http://www.maths.qmul.ac.uk/%7Elatora/report_06.pdf

Complex networks: Structure and dynamics

Mobile ad hoc routing protocols allow nodes with wireless adaptors to communicate with one another without any pre-existing network infrastructure. Existing ad hoc routing protocols, while robust to rapidly changing network topology, assume the presence of a connected path from source to destination. Given power limitations, the advent of short-range wireless networks, and the wide physical conditions over which ad hoc networks must be deployed, in some scenarios it is likely that this assumption is invalid. In this work, we develop techniques to deliver messages in the case where there is never a connected path from source to destination or when a network partition exists at the time a message is originated. To this end, we introduce Epidemic Routing, where random pair-wise exchanges of messages among mobile hosts ensure eventual message delivery. The goals of Epidemic Routing are to: i) maximize message delivery rate, ii) minimize message latency, and iii) minimize the total resources consumed in message delivery. Through an implementation in the Monarch simulator, we show that Epidemic Routing achieves eventual delivery of 100% of messages with reasonable aggregate resource consumption in a number of interesting scenarios.

/pdf/epidemic-routing-for-partially-connected-ad-hoc-networks-s5rslcaiip.pdf

Epidemic routing for partially-connected ad hoc networks

Fabric is a modular and extensible open-source system for deploying and operating permissioned blockchains and one of the Hyperledger projects hosted by the Linux Foundation (www.hyperledger.org). Fabric is the first truly extensible blockchain system for running distributed applications. It supports modular consensus protocols, which allows the system to be tailored to particular use cases and trust models. Fabric is also the first blockchain system that runs distributed applications written in standard, general-purpose programming languages, without systemic dependency on a native cryptocurrency. This stands in sharp contrast to existing block-chain platforms that require "smart-contracts" to be written in domain-specific languages or rely on a cryptocurrency. Fabric realizes the permissioned model using a portable notion of membership, which may be integrated with industry-standard identity management. To support such flexibility, Fabric introduces an entirely novel blockchain design and revamps the way blockchains cope with non-determinism, resource exhaustion, and performance attacks. This paper describes Fabric, its architecture, the rationale behind various design decisions, its most prominent implementation aspects, as well as its distributed application programming model. We further evaluate Fabric by implementing and benchmarking a Bitcoin-inspired digital currency. We show that Fabric achieves end-to-end throughput of more than 3500 transactions per second in certain popular deployment configurations, with sub-second latency, scaling well to over 100 peers.

https://dl.acm.org/doi/pdf/10.1145/3190508.3190538

Hyperledger fabric: a distributed operating system for permissioned blockchains

We consider the problem of routing in intermittently connected networks. In such networks there is no guarantee that a fully connected path between source and destination exist at any time, rendering traditional routing protocols unable to deliver messages between hosts. We propose a probabilistic routing protocol for such networks.

/pdf/probabilistic-routing-in-intermittently-connected-networks-4bq5tjuqc9.pdf

Probabilistic routing in intermittently connected networks

In this paper, we present a family of adaptive protocols, called SPIN (Sensor Protocols for Information via Negotiation), that efficiently disseminates information among sensors in an energy-constrained wireless sensor network. Nodes running a SPIN communication protocol name their data using high-level data descriptors, called meta-data. They use meta-data negotiations to eliminate the transmission of redundant data throughout the network. In addition, SPIN nodes can base their communication decisions both upon application-specific knowledge of the data and upon knowledge of the resources that are available to them. This allows the sensors to efficiently distribute data given a limited energy supply. We simulate and analyze the performance of two specific SPIN protocols, comparing them to other possible approaches and a theoretically optimal protocol. We find that the SPIN protocols can deliver 60% more data for a given amount of energy than conventional approaches. We also find that, in terms of dissemination rate and energy usage, the SPlN protocols perform close to the theoretical optimum.

/pdf/adaptive-protocols-for-information-dissemination-in-wireless-2lo594hki6.pdf

Adaptive protocols for information dissemination in wireless sensor networks

Whru a dilt~lhSC is replicated at, many sites2 maintaining mutual consistrnry among t,he sites iu the fac:e of updat,es is a signitirant problem. This paper descrikrs several randomized algorit,hms for dist,rihut.ing updates and driving t,he replicas toward consist,c>nc,y. The algorit Inns are very simple and require few guarant,ees from the underlying conllllunicat.ioll system, yc+ they rnsutc t.hat. the off(~c~t, of (‘very update is evcnt,uwlly rf+irt-ted in a11 rq1ica.s. The cost, and parformancc of t,hr algorithms arc tuned I>? c%oosing appropriat,c dist,rilMions in t,hc randoinizat,ioii step. TIN> idgoritlmls ilr(’ c*los~*ly analogoIls t,o epidemics, and t,he epidcWliolog)litc\ratiirc, ilitlh iii Illld~~rsti4lldill~ tlicir bc*liavior. One of tlW i$,oritlims 11&S brc>n implrmcWrd in the Clraringhousr sprv(brs of thr Xerox C’orporat~c~ Iiitcrnc4, solviiig long-standing prol>lf~lns of high traffic and tlatirl>ilsr inconsistcllcp.

