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Questions and Answers
What information does the Content-Type: header line provide in an HTTP response message?
What information does the Content-Type: header line provide in an HTTP response message?
- The type of content in the entity body. (correct)
- The number of bytes of the object being sent.
- The time when the object was created.
- The status code of the request.
Which header line is crucial for object caching in both local clients and proxy servers?
Which header line is crucial for object caching in both local clients and proxy servers?
- Last-Modified: (correct)
- Content-Length:
- Server:
- Content-Type:
What does a 301 status code indicate in an HTTP response?
What does a 301 status code indicate in an HTTP response?
- The request was successful, and information is returned.
- The client has issued a bad request.
- The server encountered an error while processing the request.
- The requested object has been permanently moved. (correct)
In an HTTP response message, which header line indicates the number of bytes in the object being sent?
In an HTTP response message, which header line indicates the number of bytes in the object being sent?
What does the Server: header line in an HTTP response message indicate?
What does the Server: header line in an HTTP response message indicate?
What is the purpose of the Last-Modified: header in an HTTP response?
What is the purpose of the Last-Modified: header in an HTTP response?
Which of the following is NOT a common status code in HTTP response messages?
Which of the following is NOT a common status code in HTTP response messages?
How is the object type indicated in an HTTP response message?
How is the object type indicated in an HTTP response message?
What is the purpose of the cookie header line in the HTTP response message?
What is the purpose of the cookie header line in the HTTP response message?
What is included in a cookie file managed by the user's browser?
What is included in a cookie file managed by the user's browser?
When does the server create an ID for a user in the backend database?
When does the server create an ID for a user in the backend database?
What role does the back-end database play in cookie technology?
What role does the back-end database play in cookie technology?
How does the user's browser access cookie data when the user returns to a site after a week?
How does the user's browser access cookie data when the user returns to a site after a week?
What does DNS primarily provide for the Internet?
What does DNS primarily provide for the Internet?
How do most users interact with DNS?
How do most users interact with DNS?
Which application layer functionality does DNS exemplify?
Which application layer functionality does DNS exemplify?
What aspect of users’ interaction does the Web significantly differ from traditional media?
What aspect of users’ interaction does the Web significantly differ from traditional media?
What is one significant advantage of the Web over traditional broadcast media?
What is one significant advantage of the Web over traditional broadcast media?
What is the response status code for a generic error indicating a request could not be understood?
What is the response status code for a generic error indicating a request could not be understood?
Which command should be used to view a response message including the base HTML file?
Which command should be used to view a response message including the base HTML file?
Which status code indicates that the requested HTTP protocol version is not supported?
Which status code indicates that the requested HTTP protocol version is not supported?
What is the correct format for an HTTP response as per the provided content?
What is the correct format for an HTTP response as per the provided content?
What is the purpose of using the HEAD method instead of the GET method?
What is the purpose of using the HEAD method instead of the GET method?
Which of the following phrases describes a 404 status code?
Which of the following phrases describes a 404 status code?
What is denoted by the CR LF sequence in an HTTP response message?
What is denoted by the CR LF sequence in an HTTP response message?
What does the HTTP server do with the request messages it receives?
What does the HTTP server do with the request messages it receives?
What protocol does HTTP/1.0 use for its underlying transport?
What protocol does HTTP/1.0 use for its underlying transport?
How does TCP ensure the reliability of data transfer for HTTP messages?
How does TCP ensure the reliability of data transfer for HTTP messages?
What happens when a client sends a message into its socket interface?
What happens when a client sends a message into its socket interface?
What is the primary role of the socket interface for the HTTP client?
What is the primary role of the socket interface for the HTTP client?
Which statement accurately reflects how the server manages client state information?
Which statement accurately reflects how the server manages client state information?
Which layer of the protocol stack is responsible for recovering from data loss during transmission?
Which layer of the protocol stack is responsible for recovering from data loss during transmission?
How do the browser and the server access TCP for communication?
How do the browser and the server access TCP for communication?
TCP provides encryption for data being transferred over the network.
TCP provides encryption for data being transferred over the network.
TLS enhances TCP by providing encryption, data integrity, and end-point authentication.
TLS enhances TCP by providing encryption, data integrity, and end-point authentication.
