Connecting SSC via Wireless Modem
Recently, SSC needed more room and rented another office. The remote office needed a connectivity solution to link it to the original office's LAN. Several options were available to us:
Frame relay (56k, T1...)Advantage: high speedDisadvantage: high cost of line and hardware
ISDNAdvantage: relatively high speedDisadvantage: potentially expensive hardware, long wait for installation
28.8k serialAdvantage: cheap hardware, readily availableDisadvantage: low speed
Wireless networkingsimilar to ISDN
Guerrilla Ethernet (run our own coax down the street) Advantage: 1.555-> 2.5 Mbits fastDisadvantage: street sweepers
We explored each possibility, and decided that outside of the probably illegal guerrilla Ethernet, wireless modems would be the most fun to install and use. We contacted various vendors for wireless products and found Freewave had the highest-speed wireless modems available. Freewave sent us a pair of modems to test at the office.
The Freewave modems we received were small and easy to configure. The manual stated they could potentially be used at a range of 20 miles, line-of-sight. We would soon see if that was a true statement.
Freewave wireless modems act as a null-modem cable, and unlike regular modems, do not need dialing. The modems look for other modems on their frequency and link to them. Wireless modems can link point-to-point, i.e., two modems, or multiple modems can be connected to a single modem that acts as a hub. Point-to-point, the modems are configured as a master and a slave. One calls the other and a link is established. The number they call is an internal, firmware encoded number.
The firmware of the Freewave modem is accessed by pressing a dimple on the front plate of the unit, which puts the modem into configure mode. Connecting to the serial device with minicom or xc at 38400 bps enables you to access the firmware menu. You then have the options to configure the speed the unit will use to talk with other modems, the numbers of the other Freewaves to call, and the behavior of the unit with the other modems—as a slave or a master.
Since we wanted point-to-point usage, the number was set to the number of the second modem, and the speed was set to 115200 bps.
Exiting the firmware puts the unit back in communication mode. It took several configuration tries to get each Freewave configured with the right speed as master and slave. Finally, the status lights on the units showed us a link, and flashes of packets could periodically be seen. We noticed that at 115200 bps, with the modems 20 feet apart, we weren't communicating well. Characters could not be sent either way even though a link was definitely established. Our communication test initially consisted of using minicom to send “Hello? Is it working? See this?” back and forth between modems.
We dropped the speed back to 9600 and established a reliable, clean link. We also discovered that sometimes the firmware on one of the modems would suddenly configure itself to be the master instead of the slave and talk at odd baud rates like 230400 bps.
After an hour or two of playing with the firmware, we were able to get a reliable 115200 bps connection at 20 feet. Now it was time to test a link between the two offices. The new office is south of the old at a distance of approximately 1500 feet with a large nursing home and several houses in between (read: not line-of-sight). After spending 2 or 3 hours beating on bad serial ports and slow 16450 UART-equipped hardware, we finally built a system with 16550As and were able to test the modem. The modem was placed in the window, just in case an extra wall might make a difference. After a bit more banging on the firmware, we finally established a connection with the office at 115200. We had link speed and reliability with a couple of transfers of the Linux kernel back and forth, and we also met with some problems. Occasionally the link would freeze, which meant resetting the modem, which in turn sometimes caused a glitch in the firmware. Other times it would transfer flawlessly at 7-8Kbytes/sec, a respectable performance. All in all, we decided that this performance, though quite good, was not robust enough to act as a LAN bridge to the remote office. Therefore, we packed up the modems and sent them back to Freewave.
I believe that with line-of-sight or at least minimally-blocked usage these modems could yield quality results. They're the fastest wireless modems we found—others we researched had maximum rates of 9600 bps. The initial cost was high, at about $1500 per unit, but given the costs of similar performance hardware, such as ISDN routers, DSU/CSUs and such, the overall cost was actually low, since there are no line charges. With improved reception (boosters were very costly) these units would have served their purpose quite well. Without it we decided to use an ISDN instead.
Liem Bahneman quit school at the University of Washington to pursue more important research into the area of Linux-induced insomnia. Nowadays, when Liem isn't making sure the web servers at the Cobalt Group aren't crashing, he's likely to be found playing with Legos or his Star Wars memorabilia collection. He can be reached via e-mail at roland@cobaltgroup.com.
Today’s modular x86 servers are compute-centric, designed as a least common denominator to support a wide range of IT workloads. Those generic, virtualized IT workloads have much different resource optimization requirements than hyperscale and cloud applications. They have resulted in a “one size fits all” enterprise IT architecture that is not optimized for a specific set of IT workloads, and especially not emerging hyperscale workloads, such as web applications, big data, and object storage. In this report, you will learn how shifting the focus from traditional compute-centric IT architectures to an innovative disaggregated fabric-based architecture can optimize and scale your data center.
Sponsored by AMD
Built-in forensics, incident response, and security with Red Hat Enterprise Linux 6
Every security policy provides guidance and requirements for ensuring adequate protection of information and data, as well as high-level technical and administrative security requirements for a system in a given environment. Traditionally, providing security for a system focuses on the confidentiality of the information on it. However, protecting the data integrity and system and data availability is just as important. For example, when processing United States intelligence information, there are three attributes that require protection: confidentiality, integrity, and availability.
Learn more about catching the bad guy in this free white paper.
Sponsored by DLT Solutions
| Using Salt Stack and Vagrant for Drupal Development | May 20, 2013 |
| Making Linux and Android Get Along (It's Not as Hard as It Sounds) | May 16, 2013 |
| Drupal Is a Framework: Why Everyone Needs to Understand This | May 15, 2013 |
| Home, My Backup Data Center | May 13, 2013 |
| Non-Linux FOSS: Seashore | May 10, 2013 |
| Trying to Tame the Tablet | May 08, 2013 |
- Making Linux and Android Get Along (It's Not as Hard as It Sounds)
- RSS Feeds
- New Products
- Using Salt Stack and Vagrant for Drupal Development
- Drupal Is a Framework: Why Everyone Needs to Understand This
- A Topic for Discussion - Open Source Feature-Richness?
- Home, My Backup Data Center
- Validate an E-Mail Address with PHP, the Right Way
- Readers' Choice Awards
- New Products
Enter to Win an Adafruit Prototyping Pi Plate Kit for Raspberry Pi

It's Raspberry Pi month at Linux Journal. Each week in May, Adafruit will be giving away a Pi-related prize to a lucky, randomly drawn LJ reader. Winners will be announced weekly.
Fill out the fields below to enter to win this week's prize-- a Prototyping Pi Plate Kit for Raspberry Pi.
Congratulations to our winners so far:
- 5-8-13, Pi Starter Pack: Jack Davis
- 5-15-13, Pi Model B 512MB RAM: Patrick Dunn
- Next winner announced on 5-21-13!
Free Webinar: Linux Backup and Recovery
Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.
In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.





5 min 23 sec ago
5 hours 43 min ago
11 hours 43 min ago
12 hours 6 min ago
12 hours 16 min ago
12 hours 20 min ago
12 hours 50 min ago
15 hours 41 min ago
16 hours 17 min ago
16 hours 18 min ago