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Saturday, February 4, 2023

Alcohol intoxication

From Wikipedia, the free encyclopedia

Alcohol intoxication
Other namesDrunkenness, ethanol intoxication
Michelangelo drunken Noah.jpg
The Drunkenness of Noah by Michelangelo, 1509
SpecialtyToxicology, psychiatry
SymptomsMild: Mild sedation, decreased coordination
Moderate: Slurred speech, trouble walking, vomiting
Severe: Decreased effort to breathe, coma
ComplicationsSeizures, aspiration pneumonia, injuries, low blood sugar
Usual onsetOver minutes to hours
DurationSeveral hours
CausesEthanol (alcohol)
Risk factorsSocial environment, impulsivity, alcoholism
Diagnostic methodTypically based on history of events and physical examination
Differential diagnosisHepatic encephalopathy, Wernicke encephalopathy, methanol toxicity, meningitis, traumatic brain injury
TreatmentSupportive care
FrequencyVery common (especially in the Western world)
Deathsc. 2,200 per year (U.S.)

Alcohol intoxication, also known as alcohol poisoning, commonly described as drunkenness or inebriation, is the negative behavior and physical effects caused by a recent consumption of alcohol. In addition to the toxicity of ethanol, the main psychoactive component of alcoholic beverages, other physiological symptoms may arise from the activity of acetaldehyde, a metabolite of alcohol. These effects may not arise until hours after ingestion and may contribute to the condition colloquially known as a hangover.

Symptoms of intoxication at lower doses may include mild sedation and poor coordination. At higher doses, there may be slurred speech, trouble walking, and vomiting. Extreme doses may result in a respiratory depression, coma, or death. Complications may include seizures, aspiration pneumonia, injuries including suicide, and low blood sugar. Alcohol intoxication can lead to alcohol-related crime with perpetrators more likely to be intoxicated than victims.

Alcohol intoxication typically begins after two or more alcoholic drinks. Risk factors include a social situation where heavy drinking is common and a person having an impulsive personality. Diagnosis is usually based on the history of events and physical examination. Verification of events by witnesses may be useful. Legally, alcohol intoxication is often defined as a blood alcohol concentration (BAC) of greater than 5.4–17.4 mmol/L (25–80 mg/dL or 0.025–0.080%). This can be measured by blood or breath testing. Alcohol is broken down in the human body at a rate of about 3.3 mmol/L (15 mg/dL) per hour, depending on an individual's metabolic rate (metabolism).

Management of alcohol intoxication involves supportive care. Typically this includes putting the person in the recovery position, keeping the person warm, and making sure breathing is sufficient. Gastric lavage and activated charcoal have not been found to be useful. Repeated assessments may be required to rule out other potential causes of a person's symptoms.

Acute intoxication has been documented throughout history, and alcohol remains one of the world's most widespread recreational drugs. Some religions consider alcohol intoxication to be a sin.

Symptoms

Wine is a Mocker by Jan Steen c. 1663

Alcohol intoxication leads to negative health effects due to the recent drinking of ethanol (alcohol). When severe it may become a medical emergency. Some effects of alcohol intoxication, such as euphoria and lowered social inhibition, are central to alcohol's desirability.

Pathophysiology

Stage Three of the Five stages of inebriation, c. 1863–1868, by Charles Percy Pickering

Alcohol is metabolized by a normal liver at the rate of about 8 grams of pure ethanol per hour. 8 grams or 10 mL (0.34 US fl oz) is one British standard unit. An "abnormal" liver with conditions such as hepatitis, cirrhosis, gall bladder disease, and cancer is likely to result in a slower rate of metabolism.

Ethanol is metabolised to acetaldehyde by alcohol dehydrogenase (ADH), which is found in many tissues, including the gastric mucosa. Acetaldehyde is metabolised to acetate by acetaldehyde dehydrogenase (ALDH), which is found predominantly in liver mitochondria. Acetate is used by the muscle cells to produce acetyl-CoA using the enzyme acetyl-CoA synthetase, and the acetyl-CoA is then used in the citric acid cycle.

As drinking increases, people become sleepy or fall into a stupor. After a very high level of consumption, the respiratory system becomes depressed and the person will stop breathing. Comatose patients may aspirate their vomit (resulting in vomitus in the lungs, which may cause "drowning" and later pneumonia if survived). CNS depression and impaired motor coordination along with poor judgment increase the likelihood of accidental injury occurring. It is estimated that about one-third of alcohol-related deaths are due to accidents and another 14% are from intentional injury.

