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Unformatted text preview: this is RFC 1009 [Braden and
Postel 1987], but a new version is nearing completion [Almquist 1993]. This is similar to
the host requirements RFCs, but specifies the unique requirements of routers. 1.12 Standard, Simple Services
There are a few standard, simple services that almost every implementation provides. We'll use
some of these servers throughout the text, usually with the Telnet client. Figure 1.9 describes
these services. We can see from this figure that when the same service is provided using both
TCP and UDP, both port numbers are normally chosen to be the same.
If we examine the port numbers for these standard services and other standard TCP/IP services (Telnet, FTP,
SMTP, etc.), most are odd numbers. This is historical as these port numbers are derived from the NCP port
numbers. (NCP, the Network Control Protocol, preceded TCP as a transport layer protocol for the ARPANET.)
NCP was simplex, not full-duplex, so each application required two connections, and an even-odd pair of port
numbers was reserved for each application. When TCP and UDP became the standard transport layers, only a
single port number was needed per application, so the odd port numbers from NCP were used. Name TCP
port echo 7 7 862 Server returns whatever the client sends. discard 9 9 863 Server discards whatever the client sends. daytime 13 13 867 Server returns the time and date in a human-readable
format. 864 TCP server sends a continual stream of characters,
until the connection is terminated by the client. UDP
server sends a datagram containing a random number
of characters each time the client sends a datagram. 868 Server returns the time as a 32-bit binary number. This
number represents the number of seconds since
midnight January 1, 1900, UTC. chargen time 19 37 19 37 RFC Description Figure 1.9 Standard, simple services provided by most implementations. 1.13 The Internet
In Figure 1.3 we showed an internet composed of two networks - an Ethernet and a token ring. file://...
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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.
- Spring '12