1. Fundamentals of WEB Programming

2. Server Side Programming Server Side Programming
Schedule
Alk.
Előadás 1.
Networks 2.
The Web 3.
HTML, CSS I. 4.
HTML, CSS II. 5.
HTML, CSS III. 6.
Server Side Programming
Alk.
Előadás 7.
Server Side Programming 8.
SOAP, REST 9.
Web Security
10.
Test
11.
Re-Test

3. Tests Quiz questions, 45 minutes „One good answer” question type
Good answer: 4 points
Bad answer: 0 points
„Multiple good answers” question type
One mistake: 2 points
More mistakes: 0 points

4. Bits vs characters
Electronic signal: Change of voltage level in a cable, these changes will contain the message we want to send
Data: These changes can be translated to bits
Information: These bits can be converted to characters using a transformation table (e.g. ASCII table)
„B”
Signal
Data
Information

5. Encoding characters Historical solution: ASCII UTF-8, UTF-16, UTF-32
(older alternatives: EBCDIC, …)
7 or 8 bits, 255 variation in 8 bits
0-31: control, : alphabet, 128+: codepage
UTF-8, UTF-16, UTF-32
Unicode character set, one character is 1-4 bytes
Same characters, only the base length varies
EVERY character (even including the Hungarian rovásírás)

6. OSI layers Now we can send characters over the wire
How to transfer more?
Case study: “I want to access google.com in my browser”
Somehow the request has to go from browser has to the wire, then to the google servers, and then the reply has to come back
Flexibility
De-centralization
Possibility to change parts without changing the whole
Solution: layered model
Works in every topology!

7. Network topologies
Full graph
NICs: n-1
Connections: (n(n-1))/2

8. Network topologies
Partial graph

9. Network topologies
Ring (token ring)
NICs: 2
Connections: n

10. Network topologies
Busz topológia
NICs: 1
Connections: n

11. Network topologies Csillag topológia Connections: n NICs: 1
Hálózati eszköz
NICs: 1
Connections: n

12. Network topologies
Extended star
NICs: 1
Connections: n

13. OSI Layers

14. OSI Layers - keywords Physical: Ethernet or Wi-Fi, HUB,
Data Link: MAC Address, Switch, Ethernet Frame, 1500 bytes MTU
Network: IPv4, IPv6, Router, IP Packet, ARP to map IP address to MAC, DNS to map hostname to IP address
Transport: ports, TCP and UDP differences, TCP speed control (sliding window)
Session: session/conversation management
Presentation: Encryption, SSL/TLS
Application: web browser

15. Web request
Application: user enters google.com, a HTTP request textual command is generated by the browser
Presentation: google.com prefers HTTPS, so a HTTPS (encrypted) request is created
Session: HTTP lacks protocol-level session management, so not implemented with HTTP. With other protocols: map authenticated user to the actual operation
Transport: HTTPS uses TCP port 443, Web request is encapsulated in a TCP packet (port number, packet id, checksum is in the packet)
Network: DNS shows google.com is , our IP address is – different network, so must use the default router/gateway. Default router is (according to ipconfig /all)

16. Web request
Network: according to the sender/target IP addresses, the TCP packet is encapsulated in an IP packet
Data Link: ARP shows the router’s MAC address. According to the sender/router MAC addresses, the IP packet is encapsulated in an ETH frame
Physical: The current connection is wired. According to the wired voltage rules, the contents of the Ethernet frame are transmitted on the wire
The same process is done on the server side, only reversed. Then the reply is sent using the same packet encapsulation

17. Packet encapsulation