D-Link DES-3326S - Switch - Stackable, Руководство пользователя

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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
104
Switch Management and Operating Concepts
the response are very short. There is no need to divide the
query or response between multiple packets, so the complexity
of TCP is not required. If there is no response to the query
after a period of time, the query can simply be resent.
The User Datagram Protocol (UDP) is designed for
communications that do not require division among multiple
packets and subsequent reassembly. UDP does not keep track
of what is sent.
UDP uses port numbers in a way that is directly analogous to
TCP. There are well-known UDP port numbers for servers that
use UDP.
Figure 5-13. Ethernet Packet Header
The UDP header is shorter than a TCP header. UDP also uses
a checksum to verify that data is received uncorrupted.
The Internet Control Message Protocol (ICMP) is also a
simplified protocol used for error messages and messages used
by TCP/IP. ICMP, like UDP, processes messages that will fit
into a single packet. ICMP does not, however use ports
because its messages are processed by the network software.