  Lecturer: M.S: Bùi Thư Cao Student: 1. Nguyễn Hoàng Tuấn Phương 07711271 2. Nguyễn Thị Diệu Linh 08902311 3. Nguyễn Văn Hùng 08093171 4. 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VoIP Gateway Gateways are defined in different ways by different people A network device that converts voice and fax calls, in real time, between the public switched telephone network (PSTN) and an IP network The primary functions of a VoIP gateway include voice and fax compression/decompression, packetization, call routing, and control signaling Additional features may include interfaces to external controllers,... controllers, such as Gatekeepers or Softswitches, billing systems, and network management system Click icon to add picture Figure 3 A media gateway, from one perspective API = applications program interface 15.4.2 An IP Packet as Used for VoIP Assume for argument that we use either a G.711 or G.726 packet (Table 15.1) IP packet The packet consists of a header and a payload In the case of G.711 (standard PSTN... packet can be “lost.” For example In the case of G.711, this would be the time equivalent of 16 or 26 msec (duration of a packet including its header) Another reason for a packet to be lost may be excessive error rate on a packet whereby it is deleted When the lost (discarded) packet rate begins to exceed 10%, quality of voice starts to deteriorate G.723 or G.729, it is desirable to maintain the packet. .. virtual 15.5.4 Megaco or ITU-T Rec H.248 (Ref 13) Megaco is a call-control protocol that communicates between a gateway controller and a gateway It evolved from and replaces SGCP (simple gateway control protocol) and MGCP (media gateway control protocol) An MGC is sometimes called a softswitch A Megaco (H.248) is two principal abstractions relating to the model: terminations and contexts A termination... total delay (one-way) in a voice connectivity as follows: 0–150 msec acceptable 150–400 msec acceptable but not desirable Connectivity through a geostationary satellite falls into this category Above 400 msec, unacceptable The delay objective (one-way) for a VoIP voice connectivity is . 8$#445"25$  )7=)*.,/@0%')*'%'* )! %*-/0'%,',**%'%'  2)'*.  4,+/0  *  +,',+/0  ,*+->(),,%  *)  &%,,%)*''  $  ),,(.%++'  '%*%+''&  +&'''.*'&  ' A A A A