Hot-potato Routing Research Articles

Deflection routing mechanism using BLESS and BBUS NoC

Buffer is a very crucial component in giving performance of an Network on Chip (NoC). In short buffers governs the performance of an NoC. But the major problem with Buffers is that they are power hungry. In these paper two types of deflection Routers have been discussed. One is BLESS (Buffer less Router) where total ordering sorting circuits is followed by a sequential port allocation while in second one total ordering is replaced with Golden Flit Concept. BLESS NoC includes hot potato routing including free live lock. As compared to normal VC Routers we are eliminating three stage sorting circuit. Rather than going for sequential port allocation we are going for parallel port allocation called as permutation deflection logic. Golden Flit concept together with permutation deflection logic is responsible for reduction of 29% of Routers Critical Path. Also clock based synchronization in CHIPPER based NoCs increases latency. To avoid this issue BBus NoC (Broadcast bus NoC) concept is discussed. The worst case latency is reduced by using Golden Flit concept.

Conversations with a pioneer: Paul Baran in his own words

ABSTRACTThis interview is based on two conversations the author had with Paul Baran in 2004 and 2010. The 2010 conversation represents one of last times Baran participated in an interview before his death in March 2011. Topics discussed include how Baran drew upon inspiration from Warren McCulloch's work on neural networks to bring distributedness to communication networks and how this led to Hot Potato Routing, which later became known as packet switching. The latter, being an foundational part of Internet technology, has placed Paul Baran firmly in the histories of networking and the Internet, even if the origins of packet switching are hotly contested – a topic that is also discussed in the conversations. Finally, Baran also shares his views on technological development and determinism and what the future for the Internet holds.

Bus Based Synchronization Method for CHIPPER Based NoC

Network on Chip (NoC) reduces the communication delay of System on Chip (SoC). The main limitation of NoC is power consumption and area overhead. Bufferless NoC reduces the area complexity and power consumption by eliminating buffers in the traditional routers. The bufferless NoC design should include live lock freeness since they use hot potato routing. This increases the complexity of bufferless NoC design. Among the available propositions to reduce this complexity, CHIPPER based bufferless NoC is considered as one of the best options. Live lock freeness is provided in CHIPPER through golden epoch and golden packet. All routers follow some synchronization method to identify a golden packet. Clock based method is intuitively followed for synchronization in CHIPPER based NoCs. It is shown in this work that the worst-case latency of packets is unbearably high when the above synchronization is followed. To alleviate this problem, broadcast bus NoC (BBus NoC) approach is proposed in this work. The proposed method decreases the worst-case latency of packets by increasing the golden epoch rate of CHIPPER.

Exploring Heterogeneous NoC Design Space in Heterogeneous GPU-CPU Architectures

Computer architecture is transiting from the multicore era into the heterogeneous era in which heterogeneous architectures use on-chip networks to access shared resources and how a network is configured will likely have a significant impact on overall performance and power consumption. Recently, heterogeneous network on chip (NoC) has been proposed not only to achieve performance comparable to that of the NoCs with buffered routers but also to reduce buffer cost and energy consumption. However, heterogeneous NoC design for heterogeneous GPU-CPU architectures has not been studied in depth. This paper first evaluates the performance and power consumption of a variety of static hot-potato based heterogeneous NoCs with different buffered and bufferless router placements, which is helpful to explore the design space for heterogeneous GPU-CPU interconnection. Then it proposes Unidirectional Flow Control (UFC), a simple credit-based flow control mechanism for heterogeneous NoC in GPU-CPU architectures to control network congestion. UFC can guarantee that there are always unoccupied entries in buffered routers to receive flits coming from adjacent bufferless routers. Our evaluations show that when compared to hot-potato routing, UFC improves performance by an average of 14.1% with energy increased by an average of 5.3% only.

