CSC311 Final
no loss, elastic, no
Indicate whether Email can tolerate data loss, the required throughput (or inelastic), and if it is time sensitive. (provide required time if so).
No loss, elastic, no
Indicate whether FTP can tolerate data loss, the required throughput (or inelastic), and if it is time sensitive. (provide required time if so).
no loss, elastic (few kbps), no
Indicate whether Web documents can tolerate data loss, the required throughput (or inelastic), and if it is time sensitive. (provide required time if so)
loss-tolerant; few kbps-10kbps; yes: 100s of msec
Indicate whether interactive games can tolerate data loss, the required throughput (or elastic), and if it is time sensitive (provide required time if so).
loss-tolerant; audio: few kbps-1Mbps video: 10kbps-5Mbps; yes: 100s of msec
Indicate whether internet telephony/video conferencing can tolerate data loss, the required throughput (or elastic), and if it is time sensitive (provide required time if so).
no loss, elastic, yes and no
Indicate whether smartphone messaging can tolerate data loss, the required throughput (or inelastic), and if it is time sensitive. (provide required time if so).
loss-tolerant; audio: few kbps-1Mbps video: 10kbps-5Mbps; yes: few seconds
Indicate whether streaming stored audio/video can tolerate data loss, the required throughput (or elastic), and if it is time sensitive (provide required time if so).
Stateful
Is FTP stateful or stateless?
Stateless
Is HTTP a stateless or stateful protocol?
persistent
Is the control connection for FTP persistent or non-persistent?
Non-persistent
Is the data connection for FTP persistent or non-persistent?
status line, header line, entity body
3 sections in the HTTP response message
Confidentiality
A transport protocol can provide___by transmitting encrypted data
socket
The interface between the application process and the transport layer protocol
specifies the browser type that is making the request to the server
User agent header line
a network entity that satisfies HTTP requests on the behalf of an origin Web server. Has its own disk storage and keeps copies of recently requested objects in this storage.
Web cache (proxy server)
Connection oriented, reliable data transfer, congestion control
What Characteristics and services belong to TCP?
header line in HTTP response, header line in HTTP request, file kept on user's end system, back-end database at the web site
What are the 4 components of cookie technology and what are their locations?
Reliable data transfer, throughput, timing, security
What are the services that transport layer protocol can offer to applications?
indicates that the user prefers a certain language version, if such an object exists on the server, otherwise, default is used.
accept language header
400
bad request
browser tells the server what to do after sending an object
connection header line
the number of bytes in the object being sent
content-length header field
the type of the object in the entity body
content-type header field
time and date when the HTTP response was created and sent by the server
date header line
DELETE
deletes an object in the URL field
indicates the message what server the message was generated by
server header field
identification number for the cookie
set-cookie header
POST
submits data (input) to be processed to a specified resource
header lines
the lines following the request line of an HTTP request message
HTTP, TCP
What is the application layer protocol and underlying transport protocol for web?
Persistent connections with pipelining. Typically the HTTP server utilizes a configurable timeout interval.
What is the default mode of HTTP?
Control connection
What is used for sending information between the two hosts — information such as user identification, password, commands to change remote directory, and commands to put and get files in FTP?
Data connection
What is used to actually send files in FTP?
Control, data
What kind of connections does FTP use when transferring a file?
The server must associate the control connection with a specific user account, and the server must keep track of the users current directory as the user wanders about the remote directory tree
What must FTP keep track of?
HTTP, SMTP
What protocols send their control information in band?
FTP
What protocols send their control information out of band?
UDP, TCP
What two transport protocols are made available to applications by the Internet?
when a web site wants to identify users, either to restrict user access or to serve content as a function of the user identity
When are cookies used by an HTTP web server?
indicates time and date when object was last modified
last-modified header field
301
moved permanently
404
not found
GET
requests object from a specified resource
HEAD
same as GET but returns only HTTP headers and no object
Elastic applications
Applications that can make use of as much or as little throughput as happens to be available
bandwidth-sensitive applications
Applications that have throughput requirements
FTP user agent
Deezer interacts with FTP through a _____
Application layer protocol
Define how an applications processes running on different end systems pass messages to each other
Secure Sockets Layer (SSL)
Enhancement of TCP that provides critical process to process security services including encryption data integrity and endpoint authentication
505
HTTP version not supported
specifies the host on which the object resides
Host header line
By sending messages into sockets
How do network processes communicate with each other?
Pick the protocol with services that best match your application's needs
How do you select a transport protocol to use?
Client side first initiates a control TCP connection with the server side on server port number 21. When the server side receives a command for a file transfer over the control connection, the server-side initiates a TCP data connection to the client side.
How does FTP work?
The HTTP client first initiates a TCP connection with the server. Once the connection is established, the browser and the server processes access TCP through their socket interfaces.
How does HTTP initiate and access TCP?
Implemented in client and server, executing on different end systems, Client server communicate to each other by exchanging HTTP messages
How does HTTP work?
Sending process passes cleartext data to SSL socket; SSL in sending host encrypts the data and passes it to TCP socket; encrypted data travels over Internet to the receiving process TCP socket; receiving socket passes encrypted data to SSL which decrypts the data; SSL passes clear text data through SSL socket to receiving process
How does SSL work?
the user provides the hostname of the remote host, causing the FTP client process in the local host to establish a TCP connection with the FTP server process in the remote host. The user then provides the user identification and password, which I sent over the TCP connection as part of FTP commands.
