Per-Linkset Random SLS

To achieve load balancing of outgoing traffic on ITU linksets, linksets that have either an ITU-I, 14-bit ITU-N, or 24-bit ITU-N adjacent point code assigned, the EAGLE 5 ISS currently uses the Random SLS option to generate a new SLS (signaling link selector) value. The randomly generated SLS value is used to select an outgoing signaling link and linkset. Random SLS generation applies to either Class 0 SCCP messages or to both Class 0 and Class 1 SCCP messages. The Random SLS option is configured using the randsls parameter of the chg-stpopts command. Refer to Configuring the System for Random SLS Generation for more information on configuring the Random SLS option.

This method of selecting outgoing signaling links and linksets is applied system-wide to all ITU linksets. This may cause problems for some end nodes that may have specific requirements for handling incoming SCCP messages, such as sequencing of Class 1 SCCP messages.

The Per-Linkset Random SLS feature provides the ability to apply Random SLS generation to Class 0 and Class 1SCCP messages on specific outgoing ITU linksets and to Class 0 SCCP messages and ISUP messages on specific incoming ANSI linksets. The randsls parameter of either the ent-ls or chg-ls command applies this feature to the linkset. The randsls parameter has three values:

off – Random SLS generation is not applied to the specified linkset.
class0 – Random SLS generation is applied to only Class 0 SCCP messages.
all – Random SLS generation is applied to both Class 0 and Class 1 SCCP messages on a specific outgoing ITU linksets, and to both Class 0 SCCP and ISUP messages on specific ANSI linksets.

When per-linkset random SLS is applied to ANSI linksets, linksets that have ANSI adjacent point codes, the SLS of the message is replaced with a randomly generated SLS, only if the slsreplace parameter value is set to yes. The slsreplace parameter value is shown in the rtrv-ss7opts output. If the slsreplace parameter value is no, the EAGLE 5 ISS uses the randomly generated SLS to select the signaling link, but the message retains the original SLS. If the linkset’s asl8 or slsci parameter value is off, or the chg-stpopts slscnv parameter is off, a 5-bit SLS is placed in the message. The three most significant bits of the SLS are zeroes. If the linkset’s asl8 or slsci parameter value is on, or the slscnv parameter of the chg-stpopts command is on, an 8-bit SLS is placed in the message. The linkset’s asl8 parameter value is not used for internal linkset and signaling link selection. The linkset's asl8 parameter applies only to incoming linksets. The linkset's slsci parameter applies only to outgoing linksets. The randomly generated SLS value is used for internal linkset and signaling link selection. When an ANSI to ITU conversion takes place, the randomly generated SLS value for the incoming ANSI linkset is used for internal linkset and signaling link selection and Random SLS generation on outgoing linkset is not performed.

The randsls parameter is optional. If the randsls parameter is not specified when adding a linkset with the ent-ls command, the value of the randsls parameter is off. If the randsls parameter is not specified when changing a linkset with the chg-ls command, the value of the randsls parameter is not changed.

The value of the randsls parameter assigned to the linkset is displayed in the RANDSLS column of the rtrv-ls command output. The RANDSLS column is displayed only when a specific linkset is being displayed with the rtrv-ls:lsn=<linkset name> command. All linksets having a particular randsls value can be displayed by entering the rtrv-ls command with the randsls parameter with one of these values:

off – Displays the linksets where random SLS generation is disabled.
class0 – Displays the linksets where random SLS generation for Class 0 SCCP traffic is enabled.
all – Displays the linksets where random SLS generation for Class 0 and Class 1 SCCP traffic on a specific outgoing ITU linksetsis enabled, and Class0 SCCP and ISUP messages on specific incoming ANSI linksets is enabled..

For random SLS generation to be performed on a specific linkset, the randsls parameter value for that linkset must be set to either class0 or all. The system-wide random SLS STP option randsls must be set to perls using the chg-stpopts command with the randsls=perls parameter. Refer to Configuring the System for Random SLS Generation for more information on configuring the system-wide Random SLS option, and, if Random SLS is applied to ANSI linksets, to configure the SS7 option for replacing the SLS in the message with the randomly generated SLS.

It is recommended that when configuring randsls values on two linksets that are in a combined linkset that the randsls values for these linksets are the same. If these values are not the same, undesired SLS distribution of the traffic on these linksets may result.