8 Flashcards
What is H.323 and when was it introduced?
H.323 is a recommended protocol introduced by the ITU Telecommunication standardization sector, formally recognized in October 1996. It defines audiovisual communication sessions on a packet network, particularly known for its video conferencing capability.
What are the functions of an H.323 gatekeeper?
The functions of an H.323 gatekeeper include address translation, call admission control, bandwidth control, and zone management for all registered endpoints within a zone.
What is the purpose of a voice gateway in enterprise networks?
Voice gateways are used to connect enterprise voice over IP networks to traditional telephony systems such as PBX and public land and mobile networks. They facilitate connectivity to remote branches, international locations, and mobile units.
What is the Media Gateway Control Protocol (MGCP) also known as?
The Media Gateway Control Protocol is also known as H.248 or Megaco. It is a plain text protocol used by calling devices to manage IP telephony gateways, specified under IETF RFC 2705.
What is Session Initiation Protocol (SIP) used for?
Session Initiation Protocol (SIP), defined by IETF RFC 3261, is a peer-to-peer protocol used for call routing, session management, and initiation, modification, and termination of interactive multimedia sessions. It is used for various communication types, including audio-video conferencing, chat sessions, and file transfer over IP.
What are the three types of delay inherent with packet-based voice networks?
The three types of delay inherent with packet-based voice networks are propagation delay, processing delay, and serialization delay (or queuing delay).
What is jitter, and how is it managed in voice over IP networks?
Jitter refers to the variation in packet arrival times in a packet-based network. In voice over IP networks, jitter is managed using jitter buffers, which can be adjusted to compensate for delays. Cisco employs dynamic jitter buffers for superior audio quality without loss packets or excessive delay.
How does packet loss affect voice traffic in networks?
Packet loss on networks, especially in voice traffic, can lead to perceptible disruptions in voice quality. However, if dropped packets are not perceivable to the human ear, voice traffic remains reliable. Quality of service (QoS) measures are often employed to make voice traffic resistant to packet loss.
What is voice activity detection (VAD), and what are its associated problems?
Voice activity detection (VAD) is a mechanism that detects speech amplitude and transmits voice data only when speech is detected. However, it may transmit background noise and can lead to issues such as signal-to-noise threshold problems and front-end speech clipping.
What are some common voice quality problems associated with voice over IP?
Common voice quality problems include absolute silence, clicking, crackling, crosstalk, hissing, severe static, echoed voice, garbled voice, and volume distortion.
What are the differences between H.323 and SIP protocols?
H.323 is based on telephony and is recommended by ITU, while SIP is based on Internet use and was designed by the IETF. H.323 uses aliases for addressing, whereas SIP uses URLs. H.323 is often preferred for interoperability and has better performance in terms of bandwidth and load balancing compared to SIP.
