John D. Angelopoulos

Efficient transport of packets with QoS in an FSAN-aligned GPON

The standardization of passive optical networks capable of transporting Ethernet frames at gigabit-per-second speeds, currently in progress in both ITU-T and IEEE, constitutes a major milestone toward cost-effective photonization of the last (aka first) mile. The article presents an Ethernet gigabit PON (GPON) system aligned with the philosophy of the evolving FSAN (full service access network) ITU-T specification, which focuses on the efficient support of any level of quality of service. The intelligence of this system, in terms of traffic quality guarantees, lies in the MAC protocol, which controls the distributed multiplexing/concentration function by allocating variable length slots to every user of the shared upstream (toward the network) medium. The way transport of information is organized in an ITU-T GPON system and the operation of a MAC protocol that preserves all QoS guarantees are presented and evaluated.

Efficient medium arbitration of FSAN-compliant GPONs

SUMMARY The steadily rising demand for multimedia and data services, the falling cost and omnipresence of Ethernet and the maturity of passive optical networks (PON) technology, promise to radically change the landscape in the local loop. The heart of a gigabit PON system (recently standardized by FSAN/ITU) is the medium access controller (MAC), which arbitrates access to the upstream link among users with fluctuating traffic demands and effects the multiplexing and concentration policy. At the same time, it has to safeguard the service quality and enforce the parameters agreed in the service level agreements (SLAs) between the users and the service provider. In this paper, a MAC protocol designed to serve any mix of services according to their quality of service (QoS) needs, employing four priority levels along with a high number of logically separate data queues is presented. The architecture and implementation in hardware of a MAC algorithm capable of allocating bandwidth down to a resolution of a byte with QoS differentiation is the focus of this paper. It employs the bandwidth arbitration tools of the FSAN/ITU G.984.3 standard and maps SLA parameters to GPON service parameters to create an efficient, fair and flexible residential access system. Copyright # 2005 John Wiley & Sons, Ltd.

An Optical Network Architecture With Distributed Switching Inside Node Clusters Features Improved Loss, Efficiency, and Cost

The novel core network architecture presented in this paper realizes distributed all-optical switching of payload by partitioning the network into a number of geographically limited domains, where two-way reservations are effective. Thus, inside each domain, loss is eliminated, while traffic from many nodes can be aggregated into single bursts, improving efficiency. Clustered nodes contribute contiguous optical slots, which are marshaled into composite optical frames destined for other clusters, under the guidance of a reservation-based control protocol. The lossless aggregation of traffic from several core nodes allows the use of cost-effective bufferless all-optical transport among the domains with electrical buffers employed at the periphery of the system. The end result is a triple improvement in loss probabilities, efficiency, and cost. This is achieved by exploiting three features of the architecture: the distributed switching functionality (as in early LANs when centralized switching was expensive), localized reservations (avoiding the intolerable delays of end-to-end reservations), and a reduced number of source-destination pairs (by means of node clustering into reservation domains)

A TDMA based access control scheme for APON's

The cost of a dedicated fiber access to the broad-band integrated services digital network (B-ISDN) is too high for small business and sesidential customers necessitating some form of sesource sharing. Combining the asynchronous transfer mode (ATM) over a passive optical network (APON) with a suitable medium access control (MAC) protocol can provide significant cost savings and a seasonable bandwidth. In this way the customer line section can support broad-band services at an early stage. The MAC protocol presented in this paper places emphasis on service transpasency aspects with an aim to incur minimal changes to the Local Exchange for APON connections. Sharing is effected through a reservation based time division multiple access method

A transparent MAC method for bandwidth sharing and CDV control at the ATM layer of passive optical networks

In the quest for a way to bring local loop costs down and make B-ISDN affordable to small traffic customers, the passive optical networks (PONs) in combination with ATM (APONs) have been investigated extensively. To achieve the required medium sharing on a time division multiplexing (TDMA) basis, an arbitration mechanism is required in the upstream direction. The resulting multiplexing and concentration, though it is the source of significant savings, it has been plagued by the penalty of high distortion of the traffic profiles at the exit of the PON. The preventive congestion control method of ATM is rather intolerant of such distortions in the multiplexing stages. Arbitration methods which are either semistatic or based on number of arrivals per reservation period, cause very high cell delay variation (CDV). The cell clustering introduced by the arbitration method cannot be distinguished from peak rate violations of the contract by the policing unit. The result is either unwarranted rejections of conforming cells or unacceptably low utilization. The scheme presented herewith maintains a CDV behavior comparable to that of a common centralized FIFO multiplexer. It relies on a meticulous recording of the arrival timing of cells enabling a subsequent allocation of slots which produces almost the same output (and CDV) as the centralized FLFO multiplexer. A compact coding of the timing information restricts bandwidth waste for control information to the size found in other similar protocols. The most important feature is that the scheme is amenable to easy hardware implementation and does not require any call related information.

