I have been working almost the whole day resolving a problem in my newly configured Linux Predictive Dialer which will be used in our remote office. The message that keeps on flooding my asterisk screen is “HDLC Bad FCS (8) on Primary D-channel of span 1” and then the the delta channel (DCH) of the ISDN interconnection between the Digium and Telco switch keeps on failing. I began to scout for answers from other Digium users who might have experienced the same problem in the past. Finally, I got an information from Digium website that the cause of the problem can be an I/O error or bad configuration. I hurriedly checked my configuration and found no error since it is exactly the same with other six dialers I configured previously which are all working properly. I was surprised at the other information I found from Digium website that the cause of the problem can be the driver of the built-in Intel 100Mbps ethernet card in my system. I began to wonder about the relationship of a network card and a Digium card installed in my Linux machine. Since I had no other choice, I tried to compile a new ethernet driver for my Linux but the problem after recompiling a new driver is still there. I also tried to recompile the Linux Kernel hoping that the problem will be resolved after I enabled ACPI but the result is still negative. I took my dinner thinking about the problem and I began to realize that I need to check for timing and clocking issue between the Digium card and the Telco switch. Without finishing my dinner, I hurriedly get back to the office and configure the proper clocking and T1 timing between the Digium card and the Telco equipment. ALAS! I was able to resolve the problem and now I will treat myself for another dinner since I wasn’t able to finish the previous dinner I had.

Popularity: 4% [?]

1.) Get a good, fast and reliable Internet connection
To use VoIP, you need at least broadband Internet connection, sad to say that dial-up will just frustrate you. There are lots of Internet Service Providers (ISP) today who offer high speed Internet connection via broadband (DSL) or dedicated Internet (ISDN) connection.

2.) Make VoIP calls
The next step is to decide what type of VoIP calls you would like to use, there are couple of scenarios about this below:

a.) Computer to Computer VoIP call

This is the “basic VoIP connection”, the caller and the called party’s computers must be online, must have headsets attached to the computers’ sound cards. The computers must be connected to the Internet and must be running VoIP software. Most VoIP softwares available today are free and allow you to connect to any computer running the same software. Skype is the best example of this free software. There is no charge for this type of call and calls can be made to anywhere in the world if you are aware of the IP address (other VoIP softwares use phone number) of the computer you would like to call.

b.) Computer to Phone VoIP call

For this type of VoIP connection to work, one party must be online, running VoIP software and has subscribed to a VoIP provider who offers PC to Phone VoIP calls and vice versa while the other party is using a phone that is not connected to the Internet (regular or mobile phone). Let say for example the caller is the one on the computer with VoIP software and the called party is the one who has a traditional phone. The caller dials the number from the VoIP software running in the computer. The call is then routed through the Internet and was received by the VoIP provider, the VoIP provider with an interconnection to Public Switched Telephone Network (PSTN) then routes the VoIP call to the called party’s regular or mobile phone.

c.) Phone to Phone VoIP call

You can make/receive VoIP calls using an ordinary telephone or an IP Phone. If you would like to use an analog phone, you must have an Analog Terminal Adapter (ATA). ATA is a device that allows you to use a regular phone unit to make VoIP calls. An ATA must have a valid IP address and must be connected to the Internet. If you would like to use an IP Phone (sometimes called SIP Phone or VoIP Phone), you don’t need an ATA at all, the IP Phone is connected directly to your Ethernet Hub which is connected to your ISP’s baseband or DSL modem.

d.) Analog or mobile phone to another analog or mobile phone VoIP call

“YES, there is such a VoIP call folks”, you won’t notice it but majority of the telephone companies today are starting to migrate their interconnection to other carriers to VoIP. This is pretty simple, you use your regular analog line to call another analog line, your telephone provider then routes the call over a VoIP interconnection to the destination telephone provider (assuming they have VoIP interconnection) using a special commercial-type VoIP equipment (e.g. Quintum or Cisco). You are actually connected to the called party but you are unaware that the conversation is passing through VoIP channels.

NOTE: This type of VoIP call is for telephone companies only, an SMB with a remote office can also use this to dial a number from the remote corporate PBX using their local corporate PBX to save money from long distance calls.

Popularity: 2% [?]

If you are a System Administrator using Squid Proxy Server and you need a tool for securing web acccess in your company, then use the “whitetrash” plugin for Squid.

Whitelisting is a technique that makes it difficult for malware to use HTTP and SSL.

