Abstract: MSF250 is more than a service framing chip. It has the DS1/E1 connection, may maps 28 DS1 or 21 E1 signals by the position asynchronous system mapping/solution in the VT.5/TU2 way. The article elaborated MSF250 from each kind of different frame form and the framing principle in the DS1/E1 mapping/solution mapping application method.
Key word: MSF250; DS1/E1; SONET; SDH; Signal format
Through the multi-duty framing chip MSF250 DS1/E1 connection, may maps 28 DS1 or 21 E1 signals by the position asynchronous system mapping/solution in the VT.5/TU2 way, in order to through SONET/SDH connection transmission. But the DS1/E1 signal can also map enters the DS3/E3 payload, then characteristic is mapped again through DS3/E3 in functional module’s M13/E13 STS-1/VC-3/TU-3. The DS1/E1 functional module by is in the receiving and dispatching both sides each 28 DS1/E1 framing to be composed, this kind of disposition can guarantee the quite reliable expiration isolation (fault isolation).
MSF250 supports each kind of DS1/E1 signal format, simultaneously may also map enters the SONET/SDH frame form.
1 DS1/E1 SONET/SDH mapping/solution mapping
MSF250 framing asynchronous DS1 mapping including 771 information bits (I-Information bits), 6 packing control position (C-Stuff Control bits), when 2 packing seat on a plane (S-Stuff Opportunity bits) as well as 8 expenses correspondence channel position (Overhead Communica-tion Channels bits). In which packing control position uses in controlling two packing positions the packing opportunity (S1 and S2). Because in the middle of the packing position may include the information bit, and may realize through the most decision mechanisms. Therefore, in the entire mapping will possibly have 0, 1 or 2 extra information bits.
This MSF250 framing E1 asynchronous mapping including 1023 information bits, when 6 packing control position, 2 packing seat on a plane and 8 expenses correspondence channel position. Likewise, in this kind of mapping also possibly has 0, 1 or 2 extra information bits.
2 DS1 framing
Regarding the MSF250 in two framing, their each can dispose super frame SuperFrame (SF), expansion super frame Extended SuperFrame (ESF) or frame forms and so on SLC-96 work.
2.1 super (SF)
In the ordinary circumstances, a super frame (SF) is composed (or 2316) by 12 frames, each contains 193. Frame bit load bearing terminal bit and signaling bit data. Other 192 load bearing 24 DS0 channels. The SF super frame may the load bearing 2 conditions and 4 condition signaling data, these information located at 6th and 12th DS0 channel’s 8th (the SONET order). In ANSI (US National standards Association) pattern, when is in the J1 pattern (refers to Japanese telecommunication standard), SF each DS0 channel’s 2nd load bearing RAI (also had said that yellow warning) the information, SF super frame’s final F uses in the load bearing RAI symbol.
The framing may search the specific frame instruction symbol in the input symbol stream, thus determination frame and many boundaries. The framing algorithm uses Ft and the Fs two units places. Catches the state machine to be possible to search the specific frame instruction symbol in the input symbol stream, by determines the frame localization the accuracy. If does not have the error code to receive to 12 continual Ft and the Fs bits, then may determine that the standard frame localization is normal; If the standard frame localization is normal, then maintains the state machine, so long as receives again to a continual non-error code framing sequence (Ft & Fs), may determine that many localizations are normal. Therefore, determined that the standard frame and many localizations normal require more than 2 receive time at least. Once after many localizations normal, the frame out-of-step (Out of Frame, will be called OOF) to report an emergency will abolish.
Except the above main framing delimitation condition outside the aircraft, the MSF250 framing interior also has an auxiliary framing state machine, this auxiliary framing state machine’s leading role is searches in the input symbol stream other decides the frame instruction symbol, helps MSF250 when the main framing state machine frame localization makes a mistake speeds up system’s framing speed.
in 5 framing position’s 2 continual two times will make a mistake will trigger the OOF warning. This time if the auxiliary framing state machine caught another to decide the frame instruction symbol, then the main framing delimitation state machine’s condition will become by the synchronization the auxiliary framing state machine’s condition, like this, a new many localization normal state will be confirmed that simultaneously will trigger a frame localization condition to change the COFA warning. In addition, the main framing state machine and the auxiliary state machine will start a time brand-new search.
In fact, the system software may also reposition MSF250 the standard frame and many localization search circuit, starts a time brand-new frame localization instruction symbol search process.
The ultra frame’s main framing state machine and the auxiliary state machine maintain the condition to be possible through a microprocessor register direct readout.
