signal power at node a, OSNRb can be calculated as:

OSNRb=PlPASE(a,b)
(6)

4.2 Polarization mode dispersion

PMD is caused by the time delay between two orthogonal polarizations of light traveling at different speeds through an optical fiber. As the channel bit rate increase to 10Gbps and beyond, PMD strongly affects the transparent transmission length in optical networks. Let ∆tPMD(a,b) denote the PMD value of RS (a,b). PMD management requires that the PMD value of a RS be less than a fraction a of the bit duration, that is:

ΔtPMD(a,b)αB
(7)

Where B is the digital bit rate of the signal and α is the maximum dispersion fraction in a bit interval that is acceptable for the receiver. A typical value for α is 0.1. According to [9

9 . J. Strand , A. Chiu , and R. Tkach , “ Issues For Routing In The Optical Layer ,” IEEE Commun. Mag. 39 , 81 – 88 ( 2001 ). [CrossRef]

], ∆tPMD(a,b) can be expressed as:

ΔtPMD(a,b)=Σ1MDPMD2(k)·L(k)
(8)

5. Survivable lightpath provisioning in translucent optical networks

5.1 Procedures of survivable lightpath provisioning

Provisioning procedures with path protection and RSP are presented in Fig. 3. We divide the problem of establishing a lightpath (working path or protection path) into three separate phases: routing, regeneration placement and wavelength assignment. In the following, we first discuss theses problem one by one.

Fig. 3. Procedures of survivable lightpath provisioning for translucent optical networks

5.2 Routing algorithm

Since routing problem with multiple constraints is NP-complete [12

12 . S. Chen and K. Nahrstedt , “ An overview of quality of service routing for next-generation high-speed networks: Problems and solutions ,” IEEE Network. 12 64 – 79 ( 1998 ). [CrossRef]

], we calculate K candidate routes for both working path and protection path to simplify the problem. Besides, we use joint path selection method proposed in [13

13 . C. Xin , Y. Ye , S. Dixit , and C. Qiao , “ A Joint Working and Protection Path Selection Approach in WDM Optical Networks ,” in Proceedings of IEEE Global Telecommunications Conference (Globecom ’01) ( IEEE, New York , 2001 ), 2165 – 2168 .

] to select the working-protection pair with the minimum cost sum among multiple candidate working-protection pairs. The cost functions will be discussed in Section 5.4.

5.3 Regenerator placement algorithm

Regenerator placement for a lightpath determines which nodes on the lightpath are chosen as regeneration nodes and which regenerator at a regeneration node is selected. Although a regenerator can be placed for both signal regeneration and wavelength conversion, only the first case is considered in this paper. By placing regenerators at some intermediate nodes, the required signal quality of a lightpath is guaranteed.

Fig. 4. Regenerator placement algorithm

Assume a lightpath (s,…,i,…,j,…,d) from the source s to the destination d, traverse nodes i and j. The regeneration nodes are determined in order from node s to node d. Also, assume node i is the last regeneration node has been determined and subpath (i,…,j) is the maximum transparent segment from node i to node d, which means Inequalities (9) – (11) are satisfied simultaneously.

OSNRjOSNRmin
(9)
ΔtPMD(i,j)αB
(10)
OSNRj+1<OSNRminorΔtPMD(i,j+1)>αB
(11)

One node should be chosen as regeneration node from node i+1 to node j and one regenerator at the regeneration node should be selected.

The regenerator placement algorithm is presented in Fig. 4, in which a strategy to minimize the number of regenerators is used for working path, while another strategy to maximize sharing of regenerators is employed for protection path.

5.4 Wavelength assignment algorithm

Fig. 5. Wavelength assignment algorithm

5.5 Cost functions

The cost functions define the cost of a wavelength, a regenerator and a path. They help to evaluate a feasible working-protection pair. Before introducing the cost functions, we define the following notations:

  • C(λ): Cost of a free wavelength on a link.
  • C(r): Cost of a free regenerator at a node.
  • Cw(λ): Cost of a wavelength used by a working path.
  • Cw(r): Cost of a regenerator used by a working path.
  • Cp(λ): Cost of a wavelength used by a protection path.
  • Cp(r): Cost of a regenerator used by a protection path.
  • CW: Cost of a working path.
  • CP: Cost of a protection path.

