Network Design - how to determine bandwidth is enough?

[rachelhor]

Hi,

I have a question on network design

Q1) When doing network design on paper (without any tools), how to determine that the bandwidth planned is enough?

For example, given a network with the following applications

- VoIP of 1Mbps to multipoint (total 5 sites)

- video conferenc of 3Mbps to multipoint (total 5 sites)

Q2) How do I calculate the total traffic/bandwidth needed above?

Q3) Do I have to multiply the VoIP 1Mbps by 2 to get 2Mbps mean 2-way communication? (Likewise multiply 3Mbps by 2 to get 6Mbps for 2-way video conference?)

Q4) Since it is multicast, do I also have to multiply VoIP 2Mbps (see above q2) by the number of sites, in this case 5, to get 10Mbps in total? (Likewise multiply 6Mbps by 5 to get 30Mbps in total?)

Thanx!

[kyaw_thu]

If you want to know how much bw you need, first of all you need to know how many concurrent calls you except. Then multiply number of concurrent calls by which voice codec you use.

[rachelhor]

Hi

I understand the first part about concurrent calls.

But what do you mean by multiply by "which voice codec you use"?

Can you kindly elaborate in simpler terms so i can understand?

thanx!

[krozier]

A voice codec is an algorithm that coverts voice signals to digital bits. There are several different codec used in VOIP which the difference are in complexity, compression and quality. G.711 is an example of voice codec. You will need to balance voice quality vs bandwidth usage when making a decision on which codec to use between WAN links.

Glossary Term:CODEC

Coder decoder. Device that typically uses pulse code modulation to transform analog signals into a digital bit stream, and digital signals back into analog. In VoIP, it specifies the voice coder rate of speech for a dial peer.

Make sure that you do no forget packat overhead in your calculations. Here is a good link to follow and it has a bandwidth calculator:

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094ae2.shtml

Hope this helps!

Kersean.