Hi Aels,
PLR works in either IPComp or UDP. Note though if you have some NAT configurations that in v.3 some PLR control packets between the appliances are IPComp encapsulated whether UDP encapsulation is enabled or not.
The first file copy, gets compression and deduplication. Since it is the first time to see the file, byte-cache/deduplication hits are low because it is still learning the file. On the second transfer the hit ratio is high, since it is mostly the same file.
Depending on data type, Byte-Caching cold compression ratio (first copy) is similar to stream compression, since even in a cold transfer there are duplicate "words" that can be removed. As the dictionary of words (datastore) grows, the higher the cold compression hit ratio.