1. 1 Computer Networks & The Internet Lecture 3 Imran Ahmed University of Management & Technology

2. 2 Agenda Network & its types What’s the Internet? What’s a protocol? History Network edge Network core Access net, physical media Internet/ISP structure Performance: loss, delay Protocol layers, service models

3. 3 Basic architecture The Internet has a hierarchical structure. At the highest level are large national Internet Service Providers that interconnect through Network Access Points (NAPs). There are about a dozen NAPs in the U.S., run by common carriers such as Sprint and Ameritech, and many more around the world (Many of these are traditional telephone companies, others are pure data network companies).

4. 4 pop

5. 5 Backbone Map of UUNET - USA

6. 6 UUNET Mixed OC-12 – OC-48 – OC 192 backbone 1000s miles of fiber 3000 POPs 2,000,000 dial-in ports

7. 7 Backbone Map of UUNET - World

8. 8 Qwest OC-192 backbone 25,000 miles of fiber 635 POPs 85,000 dial-in ports

9. 9 AT&T OC-192 backbone 53,000 miles of fiber 2000 POPs 0 dial-in ports

10. 10 The real story Regional ISPs interconnect with national ISPs and provide services to their customers and sell access to local ISPs who, in turn, sell access to individuals and companies.

11. 11 Connecting to an ISP ISPs provide access to the Internet through a Point of Presence (POP). Individual users access the POP through a dial-up line using the PPP protocol. The call connects the user to the ISP’s modem pool, after which a remote access server (RAS) checks the userid and password.

12. 12 More on connecting Once logged in, the user can send TCP/IP/[PPP] packets over the telephone line which are then sent out over the Internet through the ISP’s POP (point of presence) Corporate users might access the POP using a T-1, T-3 or ATM OC-3 connections, for example, provided by a common carrier.

13. 13 DS (telephone carrier) Data Rates Designation Number of Voice Circuits Bandwidth DS0 1 64 kb/s DS1 (T1) 24 1.544 Mb/s DS2 (T2) 96 6.312 Mb/s DS3 (T3) 672 44.736 Mb/s

14. 14 SONET Data Rates A small set of fixed data transmission rates is defined for SONET. All of these rates are multiples of 51.84 Mb/s, which is referred to as Optical Carrier Level 1 (on the fiber) or Synchronous Transport Signal Level 1 (when converted to electrical signals) Optical LevelLine Rate, Mb/s OC-1 OC-3 OC-9 OC-12 OC-18 OC-24 OC-36 OC-48 OC-96 OC-192 OC-768 51.840 155.520 466.560 622.080 933.120 1244.160 1866.240 2488.320 4976.640 9953.280 39813.120

15. 15 Internet Backbones in 2005 As of mid-2001, most backbone circuits for national ISPs in the US are 622 Mbps ATM OC-12 lines. The largest national ISPs are planning to convert to OC-192 (10 Gbps) by the end of 2003. A few are now experimenting with OC-768 (40 Gbps) and some are planning to use OC-3072 (160 Gbps). Aggregate Internet traffic reached 2.5 Terabits per second (Tbps) by mid-2001. It is expected to reach 35 Tbps by 2006.