In addition to respiratory failure and accidents caused by its effects on the central nervous system, alcohol causes significant metabolic derangements. Hypoglycaemia occurs due to ethanol's inhibition of gluconeogenesis, especially in children, and may cause lactic acidosis, ketoacidosis, and acute kidney injury. Metabolic acidosis is compounded by respiratory failure. Patients may also present with hypothermia.

Mechanism

In the past, alcohol was believed to be a non-specific pharmacological agent affecting many neurotransmitter systems in the brain. However, molecular pharmacology studies have shown that alcohol has only a few primary targets. In some systems, these effects are facilitatory, and in others inhibitory.

Among the neurotransmitter systems with enhanced functions are: GABAA, 5-HT3 receptor agonism (responsible for GABAergic (GABAA receptor PAM), glycinergic, and cholinergic effects), nicotinic acetylcholine receptors.

Among those that are inhibited are: NMDA, dihydropyridine-sensitive L-type Ca2+ channels and G-protein-activated inwardly rectifying K+ channels.

Alcohol is also converted into phosphatidylethanol (a lipid metabolite) by phospholipase D2, and this metabolite has been shown to directly bind to and regulate ion channels. The result of these direct effects is a wave of further indirect effects involving a variety of other neurotransmitter and neuropeptide systems, leading finally to the behavioural or symptomatic effects of alcohol intoxication.

The order in which different types of alcoholic beverages are consumed ("Grape or grain but never the twain" and "Beer before wine and you'll feel fine; wine before beer and you'll feel queer") does not have any effect.

GABAA receptors

Ethanol binding to GABAA receptor

Many of the effects of activating GABAA receptors have the same effects as that of ethanol consumption. Some of these effects include anxiolytic, anticonvulsant, sedative, and hypnotic effects, cognitive impairment, and motor incoordination. This correlation between activating GABAA receptors and the effects of ethanol consumption have led to the study of ethanol and its effects on GABAA receptors. It has been shown that ethanol does in fact exhibit positive allosteric binding properties to GABAA receptors. However, its effects are limited to pentamers containing the δ-subunit rather than the γ-subunit. GABAA receptors containing the δ-subunit have been shown to be located exterior to the synapse and are involved with tonic inhibition rather than its γ-subunit counterpart, which is involved in phasic inhibition. The δ-subunit has been shown to be able to form the allosteric binding site which makes GABAA receptors containing the δ-subunit more sensitive to ethanol concentrations, even to moderate social ethanol consumption levels (30mM). While it has been shown by Santhakumar et al. that GABAA receptors containing the δ-subunit are sensitive to ethanol modulation, depending on subunit combinations receptors could be more or less sensitive to ethanol. It has been shown that GABAA receptors that contain both δ and β3-subunits display increased sensitivity to ethanol. One such receptor that exhibits ethanol insensitivity is α3-β6-δ GABAA. It has also been shown that subunit combination is not the only thing that contributes to ethanol sensitivity. Location of GABAA receptors within the synapse may also contribute to ethanol sensitivity.

Diagnosis

Alcohol intoxication is described as a mental and behavioural disorder by the International Classification of Diseases. (ICD-10). Definitive diagnosis relies on a blood test for alcohol, usually performed as part of a toxicology screen. Law enforcement officers in the United States and other countries often use breathalyzer units and field sobriety tests as more convenient and rapid alternatives to blood tests. There are also various models of breathalyzer units that are available for consumer use. Because these may have varying reliability and may produce different results than the tests used for law-enforcement purposes, the results from such devices should be conservatively interpreted.

Many informal intoxication tests exist, which, in general, are unreliable and not recommended as deterrents to excessive intoxication or as indicators of the safety of activities such as motor vehicle driving, heavy equipment operation, machine tool use, etc.

For determining whether someone is intoxicated by alcohol by some means other than a blood-alcohol test, it is necessary to rule out other conditions such as hypoglycemia, stroke, usage of other intoxicants, mental health issues, and so on. It is best if their behavior has been observed while the subject is sober to establish a baseline. Several well-known criteria can be used to establish a probable diagnosis. For a physician in the acute-treatment setting, acute alcohol intoxication can mimic other acute neurological disorders or is frequently combined with other recreational drugs that complicate diagnosis and treatment.

Management

Acute alcohol poisoning is a medical emergency due to the risk of death from respiratory depression or aspiration of vomit if vomiting occurs while the person is unresponsive. Emergency treatment strives to stabilize and maintain an open airway and sufficient breathing while waiting for the alcohol to metabolize. This can be done by removal of any vomit or, if the person is unconscious or has impaired gag reflex, intubation of the trachea.

