77-477: Port Control Protocol ( PCP ) is a computer networking protocol that allows hosts on IPv4 or IPv6 networks to control how the incoming IPv4 or IPv6 packets are translated and forwarded by an upstream router that performs network address translation (NAT) or packet filtering . By allowing hosts to create explicit port forwarding rules, handling of the network traffic can be easily configured to make hosts placed behind NATs or firewalls reachable from
154-756: A protocol stack , often constructed per the OSI model, communications functions are divided up into protocol layers, where each layer leverages the services of the layer below it until the lowest layer controls the hardware that sends information across the media. The use of protocol layering is ubiquitous across the field of computer networking. An important example of a protocol stack is HTTP (the World Wide Web protocol) running over TCP over IP (the Internet protocols) over IEEE 802.11 (the Wi-Fi protocol). This stack
231-452: A client to the server's UDP port 5351 that it listens to; unsolicited multicast server notifications (such as server restart announcements) are sent from the server's UDP port 5351 to the UDP port 5350 on hosts which they listen to. Maximum UDP payload length for all PCP messages is 1100 octets . Each PCP message consists of a request or response header containing an opcode that determines
308-671: A connection alive requires a constant exchange of empty messages between client and server. This increases network chatter, wastes network bandwidth and CPU cycles , and decreases the autonomy of battery-powered devices. Additionally, some network applications (for example, FTP ) require dynamic opening of multiple connections, which involves application-level gateways (ALGs) and additionally increases complexity. PCP allows equipment and applications to create explicit mappings between an external IP address , protocol and port , and an internal IP address, protocol and port. With such explicit mappings in place, inbound communication can reach
385-503: A diverse set of networking capabilities. The protocols have a flat addressing scheme. They operate mostly at layers 1 and 2 of the OSI model. For example, MAC bridging ( IEEE 802.1D ) deals with the routing of Ethernet packets using a Spanning Tree Protocol . IEEE 802.1Q describes VLANs , and IEEE 802.1X defines a port-based network access control protocol, which forms the basis for the authentication mechanisms used in VLANs (but it
462-517: A failure condition is expected to persist, or how long the created mapping will last. Computer networking A computer network is a set of computers sharing resources located on or provided by network nodes . Computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies based on physically wired, optical , and wireless radio-frequency methods that may be arranged in
539-440: A large, congested network into an aggregation of smaller, more efficient networks. A router is an internetworking device that forwards packets between networks by processing the addressing or routing information included in the packet. The routing information is often processed in conjunction with the routing table . A router uses its routing table to determine where to forward packets and does not require broadcasting packets which
616-679: A link is limited by the Shannon–Hartley channel capacity for these communication systems, which is dependent on the bandwidth in hertz and the noise on the channel. The consumed bandwidth in bit/s, corresponds to achieved throughput or goodput , i.e., the average rate of successful data transfer through a communication path. The consumed bandwidth can be affected by technologies such as bandwidth shaping , bandwidth management , bandwidth throttling , bandwidth cap , bandwidth allocation (for example bandwidth allocation protocol and dynamic bandwidth allocation ), etc. A bit stream's bandwidth
693-480: A month measured in gigabytes per month. The more accurate phrase used for this meaning of a maximum amount of data transfer each month or given period is monthly data transfer . A similar situation can occur for end-user Internet service providers as well, especially where network capacity is limited (for example in areas with underdeveloped internet connectivity and on wireless networks). Edholm's law , proposed by and named after Phil Edholm in 2004, holds that
770-440: A multi-port bridge. Switches normally have numerous ports, facilitating a star topology for devices, and for cascading additional switches. Bridges and switches operate at the data link layer (layer 2) of the OSI model and bridge traffic between two or more network segments to form a single local network. Both are devices that forward frames of data between ports based on the destination MAC address in each frame. They learn
847-519: A number of very large messages through the network, measuring the end-to-end throughput. As with other bandwidths, the asymptotic bandwidth is measured in multiples of bits per seconds. Since bandwidth spikes can skew the measurement, carriers often use the 95th percentile method. This method continuously measures bandwidth usage and then removes the top 5 percent. Digital bandwidth may also refer to: multimedia bit rate or average bitrate after multimedia data compression ( source coding ), defined as
