User Manual - Configuration Guide (Volume 3)
Versatile Routing Platform Chapter 1
VoIP Configuration
1-4
packet switching can identify, therefore; the key factor of router configuration lies in the
mapping of the phone numbers and the IP addresses.
The ports that support the voice function in the Quidway series routers incl ude FXS
(Foreign eXchange Station, i.e., the plain telephone service port), FX O (Foreign
eXchange Office, two-wire loop trunk), the E&M trunk port and E1 voice port.
The device with FXS port type must be connected with the device with FXO port type
(the ordinary telephone set is a standard FXO port). The ring current received by the
FXS and FXO is AC current of 25Hz and 60 volts, while the signal received and sent in
the E&M port is DC signal.
Table VC-1-1 The match table between the plain switch and the router interconnection interface
Switch Router Capacity (channel)
Loop trunk line (FXS) FXO 1
Subscriber line (FXO) FXS 1
E&M trunk E&M trunk 1
E1 trunk E1 trunk 30
1.1.3 IP Voice Feature over VRP
The IP voice over the VRP abides by G.711 (A law), G.729, G.723.1, H.225.0, H.245,
and standards such as RFC1889, 1890, etc., which can support the FXS, FXO, E&M
port and E1 port.
The IP voice characteristics over the VRP include:
z Silence suppression
Automatically detect the time segments of silence during session and pause the
generation of data flows during these time segments, so as to reduce the sent voice
data quantity.
z Comfort noise
Through generating appropriate background noise, the sharp voice between the
speaking and pause that resulted from the silence suppression is avoided.
z Jitter buffering
Jitter is caused by the variations of the data packet arrival rate in the network due to the
time delay variation. In order to compensate this jitter, we have added a buffer to the
voice devices at the receiving side to store data packets for enough time length. Thus,
even the slowest packet can arrive in time for processing in sequence. In t he mean time,
the buffer can adjust the packet length of the voice port board, and send the voice data
to the voice port board at a stable speed
z Supporting QoS
Since there is high requirement for the real-time voice service, precede nce needs to be
given to voice packet sending. You can take the measures such as setting Priority
Queuing (PQ) and Custom Queuing (CQ) at the transmit end. For t he c o nf igur at ion of
PQ and CQ, please refer to the relevant sections of the “QoS Configuration “.
z Supporting IP Fax
The IP Fax system is established on the basis of the VoIP, which serves to establish the
fax channel, transmit and receive the fax data. The IP Fax im plementation includes
modulation/demodulation, fax protocol processing, IP channel maintenance, etc .