A novel framework to mitigate the negative impacts of green techniques on BGP

Green networking techniques usually shut down the least utilized links and/or routers during off-peaks hours. In a prior work, we showed conclusively that these actions trigger what is known as hot-potato routing changes. These changes are well known to negatively impact the operation of the Border Gateway Protocol (BGP). Critically, they may cause packet loss due to slow BGP convergence and increased congestion. In order to overcome such negative impacts, in this paper, we propose a novel framework that allows Ingress Routers (IRs) to work collaboratively to determine the set of links that should be carrying their respective traffic to Egress Routers (ERs). IRs exchange information about their established paths with each other, and each IR determines whether to shift their existing paths to ERs to optimize a given objective, e.g., energy savings. The IRs repeat the process until convergence. Unused links are then shut down, and thereby, lowering the energy consumption rate of a network. In this framework, we study a number of key issues: first, we study the order in which IRs establish paths, namely (i) most savings, (ii) round robin, and (iii) random order. Our results show that similar performance is achieved regardless of employed method. However, in some cases, IRs that establish paths using round robin took up to 23% more time to converge than IRs that used the most savings method. Second, we study path selection metrics. In particular, IRs select paths according to (i) shortest path, where paths with the minimum number of hops are selected, (ii) longest path, where paths with the largest number of hops are preferred, and (iii) random, where paths are randomly selected. Our experimental results over five topologies show that using shortest paths is the most efficient where IRs use as little as 25% more active links than a global optimal solution. However, IRs establishing paths in a robin manner are able to utilize 5% fewer number of links than when they employ the shortest path to each ER.

Multi‐topology routing based egress selection approach to achieve hybrid intra‐AS and inter‐AS traffic engineering

SummaryHot‐potato routing is a border gateway protocol policy that selects the ‘closest’ egress router in terms of interior gateway protocol cost. This policy imposes inherent interactions between intra‐AS (Autonomous System) and inter‐AS traffic engineering. In light of this observation, we present a hybrid intra‐AS and inter‐AS traffic engineering scheme named egress selection based upon hot potato routing. This scheme involves link weight optimization, which can not only minimize the time that IP (Internet Protocol) packets travel across the network by assigning specified egress router but also balance the load among the internal links of the transit network. Egress selection based upon hot potato routing also incorporates multi‐topology routing technique to address the problem that one set of link weights might not guarantee specified egress routers. Accordingly, we formulate the link weights optimization problem using multi‐topology routing as a mixed integer linear programming model. And we present a new heuristic algorithm to make the problem tractable. Numerical results show that only a few topologies are needed to guarantee specified egress router, and maximum link utilization is also reduced. Copyright © 2014 John Wiley & Sons, Ltd.

ES-TMP: Inter-Domain Egress Selection Based on Traffic Migration Prediction

Hot-potato routing is commonly used to break tie among multiple equally-good exit points associating with inter-domain BGP routes. However, hot-potato routing only takes the network control plane into consideration, where it provides the routers the possibility of enabling early exit of traffic using barely protocol-related information of IGP distance. In this paper, we argue that egress selection of inter-domain routing should pay more attention to traffic forwarding, because the large traffic migration caused by egress change, although not quite often, can degrade the network performance or even make the network crash. We propose Egress Selection based on Traffic Migration Prediction (ES-TMP). We use traffic demand to predict the traffic migration, which is used as important criteria for egress selection. If the volume of traffic migration is large, ES-TMP keeps the egress unchanged. Otherwise, the small traffic migration enables the routers use the closest egress without apparent influence on network performance. ES-TMP can either be implemented with standard BGP protocol or by dedicated servers to perform global routing optimization.

Resilient Inter-Carrier Traffic Engineering for Internet Peering Interconnections

We present a novel resilient routing policy for controlling the routing across peering links between Internet carriers. Our policy is aimed at offering more dependability and better performance to the routing decision with respect to the current practice (e.g., hot-potato routing). Our work relies on a non-cooperative game framework, called Peering Equilibrium MultiPath (PEMP), that has been recently proposed. PEMP allows two carrier providers to coordinate a multipath route selection for critical flows across peering links, while preserving their respective interests and independence. In this paper, we propose a resilient PEMP execution policy accounting for the occurrence of potential impairments (traffic matrix variations, intra-AS and peering link failures) that may occur in both peering networks. We mathematically define how to produce robust equilibrium sets and describe how to appropriately react to unexpected network impairments that might take place. The results from extensive simulations show that, under a realistic failure scenario, our policy adaptively prevents from peering link congestions and excessive route deviations after failures.

