Lisa Bock covers various gateways and gatekeepers that are necessary to convert media streams from one set of communication standards to another, and include media and signaling gateways along with translators and mixers.
- [Instructor] Today, when you make a call, the communication channel will most likely pass through several different types of networks in order to get to the final destination. As we see in this graphic, a phone call may have to pass from the public switched telephone network, through the internet, to a corporate voice over IP system. As media travels through networks, gateways, or devices that adjust to the different network signaling requirements and convert media streams from one set of communication standards to another.
Signaling gateways use two main functions, media and signaling conversion. Gateways include media gateways, call agents or media gateway controllers, signaling gateways, and translators and mixers. Media gateways convert and packetize voice traffic into an RTP stream. Examples include trunking, such as a SIP trunk, that provides an interface between the legacy system and a voice over IP network, and a residential gateway that converts an analog signal to voice over IP.
Media gateway control protocol is a master slave protocol that provides a central gateway by handling the signal and session management required during a multi-media session. Megaco is also known as H.248. This performs the same functions as media gateway control protocol, but as a newer protocol that uses different commands and processes. Megaco can operate with either H.323 or Session Initiation Protocol.
Signaling gateways pass voice traffic between dissimilar networks. SIGTRAN, or signaling transport is a telephony protocol that transports SS7 signals through the internet. Session Initiation Protocol is an application layer protocol for signaling and control that establishes, maintains, and terminates sessions between parties over the internet, private networks, and cell systems.
H.323 acts as a wrapper for media control and setup, and includes H.225, which establishes communications between two hosts, and H.245, which establishes properties, such as audio codex and logical channels for the media transfer. Translators and mixers are middleboxes that are placed in the network that transform the media stream within a session, and are sometimes necessary when handling conference sessions or traversing firewalls.
Gateways and voice over IP are necessary to convert media streams, and include media and signaling gateways, along with translators and mixers.
- Voice over IP (VoIP) and Unified Communications
- Digitizing a signal
- VoIP components
- Protocols used by VoIP, including TCP/IP and DHCP
- Connecting systems
- Gateways and gatekeepers
- Factors that might affect quality on a VoIP network
- Wireshark statistics