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ISP's, Bandwidth and Compression selection for your Softphone

  ISP's, Bandwidth
  and Compression
  selection for your
How do I optimize my softphone to have the best quality with my internet connection?

To optimize your quality, selecting your compression given your actual bandwidth is important. Our client makes it easy to install and will ask you what type of connection you have (Dial-up or Cable/DSL). While the client configures automatically most if not all parameters for you, the one that it does not measure is your internet bandwidth and usage habits. By measuring this environment and gauging the usage of your connection, you will be ready to determine which type of compression is best for you.

IPS's: While Internet Service Providers try to educate the public on various offerings, at times it send out a mixed message. One of these is the speed of connection you hope to receive. Examples of this are shown below:
  • 56Kbps Dial-up
  • 64Kbps Internet Plus
  • 256Kbps Basic DSL/Cable
  • 768Kbps - Standard DSL/Cable
  • 1.5Mbps - DSL Plus
Remember: 1 Byte (B) is 8 Bits (b) - thus, 1KB/s is 8Kbps)

ADSL - "A" is for Asymmetric, meaning that the service is offering larger download bandwidth than upload bandwidth. Examples of this are 256/64Kbps, 384/128Kbps, etc.

The unfortunate reality is that you rarely reach these bandwidth values ahead of the branding. Testing your Bandwidth:

To test your internet speed must take an actual test that is impartial to your service provider, such as the one provided by

Test your Speed Enter a 3digit area code of the US, such as 210, and select your bandwidth accordingly.

This bandwidth test gives you a way to compare with your ISP's claims. However, your continuous data stream bandwidth is yet lower and much different. To give yourself a true test of your bandwidth that is going to be relevant to your softphone and connection quality, a large file upload and download is the true way to determine your bandwidth.

For ADSL customers, the download stream is NOT representative of your upload speed. Thus uploading to a server on the Internet using an FTP tool is a way to determine your continuous data bandwidth speed (Most tools will show KB/s, so multiply by 8 to get Kbps).

Our observations/experiences thus far are at the extreme limit of a central hub (4.2Km), are as follows:
  • One-way 56K analog - connects @ 33.6-40Kbps - yields ~4KB/s (32Kbps) continuous data stream
  • One-way 64K digital - yields ~6.75KB/s (54Kbps) continuous data stream
  • One way 256Kbps digital - yields ~27KB/s (216Kbps) continuous data stream
Note: this greatly depends on your ISP's network infrastructure, quality of cable placed into the ground, and from what type of server you are testing a download with. But this gives you an idea of what to expect.

Compression: Once you have polled your Internet bandwidth, you are now more equipped to understand the balance of your household/business needs and throughput. After taking several readings to reach an average of the above-mentioned test, and understanding what type of usage the connection gets (kids internet gaming, co-workers sharing one connection and downloading occasional large files, etc.) you can now select your compression given these parameters of "available talk bandwidth".

Bandwidth Requirements for Several Common VoIP Compression Algorithms
Codec Codec Bit Rate (Kbps) Nominal Ethernet Bandwidth (Kbps)
G.711 64 87.2
G.729 8 31.2
G.723.1 6.4 21.9
GSM 13.2 N/A
iLBC 13.3 N/A
G.723.1 5.3 20.8
G.726 32 55.2
G.726 24 47.2
G.728 16 31.5
Detailed Codec information (MS Excel spreadsheet) from

Our softphone client:
  • G711u/a - Requires 64+Kbps (inbound and outbound) continuous data stream for a quality call, plus the SIP signal. A 128Kbps connection has shown to be the minimal connection needed in our testing.
  • G723 - Requires 6.4+Kbps (I and O) continuous data stream and also needs room for the SIP signal, 28.8Kbps connection has shown to be the minimal connection.
Dial-up users will have to use G723, which comes as an option to our X-Pro client. Broadband users - if you have a bandwidth relatively unaffected by others on a network and you can easily reach 128x2+Kbps, then you should be pretty safe to use G711u, which is our FREE client.

Symptoms of a poor connection:
  1. Your voice is received as "jittery" and in "slow-motion". In most cases it is a marginal connection where the throughput is less than 120Kbps.
  2. Your call dials out and picks up, but cannot hear either party. In most cases it is due to having a dial-up connection using G711u, about 40-50Kbps.
  3. Word skipping - if someone is doing a large download during your connection that is infringing on your bandwidth needed to maintain a conversation, that is usually the symptom. Other resident programs on the PC will "pull" data from the Internet, such as MS updates, etc. and they must be taken into account also.
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