Main principle - as powerful as possible.

For 1 server solution:

Component	Minimum requirement	Recommended	Comment
CPU	Quad Xeon/Intel Core i5	any higher CPU
RAM	4 Gb	16 GB or more
HDD	50 Gb	100 Gb or more, SDD (Solid State Drives), RAID Type 1	all space must be assigned to / partition
OS	Centos 6	x86_64

Such server should handle up to 500 calls without problems. Calls without reencoding (also known as transcoding).

Recommended hardware

See also