The goal of this document is to give you all a basic level of understanding in cisco's voip. please see inline,this will grow up by the upcoming days!!!
Voice over IP - Foundation
Do u ever know why people move from exisiting POTS/PBX to IP telephony in an organization?
The IP telephony is very flexible in moving it from one desk to the other as it's tracked via its MAC address,but when it comes to POTS
once it's programmed we can move it from desk to desk.
Low cost - for eg if you have two sites(USA and INDIA) interconnected by a vpn, you can make calls with 4 digit extn at free of cost
or precisely the bandwidth charge that the link use.
Application based services, example if you have a nokia E series phone with wireless capability, think if you reach office
your phone sync with that wireless signal and got connected to your organization, so the user can be reachable via 4 digit extn
when he leaves the office he will be connected back the mobile carrier.
How to make people in PSTN world migrate to cisco voip ?
There are few ways cisco try to impress the customers :-)
Keep your existing pstn equipments and buy our modules that fit in to cisco router (FXS/FXO cards - VIC card )
so that you can make calls to long distance at a very cheaper cost by fiting existing PSTN devices to cisco voip interfaces.
The second way of approach is hey guys you already have our devices running on our core so why can't you migrate fully to
cisco devices for VoIP, - Buy Cisco Call manager, Cisco IP phone etc...
The Major advantage of cisco platform when it comes to ip telephony is application enablement.
Think daily when you go to office you use punch card for entering your in and out time, If you install an application
you can make your IP phone to do this capability for you
Call control on a Distributed Model ?
The call control mechanism is done with the help of a voice gateway, These are cisco devices with specific IOS to do this fn.
Think you are dialling 2222 on your phone, that request is forwarded to the voice gateway,voice gateway looks that request and forward
like you have to go to 192.168.1.2 destination, so the phone connected to destination port rings.
so overall voice gateway maintains a dial plan for each destination phones, similar to routing table.
Call control on a Centralized model ?
On centralized model the call forwading/dialplan is centralized on cisco call manager.
if a source dials a no, the gateway will be forwarded to CCM to take decision where to forward,once it CCM reply back that info go to destination device
destination device contacts the CCM to make decision on which phone to ring.
How cisco support voip services with existing old telephone used in PBX?
With the help of FXS - Foreign exchange station we can interconnect old phones with router. FXS cards sits on routers.
How to interconnect between PBX and CO ?
With the help of FXO - Foreign Exchange Office you can connect both site.
How will you trunk two PBX's?
with th help of E&M cards, Earth and Magneto you can interconnect and form a trunk.