Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Patent
1997-07-03
2000-03-14
Ton, Dang
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
370395, 370398, H04J 300
Patent
active
060382376
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of voice signal transmission in a network using ATM (Asynchronous Transfer Mode) exchanges, and to an exchange system using this.
BACKGROUND ART
FIG. 4 shows a typical layout of a prior art network of this type. In this Figure, symbols 10a, 10b, and 10c are ATM exchanges, symbols 30a, 30b, and 30c are exchanges equipped with a voice compression function (PBXs), and symbols 50-1, 50-2, 50-3, 50-4, 50-5, and 50-6 are telephone sets. Also, the dotted line portions in ATM exchanges 10a, 10b, 10c and PBXs 30a, 30b, 30c are through-routes; in particular, symbol 35 in PBX 35 indicates a relay route when a voice signal is relay-exchanged by the corresponding PBX 30b.
Next, the case will be described in which compressed voice is transferred by such a prior art network. For example, when a call is made between telephone set 50-1 and telephone set 50-3, a telephone call originated by telephone set 50-1 is transferred in the order: PBX 30a, ATM exchange 10a, ATM exchange lob, and PBX 30b, before arriving at telephone set 50-3. In this case, all the processing of the call connection information is performed between PBX 30a and PBX 30b.
The operation of PBX 30a, ATM exchange 10a, ATM exchange 10b, and PBX 30b in this case will now be described in more detail. In the present description, it will be assumed that connection between PBX 30a and ATM exchange 10a and connection between ATM exchange 10b and PBX 30b is effected by a typical interface TTC 2 Mbps interface.
FIG. 5 shows an example of the frame format of a TTC 2 Mbps interface; this is constituted by providing a frame synchronization bit F at the head, followed by one 64 kbps channel, a call control ch (channel), voice ch (channels) 1 to 30, and, in addition, an undefined channel [see FIG. 2(a)] 1ch, not particularly shown in this Figure.
In the case where voice compression is not performed by PBX 30A, PCM (64 kbps) voice is accommodated by the above voice ch, so these channels are of 8-bit type (8 Khz.times.8 bit).).
In contrast, if voice compression is performed by PBX 30A (in this example, 16 kbps compression), compressed voice allocation (16 kbps compressed voice) as shown for example in FIG. 6 is performed within each voice ch (channel); compressed voice is entered in the amount of 2 bits at the head, invalid data being inserted for the remaining 6 bits.
Usually, when a voice signal is transferred by PBX 30A without compression, at the next-stage ATM exchange 10A, as shown in FIG. 7, the frame signal (see FIG. 7(a)) of the TTC 2 Mbps interface sent from PBX 30A constitutes a continuous signal which is directly converted into cells in the AAL (ATM Adaptation Layer) type 1 before being transferred.
An ATM cell (see FIG. 7(b)) generated by this cell conversion consists of a total of 53 bytes, consisting of a 5-byte "ATM header", in which control information such as its destination is stored, and a 48-byte "information field" containing user data. An ATM cell in which a TTC 2 Mbps interface frame is directly inserted in this information field is transferred from ATM exchange 10A to remote ATM exchange 10B.
In contrast, when transfer is effected by PBX 30A with voice compression, at ATM exchange 10A, as shown in FIG. 8, each of the ch on the TTC 2 Mbps interface frame signal (see FIG. 8(a)) sent from PBX 30A, for example call control ch (see FIG. 8(b)), the 16 kbps compressed voice of voice ch1 (see FIG. 8(c)), the 16 kbps compressed voice of voice ch2, . . . and the 16 kbps compressed voice (see FIG. 8(d)) of voice ch30 are separately converted to ATM cell form and transferred to the remote party.
As described above, when a voice signal was transferred through an ATM exchange without compression, it normally occupied a bandwidth of 2 Mbps irrespective of whether or not a voice call was taking place or the busy settings. But when voice compression is employed, since the voice bandwidth can be set to 1/4 and further such that channels that are not busy can be set beforehand as non-transmitting, a transfe
REFERENCES:
patent: 4519073 (1985-05-01), Bertocci et al.
patent: 5675574 (1997-10-01), Norizuki et al.
patent: 5761197 (1998-06-01), Takefman
Obara Keiichi
Tsuruta Hidekazu
Ho Tuan
Kabushiki Kaisha Toshiba
Ton Dang
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