Dimensional Anchor vs. Banishment/Dismissal

[yennico]

Normally a higher level spell negates the effects of a lower level spell. One exception is the dimensional anchor spell.

Dimensional anchor:

A green ray springs from your outstretched hand. You must make a ranged touch attack to hit the target. Any creature or object struck by the ray is covered with a shimmering emerald field that completely blocks extradimensional travel. Forms of movement barred by a dimensional anchor include astral projection, blink, dimension door, ethereal jaunt, etherealness, gate, maze, plane shift, shadow walk, teleport, and similar spell-like or psionic abilities. The spell also prevents the use of a gate or teleportation circle for the duration of the spell.

A dimensional anchor does not interfere with the movement of creatures already in ethereal or astral form when the spell is cast, nor does it block extradimensional perception or attack forms. Also, dimensional anchor does not prevent summoned creatures from disappearing at the end of a summoning spell.

Dismissal and Banishment of summoned creatures are forced extradimensional travels.
Dismissal and Banishment are not listed in the description of the spell so they are not blocked ?
Does a dimensional anchor protect a summoned creature by a summon monster spell from being banished before! the summoning spell ends?
A planar ally spell is a summoning spell so the summoned outsider can be banished before he finished the task. Does a dimensional anchor spell protect this outsider from being banished so he can finish his task which can take longer than the dimensional anchor spell lasts?

 

[Infiniti2000]

Dismissal and Banishment are not listed in the description of the spell so they are not blocked ?
They are blocked because they are extradimensional travel.

Does a dimensional anchor protect a summoned creature by a summon monster spell from being banished before! the summoning spell ends?
No. The spell ends and the creature's manifestation disappears. Since the creature itself is not really there, there's no actual extradimensional travel.

A planar ally spell is a summoning spell so the summoned outsider can be banished before he finished the task. Does a dimensional anchor spell protect this outsider from being banished so he can finish his task which can take longer than the dimensional anchor spell lasts?
The dimensional anchor does protect the outsider from being banished too soon. It's a good tactic to use for a short-term ally, but the dimensional anchor is short-term compared to the possibilities of the planar ally spells.