VOIP is the technology which allows voice calls to be transmitted over the IP network. It converts analog signals into digital data packets which can be transmitted over the IP network and wise versa. The simplest form of VoIP is a computer-to-computer voice connection. All you need is computer and a headset with a microphone.
There are many advantages and few disadvantages of VOIP.
Advantages
- Move, Adds and Changes – When you unplug and replug phones they will get updated no matter where they are. Phones are tracked in the system via it’s MAC address.
- Bandwidth & Equipment Efficiency – In PBX world every phone call takes 64kbps. In IP telephony voice can be compressed with a very little quality drop.
- Cost – Free long distance calls. WAN can be used to take free calls between offices.
- Services and Devices – Video calls, Wireless IP Mobiles
Disadvantages
Although VoIP does provide plenty of advantages and features, there are a few disadvantages to this new technology that you should be aware of.
- Voice Quality – Audio quality is poor when you compare it with the PSNT (analog) call.
- Power – VOIP is depend on power. You need to plug your modem, router, ATA or other VoIP devices to the electric power supply for it to work A stable power source must be created for VoIP.
IP Telephony Migration
There are two types of IP telephony migration methods.
Method 1
Connect your existing PBX system to the router (Voice enabled router). Then the router will be able to convert voice into a packetized data which can be transmitted over the WAN. With this method you can make calls to other branches without any additional cost.
Method 2
Replace existing PBX system and phones with Cisco Call Manager (CCM). With this method you can have more features and benefits.
Call Control Models
Call control is routing voice around the network. You have to have a way to get voice calls from one point to another. There are two types of call control models.
Distributed Call Control
In Distributed call control model all devices on your network ( routers) controls the call.
Centralized Call Control
In centralized model call setup, signaling, resource control, etc… are done by the call agent. The main disadvantage of this method is if the centralized brain (Call Agent) goes down calls cannot be routed. It is best practice to have a backup for the centralized brain.
IP Telephony Devices and Equipments
IP Phone
Voice Gateway
H.323 MCU (Multipoint Control Unit)
-- Mix Conference CallsCall Agent
- Brain of the Network
- Controls IP Phones
- Has dial Plans
H.323 Gate Keeper
- H.323 GK is a router with a special IOS which allows it to fulfill the role of call agent.
- Controls Dial Plans
Other Application Servers
- Cisco Unity (Voice Mails)
Cisco IPCC (Call Centre)
Foreign Exchange Connections
Foreign Exchange Stations (FXS)
Foreign Exchange Stations are analog interfaces of routers which allow you to connect legacy voice equipments such as analog phones, fax machines, etc..
FXS converts legacy equipments into VOIP compatible devices.
When you plug analog device to a FXS port the router takes analog signal that are sent from the phone and converts them into VOIP communication.
Foreign Exchange Office (FXO)
FXS allows you to take typical incoming analog lines and converts them to VOIP.
Difference between FXS and FXO is FXO receive dial tone and FXS Provides dial tone.
E & M
E & M allows PBX systems to communicate.
