Panasonic NN46240-501 - Manual (Page 138)

Nortel Secure Router 8000 Series
Configuration Guide - Basic Configuration 8 FTP, TFTP, and Xmodem
8.2 Introduction
8.2.1 FTP
8.2.2 TFTP
This section describes basic FTP, TFTP, and Xmodem concepts.
File Transfer Protocol (FTP) is an application layer protocol in the TCP/IP protocol suite. It
implements file transfer between remote hosts based on corresponding file systems.
The router provides the following FTP services:
• FTP server service. Users can run the FTP client program to log on to the router and
access the files on the router.
• FTP client service. Users can establish a connection with the router by running a terminal
emulation program or a Telnet program on a PC, and then enter an FTP command to
connect with the remote FTP server and access the files on the remote host.
FTP supports two file transfer formats:
• Binary format for program files
• ASCII format for text files
Compared with FTP, Trivial File Transfer Protocol (TFTP) provides a simple interactive
access interface and authentication control. TFTP is suitable in an environment where no
complex interaction occurs between the client and the server. For example, TFTP is used to
obtain the memory image of the system when the system starts up.
TFTP is implemented based on User Datagram Protocol (UDP).
The client initiates the TFTP transfer. To download files, the client sends a read request packet
to the TFTP server, receives packets from the server, and sends acknowledgement to the
server. To upload files, the client sends a write request packet to the TFTP server, sends
packets to the server, and receives acknowledgement from the server.
The Secure Router 8000 Series can serve as the TFTP client only and, therefore, can only
transfer files in the binary format.
8.2.3 Xmodem
The Xmodem file transfer protocol is widely used due to its simplicity and performance.
Xmodem transfers files through serial interfaces. It supports packets of 128 bytes and
1 kilobyte, common checksum and cyclical redundancy check (CRC), and retransmission
(usually 10 times) when packet error occurs.
• Xmodem file transfer consists of a receiving program and a sending program. The
receiving program first sends the negotiation character to negotiate the check mode.
• After the negotiation succeeds, the sending program begins to send packets.
• When the receiving program receives a complete packet, it checks the packet according
to the negotiated mode:
• The receiving program sends the acknowledgement character after the check passes. The
sending program then sends the next packet.
Issue 5.3 (30 March 2009) Nortel Networks Inc. 8-5