Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-05-06
2001-02-27
Olms, Douglas W. (Department: 2732)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S396000
Reexamination Certificate
active
06195353
ABSTRACT:
BACKGROUND
The present invention relates to telecommunication systems in which asynchronous transfer mode (ATM) is used for transporting voice-type data as well as other types of data, for example, video and control data. More particularly, the present invention relates to a telecommunication system in which ATM is used for transporting low bit rate, circuit emulation data (i.e., synchronous data) from one or more circuit emulation connections (i.e., circuit emulation data sources).
ATM is a standard protocol that is commonly used for transmitting asynchronous telecommunication data within a telecommunication system for one or more applications. ATM is based on the transmission of data in fixed size data packets known as ATM cells. The protocol for each ATM cell is the same, wherein, each ATM cell contains a 48 octet payload and a 5 octet header. In general, ATM is well known in the art.
The telecommunication data associated with each application is initially in a data transfer format that is application specific. If ATM is to be used for transporting the data, the application specific data format is adapted so that it is compatible with the ATM protocol. This is accomplished by an ATM adaptation layer (AAL)
101
, as illustrated in FIG.
1
. Referring now to
FIG. 1
, the application layer
102
represents telecommunication data arriving from a specific telecommunication data application. The task of the AAL
101
, as mentioned, is to reformat the data so the data is compatible with the ATM protocol. Once reformatted, the ATM layer
103
can transport the data to a desired receiving unit.
One of the more common AALs is AAL
1
. AAL
1
is typically used to packetize synchronous data (i.e., circuit emulation data) into standardized data packets, which can, in turn, be structured or unstructured data. Structured data is organized into a sequence of data blocks, wherein the boundary for each data block is defined by a structured data pointer (SDP). The SDP is specifically used for alignment (i.e., recovery) of the data at a receiving unit. Unstructured data refers to raw data that includes no framing information.
AAL
1
is divided into two basic functional sublayers, as illustrated in FIG.
1
: a segmentation and reassembly (SAR) sublayer
104
and a convergence sublayer
105
. The SAR sublayer
104
packetizes the incoming data into data blocks that are
47
bytes in length. The SAR sublayer
104
then adds a 1 byte sequence number and a 1 bit data type identifier (to identify the incoming data as either structured or unstructured). For example, if the data type identifier bit is set, the first byte in the block will contain a SDP. The convergence sublayer supports data packetization, clock recovery, cell delay variation compensation and forward error correction.
There are a number of inherent problems associated with AAL
1
. Foremost is that the time delay required by AAL
1
to prepare a 47 byte data block is excessively long. For example, a typical service rate (i.e., the incoming data rate) for circuit emulation data is 64 kbits per second. The corresponding time delay for AAL
1
would be approximately 6 milliseconds (i.e., 47 bytes/8 kbytes per second). Moreover, the transportation of data from a sending unit to a receiving unit typically involves several ATM transitions; thus, the already excessive delay is compounded with each ATM transition. In addition, when dealing with low bit rate data, there is often an insufficient amount of data to completely fill each ATM cell. Pursuant to the ATM cell protocol, the AAL
1
may have to fill the remaining portion of each ATM cell with padding bits. This, in turn, results in poor bandwidth utilization. Since many applications, such as voice data, are highly sensitive to data transportation delays, and because bandwidth is very expensive, there is a real need to design a more efficient way to transport low bit rate, circuit emulation data using ATM.
SUMMARY OF INVENTION
Another commonly employed AAL is AAL
2
, which is sometimes referred to as AALm. AAL
2
, is typically used to transform low bit rate, asynchronous data, such as cellular voice data. More particularly, AAL
2
segments low bit rate data streams into small data packets, which are often called minicells or microcells. The small data packets from a particular low bit rate, asynchronous data source are then multiplexed together with small packets from other similar data sources to form ATM cells. By segmenting the data into smaller, variable size data packets and by multiplexing the small packets from multiple data sources, data transportation delays are reduced and bandwidth utilization is improved. In addition, transportation delays can be further reduced and bandwidth utilization further improved by allowing the small data packets to overlap between adjacent ATM cells, as illustrated in FIG.
2
.
The present invention improves the ATM performance for circuit emulation data using the functional capabilities associated with AAL
2
. Hence, the present invention is essentially an enhanced version of AAL
2
, and the present invention is herein referred to as the circuit emulation adaptation layer. In accordance with
FIG. 3
, the present invention is achieved by replacing the AAL
101
, illustrated in
FIG. 1
, with a circuit emulation adaptation layer
305
and a short packet multiplexing layer
310
, wherein the latter is functionally similar or identical to the AAL
2
described above.
Accordingly, it is an object of the present invention to packetize the low bit rate, circuit emulation data before transporting the data over an ATM connection.
It is another object of the present invention to improve bandwidth utilization when transporting circuit emulation data over an ATM connection.
In accordance with one aspect of the invention, the foregoing and other objects are achieved by an apparatus, system and/or method for transporting circuit emulation data. This involves the transformation of emulation data into a sequence of circuit emulation data packets, and then the insertion of the sequence of circuit emulation data packets into a data transfer cell. Next, the data transfer cell is transported to a receiving unit as a function of a data transfer cell shaping clock. In addition, the length of each data packet is controlled as a function of the data transfer cell shaping clock.
In accordance another aspect of the invention, the foregoing and other objects are achieved by an apparatus, system and/or method for transporting circuit emulation data. This involves transforming the circuit emulation data into a sequence of circuit emulation data packets and inserting the sequence of circuit emulation data packets into a data transfer cell. Then the data transfer cell is transported to a receiving unit. Here, data packet length is controlled as a function of the service rate clock.
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Hitoshi Uematsu et al., “Implementation and Experimental Results of CLAD Using SRTS Method in ATM Networks”, Proceedings of the Global Telecommunications Conference (GLOBECOM), San Francisco, Nov. 28-Dec.2, 1994, vol. 3 of 3, Nov. 28, 1994, pp. 1815-1821, XP000488836, Institute of Electrical and Electronics Engineers.
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Burns Doane Swecker & Mathis L.L.P.
Olms Douglas W.
Pizarro Ricardo M.
Telefonaktiebolaget LM Ericsson (publ)
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