2.4.2 Medium access control protocol B-PON uses standard ATM cells to carry user data and Physical Layer Operation,Administration and Maintenance (PLOAM)information.The B-PON MAC protocol has the ATM functionality with PON dedicated Operation, Administration and Maintenance (OAM)message delivery and additionally it supports broadcast.The protocol is fully compliant with the standard ATM. because the PLOAM cells are not passed to the ATM layer.The PLOAM cells are used in ONU synchronisation,in transmitting grant and alarm indications and in carrying Automatic Protection Switching (APS)messages in failure conditions.The upstream and downstream PLOAM messages have different structures. The B-PON frame structure builds up with the line rates as shown in Figure 5. The basic frame format is defined for the STM-1 line rate of 155 Mbit/s [5].In the downstream direction,the frame consists of 56 cells and each cell is 53 octets long.Every frame starts with a PLOAM cell followed by 27 ATM cells.The 29th cell is again a PLOAM cell followed by another sequence of 27 ATM cells. The higher standardised line rates are four and eight times the STM-I rate and, consequently,the corresponding frame sizes are four and eight times the basic frame size. Downstream frame format PLOAM ATM ATM ATM PLOAM ATM ATM 155 Mbit/s 1 cell 1 cell 2 cell 27 2 cell 28 cell 54 x4 PLOAM ATM ATM ATM PLOAM ATM PLOAM ATM ATM 622 Mbit/s 1 cell 1 cell 2 cell 27 2 cell 28 8 cell 190 cell 216 ×2 PLOAM ATM ATM ATM PLOAM ATM PLOAMI ATM ATM 1244 Mbit/s 1 cell 1 cell 2 cell 27 2 cell 28 16 cell 406 0 cell 432 Upstream frame format ATM ATM ATM 155 Mbit/s 3 overhead bytes per cell cell 1 cell 2 cell 53 x4 622 Mbit/s ATM ATM ATM cell 1 cell 2 cell 212 Figure 5.B-PON frame and super-frame structure (ITU-T G.983.1). 27￾  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￾#$%&''3$* ￾E*&''+6+ ,#%&''2(''(5!8) (*"F &(2￾#$%&''3 $**+6*" !"!+!'+ ""2(" !+6*+/*:$%=" !. &( F ').*&(""-( !+ 62"/+G"2(" !+6*+/*8+& 2"/+G3 H H IJK LMNNOP QRSIK T IJK LMNNT QRSIK O IJK LMNNOU IJK LMNNO IJK LMNNVW H H IJK LMNNOP QRSIK T IJK LMNNT QRSIK O IJK LMNNOU IJK LMNNO IJK LMNNOTX H QRSIK U IJK LMNNTYZ H H IJK LMNNOP QRSIK T IJK LMNNT QRSIK O IJK LMNNOU IJK LMNNO IJK LMNNW[O H QRSIK TX IJK LMNNWZX TVVK\]^_` XOOK\]^_` TOWWK\]^_` aW aO bc d d  TVVK\]^_` aW e d d  IJK H LMNNT IJK LMNNO IJK LMNNV[ XOOK\]^_` IJK H LMNNT IJK LMNNO IJK LMNNOTO f[ghMijMkl\m^M`nMiLMNN H H IJK LMNNOP QRSIK T IJK LMNNT QRSIK O IJK LMNNOU IJK LMNNO IJK LMNNVW H H IJK LMNNOP QRSIK T IJK LMNNT QRSIK O IJK LMNNOU IJK LMNNO IJK LMNNOTX H QRSIK U IJK LMNNTYZ H H IJK LMNNOP QRSIK T IJK LMNNT QRSIK O IJK LMNNOU IJK LMNNO IJK LMNNW[O H QRSIK TX IJK LMNNWZX TVVK\]^_` XOOK\]^_` TOWWK\]^_` aW aO bc d d  TVVK\]^_` aW e d d  IJK H LMNNT IJK LMNNO IJK LMNNV[ IJK H LMNNT IJK LMNNT IJK LMNNO IJK LMNNO IJK LMNNV[ IJK LMNNV[ XOOK\]^_` IJK H LMNNT IJK LMNNO IJK LMNNOTO XOOK\]^_` IJK H LMNNT IJK LMNNO IJK LMNNOTO IJK H LMNNT IJK LMNNT IJK LMNNO IJK LMNNO IJK LMNNOTO IJK LMNNOTO f[ghMijMkl\m^M`nMiLMNN opqrstuvwxyz{|s}~t}€r‚tsx|s}~tƒsr„ƒrst…†‡ˆx‡‰vŠ‹ŒvŽv