SMG digital gateway 67
T4 timer—the maximum time allotted for all retranslations of the final response.
Ignore address in R-URI—specifies that only the user part of the request URI is analysed.
Up to 64 interfaces are supported. To create, edit, or remove SIP/SIP-T interfaces, use the Objects—Add
Object, Objects—Edit Object, or Objects—Remove Object menus and the following buttons:
— Add Interface;
— Edit Interface Parameters;
— Remove Interface.
The signal processor of the gateway encodes analogue voice traffic and fax/modem data into digital
signals and performs its reverse decoding. The gateway supports the following codecs: G.711A, G.711U, G.729,
the Т.38 protocol and the CLEARMODE mode.
G.711 is a PCM codec without compression of voice data. To ensure correct operation, this codec should
be supported by all manufacturers of VoIP equipment. G.711A and G.711U codecs differ from each other in
encoding law (А-law is a linear encoding and U-law is a non-linear). The U-law encoding is used in North America,
and the A-law encoding—in Europe.
G.726 is an ADPCM ITU-T standard which describes voice data transmission using 16, 24, 32, and 40 kbps
bands. G.726-32 substitutes G.721 which describes ADPCM voice data transmission using 32 kbps band.
G.723.1 is a voice data compression codec which has two operation modes: 6.3 kbps and 5.3 kbps.
G.723.1 has a voice activity detector and generates comfort noise at the remote end during the period of silence
(Annex A).
G.729 is a voice data compression codec too; it supports the rate of 8 kbps. By analogy with G.723.1,
G.729 supports a voice activity detector and generates comfort noise (Annex B).
T.38 is a standard which describes sending facsimile messages in real time over IP networks. Signals and
data sent by a fax unit are copied to T.38 protocol packets. The generated packets may include redundancy data
from previous packets that allows reliable fax transmissions through unstable channels.
CLEARMODE—a mode which does not use signals encoding/decoding. It is supported for transparent
transmission of digital information at 64 kbps (RFC4040).
The Service Type (IP DSCP) field value for RTP, T.38, and SIP/SIP-T/SIP-I
0 (DSCP 0x00, Diffserv 0x00)—the best effort—the default value.
8 (DSCP 0x08, Diffserv 0x20)—class 1.
10 (DSCP 0x0A, Diffserv 0x28)—assured forwarding, low drop precedence (Class1, AF11).
12 (DSCP 0x0A, Diffserv 0x30)—assured forwarding, medium drop precedence (Class1, AF12).
14 (DSCP 0x0E, Diffserv 0x38)—assured forwarding, high drop precedence (Class1, AF13).
16 (DSCP 0x10, Diffserv 0x40)—class 2.
18 (DSCP 0x12, Diffserv 0x48)—assured forwarding, low drop precedence (Class2, AF21).
20 (DSCP 0x14, Diffserv 0x50)—assured forwarding, medium drop precedence (Class2, AF22).
22 (DSCP 0x16, Diffserv 0x58)—assured forwarding, high drop precedence (Class2, AF23).
24 (DSCP 0x18, Diffserv 0x60)—class 3.
26 (DSCP 0x1A, Diffserv 0x68)—assured forwarding, low drop precedence (Class3, AF31).
28 (DSCP 0x1C, Diffserv 0x70)—assured forwarding, medium drop precedence (Class3, AF32).
30 (DSCP 0x1E, Diffserv 0x78)—assured forwarding, high drop precedence (Class3, AF33).
32 (DSCP 0x20, Diffserv 0x80)—class 4.
34 (DSCP 0x22, Diffserv 0x88)—assured forwarding, low drop precedence (Class4, AF41).
36 (DSCP 0x24, Diffserv 0x90)—assured forwarding, medium drop precedence (Class4, AF42).
38 (DSCP 0x26, Diffserv 0x98)—assured forwarding, high drop precedence (Class4, AF43).
40 (DSCP 0x28, Diffserv 0xA0)—class 5.
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