79-558: In computer networking , the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model . The protocols of this layer provide end-to-end communication services for applications. It provides services such as connection-oriented communication , reliability , flow control , and multiplexing . The details of implementation and semantics of
158-504: A committed information rate (CIR) and an allowance of burstable bandwidth known as the extended information rate (EIR). The provider guarantees that the connection will always support the C rate, and sometimes the PRa rate should there be adequate bandwidth. Frames that are sent in excess of the CIR are marked as discard eligible (DE) which means they can be dropped should congestion occur within
237-756: 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
316-408: A cheaper alternative to dedicated lines ; its use in different geographic areas depended greatly on governmental and telecommunication companies' policies. Some of the early companies to make Frame Relay products included StrataCom (later acquired by Cisco Systems ) and Cascade Communications (later acquired by Ascend Communications and then by Lucent Technologies ). As of June 2007, AT&T
395-517: A consortium to focus on its development. They produced a protocol that provided additional capabilities for complex inter-networking environments. These Frame Relay extensions are referred to as the local management interface (LMI). Datalink connection identifiers ( DLCIs ) are numbers that refer to paths through the Frame Relay network. They are only locally significant, which means that when device-A sends data to device-B it will most likely use
474-490: A dedicated connection during the transmission period. Frame Relay does not provide an ideal path for voice or video transmission, both of which require a steady flow of transmissions. However, under certain circumstances, voice and video transmission do use Frame Relay. Frame Relay originated as an extension of integrated services digital network (ISDN). Its designers aimed to enable a packet-switched network to transport over circuit-switched technology. The technology has become
553-572: A different DLCI than device-B would use to reply. Multiple virtual circuits can be active on the same physical end-points (performed by using subinterfaces ). The LMI global addressing extension gives Frame Relay data-link connection identifier (DLCI) values global rather than local significance. DLCI values become DTE addresses that are unique in the Frame Relay WAN. The global addressing extension adds functionality and manageability to Frame Relay internetworks. Individual network interfaces and
632-503: 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
711-411: A fixed bandwidth through the network for each X.25 access, regardless of the current load. This resource allocation approach, while apt for applications that require guaranteed quality of service, is inefficient for applications that are highly dynamic in their load characteristics or which would benefit from a more dynamic resource allocation. Frame Relay networks can dynamically allocate bandwidth at both
790-440: 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
869-453: A mid-range service between basic rate ISDN , which offers bandwidth at 128 kbit/s, and Asynchronous Transfer Mode (ATM), which operates in somewhat similar fashion to Frame Relay but at speeds from 155.520 Mbit/s to 622.080 Mbit/s. Frame Relay has its technical base in the older X.25 packet-switching technology, designed for transmitting data on analog voice lines. Unlike X.25, whose designers expected analog signals with
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#1732779783072948-440: 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
1027-785: A relatively high chance of transmission errors, Frame Relay is a fast packet switching technology operating over links with a low chance of transmission errors (usually practically lossless like PDH ), which means that the protocol does not attempt to correct errors. When a Frame Relay network detects an error in a frame, it simply drops that frame. The end points have the responsibility for detecting and retransmitting dropped frames. (However, digital networks offer an incidence of error extraordinarily small relative to that of analog networks.) Frame Relay often serves to connect local area networks (LANs) with major backbones , as well as on public wide-area networks (WANs) and also in private network environments with leased lines over T-1 lines. It requires
1106-457: 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
1185-418: 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
1264-497: A stand-alone and cost-effective means of creating a WAN. Frame Relay switches create virtual circuits to connect remote LANs to a WAN. The Frame Relay network exists between a LAN border device, usually a router, and the carrier switch. The technology used by the carrier to transport data between the switches is variable and may differ among carriers (i.e., to function, a practical Frame Relay implementation need not rely solely on its own transportation mechanism). The sophistication of
1343-403: 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
1422-510: A technique referred to as "best-effort", whereby error-correction practically does not exist and practically no guarantee of reliable data delivery occurs. Frame Relay provides an industry-standard encapsulation, utilizing the strengths of high-speed, packet-switched technology able to service multiple virtual circuits and protocols between connected devices, such as two routers. Although Frame Relay became very popular in North America, it
