Seyedeh Sahel Sahhaf

Network service chaining with optimized network function embedding supporting service decompositions

The rise of Software-Defined Networking (SDN) and Network Function Virtualization (NFV) introduce opportunities for service providers to reduce CAPEX/OPEX and to offer and quickly deploy novel network services. In particular, SDN and NFV enable the flexible composition of network functions, a generic service concept known as network service chaining (NSC).However, the control of resources, management and configuration of network service chains is challenging. In particular, there typically exist multiple options on how an abstract network service can be decomposed into more refined, inter-connected network functions. Moreover, efficient algorithms have to be devised to allocate the network functions. The underlying algorithmic problem can be seen as a novel generalization of the Virtual Network Embedding Problem (VNEP), where there exist multiple realization options. The joint optimization of decomposition and embedding has not been studied in the literature before.This paper studies the problem of how to optimally decompose and embed network services. In particular, we propose two novel algorithms to map NSCs to the network infrastructure while allowing possible decompositions of network functions. The first algorithm is based on Integer Linear Programming (ILP) which minimizes the cost of the mapping based on the NSCs requirements and infrastructure capabilities. The second one is a heuristic algorithm to solve the scalability issue of the ILP formulation. It targets to minimize the mapping cost by making a reasonable selection of the network function decompositions. The experimental results indicate that considering network function decompositions at the time of the embedding significantly improves the embedding performance in terms of acceptance ratio while decreasing the mapping cost in the long run in both optimal and heuristic solutions.

Network service chaining with efficient network function mapping based on service decompositions

Network Service Chaining (NSC) is a service concept which promises increased flexibility and cost-efficiency for future carrier networks. The two recent developments, Network Function Virtualization (NFV) and Software-Defined Networking (SDN), are opportunities for service providers to simplify the service chaining and provisioning process and reduce the cost (in CAPEX and OPEX) while introducing new services as well. One of the challenging tasks regarding NFV-based services is to efficiently map them to the components of a physical network based on the services specifications/constraints. In this paper, we propose an efficient cost-effective algorithm to map NSCs composed of Network Functions (NF) to the network infrastructure while taking possible decompositions of NFs into account. NF decomposition refers to converting an abstract NF to more refined NFs interconnected in form of a graph with the same external interfaces as the higher-level NF. The proposed algorithm tries to minimize the cost of the mapping based on the NSCs requirements and infrastructure capabilities by making a reasonable selection of the NFs decompositions. Our experimental evaluations show that the proposed scheme increases the acceptance ratio significantly while decreasing the mapping cost in the long run, compared to schemes in which NF decompositions are selected randomly.

Link failure recovery technique for greedy routing in the hyperbolic plane

The scalability of current routing protocols is limited by the linearly increasing size of the corresponding routing tables. Greedy routing has been proposed as a solution to this scalability problem. In greedy routing, every node is assigned a coordinate. These coordinates are used in order to forward a packet to a neighbor which is closer to the destination. Current greedy methods cannot efficiently cope with failures in topology. Using methods which require large resources and have significant loss in the quality of the routing (stretch loss) makes greedy routing useless in large-scale networks. In this paper, local techniques for single and multiple link failure recovery are proposed. The methods require very limited resources and result into limited loss in routing quality. The proposed schemes allow fast switch-over and scale with the number of links in the spanning tree of the network. Scalability, simplicity and low overhead of the methods make them suitable for large networks. The proposed techniques are evaluated in an experimental environment.

Robust geometric forest routing with tunable load balancing

Although geometric routing is proposed as a memory-efficient alternative to traditional lookup-based routing and forwarding algorithms, it still lacks: (i) adequate mechanisms to trade stretch against load balancing, and (ii) robustness to cope with network topology change. The main contribution of this paper involves the proposal of a family of routing schemes, called Forest Routing. These are based on the principles of geometric routing, adding flexibility in its load balancing characteristics. This is achieved by using an aggregation of greedy embeddings along with a configurable distance function. Incorporating link load information in the forwarding layer enables load balancing behavior while still attaining low path stretch. In addition, the proposed schemes are validated regarding their resilience towards network failures.

