Ahmad Rostami

Rethinking Optical Transport to Pave the Way for 5G and the Networked Society

The fifth generation of mobile networks (5G) is the next major phase of mobile telecommunications, which will provide the foundation for the Networked Society. To support 5G, transport will need to cater for a wide range of service requirements. It will need to support emerging 5G radio systems in terms of higher capacity and increasing number of cell sites. It must also cater for increasing need for radio interference coordination between sites as well as cost effective radio access network deployment models, and provide a flexible platform for sharing of resources where different actors through transport application programming interfaces have access to network resources and diverse transport services. In this paper, we summarize the key defining factors for 5G transport and outline a concept for programmable transport based on WDM and exploiting emerging optical devices enabled by integrated photonics.

Data Plane and Control Architectures for 5G Transport Networks

Next generation 5G mobile system will support the vision of connecting all devices that benefit from a connection, and support a wide range of services. Consequently, 5G transport networks need to provide the required capacity, latency, and flexibility in order to integrate the different technology domains of radio, transport, and cloud. This paper outlines the main challenges, which the 5G transport networks are facing and discusses in more detail data plane, control architectures, and the tradeoff between different network abstraction models.

Modeling and Synthesis of Traffic in Optical Burst-Switched Networks

We analyze burst assembly process as the main building block of the optical burst switching (OBS) paradigm. The analysis is performed for time-based, volume-based, as well as hybrid burst assemblers. Under the assumption that the process of packet arrival to the assembly buffer is Poisson, exact analytical expressions are derived for length and interdeparture time of bursts that are generated by these three classes of assembly algorithms. Furthermore, we consider the issue of generating burst trace, which arises during the performance evaluation of OBS networks through discrete-event simulation. In such a simulation study, a significant part of the simulation time, particularly in the case of a network with a large number of ingress nodes, is used by the implementation of the burst assembly algorithms. This is due to the fact that each data burst is a result of aggregating several short-length packets, which-in a straightforward approach-have to be individually generated and, afterward, ldquomeltedrdquo into the burst. We present a novel approach to fast generation of bursts, which is based on the analytical models that are developed for burst length and burst interdeparture time distributions as well as an efficient generation technique (composition) supporting the generation of these distributions. The analysis is completed by numerical results that validate the accuracy of developed models and demonstrate the speedup gain of using proposed burst generation algorithms.

On performance of optical buffers with specific number of circulations

Deployment of fiber delay lines (FDLs) as a means of contention resolution is analytically studied. We consider a single-wavelength optical link equipped with a single FDL and assume that packets of fixed length arrive to the link asynchronously. The results obtained include accurate equations to calculate the congestion rate for different reservation scenarios including a prereservation scheme as well as a postreservation scheme with a specific number of circulations. Accuracy of the proposed model is validated through simulation.

Transport Abstraction Models for an SDN-Controlled Centralized RAN

In a centralized radio access network (C-RAN) scenario the joint coordination of radio (e.g., remote radio units, baseband units) and transport (e.g., optical cross connects) resources can be achieved via software defined networking (SDN) control plane, where a global orchestrator harmonizes the use of resources across all network segments. The more accurate the information about each domain (i.e., the abstraction of wireless and transport resources) is, the better will be the outcome of the orchestration work. This letter presents three transport resources abstraction models along with their corresponding orchestration policies. Their performance are compared showing that there is not a single best abstraction strategy that fits all the cases. If radio resources are scarce compared to transport resources, complex transport abstraction models are not needed. Contrariwise, if enough radio resources are widely available, more detailed abstraction models are required for achieving good network performance, but at the expense of an increased implementation complexity.

