1. ELEN 602 Lecture 11 ELEN 602 Computer Communications & Networks Instructor: Narasimha Reddy Contact: reddy@ee.tamu.edu, 845-7598, 320 F Wisenbaker Textbook: Communication Networks by Leon-Garcia & Widjaja Class notes available: http://ee.tamu.edu/~reddy/ee602_02.html Teaching Assistant/Grader: To Be Announced TA Office Hours: To Be Announced Grading: Homeworks: 30%, Tests: 60%, Project: 10%

2. ELEN 602 Lecture 12 Some Communication Networks Flying Pigeons Marathon Runners Reflecting Mirrors Telephone Telegraph Cable TV Internet Satellite-based cable/telephone

3. ELEN 602 Lecture 13 The caller picks up the phone triggering the flow of current in wires that connect to the telephone office. The current is detected and a dial tone is transmitted by the telephone office to indicate that it is ready to receive the destination number. The caller sends this number by pushing the keys on the telephone set. Each key generates a pair of tones that specify a number. (In the older phone sets the user dials a number which in turn generates a corresponding number of pulses.) The equipment in the telephone office then uses the telephone network to attempt a connection. If the destination telephone busy, then a busy tone is returned to the caller. If the destination telephone is idle, then ringing signals are sent to both the originating and destination telephones. The ringing signals are discontinued when the destination phone is picked up and communication can then proceed. Either of the users terminate the call by putting down a receiver. Telephone Office 1. Telephone Office 2. Telephone Office 3. 4. Telephone Office 5. 6. Telephone Office Telephone Office Telephone Functioning

4. ELEN 602 Lecture 14 The user clicks on a link to indicate which document is to be retrieved. The browser must determine the address that contains the document. It does this by sending a query to its local name server. Once the address is known the browser establishes a connection to the specified machine, usually a TCP connection. In order for the connection to be successful, the specified machine must be ready to accept TCP connections. The browser runs a client version of HTTP, which issues a request specifying both the name of the document and the possible document formats it can handle. The machine that contains the requested document runs a server version of HTTP. It reacts to the HTTP request by sending an HTTP response which contains the desired document in the appropriate format. The TCP connection is then closed and the user may view the document. 1. 2. 3. 4. 5. 6. Web Access Steps

5. ELEN 602 Lecture 15 Realplayer example Copyright © 1995-2000, RealNetworks, Inc. All rights reserved. RealPlayer is a trademark of RealNetworks, Inc.

6. ELEN 602 Lecture 16 Steps in Communication - US Mail Compose the letter -- based on the user/office/personal Package it for transport -- put it in an envelope, address (to and from) it, leave it in a well-known port (mailbox) Postman picks up the mail, local post office sorts it for further transport Number of letters may be bundled and transported to remote city Remote post office sorts them by local addresses, postman delivers it to the To-mailbox Remote person picks up the mail, receives the message.

7. ELEN 602 Lecture 17 Work in generic communication Addressing -how to address the comm. for transport –telephone numbers, US Mail addresses, IP addresses Name-to-address translation -- phone directory, address book, DNS name resolution Routing -- which way to send a piece of comm. to reach B from point A –East-coast US mail may go to Houston -New York Transport -- how to actually move the data/mail/bits/ –Trucks/planes with US mail, telephone wires, LAN –Multiplexing of different pieces of communication

8. ELEN 602 Lecture 18 What you will learn in this class? Addressing (IPv4 and IPv6) Routing (routing protocols) Name resoultion (DNS) Transport –Physical media (Ethernet, SONET, FDDI, ATM etc.) –Multiplexing (switches/routers) –Queuing theory -(delay/loss analysis) –Protocols (TCP/IP) Some Applications - (http/email etc.)

9. ELEN 602 Lecture 19 t0t0 t1t1 Network

10. ELEN 602 Lecture 110 Network (a) A switch provides the network to a cluster of users (b) A multiplexer connects two access networks Access network

11. ELEN 602 Lecture 111 Metropolitan network A consists of access subnetworks a, b, c, d. National network consists of regional subnetworks. Metropolitan network A is part of regional subnetwork. A A Metropolitan 1* a c b d (a) (b) 2 3 4

12. ELEN 602 Lecture 112 Transmission capacity (bits/second) Printing telegraph Baudot multiplex T-1 carrier T-4 carrier SONET OC-48 DWDM

13. ELEN 602 Lecture 113 (a) A switch in the form of an operator with a patch cord panel (not shown) (b) Cords interconnect user sockets providing end-to-end connection

14. ELEN 602 Lecture 114 Tandem CO Toll CO Tandem

15. ELEN 602 Lecture 115 (a) Time-Shared Computers & Cables for Input Devices (b) Dial In C...... TT C...... T T T Modem Pool PSTN Modem T T = terminal

16. ELEN 602 Lecture 116 C TTTT Response from terminal Poll to terminal

17. ELEN 602 Lecture 117 T T Host...... T Address Info Mux

18. ELEN 602 Lecture 118 T T...... T.................. New York City San Francisco Chicago Atlanta Host

19. ELEN 602 Lecture 119 UCLARANDTINKER USC NBS UCSB HARV SCD BBN STAN AMES McCLELLAN UTAHBOULDERGWCCASE CARN MITRE ETAC MIT ILL LINC RADC

20. ELEN 602 Lecture 120 (a) (b) transceivers

21. ELEN 602 Lecture 121 G G G G G net 1 net 2 net 3 net 4 net 5 G = gateway G

22. ELEN 602 Lecture 122 Technology Regulation Market Standards

23. ELEN 602 Lecture 123 time Capability Initial class of invention Second type of invention Third type of invention time Capability (a)(b)