User Manual

4-17
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 ROM only.
Switch mandates the name of the boot file to be boot.rom.
 Configuration file: including start up configuration file and running configuration file. The
distinction between start up configuration file and running configuration file can facilitate the
backup and update of the configurations.
 Start up configuration file: refers to the configuration sequence used in switch start up. Switch
start up configuration file stores in FLASH only, corresponding to the so called configuration save.