Protocol(TCP/IP, HTTP) 송준화 조경민 2001/03/13. Network Computing Lab.2 Layering of...
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Transcript of Protocol(TCP/IP, HTTP) 송준화 조경민 2001/03/13. Network Computing Lab.2 Layering of...
Protocol(TCP/IP, HTTP)
송준화조경민
2001/03/13
2001/03/13 Network Computing Lab. 2
Layering of TCP/IP-based protocols
HTTP FTP TELNETNFSRP C DNS SNMP
TC P UDP
IP
transportlayer
Networklayer
data linklayer
2001/03/13 Network Computing Lab. 3
TCP Characteristic
TCP is connection-oriented 3-way handshake is used for connection setup/teardown
TCP provides a stream-of-bytes service. TCP is reliable
Acknowledgements indicate delivery of data. Checksums are used to detect corrupted data. Sequence numbers detect missing, or mis-sequenced data. Corrupted data is retransmitted after a timeout. Mis-sequenced data is re-sequenced. (Window-based) Flow control prevents over-run of receiver.
TCP uses congestion control to share network capacity among users.
2001/03/13 Network Computing Lab. 4
TCP is connection-oriented
2001/03/13 Network Computing Lab. 5
Connection Establishment/Close telnet address port
Active open telnet> quit equivalent to “close”
Makes the system to send “FIN” for “active close”
Time Wait State (2MSL state) On “active close” side MSL: maximum segment lifetime Two effects:
lost ACK Port reuse
2001/03/13 Network Computing Lab. 6
TCP segment header
20 bytes
2001/03/13 Network Computing Lab. 7
(some) TCP Header Fields URG: urgent bit
One end tells the other that “urgent data” of some form has been placed into the normal stream of data
Works with 16 bit “urgent pointer” field ACK: PSH: RST: SYN: FIN:
2001/03/13 Network Computing Lab. 8
IP characteristic
Connectionless mis-sequencing
Unreliable may drop packets
Best Effort
2001/03/13 Network Computing Lab. 9
IP : Internet Protocol
2001/03/13 Network Computing Lab. 10
The IP Datagram
20 bytes
2001/03/13 Network Computing Lab. 11
(some) IP Header Fields TOS:
3 bit precedence (ignored) 4 bit TOS :
(minimize delay, maximize throughput, maximize reliability, minimize monetary cost)
Only one bit can be “on” Usually call bits “off”
ID: unique id for each datagram from a sender
TTL: upper bound for # of hops
2001/03/13 Network Computing Lab. 12
HTTP
HTTP Stateless protocol
Not include the concept of a session or interaction beyond delivery of the requested document.
Do not need to keep track of who the clients are or what requests were serviced in the past.
2001/03/13 Network Computing Lab. 13
HTTP 1.0 vs. HTTP 1.1(1)
HTTP 1.0 For each additional request, a new
TCP connection must be established. The system incurs again in a
connection setup overhead. HTTP 1.1
Persistent connection Pipeline of requests
2001/03/13 Network Computing Lab. 14
HTTP 1.0 vs. HTTP 1.1(2)
HTTP 1.1 Persistent connection
Avoids many round trip delays Improving performance Reducing the number of packets
exchanged Pipeline of requests
Allows multiple requests to be sent without waiting for a response.
2001/03/13 Network Computing Lab. 15
HTTP interaction
HTTP 1.0 HTTP 1.1
2001/03/13 Network Computing Lab. 16
Anatomy of an HTTP transaction
2001/03/13 Network Computing Lab. 17
(Network) System Overview
TC P
routeredge router
core router
edge router
router
BrowserTC PIP
ethernet card
C lient
DBfront end
ws
ws
ws
Internet
The main issue is how we can improve networksystem performance at each component.
2001/03/13 Network Computing Lab. 18
Where are the delays?(1)
Browser The end user clicks on a hyperlink and
requests a document. In the case of a hit, returns the requested
document in the local cache. In the case of a miss
mapping the server hostname to an IP address. The clients opens a TCP connection to the server. The clients sends an HTTP request to the server.
The browser formats and displays the document and renders the associated images.
2001/03/13 Network Computing Lab. 19
Where are the delays?(2)
Network The network imposes delays to
deliver information from the client to server and back from the server to client.
2001/03/13 Network Computing Lab. 20
Where are the delays?(3)
Server A request arrives from the client. The server parses the request, according to
the HTTP protocol. The server executes the method requested. The server reads the contents of the file
from disk or from its main memory cache and writes it to the network port.
Close the connection Service time and waiting time at the various
components of the server, such as processor, disk, and network
2001/03/13 Network Computing Lab. 21
QoS(Quality of Service)(1)
Customers want to have good services available at any time.
Customers do not care about site failures, traffic jams, network bandwidth, or other indicators of system activities.
Besides contents and aesthetics, online users want performance and security.
2001/03/13 Network Computing Lab. 22
QoS(Quality of Service)(2)
Users perceive Web services through performance metrics such as: Response time Availability
The percentage of time a site is available during an observation period.
Reliability Measuring the occurrence of failures during the
processing or services. Predictability Cost
2001/03/13 Network Computing Lab. 23
QoS(Quality of Service)(3)
Compounding the need for high reliability and availability is the dynamic nature of the Web, which internal and external customers rely on for up-to-date business, professional, and personal information.
2001/03/13 Network Computing Lab. 24
QoS(Quality of Service)(4)
Unpredictable For example, in a large trade show company, 250,000 hits a week during normal weeks A million hits a day at the peak of its largest Fall
show. Companies must measure traffic, performance,
and usage patterns in order to monitor the quality of service of their Web sites.
Management has to decide if additional capacity is needed to stay ahead of customer demands.