GS308E: 802.1p QoS - vlan based priority

Leaving alone most of this switch class models like the GS308E are not the right choice for various reasons (like lack of a strict management VLAN for example, lack of strong security for a direct L2 Internet exposed device, ..):

Your ISP does already deliver the frames on the VLAN 839 (IGMP Multicast traffic et all for Live TV - almost everything Internet->LAN), frames on VlAN 838 (Unicast for VOD aka. Video on Demand), readily marked with the a Type of Service (ToS) byte containing a DSCP (codepoint) that can be used for QoS prioritization. I would also imagine the STB does also set DSCP on frames originating from the STB to the two VLANs - not that there is any "importance" in that other direction to the ISP however. 

The Netgear "Plus" switches can be configured for QoS mode to manage traffic.towards handling Port-based QoS, or alternate port based QoS (not applicable for your use case). Port-based optimizes traffic by port ID while 802.1P/DSCP uses pass-through prioritization based on tagging packets (for supported devices only).

Technically, there is no reason in this use case for operating a switch with Differential Service, offering a DSCP Policy Table allowing to _change_ the codepoint for the DSCP policy. This codepoint will be written to the header of every packet containing the codepoint to which the DSCP policy is assigned. In the Priority area you can then select the priority you want to assign to the DSCP policy. Possible values are 0-7 and No Override. 

This is it. Technically, a Plus switch can be enough for your use case. All the STP will work for live TV and VOD as expected. For the security part, it depends what you expect from a non-managed core switch with some config options, for a per-port price of a better unmanaged switch.

Regards,

-Kurt

PS: Requesting a moderator to move this thread - the Plus switches are (by far!) not Managed Switches (where you posted).