When using TLS, the application layer must include TLS code on both client and server sides.
When using TLS, the application layer must include TLS code on both client and server sides.
The data passed into a TLS socket is already encrypted before it reaches the TCP socket.
The data passed into a TLS socket is already encrypted before it reaches the TCP socket.
TLS operates as a separate transport protocol comparable to TCP and UDP.
TLS operates as a separate transport protocol comparable to TCP and UDP.
Cleartext passwords are securely transmitted over the Internet when using TCP without TLS.
Cleartext passwords are securely transmitted over the Internet when using TCP without TLS.
The receiving TCP socket is responsible for decrypting the encrypted data with TLS.
The receiving TCP socket is responsible for decrypting the encrypted data with TLS.
The first line of an HTTP request message is called the header line.
The first line of an HTTP request message is called the header line.
The HTTP GET method is primarily used when the browser requests an object.
The HTTP GET method is primarily used when the browser requests an object.
An HTTP request message can have a maximum of five lines.
An HTTP request message can have a maximum of five lines.
The method field in the request line can have values such as POST and PUT.
The method field in the request line can have values such as POST and PUT.
A transport-layer protocol ensures that data sent is delivered correctly and completely, known as reliable data transfer.
A transport-layer protocol ensures that data sent is delivered correctly and completely, known as reliable data transfer.
Multimedia applications require guaranteed reliable data transfer, as any data loss significantly impairs performance.
Multimedia applications require guaranteed reliable data transfer, as any data loss significantly impairs performance.
Available throughput is defined as the rate at which data can be delivered from the receiving process to the sending process.
Available throughput is defined as the rate at which data can be delivered from the receiving process to the sending process.
A transport-layer protocol can provide a service that guarantees throughput at a specified rate for applications.
A transport-layer protocol can provide a service that guarantees throughput at a specified rate for applications.
The available throughput of a network path is static and does not change over time.
The available throughput of a network path is static and does not change over time.
Transport-layer protocols are only relevant for multimedia applications and do not impact other types of applications.
Transport-layer protocols are only relevant for multimedia applications and do not impact other types of applications.
In reliable data transfer, the sending process can send data without worrying about errors in delivery.
In reliable data transfer, the sending process can send data without worrying about errors in delivery.
Loss-tolerant applications are fine with occasional data loss without a significant impairment to user experience.
Loss-tolerant applications are fine with occasional data loss without a significant impairment to user experience.
Guaranteed available throughput at a specific rate is a desirable feature for many applications.
Guaranteed available throughput at a specific rate is a desirable feature for many applications.
The transport-layer protocol is responsible for sending messages from the receiving process to the socket.
The transport-layer protocol is responsible for sending messages from the receiving process to the socket.
Choosing a transport-layer protocol is similar to selecting between different modes of travel.
Choosing a transport-layer protocol is similar to selecting between different modes of travel.
All applications can tolerate data loss without significant consequences.
All applications can tolerate data loss without significant consequences.
Reliable data transfer is one of the four dimensions of transport-layer protocol services.
Reliable data transfer is one of the four dimensions of transport-layer protocol services.
Packets can be discarded or overflow buffers, leading to data corruption during transmission.
Packets can be discarded or overflow buffers, leading to data corruption during transmission.
The Internet supports a single transport-layer protocol.
The Internet supports a single transport-layer protocol.
Packet loss only occurs when data is transmitted over wireless networks.
Packet loss only occurs when data is transmitted over wireless networks.
Timing and security are not considered when evaluating transport-layer protocols.
Timing and security are not considered when evaluating transport-layer protocols.
For most applications, timely delivery of packets is always more critical than the data being reliably delivered.
For most applications, timely delivery of packets is always more critical than the data being reliably delivered.
The choice of a transport-layer protocol can significantly affect the performance of an application.
The choice of a transport-layer protocol can significantly affect the performance of an application.
A socket is the interface between the application layer and the transport layer within a host.
A socket is the interface between the application layer and the transport layer within a host.
The application developer has complete control over the transport-layer side of the socket.
The application developer has complete control over the transport-layer side of the socket.
The socket provides a programming interface for network applications built by the application developer.
The socket provides a programming interface for network applications built by the application developer.
What is the primary function of the cookie header line in the HTTP request message?
