Maybe it is DLNA compatibility issue.

Not all 11n devices support both 2.4GHz and 5GHz. Contact Samsung to confirm if the wireless card in your smart TV support dual bands or not.

Reset the swtich SG108E to factory defaults first. Use a computer or some other client to replace the mediabox and test if the problem continues. If SG108E works fine with other clients except the...

Gerri, the firmware of MR3420 is the latest version? L800 can be identified or not? If it can be identified but no internet, you can try to manually put APN, Dial number etc.

USB data card refers to 3G/4G card? What's the model number of it? Is it in compatibility list of W8968? Check if it can be identified. http://www.tp-link.com/en/support/3g-comp-list/?model=TD-W8968...

Ross, W8980 supports NAT loopback indeed. Did you try http://88.247.135.100/ instead of http://88.247.135.100/activecollab/public/index.php in external network?