ECOC 2014, Cannes - France Th.1.2.6
Increased Energy-Efficiency and Capacity for Mixed-Line-Rate WDM Networks with Hybrid Raman-EDFA Amplification Jorge López Vizcaíno
(1,3)
(1)
(2)
(2)
(3)
, Yabin Ye , Andrés Macho , Felipe Jiménez , Peter M. Krummrich
(1)
Huawei Technologies Duesseldorf GmbH, European Research Center, Riesstr. 25, 80992 Munich, Germany, E-mail address:
[email protected] (2) Telefónica I+D, c/ Don Ramón de la Cruz, 84, 28006 Madrid, Spain (3) Technische Universitaet Dortmund, Friedrich-Woehler-Weg 4, 44227 Dortmund, Germany Abstract The selective placement of additional Hybrid Raman-EDFA amplification provides an effective mechanism to improve the energy and spectral efficiency of mixed-line-rate WDM networks. The energy efficiency per GHz is increased up to 50% and the network capacity is doubled. Introduction Telecom carriers need to upgrade network capacity to cope with the exponential growth of Internet traffic. Augmenting the capacity of the network entails the deployment of additional equipment which results in an increase of capital expenditures (CapEx) and operational expenditures (OpEx) due to, among other aspects, higher energy consumption. In fact, telecom carriers are becoming one of the major electricity consumers in our society. Therefore, operators are developing a growing interest in making their networks more energy and spectral-efficient. The existing core networks are based on wavelength division multiplexing (WDM) technologies, with channel bit rates evolving from 10 Gbps to 40, 100, 200 and 400 Gbps. Moreover, WDM networks are also changing from a conventional single-line-rate operation to mixed-line-rate (MLR), where multiple line rates can be combined over the same fiber. This allows for the coexistence of different generations of transponders, as well as handling the heterogeneity of the traffic demands in the network (i.e. traffic might increase at different rates within a network). Higher-speed transmission systems, such as 400 Gbps, will be predominant in future network deployments, but require a higher optical signal to noise ratio (OSNR) than current systems to successfully recover the information at the receiver. The transmission reach limitation of these systems could be overcome by optical-electrical-optical 1 (OEO) regenerations at the intermediate nodes , but entailing a significant increase in cost and 2 energy consumption. In our previous work , we proposed a different approach to improve the energy and spectral-efficiency of the network, based on the selective placement of additional erbium-doped-fiber-amplifiers (EDFAs) at predefined intermediate locations in the links of the network. The energy efficiency per GHz (EEPG) and the network capacity were increased with respect to the initial configuration of amplifiers in
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up to 42% and 65%, respectively. In addition to EDFAs, hybrid Raman-EDFAs (EDFA/RA) are emerging as an effective amplification scheme to extend the transmission reach of future high3 speed systems, as recently demonstrated . The EDFA/RA provides high gain with low noise figure, but consumes significantly more energy than EDFA only amplifications. In this work, we aim at extending our previous work by evaluating whether the selective placement of additional EDFA/RA in a current network deployment scenario can result in EEPG improvements. Furthermore, network capacity increases coming from the higher spectral efficiency are assessed. The evaluation is performed for a realistic nation-wide network scenario with MLR operation (40/100/200/400 Gbps), and dedicated protection 1+1 (DP 1+1) as resilience scheme. Network and transmission model A typical core network infrastructure is considered, where the in-line amplifiers (EDFA only) are already deployed. Additionally, some pre-defined potential placements, where additional amplifiers could be placed, are considered. The WDM network assumes the International Telecommunications UnionTelecommunication (ITU-T) with 50 GHz channel spacing and up to 80 wavelengths. The network model takes three basic energyconsuming devices into account: • Transponder (TSP): Line rates (LR) of 40, 100, 200 and 400 Gbps are considered (the transmission with 400 Gbps will be realized in two contiguous 50 GHz slots).Tab. 1 contains the considered parameters for the 2 transponders : the modulation formats, power consumption (PC), launched power (Pin), and the required OSNR (ROSNR) for the different transponder types. • Optical cross-connect (OXC): It is based on a 2 multicast switch architecture and composed of several wavelength selective switches (WSS) and optical amplifiers (OAs). The OAs are
ECOC 2014, Cannes - France Th.1.2.6
Tab. 1: Transponder parameters
LinkList Link ID 4 35 40
LR Modulation Pin ROSNR PC [Gbps] Format [dBm] [dB] [W] 40 100 200 400
Noise Figure [dB]
10
QPSK DP-QPSK DP-16QAM DP-16QAM
1 1 1 4
EDFA/RA
12 14.5 20.5 23.5
No. of LPs 4 3 1
LPIDS 20, 40, 56, 76, 56, 76, 98 20
173.8 243.4 280 481.9
EDFA
8 6 4 2 0 10 12 14 16 18 20 22 24 26 28 30
Gain [dB]
Fig. 1: Gain vs. NF dependence for EDFA and EDFA/RA
Fig. 2: Initial RWA algorithm
