abt pots and E-1 lines

[shaila_rox]

hi guys, i m just starting my Voip and there is a confusion so plz help me out, a guy told me that the lines that come to our home to which my analog phones attach are infact individual channels of E-1 line that is multiplexed at some point from the CO switch. another guy rejected this concept and said that these are old pots lines. i want to ask that

1) who is right ???

2) if its a pots line than is it simply called a pots line or got some other technical name ??

plz tell me thanks in advance

[paolo bevilacqua · Accepted solution]

Hi Shila,

most likely, the lines you have at home, are never part of an E1. These go straight (more or less) to a room in the C.O. called "permutation", where they can make any type of contact an pairing. From there it goes to the line card of the CO switch that can host like 100 or 200 lines per card, and spans multiple shelf. So no E1.

But at the same time, when you must carry the lines across a long distance, or when you are giving service to larger business or communities, then the multiplexing and conversion ti digital occurs, and you have E1, T1, and other type of circuits.

For the name, I would not use pots when talking to non technical people. Regular telephone line is probably the most widely used name.

[shaila_rox]

thank u it really helped me, there is 1 more thing i dont understand i hope u could help me out in this also, i was watching cbt of jeremy and he said in his codec slide that G.729 annex A is good and more efficient than simple G.729 becoz G.729 A uses DSP, now wat i concluded that we can also perfom ANALOG to digital conversion with a DSP, m i right ?? if i have to perform this conversion is it essential to have a DSP chip ? or i can do without it also ??? plz guide me

thanks again in advance

[paolo bevilacqua]

Hi Shaila and thank you for the nice rating.

Now for the DSP/codecs thing:

A codec is essentially a software algorithm converting between analog and digital domains.

As such you can run it on any computing platform, you don't necessarily need a DSP. For example, when you use a softphone on your computer, the algorithm runs on the PC CPU.

But the computations are CPU intensive, plus there is another quantity of tasks to do, so is better to have a dedicated CPU to run codecs, and here it comes the DSP to offload the CPu and guarantee real-time processing. The leading DSP makers, and the one that Cisco has most often chosen, is Texas Instruments.

Routers, being a professional solution, always uses DSP as opposed to PC-based solutions that may or (more often) may not have DSP.

The base G.729 has two additional variants (Annex A and B) that can also be applied at the same time. All will require a DSP to the light of what discussed above.

Please see G.729 on wikipedia.org that explains that in detail.

[shaila_rox]

well thanks again just 1 thing do routers always need a DSP ?? or is it possible to use a codec without a DSP also ??? if possible can u refer me a doc on cisco that deals with this matter in a great detail

thank u

[paolo bevilacqua]

As a said, Cisco routers always use DSP for voice, fax, modem, and video support. They are a very important piece in the router architecture.

There are many many documents you can read. A basic one:

http://www.cisco.com/en/US/partner/tech/tk1077/technologies_tech_note09186a00800b6710.shtml

it is a bit dated as it does not mention the newer ISR platforms and the "flex scheme" for allocation calls.

[shaila_rox]

hi sir, i m not allowed to view this doc, why ? i have a account through which i m able to post here, isnt this account valid to view this doc ?? if u think this doc is really helpful for me can u kindly mail me its pdf form on my id, i will be gratefull, if u cant its ok but thanks for ur help my id is shaila_rox@yahoo.com

[paolo bevilacqua]

Link that works:

http://www.cisco.com/en/US/tech/tk1077/technologies_tech_note09186a00800b6710.shtml

Thanks and good luck!

[shaila_rox]

hi sir can u plz send me a link which is more comprehensive than this 1, i m really not able to understand it coz its very very technical :( and i m just a novice to this field.

thank u

[paolo bevilacqua]

Hi Shaila,

on cisco there is nothing less technical, I suggest if you want to get in this fiels, try to study anyway with the help of a glossary, slowly you will get an idea about it.