This is the most common element to built up SDH rings.Dependent on the port configuration it gives access to all containers embedded in the STM-1 signals. These containers can be dropped and inserted in the SDH hierarchy.
Each tributary can also be inserted into each container of the STM-1 streams.
An ADM155 for example is a multiplexer, which handles 126 x 2Mbps tributaries
within 2 independent STM-1 datastreams (doublering).
Also the exchange of the containers between the STM-1 signals is possible.
The ADMs are controlled via TMN commands in embedded channels or the via
the Q-interface.
It has a built in switching unit, which supports Automatic Protection Switching
(APS) , if one line has interruptet.
Sunday, September 6, 2009
What is Synchronous Cross Connect?
Digital Cross Connects(DXCs) handle signals of PDH and/or SDH technologies.They offer several inputs for those bitrates which are present as port cards in a specific hardware configuration of this network element.Today its possible to apply signals up to STM-4, in the future 2.5Gbit/s will bepossible.A cross connect extracts containers from all incoming signals. It can rout all incoming signals (or parts of them) to each outgoing signal, from one hierarcye to another, from SDH to PDH and vice versa.
Normally switching takes place at the basic container levels (VC12, VC3, VC4). Some DXCs offer access down to 64kbps by the help of byte-synchronous mapping.DXCs are located at such places where several different signals are coming together, with different bitrates. It also interconnects local levels to long distance levels, e.g. ADM rings on SLX or PDH on SLX. Its controlled via workstations and TMN and handles also all alarms and status information of different hierarchies.
A DXC requires fully structured signals (PDH 140/34/8/2Mbps) of the corresponding bitrate, otherwise it will generate alarms and measurements are more difficult or impossible.
DXCs are very complex machines - therefore the goal of most operators is to minimize the amount of DXCs and to replace them by the more cheeper Add Drop multiplexers (ADMs) wherever it's possible.
Normally switching takes place at the basic container levels (VC12, VC3, VC4). Some DXCs offer access down to 64kbps by the help of byte-synchronous mapping.DXCs are located at such places where several different signals are coming together, with different bitrates. It also interconnects local levels to long distance levels, e.g. ADM rings on SLX or PDH on SLX. Its controlled via workstations and TMN and handles also all alarms and status information of different hierarchies.
A DXC requires fully structured signals (PDH 140/34/8/2Mbps) of the corresponding bitrate, otherwise it will generate alarms and measurements are more difficult or impossible.
DXCs are very complex machines - therefore the goal of most operators is to minimize the amount of DXCs and to replace them by the more cheeper Add Drop multiplexers (ADMs) wherever it's possible.
What is Digital Cross Connects?
Digital cross connectors (DXCs)
In the area of the subscriber network nodes the users are connected to the exchanges
(DSC) via the user network interface (UNI). Instead of this central switching
points local cross connects (DXC) should be used.
Cross connect systems are the heart and as such they determine the structure of the trunk network. The physical specifications for the NNI are contained in Re. G.703 (electrical) and G.957(optical).
In the area of the subscriber network nodes the users are connected to the exchanges
(DSC) via the user network interface (UNI). Instead of this central switching
points local cross connects (DXC) should be used.
Cross connect systems are the heart and as such they determine the structure of the trunk network. The physical specifications for the NNI are contained in Re. G.703 (electrical) and G.957(optical).
Jitter and Wander Measurements
• Network output jitter (G.825)
• Network element output jitter (G.783, G.813)
• Jitter transfer function (G.958)
• Jitter and Wander tolerance (G.825, G.813)
• Network element output jitter (G.783, G.813)
• Jitter transfer function (G.958)
• Jitter and Wander tolerance (G.825, G.813)
How to Measure Jitter?
A jitter meter test set is basically made up from the following items:
- Pattern clock converter
- reference clock generator
- phase meter
- weighting filters
- peak value detector
What is the Source of Jitter?
•Interference signals
Impulsive noise or cross talk may cause phase variations (non systematic jitter). Normally high frequency jitter.
•Pattern dependent jitter
Distortion of the signal lead to so-called inter-symbol interference, which is pulse cross talk that varies with time (Pattern dependent jitter.
•Phase noise
The clock regenerators in SDH systems are generally synchronized to a reference clock. Some phase variations remain, due to thermal noise or drift in the oscillator used.
•Delay variation
Changes in the signal delay times in the transmission path lead to corresponding phase variations. These variations are generally slow (Wander). (e.g. Temperature changes in optical fibers).
•Stuffing and wait time jitter
During removing of stuffing bits gaps have to be compensated out by a smoothed clock.
•Mapping jitter
•Pointer jitter
During incrementing or decrementing of the pointer value. This shifts the payload by 8 or 24 bits corresponding to a phase hit of 8 or 24 UI.
Impulsive noise or cross talk may cause phase variations (non systematic jitter). Normally high frequency jitter.
•Pattern dependent jitter
Distortion of the signal lead to so-called inter-symbol interference, which is pulse cross talk that varies with time (Pattern dependent jitter.
•Phase noise
The clock regenerators in SDH systems are generally synchronized to a reference clock. Some phase variations remain, due to thermal noise or drift in the oscillator used.
•Delay variation
Changes in the signal delay times in the transmission path lead to corresponding phase variations. These variations are generally slow (Wander). (e.g. Temperature changes in optical fibers).
•Stuffing and wait time jitter
During removing of stuffing bits gaps have to be compensated out by a smoothed clock.
•Mapping jitter
•Pointer jitter
During incrementing or decrementing of the pointer value. This shifts the payload by 8 or 24 bits corresponding to a phase hit of 8 or 24 UI.
What is Jitter?
Jitter
Periodic or random changes in the phase of the transmission clock referred to the master or reference clock. In other words, the edges of a digital signal are advanced or retarded in time when compared with the reference clock or an absolutely regular time framework. Jitter generally referes to deviations of more than 10Hz.
Periodic or random changes in the phase of the transmission clock referred to the master or reference clock. In other words, the edges of a digital signal are advanced or retarded in time when compared with the reference clock or an absolutely regular time framework. Jitter generally referes to deviations of more than 10Hz.
What is STM-1 frame structure ?
As indicated in the figure, the STM – n signal is multiples of frames consisting of 9 rows with 270 bytes in each row.
The order of transmission of information is first from left to right and then from top to bottom.
The first 9 bytes in each row are for information and used by the SDH system itself.This area is divided into 3 parts.
Regenerator Section Overhead(RSOH)
Multiplex Section Overhead(MSOH)
Pointers
The order of transmission of information is first from left to right and then from top to bottom.
The first 9 bytes in each row are for information and used by the SDH system itself.This area is divided into 3 parts.
Regenerator Section Overhead(RSOH)
Multiplex Section Overhead(MSOH)
Pointers
What are Disadvantage of PDH?
- Inflexible and Expensive for Telecommunication Networking
- Inefficient use of transmission capacity (typically 75% fill per stage =>0.75e3=42% fill at 140 Mbps
- Extremely limited network management and maintenance support capabilities
- Higher rates are proprietary
what is SDH Transport?
- SDH was initially optimized for voice transport
- The huge demand of bandwidth for data and storage networks created new requirements
- Transport of Ethernet, Fibre Channel and Escon More efficient use of bandwidth for new services (finer granularity):
resulting in a 42% utilization
The answers
- Virtual Concatenation (VC): Allows the bandwidth to be adapted to the service requirements
- Link Capacity Access Scheme (LCAS): A signalling protocol to adjust the transport bandwidth dynamically
- Generic Framing Procedure (GFP): Adapts a frame or cell oriented service to a byte stream service.
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