A lookup algorithm based on multiple tables for high-speed routers

Address lookup is one of the main functions of the Internet routers and a very important feature in evaluating router performance. As the Internet traffic keeps growing and the number of routing table entries is continuously growing, efficient address-lookup mechanism is essential. In recent years, various fast address-lookup schemes have been proposed, but most of those schemes are not practical in terms of the memory size required for routing table and the complexity required in table update. In this paper, we have proposed a parallel IP address lookup architecture based on multiple hashing. The proposed scheme has advantages in required memory size, the number of memory accesses, and table update. We have evaluated the performance of the proposed scheme through simulation using data from MAE-WEST router. The simulation result shows that the proposed scheme requires a single memory access for the address lookup of each route when 203 kbytes of memory and a few-hundred-entry TCAM are used.

Continuing growth in traffic, the size of routing table as well as the link speeds puts great challenge on the performance of Internet address lookup. The packet forwarding engine need perform 150 million IP address lookups per second for a 100Gbps line card while accommodating up to 500,000 prefixes and very likely 1M in the near future. TCAM based lookup solutions do not scale well for the next-generation due to its high power dissipation and large footprint. Algorithmic solutions can achieve high throughputs with hardware parallelism and compact storage needs, but can hardly scale simultaneously in the three dimensions of increased table size, throughput, and prefix length as IP moves to 64 bit IPv6 addresses. We propose a novel IPv6 lookup algorithm called Prefix Range Based Binary Search (PRB-BS) using binary search over hash tables organized by the range of prefix length. By eliminating the path information of the subtrie our scheme reduces the memory demands considerably. Besides, the binary search scheme based on prefix range reduces the worst case time of hash lookups to log2L, with L being the number of subtrie layers. We also introduce asymmetry binary search to further reduce memory demands and memory accesses. Compared with the tree bitmap algorithm widely used by many modern routers the memory requirements of PRB-BS algorithm is about 55% of the tree bitmap algorithm. The experiment results also show that the average search depth of PRB-BS algorithm is stable at 2 with the increased number of prefixes, which reflects better scalability of PRB-BS algorithm.

Ternary Content-Addressable Memory (TCAM) is a popular hardware device for fast IP address lookup. High link transmission speed of Internet backbone demands more powerful IP address lookup engine. Restricted by the memory access speed, the lookup engine for next-generation routers demands exploiting parallelism among multiple TCAM chips. In this paper, we propose a fast lookup and power-saving scheme which can almost make full use of TCAM chips' capability. With N parallel TCAM chips, the scheme can achieve a worst-case speedup factor of (N−1)∗90% in cache-update state, and a worst-case speedup factor of N∗90% in normal work state.

This paper considers the collision resolution algorithm when multiple packets transmit simultaneously in each slot in a non-orthogonal multiple access (NOMA) systems. Packets are divided into two groups and two different received powers can be selected. Packets in each group can select one power level as their received power. As more than one packet may transmit in a time slot in each group, collision will happen and throughput may decrease at the same time. We introduce the collision resolution period (CRP) algorithm and the collided packets will transmit in the CRP. By controlling the transmission probability in each group, we can make a big different comparing to the system without a CRP. This paper will show the optimal transmission probability and the maximum throughput. Numerical results show that our proposed algorithm yields the maximum throughput of 0.6489.

