VOIP

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VOIP (voice over internet protocol) domain has been enhanced to include voice data and video in a single protocol and MEGACO protocol promoted by ITU-T is considered as leading protocol by telecommunications administrations following ITU-T standards. Products follow usually SIP protocol and easy to install in a service oriented network.

Terms Used

STP	Signaling Transfer Points	RFI	Request For Information
SP	Signaling Point	RFP	Request For Proposal
ISUP	ISDN User Part	SS7	Signaling System 7
SSP	Service Switching Point	PSTN	Public Switched Telephone Network
SCP	Service Control Point	IN	Intelligent Network
TGW	Trunk Gateway	UDP	User Datagram Protocol
RGW	Residential Gateway	ITU	International Telecommunication Union
EP	End Point	IETF	Internet Engineering Task Force
MGCP	Media Gateway Control Protocol	IP	Internet Protocol
CA	Call Agent	IAM	Initial Address Message
MG	Media Gateway	CIC	Circuit Identification Code
SG	Signaling Gateway	ACM	Address Complete Message
JAIN	Java API for Integrated Networks	VON	Voice On Net
SGCP	Simple gateway Control Protocol	MEGACO	Media Gate Control Protocol H-248

Network Dimensioning

•VOIP represents voice, data and video all in a single stream of IP pulses. A VOIP call uses less bandwidth than a Circuit switched call typical savings are 30% bandwidth.

•Internet has network congestion and this results in:

a.Network Delay- Transmission Delay, Queuing Delay due buffering, Switching and Processing delay and Propagation delay.

b. Network Jitter.

c.Network Packet Loss and Desequencing.

Voice quality is improved using:

•Integrated Services (IntServe) is a stateful approach where resources are reserved in a network before data starts to flow along the reserved path.

•Differentiated Services ( DiffServe) is a stateless approach where real time traffic is marked to get preferred treatment in the network.

•Forward Error Correction (FEC) algorithms reduce the impact f data loss by sending redundant data along with the audio data. The redundant data helps to reconstruct lost data.

•Loss Concealment algorithms try to reduce the impact of data loss by replacing the lost audio with an approximation.

FEC and Loss Concealment are used in VOIP user devices. IntServe and DiffServe are methods used in the IP Network.

•MEGACO/H.248

•MEGACO is a general-purpose gateway-control protocol standardized in the IETF as RFC 3015 and as recommendation H.248 in the ITU-T. It is a master-slave, transaction-oriented protocol in which Media Gateway Controllers (MGC) control the operation of Media Gateways (MG). MEGACO/H.248 is central to the VOIP solutions and may be integrated into products such as Central Office Switches, Gateways (Trunking, Residential and Access), Network Access Servers, Cable Modems, PBXs, IP Phones, Soft Phones, IADs, Middleboxes etc. to develop a convergent voice and data solution.

H.248 Stack: Functions

•Association management: Creation and management of control association between MGC and a MG

•Transaction and Command management: Transaction and Command requests and replies management

•ALF support: Ensures reliable delivery of transactions

•Encoding/Decoding in both text and binary

•IN and ATM SDP encoding support

•Easy Packages upgrade support ( validation, addition and editing of packages)

•H.248 Stack: Service User Interface

•The Service User Interface exposes Protocol APIs and Management APIs to the service user. It provides the following functions to the service user:

•Interfaces to:

–Register with the stack

–Configure the protocol parameters

–MG/MGC application for sending protocol messages to the MGC/ MG application

–Activate and deactivate management features of the stack

–Protocol trace, statistics collection, status reporting, error reporting and redundant mode operation

•Flexibility to collate commands into transactions

•Protocol message encoding and decoding services

•Parameter validation services including package parameter validation.
The interface may operate in the same process context (functional interface) or a different context (message based interface) than the core stack

•Redundancy Support

•The MEGACO/H.248 stack provides multiple redundancy configurations to support different applications. Support options include:

•Redundant applications

•Redundant MEGACO/H.248 stacks

•Scalability

•The MEGACO/H.248 stack design offers capability for scaling as the target application grows. Scalability can be achieved by following means:

•Increase the number of call agents and MG-MGC associations, which the stack handles as the system capacity grows

•Moving from uni-processor environment to multi-processor target hardware

•Moving from a single thread of control operating system to a multi-tasking real time operating system

•Init time dimensioning of parameters

•
MEGACO/H.248 Operation and Management Support

•Extensive statistics collection

•Error reporting

•Status reporting

Multi-level tracing support

•Voice over Internet Protocol

•Domain is expanded to Voice, Data and Video using IP Carrier Lines

•Saves 30% cost in Leased Lines used by Call Centers and Software Development Companies

•Virtual Private Networks create strong integration of Head Office with Branch Offices.