A Survey of PCN-Based Admission Control and Flow Termination
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paper_title: Managing flash crowds on the Internet

paper_content:

A flash crowd is a surge in traffic to a particular Web site that causes the site to be virtually unreachable. We present a model of flash crowd events and evaluate the performance of various multilevel caching techniques suitable for managing these events. By using well-dispersed caches and with judicious choice of replacement algorithms we show reductions in client response times by as much as a factor of 25. We also show that these caches eliminate the server and network hot spots by distributing the load over the entire network.
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paper_title: Flash crowd mitigation via adaptive admission control based on application-level observations

paper_content:

We design an adaptive admission control mechanism, network early warning system (NEWS), to protect servers and networks from flash crowds and maintain high performance for end-users. NEWS detects flash crowds from performance degradation in responses and mitigates flash crowds by admitting incoming requests adaptively. We evaluate NEWS performance with both simulations and testbed experiments. We first investigate a network-limited scenarion in simulations. We find that NEWS detects flash crowds within 20 seconds. By discarding 32p of incoming requests, NEWS protects the target server and networks from overloading, reducing the response packet drop rate from 25p to 2p. For admitted requests, NEWS increases their response rate by two times. This performance is similar to the best static rate limiter deployed in the same scenario. We also investigate the impact of detection intervals on NEWS performance, showing it affects both detection delay and false alarm rate. We further consider a server memory-limited scenario in testbed experiments, confirming that NEWS is also effective in this case. We also examine the runtime cost of NEWS traffic monitoring in practice and find that it consumes little CPU time and relatively small memory. Finally, we show NEWS effectively protects bystander traffic from flash crowds.
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paper_title: Flash crowds and denial of service attacks: characterization and implications for CDNs and web sites

paper_content:

The paper studies two types of events that often overload Web sites to a point when their services are degraded or disrupted entirely - flash events (FEs) and denial of service attacks (DoS). The former are created by legitimate requests and the latter contain malicious requests whose goal is to subvert the normal operation of the site. We study the properties of both types of events with a special attention to characteristics that distinguish the two. Identifying these characteristics allows a formulation of a strategy for Web sites to quickly discard malicious requests. We also show that some content distribution networks (CDNs) may not provide the desired level of protection to Web sites against flash events. We therefore propose an enhancement to CDNs that offers better protection and use trace-driven simulations to study the effect of our enhancement on CDNs and Web sites.
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paper_title: Random early detection gateways for congestion avoidance

paper_content:

The authors present random early detection (RED) gateways for congestion avoidance in packet-switched networks. The gateway detects incipient congestion by computing the average queue size. The gateway could notify connections of congestion either by dropping packets arriving at the gateway or by setting a bit in packet headers. When the average queue size exceeds a present threshold, the gateway drops or marks each arriving packet with a certain probability, where the exact probability is a function of the average queue size. RED gateways keep the average queue size low while allowing occasional bursts of packets in the queue. During congestion, the probability that the gateway notifies a particular connection to reduce its window is roughly proportional to that connection's share of the bandwidth through the gateway. RED gateways are designed to accompany a transport-layer congestion control protocol such as TCP. The RED gateway has no bias against bursty traffic and avoids the global synchronization of many connections decreasing their window at the same time. Simulations of a TCP/IP network are used to illustrate the performance of RED gateways. >
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paper_title: Overview of measurement-based connection admission control methods in ATM networks

paper_content:

An overview is given of previously-proposed measurement-based connection admission control (CAC) methods. First we address requirements for CAC methods, and then provide a taxonomy for CAC methods. Measurement-based CAC methods are discussed in detail, classified according to the taxonomy, and compared against each other with respect to the requirements. We conclude that measurement-based CAC methods based on effective bandwidth and bufferless models are promising because they do not require complex hardware and are less dependent on assumptions regarding traffic than methods in which the effect of buffer is considered.
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paper_title: Call admission control in wireless networks: a comprehensive survey

paper_content:

Radio resource management (RRM) plays a major role in Quality of Service (QoS) provisioning for wireless communication systems. The performance of RRM techniques has a direct impact on each user's individual performance and on the overall network performance. Arriving (new and handoff) calls are granted/denied access to the network by the call admission scheme (CAC) based on predefined criteria, taking the network loading conditions into consideration. CAC in wireless networks has been receiving a great deal of attention during the last two decades due to the growing popularity of wireless communications and the central role that CAC plays in QoS provisioning in terms of the signal quality, call blocking and dropping probabilities, packet delay and loss rate, and transmission rate. In the first and second generation of wireless systems, CAC has been developed for a single service environment. In the third generation and beyond wireless systems, multimedia services such as voice, video, data, and audio are to be offered with various QoS profiles. Hence, more sophisticated CAC schemes are developed to cope with these changes. This article provides a comprehensive survey of CAC schemes in modern wireless networks.
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paper_title: Resource pricing and the evolution of congestion control

paper_content:

We describe ways in which the transmission control protocol of the Internet may evolve to support heterogeneous applications. We show that by appropriately marking packets at overloaded resources and by charging a fixed small amount for each mark received, end-nodes are provided with the necessary information and the correct incentive to use the network efficiently.
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paper_title: Distributed connection acceptance control for a connectionless network

paper_content:

We describe how a packet network with a simple pricing mechanism and no connection acceptance control may be used to carry a telephony-like service with low packet loss and some call blocking. The packet network uses packet marking to indicate congestion and endsystems are charged a fixed small amount per mark received. The end-systems are thus provided with the information and the incentive to use the packet network efficiently. We demonstrate that algorithms embedded in the end-systems are able to synthesize a telephony-like service by blocking calls at times when the load in the packet network is high.
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paper_title: Packet marking for integrated load control

paper_content:

Combining low-complexity packet marking at internal nodes with path-based load observation at edge gateways enables a rich set of control mechanisms in a packet-switched network. In this paper, we propose a method to estimate the relative per-node load at internal nodes, based on only the aggregated marking signal available at edge nodes, without any knowledge of internal capacities. We present the design of an integrated network system that supports both admission control and per-node load estimation using only two bits in the packet header, which requires a specific encoding of the two distinct marking signals. Finally, we describe a prototype implementation and a few simulation and lab experiments as a proof-of-concept for this approach.
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paper_title: Distributed admission control

paper_content:

This paper describes a framework for admission control for a packet-based network where the decisions are taken by edge devices or end-systems, rather than resources within the network. The decisions are based on the results of probe packets that the end-systems send through the network, and require only that resources apply a mark to packets in a way that is load dependent. One application example is the Internet, where marking information is fed back via an ECN bit, and we show how this approach allows a rich QoS framework for flows or streams. Our approach allows networks to be explicitly analyzed, and consequently engineered.
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paper_title: Providing guaranteed services without per flow management

paper_content:

Existing approaches for providing guaranteed services require routers to manage per flow states and perform per flow operations [9, 21]. Such a stateful network architecture is less scalable and robust than stateless network architectures like the original IP and the recently proposed Diffserv [3]. However, services provided with current stateless solutions, Diffserv included, have lower flexibility, utilization, and/or assurance level as compared to the services that can be provided with per flow mechanisms.In this paper, we propose techniques that do not require per flow management (either control or data planes) at core routers, but can implement guaranteed services with levels of flexibility, utilization, and assurance similar to those that can be provided with per flow mechanisms. In this way we can simultaneously achieve high quality of service, high scalability and robustness. The key technique we use is called Dynamic Packet State (DPS), which provides a lightweight and robust mechanism for routers to coordinate actions and implement distributed algorithms. We present an implementation of the proposed algorithms that has minimum incompatibility with IPv4.
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paper_title: An approach to alleviate link overload as observed on an IP backbone

paper_content:

Shortest path routing protocols may suffer from congestion due to the use of a single shortest path between a source and a destination. The goal of our work is to first understand how links become overloaded in an IP backbone, and then to explore if the routing protocol, -either in its existing form, or in some enhanced form could be made to respond immediately to overload and reduce the likelihood of its occurrence. Our method is to use extensive measurements of Sprint's backbone network, measuring 138 links between September 2000 and June 2001. We find that since the backbone is designed to be overprovisioned, link overload is rare, and when it occurs, 80% of the time it is caused due to link failures. Furthermore, we find that when a link is overloaded, few (if any) other links in the network are also overloaded. This suggests that deflecting packets to less utilized alternate paths could be an effective method for tackling overload. We analytically derive the condition that a network, which has multiple equal length shortest paths between every pair of nodes (as is common in the highly meshed backbone networks) can provide for loop-free deflection paths if all the link weights are within a ratio 1 + 1/(d- I) of each other; where d is the diameter of the network. Based on our measurements, the nature of the backbone topology and the careful use of link weights, we propose a deflection routing algorithm to tackle link overload where each node makes local decisions. Simulations suggest that this can be a simple and efficient way to overcome link overload, without requiring any changes to the routing protocol.
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paper_title: Capacity overprovisioning for networks with resilience requirements

paper_content:

This work focuses on capacity overprovisioning (CO) as an alternative to admission control (AC) to implement quality of service (QoS) in packet-switched communication networks. CO prevents potential overload while AC protects the QoS of the traffic during overload situations. Overload may be caused, e. g., by uctuations of the traffic rate on a link due to its normal stochastic behavior (a), by traffic shifts within the network due to popular contents (b), or by redirected traffic due to network failures (c). Capacity dimensioning methods for CO need to take into account all potential sources of overload while AC can block excess traffic caused by (a) and (b) if the capacity does not suffice. The contributions of this paper are (1) the presentation of a capacity dimensioning method for networks with resilience requirements and changing traffic matrices, (2) the investigation of the impact of the mentioned sources of overload (a-c) on the required capacity for CO in networks with and without resilience requirements, and (3) a comparison of this equired capacity with the one for AC. Our results show that in the presence of strong traffic shifts CO requires more capacity than AC. However, if resilience against network failures is required, both CO and AC need additional backup capacity for the redirected traffic. In this case, CO can use the backup capacity to absorb other types of overload. As a consequence, CO and AC have similar bandwidth requirements. These findings are robust against the network size.
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paper_title: IP resilience within an autonomous system: current approaches, challenges, and future directions

paper_content:

Network survivability is gaining increasing attention from the Internet research community. The ubiquity of IP services has fueled increasing interest in ensuring their dependability, by making IP networks more disruption-tolerant. After providing a brief overview of how routing is accomplished in the Internet, this article reviews how the protocols react to failures or changes in network state within an autonomous system. The problems associated with current restoration schemes, with respect to newer and more stringent requirements posed by emerging services such as voice over IP, are identified. We present an overview of the schemes proposed to ameliorate fault recovery and critique their contributions. We also outline future research directions for improving IP resilience.
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paper_title: Threshold Configuration and Routing Optimization for PCN-Based Resilient Admission Control

paper_content:

Pre-Congestion Notification (PCN) in IP networks uses packet metering and marking within a PCN domain to notify its egress nodes whether link-specific admissible or supportable rate thresholds have been exceeded by high-priority traffic. Based on this information simple admission control and flow termination is implemented. The latter is a new flow control function and useful in case of overload through high priority traffic which can occur in spite of admission control, e.g., when traffic is rerouted in failure cases. Resilient admission control admits only so much traffic that admitted traffic can be rerouted without causing congestion on backup paths in case of a likely failures, e.g., single link failures. We propose algorithms to configure the link-specific PCN rate thresholds such that resources are utilized efficiently and fairly by competing traffic aggregates while meeting resilience constraints. This is done for the single and dual marking PCN architecture whereby the single marking case is more demanding since it requires that the supportable rate is a fixed multiple of the admissible rate on all links within a single PCN domain. Furthermore, we derive objective functions to optimize the underlying routing system for both cases. Our performance results for various network types show that the dual marking PCN architecture leads to significantly better resource efficiency than the single marking PCN architecture.
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paper_title: Resilient Network Admission Control

paper_content:

Network admission control (NAC) limits the traffic in a network to avoid overload and to assure thereby the quality of service (QoS) for admitted flows. Overload may occur due to exceptional traffic demand, but it is mostly caused by redirected traffic due to link failures. Conventional NAC methods cannot cope with network outages and fail when they are needed most. This paper categorizes existing and new NAC methods and makes them resilient to network failures by a resilient resource management. We compare the efficiency of the NAC methods with and without resilience requirements and show that they have a significant impact on the required backup capacity when resilience is required.
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paper_title: A survey of resilience differentiation frameworks in communication networks

paper_content:

Unintentional failures affect links and nodes in communication networks. Recovery mechanisms are the key tool for achieving the dependability required by the services using the network. However, high dependability in communication networks comes at a high cost in terms of the capacity needed by these mechanisms.The traffic from all services and users is carried by the same backbone network. Since the users and services have different requirements, and users have different willingness to pay for a high quality of service, it is desirable to have methods that enable provision of different levels of dependability in the same network, i.e. dependability differentiation. The thesis addresses dependability differentiation in connection-oriented backbone communication networks. Two methods to provide connections meeting differentiated guarantees on the asymptotic availability are proposed.The first of these uses a novel flexible arrangement for dedicated protection denoted a protection pattern. The protection pattern is used in a proposed distributed connection management system. The system is compared with alternative proposals based on centralized management and shows good performance. The second proposal uses shared protection, which may potentially use less resources in terms of bandwidth, but has higher complexity than dedicated protection. The proposed system is based on rules to control the sharing to enable provision of guarantees. Simulation results show that the proposed method performs significantly better than an alternative strategy based on dedicated protection.A different approach to availability-guaranteed services is to offer guarantees on the interval availability which is a measure commonly used Service Level Agreements (SLAs). The thesis contains a proposal of using adaptive management to increase compliance with interval availability guarantees. Different adaptive management policies are proposed and compared to alternative static provisioning policies in a case study. The thesis also addresses the problem of measuring dependability by simulation. To reduce the simulation effort needed to obtain precise estimates of dependability attributes, a rare-event simulation technique has been applied to the well-known Network Simulator 2 (NS2). The results show that the technique is applicable to this types of simulation scenario, but the gain is modest. The thesis also contains a broad literature survey of dependability differentiation research. This is the first survey of the topic. Hence, it is in itself a significant contribution. A classification scheme for how to approach differentiation is proposed and a critical evaluation of the state of art is given.This thesis contributes to fill in some of the ``gaps'' identified, but there are still significant challenges ahead before differentiation may be deployed in operational networks.
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paper_title: PCN-based marked flow termination

paper_content:

Pre-congestion notification (PCN) uses packet metering and marking to notify boundary nodes of a Differentiated Services IP network if configured rate thresholds have been exceeded on some links. This feedback is used for PCN-based admission control and flow termination. While admission control is rather well understood, flow termination is a new flow control function and useful especially in case of failures or during flash crowds. We present marked flow termination as a new class of termination algorithms which terminate overload traffic gradually and that work well with multipath routing. We study their termination behavior, give recommendation for their configuration, and discuss their benefits and shortcomings.
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paper_title: Comparison of Marking Algorithms for PCN-Based Admission Control

paper_content:

The PCN working group of the IETF discusses the use of pre-congestion notification (PCN) to implement flow admission control. Packet meters and markers are used on all network links and packet markings are recorded as congestion level estimates (CLEs) the egress nodes. The working group currently discusses the pros and cons of possible marking algorithms that play a major role in this new architecture. This paper provides a detailed description of threshold and ramp marking based on a virtual queue formulation. We investigate the impact of the marking threshold and the virtual queue size on the marking behavior and develop different marking strategies. We test the robustness of the CLEs obtained for both marking schemes against different CLE parameters and traffic characteristics. Furthermore, we show that ramp marking can be well approximated by appropriately configured threshold marking.
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paper_title: Three State PCN Marking

paper_content:

This document proposes metering and marking mechanisms for PCN- ::: enabled nodes to label packets with pre-congestion information. The ::: marker marks all PCN packets with an admission-stop (AS) codepoint if ::: the PCN traffic rate on a link exceeds its admissible rate (AR) and ::: when it exceeds its supportable rate (SR), it marks some of those ::: packets exceeding SR with an excess-traffic (ET) codepoint. The flows ::: with ET-marked packets will be terminated until the aggregate PCN ::: traffic on the path decreases below its SR. This document proposes ::: metering and marking mechanisms for these objectives.
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paper_title: PCN Boundary Node Behaviour for the Controlled Load (CL) Mode of Operation

paper_content:

Precongestion notification (PCN) is a means for protecting quality of ::: service for inelastic traffic admitted to a Diffserv domain. The ::: overall PCN architecture is described in ID.PCNArch. This memo is one ::: of a series describing possible boundary node behaviours for a PCN ::: domain. The behaviour described here is that for three-state ::: measurement-based load control, known informally as CL. The ::: requirement for three encoding states means that CL is for ::: experimental use only pending further standards action.
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paper_title: PCN-based marked flow termination

paper_content:

Pre-congestion notification (PCN) uses packet metering and marking to notify boundary nodes of a Differentiated Services IP network if configured rate thresholds have been exceeded on some links. This feedback is used for PCN-based admission control and flow termination. While admission control is rather well understood, flow termination is a new flow control function and useful especially in case of failures or during flash crowds. We present marked flow termination as a new class of termination algorithms which terminate overload traffic gradually and that work well with multipath routing. We study their termination behavior, give recommendation for their configuration, and discuss their benefits and shortcomings.
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paper_title: LC-PCN: The Load Control PCN Solution

paper_content:

There is an increased interest of simple and scalable resource provisioning solution for Diffserv network. The Load Control PCN (LC-PCN) addresses the following issues: ::: o Admission Control for real time data flows in stateless Diffserv Domains ::: o Flow Termination: Termination of flows in case of exceptional events, such as severe congestion after re-routing. ::: Admission control in a Diffserv stateless domain is a combination of: ::: o Probing, whereby a probe packet is sent along the forwarding path in a network to determine whether a flow can be admitted based upon the current congestion state of the network ::: o Admission Control based on data marking, whereby in congestion situations the data packets are marked to notify the PCN-egress-node that a congestion occurred on a particular PCN-ingress-node to PCN-egress-node path. ::: ::: The scheme provides the capability of controlling the traffic load in the network without requiring signaling or any per-flow processing in the PCN-interior-nodes. The complexity of Load Control is kept to a minimum to make implementation simple.
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paper_title: Three State PCN Marking

paper_content:

This document proposes metering and marking mechanisms for PCN- ::: enabled nodes to label packets with pre-congestion information. The ::: marker marks all PCN packets with an admission-stop (AS) codepoint if ::: the PCN traffic rate on a link exceeds its admissible rate (AR) and ::: when it exceeds its supportable rate (SR), it marks some of those ::: packets exceeding SR with an excess-traffic (ET) codepoint. The flows ::: with ET-marked packets will be terminated until the aggregate PCN ::: traffic on the path decreases below its SR. This document proposes ::: metering and marking mechanisms for these objectives.
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paper_title: PCN-based marked flow termination

paper_content:

Pre-congestion notification (PCN) uses packet metering and marking to notify boundary nodes of a Differentiated Services IP network if configured rate thresholds have been exceeded on some links. This feedback is used for PCN-based admission control and flow termination. While admission control is rather well understood, flow termination is a new flow control function and useful especially in case of failures or during flash crowds. We present marked flow termination as a new class of termination algorithms which terminate overload traffic gradually and that work well with multipath routing. We study their termination behavior, give recommendation for their configuration, and discuss their benefits and shortcomings.
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paper_title: Single PCN Threshold Marking by using PCN baseline encoding for both admission and termination controls

paper_content:

This document proposes an algorithm for marking and metering by using ::: pre-congestion notification (PCN) baseline encoding for both flow ::: admission and flow termination. The proposed algorithm uses threshold ::: marking whose TBthreshold.threshold is set to the number of bits of a ::: metered-packet smaller than the token bucket size. Another threshold ::: for the token bucket is required to change the marking. frequency. ::: Under the flow termination state, all the packets are to be threshold- ::: marked. Under the admission stop state, 1/Nth of packets are to be ::: threshold-marked when the meter indicates. We evaluates the ::: performance of the proposed algorithm by simulations. Our simulation ::: indicates that the performance is almost the same as that of the ::: CL[I-D.briscoe-tsvwg-cl-architecture] algorithm.
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paper_title: Comparison of Marking Algorithms for PCN-Based Admission Control

paper_content:

The PCN working group of the IETF discusses the use of pre-congestion notification (PCN) to implement flow admission control. Packet meters and markers are used on all network links and packet markings are recorded as congestion level estimates (CLEs) the egress nodes. The working group currently discusses the pros and cons of possible marking algorithms that play a major role in this new architecture. This paper provides a detailed description of threshold and ramp marking based on a virtual queue formulation. We investigate the impact of the marking threshold and the virtual queue size on the marking behavior and develop different marking strategies. We test the robustness of the CLEs obtained for both marking schemes against different CLE parameters and traffic characteristics. Furthermore, we show that ramp marking can be well approximated by appropriately configured threshold marking.
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paper_title: Pre-Congestion Notification marking

paper_content:

Pre-Congestion Notification (PCN) builds on the concepts of RFC 3168, ::: "The addition of Explicit Congestion Notification to IP". However, ::: Pre-Congestion Notification aims at providing notification before any ::: congestion actually occurs. Pre-Congestion Notification is applied to ::: real-time flows (such as voice, video and multimedia streaming) in ::: DiffServ networks. As described in [CL-DEPLOY], it enables "pre" ::: congestion control through two procedures, flow admission control and ::: flow pre-emption. The draft proposes algorithms that determine when a ::: PCN-enabled router writes Admission Marking and Pre-emption Marking in ::: a packet header, depending on the traffic level. The draft also ::: proposes how to encode these markings. We present simulation results ::: with PCN working in an edge-to-edge scenario using the marking ::: algorithms described. Other marking algorithms will be investigated in ::: the future.
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paper_title: Three State PCN Marking

paper_content:

This document proposes metering and marking mechanisms for PCN- ::: enabled nodes to label packets with pre-congestion information. The ::: marker marks all PCN packets with an admission-stop (AS) codepoint if ::: the PCN traffic rate on a link exceeds its admissible rate (AR) and ::: when it exceeds its supportable rate (SR), it marks some of those ::: packets exceeding SR with an excess-traffic (ET) codepoint. The flows ::: with ET-marked packets will be terminated until the aggregate PCN ::: traffic on the path decreases below its SR. This document proposes ::: metering and marking mechanisms for these objectives.
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paper_title: Random early detection gateways for congestion avoidance

paper_content:

The authors present random early detection (RED) gateways for congestion avoidance in packet-switched networks. The gateway detects incipient congestion by computing the average queue size. The gateway could notify connections of congestion either by dropping packets arriving at the gateway or by setting a bit in packet headers. When the average queue size exceeds a present threshold, the gateway drops or marks each arriving packet with a certain probability, where the exact probability is a function of the average queue size. RED gateways keep the average queue size low while allowing occasional bursts of packets in the queue. During congestion, the probability that the gateway notifies a particular connection to reduce its window is roughly proportional to that connection's share of the bandwidth through the gateway. RED gateways are designed to accompany a transport-layer congestion control protocol such as TCP. The RED gateway has no bias against bursty traffic and avoids the global synchronization of many connections decreasing their window at the same time. Simulations of a TCP/IP network are used to illustrate the performance of RED gateways. >
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paper_title: PCN Boundary Node Behaviour for the Controlled Load (CL) Mode of Operation

paper_content:

Precongestion notification (PCN) is a means for protecting quality of ::: service for inelastic traffic admitted to a Diffserv domain. The ::: overall PCN architecture is described in ID.PCNArch. This memo is one ::: of a series describing possible boundary node behaviours for a PCN ::: domain. The behaviour described here is that for three-state ::: measurement-based load control, known informally as CL. The ::: requirement for three encoding states means that CL is for ::: experimental use only pending further standards action.
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paper_title: Single PCN Threshold Marking by using PCN baseline encoding for both admission and termination controls

paper_content:

This document proposes an algorithm for marking and metering by using ::: pre-congestion notification (PCN) baseline encoding for both flow ::: admission and flow termination. The proposed algorithm uses threshold ::: marking whose TBthreshold.threshold is set to the number of bits of a ::: metered-packet smaller than the token bucket size. Another threshold ::: for the token bucket is required to change the marking. frequency. ::: Under the flow termination state, all the packets are to be threshold- ::: marked. Under the admission stop state, 1/Nth of packets are to be ::: threshold-marked when the meter indicates. We evaluates the ::: performance of the proposed algorithm by simulations. Our simulation ::: indicates that the performance is almost the same as that of the ::: CL[I-D.briscoe-tsvwg-cl-architecture] algorithm.
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paper_title: PCN 3-State Encoding Extension in a single DSCP

paper_content:

Pre-congestion notification (PCN) is a mechanism designed to protect ::: the quality of service of inelastic flows. It does this by marking ::: packets when traffic load on a link is approaching or has exceeded a ::: threshold below the physical link rate. This document specifies an ::: extension to the two-state PCN baseline encoding that enables three ::: encoding states to be carried in the IP header without using more than ::: one Diffserv codepoint. It presupposes a standards action has removed ::: the limit of two encoding states in current tunnelling mechanisms.
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paper_title: DSCPs for Capacity-Admitted Traffic

paper_content:

This document requests one DSCP from the IANA for real-time traffic ::: classes similar to voice conforming to the Expedited Forwarding Per ::: Hop Behavior, and admitted using a CAC procedure involving ::: authentication, authorization, and capacity admission, as compared to ::: a class of real-time traffic conforming to the Expedited Forwarding ::: Per Hop Behavior but not subject to capacity admission or subject to ::: very coarse capacity admission. It also recommends that certain ::: classes of video traffic described in RFC 4594 and which have similar ::: requirements be require admission using a CAC procedure involving ::: authentication, authorization, and capacity admission. One of the ::: reasons behind this is the need for classes of traffic that are ::: handled under special policies, such as the non-preemptive Emergency ::: Telecommunication Service, the US DoD's Assured Service (which is ::: similar to MLPP), or e-911. Capacity-admitted traffic classes need ::: separation from traffic not subject to admission control, from which ::: they can deterministically obtain their service requirements, ::: including SLA matters.
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paper_title: Pre-Congestion Notification Encoding Comparison

paper_content:

DiffServ mechanisms have been developed to support Quality of Service (QoS). However, the level of assurance that can be provided with DiffServ without substantial over-provisioning is limited. Pre-Congestion Notification (PCN) investigates the use of per-flow admission control to provide the required service guarantees for the admitted traffic. While admission control will protect the QoS under ::: normal operating conditions, an additional flow termination mechanism is necessary in the times of heavy congestion (e.g. caused by route changes due to link or node failure). ::: Encoding and their transport are required to carry the congestion and pre-congestion information from the congestion and pre-congestion points to the decision points. This document provides a survey of ::: several encoding methods, using comparisons amongst them as a way to explain their strengths and weaknesses.
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paper_title: Tunnelling of Explicit Congestion Notification

paper_content:

This document redefines how the explicit congestion notification (ECN) ::: field of the IP header should be constructed on entry to and exit from ::: any IP in IP tunnel. On encapsulation it updates RFC3168 to bring all ::: IP in IP tunnels (v4 or v6) into line with RFC4301 IPsec ECN ::: processing. On decapsulation it updates both RFC3168 and RFC4301 to ::: add new behaviours for previously unused combinations of inner and ::: outer header. The new rules ensure the ECN field is correctly ::: propagated across a tunnel whether it is used to signal one or two ::: severity levels of congestion, whereas before only one severity level ::: was supported. Tunnel endpoints can be updated in any order without ::: affecting pre-existing uses of the ECN field (backward compatible). ::: Nonetheless, operators wanting to support two severity levels (e.g. ::: for pre-congestion notification--PCN) can require compliance with this ::: new specification. A thorough analysis of the reasoning for these ::: changes and the implications is included. In the unlikely event that ::: the new rules do not meet a specific need, RFC4774 gives guidance on ::: designing alternate ECN semantics and this document extends that to ::: include tunnelling issues.
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paper_title: PCN Encoding for Packet-Specific Dual Marking (PSDM)

paper_content:

This document proposes how PCN marks can be encoded into the IP ::: header. The presented encoding reuses the ECN field of the Voice- ::: Admit DSCP in a single PCN domain. The encoding of unmarked PCN ::: packets indicates whether they are subject to either excess- or ::: exhaustive-marking. This is useful, e.g., when data and probe packets ::: require different marking mechanisms. Status This memo is posted as ::: an Internet-Draft with an intent to eventually be published as an ::: experimental RFC.
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paper_title: Pre-Congestion Notification Using Packet-Specific Dual Marking

paper_content:

Pre-congestion notification (PCN) uses packet metering and marking within a PCN domain to notify PCN egress nodes about high load regimes in the network. One question is how to encode the PCN markings in packet headers. The problem is that the IPv4 packet header is short of available codepoints and that tunnelling mechanisms constrain solutions. This paper proposes packet-specific dual marking (PSDM) as a new encoding scheme that avoids these problems and also explains how to apply it to achieve PCN-based admission control and flow termination. Therefore, our proposal may improve the deployability of PCN in spite of the limited extensibility of the current Internet architecture.
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paper_title: Performance Evaluation of PCN-Based Admission Control

paper_content:

Pre-congestion notification (PCN) marks packets when the PCN traffic rate exceeds an admissible link rate and this marking information is used as feedback from the network to take admission decisions for new flows. This idea is currently under standardization in the IETF. Different marking algorithms are discussed and various admission control algorithms are proposed that decide based on the packet markings whether further flows should be accepted or blocked. In this paper, we propose a two-layer architecture that makes the coexistence of various algorithms explicit. We propose novel control algorithms, investigate their behavior under various conditions, and compare them with existing approaches.
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paper_title: Three State PCN Marking

paper_content:

This document proposes metering and marking mechanisms for PCN- ::: enabled nodes to label packets with pre-congestion information. The ::: marker marks all PCN packets with an admission-stop (AS) codepoint if ::: the PCN traffic rate on a link exceeds its admissible rate (AR) and ::: when it exceeds its supportable rate (SR), it marks some of those ::: packets exceeding SR with an excess-traffic (ET) codepoint. The flows ::: with ET-marked packets will be terminated until the aggregate PCN ::: traffic on the path decreases below its SR. This document proposes ::: metering and marking mechanisms for these objectives.
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paper_title: Accuracy and Dynamics of Hash-Based Load Balancing Algorithms for Multipath Internet Routing

paper_content:

This paper studies load balancing for multipath Internet routing. We focus on hash-based load balancing algorithms that work on the flow level to avoid packet reordering which is detrimental for the throughput of transport layer protocols like TCP. We propose a classification of hash-based load balancing algorithms, review existing ones and suggest new ones. Dynamic algorithms can actively react to load imbalances which causes route changes for some flows and thereby again packet reordering. Therefore, we investigate the load balancing accuracy and flow reassignment rate of load balancing algorithms. Our exhaustive simulation experiments show that these performance measures depend significantly on the traffic properties and on the algorithms themselves. As a consequence, our results should be taken into account for the application of load balancing in practice.
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paper_title: Performance Evaluation of PCN-Based Admission Control

paper_content:

Pre-congestion notification (PCN) marks packets when the PCN traffic rate exceeds an admissible link rate and this marking information is used as feedback from the network to take admission decisions for new flows. This idea is currently under standardization in the IETF. Different marking algorithms are discussed and various admission control algorithms are proposed that decide based on the packet markings whether further flows should be accepted or blocked. In this paper, we propose a two-layer architecture that makes the coexistence of various algorithms explicit. We propose novel control algorithms, investigate their behavior under various conditions, and compare them with existing approaches.
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paper_title: Three State PCN Marking

paper_content:

This document proposes metering and marking mechanisms for PCN- ::: enabled nodes to label packets with pre-congestion information. The ::: marker marks all PCN packets with an admission-stop (AS) codepoint if ::: the PCN traffic rate on a link exceeds its admissible rate (AR) and ::: when it exceeds its supportable rate (SR), it marks some of those ::: packets exceeding SR with an excess-traffic (ET) codepoint. The flows ::: with ET-marked packets will be terminated until the aggregate PCN ::: traffic on the path decreases below its SR. This document proposes ::: metering and marking mechanisms for these objectives.
---
paper_title: PCN Boundary Node Behaviour for the Controlled Load (CL) Mode of Operation

paper_content:

Precongestion notification (PCN) is a means for protecting quality of ::: service for inelastic traffic admitted to a Diffserv domain. The ::: overall PCN architecture is described in ID.PCNArch. This memo is one ::: of a series describing possible boundary node behaviours for a PCN ::: domain. The behaviour described here is that for three-state ::: measurement-based load control, known informally as CL. The ::: requirement for three encoding states means that CL is for ::: experimental use only pending further standards action.
---
paper_title: Accuracy and Dynamics of Hash-Based Load Balancing Algorithms for Multipath Internet Routing

paper_content:

This paper studies load balancing for multipath Internet routing. We focus on hash-based load balancing algorithms that work on the flow level to avoid packet reordering which is detrimental for the throughput of transport layer protocols like TCP. We propose a classification of hash-based load balancing algorithms, review existing ones and suggest new ones. Dynamic algorithms can actively react to load imbalances which causes route changes for some flows and thereby again packet reordering. Therefore, we investigate the load balancing accuracy and flow reassignment rate of load balancing algorithms. Our exhaustive simulation experiments show that these performance measures depend significantly on the traffic properties and on the algorithms themselves. As a consequence, our results should be taken into account for the application of load balancing in practice.
---
paper_title: Single PCN Threshold Marking by using PCN baseline encoding for both admission and termination controls

paper_content:

This document proposes an algorithm for marking and metering by using ::: pre-congestion notification (PCN) baseline encoding for both flow ::: admission and flow termination. The proposed algorithm uses threshold ::: marking whose TBthreshold.threshold is set to the number of bits of a ::: metered-packet smaller than the token bucket size. Another threshold ::: for the token bucket is required to change the marking. frequency. ::: Under the flow termination state, all the packets are to be threshold- ::: marked. Under the admission stop state, 1/Nth of packets are to be ::: threshold-marked when the meter indicates. We evaluates the ::: performance of the proposed algorithm by simulations. Our simulation ::: indicates that the performance is almost the same as that of the ::: CL[I-D.briscoe-tsvwg-cl-architecture] algorithm.
---
paper_title: PCN-based marked flow termination

paper_content:

Pre-congestion notification (PCN) uses packet metering and marking to notify boundary nodes of a Differentiated Services IP network if configured rate thresholds have been exceeded on some links. This feedback is used for PCN-based admission control and flow termination. While admission control is rather well understood, flow termination is a new flow control function and useful especially in case of failures or during flash crowds. We present marked flow termination as a new class of termination algorithms which terminate overload traffic gradually and that work well with multipath routing. We study their termination behavior, give recommendation for their configuration, and discuss their benefits and shortcomings.
---
paper_title: PCN-based marked flow termination

paper_content:

Pre-congestion notification (PCN) uses packet metering and marking to notify boundary nodes of a Differentiated Services IP network if configured rate thresholds have been exceeded on some links. This feedback is used for PCN-based admission control and flow termination. While admission control is rather well understood, flow termination is a new flow control function and useful especially in case of failures or during flash crowds. We present marked flow termination as a new class of termination algorithms which terminate overload traffic gradually and that work well with multipath routing. We study their termination behavior, give recommendation for their configuration, and discuss their benefits and shortcomings.
---
paper_title: Three State PCN Marking

paper_content:

This document proposes metering and marking mechanisms for PCN- ::: enabled nodes to label packets with pre-congestion information. The ::: marker marks all PCN packets with an admission-stop (AS) codepoint if ::: the PCN traffic rate on a link exceeds its admissible rate (AR) and ::: when it exceeds its supportable rate (SR), it marks some of those ::: packets exceeding SR with an excess-traffic (ET) codepoint. The flows ::: with ET-marked packets will be terminated until the aggregate PCN ::: traffic on the path decreases below its SR. This document proposes ::: metering and marking mechanisms for these objectives.
---
paper_title: PCN-based marked flow termination

paper_content:

Pre-congestion notification (PCN) uses packet metering and marking to notify boundary nodes of a Differentiated Services IP network if configured rate thresholds have been exceeded on some links. This feedback is used for PCN-based admission control and flow termination. While admission control is rather well understood, flow termination is a new flow control function and useful especially in case of failures or during flash crowds. We present marked flow termination as a new class of termination algorithms which terminate overload traffic gradually and that work well with multipath routing. We study their termination behavior, give recommendation for their configuration, and discuss their benefits and shortcomings.
---
paper_title: PCN-based marked flow termination

paper_content:

Pre-congestion notification (PCN) uses packet metering and marking to notify boundary nodes of a Differentiated Services IP network if configured rate thresholds have been exceeded on some links. This feedback is used for PCN-based admission control and flow termination. While admission control is rather well understood, flow termination is a new flow control function and useful especially in case of failures or during flash crowds. We present marked flow termination as a new class of termination algorithms which terminate overload traffic gradually and that work well with multipath routing. We study their termination behavior, give recommendation for their configuration, and discuss their benefits and shortcomings.
---
paper_title: Marking Conversion for Pre-Congestion Notification

paper_content:

Pre-congestion notification (PCN) defines admissible rates (AR) and supportable rates (SR) per link and marks the PCN traffic rate above these thresholds as AR- or SR-overload. The IETF standardizes simple mechanisms for admission control (AC) and flow termination (FT) based on this PCN-feedback for high-priority DiffServ traffic. While admission control (AC) has been extensively discussed in the literature, flow termination (FT) is a new control function. In this paper we propose an algorithm that converts marked AR-overload into marked SR-overload by unmarking appropriate packets. Classic marked flow termination (MFT) is based on marked SR-overload and works well even with a small number of PCN flows per ingress-egress aggregate and in case of multipath routing. Thanks to the new marking converter MFT also works with marked AR-overload so that a single marking scheme suffices to support AC and FT. We investigate whether MFT with marking conversion based on AR-overload retains the benefits classic MFT.
---
paper_title: PCN-Based Flow Termination with Multiple Bottleneck Links

paper_content:

Pre-congestion notification (PCN) is a new packet marking scheme based on which simple measurement-based admission control (AC) and flow termination (FT) are implemented. FT is useful for traffic management in unexpected events, e.g., when admitted flows lead to overload on a link after rerouting which may be due to a link or node failure. While AC is a classic flow control function, FT is new and only little understood so far. The limited literature on FT focuses mainly on a single overloaded link. However, when a link or node fails, redirected traffic is likely to cause overload on multiple backup links (bottlenecks) at the same time. As the packet marking probability for flows traversing multiple bottlenecks is larger than for flows traversing only the most severe bottleneck, more traffic is possibly terminated than needed, i.e. overtermination occurs. This paper quantifies potential overtermination in case of multiple bottlenecks for different FT mechanisms which are currently discussed by the IETF.
---
paper_title: Marking Conversion for Pre-Congestion Notification

paper_content:

Pre-congestion notification (PCN) defines admissible rates (AR) and supportable rates (SR) per link and marks the PCN traffic rate above these thresholds as AR- or SR-overload. The IETF standardizes simple mechanisms for admission control (AC) and flow termination (FT) based on this PCN-feedback for high-priority DiffServ traffic. While admission control (AC) has been extensively discussed in the literature, flow termination (FT) is a new control function. In this paper we propose an algorithm that converts marked AR-overload into marked SR-overload by unmarking appropriate packets. Classic marked flow termination (MFT) is based on marked SR-overload and works well even with a small number of PCN flows per ingress-egress aggregate and in case of multipath routing. Thanks to the new marking converter MFT also works with marked AR-overload so that a single marking scheme suffices to support AC and FT. We investigate whether MFT with marking conversion based on AR-overload retains the benefits classic MFT.
---
paper_title: PCN-based marked flow termination

paper_content:

Pre-congestion notification (PCN) uses packet metering and marking to notify boundary nodes of a Differentiated Services IP network if configured rate thresholds have been exceeded on some links. This feedback is used for PCN-based admission control and flow termination. While admission control is rather well understood, flow termination is a new flow control function and useful especially in case of failures or during flash crowds. We present marked flow termination as a new class of termination algorithms which terminate overload traffic gradually and that work well with multipath routing. We study their termination behavior, give recommendation for their configuration, and discuss their benefits and shortcomings.
---
paper_title: An edge-to-edge Deployment Model for Pre-Congestion Notification: Admission Control over a DiffServ Region

paper_content:

This document describes a deployment model for pre-congestion notification (PCN) operating in a large DiffServ-based region of the Internet. PCN-based admission control protects the quality of service of existing flows in normal circumstances, whilst if necessary (eg after a large failure) pre-emption of some flows preserves the quality ::: of service of the remaining flows. Each link has a configured-admission-rate and a configured-pre-emption-rate, and a router marks packets that exceed these rates. Hence routers give an early warning of their own potential congestion, before packets need to be dropped. ::: Gateways around the edges of the PCN-region convert measurements of packet rates and their markings into decisions about whether to admit new flows, and (if necessary) into the rate of excess traffic that ::: should be pre-empted. Per-flow admission states are kept at the gateways only, while the PCN markers that are required for all routers operate on the aggregate traffic - hence there is no scalability impact on interior routers.
---
paper_title: Pre-Congestion Notification marking

paper_content:

Pre-Congestion Notification (PCN) builds on the concepts of RFC 3168, ::: "The addition of Explicit Congestion Notification to IP". However, ::: Pre-Congestion Notification aims at providing notification before any ::: congestion actually occurs. Pre-Congestion Notification is applied to ::: real-time flows (such as voice, video and multimedia streaming) in ::: DiffServ networks. As described in [CL-DEPLOY], it enables "pre" ::: congestion control through two procedures, flow admission control and ::: flow pre-emption. The draft proposes algorithms that determine when a ::: PCN-enabled router writes Admission Marking and Pre-emption Marking in ::: a packet header, depending on the traffic level. The draft also ::: proposes how to encode these markings. We present simulation results ::: with PCN working in an edge-to-edge scenario using the marking ::: algorithms described. Other marking algorithms will be investigated in ::: the future.
---
paper_title: PCN Boundary Node Behaviour for the Controlled Load (CL) Mode of Operation

paper_content:

Precongestion notification (PCN) is a means for protecting quality of ::: service for inelastic traffic admitted to a Diffserv domain. The ::: overall PCN architecture is described in ID.PCNArch. This memo is one ::: of a series describing possible boundary node behaviours for a PCN ::: domain. The behaviour described here is that for three-state ::: measurement-based load control, known informally as CL. The ::: requirement for three encoding states means that CL is for ::: experimental use only pending further standards action.
---
paper_title: Performance Evaluation of Pre-Congestion Notification

paper_content:

Pre-Congestion Notification (PCN) has been proposed at IETF as a framework for scalable measurement-based admission control (MBAC) for a DiffServ-capable network domain. PCN encompasses two functions: admission control of new flows and termination of admitted flows when the available capacity is unexpectedly reduced after a network failure. While there has been extensive research on MBAC, our goal is to understand practical limitations of the specific admission algorithms proposed for PCN and to understand the properties of the termination algorithms of which little is known from prior research.
---
paper_title: Three State PCN Marking

paper_content:

This document proposes metering and marking mechanisms for PCN- ::: enabled nodes to label packets with pre-congestion information. The ::: marker marks all PCN packets with an admission-stop (AS) codepoint if ::: the PCN traffic rate on a link exceeds its admissible rate (AR) and ::: when it exceeds its supportable rate (SR), it marks some of those ::: packets exceeding SR with an excess-traffic (ET) codepoint. The flows ::: with ET-marked packets will be terminated until the aggregate PCN ::: traffic on the path decreases below its SR. This document proposes ::: metering and marking mechanisms for these objectives.
---
paper_title: Pre-Congestion Notification Using Packet-Specific Dual Marking

paper_content:

Pre-congestion notification (PCN) uses packet metering and marking within a PCN domain to notify PCN egress nodes about high load regimes in the network. One question is how to encode the PCN markings in packet headers. The problem is that the IPv4 packet header is short of available codepoints and that tunnelling mechanisms constrain solutions. This paper proposes packet-specific dual marking (PSDM) as a new encoding scheme that avoids these problems and also explains how to apply it to achieve PCN-based admission control and flow termination. Therefore, our proposal may improve the deployability of PCN in spite of the limited extensibility of the current Internet architecture.
---
paper_title: Single PCN Threshold Marking by using PCN baseline encoding for both admission and termination controls

paper_content:

This document proposes an algorithm for marking and metering by using ::: pre-congestion notification (PCN) baseline encoding for both flow ::: admission and flow termination. The proposed algorithm uses threshold ::: marking whose TBthreshold.threshold is set to the number of bits of a ::: metered-packet smaller than the token bucket size. Another threshold ::: for the token bucket is required to change the marking. frequency. ::: Under the flow termination state, all the packets are to be threshold- ::: marked. Under the admission stop state, 1/Nth of packets are to be ::: threshold-marked when the meter indicates. We evaluates the ::: performance of the proposed algorithm by simulations. Our simulation ::: indicates that the performance is almost the same as that of the ::: CL[I-D.briscoe-tsvwg-cl-architecture] algorithm.
---
paper_title: LC-PCN: The Load Control PCN Solution

paper_content:

There is an increased interest of simple and scalable resource provisioning solution for Diffserv network. The Load Control PCN (LC-PCN) addresses the following issues: ::: o Admission Control for real time data flows in stateless Diffserv Domains ::: o Flow Termination: Termination of flows in case of exceptional events, such as severe congestion after re-routing. ::: Admission control in a Diffserv stateless domain is a combination of: ::: o Probing, whereby a probe packet is sent along the forwarding path in a network to determine whether a flow can be admitted based upon the current congestion state of the network ::: o Admission Control based on data marking, whereby in congestion situations the data packets are marked to notify the PCN-egress-node that a congestion occurred on a particular PCN-ingress-node to PCN-egress-node path. ::: ::: The scheme provides the capability of controlling the traffic load in the network without requiring signaling or any per-flow processing in the PCN-interior-nodes. The complexity of Load Control is kept to a minimum to make implementation simple.
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Title: A Survey of PCN-Based Admission Control and Flow Termination

Section 1: HISTORIC ROOTS OF PCN AND RELATED WORK
Description 1: Review the historic roots and related work, including Random Early Detection (RED), Explicit Congestion Notification (ECN), and stateless core concepts for Admission Control (AC).

Section 2: PCN-BASED FLOW CONTROL
Description 2: Explain the basic idea of PCN-based Admission Control (AC) and Flow Termination (FT), and discuss its application in the Internet.

Section 3: METERING AND MARKING
Description 3: Present the metering and marking algorithms used to detect pre-congestion in a PCN domain.

Section 4: ENCODING OPTIONS FOR PCN MARKING
Description 4: Discuss the encoding schemes for recording PCN marks in the IP header and address related issues and constraints.

Section 5: PCN-BASED ADMISSION CONTROL (AC)
Description 5: Review various methods for PCN-based Admission Control (AC), including probe-based AC and Ingress-Egress-Aggregate-Based AC.

Section 6: PCN-BASED FLOW TERMINATION (FT)
Description 6: Present the methods for PCN-based Flow Termination (FT) and discuss their mechanisms and related problems.

Section 7: EXISTING PROPOSALS
Description 7: Review various proposals for PCN-based AC and FT presented in the IETF, highlighting their benefits and shortcomings.

Section 8: SUMMARY AND DISCUSSION OF FT METHODS
Description 8: Provide a summary and discussion of the presented Flow Termination (FT) methods, including comparisons and their behavior under different conditions.