86-618: In computer networking , an Ethernet frame is a data link layer protocol data unit and uses the underlying Ethernet physical layer transport mechanisms. In other words, a data unit on an Ethernet link transports an Ethernet frame as its payload. An Ethernet frame is preceded by a preamble and start frame delimiter (SFD), which are both part of the Ethernet packet at the physical layer . Each Ethernet frame starts with an Ethernet header, which contains destination and source MAC addresses as its first two fields. The middle section of
172-425: A payload size over 9000 bytes. As it has been a relatively difficult, and somewhat lengthy, process to increase the path MTU of high-performance national research and education networks from 1500 bytes to 9000 bytes or so, a subsequent increase, possibly to 64,000 bytes, is under consideration. The main factor involved is an increase in the available memory buffer size in every intervening persistence mechanism along
258-756: 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
344-551: A CRC on both the received data and the FCS, which will result in a fixed non-zero "verify" value. (The result is non-zero because the CRC is post complemented during CRC generation). Since the data is received least significant bit first, and to avoid having to buffer octets of data, the receiver typically uses the right shifting CRC-32. This makes the "verify" value (sometimes called "magic check") 0x2144DF1C. However, hardware implementation of
430-503: 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
516-491: A function of packet transfer rates is related in a complex manner to payload size per packet. Theoretically, as line bit rate increases, the packet payload size should increase in direct proportion to maintain equivalent timing parameters. This however implies the scaling of numerous intermediating logic circuits along the network path to accommodate the maximum frame size required. Baby giant or baby jumbo frames are Ethernet frames that are only slightly larger than allowed by
602-623: A general-purpose transport designed to handle data chunks, and within a TCP transport designed to carry SCSI data, both provide improved error detection rates despite the use of jumbo frames where an increase of the Ethernet MTU would otherwise have resulted in a significant reduction in error detection. In networking equipment, maximum jumbo frame size may be specified using either maximum frame size (maximum layer 2 packet size, includes frame headers) or maximum transmission unit (maximum layer 3 packet size, excludes frame headers), depending on
688-440: 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
774-489: A length field. Values between 1500 and 1536, exclusive, are undefined. This convention allows software to determine whether a frame is an Ethernet II frame or an IEEE 802.3 frame, allowing the coexistence of both standards on the same physical medium. Novell's "raw" 802.3 frame format was based on early IEEE 802.3 work. Novell used this as a starting point to create the first implementation of its own IPX Network Protocol over Ethernet. They did not use any LLC header but started
860-413: A logically right shifting CRC may use a left shifting Linear Feedback Shift Register as the basis for calculating the CRC, reversing the bits and resulting in a verify value of 0x38FB2284. Since the complementing of the CRC may be performed post calculation and during transmission, what remains in the hardware register is a non-complemented result, so the residue for a right shifting implementation would be
946-440: 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
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#17327875556421032-457: 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
1118-467: A requirement for a minimum frame transmission of 64 octets (bytes). With header and FCS taken into account, the minimum payload is 42 octets when an 802.1Q tag is present and 46 octets when absent. When the actual payload is less than the minimum, padding octets are added accordingly. IEEE standards specify a maximum payload of 1500 octets. Non-standard jumbo frames allow for larger payloads on networks built to support them. The frame check sequence (FCS)
1204-418: 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
1290-403: 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
1376-877: 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)
1462-406: 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
1548-495: 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
1634-657: 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
1720-522: 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,
1806-450: Is a four-octet cyclic redundancy check (CRC) that allows detection of corrupted data within the entire frame as received on the receiver side. According to the standard, the FCS value is computed as a function of the protected MAC frame fields: source and destination address, length/type field, MAC client data and padding (that is, all fields except the FCS). Per the standard, this computation