SECTION 10
#1732793548118924-457: A repeater hub assists with collision detection and fault isolation for the network. Hubs and repeaters in LANs have been largely obsoleted by modern network switches. Network bridges and network switches are distinct from a hub in that they only forward frames to the ports involved in the communication whereas a hub forwards to all ports. Bridges only have two ports but a switch can be thought of as
1001-516: A result of the way NAT devices and firewalls are handling regular outbound client connections, meaning that PCP is safe as long as no new mapping possibilities are introduced through the explicit mapping mechanism. From the security standpoint, an important PCP feature is the THIRD_PARTY mapping request option. When used, this option signifies that the IP address specified additionally as part of
1078-418: A single failure can cause the network to fail entirely. In general, the more interconnections there are, the more robust the network is; but the more expensive it is to install. Therefore, most network diagrams are arranged by their network topology which is the map of logical interconnections of network hosts. Common topologies are: The physical layout of the nodes in a network may not necessarily reflect
1155-403: A standard voice telephone line. Modems are still commonly used for telephone lines, using a digital subscriber line technology and cable television systems using DOCSIS technology. A firewall is a network device or software for controlling network security and access rules. Firewalls are inserted in connections between secure internal networks and potentially insecure external networks such as
1232-877: A transmission medium. Power line communication uses a building's power cabling to transmit data. The following classes of wired technologies are used in computer networking. Network connections can be established wirelessly using radio or other electromagnetic means of communication. The last two cases have a large round-trip delay time , which gives slow two-way communication but does not prevent sending large amounts of information (they can have high throughput). Apart from any physical transmission media, networks are built from additional basic system building blocks, such as network interface controllers , repeaters , hubs , bridges , switches , routers , modems, and firewalls . Any particular piece of equipment will frequently contain multiple building blocks and so may perform multiple functions. A network interface controller (NIC)
1309-406: A variety of network topologies . The nodes of a computer network can include personal computers , servers , networking hardware , or other specialized or general-purpose hosts . They are identified by network addresses and may have hostnames . Hostnames serve as memorable labels for the nodes and are rarely changed after initial assignment. Network addresses serve for locating and identifying
1386-495: A variety of different sources, primarily to support circuit-switched digital telephony . However, due to its protocol neutrality and transport-oriented features, SONET/SDH also was the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames. Asynchronous Transfer Mode (ATM) is a switching technique for telecommunication networks. It uses asynchronous time-division multiplexing and encodes data into small, fixed-sized cells . This differs from other protocols such as
1463-657: A virtual system of links that run on top of the Internet . Overlay networks have been used since the early days of networking, back when computers were connected via telephone lines using modems, even before data networks were developed. The most striking example of an overlay network is the Internet itself. The Internet itself was initially built as an overlay on the telephone network . Even today, each Internet node can communicate with virtually any other through an underlying mesh of sub-networks of wildly different topologies and technologies. Address resolution and routing are
1540-522: Is computer hardware that connects the computer to the network media and has the ability to process low-level network information. For example, the NIC may have a connector for plugging in a cable, or an aerial for wireless transmission and reception, and the associated circuitry. In Ethernet networks, each NIC has a unique Media Access Control (MAC) address —usually stored in the controller's permanent memory. To avoid address conflicts between network devices,
1617-422: Is a virtual network that is built on top of another network. Nodes in the overlay network are connected by virtual or logical links. Each link corresponds to a path, perhaps through many physical links, in the underlying network. The topology of the overlay network may (and often does) differ from that of the underlying one. For example, many peer-to-peer networks are overlay networks. They are organized as nodes of
SECTION 20
