10,222 research outputs found
Rate of Convergence of Increasing Path-Vector Routing Protocols
A good measure of the rate of convergence of path-vector protocols is the number of synchronous iterations required for convergence in the worst case.
From an algebraic perspective, the rate of convergence depends on the expressive power of the routing algebra associated with the protocol.
For example in a network of nodes, shortest-path protocols are guaranteed to converge in iterations.
In contrast the algebra underlying the Border Gateway Protocol (BGP) is in some sense too expressive and the protocol is not guaranteed to converge.
There is significant interest in finding well-behaved algebras that still have enough expressive power to satisfy network operators.
Recent theoretical results have shown that by constraining routing algebras to those that are ``strictly increasing'' we can guarantee the convergence of path-vector protocols.
Currently the best theoretical worst-case upper bound for the convergence of such algebras is iterations.
However in practice it is difficult to find examples that do not converge in iterations.
In this paper we close this gap.
We first present a family of network configurations that converges in iterations, demonstrating that the worst case is iterations.
We then prove that path-vector protocols
with a strictly increasing algebra are guaranteed to converge in iterations. Together these results establish a tight bound.
This is another piece of the puzzle in showing that ``strictly increasing" is,
at least on a technical level, a reasonable constraint for practical policy-rich protocols.
{In memory of Abha Ahuja
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An algebraic perspective on the convergence of vector-based routing protocols
This thesis studies the properties of vector-based routing protocols whose underlying algebras are strictly increasing. Strict increasingness has previously been shown to be both a sufficient and a necessary condition for the convergence of path-vector protocols.
One of the key contributions of this thesis is to link vector-based routing to a much larger family of asynchronous iterative algorithms. This unlocks a significant body of existing theory, and allows asynchronous protocols to be proved correct by purely synchronous reasoning. As well as applying it to routing protocols, this thesis advances the asynchronous theory in two ways. Firstly it shows that the existing conditions required for convergence may be relaxed. Secondly it proposes the first model for ``dynamic'' asynchronous processes in which both the problem being solved and the set of participants change over time.
The thesis' attention then turns to models of routing problems, and presents a new algebraic structure that is simpler and more expressive than the state of the art. In particular this structure is capable of modelling routing problems that underlie both distance-vector and path-vector protocols. Consequently these two families of vector-based protocols may be unified for the first time. The new structure is also capable of modelling protocols that use path-dependent conditional policy.
Next the work above is used to construct a model of an abstract vector-based protocol. This is then used in the first proof of correctness for strictly increasing distance-vector protocols and a new proof of correctness for strictly increasing path-vector protocols. The latter is an improvement over previous results as it i) proves that convergence is deterministic ii) does not assume reliable communication between nodes and iii) applies to path-vector protocols with path-dependent conditional policy. The long standing question of the worst-case rate of convergence for a strictly increasing path-vector protocol is then answered by lowering the previous upper bound of to a new tight bound of~.
Finally all of the work has been formalised in the proof assistant Agda. Not only does this significantly increase users' confidence in the validity of the results, the resulting Agda library may also be used to verify the correctness of protocol implementations. To illustrate this, a formal proof of correctness is described for a path-vector protocol which contains many of the features of the Border Gateway Protocol including: local preferences, communities, an expressive conditional policy language and path inflation.EPSRC Doctoral Training gran
One More Weight is Enough: Toward the Optimal Traffic Engineering with OSPF
Traffic Engineering (TE) leverages information of network traffic to generate
a routing scheme optimizing the traffic distribution so as to advance network
performance. However, optimize the link weights for OSPF to the offered traffic
is an known NP-hard problem. In this paper, motivated by the fairness concept
of congestion control, we firstly propose a new generic objective function,
where various interests of providers can be extracted with different parameter
settings. And then, we model the optimal TE as the utility maximization of
multi-commodity flows with the generic objective function and theoretically
show that any given set of optimal routes corresponding to a particular
objective function can be converted to shortest paths with respect to a set of
positive link weights. This can be directly configured on OSPF-based protocols.
