Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2001-06-11
2004-05-11
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S755000
Reexamination Certificate
active
06735736
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for preventing errors in transmission of binary data frames via a path in a telecommunication network, when so-called temporary data channels are formed/dropped in any network portion between two end points of the path. More particularly, the invention is applicable to transmission of binary data frames via networks based on SDH and SONET standards, for example for preventing errors which might appear in the network portions called tandem connections (TC).
BACKGROUND OF THE INVENTION
Modern telecommunication networks are adapted for transmitting data organized in binary data frames of various formats. Typical examples of such binary data frames are standard frames accepted in SDH, SONET and PDH data transmission technologies. However, other telecommunication technologies using parity check (e.g., BIP) for verifying data under transmission may utilize the proposed technique.
The Synchronous Digital Hierarchy (SDH) and its North-American equivalent, the Synchronous Optical Network (SONET), are the globally accepted, closely related and compatible standards for data transmission in the public wide area network (WAN) domain. Recently, SDH/SONET has also been adopted by the ATM Forum as a recommended physical-layer transmission technology for ATM (Asynchronous Transfer Mode) network interfaces.
SONET and SDH govern interface parameters; rates, formats and multiplexing methods; operations, administration, maintenance and provisioning for high-speed signal transmission. SONET is primarily a set of North American standards with a fundamental transport rate beginning at approximately 52 Mb/s (i.e., 51.84 Mb/s), while SDH, principally used in Europe and Asia, defines a basic rate near 155 Mb/s (to be precise, 51.84×3=155.52 Mb/s). From a transmission perspective, together they provide an international basis for supporting both existing and new services in the developed and developing countries.
For transmitting data, SDH and SONET use frame formats transmitted every 125 &mgr;s (8000 frames/s). Because of compatibility between SDH and SONET, their basic frames are similarly structured, but differ in dimension, which fact reflects the basic transmission rates of 155.52 and 51.84 Mb/s, respectively. To be more specific, a basic frame format of SDH is 9 rows of 270 bytes, or 2430 bits/frame, corresponding to an aggregate frame rate of 155.52 Mb/s. For SDH systems, the mentioned basic frame transmitted at the rate 155.52 Mb/s forms the fundamental building block called Synchronous Transport Module Level-1 (STM-1 which, according to SDH mapping scheme, contains a signal called AU-
4
which, in turn, carries a signal VC-
4
). For SONET systems, the basic frame has dimensions of 9 rows by 90 bytes (270:3) and, being transmitted at the rate 51.84 Mb/s (155.52:3), forms the appropriate fundamental building block called Synchronous Transport Signal Level-1 (STS-1 containing AU-
3
that carries a signal VC-
3
).
Each basic frame of SONET or SDH comprises an information portion called Information Payload and a service portion called Overhead (OH). Information payload is usually formed by virtual container signals VC
4
, VC
3
and the like, and comprise a so-called POH (Path Overhead) portion predestined for various service and control functions.
One of the basic methods for controlling proper transmission of binary data frames is a so-called parity check. The parity check is a method of error-detection in the binary data transmission whereby an extra bit is added to a particular group of bits to be checked, which is adapted to make the sum of all the bits (always odd or always even). Instead, a parity array of several parity bits or even a parity byte can be appended to an array of bits or bytes. For example, a BIP8 procedure is one type of a widely known Bit Interleave Parity procedure, wherein each bit of a resulting BIP8 byte is a parity bit done across a specific bit position—e.g., bit 2 of the BIP8 byte is the parity of the 2
2
nd bit of all the bytes being checked, and so on. The parity check procedure traps errors in the following way. When a transmitting device frames a binary message, it counts a parity value of the message and appends to the message a selected parity array (bit, a number of bits, byte) with the parity value in it. The receiving end also counts a parity value of the received message and compares the result to the received parity value. If an error is detected, an alarm flag may be set and a retransmission may be requested.
U.S. patent application Ser. No. 09/418,219 filed Oct. 14, 1999 by the Applicant describes a situation where a binary frame transmitted from a transmitting end can be subjected to changes (which are not due to errors) before being received at the receiving end. For example, some reserve bits or bytes of the frame may be used as a data/voice/fax transmission channel for a call, which occasionally takes place in a portion of the network positioned between the transmitting and the receiving ends of the main telecommunication path. Such a channel is characterized by non-permanent presence of additional binary data in a portion of the binary frame, which is not occupied by the main message, and will be called a temporary data channel in this description. The temporary character of the channel is reflected both by the fact that transmission of the additional information may start and cease according to external commands, and by the fact that the channel may use only a portion of the path between the transmitting and the receiving end.
Another, more illustrative example of the temporary data channel can be found in the way of operation of so-called tandem connections (TC).
FIG. 1
illustrates so-called network domains, each comprising a number of network elements (NE). Each network domain, which receives a telecommunication signal (trail) arriving from one neighboring network domain for transmitting it to another neighboring network domain, may be considered a Tandem Connection network domain.
When a data stream is transmitted from one network domain (being in possession or responsibility of one provider) to another network domain (held by another company or provider), such providers are supposed to share both benefits for the telecommunication service, and responsibility for errors and faults which may happen during the transmission.
In the example of
FIG. 1
, three network domains marked 2, 3 and 4 may serve for transmission there-through either a so-called high order SDH signal VC
4
, or a so-called low order SDH signal VC
12
, and each of the domains should be respectively considered either a high order Tandem Connection, or a low order Tandem Connection. Generally, the function of the Tandem Connection is to monitor only a specific overhead portion of the arriving trail (signal). For example, one of the TC functions is to count BIP errors-the binary errors revealed by the Bit Interleaving Parity procedure. BIP errors may comprise both the errors that came to the TC with the trail, and those occurred in the TC. The TC functions usually provide for distinguishing between defects occurred in the TC and those related to data received by the TC, and are finally aimed at obtaining objective information on responsibility of each specific network domain for errors introduced in a signal while transmitting it via this domain. In each TC network domain, one of the border network elements (NE) serves as a Tandem Connection source, and the other—as a Tandem Connection sink. In domain
3
, for a particular direction of transmission, NE marked 5 is the TC source, and NE marked 6 is the TC sink. It is to be understood that the data transmission via the TC is bi-directional.
According to the term which will further be used in the present description, a temporary data channel is established between the TC source and the TC sink for creating and transmitting information which reflects the above-mentioned TC functions. An overhead byte N in the standard binary frame is assigned for this temporary
Halevi Ilan
Korall Eli
Browdy and Neimark
De'cady Albert
ECI Telecom Ltd.
Torres Joseph D.
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