1 / 27

Week 2 Lecture 1

Week 2 Lecture 1. Layers (basics) Dr. Fei Hu. Review last lecture. Dialup via modem up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: can’t be “always on”. Communication Network example 1: Residential access: point to point access.

orsin
Download Presentation

Week 2 Lecture 1

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Week 2 Lecture 1 Layers (basics) Dr. Fei Hu

  2. Review last lecture

  3. Dialup via modem up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: can’t be “always on” Communication Network example 1:Residential access: point to point access • ADSL: asymmetric digital subscriber line • up to 1 Mbps upstream (today typically < 256 kbps) • up to 8 Mbps downstream (today typically < 1 Mbps) • FDM: 50 kHz - 1 MHz for downstream • 4 kHz - 50 kHz for upstream • 0 kHz - 4 kHz for ordinary telephone

  4. ADSL

  5. HFC: hybrid fiber coax asymmetric: up to 10Mbps upstream, 1 Mbps downstream network of cable and fiber attaches homes to ISP router shared access to router among home issues: congestion, dimensioning deployment: available via cable companies, e.g., MediaOne Communication Network example 2:Residential access: cable modems

  6. Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

  7. Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified)

  8. Cable Network Architecture: Overview cable headend home cable distribution network (simplified)

  9. server(s) Cable Network Architecture: Overview cable headend home cable distribution network

  10. C O N T R O L D A T A D A T A 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 5 6 7 8 9 1 2 3 4 Channels Cable Network Architecture: Overview FDM: cable headend home cable distribution network

  11. company/univ local area network (LAN) connects end system to edge router Ethernet: shared or dedicated link connects end system and router 10 Mbs, 100Mbps, Gigabit Ethernet deployment: institutions, home LANs happening now Communication Network example 3:Company access: local area networks

  12. shared wireless access network connects end system to router via base station aka “access point” wireless LANs: 802.11b (WiFi): 11 Mbps wider-area wireless access provided by telco operator 3G ~ 384 kbps Will it happen?? WAP/GPRS in Europe router base station mobile hosts Example 4:Wireless access networks (In week 4 – some details!)

  13. Sensors Deploy Example 5: Wireless Sensor Networks

  14. How to study Comm Networks? Sprint US backbone network – so complex !

  15. Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? Communication Systems:How do I understand you?

  16. ticket (complain) baggage (claim) gates (unload) runway landing airplane routing ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing airplane routing Using “layers” – just like air travel • a series of steps

  17. ticket (complain) baggage (claim) gates (unload) runway landing airplane routing ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing airplane routing Organization of air travel: a different view Layers: each layer implements a service • via its own internal-layer actions • relying on services provided by layer below

  18. Layered air travel: services Counter-to-counter delivery of person+bags baggage-claim-to-baggage-claim delivery people transfer: loading gate to arrival gate runway-to-runway delivery of plane airplane routing from source to destination

  19. airplane routing airplane routing airplane routing Distributed implementation of layer functionality ticket (complain) baggage (claim) gates (unload) runway landing airplane routing ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing arriving airport Departing airport intermediate air traffic sites

  20. Why layering? Dealing with complex systems: • explicit structure allows identification, relationship of complex system’s pieces • layered reference model for discussion • modularization eases maintenance, updating of system • change of implementation of layer’s service transparent to rest of system • e.g., change in gate procedure doesn’t affect rest of system • layering considered harmful?

  21. application: supporting network applications FTP, SMTP, STTP transport: host-host data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire” application transport network link physical For Communication Systems: The same thing …

  22. M M H H H H H H H H H H H H t t t t l n l t n n t n M M M M application transport network link physical application transport network link physical M M Layers are actually implemented as … Each layer takes data from above • adds header information to create new data unit • passes new data unit to layer below source destination message segment datagram frame

  23. This course focuses on … • The lowest layer -- Physical Layer • It handles signal transmission (i.e. digital communications), including – -- encoding/decoding ( 3 weeks) -- Modulation (3 weeks) -- A D or D A (2 weeks) -- …

  24. Let’s talk about higher layers • Applications Layer: • Execute application-level protocols • HTTP (Web) • FTP • SMTP / POP3 / IMAP (E-mail) • DNS

  25. application: supporting network applications FTP, SMTP, STTP transport: host-host data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire” application transport network Data link physical Application Layer location

  26. Typical network app has two pieces: client and server request reply application transport network data link physical application transport network data link physical Client-server paradigm Client: initiates contact with server (“speaks first”) typically requests service from server, Web: client implemented in browser; e-mail: in mail reader Server: provides requested service to client e.g., Web server sends requested Web page, mail server delivers e-mail

  27. host or server host or server process process socket socket TCP with buffers, variables TCP with buffers, variables App Layer: Processes communicating • process sends/receives messages to/from its socket • socket analogous to door • sending process shoves message out door • sending process assumes transport infrastructure on other side of door which brings message to socket at receiving process controlled by app developer Internet controlled by OS API: (1) choice of transport protocol; (2) ability to fix a few parameters

More Related