Computer networking chapter 2

2.2-12 If-Modified-Since. What is the purpose of the If-Modified-Since field in a HTTP GET request message?

To indicate to the server that the client has cached this object from a previous GET, and the time it was cached.

2.2-05 A detailed look at an HTTP GET (1). Suppose a client is sending an HTTP GET request message to a web server, gaia.cs.umass.edu. Suppose the client-to-server HTTP GET message is the following:

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2.3-1 E-mail delays. How many RTTs are there from when a client first contacts an email server (by initiating a TCP session) to when the client can begin sending the email message itself - that is following all initial TCP or SMTP handshaking required? Recall the figure below from our class notes:

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2.7-2 TCP Sockets. Which of the following characteristics below are associated with a TCP socket? Check one or more that apply.

4: A server can perform an accept() on this type of socket is the correct option. 5: When contacted, the server will create a new server-side socket to communicate with that client is the correct option. 6: Provides reliable, in-order byte-stream transfer (a "pipe"), from client to server is the correct option. 7: socket(AF_INET, SOCK_STREAM) creates this type of socket is the correct option.

2.1-2 The peer-to-peer (P2P) paradigm. Which of the characteristics below are associated with a P2P approach to structuring network applications (as opposed to a client-server approach)?

A process requests service from those it contacts and will provide service to processes that contact it. There is not a server that is always on.

2.2-01 "HTTP is stateless." What do we mean when we say "HTTP is stateless"? In answering this question, assume that cookies are not used. Check all answers that apply.

An HTTP server does not remember anything about what happened during earlier steps in interacting with this HTTP client.

2.1-3 UDP service. When an application uses a UDP socket, what transport services are provided to the application by UDP? Check all that apply.

Best effort service. The service will make a best effort to deliver data to the destination but makes no guarantees that any particular segment of data will actually get there.

2.2-09 Why Web Caching? Which of the following are advantages of using a web cache? Select one or more answers.

Caching generally provides for a faster page load time at the client, if the web cache is in the client's institutional network, because the page is loaded from the nearby cache rather than from the distant server. Caching uses less bandwidth coming into an institutional network where the client is located, if the cache is also located in that institutional network.

2.1-4 TCP service. When an application uses a TCP socket, what transport services are provided to the application by TCP? Check all that apply.

Flow Control. The provided service will ensure that the sender does not send so fast as to overflow receiver buffers. Loss-free data transfer. The service will reliably transfer all data to the receiver, recovering from packets dropped in the network due to router buffer overflow. Congestion control. The service will control senders so that the senders do not collectively send more data than links in the network can handle.

2.2-10 HTTP/2 versus HTTP/1.1. Which of the following are changes between HTTP 1.1 and HTTP/2? Note: select one or more answers.

HTTP/2 allows a large object to be broken down into smaller pieces, and the transmission of those pieces to be interleaved with transmission other smaller objects, thus preventing a large object from forcing many smaller objects to wait their turn for transmission. HTTP/2 allows objects in a persistent connection to be sent in a client-specified priority order.

2.4-01 DNS functions. Match the function of a server to a given type of DNS server in the DNS server hierarchy.

Provides authoritative hostname to IP mappings for organization's named hosts. Authoritative DNS server Replies to DNS query by local host, by contacting other DNS servers to answer the query. Local DNS server Responsible for a domain (e.g., *.com, *.edu); knows how to contact authoritative name servers. TLD servers Highest level of the DNS hierarchy, knows how to reach servers responsible for a given domain (e.g., *.com, *.edu). DNS root server

2.3-5 Which e-mail protocol? Match the functionality of a protocol with the name of the email protocol (if any) that implements that functionality.

Pushes email from a mail client to a mail server. SMTP Pulls mail from one mail server to another mail server. Neither SMTP nor IMAP does this. Pulls email to a mail client from a mail server. IMAP

2.2-03 The HTTP GET. What is the purpose of the HTTP GET message?

The HTTP GET request message is used by a web client to request a web server to send the requested object from the server to the client.

2.2-13 Cookies. What is the purpose of a cookie value in the HTTP GET request?

The cookie value itself doesn't mean anything. It is just a value that was returned by a web server to this client during an earlier interaction.

2.4-04. The local DNS server. Check all of the phrases below that state at true property of a local DNS server.

The local DNS server record for a remote host is sometimes different from that of the authoritative server for that host. The local DNS server can decrease the name-to-IP-address resolution time experienced by a querying local host over the case when a DNS is resolved via querying into the DNS hierarchy.

2.1-1 The client-server paradigm. Which of the characteristics below are associated with a client-server approach to structuring network applications (as opposed to a P2P approach)?

There is a server that is always on. There is a server with a well-known server IP address. HTTP uses this application structure.

2.7-5 socket connect(). What happens when a socket connect() procedure is called/invoked?

This procedure creates a new socket at the client, and connects that socket to the specified server.

2.3-2 Comparing and contrasting HTTP and SMTP. Which of the following characteristics apply to HTTP only (and do not apply to SMTP)? Note: check one or more of the characteristics below.

Uses a blank line (CRLF) to indicate end of request header. Uses server port 80. Operates mostly as a "client pull" protocol.

2.2-08 A detailed look at an HTTP reply. Suppose now the server sends the following HTTP response message the client:

Yes, the server will close this connection because version 1.0 of HTTP is being used, and TCP connections do not stay open persistently.

2.7-1 UDP Sockets. Which of the following characteristics below are associated with a UDP socket? Check one or more that apply.

socket(AF_INET, SOCK_DGRAM) creates this type of socket data from different clients can be received on the same socket provides unreliable transfer of groups of bytes ("a datagram"), from client to server the application must explicitly specify the IP destination address and port number for each group of bytes written into a socket