VOIP Technologies

VoIP calls convert conversations into data packets which require a higher Quality of Service (QoS) and require security measures for Local Area Networks, Wide Area Networks, and Wireless Networks.
Signaling protocols and standards stipulate how networking equipment initiates and controls the flow of voice, video, and data communications. There are two major signaling protocol standards: H.323 and SIP.

H.323 is a suite of protocols that provides a foundation for audio, video, and data communications across IP-Based networks, including the Internet. H.323 is platform-, network-, and application-independent. It was created by the International Telecommunications Union (ITU), published in 1996. The current iteration of H.323 was published in 2006.

SIP stands for Session Initiation Protocol, and is a protocol that allows IP-Capable endpoints to create media sessions, such as telephone calls and video calls, with each other. SIP was developed by the Internet Engineering Task Force (IETF). SIP was originally started in 1996, and has evolved over the years into the current iteration. The initial SIP protocol was defined by RFC 2543, and the current version has been defined under RFC 3261. SIP is defined as a method of communication between multiple IP-based multimedia devices. SIP uses the Real-Time Transport Protocol (RTP) and the Session Description Protocol (SDP) to make communications possible between end-points. RTP transports the information, whether that is voice, video, or data. SDP is used to establish the session and session parameters. SIP is an Application-Layer protocol, and as such it allows for a variety of different applications, including voice, video, and gaming. SIP can work on IPv4 and IPv6 networks.

H.323
H.323 is comprised of six main components:
1. Media Gateway
2. H.323 Gateway
3. Call Servers
4. Gatekeepers
5. IP Terminals
6. IP Backbone Network

Starting at the top of the list, the Media Gateway converts one media stream into another. It can interact with call controllers, proxies, and soft switches using proprietary or standard protocols. It converts digital packets to analog and vice versa. It is the connecting point between the PSTN and the IP network.

The H.323 gateway transforms audio received from a telecommunications system into a format that the data network can use. It acts as a bridge to IP networks from voice networks and has built-in intelligence to select voice compression CODECs. It adjusts protocols and timing between two dissimilar computer systems, or voice-over-data networks. It performs the same functions as a media gateway.

A Call Server is responsible for helping to set up the calls on the data network. It receives call set-up request messages, determines the status of destination devices, and checks the authorization of users to originate or receive calls. The Call Server also creates and sends the necessary messages to process call requests.

A Gatekeeper provides call control, media access, and bandwidth management between endpoints. The Gatekeeper performs address translation, admissions control, and zone control. It will co-ordinate access to other servers and manage call routing. The Gatekeeper maps the destination telephone numbers to their destination end-point IP addresses. They can select the correct CODEC and translate between H.323 and other protocols. The Gatekeeper is the node that provides call control. In addition, the Gatekeeper can be used for a number of other functions, including dialing plans, call accounting, and many more. Gatekeepers can control the number of simultaneous calls, as well as the number of H.323 devices that can be supported on the network. The Gatekeeper is also responsible for managing all different zones.

IP Terminals and Clients are any end-point on the IP network. These can be hard phones or soft phones, as well as wireless devices. Basically, anything that brings voice and data communication to the end user.

The IP Backbone Network is the network on which the H.323 system is running. It must be IP-based. The number of devices that can be supported is partially defined by the bandwidth of this network. An IP network can be both wired and wireless. The IP network allows for dissimilar networks and systems to communicate and inter-connect.

H.323 is not as widely used as SIP. SIP offers greater flexibility than H.323 and is quickly eclipsing H.323 as the dominant protocol for VoIP traffic. SIP can inter-operate with H.323 networks through a SIP gateway. A SIP Gateway will sit at the edge of the SIP domain and translate what goes on inside the SIP domain into whatever the outside network needs (i.e. H.323 or PSTN, etc.). A SIP Gateway has two basic functions: translating the signaling stream and translating the media stream.