VG224 max cable length

Answered Question
Jun 15th, 2009

What is the maximum cable length that an analog device (ie. Fax, Analog Phone) can be from a VG224 port?

I'm guessing it would be at least 100 metres, but I'm not sure how much over 100 metres is possible...?

I have this problem too.
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Correct Answer by rob.huffman about 7 years 5 months ago

Hi David,

We use the VG248 (the VG224 older brother :) to supply an Analog device at one of our Grounds Buildings which is at least 600m away. This is via a Tie Cable (26 gauge wire). The max distance listed by Cisco is 975m for a phone with 1 REN. The specs are for the ATA, but the VG's are very comparable. Have a look;

This info is from an old Cisco doc;

Q. What is the maximum distance from which I can drive an analog device with a Cisco ATA?

A. Table below provides maximum distances for this question.

Ring Loads and Distances

Ring Load (per RJ-11 FXS Port) Maximum Distance

5 REN 200 feet (61 m)

4 REN 1000 feet (305 m)

3 REN 1700 feet (518 m)

2 REN 2500 feet (762 m)

1 REN 3200 feet (975 m)

**Here is the actual reference for the VG224;

Loop Length

3000 ft, 26 AWG

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6790/gatecont/ps2250/ps5516/product_data_sheet09186a00801d87f6.html

Ringer equivalence number

In telecommunication, a ringer equivalency number (REN) is a somewhat arbitrary number which denotes the loading a telephone ringer has on the line.

A ringer equivalency number of 1 represents the loading effect of a single "traditional" telephone ringing circuit, such as that within the Western Electric Model 500 desk telephone. Note that modern telephone equipment may have a REN significantly lower than 1: as a rough guide, externally-powered digital-ring phones may have a REN as low as 0.2, while modern analog-ring phones (where the ringer is powered from the phone line) typically have a REN around 0.8.

The total REN for a subscriber's line is simply the sum of the RENs of all devices connected to the line; this number expresses the overall loading effect of the subscriber's equipment on the central office ringing current generator. The local telephone company usually sets a limit on the total REN, typically 5 or less.

If the total allowable REN load is exceeded, the phone circuit may fail to ring (or otherwise malfunction). In extreme cases, the telephone service provider may temporarily disconnect an overloaded line to reduce load.

While REN is a United States-developed yardstick, analogous systems exist internationally. In some countries, (particularly in Commonwealth nations), the REN is better known as the ringer approximated loading number (RAL). In the United Kingdom it is called the ringer equivalence number and a maximum of 4 is allowed on any British Telecom (BT) line.

From Wikipedia;

http://en.wikipedia.org/wiki/Ringer_equivalence_number

Hope this helps!

Rob

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Correct Answer
rob.huffman Tue, 06/16/2009 - 04:18

Hi David,

We use the VG248 (the VG224 older brother :) to supply an Analog device at one of our Grounds Buildings which is at least 600m away. This is via a Tie Cable (26 gauge wire). The max distance listed by Cisco is 975m for a phone with 1 REN. The specs are for the ATA, but the VG's are very comparable. Have a look;

This info is from an old Cisco doc;

Q. What is the maximum distance from which I can drive an analog device with a Cisco ATA?

A. Table below provides maximum distances for this question.

Ring Loads and Distances

Ring Load (per RJ-11 FXS Port) Maximum Distance

5 REN 200 feet (61 m)

4 REN 1000 feet (305 m)

3 REN 1700 feet (518 m)

2 REN 2500 feet (762 m)

1 REN 3200 feet (975 m)

**Here is the actual reference for the VG224;

Loop Length

3000 ft, 26 AWG

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6790/gatecont/ps2250/ps5516/product_data_sheet09186a00801d87f6.html

Ringer equivalence number

In telecommunication, a ringer equivalency number (REN) is a somewhat arbitrary number which denotes the loading a telephone ringer has on the line.

A ringer equivalency number of 1 represents the loading effect of a single "traditional" telephone ringing circuit, such as that within the Western Electric Model 500 desk telephone. Note that modern telephone equipment may have a REN significantly lower than 1: as a rough guide, externally-powered digital-ring phones may have a REN as low as 0.2, while modern analog-ring phones (where the ringer is powered from the phone line) typically have a REN around 0.8.

The total REN for a subscriber's line is simply the sum of the RENs of all devices connected to the line; this number expresses the overall loading effect of the subscriber's equipment on the central office ringing current generator. The local telephone company usually sets a limit on the total REN, typically 5 or less.

If the total allowable REN load is exceeded, the phone circuit may fail to ring (or otherwise malfunction). In extreme cases, the telephone service provider may temporarily disconnect an overloaded line to reduce load.

While REN is a United States-developed yardstick, analogous systems exist internationally. In some countries, (particularly in Commonwealth nations), the REN is better known as the ringer approximated loading number (RAL). In the United Kingdom it is called the ringer equivalence number and a maximum of 4 is allowed on any British Telecom (BT) line.

From Wikipedia;

http://en.wikipedia.org/wiki/Ringer_equivalence_number

Hope this helps!

Rob

davidblu Tue, 06/16/2009 - 06:00

Fantastic!

A wonderful answer, as always Rob.

This has all the information I require, and I learned something about REN too.

Thanks!

David

rob.huffman Tue, 06/16/2009 - 06:30

Hey David,

You are most welcome my friend! Glad to be of some small help here.

Cheers!

Rob

Javier Cuadros Mon, 10/19/2009 - 11:53

Hi Rob,

Thanks for you detailed answer, i'm triyng to understand the REN definition you get from Wiki and then as per each ata i will have two different lines and each line for my case will have only one phone i should calculate the distance of the wire with REN 1? also is there any way to know the max lengt of a wire for an fxs and fxo card?

Thanks,

rob.huffman Tue, 10/20/2009 - 04:34

Hi Javier,

The modern Analog phones will likely have a REN of somewhere between .8 to 1.0 So, yes, your calculation can be based on the REN 1 number. You should be able to find the exact REN on the base of the phone :) I have not seen a doc that has these statistics for a FXS Port.

Cheers!

Rob

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