David Gutierrez

Next-Generation Optical Access Networks

The last mile continues to be a major bottleneck in the Internet. Its low bandwidth and flexibility prevents the deployment of new services and the development of new applications. In this paper we present a summary of current efforts in access networks research, focusing in particular on fiber optic solutions. We present the Stanford University aCCESS (SUCCESS) initiative within the Photonics & Networking Research Laboratory (PNRL). As part of this initiative, two novel network architectures have been developed, SUCCESS-HPON and SUCCESS-DWA, which propose a smooth migration path from current TDM-PONs to future higher bandwidth, cost-efficient, scalable WDM-PONs. In addition, we present SUCCESS-LCO, a spectral-shaping line coding technique that enables a cost-effective shorter-term capacity upgrade of existing TDM-PONs. We discuss as well what we believe are the main open research areas in optical access networks.

SUCCESS: a next-generation hybrid WDM/TDM optical access network architecture

In this paper, the authors propose a next-generation hybrid WDM/TDM optical access network architecture called Stanford University aCCESS or SUCCESS. This architecture provides practical migration steps from current-generation time-division multiplexing (TDM)-passive optical network (PONs) to future WDM optical access networks. The architecture is backward compatible for users on existing TDM-PONs, while simultaneously capable of providing upgraded high-bandwidth services to new users on DWDM-PONs through advanced WDM techniques. The SUCCESS architecture is based on a collector ring and several distribution stars connecting the CO and the users. A semipassive configuration of the Remote Nodes (RNs) enables protection and restoration, making the network resilient to power failures. A novel design of the OLT and DWDM-PON ONUs minimizes the system cost considerably: 1) tunable lasers and receivers at the OLT are shared by all ONUs on the network to reduce the transceiver count and 2) the fast tunable lasers not only generate downstream data traffic but also provide DWDM-PON ONUs with optical CW bursts for their upstream data transmission. Results from an experimental system testbed support the feasibility of the proposed SUCCESS architecture. Also, simulation results of the first SUCCESS DWDM-PON MAC protocol verify that it can efficiently provide bidirectional transmission between the OLT and ONUs over multiple wavelengths with a small number of tunable transmitters and receivers.

SUCCESS-HPON: A next-generation optical access architecture for smooth migration from TDM-PON to WDM-PON

Optical access networks are considered to be a definite solution to the problem of upgrading current congested access networks to ones capable of delivering future broadband integrated services. However, the high deployment and maintenance cost of traditional point-to-point architectures is a major economic barrier. Current TDM-PON architectures are economically feasible, but bandwidth-limited. In this article we first discuss the possible role of WDM in access networks and investigate the associated issues. We then present the Stanford University Access Hybrid WDM/TDM Passive Optical Network (SUCCESS-HPON), a next-generation hybrid WDM/TDM optical access architecture that focuses on providing a smooth migration path from current TDM-PONs to future WDM-PONs. The first testbed for this architecture is described, along with the experimental results obtained, including feasibility of bidirectional transmission on the same wavelength on the same fiber for access networks and ONU modulation of upstream data on continuous waves provided by the OLT, eliminating the need for tunable components at the ONUs. The development of a second testbed and the issues it will address, including the implementability of the SUCCESS-HPON MAC protocol and scheduling algorithms, are also described.

Next Generation Optical Access Networks

The last mile continues to be a major bottleneck in the Internet. Its low bandwidth and flexibility prevents the deployment of new services and the development of new applications. In this paper we present a summary of current efforts in access networks research, focusing in particular on fiber optic solutions. We present the Stanford University aCCESS (SUCCESS) initiative within the Photonics & Networking Research Laboratory (PNRL). As part of this initiative, two novel network architectures have been developed, SUCCESS-HPON and SUCCESS-DWA, which propose a smooth migration path from current TDM-PONs to future higher bandwidth, cost-efficient, scalable WDM-PONs. In addition, we present SUCCESS-LCO, a spectral-shaping line coding technique that enables a cost-effective shorter-term capacity upgrade of existing TDM-PONs. We discuss as well what we believe are the main open research areas in optical access networks.