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#17327875556421892-464: Is a four-octet field that indicates virtual LAN (VLAN) membership and IEEE 802.1p priority. The first two octets of the tag are called the T ag P rotocol ID entifier (TPID) and double as the EtherType field indicating that the frame is either 802.1Q or 802.1ad tagged. 802.1Q uses a TPID of 0x8100. 802.1ad uses a TPID of 0x88a8. Payload is a variable-length field. Its minimum size is governed by
1978-422: 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
2064-568: Is almost never implemented on Ethernet, although it is used on FDDI, Token Ring, IEEE 802.11 (with the exception of the 5.9 GHz band , where it uses EtherType) and other IEEE 802 LANs. IPv6 can also be transmitted over Ethernet using IEEE 802.2 LLC SAP/SNAP, but, again, that's almost never used. By examining the 802.2 LLC header, it is possible to determine whether it is followed by a SNAP header. The LLC header includes two eight-bit address fields, called service access points (SAPs) in OSI terminology; when both source and destination SAP are set to
2150-566: 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
2236-733: Is an Ethernet frame that is less than the IEEE 802.3's minimum length of 64 octets. Runt frames are most commonly caused by collisions ; other possible causes are a malfunctioning network card , buffer underrun , duplex mismatch or software issues. 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
2322-478: 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
2408-428: Is done using the left shifting CRC-32 ( polynomial = 0x4C11DB7, initial CRC = 0xFFFFFFFF, CRC is post complemented, verify value = 0x38FB2284) algorithm. The standard states that data is transmitted least significant bit (bit 0) first, while the FCS is transmitted most significant bit (bit 31) first. An alternative is to calculate a CRC using the right shifting CRC-32 (polynomial = 0xEDB88320, initial CRC = 0xFFFFFFFF, CRC
2494-412: 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
2580-422: Is not in widespread use on common networks currently, with the exception of large corporate NetWare installations that have not yet migrated to NetWare over IP . In the past, many corporate networks used IEEE 802.2 to support transparent translating bridges between Ethernet and Token Ring or FDDI networks. There exists an Internet standard for encapsulating IPv4 traffic in IEEE 802.2 LLC SAP/SNAP frames. It
2666-404: 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
Ethernet frame - Misplaced Pages Continue
2752-666: Is placed between the Source Address and the EtherType or Length fields. The first two octets of the tag are the Tag Protocol Identifier (TPID) value of 0x8100. This is located in the same place as the EtherType/Length field in untagged frames, so an EtherType value of 0x8100 means the frame is tagged, and the true EtherType/Length is located after the Q-tag. The TPID is followed by two octets containing
2838-407: Is post complemented, verify value = 0x2144DF1C), which will result in a CRC that is a bit reversal of the FCS, and transmit both data and the CRC least significant bit first, resulting in identical transmissions. The standard states that the receiver should calculate a new FCS as data is received and then compare the received FCS with the FCS the receiver has calculated. An alternative is to calculate
2924-404: Is the most commonly used limit, smaller and larger limits exist. Many Gigabit Ethernet switches and Gigabit Ethernet network interface controllers and some Fast Ethernet switches and Fast Ethernet network interface cards can support jumbo frames. Each Ethernet frame must be processed as it passes through the network. Processing the contents of a single large frame is preferable to processing
3010-417: 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. Jumbo frame In computer networking , jumbo frames are Ethernet frames with more than 1500 bytes of payload, the limit set by the IEEE 802.3 standard. The payload limit for jumbo frames is variable: while 9000 bytes
3096-459: 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,
3182-401: Is used to indicate the size of the payload in octets, while values of 1536 and above indicate that it is used as an EtherType, to indicate which protocol is encapsulated in the payload of the frame. When used as EtherType, the length of the frame is determined by the location of the interpacket gap and valid frame check sequence (FCS). The IEEE 802.1Q tag or IEEE 802.1ad tag, if present,
3268-518: Is used. The throughput may be calculated from the efficiency where the physical layer net bit rate (the wire bit rate) depends on the Ethernet physical layer standard, and may be 10 Mbit/s , 100 Mbit/s , 1 Gbit/s or 10 Gbit/s . Maximum throughput for 100BASE-TX Ethernet is consequently 97.53 Mbit/s without 802.1Q, and 97.28 Mbit/s with 802.1Q. Channel utilization is a concept often confused with protocol efficiency. It considers only