1501-400: A telecommunication service for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN). Frame Relay puts data in variable-size units called "frames" and leaves any necessary error-correction (such as retransmission of data) up to the end-points. This speeds up overall data transmission. For most services,
1580-877: 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)
1659-406: 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
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#17327797830721738-495: 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
1817-602: 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
1896-522: 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,
1975-477: Is a very simple protocol and does not provide virtual circuits, nor reliable communication, delegating these functions to the application program. UDP packets are called datagrams , rather than segments. TCP is used for many protocols, including HTTP web browsing and email transfer. UDP may be used for multicasting and broadcasting , since retransmissions are not possible to a large amount of hosts. UDP typically gives higher throughput and shorter latency and
2054-422: 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
2133-566: 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
2212-478: 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
2291-425: Is implemented at lower protocol layers. The OSI connection-mode transport layer protocol specification defines five classes of transport protocols: TP0 , providing the least error recovery, to TP4 , which is designed for less reliable networks. Due to protocol ossification , TCP and UDP are the only widely used transport protocols on the Internet. To avoid middlebox intolerance, new transport protocols may mimic
2370-412: 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
2449-442: Is less expensive than leased lines and that is one reason for its popularity. The extreme simplicity of configuring user equipment in a Frame Relay network offers another reason for Frame Relay's popularity. With the advent of Ethernet over fiber optics, MPLS , VPN and dedicated broadband services such as cable modem and DSL , Frame Relay has become less popular in recent years. The designers of Frame Relay aimed to provide
Transport layer - Misplaced Pages Continue
2528-404: 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
2607-533: 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. Frame Relay Frame Relay is a standardized wide area network (WAN) technology that specifies the physical and data link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated Services Digital Network (ISDN) infrastructure, it may be used today in
2686-475: Is therefore often used for real-time multimedia communication where packet loss occasionally can be accepted, for example IP-TV and IP-telephony, and for online computer games. Many non-IP-based networks, such as X.25 , Frame Relay and ATM , implement the connection-oriented communication at the network or data link layer rather than the transport layer. In X.25, in telephone network modems and in wireless communication systems, reliable node-to-node communication
2765-459: 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,
2844-462: 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
2923-477: 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
3002-624: The wire image of a tolerated protocol, or be encapsulated in UDP, accepting some overhead (e.g., due to outer checksums made redundant by inner integrity checks). QUIC takes the latter approach, rebuilding reliable stream transport on top of UDP. This list shows some protocols that are commonly placed in the transport layers of the Internet protocol suite , the OSI protocol suite , NetWare 's IPX/SPX , AppleTalk , and Fibre Channel . ISO/IEC 8073/ITU-T Recommendation X.224, "Information Technology - Open Systems Interconnection - Protocol for providing
3081-595: The Frame Relay network. Frames sent in excess of the EIR are dropped immediately. Frame Relay aimed to make more efficient use of existing physical resources, permitting the over-provisioning of data services by telecommunications companies to their customers, as clients were unlikely to be using a data service 45 percent of the time. In more recent years, Frame Relay has acquired a bad reputation in some markets because of excessive bandwidth overbooking . Telecommunications companies often sell Frame Relay to businesses looking for
3160-510: The Frame Relay: FECN and BECN. The basic idea is to avoid data accumulation inside the network. FECN means forward explicit congestion notification. The FECN bit can be set to 1 to indicate that congestion was experienced in the direction of the frame transmission, so it informs the destination that congestion has occurred. BECN means backwards explicit congestion notification. The BECN bit can be set to 1 to indicate that congestion
3239-602: The Internet and are the only protocols implemented in every major operating system. Additional transport layer protocols that have been defined and implemented include the Datagram Congestion Control Protocol (DCCP) and the Stream Control Transmission Protocol (SCTP). Transport layer services are conveyed to an application via a programming interface to the transport layer protocols. The services may include
Transport layer - Misplaced Pages Continue
