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

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Presentation on theme: "1 Week 2 Lecture 1 Layers (basics) Dr. Fei Hu. Review last lecture 2."— Presentation transcript:

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

2 Review last lecture 2

3 3 Communication Network example 1: Residential access: point to point access 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” 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 4 ADSL

5 5 Communication Network example 2: Residential access: cable modems 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

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

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

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

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

10 10 Cable Network Architecture: Overview home cable headend cable distribution network Channels VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO DATADATA DATADATA CONTROLCONTROL 1234 56789 FDM:

11 11 Communication Network example 3: Company access: local area networks 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

12 12 Example 4: Wireless access networks (In week 4 – some details!) 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 base station mobile hosts router

13 13 Example 5: Wireless Sensor Networks Deploy Sensors

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

15 15 Communication Systems: How do I understand you? 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?

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

17 17 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 ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing

18 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 19 Distributed implementation of layer functionality ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Departing airport arriving airport intermediate air traffic sites airplane routing

20 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 21 For Communication Systems: The same thing … 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

22 22 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 application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame

23 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 24

25 25 Application Layer location 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

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

27 27 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 process TCP with buffers, variables socket host or server process TCP with buffers, variables socket host or server Internet controlled by OS controlled by app developer API: (1) choice of transport protocol; (2) ability to fix a few parameters

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