Design and performance analysis of scheduling algorithms for WDM-PON under SUCCESS-HPON architecture

Results of the design and performance analysis of two new algorithms for efficient and fair scheduling of variable-length frames in a wavelength division multiplexing (WDM)-passive optical network (PON) under the Stanford University aCCESS-Hybrid PON (SUCCESS-HPON) architecture are reported. The WDM-PON under the SUCCESS-HPON architecture has unique features that have direct impacts on the design of scheduling algorithms. First, an optical line terminal (OLT) uses tunable transmitters and receivers that are shared by all the optical network units (ONUs) served by the OLT to reduce the number of expensive dense WDM (DWDM) transceivers. Second, also for cost reduction, ONUs have no local DWDM light sources but use optical modulators to modulate optical continuous wave (CW) bursts provided by the OLT for upstream transmissions. Therefore, the tunable transmitters at the OLT are used for both upstream and downstream transmissions. To provide efficient bidirectional communications between the OLT and the ONUs and guarantee fairness between upstream and downstream traffic, two scheduling algorithms have been designed: 1) batching earliest departure first (BEDF); and 2) sequential scheduling with schedule-time framing (S/sup 3/F). The BEDF is based on the batch scheduling mode where frames arriving at the OLT during a batch period are stored in virtual output queues (VOQs) and scheduled at the end of the batch period. It improves transmission efficiency by selecting the frame with the earliest departure time from a batch of multiple frames, which optimizes the usage of tunable transmitters in scheduling. Considering the high complexity of the optimization process in BEDF, the S/sup 3/F based on the sequential scheduling mode has also been designed as in the original sequential scheduling algorithm proposed earlier. In S/sup 3/F, the authors use VOQs to provide memory space protection among traffic flows and a granting scheme together with schedule-time framing for both upstream and downstream traffic to reduce framing and guard band overhead. Through extensive simulations under various configurations of the tunable transmitters and receivers, it has been demonstrated that both the BEDF and S/sup 3/F substantially improve the throughput and delay performances over the original sequential scheduling algorithm, while guaranteeing better fairness between upstream and downstream traffic.

TDM-PON Security Issues: Upstream Encryption is Needed

TDM-PONs (E/B/GPON) present several security issues that can easily be exploited by malicious users. We summarize these issues and present experimental results to demonstrate that, in particular, upstream encryption is required to prevent eavesdropping.

Batch scheduling algorithm for SUCCESS WDM-PON

In this paper we study the problem of scheduling variable-length frames in WDM-PON under Stanford University access (SUCCESS), a next-generation hybrid WDM/TDM optical access network architecture. The SUCCESS WDM-PON architecture has unique features that have direct impact on the design of scheduling algorithms: first, tunable transmitters and receivers at OLT are shared by ONU to reduce transceiver counts; second, the tunable transmitters not only generate downstream data traffic but also provide ONU with optical continuous wave (CW) bursts for upstream transmissions. To provide efficient bidirectional transmissions between OLT and ONU, we propose a batch scheduling algorithm based on the sequential scheduling algorithm previously studied. The key idea is to provide room for optimization and priority queueing by scheduling over more than one frame. In the batch scheduling, frames arriving at OLT during a batch period are stored in virtual output queues (VOQ) and scheduled at the end of the batch period. Through simulation with various configurations, we demonstrate that the proposed batch scheduling algorithm, compared to the original sequential scheduling algorithm, provides higher throughput, especially when the system load is high, and better fairness between upstream and downstream transmissions.

Broadcast Transmission in WDM-PON using a Broadband Light Source

A novel method to broadcast a video stream to all subscribers in WDM-PON is proposed and experimentally implemented. Using a broadband light source, we have achieved successful transmission performance with our proposed method.

Optical Burst Transport: A Technology for the WDM Metro Ring Networks

We propose a sublambda traffic-grooming scheme on wavelength-division-multiplexing ring networks, named optical burst transport. The network protocol and architecture are designed to support dynamic bandwidth allocation, which is more reasonable for bursty data traffic. To verify our network protocol and architecture, we build a testbed which supports burst-mode transmission. Also, we transmit streaming video over Ethernet as an application

Demonstration of 2.5 Gbps Optical Burst Switched WDM Rings Network

We present a 2.5 Gbps OBS network testbed named Optical Burst Transport (OBT). OBT combines a reliable control channel with a tightly controlled high speed burst mode transmission. The result is verified by burst mode BER test.