3318-493: The Internet protocol suite is the Transmission Control Protocol (TCP). It is used for connection-oriented transmissions, whereas the connectionless User Datagram Protocol (UDP) is used for simpler messaging transmissions. TCP is the more complex protocol, due to its stateful design incorporating reliable transmission and data stream services. Together, TCP and UDP comprise essentially all traffic on
3397-440: 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
3476-574: 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
3555-627: 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
3634-468: 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
3713-525: The circuit-switching concepts of the public switched telephone network (PSTN), the global phone network. Initial proposals for Frame Relay were presented to the Consultative Committee on International Telephone and Telegraph ( CCITT ) in 1984. Lack of interoperability and standardization prevented any significant Frame Relay deployment until 1990, when Cisco , Digital Equipment Corporation (DEC), Northern Telecom , and StrataCom formed
3792-580: The classes are shown in the following table: There is also a connectionless transport protocol, specified by ISO/IEC 8602/ITU-T Recommendation X.234. Computer network 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
3871-420: The congestion. Congestion control in Frame Relay networks includes the following elements: Once the network has established a connection, the edge node of the Frame Relay network must monitor the connection's traffic flow to ensure that the actual usage of network resources does not exceed this specification. Frame Relay defines some restrictions on the user's information rate. It allows the network to enforce
3950-519: The connection-mode transport service", defines five classes of connection-mode transport protocols designated class 0 (TP0) to class 4 (TP4). Class 0 contains no error recovery and was designed for use on network layers that provide error-free connections. Class 4 is closest to TCP, although TCP contains functions, such as the graceful close, which OSI assigns to the session layer. All OSI connection-mode protocol classes provide expedited data and preservation of record boundaries. Detailed characteristics of
4029-434: The context of many other network interfaces. Network providers commonly implement Frame Relay for voice ( VoFR ) and data as an encapsulation technique used between local area networks (LANs) over a WAN. Each end-user gets a private line (or leased line ) to a Frame Relay node . The Frame Relay network handles the transmission over a frequently changing path transparent to all end-user extensively used WAN protocols. It
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#17327797830724108-401: The end nodes attached to them, for example, can be identified by using standard address-resolution and discovery techniques. In addition, the entire Frame Relay network appears to be a typical LAN to routers on its periphery. LMI virtual circuit status messages provide communication and synchronization between Frame Relay DTE and DCE devices. These messages are used to periodically report on
4187-419: The end user's information rate and discard information when the subscribed access rate is exceeded. Explicit congestion notification is proposed as the congestion avoidance policy. It tries to keep the network operating at its desired equilibrium point so that a certain quality of service (QoS) for the network can be met. To do so, special congestion control bits have been incorporated into the address field of
4266-409: The following features: The transport layer is responsible for delivering data to the appropriate application process on the host computers. This involves statistical multiplexing of data from different application processes, i.e. forming data segments, and adding source and destination port numbers in the header of each transport layer data segment. Together with the source and destination IP address,
4345-480: The following fields: The Frame Relay network uses a simplified protocol at each switching node. It achieves simplicity by omitting link-by-link flow-control. As a result, the offered load has largely determined the performance of Frame Relay networks. When offered load is high, due to the bursts in some services, temporary overload at some Frame Relay nodes causes a collapse in network throughput. Therefore, Frame Relay networks require some effective mechanisms to control
4424-767: The higher-level procedures and fields used in X.25. Frame Relay was designed for use on links with error-rates far lower than available when X.25 was designed. X.25 prepares and sends packets, while Frame Relay prepares and sends frames. X.25 packets contain several fields used for error checking and flow control , most of which are not used by Frame Relay. The frames in Frame Relay contain an expanded link layer address field that enables Frame Relay nodes to direct frames to their destinations with minimal processing. The elimination of functions and fields over X.25 allows Frame Relay to move data more quickly, but leaves more room for errors and larger delays should data need to be retransmitted. X.25 packet switched networks typically allocated
4503-620: 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
4582-665: 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
4661-415: 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
4740-412: 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