Other measures may include

  • Administer the vitamin thiamine to prevent Wernicke–Korsakoff syndrome, which can cause a seizure (more usually a treatment for chronic alcoholism, but in the acute context usually co-administered to ensure maximal benefit).
  • Hemodialysis if the blood concentration is very high at >130  mmol/L (>600 mg/dL)
  • Provide oxygen therapy as needed via nasal cannula or non-rebreather mask.
  • Treat low blood sugar, with intravenous sugar solutions as ethanol-induced low blood sugar unresponsive to glucagon.
  • While the medication metadoxine may speed the breakdown of alcohol, use in alcohol intoxication requires further study as of 2017. It is approved in a number of countries in Europe, as well as India and Brazil.

Additional medication may be indicated for treatment of nausea, tremor, and anxiety.

Clinical findings

Hospital admissions

Alcohol intoxication was found to be prevalent in clinical populations within the United States involving people treated for trauma and in the age group of people aged within their 18th - 24th years (in a study of a group for the years 1999 - 2004). In the United States during the years 2010 - 2012, acute intoxication was found to be the direct cause of an average of 2,221 deaths, in the sample group of those aged within their 15th year or older. The same mortality route is thought to cause indirectly more than 30,000 deaths per year.

Prognosis

A normal liver detoxifies the blood of alcohol over a period of time that depends on the initial level and the patient's overall physical condition. An abnormal liver will take longer but still succeeds, provided the alcohol does not cause liver failure.

People having drunk heavily for several days or weeks may have withdrawal symptoms after the acute intoxication has subsided.

A person consuming a dangerous amount of alcohol persistently can develop memory blackouts and idiosyncratic intoxication or pathological drunkenness symptoms.

Long-term persistent consumption of excessive amounts of alcohol can cause liver damage and have other deleterious health effects.

Society and culture

A 1936 anti-drinking poster by Aart van Dobbenburgh

Alcohol intoxication is a risk factor in some cases of catastrophic injury, in particular for unsupervised recreational activity. A study in the province of Ontario based on epidemiological data from 1986, 1989, 1992, and 1995 states that 79.2% of the 2,154 catastrophic injuries recorded for the study were preventable, of which 346 (17%) involved alcohol consumption. The activities most commonly associated with alcohol-related catastrophic injury were snowmobiling (124), fishing (41), diving (40), boating (31) and canoeing (7), swimming (31), riding an all-terrain vehicle (24), and cycling (23).[48] These events are often associated with unsupervised young males, often inexperienced in the activity, and may result in drowning. Alcohol use is also associated with unsafe sex.

Legal issues

A drunk-driving simulator in Montreal

Laws on drunkenness vary. In the United States, it is a criminal offense for a person to be drunk while driving a motorized vehicle, except in Wisconsin, where it is only a fine for the first offense. It is also a criminal offense to fly an aircraft or (in some American states) to assemble or operate an amusement park ride while drunk. Similar laws also exist in the United Kingdom and most other countries.

In some countries, it is also an offense to serve alcohol to an already-intoxicated person, and, often, alcohol can be sold only by persons qualified to serve responsibly through alcohol server training.

The blood alcohol content (BAC) for legal operation of a vehicle is typically measured as a percentage of a unit volume of blood. This percentage ranges from 0.00% in Romania and the United Arab Emirates; to 0.05% in Australia, South Africa, Germany, Scotland, and New Zealand (0.00% for underage individuals); to 0.08% in England and Wales, the United States and Canada.

The United States Federal Aviation Administration prohibits crew members from performing their duties within eight hours of consuming an alcoholic beverage, while under the influence of alcohol, or with a BAC greater than 0.04%.

In the United States, the United Kingdom, and Australia, public intoxication is a crime (also known as "being drunk and disorderly" or "being drunk and incapable").

In some countries, there are special facilities, sometimes known as "drunk tanks", for the temporary detention of persons found to be drunk.

Religious views

Christianity

Some religious groups permit the consumption of alcohol; some permit consumption but prohibit intoxication; others prohibit any amount of alcohol consumption altogether. Many denominations of Christianity, such as Catholicism, Orthodoxy and Lutheranism, use wine as a part of the Eucharist and permit its consumption, but consider it sinful to become intoxicated.

In the Bible, the Book of Proverbs contains several chapters related to the negative effects of drunkenness and warns to stay away from intoxicating beverages. The Book of Genesis refers to the use of wine by Lot's daughters to rape him. The Book of Leviticus tells the story of Nadab and Abihu, the eldest sons of Aaron, who were killed for serving in the Temple in Jerusalem after drinking wine, presumably while intoxicated. It continues to discuss monasticism, in which drinking wine is prohibited. The story of Samson in the Book of Judges tells of a monk from the Israelite tribe of Dan who is prohibited from cutting his hair and drinking wine. Romans 13:13–14, 1 Corinthians 6:9–11, Galatians 5:19–21 and Ephesians 5:18 are among a number of other Bible passages that speak against intoxication. While Proverbs 31:4 warns against kings and other rulers drinking wine and similar alcoholic beverages, Proverbs 31:6–7 promotes giving such beverages to the perishing and wine to those whose lives are bitter as a coping mechanism against the likes of poverty and other troubles.

