WatchGuard x1000 参考指南
Transfer Protocols
Reference Guide
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addresses. On the present Internet, typical long-haul
transmissions can involve twenty or thirty hops, rendering the
record route option obsolete.
transmissions can involve twenty or thirty hops, rendering the
record route option obsolete.
Time Stamp
The time stamp option helps measure network propagation
delays. This task is done more effectively, however, with higher-
level time protocols or time-stamp messages.
delays. This task is done more effectively, however, with higher-
level time protocols or time-stamp messages.
Transfer Protocols
The IP protocol encapsulates information contained in the transport layer.
The transport layer has several protocols that specify how to transmit
data between applications: for example, UDP, TCP, ICMP, and others.
The transport layer has several protocols that specify how to transmit
data between applications: for example, UDP, TCP, ICMP, and others.
UDP
User Datagram Protocol (UDP) is a connectionless, potentially unreliable
datagram protocol. It trades reliability for speed and low overhead. To
ensure accurate transmission, it requires that the application layer verify
that packets arrive at their destination.
datagram protocol. It trades reliability for speed and low overhead. To
ensure accurate transmission, it requires that the application layer verify
that packets arrive at their destination.
Characteristics of UDP include:
•
•
Often used for services involving the transfer of small amounts of
data where retransmitting a request is not a problem.
data where retransmitting a request is not a problem.
•
Used for services such as time synchronization in which an
occasionally lost packet will not affect continued operation. Many
systems using UDP resend packets at a constant rate to inform their
peers about interesting events.
occasionally lost packet will not affect continued operation. Many
systems using UDP resend packets at a constant rate to inform their
peers about interesting events.
•
Primarily used on LANs, in particular for Network File System (NFS)
services where its low overhead gives it a substantial performance
advantage. (Network File System is a popular TCP/IP service for
providing shared file systems over a network.) A lack of congestion
control means that using UDP for bulk data transfer over long-haul
connections is not recommended.
services where its low overhead gives it a substantial performance
advantage. (Network File System is a popular TCP/IP service for
providing shared file systems over a network.) A lack of congestion
control means that using UDP for bulk data transfer over long-haul
connections is not recommended.
•
Supports broadcasts.
•
Provides abstraction of ports.