The network uses physical links to isolate eachworkstationorhostConnected together to formdata link To achieveresource sharingAnd communication purposes.Communication is the exchange and transmission of information between people through certain media.Network communication is to connect each isolated device through the network, and realize the communication between people, people and computers, computers and computers through information exchange.
The most important thing in network communication isNetwork communication protocol。todayNetwork ProtocolThere are many,LANThere are three most commonly used network protocols in: NETBEUI of MICROSOFT and NOVELLIPX/SPXandTCP/IP protocol。The appropriate network protocol shall be selected as required.
To put it plainly,Network ProtocolIt is a bridge for communication and exchange between networks, only with the same network protocolcomputerTo communicate and exchange information.This is just like all kinds of languages used in interpersonal communication. Only using the same language can we communicate normally and smoothly.From a professional perspective,Network ProtocolyescomputerThe agreement that must be followed when realizing communication in the network, that iscommunication protocol。Mainly rightinformation transmissionRate and transmission ofcode, code structure, transmission controlstep, error control, etcstandard。
Protocol Selection
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Network Communications
Faced with numerousNetwork Protocol, we may have no choice.But if you know in advanceNetwork ProtocolThe main purpose of the can be targeted choice.Here are some commonly usedNetwork Protocol：
NetBEUI (NetBIOS Enhanced UserInterface) Network Basic Input/Output System ExtensionUser interface
NetBEUI protocolIt was proposed by IBM in 1985.NetBEUI is mainly for 20 to 200 workstationsSmall LANDesigned for NetBEUI, LanMan, Windows For WorkgroUPS and Windows NT.NetBEUI is a compact and fast protocol, but since NetBEUI does notrouteCapability, that is, it is not possible to accessRouterTo another LAN, it can no longer adapt to a larger network.if necessaryrouteTo other LAN, you must install TCP/IP orIPX/SPXagreement.
It is proposed by Novell for customers/The serverConnectedNetwork Protocol。useIPX/SPX protocolCapable of running those that usually need NetBEUI supportprogram, which can be crossed through the IPX/SPX protocolRouterAccess other networks.
It is a set ofNetwork nodeA protocol for transferring data between.In HDLC, data is sent through the network in units (called frames), and received by the receiver.HDLC protocolAlso managedata streamAnd data transmission interval.HDLC isdata link layerOne of the most widely used protocols in.As an ISO standard, HDLC is based on IBM's SDLC protocol, which is widely used in IBM's mainframe environment.In HDLC, SDLC is called pass responsepattern（NRM）。In normal responsepatternIn, the base station (usually a mainframe) sends data to a local or remote secondary station.Different types of HDLC are used10. 25 Protocol's network andFrame relayNetwork, this protocol can be used in the LAN orWANWhether the network is public or private.
It is a delivery protocol used to deliver hypertext on the Internet.It is an HTTP application protocol running on the TCP/IP protocol family. It can makebrowserMore efficientnetwork transmissionDecrease.whateverThe serverIn addition to includingHTML fileIn addition, there is an HTTPResident program, used to respond to user requests.YourbrowserIt is an HTTP clientThe serverSend a request when a start file is entered or clicked in the browserHyperlinkThe browser sends theHTTP Request, the request is sent to the URL specified by the IP address.Resident programAfter receiving the request, send back the required file after necessary operations.
It is developed by Netscape and built into itsbrowserIt is used to compress and decompress data and return the results sent back by network upload.HTTPS actually applies Netscape's completesocketLayer (SSL) as HTTPapplication layerSublayer of.(HTTPS uses port 443 instead of port 80 to communicate with TCP/IP as HTTP does.) SSL uses 40 bit keywords as RC4 streamsencryption algorithm , which is suitable for the encryption of business information.X.509 is supported for HTTPS and SSLDigital authenticationIf necessary, the user can confirm who the sender is.
It is ahostandgatewayMessage control and error betweenpresentationagreement.ICMP usageIP datagram, but messages areSoftwareProcessing, forapplication programThe user is invisible.In a system called Catenet, the IP protocol is used ashostTo hostDatagram service。Network connection devicebe calledgateway。these ones heregatewayInformation for control is exchanged between each other through the Gateway to Gateway Protocol (GGP).Usually, maintenance or purposehostWill communicate with the source host, for examplepresentationError during datagram.ICMP is used for this purpose. It uses IP as the underlying support, as if it is a high-level protocol, but actually it is part of IP and must be implemented by other IP modules.ICMP messages are sent in the following cases: when datagrams cannot reach the destination, whengatewayHas been lostcacheFunction, when the gateway can boothostSend on shorter routes.IP is not designed to be absolutely reliable. The purpose of this protocol is to return control information in case of network problems, not to make the IP protocol absolutely reliable. It does not guarantee that datagrams or control information can be returned.Some datagrams will still have nopresentationIs lost.[1]
Common protocols
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Different workstations in the network,The serverThe data can be transferred between, which is due to the existence of the protocol.With the development of network, different developers have developed different communication methods.In order to make communication successful and reliable, allhostAll must use the same language, without dialects.Therefore, strict standard definitions must be developedhostEvery bit in every word in every packet between.These standards come from the efforts of many organizations to agree on a common communication mode, that is, protocol.These make communication easier.Many protocols have been developed, but only a few have been retained.There are many reasons for the obsolescence of those protocols - poor design, poor implementation or lack of support.Those protocols that remain have experienced the test of time and become effective communication methods.
