Transcript Persistent with pipelining

HyperText Transfer Protocol
(HTTP)
Deepti Kulkarni
CISC 856: TCP/IP and Upper Layer Protocols
Fall 2008
Acknowledgements
Professor Amer
Richi Gupta
Motivation ?
 Single informational network
 Light protocol
 Speed
Tim-Berners Lee
HTTP Versions
Format : HTTP/<major>.<minor>
 HTTP/0.9 – No RFC
 HTTP/1.0 – RFC 1945
 HTTP/1.1 – RFC 2616
Director of the W3C
Position of HTTP in the TCP/IP Protocol suite
Application-layer
Transport layer
HTTP
TCP
IGMP ICMP
Network layer
IP
ARP
RARP
Data link layer
Physical layer
Underlying LAN or
WAN
Quick overview of HTTP
• Generic protocol for communication
• Stateless protocol
•
In-band protocol
•
control information is sent in-band (unlike FTP)
• Pull protocol
•
pulls information from the server (unlike SMTP which is push
protocol)
Client-Server protocol
Server running
Apache Web server
HTTP
Request/Response
are over TCP
connections
HTTP
Request
PC running
Explorer/MAC running
Navigator
HTTP
Response
A-PDU format
Request Line
Status Line
General Headers
General Headers
Request Headers
Response Headers
Entity Headers
Entity Headers
A Blank Line
A Blank Line
Body
Body
Request Message
Response Message
Note: Each line ends with ‘cr lf ‘ control characters.
A-PDU format (cont’d)
Request Line
Request Type
Header format
space
Request
Type
space
HTTP
version
URL
GET , HEAD, POST, PUT , TRACE , CONNECT ,
OPTION
space
Header
Name
:
Header
Value
General Header
Date , Pragma, Cache control ,Connection,
MIME-version, Upgrade, Transfer encoding
Request Header
From, Referer, User-agent, Authorization,
If-Modified-Since, Accept
Entity Header
Content-length, Content-type, Contentencoding, Last-modified, Expires, Upgrade
Response Header
Location, Age, Retry-after, Server
A-PDU format (cont’d)…
Status Line
space
HTTP
Version
space
Status Code
Status
Phrase
1xx: Informational
Continue (100) , Switching Protocols(101)
2xx: Success - action was successfully received, understood, and accepted
Created (201), Accepted (202), No Content (204), OK (200)
3xx: Redirection - further action needed to complete request
Moved Permanently (301) , Moved Temporarily (302), Not Modified (304)
4xx: Client Error - request contains bad syntax or cannot be fulfilled
Bad Request (400), Unauthorized (401), Forbidden (403), Not Found (404)
5xx: Server Error - server failed to fulfill an apparently valid request
Internal Server Error (500), Not Implemented (501), Bad Gateway (502),
Service Unavailable (503)
Variations of HTTP
• Nonpersistent connections
•
with serial connections
• with parallel connections
• Persistent connections
•
without pipelining
• with pipelining
Nonpersistent (HTTP /1.0 default)
Client
Server
SYN
3-way
handshake
SYN-ACK
ACK
GET web page HTTP/1.0
Get web page
OK
Web page
Web page
transferred
Client parses
HTML web
page
FIN
Ack
Data
Connection
close
1.Found referenced object
“Image 1”
2. Found referenced object
“Image 2”
FIN
ACK
Nonpersistent (cont’d)
Client
Server
SYN
SYN-ACK
3-Way
Handshake
ACK
GET image1 HTTP/1.0
Get image1
Image1
OK
Image 1
Transferred
FIN
Connection
close
ACK
FIN
ACK
Client
Server
SYN
3-Way
Handshake
SYN-ACK
ACK
GET image2 HTTP/1.0
OK
Image 2
Transferred
FIN
Connection
close
ACK
FIN
ACK
Get image2
Image2
Ack
Data
Key points
 Connection does not persist for other objects
 Connections are sequential
Rough calculation for number of RTTS
Client
Server
Web Page
Can we reduce the number of RTTS?