What is the primary function of the cookie header line in the HTTP request message?
Which component of cookie technology is maintained entirely on the client side?
Which component of cookie technology is maintained entirely on the client side?
What does the back-end database primarily do within cookie technology?
What does the back-end database primarily do within cookie technology?
How does a server utilize the cookie ID for user requests after a significant time has passed?
How does a server utilize the cookie ID for user requests after a significant time has passed?
Which of the following best describes the initial action taken by a server when a client interacts for the first time using cookies?
Which of the following best describes the initial action taken by a server when a client interacts for the first time using cookies?
Which of the following best describes the role of HTTP within the Web application?
Which of the following best describes the role of HTTP within the Web application?
In terms of complexity, how does electronic mail differ from web applications like HTTP?
In terms of complexity, how does electronic mail differ from web applications like HTTP?
How is the Web application defined beyond merely the use of HTTP?
How is the Web application defined beyond merely the use of HTTP?
What distinguishes application software from network-core device software?
What distinguishes application software from network-core device software?
Why are servers typically housed in data centers?
Why are servers typically housed in data centers?
What is a primary requirement when developing network applications?
What is a primary requirement when developing network applications?
What role does the network layer play in the context of application software?
What role does the network layer play in the context of application software?
What is a consequence of confining application software to end systems?
What is a consequence of confining application software to end systems?
How does the relationship between the browser program and web server program function?
How does the relationship between the browser program and web server program function?
What does the User-agent: header line signify in an HTTP request?
What does the User-agent: header line signify in an HTTP request?
Why is the Accept-language: header important in an HTTP request?
Why is the Accept-language: header important in an HTTP request?
What effect does including the Connection: close header line have?
What effect does including the Connection: close header line have?
What does the presence of a persistent connection allow in an HTTP context?
What does the presence of a persistent connection allow in an HTTP context?
How does the HTTP request format generally appear?
How does the HTTP request format generally appear?
What is the primary purpose of the Connection: close header in an HTTP request?
What is the primary purpose of the Connection: close header in an HTTP request?
What defines the message types in an application-layer protocol?
What defines the message types in an application-layer protocol?
What aspect of an application-layer protocol ensures that messages are understood correctly?
What aspect of an application-layer protocol ensures that messages are understood correctly?
Which of the following describes the semantics of fields in an application-layer protocol?
Which of the following describes the semantics of fields in an application-layer protocol?
What is a primary feature of the Web as a client-server application?
What is a primary feature of the Web as a client-server application?
Which statement accurately describes an application-layer protocol's rules?
Which statement accurately describes an application-layer protocol's rules?
What determines the fields in a message as per an application-layer protocol?
What determines the fields in a message as per an application-layer protocol?
Which characteristic is often typical of proprietary application-layer protocols?
Which characteristic is often typical of proprietary application-layer protocols?
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Study Notes
HTTP Response Messages
- The
Server:header line identifies the web server (likeUser-agent:in HTTP requests). Last-Modified:header shows the object's creation or last modification time; crucial for caching.Content-Length:header specifies the object's size in bytes.Content-Type:header indicates the object type (e.g., HTML), not relying on file extensions.- HTTP response message format: status line (version, status code, phrase), header lines, blank line, entity body.
- Common status codes:
200 OK: Successful request.301 Moved Permanently: Object moved; new URL inLocation:header.400 Bad Request: Server couldn't understand the request.404 Not Found: Requested document doesn't exist.505 HTTP Version Not Supported: Server doesn't support the HTTP version.
- To see an HTTP response, use
telnetto connect to a web server, send a request (e.g.,GET), and examine the response. UsingHEADinstead ofGETonly retrieves headers, not the object itself. - HTTP uses TCP for reliable data transfer, ensuring message integrity. This is handled by lower layers, making HTTP independent of loss or reordering concerns.
- Servers are stateless; they don't remember past interactions with clients.
Web and HTTP
- Before the early 1990s, internet use was primarily among researchers, for tasks like remote login, file transfer, and email.
- The World Wide Web's arrival in the early 1990s made the internet accessible to the general public.
- The Web's on-demand nature, unlike traditional broadcast media, is a key appeal, offering users content when they want it.
