SLS

Signaling Link Selector

Description

The signaling link selection (or SLS) is a field in the Message Transfer Part level 3 (MTP3) frame of SS7.

The SLS is used as a label to route MTP level 3 messages in the SS7 network.

SLS can also be used in reference to the algorithm that an SS7 node uses for selection of the appropriate signaling link to use for communicating with an adjacent SS7 node. Factors such as load balancing and link availability are used to determine the appropriate link.

SLS lenght	Variants	Description
4 bits	ITU,TTC,CHINA	The SLS is 4 bits wide
5 bits	ANSI	Prior to ANSI96, this bit is 5 bits wide
8 bits	ANSI96	This field was extended to 8 bits in ANSI96

Example

ITU MTP3 SLS field

SCCP MTP3 SLS

Reference

Ref: SLS on Wikipedia