1. Internet applications Bill Chu

2. © Bei-Tseng Chu Aug 2000 Need for Domain Name Service (DNS) Natively, a TCP host is identified by its IP address hosts uses IP addresses to communicate to each other the whole TCP/IP system software is based on using IP address IP address is not user friendly names can not be easily remembered User should use meaningful names to human instead of IP address Domain name service fills the gap let user use domain names for hosts (human friendly) map domain names into IP addresses machines use for TCP/IP application layer

3. © Bei-Tseng Chu Aug 2000 Domain name service (DNS) is basically a naming scheme to name IP hosts in the Internet a service that provides mappings from domain names to corresponding IP addresses IP addresses to corresponding domain names Common naming schemes flat scheme: no structure in names e.g., SSN and Ethernet addresses hierarchical scheme: tree structures in names e.g., UNIX file path DNS uses a hierarchical scheme names organized as recursive domains of names DNS Concepts

4. © Bei-Tseng Chu Aug 2000 Domain Name: a Hierarchy of Domains Domain is a collection of hosts and a collection of subdomains is represented as a tree domain name is the root name a host name is a path from the root to the host a subdomain is a path to the domain host subdomain …... Domain X Y W V a a b 1 2 3 YW V a 1 a=X.W.a a3 ws1 ws2 = X.Y.a.ws2

5. © Bei-Tseng Chu Aug 2000 Typical Domains Educational: edu uncc.edu is a subdomain in edu ws101.uncc.edu is a host under uncc.edu domain cs.uncc.edu is a subdomain in uncc.edu domain Commercial: com Nonprofit organization: org governmental: gov geographical country: au, cn, ca, … state: california.us One host can be in multiple domains!

6. © Bei-Tseng Chu Aug 2000 DNS Server Who Does the Mappings DNS server is responsible for mappings each domain must have at least one DNS server duplicated DNS servers are common need to some mappings, talk to your local DNS servers DNS is an application protocol address: IP + TCP port number of 53 format: request and reply message format Behaviors; iterative resolution recursive resolution

7. © Bei-Tseng Chu Aug 2000 DNS Name Resolutions Iterative resolution client makes iterative queries from the top DNS server to low-level DNS server to obtain the mapping Recursive resolution client makes one query to a DNS server The DNS server can eithter do an iterative resolution on the behalf of the client a recursive resolution using another DNS server

8. © Bei-Tseng Chu Aug 2000 FTP and File Transfer FTP is a TCP/IP application protocol transfer files from one TCP host to another Why FTP? Files are most common mechanisms that people use to exchange information How can it be implemented? Use TCP/IP sockets

9. © Bei-Tseng Chu Aug 2000 FTP and File Transfer FTP is a TCP/IP application protocol transfer files from one TCP host to another Why FTP? Files are most common mechanisms that people use to exchange information How can it be implemented? Use TCP/IP sockets

10. © Bei-Tseng Chu Aug 2000 How are Emails exchanged? SMTP is used to transfer emails between TCP hosts Each host has a queue for sending and a mailbox for receiving mails User uses user agent programs to interact with the mail queue and box. TCP connection (SMTP) Mail transfer agent Mail transfer agent Mail Queue for send Mailbox for receive user agent user agent User sends emails User receives emails mailtool netscape

11. © Bei-Tseng Chu Aug 2000 Simple Mail Transfer Protocol (SMTP) Address: IP address + TCP port 25 Format: three parts Email Envelope MAIL From: RCPT To: Email header Received, Message-Id, From, Date, Reply-To and so on Email body: text ended with a period.

12. © Bei-Tseng Chu Aug 2000 Email: an internet killer app Web-based email POP: downloading emails IMAP: storing email remotely Mail spams Email viruses

13. © Bei-Tseng Chu Aug 2000 SNMP Managed nodes Management states Management information A management protocol

14. © Bei-Tseng Chu Aug 2000 MIB: Management Information Base System: name, location, and description of equipment Interface: network interfaces and their measured traffic AT: address translation IP: IP package statistics ICMP: Statistics about ICMP messages received TCP: TCP algorithms, parameters and statistics UDP: UDP traffic statistics EGP: exterior gateway protocol traffic statistics Transmission: reserved for media specific MIBs SNMP: SNMP traffic statistics

15. © Bei-Tseng Chu Aug 2000 SNMP protocol Get-request: requests the value of one or more variables Get-next-request: requests the variable following this one Get-bulk-request: fetch a large table Set-request: updates one or more variables Inform-request: Manager-to-manager message describing local MIB SnmpV2-trap: agent-to-manager trap report

16. © Bei-Tseng Chu Aug 2000 Anatomy of a web application Sanctum systems Data Database Backend systems frontend systems Web Server User interface code Valid Input Browser Custom code: e.g. html, forms, javascript Off the shelf application: e.g. websphere Custom code: e.g. servelet, jsp, asp Applications: e.g. SAP, ORACLE Applications: e.g. ORACLE, DB2