2.2 ESF frames
MSF250 framing expansion super frame 煟 Niu Ying weary 犕 ǔS Sang Bocu. ɑ the buffalo gnat lu bites Chang Can fool ┳ mallet umbrella C toweringly to be earnestly extensive ‘has 193. In the frame the load bearing data includes: Frame localization byte, 4kbit/s HDLC channel (D channel) and CRC-6. And the D channel uses on the DS1 link transmitting the managerial data. CRC-6 uses for to inspect DS1 many integrities and to have the choice to use in strengthening the framing electric circuit’s reliability. Other 192 load bearing 24 DS0 channels. ESF super frame load bearing 2, 4 or 6 condition signaling information, these information located at 6th, 12, 18 as well as 24th each DS0 channel’s 8th (SONET order). When transmits 8 in the HDLC channel 0, is following closely when sends 8 again 1, will trigger the yellow warning.
The framing may search the frame localization byte in the input symbol stream, by determines between the frame and the frame boundary. What capture state machine execution searching algorithm use is the frame locates byte sequence FPS. If 18 continual FPS bytes are received correctly in turn (for example 3 continual many), then MSF250 thought that already established the normal standard frame localization. Once determined that the standard frame localization will be normal, maintains the state machine after examining the next continual many pulses the position normal, the MSF250 confirmation was already established the normal many localization mechanism. Therefore, confirmed that the standard frame and many localizations normal require more than 4 pull-in times at least. When MSF250 confirmed after many localizations normal, will abolish the OOF warning.
Confirmed that before many localizations normal, may inspect the CRC-6 byte first. If uses the CRC-6 examination, the framing normal will inspect certain before the confirmation localization (to be possible most much to look up 32, default situation is 2) continuously many CRC-6 examination sum. If verification and not wrong, then may recognize that the frame localization is normal, simultaneously OOF warning rescission; If the verification and has the mistake, then the main maintenance state machine will return to the OOF condition. , If was this time auxiliary the state machine to catch another to decide the frame instruction symbol, then the main framing delimitation state machine’s condition will become by the synchronization the auxiliary framing state machine’s condition, this time a new many localization normal state will be confirmed that simultaneously will trigger a frame localization condition to change the COFA alarm signal. In addition, the main framing state machine and the auxiliary state machine will start a time brand-new search.
Once the framing discovery frame localization byte, in the frame the bit will be compared continuously with the expectation frame localization byte. in 5 framing position’s 2 continual two times will make a mistake will trigger the OOF warning. This time if the auxiliary framing state machine caught another to decide the frame instruction symbol, then the main framing delimitation state machine’s condition will become by the synchronization the auxiliary framing state machine’s condition, this time a new many localization normal state will be confirmed. In addition, the main framing state machine and the auxiliary state machine will start a time brand-new search. Meanwhile, the system software may reposition MSF250 the standard frame and many localization search circuit, starts a time brand-new frame localization instruction symbol search process.
Expands the super frame the main framing state machine and the auxiliary state machine maintains the condition to be possible through a microprocessor register direct readout.
2.3 SLC-96 frames
In the SLC-96 pattern, 72 are usually treated as an independent super frame to process.
In SLC-96 frame including 36 terminal information bits (wonderful position) and 36 signaling positions (occasionally position). In 36 signaling positions, 20 Fs positions use in the support data link, 11 units places use in concentrating (C), 3 units places use in maintaining (M), 2 units places use in reporting an emergency (A), 4 units places use in the line exchange (S); Is left over 16 Fs, the Ft positions use for to realize the frame, the ultra frame localization, the fixture 0101 positions are called the spoiler position, usually is put in 46th, 48, 50, 70. Moreover, the SLC-96 frame in 2 will also carry the RAI signal in each DS0 channel’s bit (yellow warning).
Searches the frame localization byte through the framing in the input symbol stream to be possible to determine between the frame and the frame boundary. The capture state machine execution searching algorithm uses Ft, Fs and the spoiler position. If 48 continual Ft, the Fs positions are received correctly in turn (for example 48 continual frames), then MSF250 thought that already established the normal standard frame localization. In the frame boundary search process, may use 4 spoiler positions. Once determined that the standard frame localization will be normal, maintains the state machine at will examine after 12 continual many pulse positions normal, the MSF250 confirmation was already established the normal many localization mechanism. When MSF250 confirmed after many localizations normal, will abolish the OOF warning.
Except above host framing delimitation condition outside the aircraft, the MSF250 interior also has an auxiliary framing state machine, its leading role is searches in the input symbol stream other decides the frame instruction symbol, helps MSF250 when the main framing state machine frame localization makes a mistake speeds up system’s framing speed.
