Service tunnels and transport tunnels are bidirectional and only require the operator to configure the tunnel on one router.

In Nokia's Service Router Operating System (SR OS), both transport tunnels (like MPLS LSPs) and service tunnels (Service Distribution Paths or SDPs) are unidirectional. To establish a bidirectional communication path for a service between two routers, two separate unidirectional tunnels must be configured—one for each direction. For example, an SDP must be configured from PE1 to PE2, and a second SDP must be configured from PE2 to PE1. Configuration is required on both endpoint routers.

A. (The statement is True) This is incorrect because tunnels in SR OS are fundamentally unidirectional constructs, requiring explicit configuration for each direction of traffic flow.

1. Nokia 7750 SR OS, Services Architecture Guide, Release 21.10.R1, Chapter: Service Distribution Paths (SDPs). The guide states, "An SDP is a unidirectional service tunnel between two 7750 SR routers."

2. Nokia 7750 SR OS, MPLS Guide, Release 21.10.R1, Chapter: Label Distribution Protocol (LDP). The guide describes LSPs as unidirectional paths from an ingress LER to an egress LER.