Cooperative Interdomain Traffic Engineering Using Nash Bargaining and Decomposition

We present a novel approach to interdomain traffic engineering based on the concepts of Nash bargaining and dual decomposition. Under this scheme, ISPs use an iterative procedure to jointly optimize a social cost function, referred to as the Nash product. We show that the global optimization problem can be separated into subproblems by introducing appropriate shadow prices on the interdomain flows. These subproblems can then be solved independently and in a decentralized manner by the individual ISPs. Our approach does not require the ISPs to share any sensitive internal information, such as network topology or link weights. More importantly, our approach is provably Pareto-efficient and fair. Therefore, we believe that our approach is highly amenable to adoption by ISPs when compared to past approaches. We also conduct simulation studies of our approach over several real ISP topologies. Our evaluation shows that the approach converges quickly, offers equitable performance improvements to ISPs, is significantly better than unilateral approaches (e.g., hot-potato routing) and offers the same performance as a centralized solution with full knowledge.

Impact of Hot-Potato Routing Changes in IP Networks

Despite the architectural separation between intradomain and interdomain routing in the Internet, intradomain protocols do influence the path-selection process in the Border Gateway Protocol (BGP). When choosing between multiple equally-good BGP routes, a router selects the one with the closest egress point, based on the intradomain path cost. Under such hot-potato routing, an intradomain event can trigger BGP routing changes. To characterize the influence of hot-potato routing, we propose a technique for associating BGP routing changes with events visible in the intradomain protocol, and apply our algorithm to a tier-1 ISP backbone network. We show that (i) BGP updates can lag 60 seconds or more behind the intradomain event; (ii) the number of BGP path changes triggered by hot-potato routing has a nearly uniform distribution across destination prefixes; and (iii) the fraction of BGP messages triggered by intradomain changes varies significantly across time and router locations. We show that hot-potato routing changes lead to longer delays in forwarding-plane convergence, shifts in the flow of traffic to neighboring domains, extra externally-visible BGP update messages, and inaccuracies in Internet performance measurements.

Combined intra- and inter-domain traffic engineering using hot-potato aware link weights optimization

A well-known approach to intradomain traffic engineering consists in finding the set of link weights that minimizes a network-wide objective function for a given intradomain traffic matrix. This approach is inadequate because it ignores a potential impact on interdomain routing due to hot-potato routing policies. This may result in changes in the intradomain traffic matrix that have not been anticipated by the link weights optimizer, possibly leading to degraded network performance. We propose a BGP-aware link weights optimization method that takes these hot-potato effects into account. This method uses the interdomain traffic matrix and other available BGP data, to extend the intradomain topology with external virtual nodes and links, on which all the well-tuned heuristics of a classical link weights optimizer can be applied. Our method can also optimize the traffic on the interdomain peering links.

In search for an appropriate granularity to model routing policies

Routing policies are typically partitioned into a few classes that capture the most common practices in use today[1]. Unfortunately, it is known that the reality of routing policies[2] and peering relationships is far more complex than those few classes[1,3]. We take the next step of searching for the appropriate granularity at which policies should be modeled. For this purpose, we study how and where to configure per-prefix policies in an AS-level model of the Internet, such that the selected paths in the model are consistent with those observed in BGP data from multiple vantage points. By comparing business relationships with per-prefix filters, we investigate the role and limitations of business relationships as a model for policies. We observe that popular locations for filtering correspond to valleys where no path should be propagated according to inferred business relationships. This result reinforces the validity of the valley-free property used for business relationships inference. However, given the sometimes large path diversity ASs have, business relationships do not contain enough information to decide which path will be chosen as the best. To model how individual ASs choose their best paths, we introduce a new abstraction: next-hop atoms . Next-hop atoms capture the different sets of neighboring ASs an AS uses for its best routes. We show that a large fraction of next-hop atoms correspond to per-neighbor path choices. A non-negligible fraction of path choices, however, correspond to hot-potato routing and tie-breaking within the BGP decision process, very detailed aspects of Internet routing.