On these bases, we employ the Network Entropy Maximization(NEM) framework and
develop a new OSPF-based routing protocol, SPEF, to realize a flexible way to
split traffic over shortest paths in a distributed fashion. Actually, comparing
to OSPF, SPEF only needs one more weight for each link and provably achieves
optimal TE. Numerical experiments have been done to compare SPEF with the
current version of OSPF, showing the effectiveness of SPEF in terms of link
utilization and network load distribution
Jointly Optimal Routing and Caching for Arbitrary Network Topologies
We study a problem of fundamental importance to ICNs, namely, minimizing
routing costs by jointly optimizing caching and routing decisions over an
arbitrary network topology. We consider both source routing and hop-by-hop
routing settings. The respective offline problems are NP-hard. Nevertheless, we
show that there exist polynomial time approximation algorithms producing
solutions within a constant approximation from the optimal. We also produce
distributed, adaptive algorithms with the same approximation guarantees. We
simulate our adaptive algorithms over a broad array of different topologies.
Our algorithms reduce routing costs by several orders of magnitude compared to
prior art, including algorithms optimizing caching under fixed routing.Comment: This is the extended version of the paper "Jointly Optimal Routing
and Caching for Arbitrary Network Topologies", appearing in the 4th ACM
Conference on Information-Centric Networking (ICN 2017), Berlin, Sep. 26-28,
201
Optimal Network Control in Partially-Controllable Networks
The effectiveness of many optimal network control algorithms (e.g.,
BackPressure) relies on the premise that all of the nodes are fully
controllable. However, these algorithms may yield poor performance in a
partially-controllable network where a subset of nodes are uncontrollable and
use some unknown policy. Such a partially-controllable model is of increasing
importance in real-world networked systems such as overlay-underlay networks.
In this paper, we design optimal network control algorithms that can stabilize
a partially-controllable network. We first study the scenario where
uncontrollable nodes use a queue-agnostic policy, and propose a low-complexity
throughput-optimal algorithm, called Tracking-MaxWeight (TMW), which enhances
the original MaxWeight algorithm with an explicit learning of the policy used
by uncontrollable nodes. Next, we investigate the scenario where uncontrollable
nodes use a queue-dependent policy and the problem is formulated as an MDP with
unknown queueing dynamics. We propose a new reinforcement learning algorithm,
called Truncated Upper Confidence Reinforcement Learning (TUCRL), and prove
that TUCRL achieves tunable three-way tradeoffs between throughput, delay and
convergence rate
Optimisation of Mobile Communication Networks - OMCO NET
The mini conference âOptimisation of Mobile Communication Networksâ focuses on advanced methods for search and optimisation applied to wireless communication networks. It is sponsored by Research & Enterprise Fund Southampton Solent University.
The conference strives to widen knowledge on advanced search methods capable of optimisation of wireless communications networks. The aim is to provide a forum for exchange of recent knowledge, new ideas and trends in this progressive and challenging area. The conference will popularise new successful approaches on resolving hard tasks such as minimisation of transmit power, cooperative and optimal routing
A novel cooperative opportunistic routing scheme for underwater sensor networks
Increasing attention has recently been devoted to underwater sensor networks (UWSNs) because of their capabilities in the ocean monitoring and resource discovery. UWSNs are faced with different challenges, the most notable of which is perhaps how to efficiently deliver packets taking into account all of the constraints of the available acoustic communication channel. The opportunistic routing provides a reliable solution with the aid of intermediate nodesâ collaboration to relay a packet toward the destination. In this paper, we propose a new routing protocol, called opportunistic void avoidance routing (OVAR), to address the void problem and also the energy-reliability trade-off in the forwarding set selection. OVAR takes advantage of distributed beaconing, constructs the adjacency graph at each hop and selects a forwarding set that holds the best trade-off between reliability and energy efficiency. The unique features of OVAR in selecting the candidate nodes in the vicinity of each other leads to the resolution of the hidden node problem. OVAR is also able to select the forwarding set in any direction from the sender, which increases its flexibility to bypass any kind of void area with the minimum deviation from the optimal path. The results of our extensive simulation study show that OVAR outperforms other protocols in terms of the packet delivery ratio, energy consumption, end-to-end delay, hop count and traversed distance
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