최근 HFC(Hybrid Fiber Coax) CATV 망이 초고속망의 하부구조로 자리를 잡아가고 있다. HFC-CATV 망의 상향채널은 가입자에서 헤드엔드로 데이터 전송시 500가입자 이상이 공유하기 때문에 충돌이 발생하게 된다. 특히, 음성, 비디오 그리고 데이터와 같은 다양한 종류의 트래픽 QoS(Qualify of Service)를 만족시키기 위해서 서비스별로 우선순위를 고려한 알고리즘이 요구되어진다. IEEE 802.14에서 제안된 우선순위 기반 3진 트리(Ternary tree)알고리즘은 정적 PNA(Priority New Access) 슬롯 구조를 가진다. 이 방법은 실시간으로 변화하는 트래픽의 요구 지연(request delay)이 높게 유지되며 서로 다른 우선순위 트래픽의 요구 경쟁 확률이 동일하다는 문제점을 가지고 있다. 따라서, 본 논문에서는 동적 PNA(Priority New Access) 슬롯 구조를 제안하여 높은 우선순위 트래픽의 요구지연을 낮게 하고 새로운 스테이션에 대해 우선순위 별로 경쟁 확률을 다르게 하는 알고리즘을 제안한다. 동일한 조건하에 두 알고리즘에 대해 요구지연 값을 비교 분석하였다. 성능 분석 결과 동적 PNA 우선순위 충돌해결알고리즘이 정적 PNA 우선순위 충돌해결알고리즘보다 낮은 요구지연을 가진다는 것을 확인할 수 있었다. Recently, the HFC-CATV network stand in a substructure of superhighway information network. Because of sharing up to 500 of subscribes, the Collision Resolution Algorithm needs in the upstream channel of HFC-CATV network. In order to provide Quality of Service (QoS) to users with real-time data such as voice, video and interactive service, the research of Collision Resolution Algorithm must include an effective priority scheme. In IEEE 802.14, the Collision Resolution Algorithm has high request delay because of static PNA(Priority New Access) slots structure and different priority traffics with the same probability. In order to resolve this problem, this paper proposed dynamic priority collision resolution algorithm with ternary tree algorithm. It has low request delay according to an increase of traffic load because high priority traffic first resolve and new traffic content with different probability. In the result of the simulation, it demonstrated that the proposed algorithm needs lower request delay than that of ternary tree algorithm with static PNA slots structure.

In the field of networking, storing and fast lookup from the large amount of data are two important measures. Hashing is one of the well-known techniques for indexing and retrieving data from the database efficiently. It is mostly used for fast lookups in the fields which require quick results from the database. As the size of the database increases, the number of collisions in the hash table also increases which handled through collision resolution techniques. Traditional algorithms like Separate Chaining, Linear Probing, and Quadratic probing takes linear search time. The tremendous increase of data in recent years requires more profound hash table implementation. In this paper, we have proposed a new and innovative way of implementing hash table to handle collisions more efficiently in logarithmic time i.e. M-N Hashing. To handle the collisions with a scalable sized hash table, the proposed algorithm used the concept of the AVL tree. The performance of the proposed algorithm is analyzed using continuous integer dataset that varies from 0 to 100000. Through experiments, it is depicted that M-N hashing improved the search time up to 99.97% with respect to contemporary algorithms i.e. Separate Chaining, Linear Probing, and Quadratic probing.

Collision resolution for buffered users

The performance of hybrid random-access systems (HRAS) which use a combination of multiuser codes (MUC) and collision resolution algorithms (CRA) to accommodate the bursty transmissions of many independent users on a single communication channel is analyzed. Besides the computation of the system throughput, another contribution of this paper is the determination of the properties which a MUC must possess such that resulting HRAS performs better than a system which is only based on CRA'S.

A fast IPv6 route lookup scheme implemented by hardware is proposed in this paper. It supports a fast IP address lookup and can insert and delete the prefixes effectively. A novel compressed multibit trie algorithm that decreases the memory space occupied and the average searching time is applied. The scheme proposed in this paper is superior to other IPV6 route lookup ones, for example, by using SRAM pipeline, a lookup speed of 125 x 10 6 per second can be realized to satisfy 40Gbps optical link rate with only 1.9Mbyte consumption of memory space. As there is no actual IPv6 route prefix, we generate various simulation databases in which prefix length distribution is different. Simulation results show that our scheme has reasonable lookup time, memory space for all the prefix length distribution.

Extended Minkowski Portal Refinement Algorithm for Coherent Collision Resolution in Time-marching Dynamical Simulations

As traffic on the Internet has increased exponentially, it is vital that Internet routers handle the received packets faster. When a router receives a packet, it has to make a decision where to send it next. To forward an IP packet, the routers need to lookup the destination address of the received packet in the forwarding table, implement forwarding algorithms, then forward the packet to the appropriate next hop or outgoing port. We discuss a parallel approach that combines an IP packet forwarding technique based on a partitioned lookup table with linear search on prefix lengths, binary search on prefix lengths, and LC (level-compressed) trie. Simulation results show that the proposed partition schemes speeds up the IP address lookup process.