placed at the input and output of the node (pre-amp and booster), and at the add/drop stage to compensate the splitting/insertion losses: 31.5 dB for through channels, and 2 19dB for each added/dropped channel .The PC in watts of the OXC is assumed to depend on the node degree (N) and the add/drop degree (a) as follows: ൌ ȉ ͺͷ ܽ ȉ ͳͲͲ 3 ͳͷͲ, where 150W is the node overhead . • Optical amplifier (OA): The OAs deployed at the node are assumed to be EDFAs, whereas the in-line amplifiers, depending on the optimization strategy, could be either EDFA or EDFA/RA (backward Raman and EDFA hybrid amplifier). These amplifiers are assumed to provide the same gain for all the wavelengths, and a noise figure (NF) versus gain dependence as depicted in Fig. 1 (based con commercial products from several vendors). 4 4 PC values of 30W and 60W per direction are considered for the EDFA and the EDFA/RA respectively, with a common overhead 4 contribution of 140W per in-line amplifier location. The span losses in dB are calculated as 5 follows : ߙ ܮ ሺͲǤͲͷܮȀʹሻ ʹ ͳǤͷ, where ߙ is the attenuation coefficient (0.22 dB/km) and L is the span length in km. The second factor accounts for the losses due to a fused splice after each 2 km fiber segment (typical value for field deployments). Additionally, 2 dB and 1.5 dB are assumed for the extra loss inserted by the connectors between amplifiers and line cards, and the potential splices derived from maintenance tasks, respectively. Transparent reach feasibility for a particular line rate and path is determined as in Eq. (1), i.e., whenever the received OSNR ሺܱܴܵܰோ ) is greater or equal than the ROSNR value (in
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Fig. 3: Optimization phase
Tab.1) plus a margin of 3 dB (ݎܽܯௗ ) to account for potential nonlinear penalties. ܱܴܵܰோ ሾሿ ܴܱܴܵܰሾሿ ݎܽܯௗ ሾሿ
(1)
Routing and wavelength assignment (RWA) and amplifier placements optimization Heuristics algorithms for the RWA and the amplifier placement optimization have been 2 used in this study . The operation of the algorithms is divided into two stages: Initial RWA (Fig. 2) and optimization phase (Fig. 3). The EEPG (i.e., traffic [Gbps] / PC[W]/ spectrum occupancy [GHz]) is set as the optimization objective. In a MLR network, a particular demand can be served by different line rate combinations (LRComb). Following the defined optimization objective, the algorithm attempts to establish lightpaths (LP) with the LRcomb with the highest EEPG (provided that enough and common wavelengths are available on the path, and Eq. (1) is fulfilled). If this is possible, a LP is established and marked as “OPTIMUM”. Otherwise, if a LP is established with a LRComb different from the optimum one, the LP will be marked as “non-optimized” and included in the list of links traversed by LPs to optimize (LinkList). After evaluating the RWA for all the demands, the optimization phase will be carried out if there is some “non-optimized” LP. This stage will consider placement of additional inline amplifiers (either EDFA or EDFA/RA) at some pre-defined intermediate locations at those links traversed by “non-optimized” LPs. Then, the OSNR of those LPs will be recomputed to check whether the transmission with optimum LRComb in terms of EEPG is feasible. If the change of LRComb for one or several LPs allows for the improvement of the overall EEPG (taking into account the spectral occupancy reduction, as well as the difference
ECOC 2014, Cannes - France Th.1.2.6
200 100
33.06
34.72
36.37
38.02 38.02
31.41
29.76
28.10
26.45
24.80
23.14
21.49
19.84
18.19
16.53
36.37
Opt. EDFA/RA
100
1.E-02
60 40
34.72
Opt. EDFA
1.E-01
80
Energy Efficiency per GHz (EEPG) 250
Initial
14.88
9.92
13.23
8.27
11.57
0
6.61
38.02
36.37
34.72
33.06
31.41
29.76
28.10
26.45
24.80
23.14
21.49
19.84
18.19
300
Total traffic [Tbps]
1.E+00
Opt. EDFA/RA
40G
400
(f)
Service blocking ratio (SBR)
EEPG [kb/J/GHz]
Opt. EDFA
120
SBR
1.E-03
20
Initial
230
Opt. EDFA
Opt. EDFA/RA
210 190 170 150 130 110 90 70
Total Traffic [Tbps]
Total Traffic [Tbps]
31.41
29.76
28.10
26.45
24.80
23.14
21.49
19.84
18.19
16.53
14.88
13.23
11.57
9.92
8.27
6.61
4.96
3.31
38.02
36.37
34.72
33.06
31.41
29.76
28.10
26.45
24.80
23.14
21.49
19.84
18.19
16.53
14.88
13.23
11.57
9.92
8.27
6.61
4.96
50
3.31
38.02
36.37
34.72
33.06
31.41
29.76
28.10
26.45
24.80
23.14
21.49
19.84
18.19
16.53
14.88
13.23
11.57
9.92
8.27
6.61
4.96
3.31
1.65
1.E-04
1.65
0
1.65
Total capacity [Tbps]
160
Initial
100G
Total traffic [Tbps]
(e)
Total capacity of the network 140
200G
500
33.06
Total traffic [Tbps]
(d)
16.53
0
400G
600
4.96
100
Final distribution of transponders after optimization with additional EDFA/RA
3.31
200
700
1.65
300
38.02
36.37
34.72
33.06
31.41
29.76
28.10
26.45
24.80
23.14
21.49
19.84
18.19
16.53
14.88
9.92
13.23
8.27
11.57
6.61
4.96
3.31
0
400
14.88
100
40G
500
9.92
200
100G
13.23
300
600
200G
8.27
400
400G
11.57
500
(c)
with additional EDFA
700
6.61
40G
4.96
100G
1.65
600
200G
3.31
Number of transponders
400G
1.65
Number of transponders
(b) (b)Final distribution of transponders after optimization
700
Number of transponders
Initial distribution of transponders before optimization
(a)
Total Traffic [Tbps]
Fig. 4: Simulation results: (a) Initial distribution of transponders with initial configuration of amplifiers; (b) Distribution of transponders after optimization with additional EDFAs; (c) Distribution of transponders after optimization with additional EDFA/RA; (d) Total capacity of the network. (e) Service blocking ratio; (f) EEPG.