Some Protestant Christian denominations prohibit the consumption of alcohol based upon biblical passages that condemn drunkenness, but others allow a moderate rate of consumption.

In the Church of Jesus Christ of Latter-day Saints, alcohol consumption is forbidden, and teetotalism has become a distinguishing feature of its members. Jehovah's Witnesses allow moderate alcohol consumption among its members.

Islam

In the Quran, there is a prohibition on the consumption of grape-based alcoholic beverages, and intoxication is considered an abomination in the hadith of Muhammad. The schools of thought of Islamic jurisprudence have interpreted this as a strict prohibition of the consumption of all types of alcohol and declared it to be haram (lit.'forbidden [in Islam]'), although other uses may be permitted.

Buddhism

In Buddhism, in general, the consumption of intoxicants is discouraged for both monastics and lay followers. Many Buddhists observe a basic code of ethics known as the five precepts, of which the fifth precept is an undertaking to refrain from the consumption of intoxicating substances (except for medical reasons). In the bodhisattva vows of the Brahmajala Sutra, observed by Mahayana Buddhist communities, distribution of intoxicants is likewise discouraged, as well as consumption.

Hinduism

In the Gaudiya Vaishnavism branch of Hinduism, one of the four regulative principles forbids the taking of intoxicants, including alcohol.

Judaism

Drunken Lot and his daughters, from an illustrated Torah

In Judaism, in accordance with the biblical stance against drinking, wine drinking is not permitted for priests and monks. The biblical command to sanctify the Sabbath and other holidays has been interpreted as having three ceremonial meals with wine or grape juice, known as Kiddush. A number of Jewish marriage ceremonies end with the bride and groom drinking a shared cup of wine after reciting seven blessings; this occurs after a fasting day in some Ashkenazi traditions. It has been customary and in many cases even mandated to drink moderately so as to stay sober, and only after the prayers are over.

During the Seder on Passover, there is an obligation to drink four ceremonial cups of wine while reciting the Haggadah. It has been assumed as the source of the wine-drinking ritual at communion in some Christian groups. During Purim, there is an obligation to become intoxicated; however, as with many other decrees, this has been avoided in many communities by allowing sleep during the day as a replacement.

During the U.S. Prohibition era in the 1920s, a rabbi from the Reform Judaism movement proposed using grape juice for the ritual instead of wine. Although refuted at first, the practice became widely accepted by orthodox Jews as well.

Other animals

In the movie Animals are Beautiful People, an entire section was dedicated to showing many different animals including monkeys, elephants, hogs, giraffes, and ostriches, eating over-ripe marula tree fruit causing them to sway and lose their footing in a manner similar to human drunkenness. Birds may become intoxicated with fermented berries and some die colliding with hard objects when flying under the influence.

In elephant warfare, practiced by the Greeks during the Maccabean revolt and by Hannibal during the Punic wars, it has been recorded that the elephants would be given wine before the attack, and only then would they charge forward after being agitated by their driver.

It is a regular practice to give small amounts of beer to race horses in Ireland. Ruminant farm animals have natural fermentation occurring in their stomach, and adding alcoholic beverages in small amounts to their drink will generally do them no harm, and will not cause them to become drunk.

Alcoholic beverages are extremely harmful to dogs, and often for reasons of additives such as xylitol, an artificial sweetener in some mixers. Dogs can absorb ethyl alcohol in dangerous amounts through their skin as well as through drinking the liquid or consuming it in foods. Even fermenting bread dough can be dangerous to dogs. In 1999, one of the royal footmen for Britain's Queen Elizabeth II was demoted from Buckingham Palace due to his "party trick" of spiking the meals and drinks of the Queen's pet corgi dogs with alcohol which in turn would lead the dogs to run around drunk.

Peer-to-peer

From Wikipedia, the free encyclopedia
A peer-to-peer (P2P) network in which interconnected nodes ("peers") share resources amongst each other without the use of a centralized administrative system
 
A network based on the client–server model, where individual clients request services and resources from centralized servers

Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the network. They are said to form a peer-to-peer network of nodes.

Peers make a portion of their resources, such as processing power, disk storage or network bandwidth, directly available to other network participants, without the need for central coordination by servers or stable hosts. Peers are both suppliers and consumers of resources, in contrast to the traditional client–server model in which the consumption and supply of resources are divided.