#17327935481181694-566: Is also found in WLANs ) – it is what the home user sees when the user has to enter a "wireless access key". Ethernet is a family of technologies used in wired LANs. It is described by a set of standards together called IEEE 802.3 published by the Institute of Electrical and Electronics Engineers. Wireless LAN based on the IEEE 802.11 standards, also widely known as WLAN or WiFi, is probably
1771-889: Is also supported. PCP is designed to be used on both large-scale aggregation points (for example, as part of carrier-grade NATs ), and inside less expensive consumer-grade devices. Both long-term (for an IP camera or a temperature sensor acting as a server, for example) and short-term mappings (while playing an online computer game, for example) are supported. PCP supports transport layer protocols that use 16-bit port numbers (for example, TCP , UDP , Stream Control Transmission Protocol (SCTP) or Datagram Congestion Control Protocol (DCCP). Protocols that do not use port numbers (for example, Resource Reservation Protocol (RSVP), Encapsulating Security Payload (ESP), ICMP or ICMPv6 ) are supported for IPv4 firewall, IPv6 firewall and NPTv6 (IPv6 prefix translation) functions, but cannot be supported by more than one client per external IP address in
1848-447: Is an IP camera , which includes a network server that provides remote surveillance over IP networks. Usually, network equipment deployments place the devices behind routers or firewalls that perform NAT (to enable sharing of an IPv4 address , for example) or packet filtering (for improved network security and protection), ending up with breaking the end-to-end connectivity and rendering the equipment and applications inaccessible from
1925-478: Is an electronic device that receives a network signal , cleans it of unnecessary noise and regenerates it. The signal is retransmitted at a higher power level, or to the other side of obstruction so that the signal can cover longer distances without degradation. In most twisted-pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. With fiber optics, repeaters can be tens or even hundreds of kilometers apart. Repeaters work on
2002-433: Is in contrast to the field of signal processing, wireless communications, modem data transmission, digital communications , and electronics , in which bandwidth is used to refer to analog signal bandwidth measured in hertz , meaning the frequency range between lowest and highest attainable frequency while meeting a well-defined impairment level in signal power. The actual bit rate that can be achieved depends not only on
2079-412: Is inefficient for very big networks. Modems (modulator-demodulator) are used to connect network nodes via wire not originally designed for digital network traffic, or for wireless. To do this one or more carrier signals are modulated by the digital signal to produce an analog signal that can be tailored to give the required properties for transmission. Early modems modulated audio signals sent over
2156-402: Is less than or equal to the actual channel capacity minus implementation overhead. The asymptotic bandwidth (formally asymptotic throughput ) for a network is the measure of maximum throughput for a greedy source , for example when the message size (the number of packets per second from a source) approaches close to the maximum amount. Asymptotic bandwidths are usually estimated by sending
2233-404: Is not sending packets, the link can be filled with packets from other users, and so the cost can be shared, with relatively little interference, provided the link is not overused. Often the route a packet needs to take through a network is not immediately available. In that case, the packet is queued and waits until a link is free. The physical link technologies of packet networks typically limit
2310-462: Is proportional to the average consumed signal bandwidth in hertz (the average spectral bandwidth of the analog signal representing the bit stream) during a studied time interval. Channel bandwidth may be confused with useful data throughput (or goodput). For example, a channel with x bit/s may not necessarily transmit data at x rate, since protocols, encryption, and other factors can add appreciable overhead. For instance, much internet traffic uses
2387-431: Is the process of selecting network paths to carry network traffic. Routing is performed for many kinds of networks, including circuit switching networks and packet switched networks. Network bandwidth In computing , bandwidth is the maximum rate of data transfer across a given path. Bandwidth may be characterized as network bandwidth , data bandwidth , or digital bandwidth . This definition of bandwidth
Port Control Protocol - Misplaced Pages Continue
2464-459: Is used between the wireless router and the home user's personal computer when the user is surfing the web. There are many communication protocols, a few of which are described below. The Internet protocol suite , also called TCP/IP, is the foundation of all modern networking. It offers connection-less and connection-oriented services over an inherently unreliable network traversed by datagram transmission using Internet protocol (IP). At its core,