3354-693: The Castagnoli CRC polynomial . The Castagnoli polynomial 0x1EDC6F41 achieves the Hamming distance HD=6 beyond one Ethernet MTU (to a 16,360-bit data word length) and HD=4 to 114,663 bits, which is more than 9 times the length of an Ethernet MTU. This gives two additional bits of error detection ability at MTU-sized data words compared to the Ethernet CRC standard polynomial while not sacrificing HD=4 capability for data word sizes up to and beyond 72 kbits. Support of Castagnoli CRC polynomial within
3440-462: 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
3526-491: The Internet Protocol (IP) MTU, however, are reached only on networks that have a suitable link-layer infrastructure. Large send offload and large receive offload offload per-frame processing making CPU load largely independent of frame size. It is another way to eliminate the per-packet overhead that jumbo frames were designed to reduce. Jumbo frames are still useful from a bandwidth perspective, as they reduce
Ethernet frame - Misplaced Pages Continue
3612-477: 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
3698-465: The protocol overhead for Ethernet as a percentage (packet size including IPG) We may calculate the protocol efficiency for Ethernet Maximum efficiency is achieved with largest allowed payload size and is: for untagged frames, since the packet size is maximum 1500 octet payload + 8 octet preamble + 14 octet header + 4 octet trailer + minimum interpacket gap corresponding to 12 octets = 1538 octets. The maximum efficiency is: when 802.1Q VLAN tagging
3784-512: The IEEE Ethernet standards. Baby giant frames are, for example, required for IP/ MPLS over Ethernet to deliver Ethernet services with standard 1500 byte payloads. Most implementations will require non-jumbo user frames to be encapsulated into MPLS frame format which in turn may be encapsulated into a proper Ethernet frame format with EtherType values of 0x8847 and 0x8848. The increased overhead of extra MPLS and Ethernet headers means that
3870-514: The IPX packet directly after the length field. This does not conform to the IEEE 802.3 standard, but since IPX always has FF as the first two octets (while in IEEE 802.2 LLC that pattern is theoretically possible but extremely unlikely), in practice this usually coexists on the wire with other Ethernet implementations, with the notable exception of some early forms of DECnet which got confused by this. Novell NetWare used this frame type by default until
3956-440: 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
4042-574: 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
4128-568: The Tag Control Information (TCI) (the IEEE 802.1p priority ( quality of service ) and VLAN id). The Q-tag is followed by the rest of the frame, using one of the types described above. Ethernet II framing (also known as DIX Ethernet , named after DEC , Intel and Xerox , the major participants in its design), defines the two-octet EtherType field in an Ethernet frame , preceded by destination and source MAC addresses, that identifies an upper layer protocol encapsulated by
4214-627: 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
4300-468: 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
4386-547: The carrier is continually sent between frames; an example is Gigabit Ethernet with its 8b/10b encoding scheme that uses special symbols which are transmitted before and after a frame is transmitted. Interpacket gap (IPG) is idle time between packets. After a packet has been sent, transmitters are required to transmit a minimum of 96 bits (12 octets) of idle line state before transmitting the next packet. There are several types of Ethernet frames: The different frame types have different formats and MTU values but can coexist on
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#17327875556424472-502: The complement of 0x2144DF1C = 0xDEBB20E3, and for a left shifting implementation, the complement of 0x38FB2284 = 0xC704DD7B. The end of a frame is usually indicated by the end-of-data-stream symbol at the physical layer or by loss of the carrier signal; an example is 10BASE-T , where the receiving station detects the end of a transmitted frame by loss of the carrier. Later physical layers use an explicit end of data or end of stream symbol or sequence to avoid ambiguity, especially where
4558-560: The concept of an envelope where up to 482 bytes of header and trailer could be included, and the largest IEEE 802.3 supported Ethernet frame became 2000 bytes. The use of 9000 bytes as preferred payload size for jumbo frames arose from discussions within the Joint Engineering Team of Internet2 and the U.S. federal government networks. Their recommendation has been adopted by all other national research and education networks. Manufacturers have in turn adopted 9000 bytes as
4644-595: The conventional MTU size, with a total jumbo frame size of between 9014 and 9022 bytes with Ethernet headers included. Most Ethernet equipment can support jumbo frames up to 9216 bytes. IEEE 802.1AB -2009 and IEEE 802.3bc -2009 added LLDP discovery to standard Ethernet for maximum frame length ( TLV subtype 4). It allows frame length detection on a port by a two-octet field. As of IEEE 802.3-2015, allowed values are 1518 (only basic frames), 1522 (802.1Q-tagged frames), and 2000 (multi-tagged, envelope frames). Errors in jumbo frames are more likely to go undetected by