http://bitsavers.informatik.uni-stuttgart.de/pdf/xerox/parc/techReports/CSL-89-1_Epidemic_Algorithms_for_Replicated_Database_Maintenance.pdf

Epidemic algorithms for replicated database maintenance

When a database is replicated at many sites, maintaining mutual consistency among the sites in the face of updates is a significant problem. This paper describes several randomized algorithms for distributing updates and driving the replicas toward consistency. The algorithms are very simple and require few guarantees from the underlying communication system, yet they ensure that the effect of every update is eventually reflected in all replicas. The cost and performance of the algorithms are tuned by choosing appropriate distributions in the randomization step. The algorithms are closely analogous to epidemics, and the epidemiology literature aids in understanding their behavior. One of the algorithms has been implemented in the Clearinghouse servers of the Xerox Corporate Internet. solving long-standing problems of high traffic and database inconsistency.

The voice manager in the Etherphone system provides facilities for recording, editing, and playing stored voice in a distributed personal-computing environment. It provides the basis for applications such as voice mail, annotation of multimedia documents, and voice editing using standard text-editing techniques. To facilitate sharing, the voice manager stores voice on a special voice file server that is accessible via the local internet. Operations for editing a passage of recorded voice simply build persistent data structures to represent the edited voice. These data structures, implementing an abstraction called voice ropes, are stored in a server database and consist of lists of intervals within voice files. Clients refer to voice ropes solely by reference. Interests, additional persistent data structures maintained by the server, serve two purposes: First, they provide a sort of directory service for managing the voice ropes that have been created. More importantly, they provide a reliable reference-counting mechanism, permitting the garbage collection of voice ropes that are no longer needed. These interests are grouped into classes; for some important classes, obsolete interests can be detected and deleted by a class-specific algorithm that runs periodically.

Managing stored voice in the Etherphone system

The Etherphone™ system was developed at Xerox PARC to explore methods of integrating voice into existing distributed personal computing environments. An important component of the Etherphone system, the voice manager, provides operations for recording, playing, editing, and otherwise manipulating digitized voice based on an abstraction that we call voice ropes. It was designed to allow:unrestricted use of voice in client applications,sharing among various clients,editing of voice by programs,integration of diverse workstations into the system,security at least as good as that of conventional file servers, andautomatic reclamation of the storage occupied by unneeded voice. As with text, we want the ability to incorporate voice easily into electronic mail messages, voice-annotated documents, user interfaces, and other interactive applications. Because the characteristics of voice differ greatly from those of text, special mechanisms are required for managing and sharing stored voice. The voice manager reduces the work generally associated with building voice applications by providing a convenient set of application-independent abstractions for stored voice.Clients view voice ropes as immutable sequences of voice samples referenced by unique identifiers. In actuality, a voice rope consists of a list of intervals within voice files that are stored on a special voice file server. A database stores the many-to-many relationships that exist between voice ropes and files. Maintaining voice on a publicly accessible server facilitates sharing among various clients.These facilities for managing stored voice in the Etherphone system were designed with the intent of moving voice data as little as possible. Once recorded in the voice file server, voice is never copied until a workstation sends a play request; at this point the voice is transmitted directly to an Etherphone, a microprocessor-based telephone instrument. In particular, although workstations initiate most of the operations in the Etherphone system, there is little reason for them to receive the actual voice data since they have no way of playing it.Adding such voice facilities to a diverse and complex software base presents challenging problems to the systems builder since much of the existing workstation and server software cannot be changed or extended. Manipulating stored voice solely by textual references, besides allowing efficient sharing and resource management, has made it easy to integrate voice into documents. The only requirements placed on a workstation in order to make use of the voice services are that it have an associated Etherphone and an RPC implementation.The Etherphone system uses secure RPC for all control functions and DES encryption for transmitted voice. These ensure the privacy of voice communication, which is important even in a research environment, although the network is inherently vulnerable to interception of information. Storing the voice in its encrypted form protects the voice on the server and also means that the voice need not be reencrypted when played. All in all, the voice manager provides better security than most conventional file servers.The performance of operations for editing and managing recorded voice must be compatible with human response times: sub-second response at a peak rate of several operations per second is more than adequate. Performance measurements confirm that the voice manager easily meets these requirements.In conclusion, the major technical contributions presented in this paper involve the use of simple databases to:describe the results of editing operations such that existing voice passages need not be moved, copied, or decrypted, andprovide a modified style of reference counting that allows the automatic reclamation of obsolete voice. Approximately 50 Etherphones are in daily use in the Computer Science Laboratory at Xerox PARC. We have had a voice mail system running since 1984 and a prototype voice editor available for demonstrations and experimental use since the spring of 1986.

Dan Swinehart

Papers

Epidemic algorithms for replicated database maintenance

Epidemic algorithms for replicated database maintenance

Managing stored voice in the Etherphone system

Managing stored voice in the etherphone system