Generally, we assign a larger value to C(r) than C(λ) because regenerators are usually considered more rare resources than wavelengths in the network. In addition, since a working path uses network resources exclusively, we have: Cw(λ) = C(λ), and Cw(r) = C(r). However, a protection path will share a wavelength or a regenerator with other protection paths, or share a regenerator with its working path, and accordingly, the cost of the specific wavelength or regenerator should be significantly reduced. We define Cp(λ) and Cp(r) as:

Cp(λ)={ε1×C(λ)ifλis usd by other protection paths and sharableC(λ)ifλis free
(12)
Cp(r)={0if r is usedby thecorresponding working pathε2×C(r)if r is usedby other protectionpaths and sharableC(r)ifrisfree
(13)

Where ε1 and ε2 are small constants such as 0.01.

The path cost is the sum of costs of all wavelengths and regenerators on a path p. Therefore, CW and CP can be calculated by:

CW=ΣλpCw(λ)+ΣλpCw(r)
(14)
CP=ΣλpCp(λ)+ΣλpCp(r)
(15)

6. Numeric results

Fig. 6. Topology of USA network

Table 1. Physical parameters used in the simulations

table-icon
View This Table

We evaluate the performances in terms of blocking probability and recovery time under various network scenarios. For path protection, recovery time for a lightpath can be calculated based on the hop count of the working-protection pair. For regeneration-segment protection, recovery time for a RS can be calculated based on the hop count of the working RS and its protection path, since the protection entity is a RS.

Fig. 7. Network performances for different required BER, with β = 0.5 and Nr = 20

Figure 7 compares the performances of RSP with that of path protection for different values of required BER, with β = 0.5 and Nr = 20. From Fig. 7(a), we make the following observations: (a) For the same required BER, RSP obtains lower blocking probability than path protection when the load is low or modest, but this improvement is weakened with decreasing of the required BER. This is because RSP can achieve better resource sharing as discussed in Section 3. With a lower required BER, this advantage is more obvious since a lightpath is likely to contain more RSs. (b) Both protection schemes have similar blocking probability for the same required BER when the load is high. The reason for this is that, when the load is high, some RSs become very short due to unavailability of regenerators at some nodes, which leads to RSP work inefficiently. Accordingly, for RSP, the advantage of better resource sharing is counteracted by the disadvantage of inefficient resource utilization. (c) The blocking probabilities for both protection schemes increase when the required BER decreases. This is because that, for a lower required BER, more regenerators are needed to clean the transmission impairments for a lightpath, which results in higher blocking probabilities.

Figure 7(b) shows that in all cases, the number of hops of the work-protection path pair does not increase, but decreases a little with the increasing of offered load. The reason for this is that, with the increasing of offered load, a connection may use a long path as its working path. However, long working paths use more regenerators and are more difficult to find protection paths than short ones. As a result, connections using long working paths are more likely to be blocked than connections using short working paths, which leads to the decreasing of number of hops of the work-protection path pair.

Figure 7(b) also indicates that the average hop count of working-protection pair in RSP is smaller than that in path protection, which means shorter recovery time is achieved for RSP. This is because that the protection entity of RSP is RS, while the protection entity of path protection is the whole path. The figure also shows that in path protection, the required BER nearly has no effect on the performance, while in RSP, performance decreases with decreasing of the required BER. The reason for this is that, since path protection is an end-to-end protection scheme, for a given connection request, the working and protection paths are the same for different BER values if there are enough regenerators in the paths. However, in RSP, lower BER value will lead to shorter working segments, which results in the number of hops of working-protection pair decreases with decreasing of the BER value.

Fig. 8. Network performances for different values of Nr, with β = 0.5. The required BER follows 10-16 : 10-14 : 10-10 = 1 : 1 : 1

Figure 8 compares the performances of RSP with that of path protection for different values of Nr, with β = 0.5 and the required BER following the distribution 10-16 : 10-14 : 10-10 =1 : 1 : 1. Fig. 8(a) shows that the blocking probabilities of both protection schemes decrease when Nr increases. It is obvious that a larger value of Nr means more regenerators in the network and leads to lower blocking probabilities. For the same value of Nr, the curves in Fig. 8(a) have similar trend to the ones in Fig. 7(a), and can be explained similarly.

Figure 8(b) indicates that the average hop count of working-protection pair in RSP is much smaller than that in path protection as shown in Fig. 7(b). The figure also shows that the value of Nr nearly has no impact on the network performance for both protection schemes.

