Grandstream Networks 200 ユーザーズマニュアル

 

52

Network Address Translation 

, a protocol to exchange and synchronize time over 

networks 
The port used is UDP 123 
Grandstream products using NTP to get time from Internet 

Outbound Proxy or another name Session Border Controller. A device used in 

VoIP

 networks. OBP/SBCs are put into the signaling and media path between 

calling and called party. The OBP/SBC acts as if it was the called VoIP phone and 
places a second call to the called party. The effect of this behaviour is that not 
only the signaling traffic, but also the media traffic (voice, video etc) crosses the 
OBP/SBC. Without an OBP/SBC, the media traffic travels directly between the 
VoIP phones. Private OBP/SBCs are used along with 

firewalls

 to enable VoIP 

calls to and from a protected enterprise network. Public VoIP service providers 
use OBP/SBCs to allow the use of VoIP protocols from private networks with 

internet

 connections using 

NAT

. 

Point-to-Point Protocol over Ethernet, is a network protocol for encapsulating 
PPP frames in Ethernet frames. It is used mainly with cable modem and DSL 
services. 

 
PSTN  

Public Switched Telephone Network 

i.e. the phone service we use for every ordinary phone call, or called POT (Plain 
Old Telephone), or circuit switched network. 

Real-time Transport Control Protocol, defined in 

RFC 3550

, a sister protocol of 

the 

Real-time Transport Protocol

 (RTP), It partners RTP in the delivery and 

packaging of multimedia data, but does not transport any data itself. It is used 
periodically to transmit control packets to participants in a streaming multimedia 
session. The primary function of RTCP is to provide feedback on the quality of 
service being provided by RTP.