While P2P systems had previously been used in many application domains, the architecture was popularized by the file sharing system Napster, originally released in 1999. The concept has inspired new structures and philosophies in many areas of human interaction. In such social contexts, peer-to-peer as a meme refers to the egalitarian social networking that has emerged throughout society, enabled by Internet technologies in general.

Historical development

SETI@home was established in 1999

While P2P systems had previously been used in many application domains, the concept was popularized by file sharing systems such as the music-sharing application Napster (originally released in 1999). The peer-to-peer movement allowed millions of Internet users to connect "directly, forming groups and collaborating to become user-created search engines, virtual supercomputers, and filesystems." The basic concept of peer-to-peer computing was envisioned in earlier software systems and networking discussions, reaching back to principles stated in the first Request for Comments, RFC 1.

Tim Berners-Lee's vision for the World Wide Web was close to a P2P network in that it assumed each user of the web would be an active editor and contributor, creating and linking content to form an interlinked "web" of links. The early Internet was more open than the present day, where two machines connected to the Internet could send packets to each other without firewalls and other security measures. This contrasts to the broadcasting-like structure of the web as it has developed over the years. As a precursor to the Internet, ARPANET was a successful client-server network where "every participating node could request and serve content." However, ARPANET was not self-organized, and it lacked the ability to "provide any means for context or content-based routing beyond 'simple' address-based routing."

Therefore, Usenet, a distributed messaging system that is often described as an early peer-to-peer architecture, was established. It was developed in 1979 as a system that enforces a decentralized model of control. The basic model is a client–server model from the user or client perspective that offers a self-organizing approach to newsgroup servers. However, news servers communicate with one another as peers to propagate Usenet news articles over the entire group of network servers. The same consideration applies to SMTP email in the sense that the core email-relaying network of mail transfer agents has a peer-to-peer character, while the periphery of Email clients and their direct connections is strictly a client-server relationship.

In May 1999, with millions more people on the Internet, Shawn Fanning introduced the music and file-sharing application called Napster. Napster was the beginning of peer-to-peer networks, as we know them today, where "participating users establish a virtual network, entirely independent from the physical network, without having to obey any administrative authorities or restrictions."

Architecture

A peer-to-peer network is designed around the notion of equal peer nodes simultaneously functioning as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the client–server model where communication is usually to and from a central server. A typical example of a file transfer that uses the client-server model is the File Transfer Protocol (FTP) service in which the client and server programs are distinct: the clients initiate the transfer, and the servers satisfy these requests.

Routing and resource discovery

Peer-to-peer networks generally implement some form of virtual overlay network on top of the physical network topology, where the nodes in the overlay form a subset of the nodes in the physical network. Data is still exchanged directly over the underlying TCP/IP network, but at the application layer peers are able to communicate with each other directly, via the logical overlay links (each of which corresponds to a path through the underlying physical network). Overlays are used for indexing and peer discovery, and make the P2P system independent from the physical network topology. Based on how the nodes are linked to each other within the overlay network, and how resources are indexed and located, we can classify networks as unstructured or structured (or as a hybrid between the two).

Unstructured networks

Overlay network diagram for an unstructured P2P network, illustrating the ad hoc nature of the connections between nodes

Unstructured peer-to-peer networks do not impose a particular structure on the overlay network by design, but rather are formed by nodes that randomly form connections to each other. (Gnutella, Gossip, and Kazaa are examples of unstructured P2P protocols).

Because there is no structure globally imposed upon them, unstructured networks are easy to build and allow for localized optimizations to different regions of the overlay. Also, because the role of all peers in the network is the same, unstructured networks are highly robust in the face of high rates of "churn"—that is, when large numbers of peers are frequently joining and leaving the network.

However, the primary limitations of unstructured networks also arise from this lack of structure. In particular, when a peer wants to find a desired piece of data in the network, the search query must be flooded through the network to find as many peers as possible that share the data. Flooding causes a very high amount of signaling traffic in the network, uses more CPU/memory (by requiring every peer to process all search queries), and does not ensure that search queries will always be resolved. Furthermore, since there is no correlation between a peer and the content managed by it, there is no guarantee that flooding will find a peer that has the desired data. Popular content is likely to be available at several peers and any peer searching for it is likely to find the same thing. But if a peer is looking for rare data shared by only a few other peers, then it is highly unlikely that search will be successful.

Structured networks

Overlay network diagram for a structured P2P network, using a distributed hash table (DHT) to identify and locate nodes/resources

In structured peer-to-peer networks the overlay is organized into a specific topology, and the protocol ensures that any node can efficiently search the network for a file/resource, even if the resource is extremely rare.

