Lec 2(intoduction of computer networkes)
1 like197 views
This document discusses different types of networks: 1. The Internet is the common network used for activities like reading news and social media. 2. The Deep Web is a subset not indexed by search engines so it requires directly visiting sites instead of searching. It exists because the Internet is too large to fully index. 3. The Dark Web requires special software to access and is often associated with illegal activities like drug sales, though it also has legitimate uses. It sits on additional private networks like Tor and I2P.
Lec 2(intoduction of computer networkes)
- 1. Network Core Part Computer Networks – CSE331 Lecture 2
- 2. The Internet: This is the easy one. It’s the common Internet everyone uses to read news, visit Facebook, and shop. Just consider this the “regular” Internet. The Deep Web: The deep web is a subset of the Internet that is not indexed by the major search engines. This means that you have to visit those places directly instead of being able to search for them. So there aren’t directions to get there, but they’re waiting if you have an address. The Deep Web is largely there simply because the Internet is too large for search engines to cover completely. So the Deep Web is the long tail of what’s left out (your email, dropbox, fb account etc). The Dark Web: The Dark Web (also called Darknet) is a subset of the Deep Web that is not only not indexed, but that also requires something special to be able to access it, e.g., specific proxying software or authentication to gain access. The Dark Web often sits on top of additional sub-networks, such as Tor, I2P, and Freenet, and is often associated with criminal activity of various degrees, including buying and selling drugs, etc. While the Dark Web is definitely used for those things more than the standard Internet or the Deep Web, there are many legitimate uses for the Dark Web as well.
- 3. Why search engine can not index deep web But I hope you will prefer the light
- 4. central office ISP telephone network DSLAM voice, data transmitted at different frequencies over dedicated line to central office use existing telephone line to central office DSLAM data over DSL phone line goes to Internet voice over DSL phone line goes to telephone net < 2.5 Mbps upstream transmission rate (typically < 1 Mbps) < 24 Mbps downstream transmission rate (typically < 10 Mbps) DSL modem splitter DSL access multiplexer
- 5. cable modem splitter … cable headend Channels V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 frequency division multiplexing: different channels transmitted in different frequency bands
- 6. data, TV transmitted at different frequencies over shared cable distribution network cable modem splitter … cable headend CMTS ISP cable modem termination system HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate network of cable, fiber attaches homes to ISP router homes share access network to cable headend unlike DSL, which has dedicated access to central office
- 7. typically used in companies, universities, etc 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates today, end systems typically connect into Ethernet switch Ethernet switch institutional mail, web servers institutional router institutional link to ISP (Internet)
- 8. shared wireless access network connects end system to router via base station aka “access point” wireless LANs: within building (100 ft) 802.11b/g (WiFi): 11, 54 Mbps transmission rate wide-area wireless access provided by cellular operator, 10’s km between 1 and 10 Mbps 3G, 4G: LTE to Internet to Internet
- 9. host sending function: takes application message breaks into smaller chunks, known as packets, of length L bits transmits packet into access network at transmission rate R link transmission rate, aka link capacity, aka link bandwidth R: link transmission rate host 12 two packets, L bits each packet transmission delay time needed to transmit L-bit packet into link L (bits) R (bits/sec) = =
- 10. mesh of interconnected routers packet-switching: hosts break application-layer messages into packets forward packets from one router to the next, across links on path from source to destination each packet transmitted at full link capacity
- 11. takes L/R seconds to transmit (push out) L-bit packet into link at R bps store and forward: entire packet must arrive at router before it can be transmitted on next link end-end delay = 2L/R (assuming zero propagation delay) one-hop numerical example: L = 7.5 Mbits R = 1.5 Mbps one-hop transmission delay = 5 sec more on delay shortly … source R bps destination 123 L bits per packet R bps Time to reach 3 packets to destination? 4L/R
- 12. A B CR = 100 Mb/s R = 1.5 Mb/s D Equeue of packets waiting for output link queuing and loss: If arrival rate (in bits) to link exceeds transmission rate of link for a period of time: packets will queue, wait to be transmitted on link packets can be dropped (lost) if memory (buffer) fills up
- 13. forwarding: move packets from router’s input to appropriate router output routing: determines source-destination route taken by packets routing algorithms routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 1 23 dest address in arriving packet’s header
- 14. LB-3 Computer Science Department, UET, Lahore, Punjab, Pakistan LB-3 Computer Science Department, UET, Lahore, Punjab LB-3 Computer Science Department, UET, Lahore LB-3 Computer Science Department, UET LB-3 Computer Science Department LB-3
- 15. forwarding: move packets from router’s input to appropriate router output routing: determines source-destination route taken by packets routing algorithms routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 1 23 dest address in arriving packet’s header
- 16. end-end resources allocated to, reserved for “call” between source & dest: In diagram, each link has four circuits. call gets 2nd circuit in top link and 1st circuit in right link. dedicated resources: no sharing circuit-like (guaranteed) performance circuit segment idle if not used by call (no sharing) Commonly used in traditional telephone networks
- 18. A have to send 64000 bits to B over circuit switch over TDMA Link speed 1Mbps Link has 20 slots Setup time 0.2s Sol: Per circuit speed 1Mbps/20 = 50Kbps 64000/50000 = 1.28s 1.28+0.2 = 1.3s Did not has other delays like propogation
- 19. example: 1 Mb/s link each user: • 100 kb/s when “active” • active 10% of time circuit-switching: 10 users => 1Mbps/100kbps packet switching: with 35 users, probability > 10 active at same time is less than .0004 packet switching allows more users to use network! N users 1 Mbps link http://www.danielsoper.com/statcalc/calculator.aspx?id=71
- 20. is packet switching a “winner?” great for bursty data resource sharing simpler, no call setup excessive congestion possible: packet delay and loss protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 7) Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?
- 21. History (Reading Assignment) Ross book 1.3, 1.6