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Re: B3 question


Please refer to slide 9 of the following July presentation:

The SPE has 150336 octets. When seen as 9 rows by 16704 columns,
the first column is the Path overhead, the next 63 columns are the
fixed stuff, and the remaining columns are the Payload Capacity
(149760 octets). At the transmitter WIS, the SPE is wholly contained
in the "Envelop Capacity" of the WIS (i.e., SONET) frame. This means
that the first octet of the SPE (i.e., J1) is in column 577 of
the first row of the WIS frame.

Now please refer to slide 15 of that presentation.

The H1/H2 pointer (Payload Pointer) value corresponding to column 577
of the first row of the WIS frame is 522.

The B3 octet is the BIP-8 of the previous SPE. At the
transmitter WIS, this mean that B3 is the BIP-8 of the
Envelop Capacity of the previous WIS frame, because the
Envelop Capacity wholly contains the SPE. The receiver WIS
uses the Payload Pointer value to locate the position of the
SPE (which may have been changed by a transport network).
If the Payload Pointer value is different from 522, the SPE
will cross two WIS frames.

Please note that B3 is the BIP-8 of the previous SPE. The receiver
WIS saves the BIP-8 of the previous SPE to compare with the B3 octet
of the current SPE.

At transmitter startup (e.g., main reset), the first WIS frame
contains an SPE with no data (e.g., payload set to zero). H1/H2
should indicate a "set payload pointer" to 522 (i.e., bits 4-7 of
the first H1 will indicate a "set NDF" -- NDF = new data flag).

At receiver startup (i.e., receiver WIS frame re-sync), the first
SPE is retrieved only after a **valid** Payload Pointer is found.
If this Payload Pointer value is 522, the SPE begins in the next
WIS frame. The B3 octet of the first SPE will not be compared to the
BIP-8 of a previous SPE (because there is no previous SPE in this

Please note that the receiver "Payload Pointer processor" follows
strict rules to determine when a Payload Pointer value is valid.
For example, a "set NDF" immediately provides a valid Payload Pointer
value. These rules are implied by the cross-reference to ANSI

One cannot forget the fact that a receiver will also need to sync
to the WIS frame before any of the stuff described above can take
place. Therefore, the first WIS frame generated by a transmitter
WIS will usually be discarded by a receiver WIS, since it usually
takes more than two frames to get in sync. After sync is achieved,
the Payload Pointer processor will need to validate a Payload
Pointer before the first SPE is retrieved.

I hope this helps.


At 11:00 AM 7/24/00 -0400, bebrown@xxxxxxxxxxxxxxx wrote:
>"Trounce, Erik [CRK:5S21:EXCH]" wrote:
>> Hi Ben,
>> The B3 octet covers the previous SPE.  Also note that the SPE
>> includes the path overhead, the fixed stuff, and the payload.
>> The SPE from the transmitter is fixed to start after the
>> last Z0 octet in the 1st row, 577th column, of the next SONET frame.
>Is that what the 522 means in the first payload pointer? The
>first SONET frame delivered to the medium contains an SPE with
>invalid payload data and the first SPE which actually contains
>valid payload data starts at the beginning of the payload space
>in the next SONET frame.
>> So for the transmit case, the B3 octet located in the 2nd row,
>> 577th column of WIS frame #N+1 covers the SPE which is entirely
>> in the envelope capacity (all octets in columns 577 to 17280,
>> rows 1 to 9) of WIS frame #N.
>That makes sense now.
>> Cheers,
>> Erik
>> In message "B3 question", bebrown@xxxxxxxxxxxxxxx writes:
>> >Hi,
>> >
>> >B3 is in the path overhead column of the 2nd row in the WIS frame.
>> >It is specified to cover the most recent SPE. However, the SPE from
>> >the transmitter starts after the "fixed stuff" in the 4th row and
>> >runs to the end of the next 3rd row.
>> >
>> >Does this mean that the B3 octet in WIS frame #N covers the SPE
>> >that starts in WIS frame N-2 and ends in WIS frame N-1?
>> >
>> >Thanks,
>> >Ben
>> >
>> >--
>> >-----------------------------------------
>> >Benjamin Brown
>> >Router Products Division
>> >Nortel Networks
>> >1 Bedford Farms,
>> >Kilton Road
>> >Bedford, NH 03110
>> >603-629-3027 - Work
>> >603-624-4382 - Fax
>> >603-798-4115 - Home
>> >bebrown@xxxxxxxxxxxxxxxxxx
>> >-----------------------------------------
>Benjamin Brown
>Router Products Division
>Nortel Networks
>1 Bedford Farms,
>Kilton Road
>Bedford, NH 03110
>603-629-3027 - Work
>603-624-4382 - Fax
>603-798-4115 - Home