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Rising star

Understanding E1,T1,CAS,CCS,ISDN

Dear Gents,

I am confused about the above terms and highly appreciate if someone can explain them in plain english.From my side i understand them as below.

E1:This is a digital circuit provided by the telco which can be used for voice or data.

T1:Same usage as E1.

ISDN:This is also a service provided by the telco which can be used for voice or data.

CAS:Signalling mechanism which can be used on E1 circuits when the circuit is used for voice purpose.

CCS:Signalling mechanis, which can be used on T1 circuits when the circuit is used for voice purpose.

ISDN can support CAS signalling as well,please correct me.

Thanks

8 REPLIES 8
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Advocate

Yes your understanding is close. E1/T1 are physical circuits - E1 being the European standard and T1 American. ISDN runs on top of the T1/E1 circuits - Its more like a protocol or set of protocols.

CAS and CCS are just the signalling methods.

CAS = Shared Channel for signalling and voice

CCS = One dedicated Channel for signalling


E1 CCS =30 B channels and 1 D  channel
T1 CCS = 23 B channels and 1 D channel
CAS E1 = 31 B Channels
CAS T1 = 24 B Channels

-Terry

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Hi,

Thanks for the reply.

So if ISDN can run on E1 and T1 circuits which signalling method is used,please clarify.

In addition what is the significance of PRI and BRI as they can be used with ISDN and what could be the circuit when using PRI and BRI.

Thanks

Highlighted

In addition to the nice info from Terry, ISDN elements and PRI / BRI are explained in very simple language in the following link

https://en.wikipedia.org/wiki/Integrated_Services_Digital_Network#Basic_Rate_Interface

Manish

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Hi,

What will be the signalling method used on ISDN,will it be CAS or CCS.

Thanks

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Its actually the other way around.

CCS is the transmission of signaling information out of the information band. The most notable and widely used form of this signaling type is ISDN. Another type is SS7.

Various types of CAS signaling are available in the T1 world. The most common forms of CAS signaling are loopstart, groundstart, and E&M signaling.

Manish

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Hi Manish,

I am totally confused.

Kindly explain when CCS,CAS and ISDN are used.

From the above what i understand is that CCS and CAS are signalling methods which run on E1 and T1 etc.

So you mean that ISDN=CCS signalling method.

BTW by signalling i.e the onhook,off hook status etc.

Moreover,kindly let me know does CCS and CAS carry the calling and the called number info as well.

Thanks

Highlighted

Hi Manish,

I am totally confused.

Kindly explain when CCS,CAS and ISDN are used.

From the above what i understand is that CCS and CAS are signalling methods which run on E1 and T1 etc.

So you mean that ISDN=CCS signalling method.

BTW by signalling i.e the onhook,off hook status etc.

Moreover,kindly let me know does CCS and CAS carry the calling and the called number info as well.

Thanks

Highlighted

Hi,

I would request you to read the following before firing any further questions, it is very clearly explained in the documentation.

http://www.cisco.com/c/en/us/support/docs/voice/digital-ccs/14079-voip-ccs.html#backinfo

T1 Signaling: CAS and CCS

Signaling in the Telephony world provides functions such as supervising and advertising line status, alerting devices when a call is trying to connect, and routing and addressing information.

There are two different types of signaling information within the T1 world:

  • CCS

  • Channel Associated Signaling (CAS)

CCS

CCS is the transmission of signaling information out of the information band. The most notable and widely used form of this signaling type is ISDN. One disadvantage to the use of an ISDN PRI is the removal of one DS0, or voice channel. In this case, for signaling use. Therefore, one T1 would have twenty-three DS0s, or B-channels for user data, and one DS0, or D-channel for signaling. It is possible to control multiple PRIs with a single D-channel with each using Non Facility Associated Signaling (NFAS). Therefore, you can configure the other PRIs in the NFAS group to use all twenty-four DS0s as B-channels. The use of PRI signaling ensures the maximum possible connection rates, especially with the advent of 56 K modems. This illustrates the clear channel capability of ISDN.

Another disadvantage of using CCS (as seen in the network diagram) is that the PBX needs a digital T1 PRI card, which is more expensive than an E&M signaling card. An E&M signaling card is used in the same network diagram if you run CAS between the AS5300 and the PBX.

CAS

CAS is the transmission of signaling information within the information band, or in-band signaling. This means that voice signals travel on the same circuits as line status, address, and alerting signals. As there are twenty-four channels on a full T1 line, CAS interleaves signaling packets within voice packets. Therefore, there are a full twenty-four channels to use for voice.

Various types of CAS signaling are available in the T1 world. The most common forms of CAS signaling are loopstart, groundstart, and E&M signaling. The biggest disadvantage of CAS signaling is that the network uses bits from information IP packets, such as voice packets, to perform signaling functions. CAS signaling is thus often referred to as robbed-bit signaling.

CAS is not the optimal choice when one attempts to achieve the highest possible connection rates with modems. Most modems can adjust to the signal quality and still give high-speed reliable connections. However, the use of 56 K modems on CAS lines drops the connection speeds by almost 2 K in the downstream direction of communication per trunk that uses CAS signaling.

Manish

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