As a result of Ethernet and SDH payload rate does not match ,so when using existing technology will be the Ethernet frame to the SDH frame mapping ,often want to use a larger SDH container ,thereby causing the transmission bandwidth waste .
Using SDH virtual concatenation technology for Gigabit Ethernet data transmission opening size suitable for the SDH channel ,not only can improve the SDH network bandwidth utilization rate and can dynamically allocate bandwidth resources .
Keywords :synchronous digital system ( SDH ) virtual cascade Ethernet with 1000MHz Ethernet technology is gradually mature and 10GHz Ethernet standard forthcoming ,Ethernet technology is being used by LAN extensions for the metropolitan area network ( MAN ) and wide area network ( WAN ) technology .
But the Ethernet performance monitoring and fault location of weak, in order to remedy these flaw ,make full use of the existing network infrastructure ,network providers are trying to make use of existing SDH optical network for transmitting Ethernet data ( EOS ) .
But ,as a result of Ethernet and SDH standard rate does not fully match ,when the Ethernet frame to frame SDH mapping of the time, often want to use a larger SDH container ,Ralph Lauren Italia,thereby causing the transmission bandwidth waste .
For example ,the transmission of a Gigabit Ethernet data often requires a complete 2.5Gbps SDH transmission channel ,which will cause huge waste of bandwidth ,in theory, you can use the SDH cascade structure of suitable size for SDH transmission channel ,transmission of Ethernet data ,but unfortunately many existing SDH network does not support cascading process ,to update the network infrastructure is too high a price to pay .
This cascade transmission method is not reality .This paper adopts a plurality of virtual cascade SDH virtual container ( VC-3 ) for Gigabit Ethernet data flow opening size suitable for the SDH transmission channel ,with the use of link capacity adjustment configuration ( LCAS ) technology ,not only can improve the bandwidth utilization rate, and can dynamically allocate bandwidth resources .
1 SDH virtual cascade principle virtual concatenation is used to form a plurality of virtual container SDH channel ( VC-n ) and no substantial relation between cascade ,they in the network are processed independently transmitted ,they just pass data having cascaded relationship .
The data in data into the container prior cascaded relationship that mark ,for each VC-n data arriving at the destination terminal ,then in accordance with the original cascade relationship were reassembled .
SDH cascade transmission needs of each SDH element has a cascade processing functions ,while the virtual cascade transmission need only terminal equipment has the corresponding function can be easily realized ,therefore .
As shown in Figure 1 ,the use of virtual concatenation technology can be a complete client bandwidth apart ,nike free,mapped to multiple independent VC-n for transmission ,then a destination terminal to the VC-n recombined into a complete client bandwidth .
Contains the X VX-3 virtual cascade channel can be denoted by VC-3-Xv .As shown in Figure 2 ,the VC-3-Xv provided by a X C-3 container constituting the net charge domain ,X C-3 was mapped in the VC-3-Xv X VC-3 .
Each VC-3 has its own path overhead ( POH ) ,where POH of HR bytes used to make the virtual concatenation processing of sequences of instructions ( SQ ) and multi-frame indicator ( MFI ) ,the following will be described in detail .
VC-3 and upper section overhead (SOH) can form a complete STS-1 channel ,so the X virtual concatenation can be expressed as STS-1-Xv STS-1 .Because the STS-1-Xv in each STS-1 channel data may be in the network independent transmission ,each STS-1 channel data through the transmission will have different transmission delay .
Therefore ,when the STS-1-Xv in each STS-1 channel data arriving at the destination terminal ,must first to them by the time delay between the compensation ,after resynchronization after positioning ,to reconstruct a and send the same payload domain .
Payload information carried by reconstruction of H4 bytes ,H4 coding structure as shown in table 1 .Table 1 byte encoding H4 Bits 7-4Bits3-0 ( ) (0000 ) 0010n+2 (0000 ) 0011n+3 retention retention ( 0000) .
.. ... ... ... Retention ( 0000 ) MFI used to indicate various virtual cascade STS-1 data frames between phase relationship ( delay ) .In H4 bytes ,MFI by two level code ,corresponding to a two stage MFI .
The first level of the MFI H4 from the low 4 bits ( 0 - 3 ) ,along with a basic frame arrival,nike free sko, each level of MFI increased from 0 to 15 ;second MFI 8 bit ,the 8 bit respectively by the first level MFI zeroth frame and the first frame 4 ( 4 ～ 7) .
Thus, a complex frame consists of 4096 basic frame structure, complex frame cycle for 512ms ,so that they can be expressed in 256ms phase difference .SQ used to indicate various virtual cascade STS-1 channel in STS-1-Xv sequence .
Each STS-1 has a fixed SQ ,STS-1-Xv each transmitted STS-1 channel SQ is 0 ,and so on ,the X transmits the STS-1 channel SQ ( X-1 ) .SQ has 8 bits ,the 8 bit from the fourteenth and fifteenth frames in high H4 4 ( 4 ~ 7 ) ,a total of 8 bits can be expressed in 256 STS-1 channels .
