ZyXEL Communications P-2304R, Руководство пользователя

Страница: 112 / 300

Chapter 9 SIP
P-2304R-P1 Series User’s Guide
112
• G.729 is an Analysis-by-Synthesis (AbS) hybrid waveform codec that uses a filter based
on information about how the human vocal tract produces sounds. G.729 provides good
sound quality and reduces the required bandwidth to 8kbps.
9.1.9 PSTN Call Setup Signaling
PSTNs (Public Switched Telephone Networks) use DTMF or pulse dialing to set up telephone
calls.
Dual-Tone Multi-Frequency (DTMF) signaling uses pairs of frequencies (one lower frequency
and one higher frequency) to set up calls. It is also known as Touch Tone®. Each of the keys
on a DTMF telephone corresponds to a different pair of frequencies.
Pulse dialing sends a series of clicks to the local phone office in order to dial numbers.
1
9.1.10 MWI (Message Waiting Indication)
Enable Message Waiting Indication (MWI) enables your phone to give you a message–
waiting (beeping) dial tone when you have one or more voice messages. Your VoIP service
provider must have a messaging system that sends message-waiting-status SIP packets as
defined in RFC 3842.
9.1.11 Quality of Service (QoS)
Quality of Service (QoS) refers to both a network's ability to deliver data with minimum delay
and the networking methods used to provide bandwidth for real-time multimedia applications.
9.1.11.1 Type Of Service (ToS)
Network traffic can be classified by setting the ToS (Type Of Service) values at the data
source (for example, at the ZyXEL Device) so a server can decide the best method of delivery,
that is the least cost, fastest route and so on.
9.1.11.2 DiffServ
DiffServ is a class of service (CoS) model that marks packets so that they receive specific per-
hop treatment at DiffServ-compliant network devices along the route based on the application
types and traffic flow. Packets are marked with DiffServ Code Points (DSCPs) indicating the
level of service desired. This allows the intermediary DiffServ-compliant network devices to
handle the packets differently depending on the code points without the need to negotiate
paths or remember state information for every flow. In addition, applications do not have to
request a particular service or give advanced notice of where the traffic is going.
2
9.1.11.3 DSCP and Per-Hop Behavior
DiffServ defines a new DS (Differentiated Services) field to replace the Type of Service
(TOS) field in the IP header. The DS field contains a 2-bit unused field and a 6-bit DSCP field
which can define up to 64 service levels. The following figure illustrates the DS field.
1. The ZyXEL Device supports DTMF at the time of writing.
2. The ZyXEL Device does not support DiffServ at the time of writing.