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.It also considerswit wants avoiding the unnecessary trans-algorithms and strategies for improvingmission of what could be dozens of mega-xaccuracy or at least minimizing lossbytes.This selective capability also comes inof accuracy during the multistep process.yz836 Protocol, OSPF (Open Shortest Path First)Depending on the host s location in relation Because the protocol monitors the trans-to a time server, NTP is accurate to within mission, only lost or erroneous packets need1 50 milliseconds.to be retransmitted, not the entire burst.TheServers can disseminate the time informa- figure  Communications with and withouttion by unicasts (point-to-point transmis- packet burst illustrates how Packet Burstsions) or by multicasts (transmission to works in contrast to other methods.Use ofall parties on a multicast list).The group this protocol is sometimes known as operat-address and memberships are determined by ing in burst mode.the Internet Group Management Protocol(IGMP).Protocol, PAP (Printer AccessProtocol)PRIMARY SOURCESNTP version 3 is described in RFC 1305.In the AppleTalk protocol suite, the protocolA simpler, less accurate, variant SNTP,used for communication between nodesor simple network time protocol is(Macintoshes) and printers.PAP is used toproposed in RFC 1769.set up, maintain, and terminate the connec-tion between node and printer, and also totransfer the data.Protocol, OSPF (Open ShortestPath First)Protocol, PEP (Packet ExchangeIn internetworks that use the TCP/IP proto-Protocol)col suite, a routing protocol for passingpackets between routers in networks withinA transport level protocol in the XNS proto-a given domain.(The open in the name is ancol suite from Xerox.adjective, not a verb, and is in contrast toproprietary.) OSPF is an example of a link-Protocol, PLP (Packet Level Protocol)state protocol, in which routers provideA protocol that specifies the details ofupdated information only when there isdata transfer between sender and receiversomething new to report.OSPF is also anin an X.25 connection.PLP is full duplexexample of an Interior Gateway Protocoland supports error detection and correc-(IGP).tion, packet sequencing, and transfer-rateadjustment.Protocol, Packet BurstIn Novell s NetWare, the Packet Burst proto-Protocol, POP3 (Post Officecol can be used on top of IPX (InternetworkProtocol, 3)Exchange Protocol) to send multiple NCPPOP3 is the most recent version of the(NetWare Control Protocol) packets.It canPost Office Protocol used to provide clientssend an entire burst, without waiting for anwith access to a mail drop (post office) inacknowledgment after each packet.which messages for the user may be stored.Protocol, POP3 (Post Office Protocol, 3) 837COMMUNICATIONS WITH AND WITHOUT PACKET BURSTabWithout Packet Burst ModecPacket 1 SentdPacket 1 ACKefPacket 2 SentgClient ServerPacket 2 ACKh.iPacket n SentjPacket n ACKklmWith Packet Burst ModenPacket Burst 1 SentoBurst 1 ACKpqPacket Burst 2 SentClient Server rBurst 2 ACKs.tPacket Burst n SentuBurst n ACKvwxyz838 Protocol, PPP (Point-to-Point Protocol)PRIMARY SOURCESWith POP3, users can retrieve any e-mailmessages being held in temporary storage POP3 is described in RFC 1725.on a POP3 server.By default, POP3 service is providedProtocol, PPP (Point-to-Pointon Port 110.POP3 sessions involve theProtocol)exchange of messages between the client andPPP is used to transmit TCP/IP packets overserver.Messages passing between them con-telephone lines.The protocol provides a wayform to the message format specified in RFCof encapsulating datagrams so that they can822.The session consists of two kinds ofbe transmitted over a serial connection.Inmessages: commands and responses.addition to the encapsulation mechanisms,A POP3 session proceeds throughPPP includes a Link Control Protocol (LCP)several phases:component that is used to establish, config-Connection: The client opens a connec-ure, maintain, and terminate the connection.tion, and the server replies with a posi-Finally, PPP includes a collection of Net-tive greeting for example,work Control Protocols (NCPs) to deal withthe various network layer protocols thatS: +OK POP3 server readymight be encountered.Authorization: Once a connection isTo establish point-to-pointestablished, the server requires the cli-communications,ent to provide authentication.TwoPPP first uses LCP to establish and testmechanisms are available for doinga link, and to agree on a configurationthis.One of these involves encryption(for example, what packet framingand is used when a user doesn t wantmethod to use).The LCP may requireto be sending passwords.authentication from its peer at theTransaction: During this phase, theother end [ Pobierz całość w formacie PDF ]