1. Virtual Signaling Transfer Point User Guide
  2. vSTP Features
  3. SLS Rotation
  4. Incoming Bit Rotation

2.12.3 Incoming Bit Rotation

If the Incoming Bit Rotation option is selected, then vSTP rotates the 4 bits of ITU SLS and 5 or 8 bits of ANSI SLS according to the incoming linkset. Thus, changing the LSB of the SLS.

This option provides additional capability to fairly distribute traffic across links and linksets, however it still does not guarantee an even distribution of messages for all set of input SLS values. It is applicable to all ITU and ANSI messages.

  • ITU Messages
    For ITU messages, the SLS value is only 4 bits and all 4 bits are considered for rotation. The Incoming Bit Rotation is applied on ITU MSUs based on the combination of islsrsb and islsbrEnabled parameters. User needs to set the value of the islsbrEnabled parameter in m3rloptions MO to true and configure islsrsb in Linkset MO to specify the bit to be used as LSB. This rotation affects the 4 bits of SLS selection in the following manner:

    • If bit position 4 is selected (islsrsb =4) for the incoming linkset, then bit locations 4 3 2 1 are rotated to positions 3 2 1 4.

      For example, SLS = 1101 becomes Rotated SLS = 1011

    • If bit position 3 is selected (islsrsb =3) for the incoming linkset, then bit locations 4 3 2 1 are rotated to positions 2 1 4 3.

      For example, SLS = 1110 becomes Rotated SLS = 1011

    • If bit position 2 is selected (islsrsb =2) for the incoming linkset, then bit locations 4 3 2 1 are rotated to positions 1 4 3 2.

      For example, SLS = 0110 becomes Rotated SLS = 0011

    • If bit position 1 is selected (islsrsb =1) for the incoming linkset, then no rotation is performed since bit 1 is the existing LSB. Bit 1 is the default value.

      For example, SLS = 0110 remains 0110 only.

  • ANSI Messages

    The Incoming Bit Rotation is applied on ANSI messages as per the combination of the following parameters.

    Table 2-11 Parameters used for Incoming Bit Rotation of ANSI

    Parameter Name Description
    islsbrEnabled User needs to set the value of the islsbrEnabled parameter in m3rloptions MO to true.
    asls8

    Specifies if the adjacent node is sending MSUs with 5 or 8 bits SLS. This parameter value is configured in Linkset MO.

    rsls8 The inclusion of 5 or 8 bits of SLS in the rotation depends on the value of the rsls8 parameter in Linkset MO.
    • If the value is true: 8 bits SLS is considered for rotation
    • If the value is false: the least significant 5 bits of SLS are considered for rotation
    slscnv and slsci

    The combination of both these parameters with asls8 decides if 5 to 8 bits SLS conversion option is applied on incoming 5 bits SLS or not.

    slscnv is configured in m3rloptions MO and slsci is configured in Linkset MO.

    islsrb Configure islsrsb in Linkset MO to specify the bit to be used as LSB.

    The combination of values provided to these parameters on incoming linkset decides the SLS bits (5 or 8) to be considered for rotation. The following table describes the combination of parameter values with respective rotation rule:

    Note:

    In below table, the values of CNV represents combination of the following parameters:

    CNV = YES : (SLSCNV=On) or (SLSCNV= PerLs and SLSCI on the outgoing linkset =true)

    CNV=NO : (SLSCNV=Off) or (SLSCNV= PerLs and SLSCI on the outgoing linkset =false)

    Table 2-12 Rules applied for Incoming Bit Rotation of ANSI

    Rule asls8 rsls8 islsbr CNV Incoming SLS Bits Rotation (islsbr)
    1 false false 1-5 NO The least significant 5 bits of SLS will be considered for rotation.
    2 false false 1-5 YES The least significant 5 bits of SLS will be considered for rotation.
    3 false true 1-8 NO No ISLSBR will be performed.

    Note: Enable 5-bit to 8-bit ANSI SLS conversion on outgoing linkset to perform ISLSBR

    4 false true 1-8 YES The 8-bit SLS value obtained after 5-8 bit conversion is considered for rotation.
    5 true false 1-5 Has No Impact The least significant 5 bits of SLS will be considered for rotation.
    6 true true 1-8 Has No Impact The 8-bits SLS will be considered for rotation.

Incoming Bit Rotation Example:

The following table shows an example of Incoming Bit Rotation for ANSI messages:
Incoming ANSI SLS RSLS8 on incoming linkset Chosen LSB Rotated SLS Applied Rule from Table 2-11
11000110 false 2 11000011 5
01011110 true 7 01111001 6
10010 false 4 10101010

Note: The highlighted bits indicates the 3 new SLS bits introduced by 5-bit ANSI to 8-bit ANSI SLS conversion.

2
10010 true 8 01100101

Note: The highlighted bits indicates the 3 new SLS bits introduced by 5-bit ANSI to 8-bit ANSI SLS conversion.

4
01101 false 4 10101 1
01101 true 7 No Rotation 3