Impact of Edge Traffic Aggregation on the Performance of FDL-Assisted Optical Core Switching Nodes

In this paper we consider optical burst/packet switching networks with core nodes in which contentions are resolved by means of a hybrid scheme incorporating FDL buffering and wavelength conversion. For such a network we investigate the influence of traffic shaping at the edge nodes, as introduced by optical burst generation algorithms, on the packet drop rate at the core nodes. In particular we focus our attention on the impact of the algorithms that generate fixed-size optical bursts, i.e., volume-based burst assembly. The simulative investigation reveals that the total number of burst flows multiplexed at the core node under consideration as well as the assembly threshold are the two most influential factors, and that the influence of these factors on the drop rate could be as high as several orders of magnitude. Additionally, it is discussed that the assembly process can negatively influence the performance of the so-called void-filling channel scheduling algorithms.

Virtual Optical Bus: An Efficient Architecture for Packet-Based Optical Transport Networks

The virtual optical bus (VOB) is presented as a novel architecture for packet-based optical transport networks. The VOB is an evolutionary networking architecture based on the optical burst/packet switching (OBS/OPS) paradigm with a higher performance-in terms of packet loss rate and network throughput. The achieved gain comes at a cost of a marginal increase in the delay that packets experience at the ingress edge of the network, where we can still use inexpensive electrical buffers. In the VOB architecture, flows of traffic between nodes in the network are grouped into clusters and within each of the clusters a special form of coordination on packet transmission is introduced. This coordination ensures collision-free packet transmission within each cluster. Additionally, clustering of flows and selection of paths for clusters are done in a way that the interaction among routes of clusters in the network is minimized. This leads to a reduction of packet collisions in the network and also an increase in the network throughput. Design issues related to the VOB architecture are discussed and two design examples are presented that illustrate the high potential of this approach.

Traffic Analysis in Optical Burst Switching Networks: {A} Trace-based Case Study

Optical burst switching (OBS) appears as a promising technology for building dynamic optical transport networks. The main advantage of OBS is that it allows for dynamic allocation of resources at sub-wavelength granularity. Nevertheless, the burst contention problem, which occurs frequently inside the network, has to be addressed before OBS can be really deployed as the next generation optical transport network. Recently a lot of attention is devoted to different approaches for resolving contentions in OBS networks. Although performance analysis of these approaches is strongly dependent on the traffic characteristics in the network, the majority of the studies is so far based on very hypothetical traffic assumptions. In this study we use traces of real measurements in the Internet to derive realistic data about the traffic that is injected into the OBS network. Specifically, we investigate the marginal distributions of burst size, burst interdeparture time, assembly delay and number of packets per burst as well as the burstiness of the burst traces. We demonstrate that the performance of an OBS core node using the real traces is pretty similar to the results obtained when the traffic arriving to the core node is assumed to be Poisson. In fact, usage of the Poisson as the process of burst arrival to the core node leads in all the investigated cases to an upper bound on the burst drop rate at that node. Copyright

Orchestration of RAN and Transport Networks for 5G: An SDN Approach

The fifth generation of mobile networks is planned to be commercially available in a few years. The scope of 5G goes beyond introducing new radio interfaces, and will include new services like low-latency industrial applications, as well as new deployment models such as cooperative cells and densification through small cells. An efficient realization of these new features greatly benefit from tight coordination among radio and transport network resources, something that is missing in current networks. In this article, we first present an overview of the benefits and technical requirements of resource coordination across radio and transport networks in the context of 5G. Then, we discuss how SDN principles can bring programmability to both the transport and radio domains, which in turn enables the design of a hierarchical, modular, and programmable control and orchestration plane across the domains. Finally, we introduce two use cases of SDN-based transport and RAN orchestration, and present an experimental implementation of them in a testbed in our lab, which confirms the feasibility and benefits of the proposed orchestration.

Multi-Domain Orchestration across RAN and Transport for 5G

End-to-End programmability across radio, transport and compute resources is a key enabler for the fifth generation of mobile communication networks (5G). In our work we look into how SDN can realize the required cross-domain programmability, as well as slicing of resources towards multiple clients. We present design and implementation of a hierarchical, modular and programmable orchestration architecture across radio access networks and transport networks. We demonstrate how the developed multi-domain orchestration improves the service creation as well as resource utilization across the domains using real-time monitoring.