Efficient use of protocol stacks for LAN/MAN-ATM interworking

Connectionless (CL) services as already developed in LANs, have to interwork with emerging asynchronous transfer mode (ATM) connection-oriented (CO) networks. MANs are a significant evolutionary step and CO MANs, in particular, constitute a technically appealing method to integrate both environments and provide shared medium access for all services. The functions required for enhancing distributed-queue dual-bus (DQDB) MANs with CO services in a way compatible with ATM are described. Within the integrating framework of B-ISDN, the practically useful scenarios for interworking LANs, CO and CL MANs, and ATM are investigated and classified in order to exploit the advantages of an efficient protocol relay utilizing the resources of the lowest possible layer. This is aimed at assisting interworking unit (IWU) designers and implementors to decide on key options in this versatile and evolving environment. The CO DQDB case emerges as the most advantageous development in terms of interworking simplicity and robustness. >

TDMA multiplexing of ATM cells in a residential access SuperPON

Time division multiple access (TDMA) multiplexing of ATM cells from thousands of residential customers toward the common feeder of a passive optical network (SuperPON) tree obviates the need for an equal number of optical line terminations (OLTs). All upstream transmissions converge by means of the passive splitters/combiners to just one OLT unit which serves all by time sharing. The ability to reach such a high splitting ratio became possible by the development of bursty mode optical amplifiers (OAs). In addition, OAs make possible a 100-km-long feeder which can bypass the local exchange into the first core switch, bringing further savings to both initial and running costs. These techniques allow SuperPONs to lower the access cost per customer, holding for the promise of ushering into domestic local loops the photonics revolution which has already transformed the transmission plant. These savings, however, can only be realized under the assumption that the system can accept high loading before exceeding the limits of quality of service (QoS) requirements and without distorting the egress traffic in a way that jeopardizes the statistical estimates on which ATM connection acceptance was based. Solutions to the problem of traffic arbitration, respecting the idiosyncrasies of each traffic class and suitable for fast implementation, are offered.

Architectures for 100-km 2048 split bidirectional SuperPONs from ACTS-PLANET

This paper presents different architectures for high split, wide range bidirectional SuperPONs.One of the ways to achieve such SuperPONs is by the introduction of erbium- doped-fiber-amplifiers or semiconductor optical amplifiers (SOA) in order to overcome the strongly increased power budgets in comparison to conventional PONs. This will however present new challenges in overcoming the noise- funneling effect caused by the parallel amplifiers. Four different approaches are studied: 1) using of on/off switchable semiconductor optical amplifiers, 2) using parallel erbium-doped-fiber amplifiers, 3) using electro- optic regeneration, and 4) using conventional SDH, ATM and APON technology. A description is given of each architecture, including advantages and drawbacks. These architectures serve as input to further studies performed by the ACTS-PLANET consortium. The power-budget studies showed that it is technically feasible to develop a SuperPON with a 2048 split and a 70-100 km range.

Using explicit reservations to arbitrate access to a metropolitan system of slotted interconnected rings combining TDMA and WDMA

A system of slotted interconnected wavelength-division-multiplexing (WDM) rings controlled by a medium access control (MAC) protocol is shown to offer very high utilization within a queuing delay less than a few round-trip times, by means of a very-fast-reacting explicit reservation mechanism. The system can be used to provide interconnectivity in a metropolitan area transferring optical payloads on-the-fly without buffering or converting from the optical domain. All necessary control information is transferred on a dedicated wavelength and is processed in the electrical domain to provide both collision-free packet access at the ring nodes and contention resolution at the hub interconnecting the rings. The end result is a flexible and efficient metropolitan network suitable for bursty data services.

Slotted optical switching with pipelined two-way reservations

Optical burst switching is a core architecture designed to reconcile the available optical technology with the increasing burstiness of traffic. However, disappointing performance in terms of high packet loss and/or low system utilization discouraged broader experimental implementations. A method to avoid these losses by first sending over the control channel a short scout packet that simulates the events that the actual burst will experience is proposed in this paper. Once the scout message detects a drop at any intermediate node, it returns back to the source to avert the payload emission and repeat the process. The way the control works results in essential service quality features, i.e., no loss of bursts, no out-of-order emissions, increased efficiency, much reduced delay variation, and graceful throttling of the load respecting the contracted rates