Figure 9 compares the performances of RSP with that of path protection for different values of β, with Nr = 20 and the required BER following the distribution 10-16 : 10-14 : 10-10 = 1 : 1 : 1. In Fig. 9(a), we observe that the blocking probabilities decrease significantly when β decreases from 0.7 to 0.5, but this decrease stops when β decreases from 0.5 to 0.3. The reason for this is that, when β equals 0.7, more regenerators are needed to regenerate a lightpath in such a large-size network. As a result, the blocking probability becomes higher because less free regenerators can be assigned to the following requests. However, when β equals 0.5, the network performance can be improved a certain extent because regenerators serve for wavelength conversion at the same time. We also observe that for the same value of β, the curves in Fig. 9(a) have similar trend to the ones in Fig. 7(a).

Fig. 9. Network performances for different values of β, with Nr = 0.5. The required BER follows 10-16 : 10-14 : 10-10 = 1 : 1 : 1

Figure 9(b) shows that the average hop count of working-protection pair in RSP is smaller than that in path protection as shown in Fig. 7(b). The figure also indicates that for RSP, the average hop count of working-protection pair decreases when β increase. This is because that a lightpath will contain more RSs and a RS will become shorter in a large-size network than in a small-size network. Thus, the length of the RS and its protection path will become smaller.

Based on the results discussed above, we can conclude that, in a moderate-size network, RSP has less blocking probability than path protection when the network load is low or modest. Besides, in terms of recovery time, RSP obtains better performance than path protection in all network scenarios.

7. Conclusion

In this paper, we study dynamic lightpath provisioning with signal-quality-guarantees in survivable translucent optical networks. We propose a new protection scheme, called regeneration-segment protection (RSP). We present provisioning approaches with shared path protection and shared RSP taking into account two main signal quality constraints. With the proposed approaches, signal-quality-guaranteed and survivable lightpath provisioning in translucent optical network is achieved in a cost-efficient manner. Simulation results show that in a moderate-size network, RSP has less blocking probability than path protection when the network load is low or modest. Besides, RSP obtains better performance in terms of recovery time than path protection in all network scenarios.

References and Links

1 .

A. L. S. Filho and H. Waldman , “ Strategies for Designing Translucent Wide-Area Networks ,” in Proceedings of International Microwave and Optoelectronics Conferenc-IMOC’03 ( Foz do Iguacu, PR, Brazil , 2003 ), 931 – 936 .

2 .

B. Ramamurthy , S. Yaragorla , and X. Yang , “ Translucent optical WDM networks for the next-generation backbone networks ,” in Proceedings of IEEE GLOBECOM 2001 Symposium on Optical and Photonic Communications ( San Antonio, TX , 2001 ), 60 – 64 .

3 .

H. Zang and R. P. J. Huang , “ Methodologies on Designing a Hybrid Shared-Mesh-Protected WDM Network with Sparse Wavelength Conversion and Regeneration ,” in Asia-Pacific Optical Communications Conference and Exhibition 2000 , S. Xie , C. Qiao , and Y. C. Chung , eds., Proc. SPIE 4910 , 188 – 196 ( 2000 ). [CrossRef]

4 .

E. Yetginer and E. karasan , “ Regenerator Placement and Traffic Engineering with Restoration in GMPLS Networks ,” Photonic Network Commun. 6 , 134 – 149 ( 2003 ). [CrossRef]

5 .

M. Ali , “ Shareability in Optical Networks: Beyond Bandwidth Optimization ,” IEEE Commun. Mag. 42 , 11 – 15 ( 2004 ). [CrossRef]

6 .

X. Yang , L. Shen , and B. Ramamurthy , “ Survivable Lightpath Provisioning in WDM Mesh Networks under Shared Path Protection and Signal Quality Constraint ,” J. Lightwave Technol. 23 , 1556 – 1567 ( 2005 ). [CrossRef]

7 .

S. Ramamurthy and B. Mukherjee , “ Survivable WDM mesh networks, part I - protection ,” in Proceedings of IEEE’99 ( New York, NY , 1999 ), 744 – 751 .

8 .

J. Cao , L. Guo , H. Yu , and L. Li , “ Dynamic segment shared protection algorithm for reliable wavelength-division-multiplexing mesh networks ,” Opt. Express. 13 , 3087 – 3095 ( 2005 ). [CrossRef] [PubMed]

9 .

J. Strand , A. Chiu , and R. Tkach , “ Issues For Routing In The Optical Layer ,” IEEE Commun. Mag. 39 , 81 – 88 ( 2001 ). [CrossRef]

10 .