Once the framing discovery frame localization byte, in the frame the bit will be compared continuously with the expectation frame localization byte. When in 4 framing position’s 2 continual two times make a mistake, the component will trigger the OOF warning. If SPOILER_CHECK enables, the spoiler position will be included in row of by the comparison. This time if the auxiliary framing state machine caught another to decide the frame instruction symbol, then the main framing delimitation state machine’s condition will become by the synchronization the auxiliary framing state machine’s condition, this time will have a new many localization normal state to confirm that simultaneously will trigger a frame localization condition to change the COFA warning. In addition, the main framing state machine and the auxiliary state machine will start a time brand-new search.
At the same time, the system software may reposition MSF250 the standard frame and many localization search circuit, starts a time brand-new frame localization instruction symbol search process.
In the SLC-96 frame form’s main framing state machine and the auxiliary state machine maintain the condition usually to be possible through a microprocessor register direct readout.
3 E1 frame form
The single E1 frame has 256, is divided 32 time slots. It is not all time slots may use in the load bearing pronunciation or the data. The E1 frame (Frame Alignment Signalling) locates the frame and the non-FAS frame including FAS. Locates in the frame the time slot 0 to carry the frame localization byte, therefore may use in realizing the E1 frame localization. But in the non-localization frame’s time slot 0 pieces carry the signaling or the data link news. The fixed FAS sequence uses in the frame and many boundary alignments. CRC many structure’s Si 熌 kuang dredge ┪ wields the broom corn millet eulogy high-rising vast remote vast 4 operation result.
Si (interior) the position load bearing usually uses in the CRC many formation goals a designated value. Second including one “1″, may use in the frame and many formations. Third carries RAI (yellow to report an emergency, examines when LOS or LOF triggers juxtaposes 1, is normal when sets 0) and transmits to the far-end. May provide a speed fourth to eighth is the 20kbit/s data link.
E1 framing support CRC many and CAS multi-frames.
3.1 CRC multi-frames
CRC many have two sub-many (Sub Multi Frames), their each includes 8 frames. Carries C1 the CRC-4 data which to C4 may by the preceding SMF computation obtain. Each non-FAS the frame bit 1 fixed value is 001011, may take the CRC many localization bytes. E is used for to attribute local E1 framing examination wrong sub-multi-frames.
3.2 CAS multi-frames
CAS many are composed of 16 continual E1 frames.
The CAS many first 16th time slots carry have this CAS many localization bytes, simultaneously, this time slot also carries the performance information and is responsible its transmission to the far-end. The 1st 16th time slot carries the pronunciation channel 1, 16 signaling information, the 2nd 16th time slot carries the pronunciation channel 2, 17 signaling information, ex analogia.
The framing capture state machine searches frame localization byte FAS in the input symbol stream. When examines FAS, MSF250 will inspect non-FAS frame time slot 0 bit 2, if its value is 0, then this state machine will start a time brand-new frame search process; If its value is 1, and next FAS is examined correctly, the framing will confirm the frame localization basically normal. If continual three FAS makes a mistake, will have the localization loss to report an emergency, and will trigger a time brand-new frame search process.
After framing confirmation frame localization basic normal, the framing state machine may further through CRC-4 many localizations or the CAS many localization precise definite frame boundary. The CRC-4 many localization attachment in non-FAS frame 1, 3, 5, 7, 9, 11 bit in 1 search the frame localization byte 001011, if the state machine discovers n continual CRC-4 frame framing signal in the 8ms internal energy, then thought that CRC-4 many localizations are normal. After entering the localization normal state, the state machine will start to monitor the frame loss situation, if the state machine examines to n continual CRC is wrong, then after having a CRC many localization loss warning 熤, the state machine will force to make a fresh start to search the brand-new frame in the input symbol stream.
The CAS many localization state machines use in monitoring each 16th time slot, if after receiving a localization byte, next 16th time slot’s 1st to 4th is 0 values, then may confirm that CAS many localizations are normal, simultaneously the CAS frame loss warning will be abolished.
(This will trigger CAS frame localization loss warning directly) besides the basic frame localization loss situation, two continual 16th time slot 4 entire 0 symbol receives make a mistake, when for a period of time or two continual many 16th time slot’s all positions are 0, may also trigger the CAS frame localization loss warning.
At the same time, the system software may make the MSF250 replacement framing, starts a time brand-new frame localization instruction symbol search process. The FAS framing’s condition may through a microprocessor register direct readout.
4 concluding remark
MSF250 is a function very formidable chip, may widely apply in the SONET/SDH equipment. It not only has the DS1/E1 connection, but also has DS3/E3, the 10M/100M/1000M ethernet and so on many kinds of service connections. In the SDH equipment, DS1/E1 is the most basic electrical signal base group. Understood that MSF250 DS1/E1 the signal format to familiar, the understanding, applies this chip to have the advantage.
