ok

According to my knowledge...

The Main Internet Back bone is National Science Foundation Network

& Tier 1 networks have closest relation with this back bone...



There are almost 8-9 T1 networks, sorry if i missed some...

AT&T
Global Crossing
Savvis
Level3 Communication
Verio
Sprint
Verizon
Tellia Sonera

Verio is the largest Tier 1 Network and is headquartered in TOKYO JAPAN ( Not tokyo drift ) lol

There are others networks which work under these T1 Networks & Purchase services from them

Tier 2 Networks may be connected with more that one T1 Networks to get/provide more reliability...
Like Cogent Communication have pairing with Level3, Tellia Sonera, Sprint etc...

After that There are Tier 3 and Tier 4 Networks...

I have posted their details on this Page Tier1,2,3,4



Ok Now come to your Questions:

Ans1) Internet is provided by the NSFN (National Science Foundation Network), Before it was provided by ArpaNet but was replaced by NSFN , I think in 1998...

Ans2) The same as answer 1

Ans3) Domain Name System is managed by ICANN (http://icann.org) Here is the root database which shows that who manages the specific TLD (Top Level Domain) http://www.iana.org/domains/root/db/
1 thing I want to clear that the name of companies given on the page I provided on above line, are the base for providing that specific domain (like for .com domain there is only 1 company Verisign who manages it) However is managed at backend by ICANN but ICANN don't provide Domain Names they just give services to these companies and they almost probably don't give domain names directly they have other registrars who provide domains...

After thesec companies who are managing root TLD's , they have their Registrars, which sell domains in bulk or whatever they want...

There are some registrars who have the approved existance (given authority by ICANN) are called ICANN ACCREDITED REGISTRARS ... List of such registrars is given here http://www.icann.org/en/registrars/accredited-list.html

Ans4) Who provides? is some how not clear... But IANA (Internet Assigned Numbers Authority) http://iana.org is the base for managing these IP's ... I am not clear that by which process/procedure these are given to companies in Pakistan like PTCL , But they get the IP's in form of Blocks & they Manage that blocks here in their datacenter... & the IP provided while we connect to internet is provided by these local Companies... There is somehow APNIC.NET is involved ... I am not sure about what is this

Ans5) Yes offcourse, PTCL has purchase bandwidth, while they connect to Tier Networks they must have to purchase...

Ans6) Where to get, It depends on you, & I am not Clear about price... If you're going to start an ISP or Data Center for Webhosting (One of My Dreams :D) then you must have to get service from them..
There are many companies who provide & I had contacted 1 of them almost 7-9 months ago, They asked me to send my company details, is it registered or not... lol :D
In Our University there is IP & Internet Service provided by CE-TEL for PAKSAT ... Details can be found here http://ce-tel.com/paksat.htm ... IP of Computers in BZU is of Germeny because CE-TEL is based in Germany & they are providing that IP's Through Satelite... Price ka CE-TEL se contact kar kay kar lo pata ... Mujhay bhi Bata Daina :D

Ans7) Submarine ka mujhay nai pata ... but I think It would be some of Tier Networks...

Ans8) It should be clear by reading the above Answers...

Note: I have Just Given Answers according to my Knowledge... These may be wrong ... If you found any thing wrong please do correct it...

Thanks