VOIP

hi to all,

its been awhile since this post was revived... :lol:

anyway since we are in the voip subject does it has any difference in configuring a voip box from different vendors (e.g. CLIs and interfaces) or are they just all the same thing when it comes to configuration?i'm currently handling a quitum box.

also anyone knows how to configure or at least have an idea on how to setup a voip system wherein it is initially linked to a pabx system of the company but also wishes to link the voip system to cellular phones?is this possible? voip gurus put on your thinking hats... :lol:


thanks...

I'd just like to add some input as far as Tracer's note regarding heavy traffic on links which also happen to contain VOIP packets.

On a small network with a fast backbone (gigabit), you usually won't have any problems with your VoIP packet running through it and reaching its destination, assuming the backbone is not heavily utilised.

When Jitter and other voice problems start to occur, it's usually due to heavy traffic on the port that the IP Phone and in some cases, PC, connects to.

Nearly all Cisco IP Phones have a small switch embedded inside them, so that the cable from the rack switch e.g Catalyst 3550, connects to the IP phone, and from there another UTP cable runs to the PC. The link from the Catalyst switch to the IP phone and PC is always 100Mbit.

Now, if the user on the PC starts to transfer a large file at fast speeds, then you might very well get Voice packets dropped due to excessive load of the local switch port.

To resolve these problems, and other similar ones, you usually implement the same physical setup, but with a different logical layout - meaning the IP phones are set to their own network.

For example:

Switch

---

IP Phone

---

PC

The ip phone can be on network 192.168.0.0 while the PC is on network 192.160.10.0.

How can this be possible? Easy!

The link between the Switch and the IP Phone is what we call a 'Trunk' link ( for those who are scratching their head.... read up on our latest VLAN article!):

Switch---[trunk link]----IP Phone


While the link between the IP Phone and PC is a normal 'Access link' with a different logical network:

IP Phone----[Access link]---PC

This setup ensures traffic from one network will not interfere with traffic from the other, increasing dramatically the quality and stability of the IP phone and PC network. In addition, the fact you have created two different broadcast domains is also very good. Windows machines tend to 'shout' all the time, consuming valuable bandwith and causing other silly problems, so mixing IP Phones and PC's into one logical network is not really that much of a good idea. Separating them in their own networks is ideal as no broadcasts originating from silly Windows machines will ever reach the IP Phone network.

Closing, the amount of bandwidth required for an IP Phone call is varies and really depends on the type of codec used to 'encode/decode' your voice! There are a number of codecs supported by Cisco's Call Manager, the most popular being the G.711 and G.729 which requirements are 64kbit/sec and 10 kbit/sec respectively. In a local LAN, you would use G.711 since most LANs run at speeds of 100Mbits, where as over WAN links - G.729 is a favorite, requiring only 8Kbps of bandwidth!

I think I'll just finish off here - expect to see a detailed analysis of VoIP once we have the VLAN topic out of the way and our Cisco lab complete!!!

Cheers,

hi to all

i just want to know if you have any idea, suggestions, or solutions to a voip imlementation wherein it involves remote access by a user wishing to call an international line via cellular phone.

the user will use a cellular phone to access the voip box on a local office interconnected via IP to another voip box located at an international office to call a recipient.

correct me if i'm wrong, but as far as i've read about voip, it is possible to make a remote access to a voip system but on how to implement it is really a puzzle to me.

if anyone can help me with my dilemma it would be highly appreciated. thank you very much...

hi its me again :lol:

has anyone encountered a voip box not giving out dial tones? how di you go about in solving this? as far as troubleshooting, i've already checked the whole system for possible errors as well as the alarms for any possible misconfiguration but unfortunately the problem still persists. any suggestions and advice would be highly appreciated. thanks a million.

jhun,

Can you let us know what type of a device this is and what type of a system your connecting it to e.g call manager?

hi chris,

it is just a quintum a800 multipath switch. it is directly connected to a public ip address and is a standalone and is linked to our voip box located at the states.

i'm currently setting it up as it was previously functional and then it just suddenly stop giving dialtones, thus unable to make/receive a call.