TIE Breaking: Tunable Interdomain Egress Selection

In a large backbone network, the routers often have multiple egress points they could use to direct traffic toward an external destination. Today's routers select the ldquoclosestrdquo egress point, based on the intradomain routing configuration, in a practice known as early-exit or hot-potato routing. In this paper, we argue that hot-potato routing is restrictive, disruptive, and convoluted and propose an alternative called TIE (Tunable Interdomain Egress selection). TIE is a flexible mechanism that allows routers to select the egress point for each destination prefix based on both the intradomain topology and the goals of the network administrators. In fact, TIE is designed from the start with optimization in mind, to satisfy diverse requirements for traffic engineering and network robustness. We present two example optimization problems that use integer-programming and multicommodity-flow techniques, respectively, to tune the TIE mechanism to satisfy networkwide objectives. Experiments with traffic, topology, and routing data from two backbone networks demonstrate that our solution is both simple (for the routers) and expressive (for the network administrators).

Traffic Engineering an Operational Network with the TOTEM Toolbox

We explain how the TOTEM toolbox can be used to engineer an operational network. TOTEM is an open source TOolbox for Traffic Engineering Methods which covers IP- based and MPLS-based intradomain traffic engineering (TE) algorithms, but also interdomain TE. In this paper, we use the toolbox as an off-line simulator to optimise the traffic of an operational network. To help an operator choose between an IP-based or MPLS-based solution, or find the best way to load- balance a network for a given traffic, our case study compares several IP and MPLS routing algorithms, evaluates the impact of hot-potato routing on the intradomain traffic matrix, and analyses the worst-case link failure. This study reveals the power of a toolbox that federates many traffic engineering algorithms.

Network sensitivity to hot-potato disruptions

Hot-potato routing is a mechanism employed when there are multiple (equally good) interdomain routes available for a given destination. In this scenario, the Border Gateway Protocol (BGP) selects the interdomain route associated with the closest egress point based upon intradomain path costs. Consequently, intradomain routing changes can impact interdomain routing and cause abrupt swings of external routes, which we call hot-potato disruptions . Recent work has shown that hot-potato disruptions can have a substantial impact on large ISP backbones and thereby jeopardize the network robustness. As a result, there is a need for guidelines and tools to assist in the design of networks that minimize hot-potato disruptions. However, developing these tools is challenging due to the complex and subtle nature of the interactions between exterior and interior routing. In this paper, we address these challenges using an analytic model of hot-potato routing that incorporates metrics to evaluate network sensitivity to hot-potato disruptions. We then present a methodology for computing these metrics using measurements of real ISP networks. We demonstrate the utility of our model by analyzing the sensitivity of a large AS in a tier~1 ISP network.

Dynamics of hot-potato routing in IP networks

Despite the architectural separation between intradomain and interdomain routing in the Internet, intradomain protocols do influence the path-selection process in the Border Gateway Protocol (BGP). When choosing between multiple equally-good BGP routes, a router selects the one with the closest egress point, based on the intradomain path cost. Under such hot-potato routing, an intradomain event can trigger BGP routing changes. To characterize the influence of hot-potato routing, we conduct controlled experiments with a commercial router. Then, we propose a technique for associating BGP routing changes with events visible in the intradomain protocol, and apply our algorithm to AT&T's backbone network. We show that (i) hot-potato routing can be a significant source of BGP updates, (ii) BGP updates can lag 60 seconds or more behind the intradomain event, (iii) the number of BGP path changes triggered by hot-potato routing has a nearly uniform distribution across destination prefixes, and (iv) the fraction of BGP messages triggered by intradomain changes varies significantly across time and router locations. We show that hot-potato routing changes lead to longer delays in forwarding-plane convergence, shifts in the flow of traffic to neighboring domains, extra externally-visible BGP update messages, and inaccuracies in Internet performance measurements.

