The following networking information relates to HelixNet v3.0 and later; 

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Here are the IP ports that have to be exposed on an HMS-4X for the system to work. 

tcp 655 Linking 
tcp 80 HTML, CCM, Stacking 
tcp 6001 Authenticate, Update, Reboot 
tcp 6000 Pairing with HKB/HRM 
udp 6001 Audio 
udp 5353 mDNS, Expansion, Pair/Link by Name 

Bandwidth required is mostly about Audio. Everything else is not significant. Audio is 300kbps per audio stream. 

Detailed breakdown of audio requirements is: 

HBP-2X and HKB-2X send 1 stream when Talking, can receive up to 4 simultaneous streams (Loudest) = 300kbs to HMS, up to 1.2Mbps from HMS 
HRM-4X send 2 streams, one from Mic, one from PGM, and can receive up to 8 simultaneous streams (Loudest), 4 to HSet/LS and 4 to Audio Out
(if Channel Assigned) = 600kbps to HMS, up to 2.4Mbps from HMS 
Between HMS-4X we send/forward audio only when required (i.e. there is at least one listener on the other HMS-4X or one of its connected endpoint).
Bandwidth requirement varies depending on the workflow. 

Example 
If I have 3 linked HMS, using 12 channels, all of them assigned to a 4W interface and 20 endpoints per HMS (e.g. total 60 HBP) with roughly 12 persons
talking at the same time at any given time (i.e. 1 per channel) I would recommend 

2.4Mbps for distribution of 4W audio 
2.4Mbps for distribution of Channel audio 
For a total of 4.8Mbps 

Enabling VOX on 2W/4W does reduce the bandwidth significantly as we don't send anything when there is no voice activity. Same thing for the distribution
of the Program. We also don't send anything when Talk is not latched, so workflow where no one is latching Talk keys will use much less bandwidth.