Switching to VoIP
by Theodore Wallingford

The unconfirmed error reports are from readers.  They have not yet been 
approved or disproved by the author or editor and represent solely the
opinion of the reader.

Here's a key to the markup:
        [page-number]: serious technical mistake
        {page-number}: minor technical mistake
        <page-number>: important language/formatting problem
        (page-number): language change or minor formatting problem
        ?page-number?: reader question or request for clarification

This page was updated July 30, 2008.


UNCONFIRMED  errors and comments from readers: 

{2} Mesh Vs Switched (bottom of page);
The number of links (L) in a mesh network is = (L * (L-1))/2.

For 10 end points, this is 45 and for 100 end points this is 4950.


{16} Thirs para from bottom;
The explanation is slightly confusing. I suggest something along the lines of:

"An IP address consists of 32 binary bits, commonly represented by 4 decimal numbers separated by dots:

192.12.12.204"

The example given, 10.1.1.204, has a binary look, and it took me a little while to figure out exactly what the author meant. Also, I suggest the word "number" is used in place of figure, as figure refers to diagrams.


[41]bottom of page;
Digium uses svn (subversion) now instead of CVS for its versioning system. In light of that, the commands on page 41 should read:

# cd /usr/src
# svn checkout http://svn.digium.com/svn/zaptel/branches/1.4 zaptel (drivers for the X100P card)
# svn checkout http://svn.digium.com/svn/libpri/branches/1.4 libpri (drivers for Digium T1 cards)
# svn checkout http://svn.digium.com/svn/asterisk/branches/1.4 asterisk

Page 36 paragraph 3 perhaps should also be updated to indicate that subversion package also needs to be installed.


[42]middle of the page;
Commands for compiling asterisk are incomplete. Here is what I found works (see the notes for lines that were added):

# cd zaptel
# ./configure ##needed before following make commands
# make clean ; make install
# make config ##creates init.d scripts
# cd ../libpri
# make clean ; make install
# cd ../asterisk
# ./configure ##needed before following make commands
# make clean ; make install
# make samples
# make config ##creates init.d scripts


<43>middle of the page;
It might be helpful to include some troubleshooting tips for the X100P. Apparently this card is very sensitive to IRQ conflicts. I couldn't get mine to work till I moved it to a different machine. Perhaps you could provide a link to the following document installation guide which includes troubleshooting instructions:

http://www.x100p.com/support/doc/novavox-x100p-se-installation-guide.pdf

The X100P cards can also be purchased new from this site.


{48}full page;
Not sure what is wrong here, but I was unable to "secure" asterisk using these instructions.


{50}2nd paragraph;
Book says, "you should get a 404 message on the phone's display". I did not, rather I got the automated attendant.


(62) Third para from top;
"At the edge of the PSTN are large, mainframe-like switches CALLED exchanges"


{72}second to last paragraph;
/etc/asterisk/zapata.conf file does not exist initially. I had to create it using the following syntax (note the [channels]):

[channels]
context=default
signalling=fxs_ks
usecallerid=yes
echocancel=yes
callgroup=1
pickupgroup=1
immediate=no
callerid="* X100P POTS"<(314) 514-8528>
channel=>1


{86}last paragraph;
/etc/extensions.conf should be /etc/asterisk/extensions.conf


(112)  6.2.1, 3rd para;
"DAC includes of quantizing or digital "sampling" of sounds,"
              ^^
Missing word?


{111/112} Third para from top;
The section called "Sampling and Digitizing"

This section mostly deals with ADC not DAC, yet DAC is used exclusively. There are one or two language errors as well. For instance, the last para in the section makes it clear that ADC is being discussed, and should read:

"ADC includes quantizing or digital "sampling" of sounds, filtering for bandwidth?"

I suggest the whole section be rewritten, starting with:

"Analog-to-digital conversion (ADC) and digital-to-analog conversion (DAC) are the processes that convert?"

In some places the term ADC/DAC should be used when both processes are being referred to.


{117} First para;
"A 30ms sound frame takes a third longer to encode than a 20 ms one?"

No it doesn't. It takes 50% longer.


{119} Table at top;
The "Voice bits per packet" for G.729A and GSM may be incorrect. For G.729A it should be 80 bits, and for GSM 260 bits.


{195} 2nd para;
"Chances are, if the echo occurs less than 150 ms from the time you actually said the words, then you won't notice it".

Wrong. I think the figure is only 15 ms.