TCP IP Illustrated

5 and 515 ms fast alternatives there are other ways

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Unformatted text preview: ne of ASCII characters. We can test this service using the telnet command: sun % telnet bsdi daytime Trying ... Connected to bsdi. Escape character is "^]" Wed Feb 3 16:38:33 1993 Connection closed by foreign host. first three lines output are from the Telnet client here's the daytime service output this is also from the Telnet client The time server, on the other hand, returns a 32-bit binary value with the number of seconds since midnight January 1, 1900, UTC. While this provides the date, the time value is in units of a second. (The rdate command that we mentioned earlier uses the TCP time service.) 2. Serious timekeepers use the Network Time Protocol (NTP) described in RFC 1305 [Mills 1992]. This protocol uses sophisticated techniques to maintain the clocks for a group of systems on a LAN or WAN to within millisecond accuracy. Anyone interested in precise timekeeping on computers should read this RFC. 3. The Open Software Foundation's (OSF) Distributed Computing Environment (DCE) defines a Distributed Time Service (DTS) that also provides clock synchronization between computers. [Rosenberg, Kenney, and Fisher 1992] provide additional details on this service. file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/icmp_int.htm (9 of 16) [12/09/2001 14.46.42] Chapter 6. ICMP: Internet Control Message Protocol 4. Berkeley Unix systems provide the daemon timed(8) to synchronize the clocks of systems on a local area network. Unlike NTP and DTS, timed does not work across wide area networks. 6.5 ICMP Port Unreachable Error The last two sections looked at ICMP query messages-the address mask and time-stamp queries and replies. We'll now examine an ICMP error message, the port unreachable message, a subcode of the ICMP destination unreachable message, to see the additional information returned in an ICMP error message. We'll watch this using UDP (Chapter 11). One rule of UDP is that if it receives a UDP datagram and the destination port does not correspond to a port that some process has in use, UDP responds with an ICMP port unreachable....
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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