2541-462: The Institute of Electrical and Electronics Engineers (IEEE) maintains and administers MAC address uniqueness. The size of an Ethernet MAC address is six octets . The three most significant octets are reserved to identify NIC manufacturers. These manufacturers, using only their assigned prefixes, uniquely assign the three least-significant octets of every Ethernet interface they produce. A repeater
2618-623: The Internet Gateway Device Protocol (UPnP IGD), which was standardized in 2001 as part of the UPnP specification. While the UPnP IGD is complex and tailored toward manual configuration, PCP is designed for simplicity and automated use within software applications. The NAT-PMP specification contains a list of the problems with UPnP IGD that prompted the creation of NAT-PMP, and subsequently, its successor PCP. Excluding
2695-477: The World Wide Web , digital video and audio , shared use of application and storage servers , printers and fax machines , and use of email and instant messaging applications. Computer networking may be considered a branch of computer science , computer engineering , and telecommunications , since it relies on the theoretical and practical application of the related disciplines. Computer networking
2772-424: The attackers capable of altering network packets exchanged while an explicit PCP mapping is created (packets that contain negotiation required for establishing an explicit mapping, which is exchanged between hosts and PCP-enabled NAT devices or firewalls), PCP is considered to be secure as long as created explicit mappings do not exceed the domain of implicit mappings. In other words, implicit mappings are created as
2849-478: The transmission control protocol (TCP), which requires a three-way handshake for each transaction. Although in many modern implementations the protocol is efficient, it does add significant overhead compared to simpler protocols. Also, data packets may be lost, which further reduces the useful data throughput. In general, for any effective digital communication, a framing protocol is needed; overhead and effective throughput depends on implementation. Useful throughput
2926-576: The IPv6 prefix(es) used by a PCP-controlled NAT64 device to build IPv4-converted IPv6 addresses by the NAT64 (RFC7225). Many applications and network equipment deployments require their network locations to be reachable from outside their local networks , following the originally envisioned model of IP end-to-end connectivity across the Internet, so they can operate as network servers and accept connections from remote clients . An example of such equipment
3003-440: The Internet protocol suite or Ethernet that use variable-sized packets or frames . ATM has similarities with both circuit and packet switched networking. This makes it a good choice for a network that must handle both traditional high-throughput data traffic, and real-time, low-latency content such as voice and video. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before
3080-574: The Internet. Firewalls are typically configured to reject access requests from unrecognized sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in cyber attacks . A communication protocol is a set of rules for exchanging information over a network. Communication protocols have various characteristics. They may be connection-oriented or connectionless , they may use circuit mode or packet switching, and they may use hierarchical addressing or flat addressing. In
3157-629: The UPnP IGD and PCP is required to be embedded in the IGD. The UPnP IGD-PCP Interworking Function is specified in RFC6970. DHCP (IPv4 and IPv6) options to configure hosts with Port Control Protocol (PCP) server IP addresses are specified in RFC7291. The procedure to follow for selecting a server among a list of PCP servers is discussed in RFC7488. In environments where NAT64 is deployed, PCP allows to learn
Port Control Protocol - Misplaced Pages Continue
3234-484: The actual clients. Both approaches have their downsides – manual CPE configuration is usually either inconvenient or not possible, while using additional intermediate servers increases complexity and cost. For example, an online computer game (which acts as a client) requires communication with a game server for exchanging gameplay data. In order to make it possible for a game server to provide data to its clients, those clients must be made accessible to
3311-627: The actual data exchange begins. ATM still plays a role in the last mile , which is the connection between an Internet service provider and the home user. There are a number of different digital cellular standards, including: Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), cdmaOne , CDMA2000 , Evolution-Data Optimized (EV-DO), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-136/TDMA), and Integrated Digital Enhanced Network (iDEN). Routing
3388-399: The amount of memory and bandwidth required for digital signals, capable of achieving a data compression ratio of up to 100:1 compared to uncompressed media. In Web hosting service , the term bandwidth is often incorrectly used to describe the amount of data transferred to or from the website or server within a prescribed period of time, for example bandwidth consumption accumulated over