For example, an attacker sends you a malware in the form of a MSWord document attached to an email. You open the attached MSWord document and then the malware executes. The malware will then use HTTP to download tools from the attacker’s domain and use these tools to damage your PC. With a whitelist, all of these actions will be blocked because the attacker’s domain is not in the whitelist.

The Goal

The goal of Whitetrash is to provide a user-friendly and sysadmin-friendly proxy that makes it significantly harder for malware to use HTTP and SSL for:

• initial compromise;
• data exfiltration;
• command and control.

Whitetrash features:

• Provides whitelisting for HTTP and SSL that is good for both users and sysadmins, but defends against malware and browser exploits.
• A HTML rendered whitelist report that can be viewed by all users. Can also be used to generate static whitelists for popular domains.
• Fast: no noticeable impact on users browsing urls already in the whitelist, and adding a new URL is very quick.
• Secure: As this is a security product, great care has been taken to sanitise input, flow control etc. so that the whitelist cannot be easily circumvented or exploited.

• Users can delete their own whitelist entries (optional). Admins can delete any whitelist entry.

• A HTML report that lists all domains requested but not whitelisted - good for tracking down malware/adware and generating static blacklists.
• Configurable authentication: any sort of authentication can be used. Squid provides plugins for NTLM, basic, and digest but has an extensible interface for other authentication schemes.
• NEW: A CAPTCHA system has been implemented to prevent malware adding itself to the whitelist. CAPTCHA can be enabled for HTTP, SSL, or both. This is available in the source tree and will be included in the next release.

Popularity: 5% [?]

Slingbox is a TV streaming device that enables consumers to remotely view their cable sattelite or personal video recorder (PVR) programming from an Internet-enabled computer with abroadband Internet connectio.

I was in New York, more than a year ago when a friend of mine had a problem with his Slingbox after moving to another Internet Service Provider in uptown NY area. The thing is, even if he use public IP address, the SlingBox just wouldn’t work. He’s a little pissed since the ISP and SlingBox customer support were unable to make his Slingbox work. I told him I will help him resolve the problem, and that I have a little trick for him but he has to configure his SlingBox to use private IP address (He has several computers inside NAT in his place). He told me that it is not possible so I had to prove to him that it is absolutely possible.

Below are iptables statements I used to make my friend’s SlingBox work inside NAT.

iptables -A FORWARD -i eth0 -p tcp –dport 5001 -d 192.168.30.100 -j ACCEPT
iptables -t nat -A PREROUTING -i eth0 -p tcp –dport 5001 -j DNAT –to-destination 192.168.30.100:5001

He was very happy after I was able to resolve his problem, In fact he asked me to bring one to Manila so he could access it and watch his favorite Filipino shows live.

By the way, I assigned 192.168.30.100 as the IP address of his Slingbox.

Popularity: 5% [?]

Transmission Control Protocol/Internet Protocol or simply TCP/IP is the communication “language” or “protocol” used by the computers and devices connected to the Internet to communicate to each other.

When you connect to the Internet, your internet browser uses TCP/IP to communicate with a web server and a web server uses TCP/IP to send the web page to your browser.

Your favorite e-mail client uses TCP/IP to connect to the Internet to send and receive e-mails.

The IP address of your computer and your domain name (www.reodica.org) are part of the standard TCP/IP protocol.

Behind the TCP/IP standard are different protocols that handle data communication, they are:

a.) TCP (Transmission Control Protocol) communication between applications
b.) UDP (User Datagram Protocol) simple communication between applications
c.) IP (Internet Protocol) communication between computers
d.) ICMP (Internet Control Message Protocol) for errors and statistics
e.) DHCP (Dynamic Host Configuration Protocol) for dynamic addressing

Transmission Control Protocol is the reliable transport protocol within the TCP/IP protocol suite and uses a “fixed connection” (and requires handshake before a session can start) to ensure that all data arrive accurately and 100% intact at the other end. TCP is mostly used as communication protocol between applications.

Internet Protocol is a “connection-less” communication protocol responsible for the communication between computers in a network. IP is responsible for routing each packet to its destination.

In layman’s term TCP is used by your web-browsers (e.g. firefox, Internet Explorer) and web-server-software (e.g. Apache) while IP is used by your computer and the computer where the web-server-software is running.

Popularity: 2% [?]

Perhaps this flash enabled website is one of the most comprehensive demonstration of different VoIP phones in the market. A very useful website for technical people who would like to master the operation of the VoIP phones included in the website.

Popularity: 1% [?]