Experimental validation of resilient tree-based greedy geometric routing

Geometric routing is an alternative for IP routing based on longest prefix matching. Using this routing paradigm, every node in the network is assigned a coordinate and packets are forwarded towards their intended destination following a distance-decreasing policy (greedy forwarding). This approach makes the routers significantly more memory-efficient compared to the current IP routers. In this routing, greedy embeddings are used to guarantee a 100% successful delivery to every destination in the network. Most of the existing proposals lack resiliency mechanisms to react efficiently to network changes. We propose a distributed algorithm to calculate a greedy embedding based on a spanning tree of the network. In this algorithm, nodes are triggered to re-calculate their coordinates upon a change in the topology such as link or node failures. The advantage of this approach is that it recovers from topology failures within a very short period of time. We further extend the algorithm to generate backups to apply protection in distributed setups. Different trade-offs and trends of re-convergence for geometric routing have been evaluated in an emulation environment. Realistic results are achieved through emulation as no model or abstraction is involved. The proposed routing scheme is implemented in Quagga routing software and new elements are developed in Click modular router to enable greedy forwarding. For the first time, the performance of this scheme is evaluated through emulation on a large topology of 1000 nodes and the results are compared with BGP. The experimental results indicate that the proposed scheme has interesting characteristics in terms of convergence time upon a change in the network topology.

Experimentation of Geometric Information Routing on Content Locators

Information-centric networking has been proposed to achieve efficient and reliable distribution of content. We propose a model to assign content locators to content names. Information routing decision is made based on geometric routing using the assigned locators. We consider a geometric routing scheme known as geodesic geometric routing. We demonstrate on the iLab.t virtual wall the successful operation of the proposed scheme and the gain of using content locators on capacity utilization by means of caching.

Fault-tolerant Greedy Forest Routing for complex networks

Geometric routing has been proposed in literature as a memory-efficient alternative to traditional lookup-based routing and forwarding algorithms. However, existing geometric routing schemes lack the ability to address network link and node failures in a natural way, while maintaining a low path stretch. The main contribution of this paper is a novel routing scheme called Greedy Forest Routing (GFR) based on the principles of geometric routing. By employing a graph embedding based on low-redundancy spanning trees, its fault-tolerant characteristics are enhanced. Using a multi-dimensional tree embedding enables natural traffic redirection while still attaining a low average hop count.

A model to select the right infrastructure abstraction for Service Function Chaining

Through network function virtualization (NFV), telecom providers aim to flexibly re-use generic-purpose hardware to provide services on-demand and in an agile way. Service function chaining is becoming the preferred model to describe the characteristics of the packet-processing network functions which, together, form these services. NFV allows for network function embedding freedom, creating new dynamics between providers and the users requesting services. Users want this freedom to optimise the performance of their requested services, while providers aim to optimise their resource cost with it. This trade-off is heavily influenced by how the available infrastructure is exposed to the users. In this paper, we present an infrastructure abstraction model for network, compute and storage resources that exposes the infrastructure in an abstracted manner. We use this abstraction to propose a solution for the placement freedom trade-off problem by studying its relation with metrics that capture both the users and the providers aspects. We conclude with a heuristic that determines the right abstraction for particular scenarios.

All-Optical Tree-based Greedy Router

Forwarding logic in greedy routing systems requires less memory and fewer components than longest-prefix match-based forwarding in IP routing. We demonstrate an all-optical design of a greedy router with desirable scalability and energy-efficiency characteristics enabling high data rate throughput.

Availability analysis of resilient geometric routing on Internet topology

Scalable routing schemes for large-scale networks, especially future Internet, are required. Geometric routing scheme is a promising candidate to solve the scalability issue of routing tables in conventional IP routing based on longest prefix matching. In this scheme, network nodes are assigned virtual coordinates and packets are forwarded towards their intended destination following a distance-decreasing policy. Dynamics in the network such as node/link failures might affect this forwarding and lead packets to a dead end. We proposed recovery techniques in geometric routing to deliver packets to the destination in case of failures. In this paper, we perform an analysis on the availability of the proposed protection techniques on the Internet graph. The routing scheme over optical transport network is considered and the reliability data of physical components and a known network availability model are used. This evaluation is compared with the shortest cycle scheme which finds two node disjoint paths between every source and destination in the topology and also with geometric routing with no protection. The results show that the proposed scheme performs reasonably well compared to the shortest cycle scheme and significantly enhances the availability compared to geometric routing without any protection.