Image 1
Image 2
Delay due to connection request/handshake
Time delay in RTTs = 6
Delay Due to HTML Page Request
Delay Due to Object Request
Nonpersistent with parallel connections
( browser dependent)
Client
Server
SYN
SYN-ACK
3-Way
Handshake
ACK
GET web page HTTP/1.0
Get web page
Web page
OK
Web page
Client parses
Transferred
HTML web page
FIN
1. Referenced object
“Image 1”
2. Referenced object Connection close
“Image 2”
ACK
FIN
ACK
Parallel connections
Client
Client
SYN
SYN
3-Way
Handshake
Server
Server
3-Way
Handshake
SYN-ACK
SYN-ACK
ACK
GET image2 HTTP/1.0
GET image1 HTTP/1.0
OK
Image 1
Transferred
Get image2
Get image1
Image1
OK
Image 2
Image2
Transferred
FIN
FIN
Connection
close
ACK
FIN
ACK
Connection
close
ACK
FIN
Ack
ACK
Data
Rough calculation
Client
Server
Web page
Image1 &
Image2
Time delay in RTTs = 4
Delay due to connection request/handshake
Delay due to HTML page request
Delay due to object request
Disadvantages:
• Overhead of multiple TCP connections.
• A busy server could end up with lots of connections in the ‘TIME-
WAIT’ state
• Rarely does each connection get past the ‘slow-start’ region
• Failure to use the full end-to-end available bandwidth
• Extra time opening connections increases user-perceived latency
Persistent without pipelining
Client
3-Way
Handshake
Web page
Transferred
Server
SYN
SYN-ACK
GET web page HTTP/1.1
Get web page
OK
Get image2
Image2
OK
Image 2
Web
Transferred
page
Timer started
Timer started
OK
GET image1 HTTP/1.1
Image 1
Transferred
GET image2 HTTP/1.1
Timer starte
Time Out
Get image1
Image1
FIN
Timer started
Connection
close
ACK
FIN
ACK
Ack
Note: 1) Requests are sequential
2) Timer is at application layer
Data
Rough calculation
Client
Server
Web page
Image1
Image2
Time delay in RTTs = 4
Delay due to connection request/handshake
Delay due to HTML page request
Delay due to object request
Persistent with pipelining
Client
3-Way
Handshake
Web page
Transferred
Server
SYN
SYN-ACK
GET webpage HTTP/1.1
OK
GET image1 HTTP/1.1
Get web
page
GET image2 HTTP/1.1
ACK
ACK
Web
page
Get
image1
Get
image2
Back to back requests
OK
Client parses
Image 1
web page;
Gets Image 1
Gets Image 2
Image 1
Image 2
OK
Image 2
Timer started
Time Out
Note: Requests are
serviced in order
Timer started
FIN
ACK
FIN
Connection
close
ACK
Ack
Data
Rough calculation
Client
Server
Web page
24
Image1 &
Image2
Time delay in RTTs = 3
Delay due to connection request/handshake
Delay due to HTML page request
Delay due to object request
Advantages:
• Fewer connections
• Reduced network traffic
• CPU time is saved in routers and hosts
• Less overhead for the servers
• Reduced perceived latency for clients on subsequent requests
• Either client or server can close the connection
Disadvantages:
• Connections stay open longer at the server
Network Latency (seconds)
Experimental Results
(NP HTTP/1.0) without parallel connections
(Persistent without pipelining)
(Persistent with pipelining)
Number of in lined images
Figure 6-1: Latencies for a remote server, image size = 2544 bytes
Network Latency (seconds)
Experimental Results (cont’d)
(NP HTTP/1.0) without parallel connections
(Persistent without pipelining)
(Persistent with pipelining)
Number of in lined images
Figure 6-2: Latencies for a remote server, image size = 45566 bytes
Questions?
Thanks
Example Of Request/Response
Lets have a live demo!
• telnet cis.poly.edu 80
• GET /~ross/ HTTP/1.1
Host: cis.poly.edu