Information Technology Reference
In-Depth Information
An architecture framework for media services supports different models of video models.
As shown in Figure 14-13, the network provides service to video media in the Media Ser-
vices Framework. Those services are access services, transport services, bridging services,
storage servers, and session control services, which are provided to endpoints.
Access services
provide identity of end devices, mobility, and location services.
■
Tr anspor t ser v ices
provide QoS for reliable packet delivery.
■
Bridging services
provide transcoding, conferencing, and recording services of media
streams.
■
Storage services
provide capture and storage of media streams and content manage-
ment and distribution.
■
Session control services
provide session signaling and control and gateway services.
■
End
Points
Session Control Services
Gateways
V
V
Access
Services
Transport
Services
Bridging
Services
Storage
Services
HDTV
V
V
Figure 14-13
Media Services Architectural Framework
Codecs
Because speech is an analog signal, it must be converted into digital signals for transmis-
sion over digital systems. The first basic modulation and coding technique was pulse-code
modulation (PCM). The international standard for PCM is G.711. With PCM, analog
speech is sampled 8000 times a second. Each speech sample is mapped onto 8 bits. Thus,
PCM produces (8000 samples per second) * (8 bits per sample) = 64,000 bits per second =
64-kbps coded bit rate. Other coding schemes have been developed to further compress
the data representation of speech. G.711 is used as the primary with IPT over LANs where
high bandwidth is available.