3465-485: The application with associated externally visible parameters (IP address, protocol and port) that can then be announced to other clients in application-specific ways so incoming connections can be established. Additionally, PCP can inform applications when the external IP address is changed while a mapping is already established. Various types of NAT can be handled by PCP, providing support for NAT64 , NAT66 , and NAT44 ; inclusion of PCP into IPv4 and IPv6 firewall devices
3542-481: The associated operation, any relevant opcode-specific information (such as which ports are to be mapped), and zero or more options (such as the THIRD_PARTY option described above ). Result codes are returned as part of server responses; each result code has an associated lifetime, which tells the hosts when certain operations may be retried or should be repeated. For example, result lifetimes can specify how long
3619-468: The association of physical ports to MAC addresses by examining the source addresses of received frames and only forward the frame when necessary. If an unknown destination MAC is targeted, the device broadcasts the request to all ports except the source, and discovers the location from the reply. Bridges and switches divide the network's collision domain but maintain a single broadcast domain. Network segmentation through bridging and switching helps break down
3696-427: The authentication between devices involved in a PCP negotiation session. Such PCP-enabled NAT devices or firewalls may still accept unauthenticated mapping requests; at the same time, all previously described explicit mapping constraints still apply. Internally, PCP works by exchanging control messages between hosts and PCP-enabled NAT devices or firewalls (referred to as servers), using User Datagram Protocol (UDP) as
3773-409: The bandwidth of telecommunication networks double every 18 months, which has proven to be true since the 1970s. The trend is evident in the cases of Internet , cellular (mobile), wireless LAN and wireless personal area networks . The MOSFET (metal–oxide–semiconductor field-effect transistor) is the most important factor enabling the rapid increase in bandwidth. The MOSFET (MOS transistor)
3850-402: The case of NAT. The PCP specification does not define a mechanism for dealing with multi-homed networks (which have multiple network gateways or default routes ). It is nonetheless possible to implement PCP in such networks using a coordination mechanism such as conntrackd . However, if the different networks each have their own external IP address(es), a given PCP mapping can only use one or
3927-433: The external IP address. Exchanged messages contain no means for determining either the transaction they belong to, or which stage of a "session" they represent. Such a simplified design is based on having all messages self-describing and complete, with no additional context required for each message to be successfully processed. Servers may decide to silently ignore host requests, in case they are unable to process them at
SECTION 50
#17327935481184004-504: The hosts behind a NAT or firewall, which either expands their server roles beyond boundaries of local networks, or makes use of various services simplified and less resource-consuming. Created mappings are permanent to the extent of having a known lifetime that can be extended, which is similar to the way Dynamic Host Configuration Protocol (DHCP) implements its leases . At the same time, PCP allows applications to create additional mappings dynamically as required, which reduces or eliminates
4081-668: The literature as the physical medium ) used to link devices to form a computer network include electrical cable , optical fiber , and free space. In the OSI model , the software to handle the media is defined at layers 1 and 2 — the physical layer and the data link layer. A widely adopted family that uses copper and fiber media in local area network (LAN) technology are collectively known as Ethernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3 . Wireless LAN standards use radio waves , others use infrared signals as
4158-414: The mapping request should be used as the internal address for the created explicit mapping, rather than following the default behavior of using source IP address of the actual mapping request packet for that purpose. Such mapping requests can end up with a PCP-enabled NAT device or firewall granting explicit mapping privileges higher than allowed by implicit mappings due to unknown rules imposed elsewhere for
4235-665: The means that allow mapping of a fully connected IP overlay network to its underlying network. Another example of an overlay network is a distributed hash table , which maps keys to nodes in the network. In this case, the underlying network is an IP network, and the overlay network is a table (actually a map ) indexed by keys. Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees achieve higher-quality streaming media . Previous proposals such as IntServ , DiffServ , and IP multicast have not seen wide acceptance largely because they require modification of all routers in
