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IP Telephony Configuration Guide
Appendix E
Quality of Service
The users of corporate voice and data services expect these services to meet a level of quality of
service (QoS). This, in turn, affects network design. The purpose of planning is to design and
allocate enough resources in the network to meet user needs. QoS metrics or parameters help in
meeting the needs required by the user of the service.
Setting QoS
There are two interfaces that must be considered:
• IP telephony interfaces with the end users: voice services made available need to meet user
QoS objectives.
• The gateways interface with the intranet: the service provided by the intranet is “best-effort
delivery of IP packets,” not guaranteed QoS for real-time voice transport. IP telephony
translates the QoS objectives set by the end users into IP adjusted QoS objectives. The
guidelines call these objectives the intranet QoS objectives.
Figure 50 Relationship between users and services
The IP gateway can monitor the QoS of the Intranet. In this mode, two parameters, the receive
fallback threshold and the transmit fallback threshold, control the minimum QoS level of the
intranet. Fallback thresholds are set on pair-per-site basis.
- Fallback threshold
- Codec
Business Communications Manager IP telephony parameters
- Silence compression
- Echo cancellation
- Non-linear programming
Corporate intranet
Deliver voice/fax service
Deliver IP service
User oriented QoS
- Roundtrip conversation delay
- Clipping and dropout
- echo
Network QoS metrics
- One-way delay
- Packet loss
Business
Communications
Manager VoIP
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