QTECH QSW-3400 Инструкция по настройке - Manual (Page 52)

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connection through the management connection.
There are two types of data connections: active connection and passive connection.
In active connection, the client transmits its address and port number for data transmission to
the server, the management connection maintains until data transfer is complete. Then, using
the address and port number provided by the client, the server establishes data connection on
port 20 (if not engaged) to transfer data; if port 20 is engaged, the server automatically
generates some other port number to establish data connection.
In passive connection, the client, through management connection, notify the server to
establish a passive connection. The server then creates its own data listening port and informs
the client about the port, and the client establishes data connection to the specified port.
As data connection is established through the specified address and port, there is a third party
to provide data connection service.
TFTP builds upon UDP, providing unreliable data stream transfer service with no user
authentication or permission-based file access authorization. It ensures correct data
transmission by sending and acknowledging mechanism and retransmission of time-out
packets. The advantage of TFTP over FTP is that it is a simple and low overhead file transfer
service.
Switch can operate as either FTP/TFTP client or server. When switch operates as a FTP/TFTP
client, configuration files or system files can be downloaded from the remote FTP/TFTP
servers (can be hosts or other switches) without affecting its normal operation. And file list can
also be retrieved from the server in ftp client mode. Of course, switch can also upload current
configuration files or system files to the remote FTP/TFTP servers (can be hosts or other
switches). When switch operates as a FTP/TFTP server, it can provide file upload and
download service for authorized FTP/TFTP clients, as file list service as FTP server.
Here are some terms frequently used in FTP/TFTP.
ROM: Short for EPROM, erasable read-only memory. EPROM is repalced by FLASH memory
in switch.
SDRAM: RAM memory in the switch, used for system software operation and configuration
sequence storage.
FLASH: Flash memory used to save system file and configuration file.
System file: including system image file and boot file.
System image file: refers to the compressed file for switch hardware driver and software
support program, usually refer to as IMAGE upgrade file. In switch, the system image file is
allowed to save in FLASH only. Switch mandates the name of system image file to be
uploaded via FTP in Global Mode to be nos.img, other IMAGE system files will be rejected.
Boot file: refers to the file initializes the switch, also referred to as the ROM upgrade file
(Large size file can be compressed as IMAGE file). In switch, the boot file is allowed to save in