Õ(Congestion + Dilation) Hot-Potato Routing on Leveled Networks

We study packet routing problems, in which we are given a set of N packets which will be sent on preselected paths with congestion C and dilation D. For store-and-forward routing, in which nodes have buffers for packets in transit, there are routing algorithms with a performance that matches the lower bound Ω(C+D). Motivated from optical networks, we study hot-potato routing in which the nodes are bufferless. Due to the lack of buffers, in hot-potato routing the packets may be delayed more than in store-and-forward routing. An interesting question is how much is the performance of routing algorithms affected by the absence of buffers.Here, we answer this question for the class of leveled networks, in which the nodes are partitioned into L+1 distinct levels. We present a randomized hot-potato routing algorithm for leveled networks, which routes the packets in O((C + L) ln9 (LN)) time with high probability. For routing problems with dilation Ω(L), and where N is a polynonial in L, this bound is within polylogarithmic factors of the lower bound Ω(C+L). Our algorithm demonstrates that for such routing problems the benefit from using buffers is no more than polylogarithmic; thus, hot-potato routing is an efficient way to route packets in leveled networks.In hot-potato routing, due to the lack of buffers, the packets may not be able to remain on their preselected paths during the course of routing (while in store-and-forward routing the packets remain on their preselected paths). However, in our algorithm the actual path that each packet follows contains its original preselected path; thus the lower bound Ω(C+L) is also a lower bound for the new paths. Our algorithm is distributed, that is, routing decisions are taken locally at each node while packets are routed in the network. To our knowledge, this is the first hot-potato algorithm designed and analyzed, in terms of congestion and dilation, for leveled networks.

Performance of wavelength-convertible multihop optical ShuffleNets employing convolutional coding under hot-potato routing

Performance analysis is carried out for a multihop optical ShuffleNet with full wavelength conversion to evaluate the effect of wavelength converters on the bit-error-rate (BER) and packet-error-rate (PER) performance. Computed results show that there is a significant decrease in BER with an increase in the number of wavelength converters nw for the same transmitter power. Further, an increase of nw is needed at increased network load g; for example, to achieve the maximum throughput, nw ≈ 10 and nw ≈ 20 are needed corresponding to g = 0.5 and g = 1.0. It is found that when convolutional coding is applied, the required number of wavelength converters is greatly reduced at the full load g = 1.0.

Wait-free deflection routing of long messages

In order to obtain the lowest possible latency, routing algorithms should try to avoid a message waiting for resources (network links) blocked by other messages or multiplexing of more messages over one physical channel. This requirement becomes especially important in the case of long messages. The only type of protocols able to guarantee waiting free routing under heavy load are algorithms based on deflection (also called nonminimal adaptive or hot potato) routing. This paper deals with problems connected with the use of deflection algorithms. In contrast to the case of nonadaptive or partially (e.g., minimal) adaptive routing, it is very infrequent that an unrestricted deflection routing becomes deadlocked and, similarly, livelock is not a serious problem. On the other hand, there is another phenomenon, called a deflection jam, that limits throughput of deflection algorithms used to route long messages. It has been observed for many deflection heuristics, interconnection network topologies, and both virtual cut-through and wormhole routing. A deflection jam is a sudden and persistent saturation of a network which sometimes occur, after a very long period of undisturbed communication. This paper describes events that trigger this saturation which suggest ways to design improved and stable deflection routing algorithms.

Networks on which hot-potato routing does not livelock

Hot-potato routing is a form of synchronous routing which makes no use of buffers at intermediate nodes. Packets must move at every time step, until they reach their destination. If contention prevents a packet from taking its preferred outgoing edge, it is deflected on a different edge. Two simple design principles for hot potato routing algorithms are minimum advance, that advances at least one packet towards its destination from every nonempty node (and possibly deflects all other packets), and maximum advance, that advances the maximum possible number of packets. Livelock is a situation in which packets keep moving indefinitely in the network without any packet ever reaching its destination. It is known that even maximum advance algorithms might livelock on some networks. We show that minimum advance algorithms never livelock on tree networks, and that maximum advance algorithms never livelock on triangulated networks.