Alcatel’s White Contribution COM 15-33-E: Electrical (BER, Q-factor, el. SNR) and Optical (OSNR, OCR) System Performance Parameters for G.DSN ITU-T SG 15 Contribution, ( 2000 ).

11 .

B. Ramamurthy , D. Datta , H. Feng , J. P. Heritage , and B. Mukherjee , “ Impact of transmission impairments on the teletraffic performance of wavelength-routed optical networks ,” J. Lightwave Technol. 17 , 1713 – 1723 ( 1999 ). [CrossRef]

12 .

S. Chen and K. Nahrstedt , “ An overview of quality of service routing for next-generation high-speed networks: Problems and solutions ,” IEEE Network. 12 64 – 79 ( 1998 ). [CrossRef]

13 .

C. Xin , Y. Ye , S. Dixit , and C. Qiao , “ A Joint Working and Protection Path Selection Approach in WDM Optical Networks ,” in Proceedings of IEEE Global Telecommunications Conference (Globecom ’01) ( IEEE, New York , 2001 ), 2165 – 2168 .

OCIS Codes
(060.4250) Fiber optics and optical communications : Networks
(060.4510) Fiber optics and optical communications : Optical communications

ToC Category:
Research Papers

Citation
Yong Ouyang, Qingji Zeng, and Wei Wei, "Dynamic lightpath provisioning with signal quality guarantees in survivable translucent optical networks," Opt. Express 13, 10457-10468 (2005)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-26-10457


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References

  1. A. L. S. Filho and H. Waldman, "Strategies for Designing Translucent Wide-Area Networks," in Proceedings of International Microwave and Optoelectronics Conferenc-IMOC'03 (Foz do Iguacu, PR, Brazil, 2003), 931-936.
  2. B. Ramamurthy, S. Yaragorla and X. Yang, "Translucent optical WDM networks for the next-generation backbone networks," in Proceedings of IEEE GLOBECOM 2001 Symposium on Optical and Photonic Communications (San Antonio, TX, 2001), 60-64.
  3. H. Zang and R. P. J. Huang, "Methodologies on Designing a Hybrid Shared-Mesh-Protected WDM Network with Sparse Wavelength Conversion and Regeneration," in Asia-Pacific Optical Communications Conference and Exhibition 2000, S. Xie, C. Qiao and Y. C. Chung, eds., Proc. SPIE 4910, 188-196 (2000). [CrossRef]
  4. E. Yetginer and E. karasan, "Regenerator Placement and Traffic Engineering with Restoration in GMPLS Networks," Photonic Network Commun. 6, 134-149 (2003). [CrossRef]
  5. M. Ali, "Shareability in Optical Networks: Beyond Bandwidth Optimization," IEEE Commun. Mag. 42, 11-15 (2004). [CrossRef]
  6. X. Yang, L. Shen, and B. Ramamurthy, "Survivable Lightpath Provisioning in WDM Mesh Networks under Shared Path Protection and Signal Quality Constraint," J. Lightwave Technol. 23, 1556-1567 (2005). [CrossRef]
  7. S. Ramamurthy and B. Mukherjee, "Survivable WDM mesh networks, part I - protection," in Proceedings of IEEE’99 (New York, NY, 1999), 744-751.
  8. J. Cao, L. Guo, H. Yu, and L. Li, "Dynamic segment shared protection algorithm for reliable wavelengthdivision-multiplexing mesh networks," Opt. Express. 13, 3087-3095 (2005). [CrossRef] [PubMed]
  9. J. Strand, A. Chiu, and R. Tkach, "Issues For Routing In The Optical Layer," IEEE Commun. Mag. 39, 81-88 (2001). [CrossRef]
  10. Alcatel's White Contribution COM 15-33-E: Electrical (BER, Q-factor, el. SNR) and Optical (OSNR, OCR) System Performance Parameters for G.DSN ITU-T SG 15 Contribution, (2000).
  11. B. Ramamurthy, D. Datta, H. Feng, J. P. Heritage, and B. Mukherjee, "Impact of transmission impairments on the teletraffic performance of wavelength-routed optical networks," J. Lightwave Technol. 17, 1713-1723 (1999). [CrossRef]
  12. S. Chen and K. Nahrstedt, "An overview of quality of service routing for next-generation high-speed networks: Problems and solutions," IEEE Network. 12 64-79 (1998). [CrossRef]

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