| dc.description.abstract | Recently there is an emergence of many Internet applications such as multimedia, video conferencing, distributed interactive simulations (DIS), and high-performance scientific computations like Grid computing. These applications require huge amount of bandwidth and a viable communication paradigm to coordinate with multiple sources and destinations. Optical networks are the potential candidates for providing high bandwidth requirement. Existing communication paradigms include broadcast, and multicast. Hence supporting these paradigms over optical networks is necessary. Multicasting over optical networks has been well investigated in the literature. QoS policies implemented in IP does not apply for Wavelength division multiplexed (WDM) or optical burst switched (OBS) networks, as the optical counterpart for store-and-forward model does not exist. Hence there is a need to provision QoS over optical networks. These QoS requirements can include contention, optical signal quality, reliability and delay. To support these diverse requirements, optical networks must be able to manage the available resources effectively.
Destinations participating in the multicast session are fixed (or rather static). Due to the random contention in the network, if at least one or more destination(s) is not reachable, requested multicast session cannot be established. This results in loss of multicast request with high probability of blocking. Incorporating wavelength converters (WCs) at the core nodes can decrease the contention loss, however WCs require optical-electrical-optical (O/E/O) conversion. This increases the delay incurred by optical signal. On the other hand all-optical WCs are expensive and increase the cost of the network if deployed.
Goal of this thesis is, to provide hop-to-hop QoS on an existing all-optical network (AON) with no WC and optical regeneration capability. In order to minimize the request vi Abstract vii lost due to contention in AON, we propose a variation of multicasting called Quorumcasting or Manycasting. In Quorumcasting destinations can join (or leave) to (or from) the group depending on whether they are reachable or not. In other words destinations have to be determined rather than knowing them prior, as in the case of multicasting. Quorum pool is minimum number of destinations that are required to be participated in the session for successful accomplishment of the job (k be the size of quorum pool). Providing QoS for manycasting over OBS has not been addressed in the literature. Given the multicast group (with cardinality m > k) and the number of destinations required to be participated, the contribution of this work is based on providing necessary QoS.
In this thesis we study the behavior of manycasting over OBS networks. In OBS networks, packets from the upper-layer (such as IP, ATM, STM) are assembled and a burst is created at the edge router. By using O/E/O conversion at the edge nodes, these optical bursts are scheduled to the core node. Control header packet or burst header packet (BHP) is sent to prior to the transmission of burst. The BHP configures the core nodes and the burst is scheduled on the channel after certain offset time.
In the first part of the thesis, we explain the different distributed applications with primary focus on Grid over OBS (GoOBS). We study the loss scenario due contention and inadequate signal quality for an unicast case in OBS network. We further extend this to manycasting. We modify the BHP header fields to make the burst aware of not only contention on the next-hop link, but also bit-error rate (BER). By using recursive signal and noise power relations, we calculate the BER (or q-factor) of the link and schedule the burst only if the required BER threshold is met. Thus all the bursts that reach the next-hop node ensure that contention and BER constraint are met. This are called “Impairment-Aware (IA) Scheduling”. Burst loss in the network increases due to BER constraint. Hence we propose algorithms to decrease the burst loss and simultaneously providing the sufficient optical signal quality. We propose three algorithms called IA-shortest path tree (IA-SPT), IA-static over provisioning (IA-SOP), and IA-dynamic membership (IA-DM). In IA-SPT destination set is sorted in the non-decreasing order of the hop-distance from source. First k of them are selected and bursts are scheduled to Abstract viii these destinations along the shortest path. In IA-SOP we select additional k0(_ m − k) destinations where k0 is the over provisioning factor. Over provisioning ensures that burst at least reach k of them, decreasing the contention blocking. However as the burst has to span more destinations, the fan-out of the multicast capable switch will be more and the BER could be high. In IA-DM destinations are dynamically added or removed, depending on contention and BER. Destination is removed and new destination is added based on the two constraints. Our simulation results shows that IA-DM out performs the other two algorithms in terms of request blocking. We show that IP-based many casting has poor performance and hence there is a need for supporting many casting over OBS networks. We verify our simulation results with the proposed analytical method.
In the next part, we focus on provisioning QoS in many casting. QoS parameters considered for analysis include, signal quality i.e., optical signal to noise ratio (OSNR), reliability of the link and, propagation delay. In this work we consider application based QoS provisioning. In other words, given the threshold requirements of an application, our aim is to successfully schedule the burst to the quorum pool satisfying the threshold conditions. We use a de-centralized way of the scheduling the burst, using BHP. With the help of local-network state information, the burst is scheduled only if it satisfies multiple set of constraints. Corresponding reception of burst at the node ensures that all the QoS constraints are met and burst is forwarded to the next hop. QoS attributes are either multiplicative or additive. Noise factor of the optical signal and reliability factor are multiplicative constraints, where as propagation delay is additive. We define a path information vector, which provides the QoS information of the burst at every node. Using lattice theory we define an ordering, such that noise factor and propagation delay are minimum and reliability is maximum. Using path algebra we compute the overall QoS attributes. Due to multiple set of constraints, the request blocking could be high. We propose algorithms to minimize request blocking for Multiple Constrained Many cast Problem (MCMP). We propose two algorithms MCM-SPT and MCM-DM. We consider different set of service thresholds, such as real time and data service thresholds. Real time services impose restriction on signal quality and the propagation delay. On the other hand Abstract ix data services require high reliability and signal quality. Our simulation study shows that MCM-SPT performs better than MCM-DM for real-time services and the data services can be provisioned using MCM-DM. | en_US |