Cookies
- Four components of cookie technology:
- Cookie header line in HTTP response messages.
- Cookie header line in HTTP request messages.
- Cookie file on the user's system, managed by their browser.
- Backend database at the website.
- Example: When a user first interacts with a site, the server creates an ID and stores it in the database and sends a cookie to the client. Subsequent visits use cookies to identify the user and retrieve their information stored in the database.
TCP Security and TLS
- TCP and UDP do not inherently provide encryption; data sent is transmitted in plain text.
- Transport Layer Security (TLS) enhances TCP by adding encryption, data integrity, and endpoint authentication.
- TLS is not a separate transport protocol like TCP or UDP; it's an application-layer enhancement.
- Applications using TLS include TLS code (libraries) in both client and server sides.
- TLS uses a socket API similar to the standard TCP socket API. Data is encrypted by TLS before being passed to the TCP socket, and decrypted by TLS upon receiving.
Sockets and Transport Layer Protocols
- A socket is the interface between the application layer and transport layer within a host. It's also the Application Programming Interface (API) between the application and the network.
- Application developers control the application-layer side of the socket but have limited control over the transport layer. The only real controls are the choice of transport protocol and setting a few transport-layer parameters (like buffer sizes).
- Applications choose transport protocols (like TCP or UDP) based on which services best meet their needs. This is analogous to choosing train vs. airplane travel.
Transport Layer Services
- Four key services transport-layer protocols can offer: reliable data transfer, throughput, timing, and security.
Reliable Data Transfer
- Reliable data transfer ensures data sent by an application arrives correctly and completely. This is critical for applications where data loss is unacceptable (e.g., email, file transfer, finance).
- Some applications (e.g., multimedia) can tolerate data loss.
Throughput
- Throughput is the rate at which data is delivered. It can fluctuate due to shared network bandwidth.
- A guaranteed throughput service means a transport protocol ensures data is delivered at a minimum specified rate, which is important for real-time applications (e.g., Internet telephony).
HTTP Message Format
- HTTP messages are in ASCII text and consist of header lines and a request line (for requests).
- A request line has three fields: method (e.g., GET, POST), URL, and HTTP version.
- Header lines provide additional information (e.g., host, user-agent, accept-language).
- GET method is commonly used to request an object specified in the URL.
Network Application Development
- Network applications involve programs running on different end systems that communicate over a network.
- Examples include web applications (browser and web server) and video-on-demand services (client app and server).
- Application software runs on end systems, not network core devices (routers, switches).
- Application-layer protocols define how applications on different systems exchange messages. They specify message types, syntax, semantics, and communication rules.
- Some protocols are public (e.g., HTTP), while others are proprietary (e.g., Skype).
The Web and HTTP
- The Web is a client-server application using HTML, browsers, servers, and HTTP.
- HTTP defines message format and sequence between browser and server. It's a crucial part, but not the only component of the web application.
- Other applications like Netflix utilize multiple components, including servers, clients, and application-level protocols (e.g., DASH) to manage various functions and message exchanges.
HTTP Request Message Example
- The example HTTP request includes header lines providing information about the host, connection type, user agent, and preferred language.
- The
Host:header line specifies the requested server (e.g.,ebay:8734). While a TCP connection exists, this header is critical for web proxy caches. - The
Connection: closeline signals the browser's preference for the server to close the connection after sending the requested object. - The
User-agent:header identifies the browser type (e.g., Mozilla/5.0 for Firefox). Servers can tailor responses based on the user agent. - The
Accept-language:header indicates the user's preferred language (e.g., French). This is one example of content negotiation in HTTP.
Cookies and User State
- Cookie technology involves four components:
- A cookie header line in the HTTP response message.
- A cookie header line in the HTTP request message.
- A cookie file on the user's end system, managed by the browser.
- A backend database at the website.
- Cookies maintain user state across multiple interactions with a website. For instance, using Amazon as an example, a unique ID for a user is generated and stored upon their first visit, allowing the website to identify a returning user.
Key Applications in the Book
- The book focuses on key network applications: the Web, email, directory service, video streaming, and P2P applications.
- The Web serves as a primary example due to its popularity and the relative simplicity of its protocol (HTTP).
- Email is presented as a complex application because it uses multiple application-layer protocols.
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