How does a user gain access to FTP?
200
OK
HTTP does not need to worry about lost data as that is TCP's job
What is the advantage of a layered architecture that we can see from HTTP?
Throughput
Rate at which the sending process can deliver bits to the receiving process
Non-persistent connections
Request response pairs are sent over separate TCP connections
Persistent Connection
Request response pairs are sent over the same TCP connection
SMTP, TCP
What is the application layer protocol and underlying transport protocol for email?
FTP, TCP
What is the application layer protocol and underlying transport protocol for file transfer?
SIP or proprietary; UDP or TCP
What is the application layer protocol and underlying transport protocol for internet telephony
Telnet, TCP
What is the application layer protocol and underlying transport protocol for remote terminal access?
HTTP, TCP
What is the application layer protocol and underlying transport protocol for streaming multimedia?
1. The HTTP client process initiates a TCP connection to the server on port number 80. There will be a TCP socket at the client and the TCP socket at the server. 2. The HTTP client sends an HTTP request message to the server via socket the request message includes the path name. 3. The HTTP server process received the request message from it's socket, retrieves the object from its storage, encapsulates the object in an HTTP response message, and sends the response message to the client via its socket. 4. The HTTP server process tells the TCP to close the TCP connection (doesn't close yet). 5. The HTTP client receives the response message. The TCP connection terminates. The message indicates that the encapsulated object is an HTML file. The client extracts the file from the response message, examines the HTML file, and finds references to the 10 JPEG objects. 6. The first four steps are then repeated for each of the referenced JPEG objects
What are the steps for HTTP with a non-persistent connection given a website consisting of a base HTML file and 10 JPEG images?
Server leaves the TCP connection open after sending a response. Subsequent request and responses between the same client server can be sent over the same connection
What are the steps for HTTP with persistent connections?
1. The browser establishes a TCP connection to the Web cache and sends an HTTP request for the object to the Web cache. 2. The web cache checks to see if it has a copy of the object stored locally. If it does, the web cache returns the object within an HTTP response message to the client browser 3. If the web cache does not have the object, the Web cache opens a TCP connection to the origin server. The web cache then sends an HTTP request for the object into the cache-to-server TCP connection. After receiving this request, the origin server sends this object within an HTTP response to the web cache.
What are the steps for a browser requesting an object using web cache?
1. Request is sent to Amazon web server. 2. Server creates unique id and creates an entry in back-end database that is indexed by the id 3. Server responds to client, including the id number in the set-cookie header. 4. Client receives response message and appends line to the special cookie file specifying the hostname and the cookie id in the set-cookie header 5. Every subsequent request from the client now includes the cookie id extracted from the cookie file under the cookie header 6. web browser receives request and accesses the database for the specified id
What are the steps for keeping user state with cookies?
Email, file transfer, web transfer
What are three examples of elastic applications?
Can substantially reduce the response time for a client request, can substantially reduce traffic on an institutions access link to the Internet. By reducing traffic, the institution does not have to upgrade bandwidth as quickly, thereby reducing costs.
What are two advantages of web cache?
Significant burden can be placed on the web server (TCP buffers must be allocated and variables must be kept in both the client and server for each of the TCP connections), Each object suffers a delivery delay of two RTTs (one to establish the connection and one to request and receive an object)
What are two cons of non-persistent connections?
Apache, Microsoft Internet information server
What are two examples of popular Web servers?
Data integrity, end-point authentication
What are two other security services that a transport protocol can provide besides confidentiality?
Connectionless, Unreliable data transfer
What characteristics and services does UDP offer?
Two parallel TCP connections
What does FTP used to transfer a file?
Defines how web clients request webpages from Web servers and how servers transfer webpages to clients
What does HTTP do?
The sending and receiving processes can both send messages over the connection at the same time
What does a full duplex connection insinuate?
The total number of simultaneous session
What does keeping track of state information for each ongoing user session constrain in FTP?
Using the same connection for both control and main data
What does sending control information in band mean?
Using a separate control connection from the main data
What does sending control information out-of-band mean?
Throttles sending process when network is congested, Attempt to limit each TCP connection to its fair share of bandwidth
What does the TCP congestion control mechanism do in summary?
method, url, HTTP version
What fields are included in the request line?
7-bit ASCII format
What format are FTP commands sent across the control connection?
The types of messages exchanged, the syntax of the various message types, the semantics of the fields, rules for determining when and how a process sends messages and responds to messages
What four things are defined by an application layer protocol?
Web browsers
What implement the client side of HTTP?
Web servers
What implements the server side of HTTP?
Closing a connection when it isn't used for a certain time
What is a configurable time out interval?
A server maintains no information about the clients
What is a stateless protocol?
Can substantially reduce web traffic in the Internet as a whole, thereby improving performance for all applications.
What is an advantage the utilization of Web Cache brings to the internet as a whole?
carriage return and line feed, last line followed by additional carriage return and line feed
What is at the end of each line in an HTTP request and response message?
Request for objects can be made back to back without waiting for replies to pending requests
What is pipelining?
The time it takes for a packet to travel from client a server and then back to the client
What is round-trip time?
request line
first line of an HTTP request message
PUT
uploads an object to a specific path specified in URL field
protocol version, status code corresponding status message
what are the 3 sections of the status line in an HTTP response message?