Specifications

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DCS-3950 series Ethernet switch manual
between the client and the server: a management connection and a data connection. A
transfer request should be sent by the FTP client to establish management connection on
port 21 in the server, and negotiate a data 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.
DCS-3950 series switch can operate as either FTP/TFTP client or server. When
DCS-3950 series switch operated 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, DCS-3950 series switch can also upload current configuration
files or system files to the remote FTP/TFTP servers (can be hosts or other switches).
When DCS-3950 series 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 DCS-3950 series 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 DCS-3950 series switch, the
system image file is allowed to save in FLASH only. DCS-3950 series 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 DCS-3950 series switch, the boot