Private Infrastructure vs Public Infrastructure

[Andrew Lutz]

Good Day,

I'm going through the Cisco Networking Academy book on Connecting Networks, and it discusses Private vs Public Infrastructure WAN technologies.  It notes the types such as private being leased lines, circuit switches links such as PSTN and ISDN, and packet switched links such as Ethernet WAN, ATM or frame relay.  Public being DSL, cable, satellite, etc. 

I understand the types and the fundamentals of what they are.  What I'm having trouble grasping is what really defines public vs private infrastructure?  Since packet switching and frame relay for instance can allow shared bandwidth with other customers I thought those would be more "public."  Does private just indicate the ISP takes responsibility of ensuring your traffic is securely delivered end to end whereas public options they do not?  Or does public just indicate a service generally offered to the public and residential customers and therefore is inherently less secure?  Thanks.

[Joseph W. Doherty · Accepted solution]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Private means the WAN service provider provides networking isolation between some/most customers, public (e.g. Internet) means they do not.

Perhaps your confusion is because physical WAN (service provider) infrastructures are almost always (in US, anyway) privately owned yet such privately owned WAN infrastructures might only support private networking for the service provider's customers, or public (i.e. Internet) networking for the Internet service provider's customers, or both.

The same physical media networking technologies can often by used by the provider for either private or public or both networking.

As a rough analogy, consider a VLAN capable switch.  If you place all your "customers" into the same VLAN, you've built a "public" LAN.  If your "customers" are placed into different VLANs, you've built "private" LANs.  Notice you can do either on the same physical switch.

[Andrew Lutz]

Thank you, Joseph.  The ISP is essentially taking on the responsibility to isolate the traffic in private, and in public they don't.  Good analogy by the way, thanks.