The most common type of structured P2P networks implement a distributed hash table (DHT), in which a variant of consistent hashing is used to assign ownership of each file to a particular peer. This enables peers to search for resources on the network using a hash table: that is, (key, value) pairs are stored in the DHT, and any participating node can efficiently retrieve the value associated with a given key.

Distributed hash tables

However, in order to route traffic efficiently through the network, nodes in a structured overlay must maintain lists of neighbors that satisfy specific criteria. This makes them less robust in networks with a high rate of churn (i.e. with large numbers of nodes frequently joining and leaving the network). More recent evaluation of P2P resource discovery solutions under real workloads have pointed out several issues in DHT-based solutions such as high cost of advertising/discovering resources and static and dynamic load imbalance.

Notable distributed networks that use DHTs include Tixati, an alternative to BitTorrent's distributed tracker, the Kad network, the Storm botnet, and the YaCy. Some prominent research projects include the Chord project, Kademlia, PAST storage utility, P-Grid, a self-organized and emerging overlay network, and CoopNet content distribution system. DHT-based networks have also been widely utilized for accomplishing efficient resource discovery for grid computing systems, as it aids in resource management and scheduling of applications.

Hybrid models

Hybrid models are a combination of peer-to-peer and client–server models. A common hybrid model is to have a central server that helps peers find each other. Spotify was an example of a hybrid model [until 2014]. There are a variety of hybrid models, all of which make trade-offs between the centralized functionality provided by a structured server/client network and the node equality afforded by the pure peer-to-peer unstructured networks. Currently, hybrid models have better performance than either pure unstructured networks or pure structured networks because certain functions, such as searching, do require a centralized functionality but benefit from the decentralized aggregation of nodes provided by unstructured networks.

CoopNet content distribution system

CoopNet (Cooperative Networking) was a proposed system for off-loading serving to peers who have recently downloaded content, proposed by computer scientists Venkata N. Padmanabhan and Kunwadee Sripanidkulchai, working at Microsoft Research and Carnegie Mellon University. When a server experiences an increase in load it redirects incoming peers to other peers who have agreed to mirror the content, thus off-loading balance from the server. All of the information is retained at the server. This system makes use of the fact that the bottle-neck is most likely in the outgoing bandwidth than the CPU, hence its server-centric design. It assigns peers to other peers who are 'close in IP' to its neighbors [same prefix range] in an attempt to use locality. If multiple peers are found with the same file it designates that the node choose the fastest of its neighbors. Streaming media is transmitted by having clients cache the previous stream, and then transmit it piece-wise to new nodes.

Security and trust

Peer-to-peer systems pose unique challenges from a computer security perspective.

Like any other form of software, P2P applications can contain vulnerabilities. What makes this particularly dangerous for P2P software, however, is that peer-to-peer applications act as servers as well as clients, meaning that they can be more vulnerable to remote exploits.

Routing attacks

Since each node plays a role in routing traffic through the network, malicious users can perform a variety of "routing attacks", or denial of service attacks. Examples of common routing attacks include "incorrect lookup routing" whereby malicious nodes deliberately forward requests incorrectly or return false results, "incorrect routing updates" where malicious nodes corrupt the routing tables of neighboring nodes by sending them false information, and "incorrect routing network partition" where when new nodes are joining they bootstrap via a malicious node, which places the new node in a partition of the network that is populated by other malicious nodes.

Corrupted data and malware

The prevalence of malware varies between different peer-to-peer protocols. Studies analyzing the spread of malware on P2P networks found, for example, that 63% of the answered download requests on the gnutella network contained some form of malware, whereas only 3% of the content on OpenFT contained malware. In both cases, the top three most common types of malware accounted for the large majority of cases (99% in gnutella, and 65% in OpenFT). Another study analyzing traffic on the Kazaa network found that 15% of the 500,000 file sample taken were infected by one or more of the 365 different computer viruses that were tested for.

Corrupted data can also be distributed on P2P networks by modifying files that are already being shared on the network. For example, on the FastTrack network, the RIAA managed to introduce faked chunks into downloads and downloaded files (mostly MP3 files). Files infected with the RIAA virus were unusable afterwards and contained malicious code. The RIAA is also known to have uploaded fake music and movies to P2P networks in order to deter illegal file sharing. Consequently, the P2P networks of today have seen an enormous increase of their security and file verification mechanisms. Modern hashing, chunk verification and different encryption methods have made most networks resistant to almost any type of attack, even when major parts of the respective network have been replaced by faked or nonfunctional hosts.

