Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-07-21
2003-04-29
Kizou, Hassan (Department: 2662)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S535000, C370S536000, C370S907000
Reexamination Certificate
active
06556593
ABSTRACT:
The present invention concerns a multiplexing device for providing a digital cross connect and add/drop functionality to a SONET and/or SDH compliant signal intercon- nection device. The invention more particularly relates to a modular, non-blocking, expandable, digital interconnection system capable of cross-connecting lower-rate signals (tributaries), where these signals are components of higher rate signals, or may terminate on low speed lines (local ports). It even more specifically concerns a multi- plexing device for a SONET/SDH interconnection circuit employing like modules arranged in parallel, with the number of modules depending on the transmission speed of the SONET/SDH links served.
BACKGROUND OF THE INVENTION
The American National Standards Institute has recently established a new basic standard for high-speed, multiplexed digital data transmission. This is the “synchronous optical network” standard, henceforth referred to as SONET. The SONET standard specifies optical interfaces, data rates, operation procedures and frame structures for multiplexed digital transmission via fiber optic networks.
The International Telecommunications Union (ITU) has adopted the interface principles of SONET and recommended a new global transmission standard for high-speed digital data transmission. This standard is the “synchronous digital hierarchy” (SDH).
For an account of the SDH standard on the “General Aspects of Digital Transmission Systems”, reference is made to the ITU standards documents G.707 (Synchronous Digital Hierarchy Bit Rates), G.708 (Network Node Interface for the Synchronous Digital Hierarchy), G.709 (Synchronous Multiplexing Structure), G.782 (Types and General Characteristics of Synchronous Digital Hierarchy (SDH) Equipment), and G.783 (Characteristics of Synchronous Digital Hierarchy (SDH) Equipment Functional Blocks), all issued March 1993.
The SDH standard is designed to enable manufacturers to develop telecommunications equipment which:
a) will be interchangeable in all telecommunication networks built around the world to its standard; and which
b) is backwards compatible, i.e. can be used with data which is in the older telecommunications formats used in North America, Europe and Japan.
This is achieved by a hierarchy of so-called “Containers” (C) and “Virtual Containers” (VC), see FIG.
1
. The containers, e.g. C-
4
, C-
3
, C-
12
, etc., are information structures designed to accommodate data traffic with specific transmission rates. The. C-
4
container carries traffic with a base rate of up to 139 264 kbit/s, C-
3
carries either up to 44 736 or 34 368 kbit/s, etc. The containers are turned into virtual containers by adding “Path Overhead” information (POH) to it. By procedures defined as multiplexing, mapping, or aligning, data structures are generated which are constitutive to the SDH. These data structures are named “Administrative Unit Groups” (AUG) and “Synchronous Transport Module” (STM). The label of an STM is defined by the number of AUGs it carries: a STM-
4
contains for example four AUGs. An AUG contains either one “Administration Unit” (AU) of type
4
or three AU-
3
. Referring to the simplest case, in turn one AU-
4
contains one C-
4
signal and one AU-
3
carries one C-
3
signal.
The SDH/SONET data frames, i.e., the STM-N signals, are 125 msec long. The amount of data transmitted in each frame depends on the hierarchy level N of the signal. The higher hierarchical levels are transmitted at higher data rates than the basic STM-
1
level of approximately 155 Mbit/s. (The exact transmission rate is defined as 155.52 Mbit/s. However here and in the following transmission rates are often denoted by their approximate values. This in particular due to the fact that the exact data transmission rates are distorted by overhead data traffic and idle cell stuffing.) The integer N indicates how many times faster the data is transmitted than in the STM-
1
level. For example STM-
4
denotes a data transmission rate of 622 Mbit/s, whereby each data frame contains four times as many bytes as does a frame of STM-
1
. Currently, the highest defined level is STM-
64
which has a data rate of 9.95 Gb/s. Clearly, each part of the STM-N signal is broadcast in the same time as the corresponding part of an STM-
1
signal, but contains N times as many bytes.
The STM-
1
signal, as shown in
FIG. 2
, contains an information rectangle of 9 rows with 270 bytes/row corresponding to a SONET/SDH data rate of 155.52 Mbit/s. The first 9 bytes/row represent the “Section Overhead”, henceforth SOH. The remaining 261 bytes/row are reserved for the VCs, which in
FIG. 1
is a VC-
4
. The first column of a VC-
4
container consists of the “Path Overhead” (POH). The rest is occupied by the payload (a C-
4
signal). Several VCs can be concatenated to provide a single transmission channel with a corresponding bandwidth. For example, four VC-
4
in a STM-
4
signal can be concatenated to form a single data channel with approximately 600 Mbit/s capacity: in this case the four VC are referred to in the standard terminology as VC-
4
-
4
c
and the signal as STM-
4
c.
This flexibility of the SDH standard is partly due to the pointer concept. In SDH, the frames are synchronized, but the VCs within them are not locked to the frames. So the individual containers of the SDH signals do not have to be frame aligned or synchronized among each other. A “pointer” is provided in the Section Overhead which indicates the position of the above introduced POH, i.e. the start of a virtual container in the SDH frame. The POH can thus be flexibly positioned at any position in the frame. The multiplexing of information into higher order SDH frames becomes simpler than in the old data standards, and an expensive synchronization buffer is not required in SDH. Similarly, lower order signals can be extracted out of and inserted into the higher order SDH signals without the need to demultiplex the entire signal hierarchy. The pointers are stored in the fourth row of the Section Overhead.
The Section Overhead is further subdivided into:
I. The “Regenerator Section Overhead” or RSOH. This contains bytes of information which are used by repeater stations along the route traversed by the SONET/SDH Signal. The Regenerator Section Overhead occupies rows
1
-
3
of the Section Overhead.
II. The “Multiplexer Section Overhead” or MSOH. This contains bytes of information used by the multiplexers along the SONET/SDH signal's route. The Multiplexer Section Overhead occupies rows
5
-
9
of the Section Overhead. These sections are assembled and dissembled at different stages during the transmission process.
FIG. 2
also shows an exploded view of the MSOH.
In the SONET system, a base signal of 51.84 Mbit/s is used. It is called the Synchronous Transport Signal level
1
, henceforth STS-
1
. This has an information rectangle of 9 rows with 90 bytes/row. The first three bytes/row are the section overhead and the remaining 87 bytes/row are the “Synchronous Payload Envelope”, henceforth SPE. Three of these SPEs fit exactly into one Virtual Container-
4
. Thus signals in the STS-
1
signal format can be mapped into an STM-
1
frame. Furthermore, frame-aligned STS-
1
or STM-
1
signals can be multiplexed into higher order STM-N frames.
In general, any lower data rate signal which is combined with other such signals into new data frames of higher rate is referred to as a “tributary” signal. For example in the previous paragraph, the three STS-
1
signals which are combined into one STM-
1
signal are tributary signals.
Digital Cross-Connect (DCC) functionality provides the possibility of rearranging the temporal (in case of a serial high-rate signal) or the spatial (in case of a demultiplexed high-rate signal) order of the low-rate signals or tributaries within the high-rate signal.
Add/Drop functionality allows to extract and/or replace one or more tributary signals from the high-rate signal. It is also known as Drop/Insert functionality.
A modular, expandable, non-blocking system for cross-connecting high speed dig
Herkersdorf Andreas
Lemppenau Wolfram
van As Harmen R.
Cameron Douglas W.
Dougherty Anne Vachon
Kizou Hassan
Tsegaye Saba
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