Computer Networks
- 3. Internet Architecture • Hot spot The area within the AP’s range • Modems (short for modulator/ demodulator) that convert the digital data to be transferred into a form compatible with the transmission medium being used • DSL (digital subscriber line) in which the frequency range below 4 KHz (4,000 kilocycles per second) is reserved for traditional voice communication and the higher frequencies are used for transferring digital data • Dial up it is used for temporary connections in which the user places a traditional telephone call to an access ISP’s router and then connects his or her telephone to the end system to be used
- 4. Internet Addressing • Internet Protocol(IP) Addresses • Originally 32 bit long written in dotted decimal notation • Mnemonic form of addressing domain, registrars, domain names • Top level domains ( TLDs), country code TLDs • domain name system (DNS) , DNS Lookup
- 5. Internet Applications • Electronic mail(email) • Email Sending SMTP • SMTP was initially designed for transferring text messages encoded with ASCII, additional protocols such as MIME (Multipurpose Internet Mail Extensions) have been developed to convert non- ASCII data to SMTP compatible form • Email Receiving protocols • POP3 (Post Office Protocol version 3) • IMAP (Internet Mail Access Protocol) • Email Address structure
- 6. Internet Applications • File Transfer protocol • Guarded Vs Anonymous FTP • Telnet, Secure Shell (SSH)
- 7. Internet Protocols • how messages are transferred over the Internet. This transfer process requires the cooperation of all the computers in the system, and therefore software for controlling this process resides on every computer in the Internet
- 9. Internet Protocols • A message typically originates in the Application Layer • Transport Layer divides message into packets • Network Layer directs each packet through internet • Data Link Layer transfers packets according to transmission system
- 12. Application Layer • Provide an address compatible with internet infrastructure • Define protocols how host program will interface with Transport • All high level protocols like DNS (Domain Naming System), HTTP (Hypertext Transfer Protocol), Telnet, SSH, FTP (File Transfer Protocol), RDP (Remote Desktop Protocol) etc.
- 13. Transport Layer • Format messages for internet • Dividing and creating packets • Add sequence numbers • Reconstruct at other end • Reliability: Packets might lost during transport so error detection like checksum are used. Sending ACK or NACK message to sender is also its responsibility
- 14. Network and Link Layers • Network • Logical addressing • Routing is defining function of network layer • Error Handling and Diagnostics • Data Link • Receiving and transmitting packets • Communication detail of each network