Radio E-Mail in West Africa
D. J. Bernstein, author of qmail, also has developed a number of special-purpose tools and applications perfectly suited to the Radio E-mail Project. Central among these, qmail includes a QMTP server, implementing Bernstein's own Quick Mail Transport Protocol. QMTP is a supplemental suite of programs designed for moving mail over slow connections.
As shown in the reference network in Figure 1, qmail runs on five hosts: the central mail server coyah, the radiohub server congo and each of the three field office hosts.
Once qmail considers the message delivered, we wait for the next PPP connection with the remote host kenya in Kissidougou. Then we can make use of the serialmail package to blast (relatively speaking) all the mail collected in the /var/qmail/qturn/kissidougou/.QMAIL.PPP/ mailbox across the link using QMTP.
Each of the radio e-mail servers in the field run headlessly, controlled from a simple command-line interface via Telnet session from the operator's desktop PC. The basic interface consists of four commands, usually run in the following sequence:
ppp.start mail.get mail.send ppp.stop
These commands are simple shell scripts that perform their respective tasks, each providing the operator with a modest amount of feedback about what is happening at the time. The functions could be further collected into a single command, such as mail.run, but we want to enable the operator to maintain some discretion over radio access, depending on the demands for voice communication.
We don't try to get and send mail simultaneously; we first do one, and then the other. This is another accommodation for the anemic, half-duplex bandwidth of the HF radio link. As far as network traffic goes, this link is like a one-lane back road—more than a little traffic creates a long skinny parking lot.
As we may have mentioned, the HF radio link is a tad on the slow side. Nevertheless, we manage to move a decent amount of mail with it. On an average day, over 300 messages travel the air waves between Conakry and field offices, over two to three brief connections per office. And as is typical with all internet technologies, every taste stimulates an even greater appetite.
Given the limitations inherent in radio e-mail, we try to maintain a usage policy that is as open as possible. For example, staff members are free to use radio e-mail for personal correspondence with friends and family anywhere in the world, and there is no limit to the number of messages any user may send. Our only explicit policy restriction is the request that users not subscribe to mailing lists.
To prevent the radio links from getting choked-up for hours on huge attachments, such as large documents and graphic files, all qmail servers connected to radios (that is, the radiohub in Conakry and each of the field office servers) are run with a message size limit of 8,000 characters. This is sufficient for three to four pages of text. Whatever can be squeezed into the 8,000-byte limit by way of attachment and file compression is free to go.
The system has proven extremely reliable. Despite the intermittent power outages typical in Conakry, we do try to keep the mailhub server coyah running at all times by using a generator and battery backup. So far, these measures have kept this machine serving flawlessly since it was first installed, with a continuous uptime at this writing of over three months without reboot.
Yet this reliability would mean nothing if the system were not sustainable over the long term. Two months before we installed the first radio server in the field, we formed a Network Users/UNIX Group (IRC-NU/UG) among interested and capable IRC staff. This group meets regularly and enthusiastically to learn Linux/UNIX and to develop network administration skills. The group now has a number of functional production systems on which to work and play, using mostly recycled hardware. The Linux servers installed for this project also host a typical range of other servers and services, including DHCP, DNS, NATD, Apache, FTP, Samba and PostgreSQL. The IRC-NU/UG provides a human network that will continue to sustain and grow the technical network in the years to come.
The successes of this project are readily duplicated anywhere in the world. Schools, government ministries and other organizations can build remote networking solutions easily over HF radio where access is otherwise not available and do it at a minimal cost. Once installed, these systems are almost trivial to administer and may be adapted quickly to alternative TCP/IP carriers. Maintenance of the e-mail system itself involves only the routine addition and deletion of user accounts and keeping the /etc/aliases files up-to-date.
We are now serving mail to over 50 desktops and 150 staff in four offices throughout Guinea. The entire wide area network is serviced behind a single public IP address, at a total ISP cost of $150 US per month. Best of all, the system has deployed standard network and internet technologies throughout the organization (and throughout Guinea) utilizing freely available technologies. Not only does this plant grassroots networking infrastructure where there is no Internet yet, it helps build the core competencies and capabilities essential for Africa's connected future.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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