29-07-2011, 02:26 PM
ABSTRACT
PON-based access networks envisage the demonstration of scalability to allow gradual deployment of time and
wavelength multiplexed architectures in a single-platform without changes in fibre infrastructure and also
highly-efficient bandwidth allocation for service provision and upgrade on-demand. This is achieved by the
application of coarse-fine grooming to route reflective-ONUs of time and wavelength PONs collectively and the
development of MAC protocols enabling the OLT to dynamically assign available time slots among ONUs and
demonstrate efficient bandwidth and wavelength assignment.
Keywords: PON, coarse WDM (CWDM), dynamic bandwidth allocation (DBA), quality of service (QoS).
1. INTRODUCTION
The emergence of new bandwidth-intensive applications articulated by distance learning, online gaming, Web
2.0 and movie delivery by means of high-definition video, has ultimately justified the necessity of upgrading the
access network infrastructure to provide fat-bandwidth pipelines at subscriber close proximity. Passive optical
networks (PONs) offer currently more opportunities to communicate these services than ever before, with
potential connection speeds of up to 100 Mbit/s in mind [1]. A scalable multi-PON access network architecture
[2] has been investigated in that direction to provide interoperability among dynamic time division multiplexing
(TDM) and wavelength division multiplexing (WDM)-PONs through coarse WDM (CWDM) routing in the
optical line terminal (OLT). To provide bandwidth on demand, a novel TDM dynamic minimum bandwidth
(DMB) allocation protocol and an upgraded version have been proposed to achieve quality of service (QoS) at
three different service levels and diverse network throughputs [3]. In addition, to allow for WDM-PON resource
allocation, to overcome the inevitable network congestion of single wavelength networks, the developed medium
access control (MAC) protocols have been extended to implement logical point-to-point topologies based on
general loop-back WDM-PON architectures [2] to increase service provisioning between reflective optical
network units (ONUs) and the OLT by vigorously distributing network capacity simultaneously between the
upstream and downstream.
2. NETWORK ARCHITECTURE
The network architecture in Fig. 1 exhibits a single 4x4 coarse array waveguide grating (AWG) in the OLT to
route multiple TDM and WDM-PONs by means of a single tunable laser (TL1) and receiver (RX1) allowing for
coarse-fine grooming to display smooth network upgrade. Proposed coarse AWG devices display 7 nm, 3 dB
Gaussian passband windows [4], denoted in Fig. 1 by coarse ITU-T channels λ1 = 1530 nm and λ2 = 1550 nm, set
to accommodate up to 16, 0.4 nm-spaced wavelengths to address a total of 16 ONUs per PON. In downstream,
TL1 will optimally utilise λ1
9, placed at the centre of the AWG coarse channel λ1, to broadcast information to all
ONUs of TDM-PON1. To address a WDM-PON, TL1 will switch on all 16 wavelengths, centred ±3.2 nm
around coarse channel λ2, i.e. λ2
1-16, to address jointly all ONUs in WDM-PON4
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