Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Patent
1994-09-30
1998-01-06
Olms, Douglas W.
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
370391, H04L 1256
Patent
active
057062854
DESCRIPTION:
BRIEF SUMMARY
FILED OF THE INVENTION
The invention relates to a method for establishing a user-network interface in a digital transmission network for a cell-based digital signal comprising cells of fixed length and having a high nominal bit rate, preferably 140 or 155 Mbit/s for an ATM signal.
BACKGROUND OF THE INVENTION
Cell-based data transmission at high bit rates is emerging in the public data and telecommunication networks with the standardization of the international ATM (Asynchronous Transfer Mode) user-network interfaces (UNI) and network-network interfaces (NNI). The asynchronous transfer mode ATM is based on a high-speed packet switched transmission technique where data is transferred in packets of fixed length, called cells in the ATM technique. The cell typically comprises an overhead of five octets and a payload of 48 octets. Cells belonging to different links are identified on the basis of their overhead. The ATM technique allows the transmission capacity to be utilized extremely flexibly. In addition, the packet switched transmission technique allows a variable band-width and dynamic channel allocation. The protocol used in the ATM technique is as simple as possible in order that the required transmission operations could be realized at very high speeds. The ATM is independent of the technique used for the transmission of cells, and so ATM cells can be transferred in the present plesiochronous transmission systems, in the transmission systems according to the synchronous hierarchical system SDH, or they may be transmitted as such e.g. in an optical fiber.
ATM interfaces are being standardized for the bit rates 140 Mbit/s (E4), 155 Mbit/s (SDH STM-1), 44 Mbit/s (D3) and 53 Mbit/s (SONET). Cell-based El/D1 (2/1.5 Mbit/s), E2/D2 (8/6 Mbit/s) and E3/D3 (34/44 Mbit/s) standard interfaces are being specified for MAN networks. Many new applications will require a flexible bit rate ranging between El/D1 and E3/D3, particularly from 4 to 16 Mbit/s for local area networks (LAN) links and for compressed digital video.
A high-speed 140/155 Mbit/s ATM interface can be used for a wide variety of services; in practice, however, the transfer of this type of signal over a subscriber network requires a separate optical fiber network, being thus expensive. The transfer of the ATM signal at 140 Mbit/s is not possible with copper twisted pair cables in the subscriber network, not even when the information signal itself (payload) has a lower bit rate. The transfer of a standard ATM signal in the SDH transmission system requires a complete VC-4 path (VC=virtual container), again even in cases where the transmission speed of net information would be low.
SUMMARY OF THE INVENTION
The object of the invention is a high-speed cell-based user-network interface complying with the standards towards the user and allowing an efficient transmission of the payload of the high-speed cell-based digital signal over a transmission network.
This is achieved by means of a method of the type described in the foregoing Background section, which according to the invention is characterized by adapting the rate of the cell-based signal by a policing function to an actual transmission speed lower than said nominal bit rate; and mapping the rate-adapted cell-based signal into a group of lower-speed transmission signals of about 1.5 Mbit/s, 2 Mbit/s, 6 Mbit/s or 8 Mbit/s for transmission over the transmission network.
The basic idea of the present invention is to utilize a standard cell-based high-speed (e.g. 140/155 Mbit/s) interface towards the user while adjusting the service bit rate to a fraction of the nominal high bit rate by using a policing function and while mapping the rate-adjusted payload signal into a group of standard transmission signals of a lower transmission speed. In the invention, a single high-speed cell-based signal is multiplexed at the transmission end into a number of lower-speed transmission signals, which allows an efficient utilization of the existing E1/D1, E2/D2 transmission channels, thus avoiding the use of separ
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Pyhalammi Seppo
Saijonmaa Jaakko
Nokia Telecommunications Oy
Olms Douglas W.
Ton Dang
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