Guru Guide: CVOICE (IOS Gateways)

I have a confession to make: I love gateways and gatekeepers. There’s something about diving into the command line that appeals to my personality. The black of the terminal… The blinking white cursor…

Truth be told, I didn’t always enjoy gateways. They were difficult to wrap my head around at first, but now they’re a piece of cake. I used to enjoy MGCP gateways for the ease of configuration, but now H.323 is my preferred method. Yes, there is a great deal more configuration when running H.323 or SIP, but you have much more control.

And control is something we engineers like to have (and keep)!

If you’re studying for the CVOICE lab or just generally interested in a concise reference on basic commands and theory surrounding gateways and gatekeepers, refer to this “Guru Guide” below. Read the rest of this entry »

Configuring RAS Retries and Timers

I am reading in the Cisco IOS H.323 Configuration guide this morning.  Yes, it’s exhilarating to read at 5:00am (NOT!).  Since I’m nodding off to sleep, I am writing another post to pass on the next bit of knowledge – configuring RAS retries and timers.

Normally, you would never need to touch this piece of H.323 gateways, but we’re not dealing with “normal,” real-world experience.  We’re dealing with the psychotic CCIE voice lab.  You need to know everything.

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Debug RAS Command

Usage Guidelines

Use the debug ras command to display the types and addressing of RAS messages sent and received. The debug output lists the message type using mnemonics defined in International Telecommunications Union-Telecommunication (ITU-T) specification H.225.
Examples

Practical Example

In the following output, gateway GW13.cisco.com sends a RAS registration request (RRQ) message to gatekeeper GK15.cisco.com at IP address 10.9.53.15. GW13.cisco.com then receives a registration confirmation (RCF) message from the gatekeeper.

If there is no response, it could mean that the gatekeeper is offline or improperly addressed.

If you receive a reject (RRJ) message, it could mean that the gatekeeper is unable to handle another gateway or that the registration information is incorrect.

Router# debug ras
*Mar 13 19:53:34.231: RASlib::ras_sendto:msg length 105 from 10.9.53.13:8658 to 10.9.53.15:1719
*Mar 13 19:53:34.231: RASLib::RASSendRRQ:RRQ (seq# 36939) sent to 10.9.53.15
*Mar 13 19:53:34.247: RASLib::RASRecvData:successfully rcvd message of length 105 from 10.9.53.15:1719
*Mar 13 19:53:34.251: RASLib::RASRecvData:RCF (seq# 36939) rcvd from [10.9.53.15:1719] on sock [0x6168356C]

IOS Dial-Peer Destination-Pattern Commands

Below are the following destination-pattern operators that can be used in IOS dial-peers for voice:

Standard Operators

• Asterisk (*) and pound sign (#)—Keys that appear on standard touchtone dial pads.
• Brackets ([ ])—Range of digits. Digits (0 to 9) are enclosed in brackets. Similar to a regular expression rule.
• Parentheses (( ))—Define specific pattern. Same as the regular expression rule—for example, 408(555). Use parentheses in conjunction with symbols ? or %.
• Period (.)—Match to any entered digit (used as a wildcard).
• Comma (,)—Pause between digits.

“Repeating” Operators

• Percent sign (%)—The previous digit or pattern zero or multiple times, similar to wildcard usage in the regular expression.
• Question mark (?)—The previous digit occurred zero or one time.

Other Operators

• Circumflex (^)—Match to the beginning of the string.
• Dollar sign ($)—Match to the null string at the end of the input string.
• Backslash (\)—Is followed by a single character matching that character or used with a single  character having no other significance (matching that character).
• T—Control character indicating that the destination-pattern value is a variable-length dial string.

Shutting Down and Enabling VoIP Services

This is just a thought, but I wouldn’t be surprised to see the proctor try to “pull a fast one” by shutting down VoIP services on an H.323 gateway.  I suppose this could be easily identified by executing a “show gateway” or “show run.”  I came across this while reading the Cisco IOS H.323 Configuration Guide.

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