Access Node is a technology which adds stealth capability for any RSI by adding a blending algorithm to it. Although this technology doesn't render the carrier invisible to Agents, it reduces the risk to draw an Agent's attention towards him.
Prior to the Truce, the Access Node technology was a secret and only used by exiled programs to hide from Agents. After the end of the war, Resistance members use it to circumvent the restrictions regarding the freeing of humans from the Matrix.