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tramadol hcl 50mg Compressed TCP/IP-Sessions using SSH-like tools Sebastian Schreiber 2.2.2000 1. Introduction In the past, w tramadol hcl 50mg used to compress files in order to save disk space. Today, disk space is cheap - but bandwidth is limited. By compressing data tramadol hcl 50mg treams, you achieve two goals: 1) You save bandwidth/transfered volume (that is important if you have to pay for traffic or if y tramadol hcl 50mg ur network is loaded.). 2) Speeding up low-bandwidth connections (Modem, GSM, ISDN). This HowTo explains how to save both bandwi tramadol hcl 50mg h and connection time by using tools like SSH1, SSH2, OpenSSH or LSH. 2. Compressing HTTP/FTP,... My office is connected with tramadol hcl 50mg 64KBit ISDN line to the internet, so the maximum transfer rate is about 7K/s. You can speed up the connection by compressing it tramadol hcl 50mg when I download files, Netscape shows up a transfer rate of up to 40K/s (Logfiles are compressable by factor 15). SSH is a tool tramadol hcl 50mg that is mainly designed to build up secure connections over unsecured networks. Further more, SSH is able to compress connections tramadol hcl 50mg and to do port forwarding (like rinetd or redir). So it is the appropriate tool to compress any simple TCP/IP connection. "Simp tramadol hcl 50mg e" means, that only one TCP-connection is opened. An FTP-connections or the connection between M$-Outlook and MS-Exchange are no tramadol hcl 50mg simple as several connections are established. SSH uses the LempleZiv (LZ77) compression algorithm - so you will achieve the sa tramadol hcl 50mg e high compression rate as winzip/pkzip. In order to compress all HTTP-connections from my intranet to the internet, I just have tramadol hcl 50mg to execute one command on my dial-in machine: ssh -l -C -L8080::80 -f sleep 10000 = host that is located at my ISP. SSH-access is required. = my login-ID on =the web proxy tramadol hcl 50mg of my ISP My browser is configured to use localhost:8080 as proxy. My laptop connects to the same socket. The connection is comp tramadol hcl 50mg essed and forwarded to the real proxy by SSH. The infrastructure looks like: 64KBit ISDN My PC--------------- tramadol hcl 50mg ----------------A PC (Unix/Linux/Win-NT) at my ISP SSH-Client compressed SSH-Server, Port 22 Port 8080 tramadol hcl 50mg | | | | | | tramadol hcl 50mg | |10MBit Ethernet |100MBit |not compressed |not compressed | tramadol hcl 50mg | | | My second PC ISP's WWW-proxy with Netsc tramadol hcl 50mg pe,... Port 80 (Laptop) 3. Compressing Email 3.1. Incoming Emails (POP3, IMAP4) Most people fetch their e tramadol hcl 50mg ail from the mailserver via POP3. POP3 is a protocol with many disadvantages: 1. POP3 transfers password in clear text. (There a tramadol hcl 50mg e SSL- implementations of POP/IMAP and a challenge/response authentication, defined in RFC-2095/2195). 2. POP3 causes muc tramadol hcl 50mg protocol overhead: first the client requests a message than the server sends the message. After that the client requests tramadol hcl 50mg he transferred article to be deleted. The server confirms the deletion. After that the server is ready for the next transa tramadol hcl 50mg tion. So 4 transactions are needed for each email. 3. POP3 transfers the mails without compression although email is highly c tramadol hcl 50mg mpressible (factor=3.5). You could compress POP3 by forwarding localhost:110 through a compressed connection to your ISP's POP3- tramadol hcl 50mg ocket. After that you have to tell your mail client to connect to localhost:110 in order to download mail. That secures and spee tramadol hcl 50mg s up the connection -- but the download time still suffers from the POP3-inherent protocol overhead. It makes sense to substitut tramadol hcl 50mg POP3 by a more efficient protocol. The idea is to download the entire mailbox at once without generating protocol overhead. Fu tramadol hcl 50mg thermore it makes sense to compress the connections. The appropriate tool which offers both features is SCP. You can download yo tramadol hcl 50mg r mail-file like this: scp -C -l loginId:/var/spool/mail/loginid /tmp/newmail But there is a problem: what happens if a new emai tramadol hcl 50mg arrives at the server during the download of your mailbox? The new mail would be lost. Therefore it makes more sense to use the tramadol hcl 50mg following commands: ssh -l loginid mailserver -f mv /var/spool/mail/loginid /tmp/loginid_fetchme scp -C -l loginid:/tmp/my_new_ tramadol hcl 50mg ail /tmp/loginid_fetchme A move (mv) is a elementary operation, so you won't get into truble if you receive new mail during the tramadol hcl 50mg xecution of the comands. But if the mail server directories /tmp/ and /var/spool/mail are not on the same disc you might get pro tramadol hcl 50mg lems. A solution is to create a lockfile on the server before you execute the mv: touch /var/spool/mail/loginid.lock. You should tramadol hcl 50mg remove it, after that. A better solution is to move the file loginid in the same directory: ssh -l loginid mailserver -f mv /va tramadol hcl 50mg /spool/mail/loginid /var/spool/mail/loginid_fetchme After that you can use formail instead of procmail in order to filter /tmp/ tramadol hcl 50mg ewmail into the right folder(s): formail -s procmail < /tmp/newmail 3.2. Outgoing Email (SMTP) You send email over compresses tramadol hcl 50mg nd encrypted SSH-connections, in order to: ˇ Save network traffic ˇ Secure the connection (This does not make sense, if the m tramadol hcl 50mg il is transported over untrusted networks, later.) ˇ Authenticate the sender. Many mail servers deny mail relaying in o tramadol hcl 50mg der to prevent abuse. If you send an email over an SSH- connection, the remote mail server (i.e. sendmail or MS-exchange) tramadol hcl 50mg hinks to be connected, locally. If you have SSH-access on the mail server, you need the following command: ssh -C -l loginid ma tramadol hcl 50mg lserver -L2525:mailserver:25 If you don't have SSH-access on the mail server but to a server that is allowed to use your mail se tramadol hcl 50mg ver as relay, the command is: ssh -C -l loginid other_server -L2525:mailserver:25 After that you can configure your mail client tramadol hcl 50mg or mail server: see "smarthost") to send out mails to localhost port 2525. 4. Thoughts about performance. Of course compressio tramadol hcl 50mg /encryption takes CPU time. It turned out that an old Pentium-133 is able to encrypt and compress about 1GB/hour -- that's quite tramadol hcl 50mg a lot. If you compile SSH with the option "--with-none" you can tell SSH to use no encryption. That saves a little performance. tramadol hcl 50mg ere is a comprise between several download methods (during the test, a noncompressed 6MB-file was transfered from a 133MHz-Pentium-1 to a 233MHz Pentium2 laptop over a 10MBit ethernet without other load). +-------------------+--------+----------+-----------+----------------------+ | | FTP |encrypted |compressed |compressed & encrypted| +-------------------+--------+----------+-----------+----------------------+ +-------------------+--------+----------+-----------+----------------------+ | Elapsed Time | |7.6s | 26s | 9s | 23s | +-------------------+--------+----------+-----------+----------------------+ | Throughput | 790K/s | 232K/s | 320K/s | 264K/s | +-------------------+--------+----------+-----------+----------------------+ |Compression Factor | 1 | 1 | 3.8 | 3.8 | +-------------------+--------+----------+-----------+----------------------+ 5. Greetings Thanks to Harald König
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