Resilient and scalable computer networks

The decentralized nature of P2P networks increases robustness because it removes the single point of failure that can be inherent in a client–server based system. As nodes arrive and demand on the system increases, the total capacity of the system also increases, and the likelihood of failure decreases. If one peer on the network fails to function properly, the whole network is not compromised or damaged. In contrast, in a typical client–server architecture, clients share only their demands with the system, but not their resources. In this case, as more clients join the system, fewer resources are available to serve each client, and if the central server fails, the entire network is taken down.

Distributed storage and search

Search results for the query "software libre", using YaCy a free distributed search engine that runs on a peer-to-peer network instead of making requests to centralized index servers (like Google, Yahoo, and other corporate search engines)

There are both advantages and disadvantages in P2P networks related to the topic of data backup, recovery, and availability. In a centralized network, the system administrators are the only forces controlling the availability of files being shared. If the administrators decide to no longer distribute a file, they simply have to remove it from their servers, and it will no longer be available to users. Along with leaving the users powerless in deciding what is distributed throughout the community, this makes the entire system vulnerable to threats and requests from the government and other large forces. For example, YouTube has been pressured by the RIAA, MPAA, and entertainment industry to filter out copyrighted content. Although server-client networks are able to monitor and manage content availability, they can have more stability in the availability of the content they choose to host. A client should not have trouble accessing obscure content that is being shared on a stable centralized network. P2P networks, however, are more unreliable in sharing unpopular files because sharing files in a P2P network requires that at least one node in the network has the requested data, and that node must be able to connect to the node requesting the data. This requirement is occasionally hard to meet because users may delete or stop sharing data at any point.

In this sense, the community of users in a P2P network is completely responsible for deciding what content is available. Unpopular files will eventually disappear and become unavailable as more people stop sharing them. Popular files, however, will be highly and easily distributed. Popular files on a P2P network actually have more stability and availability than files on central networks. In a centralized network, a simple loss of connection between the server and clients is enough to cause a failure, but in P2P networks, the connections between every node must be lost in order to cause a data sharing failure. In a centralized system, the administrators are responsible for all data recovery and backups, while in P2P systems, each node requires its own backup system. Because of the lack of central authority in P2P networks, forces such as the recording industry, RIAA, MPAA, and the government are unable to delete or stop the sharing of content on P2P systems.

Applications

Content delivery

In P2P networks, clients both provide and use resources. This means that unlike client–server systems, the content-serving capacity of peer-to-peer networks can actually increase as more users begin to access the content (especially with protocols such as Bittorrent that require users to share, refer a performance measurement study). This property is one of the major advantages of using P2P networks because it makes the setup and running costs very small for the original content distributor.

File-sharing networks

Many peer-to-peer file sharing networks, such as Gnutella, G2, and the eDonkey network popularized peer-to-peer technologies.

Copyright infringements

Peer-to-peer networking involves data transfer from one user to another without using an intermediate server. Companies developing P2P applications have been involved in numerous legal cases, primarily in the United States, over conflicts with copyright law. Two major cases are Grokster vs RIAA and MGM Studios, Inc. v. Grokster, Ltd.. In the last case, the Court unanimously held that defendant peer-to-peer file sharing companies Grokster and Streamcast could be sued for inducing copyright infringement.

Multimedia

  • The P2PTV and PDTP protocols.
  • Some proprietary multimedia applications use a peer-to-peer network along with streaming servers to stream audio and video to their clients.
  • Peercasting for multicasting streams.
  • Pennsylvania State University, MIT and Simon Fraser University are carrying on a project called LionShare designed for facilitating file sharing among educational institutions globally.
  • Osiris is a program that allows its users to create anonymous and autonomous web portals distributed via P2P network.

Other P2P applications

Torrent file connect peers

Social implications

Incentivizing resource sharing and cooperation

The BitTorrent protocol: In this animation, the colored bars beneath all of the 7 clients in the upper region above represent the file being shared, with each color representing an individual piece of the file. After the initial pieces transfer from the seed (large system at the bottom), the pieces are individually transferred from client to client. The original seeder only needs to send out one copy of the file for all the clients to receive a copy.

Cooperation among a community of participants is key to the continued success of P2P systems aimed at casual human users; these reach their full potential only when large numbers of nodes contribute resources. But in current practice, P2P networks often contain large numbers of users who utilize resources shared by other nodes, but who do not share anything themselves (often referred to as the "freeloader problem"). Freeloading can have a profound impact on the network and in some cases can cause the community to collapse. In these types of networks "users have natural disincentives to cooperate because cooperation consumes their own resources and may degrade their own performance." Studying the social attributes of P2P networks is challenging due to large populations of turnover, asymmetry of interest and zero-cost identity. A variety of incentive mechanisms have been implemented to encourage or even force nodes to contribute resources.

