András Császár

Resource Management in Diffserv (RMD): A Functionality and Performance Behavior Overview

The flexibility and the wide deployment of IP technologies have driven the development of IP-based solutions for wireless networks, like IP-based Radio Access Networks (RAN). These networks have different characteristics when compared to traditional IP networks, imposing very strict requirements on Quality of Service (QoS) solutions, such as fast dynamic resource reservation, simplicity, scalability, low cost, severe congestion handling and easy implementation. A new QoS framework, called Resource Management in Differentiated Services (RMD), aims to satisfy these requirements. RMD has been introduced in recent publications. It extends the IETF Differentiated Services (Diffserv) architecture with new admission control and resource reservation concepts in a scalable way. This paper gives an overview of the RMD functionality and its performance behavior. Furthermore, it shows that the mean processing delay of RMD signaling reservation messages is more than 1330 times smaller then the mean processing delay of RSVP signaling reservation messages.

IP fast ReRoute: Loop Free Alternates revisited

IP Fast ReRoute (IPFRR) is the IETF standard for providing fast failure protection in IP and MPLS/LDP networks and Loop Free Alternates (LFA) is a basic specification for implementing it. Even though LFA is simple and unobtrusive, it has a significant drawback: it does not guarantee protection for all possible failure cases. Consequently, many IPFRR proposals have appeared lately, promising full failure coverage at the price of added complexity and non-trivial modifications to IP hardware and software. Meanwhile, LFA remains the only commercially available, and therefore, the only deployable IPFRR solution. Deployment, however, crucially depends on the extent to which LFA can protect failures in operational networks. In this paper, therefore, we revisit LFA in order to give theoretical insights and practical hints to LFA failure coverage analysis. First, we identify the topological properties a network must possess to profit from good failure coverage. Then, we study how coverage varies as new links are added to a network, we show how to do this optimally and, through extensive simulations, we arrive to the conclusion that cleverly adding just a couple of new links can improve the quality of LFA protection drastically.

IP Fast ReRoute: Lightweight Not-Via without Additional Addresses

In order for IP to become a full-fledged carrier- grade transport technology, a native IP failure-recovery scheme is necessary that can correct failures in the order of milliseconds. IP fast reroute (IPFRR) intends to fill this gap, providing fast, local and proactive handling of failures right in the IP layer. Building on experiences and extensive measurement results collected with a prototype implementation of the prevailing IPFRR technique, Not-via, in this paper we identify high address management burden and computational complexity as the major causes of why commercial IPFRR deployment still lags behind, and we present a lightweight not-via scheme, which, according to our measurements, improves these issues.

Converging the Evolution of Router Architectures and IP Networks

Although IP is widely recognized as the platform for next-generation converged networks, unfortunately, it is heavily burdened by its heritage of almost 30 years. Nowadays, network operators must devote significant resources to perform essential tasks, such as traffic engineering, policy enforcement, and security. In this article, we argue that one of the principal reasons for this is the way control and forwarding planes are interspersed in IP networks today. We review the architectural developments that led to the current situation, and we reason that centralization of network control functionality can constitute a solution to the pressing problems of the contemporary Internet.

Elastic network functions: opportunities and challenges

Network function virtualization (NFV) and software defined networking (SDN) are key technology enablers for cost reductions and new business models in networking. The possibility to automatically and dynamically scale network services at run time is one of the main claims of NFV. Elastic NFV could be similar to what elastic cloud services provide for compute, with pay-per-use cost models for customers. However, control of resources for elastic services is far from trivial. We show how current NFV and SDN architectures could support elastic resource services for network functions (NFs). We reveal that the current NFV architecture does not allow recursive resource orchestration, therefore preventing resource scaling requests from being handled by a resource orchestrator overseeing the entire domain where an NF is executed. We introduce a logical centralization of joint compute and network resource orchestration as a UNIFY framework, which enables direct control of elastic resources for the NFs. We show opportunities and challenges associated with such an architecture.

Severe Congestion Handling with Resource Management in Diffserv on Demand

Quality of Service (QoS) for the Internet has been discussed for a long time without any major breakthrough. There are several reasons, the main one being the lack of a scalable, simple, fast and low cost QoS solution. A new QoS-framework, called resource management in differentiated services (RMD), aims to correct this situation. This framework has been published in recent papers and is extending the IETF differentiated services (diffserv) architecture with new admission control and resource reservation concepts in a scalable way. This paper focuses on proposing and investigating two resource reservation solutions on the problem of severe congestion situation within a diffserv-aware network utilizing an admission control scheme called Resource Mananagement in Diffserv (RMD). The different severe congestion solutions are compared using extensive simulation experiments.

On Finding maximally redundant trees in strictly linear time

Redundant trees are commonly used for protection and restoration in communications networks. Zhang et al. presented a linear time algorithm to compute node-redundant trees in 2-node-connected networks, which has become widely cited in the literature. In this paper, we show that it is difficult to implement this algorithm providing both correctness and linear complexity at the same time. Therefore, we present a revised algorithm with strict linear time complexity. Moreover, we generalize the concept of node-redundant trees from 2-node-connected networks to arbitrary topologies, a crucial development since real networks can not always satisfy 2-connectedness, especially after a failure.

Comparative Performance Analysis of RSVP and RMD

Service evolution towards QoS capable applications requires efficient resource reservation protocols. Currently, RSVP is a widely known protocol for this functionality in IntServ networks. Unfortunately, the processing power needs of RSVP make it to a less favoured candidate in high-speed environments. In these scenarios low-complexity DiffServ solutions have a clear advantage. A currently studied and industrially supported DiffServ conform resource management protocol is RMD. In this paper, we certify RMD as a simple and efficient protocol for unicast traffic by comparing the performance of RMD with RSVP, and also verify that the reduction of complexity does not entail loss in performance.

Optimizing IGP link costs for improving IP-level resilience

Recently, major vendors have introduced new router platforms to the market that support fast IP-level failure protection out of the box. The implementations are based on the IP Fast ReRoute-Loop Free Alternates (LFA) standard. LFA is simple, unobtrusive, and easily deployable. This simplicity, however, comes at a severe price, in that LFA usually cannot protect all possible failure scenarios. In this paper, we give new graph theoretical tools for analyzing LFA failure case coverage and we seek ways for improvement. In particular, we investigate how to optimize IGP link costs to maximize the number of protected failure scenarios, we show that this problem is NP-complete even in a very restricted formulation, and we give exact and approximate algorithms to solve it. Our simulation studies show that a deliberate selection of IGP costs can bring many networks close to complete LFA-based protection.

A practical method for the efficient resolution of congestion in an on-path reduced-state signalling environment

Currently, the standardisation of on-path signalling protocols is going on within the Next Steps in Signalling (NSIS) Working Group of the IETF. NSIS is responsible for the definition of a general IP signalling protocol. The first use case of the proposed protocol is flow-level resource management. One of the considered reservation methods, reduced-state mode, is based on the Resource Management in DiffServ (RMD) framework. Since it relies only on per-class state information in interior routers, it has a number of benefits including scalability, low complexity, and low memory consumption. However, the price of simplicity is decreased efficiency in case of exceptional situations. The most demanding task for RMD is the handling of congestion that may occur after a failure resulting in re-routing of flows onto a new path. Resolving a suddenly evolved overload without per-flow states is a highly non-trivial task. We present a low complexity mechanism which easily handles the undesirable situation, and we give guidelines to set the parameters of our scheme based on worst-case calculations.