4312-413: The moment; in such cases, hosts need to retransmit the request. Also, hosts may safely decide to silently ignore any unwanted mapping responses. For the purpose of creating PCP requests, IP address of the server is either manually configured on the host, found as part of the host's DHCP lease , or set to the host's configured default gateway . Host request messages are sent from any source UDP port on
4389-415: The most well-known member of the IEEE 802 protocol family for home users today. IEEE 802.11 shares many properties with wired Ethernet. Synchronous optical networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers. They were originally designed to transport circuit mode communications from
4466-472: The need for having ALG -enabled NAT devices and firewalls. Created explicit mappings have a known lifetime, commonly several hours, with no need for application-level keepalive messages to be exchanged between hosts and servers for the purpose of preserving the mapping. As a result, network usage and power consumption are reduced, and application-level keepalive logic no longer needs to be implemented at client and server sides. The PCP mapping response provides
4543-412: The network needs to deliver the user data, for example, source and destination network addresses , error detection codes, and sequencing information. Typically, control information is found in packet headers and trailers , with payload data in between. With packets, the bandwidth of the transmission medium can be better shared among users than if the network were circuit switched . When one user
4620-420: The network topology. As an example, with FDDI , the network topology is a ring, but the physical topology is often a star, because all neighboring connections can be routed via a central physical location. Physical layout is not completely irrelevant, however, as common ducting and equipment locations can represent single points of failure due to issues like fires, power failures and flooding. An overlay network
4697-729: The network. On the other hand, an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without cooperation from Internet service providers . The overlay network has no control over how packets are routed in the underlying network between two overlay nodes, but it can control, for example, the sequence of overlay nodes that a message traverses before it reaches its destination . For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast ). Academic research includes end system multicast, resilient routing and quality of service studies, among others. The transmission media (often referred to in
SECTION 60
#17327935481184774-494: The nodes by communication protocols such as the Internet Protocol . Computer networks may be classified by many criteria, including the transmission medium used to carry signals, bandwidth , communications protocols to organize network traffic , the network size, the topology, traffic control mechanisms, and organizational intent. Computer networks support many applications and services , such as access to
4851-632: The other because the protocol requires one specific external IP address to be provided to the client. If that network should then become unavailable the PCP mapping would have to be updated to use an external IP address from the other network. The PCP specification does not define a mechanism for dealing how to inform remote computers about the IP address, protocol, and port for the incoming connection. RFC6887 states, that PCP does not provide any rendezvous function and this has to been done in an application-specific manner, like using external nameservice servers. PCP
4928-520: The physical layer of the OSI model but still require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance and may affect proper function. As a result, many network architectures limit the number of repeaters used in a network, e.g., the Ethernet 5-4-3 rule . An Ethernet repeater with multiple ports is known as an Ethernet hub . In addition to reconditioning and distributing network signals,
5005-456: The protocol suite defines the addressing, identification, and routing specifications for Internet Protocol Version 4 (IPv4) and for IPv6 , the next generation of the protocol with a much enlarged addressing capability. The Internet protocol suite is the defining set of protocols for the Internet. IEEE 802 is a family of IEEE standards dealing with local area networks and metropolitan area networks. The complete IEEE 802 protocol suite provides
5082-447: The rest of the Internet (so they can also act as network servers ), which is a requirement for many applications. Additionally, explicit port forwarding rules available through PCP allow hosts to reduce the amount of generated traffic by eliminating workarounds in form of outgoing NAT keepalive messages, which are required for maintaining connections to servers and for various NAT traversal techniques such as TCP hole punching . At