Some researchers have explored the benefits of enabling virtual communities to self-organize and introduce incentives for resource sharing and cooperation, arguing that the social aspect missing from today's P2P systems should be seen both as a goal and a means for self-organized virtual communities to be built and fostered. Ongoing research efforts for designing effective incentive mechanisms in P2P systems, based on principles from game theory, are beginning to take on a more psychological and information-processing direction.

Privacy and anonymity

Some peer-to-peer networks (e.g. Freenet) place a heavy emphasis on privacy and anonymity—that is, ensuring that the contents of communications are hidden from eavesdroppers, and that the identities/locations of the participants are concealed. Public key cryptography can be used to provide encryption, data validation, authorization, and authentication for data/messages. Onion routing and other mix network protocols (e.g. Tarzan) can be used to provide anonymity.

Perpetrators of live streaming sexual abuse and other cybercrimes have used peer-to-peer platforms to carry out activities with anonymity.

Political implications

Intellectual property law and illegal sharing

Although peer-to-peer networks can be used for legitimate purposes, rights holders have targeted peer-to-peer over the involvement with sharing copyrighted material. Peer-to-peer networking involves data transfer from one user to another without using an intermediate server. Companies developing P2P applications have been involved in numerous legal cases, primarily in the United States, primarily over issues surrounding copyright law. Two major cases are Grokster vs RIAA and MGM Studios, Inc. v. Grokster, Ltd. In both of the cases the file sharing technology was ruled to be legal as long as the developers had no ability to prevent the sharing of the copyrighted material. To establish criminal liability for the copyright infringement on peer-to-peer systems, the government must prove that the defendant infringed a copyright willingly for the purpose of personal financial gain or commercial advantage. Fair use exceptions allow limited use of copyrighted material to be downloaded without acquiring permission from the rights holders. These documents are usually news reporting or under the lines of research and scholarly work. Controversies have developed over the concern of illegitimate use of peer-to-peer networks regarding public safety and national security. When a file is downloaded through a peer-to-peer network, it is impossible to know who created the file or what users are connected to the network at a given time. Trustworthiness of sources is a potential security threat that can be seen with peer-to-peer systems.

A study ordered by the European Union found that illegal downloading may lead to an increase in overall video game sales because newer games charge for extra features or levels. The paper concluded that piracy had a negative financial impact on movies, music, and literature. The study relied on self-reported data about game purchases and use of illegal download sites. Pains were taken to remove effects of false and misremembered responses.

Network neutrality

Peer-to-peer applications present one of the core issues in the network neutrality controversy. Internet service providers (ISPs) have been known to throttle P2P file-sharing traffic due to its high-bandwidth usage. Compared to Web browsing, e-mail or many other uses of the internet, where data is only transferred in short intervals and relative small quantities, P2P file-sharing often consists of relatively heavy bandwidth usage due to ongoing file transfers and swarm/network coordination packets. In October 2007, Comcast, one of the largest broadband Internet providers in the United States, started blocking P2P applications such as BitTorrent. Their rationale was that P2P is mostly used to share illegal content, and their infrastructure is not designed for continuous, high-bandwidth traffic. Critics point out that P2P networking has legitimate legal uses, and that this is another way that large providers are trying to control use and content on the Internet, and direct people towards a client–server-based application architecture. The client–server model provides financial barriers-to-entry to small publishers and individuals, and can be less efficient for sharing large files. As a reaction to this bandwidth throttling, several P2P applications started implementing protocol obfuscation, such as the BitTorrent protocol encryption. Techniques for achieving "protocol obfuscation" involves removing otherwise easily identifiable properties of protocols, such as deterministic byte sequences and packet sizes, by making the data look as if it were random. The ISP's solution to the high bandwidth is P2P caching, where an ISP stores the part of files most accessed by P2P clients in order to save access to the Internet.

Current research

Researchers have used computer simulations to aid in understanding and evaluating the complex behaviors of individuals within the network. "Networking research often relies on simulation in order to test and evaluate new ideas. An important requirement of this process is that results must be reproducible so that other researchers can replicate, validate, and extend existing work." If the research cannot be reproduced, then the opportunity for further research is hindered. "Even though new simulators continue to be released, the research community tends towards only a handful of open-source simulators. The demand for features in simulators, as shown by our criteria and survey, is high. Therefore, the community should work together to get these features in open-source software. This would reduce the need for custom simulators, and hence increase repeatability and reputability of experiments."

Besides all the above stated facts, there has also been work done on ns-2 open source network simulators. One research issue related to free rider detection and punishment has been explored using ns-2 simulator here.

Science fiction magazine

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