NETBEUI
NETBEUI is developed for IBMRouting Protocol, used to carry NETBIOS communication.NETBEUI lacks routing and network layersaddressingFunction is both its greatest advantage and its biggestshortcoming。Because it doesn't need additionalnetwork addressAnd the head and tail of the network layer, so it is fast and effective and suitable for only a single network or the entire environmentbridgingLittle upWorking GroupEnvironmental Science.
Network Communications
Because it is not supportedroute, so NETBEUI will never become the main protocol for enterprise networks.NETBEUI frame
The bridge is responsible forData link layer addressForwarding communication between networks has many disadvantages.Because all the wide
The broadcast communication must be forwarded to each network, so the scalability of the bridge is not good.NETBEUI specifically includes the counting of broadcast communications and relies on it to resolve naming conflicts.In general, bridging NETBEUI networks rarely exceeds 100 hosts.Depends on the second layerexchangerThe Internet has become more common.The complete conversion environment reduces the utilization rate of the network, although the broadcast is still forwarded to each host in the network.In fact, the joint use of 100-BASE-T Ethernet allows the NetBIOS network to be converted to 350 hosts, so as to avoid the broadcast communication becoming a serious problem.
IPX/SPX
IPX is NOVELL for NETWAREclient/The serverThis protocol group avoids the weakness of NETBEUI.However, it brings new and different weaknesses.
IPX has full routing capability and can be used in large enterprise networks.It includes 32 bitsnetwork address, many routing networks are allowed in a single environment.
The scalability of IPX is limited by its high-level broadcast communication and high overhead.Service advertisementService Advertising Protocol (SAP) willrouteThe number of hosts in the network is limited to several thousand.Although SAP's limitations have beenIntelligent routerandServer ConfigurationHowever, large-scale IPX networkadministratorsIt is still very difficult work.
TCP/IP
EachNetwork ProtocolBoth have their own advantages, but only TCP/IP allows a complete connection to the Internet.TCP/IP was developed byMassachusetts Institute of TechnologyAnd some business organizationsU.S. Department of DefenseDeveloped, TCP/IP can still maintain effective communication even if most networks are damaged by nuclear attacks.ARPANET was developed based on protocols and developed into the Internet as a communication medium for scientists and engineers.
TCP/IP has both scalability and reliabilitydemand。Unfortunately, the speed andefficiency(However, the development of TCP/IP was funded by the government.).
After the Internet became public, people began to discover the powerful functions of the global network.The universality of the Internet is the reason TCP/IP is still used.Often without realizing it, users install TCP/IP stacks on their PCsNetwork ProtocolIt is the most widely used in the world.
The 32-bit addressing function scheme of TCP/IP is insufficient to support the number of hosts and networks that will join the Internet.Therefore, the standard that may replace the current implementation is IPv6.
RS-232-C
RS-232-CIs OSI basicreference model The specification of the physical layer part, which determines the physical characteristics such as the connector shape, the electrical characteristics represented by 0 and 1, and the logical characteristics representing the signal meaning.RS-232-C is a modified version of RS-232-B published by EIA.Originally for connection simulationCommunication lineInModemSuch as DCE and DTE such as teletype printerInterfaceAnd standardized.quite a lotpersonal computerAlso use RS-232-C asI/O interfacePersonal computers with RS-232-C as the interface are also very popular.RS-232-C has the following characteristics: straight through mode, two-way communication, basic frequency band, current loop mode, serial transmission mode, signal form used between DCE-DTEs, handover mode,Full duplex communication。RS-232-C 25 pin connector specified in V.24 and V.28 recommended by ITU is functionally interchangeable.The connector used for RS-232-C is a 25 pin plug-in connector, commonly referred to as a 25 pin D-SUB.The top of the cable at DTE end is connected to the male plug, and the DCE end is connected to the female socket.The shape of the cable used for RS-232-C is not fixed, but mostly 24 core cable with shielding is used.The maximum length of cable is 15m.Data transmission can be carried out at any rate below 200K bit/s using RS-232-C.