5159-433: The rest of the Internet. Making the deployed equipment accessible, by extending its server role beyond the local network, requires either manual configuration of port forwarding at the network gateway (which is usually a CPE ), or application-level workarounds that initiate connections from the deployed equipment to additional intermediate servers used for "merging" those "firewall punching" connections and connections from
5236-526: The same time, less generated traffic reduces the power consumption , directly improving the battery runtime for mobile devices . PCP was standardized in 2013 as a successor to the NAT Port Mapping Protocol (NAT-PMP), with which it shares similar protocol concepts and packet formats. PCP adds support for IPv6 and additional NAT scenarios. In environments where a UPnP IGD is used in the local network, an interworking function between
5313-480: The server. Usually, clients initiate connections to the game server to open communication channels. However, such open connections can become idle and can subsequently be closed by network gateways, leading to the necessity of maintaining them by using a form of keepalive messages. Keepalive messages are small messages that are sent between client and server that create traffic over a communication channel and therefore prevent gateway servers from closing it. Thus, keeping
5390-515: The sharing of files and information, giving authorized users access to data stored on other computers. Distributed computing leverages resources from multiple computers across a network to perform tasks collaboratively. Most modern computer networks use protocols based on packet-mode transmission. A network packet is a formatted unit of data carried by a packet-switched network . Packets consist of two types of data: control information and user data (payload). The control information provides data
5467-449: The signal bandwidth but also on the noise on the channel. The term bandwidth sometimes defines the net bit rate peak bit rate , information rate , or physical layer useful bit rate , channel capacity , or the maximum throughput of a logical or physical communication path in a digital communication system. For example, bandwidth tests measure the maximum throughput of a computer network. The maximum rate that can be sustained on
5544-493: The size of packets to a certain maximum transmission unit (MTU). A longer message may be fragmented before it is transferred and once the packets arrive, they are reassembled to construct the original message. The physical or geographic locations of network nodes and links generally have relatively little effect on a network, but the topology of interconnections of a network can significantly affect its throughput and reliability. With many technologies, such as bus or star networks,
5621-435: The specified IP address, allowing that way an attacker to steal some traffic, or to conduct a denial-of-service (DoS) attack. Additionally, explicit PCP security mechanisms are available as extensions to the PCP protocol, providing authentication and access control mechanisms by using an authenticated and integrity-protected in-band signalling channel, which relies on Extensible Authentication Protocol (EAP) to perform
5698-450: The total amount of data divided by the playback time. Due to the impractically high bandwidth requirements of uncompressed digital media , the required multimedia bandwidth can be significantly reduced with data compression. The most widely used data compression technique for media bandwidth reduction is the discrete cosine transform (DCT), which was first proposed by Nasir Ahmed in the early 1970s. DCT compression significantly reduces
5775-582: The underlying protocol. This communication consists of port mapping requests created by the hosts that result in responses once submitted to and processed by the servers. Following UDP's nature of unreliability, which means that UDP datagrams can be lost, duplicated or reordered, after submitting a request there is no guarantee for a response of any kind, thus host requests are also referred to as "hints". In addition to direct responses, servers also generate gratuitous notifications – for example, unicast notifications to inform hosts of changes in
5852-462: Was influenced by a wide array of technological developments and historical milestones. Computer networks enhance how users communicate with each other by using various electronic methods like email, instant messaging, online chat, voice and video calls, and video conferencing. Networks also enable the sharing of computing resources. For example, a user can print a document on a shared printer or use shared storage devices. Additionally, networks allow for
5929-490: Was standardized in 2013 as a successor to the NAT Port Mapping Protocol ( NAT-PMP ), sharing similar protocol concepts and packet formats with it. As one of the design differences, NAT-PMP is pretty much limited to the deployment on consumer-grade devices, while PCP is designed to also support carrier-grade equipment. Since 2005, NAT-PMP has been implemented in various Apple products. PCP relates to
#117882