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tramadol overnight Compressed TCP/IP-Sessions using SSH-like tools Sebastian Schreiber < tramadol overnight chreib@SySS.de> 2.2.2000 1. Introduction In the past, we used to c tramadol overnight mpress files in order to save disk space. Today, disk space is cheap tramadol overnight but bandwidth is limited. By compressing data streams, you achieve t tramadol overnight o goals: 1) You save bandwidth/transfered volume (that is important i tramadol overnight you have to pay for traffic or if your network is loaded.). 2) Spee tramadol overnight ing up low-bandwidth connections (Modem, GSM, ISDN). This HowTo expla tramadol overnight ns how to save both bandwith and connection time by using tools like tramadol overnight SH1, SSH2, OpenSSH or LSH. 2. Compressing HTTP/FTP,... My office is tramadol overnight connected with a 64KBit ISDN line to the internet, so the maximum tra tramadol overnight sfer rate is about 7K/s. You can speed up the connection by compressi tramadol overnight g it: when I download files, Netscape shows up a transfer rate of up tramadol overnight o 40K/s (Logfiles are compressable by factor 15). SSH is a tool that tramadol overnight s mainly designed to build up secure connections over unsecured netwo tramadol overnight ks. Further more, SSH is able to compress connections and to do port tramadol overnight orwarding (like rinetd or redir). So it is the appropriate tool to c tramadol overnight mpress any simple TCP/IP connection. "Simple" means, that only one TC tramadol overnight -connection is opened. An FTP-connections or the connection between M tramadol overnight -Outlook and MS-Exchange are not simple as several connections are es tramadol overnight ablished. SSH uses the LempleZiv (LZ77) compression algorithm - so yo tramadol overnight will achieve the same high compression rate as winzip/pkzip. In orde tramadol overnight to compress all HTTP-connections from my intranet to the internet, I tramadol overnight just have to execute one command on my dial-in machine: ssh -l -C -L8080::80 -f sleep 10000 tramadol overnight = my login-ID on =the web proxy of my ISP tramadol overnight y browser is configured to use localhost:8080 as proxy. My laptop con tramadol overnight ects to the same socket. The connection is compressed and forwarded t tramadol overnight the real proxy by SSH. The infrastructure looks like: tramadol overnight 64KBit ISDN My PC--------------------------------A PC (Unix/Linux/ tramadol overnight in-NT) at my ISP SSH-Client compressed SSH-Server, Por tramadol overnight 22 Port 8080 | | tramadol overnight | | | | tramadol overnight | |10MBit Ethernet |100M tramadol overnight it |not compressed |not compressed | tramadol overnight | | | tramadol overnight y second PC ISP's WWW-proxy with Netscape,... tramadol overnight Port 80 (Laptop) 3. Compressing Email 3.1. Inc tramadol overnight ming Emails (POP3, IMAP4) Most people fetch their email from the mail tramadol overnight erver via POP3. POP3 is a protocol with many disadvantages: 1. POP3 tramadol overnight ransfers password in clear text. (There are SSL- implementations o tramadol overnight POP/IMAP and a challenge/response authentication, defined in RFC- tramadol overnight 095/2195). 2. POP3 causes much protocol overhead: first the client re tramadol overnight uests a message than the server sends the message. After that the tramadol overnight lient requests the transferred article to be deleted. The server c tramadol overnight nfirms the deletion. After that the server is ready for the next tramadol overnight transaction. So 4 transactions are needed for each email. 3. POP3 t tramadol overnight ansfers the mails without compression although email is highly com tramadol overnight ressible (factor=3.5). You could compress POP3 by forwarding localhos tramadol overnight :110 through a compressed connection to your ISP's POP3-socket. After that you have to tell your mail client to connect to localhost:110 in order to download mail. That secures and speeds up the connection -- but the download time still suffers from the POP3-inherent protocol overhead. It makes sense to substitute POP3 by a more efficient protocol. The idea is to download the entire mailbox at once without generating protocol overhead. Furthermore it makes sense to compress the connections. The appropriate tool which offers both features is SCP. You can download your mail-file like this: scp -C -l loginId:/var/spool/mail/loginid /tmp/newmail But there is a problem: what happens if a new email arrives at the server during the download of your mailbox? The new mail would be lost. Therefore it makes more sense to use the following commands: ssh -l loginid mailserver -f mv /var/spool/mail/loginid /tmp/loginid_fetchme scp -C -l loginid:/tmp/my_new_mail /tmp/loginid_fetchme A move (mv) is a elementary operation, so you won
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