2 SDH virtual concatenation technology to realize this section based on the virtual cascade principle ,implementing Gigabit and network data in the 2.5Gbps rate of SDH network virtual cascade transmission .
Virtual concatenation processing including the sending end virtual concatenation processing ( TVCP ) and the receiving end of virtual concatenation processing ( RVCP ) the two part .2.1 sending virtual concatenation processing to achieve TVCP Ethernet data in SDH physical channel is mapping and virtual cascade multiframe indication and sequence indicative processing .
Figure 3 general sealing frame processor ( GFP ) is responsible for the Ethernet data package and delimitation .Ethernet data after treatment with GFP ,can be called the Ethernet data .
The dashed box part is the originator of virtual concatenation processing module ( TVCM ) next .The core of TVCM is a copy machine ,it will Ethernet data from the input buffer logic into an output buffer ,in this process will Ethernet logical data is mapped to the SDH channel corresponding to the STS-1 channel .
Mapping control based on virtual cascade configuration for the programmable information ,these signals include logic for Ethernet data allocated bandwidth of SDH ( STS-1 channel number ) and Dual Ethernet data in the SDH data time slots in a frame position ( STS-1 channel number ) .
SDH channel overhead processor is mainly to the completion of each virtual cascade STS-1 channel data frame in the MFI value and SQ value calculation ,as well as H4 byte code and insert ,the methods have been described in the basic principle of virtual cascade .
The rate of 2.5Gbps SDH transmission channels for a total of 48 channels STS-1, because the C-3 capacity of 44.73Mbit ,therefore a Gigabit Ethernet data to occupy the 22 STS-1 channels ,remaining channel can be used to transport other business ,so virtual concatenation technology improves the bandwidth utilization rate .
In addition ,due to only use LCAS protocol change virtual cascade configuration for the programmable information ,you can dynamically adjust the data transmission bandwidth therefore virtual concatenation technology to improve the bandwidth of the network configuration flexibility .
2.2 receiving end virtual concatenation processing ( RVCP ) RVCP main SDH channel in each virtual cascade STS-1 channel cascade recombination and Ethernet data demapping .The receiving end of virtual concatenation processing module ( RVCM ) as shown in Figure 4 ,Polo Ralph Lauren,including SQ and MFI extractor ,synchronization statistics memory ,logic ,synchronous buffer solution and step mapper .
Letter RVCM from bus receives a SDH data frame ,and by SQ and MFI extractor directly from the SDH path overhead catch H4 byte .According to H4 bytes SQ value judge each virtual cascade STS-1 channel are arranged in the order ,at the same time ,according to the MFI value, and utilizes the synchronous buffer for each STS-1 channel data to synchronous positioning ,to compensate the time delay difference between them .
Data relocation ,solution mapping of data from the SDH telecommunications bus data format conversion for the Ethernet logical channel data format .Synchronous buffer for each virtual cascade STS-1 channel of data synchronization processing ,to achieve the various channel data frame alignment .
As shown in Figure 5 ,with each virtual cascade STS-1 channel data frame in SQ, write data synchronization buffer corresponding to the area .Each STS-1 channel data write address from the channel data frame MFI value is determined ,data according to MFI values are jumping into corresponding cache memory address ,and then by a common reading means sequentially read out .
So ,through the synchronous buffer data to synchronous positioning ,can compensate for various STS-1 between the transmission time delay difference .In the relocation process, the synchronization logic to synchronize register in each STS-1 channel data to identify a common read address ,this process is called synchronization process .
The synchronization process is divided into synchronous capture ( SYN-ACQ ) and ( SYN ) a two state synchronization .The circuit is initialized, the synchronization process into the SYN-ACQ state ,MFI and SQ extractor to each of the input STS-1 data frame of MFI, and stored in a synchronization statistics memory .
Synchronous logic hardware continuously scanning synchronization statistics memory each virtual cascade STS-1 channel data frame MFI .When having a determined MFI value of each STS-1 channel data frame head comes, the synchronization logic will be the MFI value corresponding to the synchronous buffer address is determined for each STS-1 channel data common to read data ,the synchronization process into the SYN state ,synchronization of data in the buffer to the common read address for the starting address sequential read .
If the MFI value does not jump ,synchronization logic to the read address will sequentially incremented ,and the maximum MFI flip .Once the value of MFI jump occurs ,that is to say a STS-1 channel before and after the data frame H4 byte contains discontinuous MFI value, then the synchronization process to enter SYN-ACQ state ,the beginning of a new synchronous capture process .
Solution mapping and TVCM copy machine function similar to ,when the synchronous buffer to each virtual cascade STS-1 channel after relocating ,demapping unit will be in accordance with the requirements of virtual cascade configuration information ,through the input stage to the output cache data reordering, completed SDH telecommunications bus data format to the Ethernet data format conversion .
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