4730-432: The equipment's configuration interface. A network that has a mixture of devices configured for jumbo frames and devices not configured for jumbo frames may have performance issues. Jumbo frames can increase the efficiency of Ethernet and network processing in hosts by reducing the protocol overhead , as shown in the following example with TCP over IPv4 . The processing overhead of the hosts can potentially decrease by
4816-411: The frame data. Most notably, an EtherType value of 0x0800 indicates that the frame contains an IPv4 datagram, 0x0806 indicates an ARP datagram, and 0x86DD indicates an IPv6 datagram. See EtherType § Values for more. As this industry-developed standard went through a formal IEEE standardization process, the EtherType field was changed to a (data) length field in the new 802.3 standard. Since
4902-451: The frame is payload data including any headers for other protocols (for example, Internet Protocol ) carried in the frame. The frame ends with a frame check sequence (FCS), which is a 32-bit cyclic redundancy check used to detect any in-transit corruption of data. A data packet on the wire and the frame as its payload consist of binary data. Ethernet transmits data with the most-significant octet (byte) first; within each octet, however,
4988-412: The frame. Field sizes for this option are shown in brackets in the table above. IEEE 802.1ad (Q-in-Q) allows for multiple tags in each frame. This option is not illustrated here. An Ethernet packet starts with a seven-octet (56-bit) preamble and one-octet (8-bit) start frame delimiter (SFD). The preamble bit values alternate 1 and 0, allowing receivers to synchronize their clock at the bit-level with
5074-501: The least-significant bit is transmitted first. The internal structure of an Ethernet frame is specified in IEEE 802.3. The table below shows the complete Ethernet packet and the frame inside, as transmitted, for the payload size up to the MTU of 1500 octets. Some implementations of Gigabit Ethernet and other higher-speed variants of Ethernet support larger frames, known as jumbo frames . The optional 802.1Q tag consumes additional space in
5160-668: 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
5246-482: The lowest frame size in intermediate links. 802.5 Token Ring can support frames with a 4464-byte MTU , FDDI can transport 4352-byte, ATM 9180-byte and 802.11 can transport 7935-byte MTUs. The IEEE 802.3 Ethernet standard originally mandated support for 1500-byte MTU frames, 1518 byte total frame size (1522 byte with the optional IEEE 802.1Q VLAN / QoS tag). The IEEE 802.3as update grandfathered in multiple common headers, trailers, and encapsulations by creating
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#17327875556425332-665: 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
5418-512: The mid-nineties, and since NetWare was then very widespread, while IP was not, at some point in time most of the world's Ethernet traffic ran over "raw" 802.3 carrying IPX. Since NetWare 4.10, NetWare defaults to IEEE 802.2 with LLC (NetWare Frame Type Ethernet_802.2) when using IPX. Some protocols, such as those designed for the OSI stack , operate directly on top of IEEE 802.2 LLC encapsulation, which provides both connection-oriented and connectionless network services. IEEE 802.2 LLC encapsulation
5504-415: 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
5590-412: 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
5676-420: 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
5762-729: 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
5848-427: 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
5934-491: The original version of 802.3 framing to be used on the same Ethernet segment, EtherType values must be greater than or equal to 1536 (0x0600). That value was chosen because the maximum length of the payload field of an Ethernet 802.3 frame is 1500 octets (0x05DC). Thus if the field's value is greater than or equal to 1536, the frame must be an Ethernet II frame, with that field being a type field. If it's less than or equal to 1500, it must be an IEEE 802.3 frame, with that field being
6020-483: The path. Another important factor to consider is the further reduction of CRC32's effectiveness in detecting errors within even larger frame sizes. The Total Length field of IPv4 and the Payload Length field of IPv6 each have a size of 16 bits, thus allowing data of up to 65 535 octets . IPv6's jumbo payload option allows for up to 4 GiB (2 -1 bytes) payload. These theoretical limits for
6106-464: 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,
6192-456: 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
6278-457: The ratio of the payload sizes (approximately six times improvement in this example). Whether this is significant depends on how packets are processed in the host. A host that uses its network interface controller 's TCP offload engine with already reduced overhead receives less benefit than a host that processes frames with its CPU. The throughput by bandwidth efficiency can increase by 4.4%. The relative scalability of network data throughput as
