User Datagram Protocol

Résumé

Le User Datagram Protocol (UDP, en français protocole de datagramme utilisateur) est un des principaux protocoles de télécommunication utilisés par Internet. Il fait partie de la couche transport du modèle OSI, quatrième couche de ce modèle, comme TCP. Il a été défini en 1980 par et est détaillé dans la . Le rôle de ce protocole est de permettre la transmission de données (sous forme de datagrammes) de manière très simple entre deux entités, chacune étant définie par une adresse IP et un numéro de port. Aucune communication préalable n'est requise pour établir la connexion, au contraire de TCP (qui utilise le procédé de handshaking). UDP utilise un mode de transmission sans connexion. L'intégrité des données est assurée par une somme de contrôle sur l'en-tête. L'utilisation de cette somme est cependant facultative en IPv4 mais obligatoire avec IPv6. Si un hôte n'a pas calculé la somme de contrôle d'un datagramme émis, la valeur de celle-ci est fixée à zéro. La somme de contrôle in

Source officielle

https://fr.wikipedia.org/wiki/User_Datagram_Protocol

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Evaluating Latency of Distributed Algorithms Using Petri Nets

Nicoleta Sergent

Evaluating Latency of Distributed Algorithms Using Petri Nets N. Sergent The time it takes to a distributed algorithm to finish (the distributed algorithm latency) cannot be directly measured in asynchronous systems if the algorithm starts and ends on different processors, since the system has no global time. A simple method to evaluate this latency is to build and simulate a unified model which includes the network and the distributed algorithm sub-models. In this paper we introduce a network model for UDP (User Datagram Protocol) which allows to establish a relationship between the number of messages exchanged in a distributed algorithm and the communication delays. As an application, we consider the two-phase commitment algorithm. Numerical results derived from simulating the model are compared with data obtained from performance measures.

1997

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, , , ,

Remote Procedure Calls are widely used to connect datacenter applications with strict tail-latency service level objectives in the scale of µs. Existing solutions utilize streaming or datagram-based transport protocols for RPCs that impose overheads and limit the design flexibility. Our work exposes the RPC abstraction to the endpoints and the network, making RPCs first-class datacenter citizens and allowing for in-network RPC scheduling. We propose R2P2, a UDP-based transport protocol specifically designed for RPCs inside a datacenter. R2P2 exposes pairs of requests and responses and allows efficient and scalable RPC routing by separating the RPC target selection from request and reply streaming. Leveraging R2P2, we implement a novel join-bounded-shortest-queue (JBSQ) RPC load balancing policy, which lowers tail latency by centralizing pending RPCs in the router and ensures that requests are only routed to servers with a bounded number of outstanding requests. The R2P2 router logic can be implemented either in a software middlebox or within a P4 switch ASIC pipeline. Our evaluation, using a range of microbenchmarks, shows that the protocol is suitable for µs-scale RPCs and that its tail latency outperforms both random selection and classic HTTP reverse proxies. The P4-based implementation of R2P2 on a Tofino ASIC adds less than 1µs of latency whereas the software middlebox implementation adds 5µs latency and requires only two CPU cores to route RPCs at 10 Gbps linerate. R2P2 improves the tail latency of web index searching on a cluster of 16 workers operating at 50% of capacity by 5.7× over NGINX. R2P2 improves the throughput of the Redis key-value store on a 4-node cluster with master/slave replication for a tail-latency service-level objective of 200µs by more than 4.8× vs. vanilla Redis.

USENIX ASSOC2019

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Frugal Event Dissemination in a Mobile Environment

Rachid Guerraoui

This paper describes an event dissemination algorithm that implements a topic-based publish/subscribe interaction abstraction in mobile ad-hoc networks (MANETs). Our algorithm is frugal in two senses. First, it reduces the total number of duplicates and parasite events received by the subscribers. Second, both the mobility of the publishers and the subscribers, as well as the validity periods of the events, are exploited to achieve a high level of dissemination reliability with a thrifty usage of the memory and bandwidth. Besides, our algorithm is inherently portable and does not assume any underlying routing protocol. We give simulation results of our algorithms in the two most popular mobility models: city section and random waypoint. We highlight interesting empirical lower bounds on the minimal validity period of any given event to ensure its reliable dissemination.

2005

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