Which of the following regarding the Source Path Tree is TRUE?

The Source Path Tree (SPT), also known as a shortest path tree, is rooted at the multicast source and provides the most direct path to the receivers. Its construction does not fundamentally depend on a Rendezvous Point (RP). This is most clearly demonstrated in Source-Specific Multicast (SSM), a mode of PIM that operates without an RP and exclusively builds SPTs. In Any-Source Multicast (ASM), while an RP is used for the initial shared tree, the eventual switchover to an SPT creates a tree directly toward the source, independent of the RP's location in the forwarding path.

A. The RP is the root of the tree. This is incorrect. The Rendezvous Point (RP) is the root of the Shared Tree (RPT or RPTree), not the Source Path Tree (SPT). The SPT is always rooted at the multicast source.
B. It is represented by a (, G) entry. This is incorrect. A (, G) entry, where '' is a wildcard, represents the state for a Shared Tree (any-source). An SPT is represented by a source-specific (S, G) entry.
C. It is the initial forwarding path in ASM mode. This is incorrect. In Any-Source Multicast (ASM) mode, the initial forwarding path is the Shared Tree (RPT). A last-hop router may subsequently switch to the SPT for a more optimal path.

1. Nokia 7750 SR OS R21.10.R1 Multicast Routing Protocols Guide, "PIM Overview" section, "PIM-SM Protocol" subsection. The guide states: "A source-specific tree, also known as a shortest path tree (SPT), is rooted at the multicast source... A shared tree, also known as a rendezvous point tree (RPT), is rooted at the RP." This confirms that the source, not the RP, is the root of the SPT (refuting A) and that the RPT is the initial tree in ASM (refuting C).

2. RFC 7761: Protocol Independent Multicast - Sparse Mode (PIM-SM), Section 4.5, "Source-Specific Multicast". This section details the operation of SSM, stating: "In SSM, delivery trees are always rooted at the source... The concept of an RP and a shared tree is not used in SSM." This directly supports that an SPT can be created without an RP (confirming D).

3. Nokia 7750 SR OS R21.10.R1 Multicast Routing Protocols Guide, "PIM Overview" section, "PIM-SM Protocol" subsection. The documentation describes multicast forwarding entries: "A (,G) entry represents the state for the shared tree... An (S,G) entry represents the state for a specific source tree." This refutes option B.