4819-554: The network provides a permanent virtual circuit (PVC), which means that the customer sees a continuous, dedicated connection without having to pay for a full-time leased line , while the service-provider figures out the route each frame travels to its destination and can charge based on usage. An enterprise can select a level of service quality , prioritizing some frames and making others less important. Frame Relay can run on fractional T-1 or E1 , or full T-carrier or E-carrier system carriers. Frame Relay complements and provides
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#17327797830724898-420: 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
4977-729: 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
5056-494: 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
5135-537: The packet mode communication for the application processes. This involves connection establishment, dividing of the data stream into packets called segments, segment numbering and reordering of out-of-order data. Finally, some transport layer protocols, for example TCP, but not UDP, provide end-to-end reliable communication, i.e. error recovery by means of error detecting code and automatic repeat request (ARQ) protocol. The ARQ protocol also provides flow control , which may be combined with congestion avoidance . UDP
5214-491: The physical and logical channel level. As a WAN protocol, Frame Relay is most commonly implemented at Layer 2 ( data link layer ) of the Open Systems Interconnection (OSI) seven layer model . Two types of circuits exist: permanent virtual circuits (PVCs) which are used to form logical end-to-end links mapped over a physical network, and switched virtual circuits (SVCs). The latter are analogous to
5293-520: 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,
5372-424: The port numbers constitute a network socket , i.e. an identification address of the process-to-process communication. In the OSI model, this function is supported by the session layer . Some transport layer protocols, for example TCP, but not UDP, support virtual circuits , i.e. provide connection-oriented communication over an underlying packet-oriented datagram network. A byte stream is delivered while hiding
5451-456: 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
5530-515: 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
5609-493: 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,
5688-457: The status of PVCs, which prevents data from being sent into black holes (that is, over PVCs that no longer exist). The LMI multicasting extension allows multicast groups to be assigned. Multicasting saves bandwidth by allowing routing updates and address-resolution messages to be sent only to specific groups of routers. The extension also transmits reports on the status of multicast groups in update messages. Frame Relay connections are often given
5767-438: The technology requires a thorough understanding of the terms used to describe how Frame Relay works. Without a firm understanding of Frame Relay, it is difficult to troubleshoot its performance. Frame-relay frame structure essentially mirrors almost exactly that defined for LAP-D. Traffic analysis can distinguish Frame Relay format from LAP-D by its lack of a control field. Each Frame Relay protocol data unit (PDU) consists of
5846-475: The transport layer of the Internet protocol suite , which is the foundation of the Internet , and the OSI model of general networking are different. The protocols in use today in this layer for the Internet all originated in the development of TCP/IP. In the OSI model the transport layer is often referred to as Layer 4 , or L4 , while numbered layers are not used in TCP/IP. The best-known transport protocol of
5925-403: Was an important early WAN protocol, and is often considered to be the grandfather of Frame Relay as many of the underlying protocols and functions of X.25 are still in use today (with upgrades) by Frame Relay. X.25 provides quality of service and error-free delivery, whereas Frame Relay was designed to relay data as quickly as possible over low error networks. Frame Relay eliminates a number of
6004-428: Was experienced in the network in the direction opposite of the frame transmission, so it informs the sender that congestion has occurred. Frame Relay began as a stripped-down version of the X.25 protocol, releasing itself from the error-correcting burden most commonly associated with X.25. When Frame Relay detects an error, it simply drops the offending packet. Frame Relay uses the concept of shared access and relies on
6083-462: 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
6162-506: Was never very popular in Europe. X.25 remained the primary standard until the wide availability of IP made packet switching almost obsolete. It was used sometimes as backbone for other services, such as X.25 or IP traffic. Where Frame Relay was used in the USA also as carrier for TCP/IP traffic, in Europe backbones for IP networks often used ATM or PoS , later replaced by Carrier Ethernet X.25
6241-482: Was the largest Frame Relay service provider in the US, with local networks in 22 states, plus national and international networks. When multiplexing packet data from different virtual circuits or flows, quality of service concerns often arise. This is because a frame from one virtual circuit may occupy the line for a long enough period of time to disrupt a service guarantee given to another virtual circuit. IP fragmentation
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