6364-471: The recipient still needs to know how to interpret the frame, the standard required an IEEE 802.2 header to follow the length and specify the type. Many years later, the 802.3x-1997 standard, and later versions of the 802.3 standard, formally approved of both types of framing. Ethernet II framing is the most common in Ethernet local area networks, due to its simplicity and lower overhead. In order to allow some frames using Ethernet II framing and some using
6450-549: The same content broken up into smaller frames, as this makes better use of available CPU time by reducing interrupts. This also minimizes the overhead byte count and reduces the number of frames needing to be processed. This is analogous to physically mailing a packet of papers instead of several single envelopes with one sheet each, saving envelopes and cutting sorting time. Jumbo frames gained initial prominence in 1998, when Alteon WebSystems introduced them in their ACEnic Gigabit Ethernet adapters. Many other vendors also adopted
6536-416: The same physical medium. Differentiation between frame types is possible based on the table on the right. In addition, all four Ethernet frame types may optionally contain an IEEE 802.1Q tag to identify what VLAN it belongs to and its priority ( quality of service ). This encapsulation is defined in the IEEE 802.3ac specification and increases the maximum frame by 4 octets. The IEEE 802.1Q tag, if present,
6622-515: 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
6708-469: The simple CRC32 error detection of Ethernet and the simple additive checksums of UDP and TCP : as packet size increases, it becomes more likely that multiple errors cancel each other out. One IETF approach for adopting jumbo frames avoids data integrity reduction of the service data unit by performing an extra CRC at the next network protocol layer above Ethernet. Stream Control Transmission Protocol (SCTP) transport (RFC 4960) and iSCSI (RFC 7143) use
6794-493: 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,
6880-404: The size; however, jumbo frames are not part of the official IEEE 802.3 Ethernet standard. Jumbo frames have the potential to reduce overheads and CPU cycles and have a positive effect on end-to-end TCP performance. The presence of jumbo frames may have an adverse effect on network latency, especially on low-bandwidth links. The frame size used by an end-to-end connection is typically limited by
6966-569: The support for frames up to 1600 bytes is required in Carrier Ethernet networks. Jumbo frames for PPPoE is defined in RFC 4638, with the purpose of removing the old 1492-byte limit (originally defined because PPP needs 8 more bytes of overhead), so that normal 1500-byte Ethernet can run without fragmentation. The "PPP-Max-Payload" tag can still accommodate much larger, non-baby jumbo frames. Super jumbo frames (SJFs) are frames that have
7052-625: The transmitter. The preamble is followed by the SFD which ends with a 1 instead of 0, to break the bit pattern of the preamble and signal the start of the actual frame. Physical layer transceiver circuitry (PHY for short) is required to connect the Ethernet MAC to the physical medium. The connection between a PHY and MAC is independent of the physical medium and uses a bus from the media-independent interface family ( MII , GMII , RGMII , SGMII , XGMII ). The preamble and SFD representation depends on
7138-494: The use of the channel disregarding the nature of the data transmitted – either payload or overhead. At the physical layer, the link channel and equipment do not know the difference between data and control frames. We may calculate the channel utilization : The total time considers the round trip time along the channel, the processing time in the hosts and the time transmitting data and acknowledgements. The time spent transmitting data includes data and acknowledgements. A runt frame
7224-593: The value 0xAA, the LLC header is followed by a SNAP header. The SNAP header allows EtherType values to be used with all IEEE 802 protocols, as well as supporting private protocol ID spaces. In IEEE 802.3x-1997, the IEEE Ethernet standard was changed to explicitly allow the use of the 16-bit field after the MAC addresses to be used as a length field or a type field. The AppleTalk v2 protocol suite on Ethernet (" EtherTalk ") uses IEEE 802.2 LLC + SNAP encapsulation. We may calculate
7310-540: The width of the bus: ( GMII bus for Gigabit Ethernet transceivers) The SFD is immediately followed by the destination MAC address , which is the first field in an Ethernet frame. The header features destination and source MAC addresses (each six octets in length), the EtherType field and, optionally, an IEEE 802.1Q tag or IEEE 802.1ad tag. The EtherType field is two octets long and it can be used for two different purposes. Values of 1500 and below mean that it
7396-462: 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
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