In automated warehouses, teams of mobile robots fulfill the packaging process by transferring inventory pods to designated workstations while navigating narrow aisles formed by tightly packed pods. This problem is typically modeled as a Multi-Agent Pickup and Delivery (MAPD) problem, which is then solved by repeatedly planning collision-free paths for agents on a fixed graph, as in the Rolling-Horizon Collision Resolution (RHCR) algorithm. However, existing approaches make the limiting assumption that agents are only allowed to move pods that correspond to their current task, while considering the other pods as stationary obstacles (even though all pods are movable). This behavior can result in unnecessarily long paths which could otherwise be avoided by opening additional corridors via pod manipulation. To this end, we explore the implications of allowing agents the flexibility of dynamically relocating pods. We call this new challenging problem Terraforming MAPD (tMAPD) and develop an RHCR-based approach to tackle it. As the extra flexibility of terraforming comes at a significant computational cost, we utilize this capability judiciously by identifying situations where it could make a significant impact on the solution quality. In particular, we invoke terraforming in response to disruptions that often occur in automated warehouses, e.g., when an item is dropped from a pod or when agents malfunction. Empirically, using our approach for tMAPD, where disruptions are modeled via a stochastic process, we improve throughput by over 10%, reduce the maximum service time (the difference between the drop-off time and the pickup time of a pod) by more than 50%, without drastically increasing the runtime, compared to the MAPD setting.

In Lifelong Multi-Agent Path Finding (L-MAPF) a team of agents performs a stream of tasks consisting of multiple locations to be visited by the agents on a shared graph while avoiding collisions with one another. L-MAPF is typically tackled by partitioning it into multiple consecutive, and hence similar, "one-shot" MAPF queries, as in the Rolling-Horizon Collision Resolution (RHCR) algorithm. Therefore, a solution to one query informs the next query, which leads to similarity with respect to the agents' start and goal positions, and how collisions need to be resolved from one query to the next. Thus, experience from solving one MAPF query can potentially be used to speedup solving the next one. Despite this intuition, current L-MAPF planners solve consecutive MAPF queries from scratch. In this paper, we introduce a new RHCR-inspired approach called exRHCR, which exploits experience in its constituent MAPF queries. In particular, exRHCR employs an extension of Priority-Based Search (PBS), a state-of-the-art MAPF solver. The extension, which we call exPBS, allows to warm-start the search with the priorities between agents used by PBS in the previous MAPF instances. We demonstrate empirically that exRHCR solves L-MAPF instances up to 39% faster than RHCR, and has the potential to increase system throughput for given task streams by increasing the number of agents a planner can cope with for a given time budget.

This paper considers time-domain equalization of fading channels for multicarrier systems with channels whose delay spread exceeds the length of the cyclic prefix. We propose to apply Regalia's Finite Interval Constant Modulus Algorithm, which directly minimizes the constant modulus criterion for finite data sets, to the output of a single sub-carrier. This results in a blind adaptive channel shortening technique which is used to design a time-domain finite impulse response equalizer or channel shortener, whose goal is to compress the overall channel impulse response to within the length of the cyclic prefix. Simulation results are provided in terms of bit error rate (BER) in the context of wireless systems.

In this paper we propose and evaluate several protocols for a random access channel. The channel is divided into a control subchannel which is used to inform all users of the approximate times of arrival of new packets and a data subchannel which is used to transmit the data. Packets arriving at different users at approximately the same time may cause a collision on the control subchannel. Such collisions are resolved on the data subchannel by a collision resolution algorithm. Eight protocols that differ in the feedback available on both channels and the time that the feedback is available are described and evaluated. The expected delay of each protocol is determined by modeling the system as a slotted concentrator. Comparisons are made among the protocols described and analyzed in this paper and between these protocols and other protocols that have been studied previously.