between the reduction of PC at the TSP and the extra PC of the new OAs), this/these amplifier location(s) will be included in the updated configuration of the network. The introduction of up to three amplifiers (NAmp) per link can be considered. Finally, after finishing the optimization phase, the RWA is repeated over the final network configuration to check whether the reduction in spectrum occupancy enables the allocation of the initially blocked demands. Simulation results The study considers the Spanish core network 5 model of Telefónica I+D , composed of 30 nodes and 46 bi-directional links (66 fixed amplifier locations and 207 potential placements) with an overall traffic ranging from 5 1.65 Tbps to 38.02 Tbps. The selective placement of EDFAs in the intermediate nodes is shown as an effective method to increase the number of high-speed transmissions (Fig. 4b) with respect to the initial configuration of the network (Fig. 4a). The deployment of EDFA/RA can further improve those results, enabling an even greater number of high-speed transmissions (Fig. 4c) thanks to the lower noise amplification. This is especially noticeable in the bigger number of feasible 400G transmission, which will result in much larger network capacity as presented in Fig. 4d (obtained by the summation of the total capacity of the transponders). Actually, at high traffic levels, the optimization with EDFA/RA permits to nearly double the overall capacity of the network with respect to the initial scenario. This result is up to 22% higher than the optimization carried out with EDFA only. The reduction of spectrum occupancy enabled by EDFA/RA is also beneficial to decrease the service blocking ratio (blocked traffic/total traffic) with respect to both the initial configuration of amplifiers and the optimization with EDFA only as shown in Fig. 4e.
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The deployment of more high-speed transponders (e.g. 400 and 200 Gbps), which are more energy- and spectrally-efficient, results in remarkable improvements on EEPG with respect to the initial configuration. As shown in Fig. 4f, EEPG increases of up to 52% can be achieved by the optimization with EDFA/RA. These improvements are around 10% higher than the optimization with EDFA only. In fact, the EDFA/RA, despite consuming more energy than EDFA, can take advantage of its lower noise figure to optimize more LPs with a similar number of amplifiers and thus increasing the overall EEPG of the network. Conclusions The selective placement of additional in-line amplifiers can facilitate the realization of more high-speed connections, and thus increase the energy and spectral-efficiency of the network. In particular, the introduction of additional EDFA/RA can improve the EEPG of the network in up to 52%, and nearly double the total network capacity with respect to the initial configuration of amplifiers. Moreover, the reduced spectral occupancy also allows for reduced network blocking.
This work was supported by the EU FP7 funded projects TREND, CHRON and DISCUS.
References [1] W. Xie et al., “Regenerator Site Selection for Mixed Line Rate Optical Networks,” J. of Optical Communications and Networking, Vol. 6, Issue 3, pp. 291-302 (2014). [2] J. López et al., “Optimized Amplifier Placements for Improved Energy and Spectral Efficiency in Protected Mixed-Line-Rate Networks,” Proc. OFC, Th1E.5, San Francisco (2014). [3] M.F. Huang et al.,”Transmission of 400G Dual-Carrier DP-16QAM and Multi-Carrier DP-QPSK Signals over Regional and Long-Haul Distances with Span Lengths Greater than 200 km,” Proc. OFC, Th4F.3, San Francisco (2014). [4] C. Dorize, et al., “GreenTouch Draft Report on Baseline Power Consumption,” v1.8 (2011). [5] F. Jiménez, EU FP7 IDEALIST project, “WP1 preliminary inputs for WP2 analysis,” (2012).