RS-449
RS-449It is a standard published by EIA in 1977, which specifies the mechanical and electrical characteristics between DTE and DCE.RS-449 is a standard developed to replace RS-232-C, but almost allData communication equipmentThe manufacturer still adopts the original standard, so RS-232-C is still the most popular interface and is widely used.The RS-449 connector uses the ISO specification 37 pin and 9-pin connectors. All connected circuits other than the secondary channel (return word channel) circuit use the 37 pin connector, while the secondary channel circuit uses the 9-pin connector.The electrical characteristics of RS-449 are specified by RS-422-A for the balance circuit, which is generally the same specification as V.11, while RS-423-A is generally the same specification as V.10.V.355. 35 is universalterminalIn fact, V.35 is for the 60-108kHz groupbandwidthThe provisions of the line for 48Kbps synchronous data transmission modem, part of which describes the provisions of the terminal interface.5. 35 The mechanical characteristics, i.e. the shape of the connector, are not specified.But because 48Dbps - 64KbpsU.S.AWith the popularity of Bell modems, 34 pin ISO2593 is widely used.The electrical conditions of audio modems for analog transmission use V.28 (unbalanced current loop interconnection circuit), while broadband modems use balanced current loop circuit.X.2110. 21 YesPublic data networkSynchronous Terminal (DTE) andLine terminal(DCE).Two functions are mainly specified: one is the same as other interfaces, the physical layer of electrical characteristics, connector shape, and functional characteristics of interconnecting circuits are specified;The second is to controlNetwork switchingThe network control steps of functions define the functions of the network layer.Only the physical layer function is used for the connection of private lines, while in the line switched data network, the physical layer and network layer functions are used.10. The connector pins used for the 21 interface also only use 15 pin electrical characteristics, respectively referring to V.10 and V.11 of the electrical conditions of the V series interface.The digital network synchronization is subordinate to the network master clock.
HDLC (Advanced Data Link Control Procedure)
HDLC is a control procedure with high reliability and high-speed transmission.Its characteristics are as follows: any bit combination can be transmitted;It can transmit data continuously without waiting for the response from the receiving end;Tight error control;Suitable forcomputerCommunication between.HDLC is equivalent to OSI basic referenceModelOfdata link layerPart of the standard way.HDLC has a wide range of applications. Most of the data link layers of modern protocols are based on HDLC.
SDLC (synchronous data link control)
It is the agreement made by IBM and becomes the SNA'sData link control layeragreement.It is actually included in HDLC.
FDDI (Fiber Distributed Data Interface)
The transmission speed of FDDI is 100Mbps, and the transmission media isOptical fiber, is the token controlled LAN.The physical transmission clock speed of FDDI is 125MHz, but the actual speed is only 100Mbps.The maximum number of workstations that can be physically connected is 500, but less than 100 are recommended.There are basically two connection forms of FDDI: one is a ring structure composed of two rings of primary loop and secondary loop;The other is based onHubForm a tree structure for the center.The distance between workstations is 2KM with optical fiberTwisted pair100M.However, for single-mode fiber, the distance between nodes can be extended to more than 2KM.FDDI has three interfaces: DAS (dual accessory station);SAS (single accessory station);Hub.Generally, only the primary loop is used, and the secondary loop is in standby status as a standby system.
SNMP (Simple Network Management Protocol)
TCP/IP protocolCentralizedNetwork Management Protocol。It has been widely adopted.The protocol that uses SNMP management model to manage Internet works in the application layer of TCP/IP.Its advantages are that protocols can be specified independent of the attributes of the network physical layer, common protocols can be used for all networks and management, and customers can be used between the manager and the managed/The serverIs called agent (tool);If the manager works as a client, it can be called a manager or a management station.The function of the agent should includeoperating systemAnd the network management layer, obtain the seven layer information about the object, and use the SNMP network management protocol to notify the manager of this information.Managers themselves should require that information about objects be stored in the virtual database of the MIB (management information base) contained in the agent.For SNMP, it is required to be able to obtain or set the objects from the management to the agent network management object itself.The agent should complete the answer required by the manager.At the same time, the agent itself should also notify the manager of events that occur because of the agent.10、 The PPP (point to point protocol), formulated as RFC1171/1172, isPoint to pointAn Internet standard protocol that relays LAN protocols, including IP, on a line.PPP corresponds to multiple protocols since its inception, and is designed to be independent of network layer protocolsdata link 。When using PPP to relay each network layer protocol, each network layer protocol must have a specification corresponding to PPP. Some of these specifications already exist.The actual installation of PPP has begun, especially the one that must adapt to multi protocolRouterThe manufacturer actively adopts PPP.PPP consists of two protocols: one is to ensure that thedata link LCP (Data Link Control Protocol);The other is to use the network layer protocol to control the NCP in the PPP environment（Network Control Protocol）。For its purpose, NCP needs to be specified in each network layer protocol.The specific names of NCPs are different in the corresponding network layer protocols.To be more precise, the protocol stipulated in PPP is only LCP. How to put NCP and network layer protocol into PPP frame is up to the manufacturers who develop various network layer protocols.PPP frame has the function of transmitting LCP, NCP and network layer protocols.There are no special restrictions on the physical layer specification using LCP.RS-232-CRS-422/423, V.35 and other general physical connectors.The application field of transmission speed is not specially specified, and the transmission speed allowed by the physical layer specification can be used.Instead, full duplex communication lines should be used.[2]
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IPnetworkCommunication isChinaA professional portal in the field of network communication, covering IP voice communication, UC unified communication, video conferencewireless communication , call center, cloud computing, IPcommunications technologyIP communication products, IP communication manufacturers, IP communication service providers, IPCommunication talents, solutions, etc.
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