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Networking Theory
| Question | Answer |
|---|---|
| True or False: For a web page with text and three images, the client sends one request and receives four responses. | False. The client sends one request for the base HTML file and then one request for each of the three images, resulting in four requests and four responses. |
| Can two distinct web pages be sent over the same persistent HTTP connection? | Yes, this is a key feature of persistent connections, which reduces the overhead of establishing new TCP connections for each object. |
| With nonpersistent HTTP connections, is it possible for a single TCP segment to carry two distinct HTTP request messages? | No, because each nonpersistent connection is established for a single request/response pair and then closed. |
| What information does the `Date:` header in an HTTP response message indicate? | It indicates the time and date when the server generated the response, not when the object was last modified. |
| What HTTP status code and phrase indicate that a server successfully found the requested document? | The status code `200` and the phrase `OK`. |
| Which header in an HTTP response specifies when the document was last modified? | The `Last-Modified:` header. |
| Which header in an HTTP response indicates the size of the document being returned in bytes? | The `Content-Length:` header. |
| How does a server signal its agreement to a persistent connection in an HTTP/1.1 response? | By including the `Connection: Keep-Alive` header in its response. |
| In a shared link scenario, why do parallel connections help a single user get web pages more quickly? | Because by opening more connections, the user can obtain a larger share of the available link bandwidth compared to users with fewer connections. |
| What is the key difference between the `MAIL FROM:` command in SMTP and the `From:` header in an email message? | `MAIL FROM:` is part of the SMTP protocol used for message transfer between servers, while `From:` is a header within the mail message body itself, displayed to the user. |
| How does the SMTP protocol mark the end of a message body? | It uses a line containing only a single period (`.`). |
| How does HTTP indicate the length of a message body? | It uses the `Content-Length:` header field to specify the exact size in bytes. |
| Why can't HTTP use the same end-of-message marker as SMTP (a line with a single period)? | Because HTTP messages can contain binary data, which might naturally include a sequence of bytes corresponding to a line with a single period, whereas SMTP messages are restricted to 7-bit ASCII. |
| In the DNS hierarchy, how does a higher-level server handle a query for a domain it doesn't manage? | It delegates the query by sending back the name of a lower-level DNS server that is authoritative for that domain. |
| How can you use the `dig` tool to determine if an external website was recently accessed from a computer in your department? | Query the local DNS server for the website; if it was accessed recently, its address will be cached, resulting in a query time of nearly 0 ms. |
| The Internet can be described from a 'nuts and bolts' view as a network of _____, _____, and _____ managed by organizations. | devices, routers, links |
| In network terminology, what are end systems also called? | Hosts. |
| What is the function of protocols like HTTP, TCP, and IP in the Internet? | They control the sending and receiving of messages among network entities. |
| What organizations are responsible for developing Internet standards like RFCs? | The Internet Engineering Task Force (IETF), which publishes documents called Request for Comments (RFCs). |
| From a 'services' perspective, what does the Internet provide to applications? | It provides an infrastructure and a programming interface that allows distributed applications to send and receive data. |
| What three things do network protocols define? | The format of messages, the order of messages sent and received, and the actions taken on message transmission or receipt. |
| What components make up the 'network edge'? | Hosts, which are divided into clients and servers. |
| What components make up the 'network core'? | A mesh of interconnected routers that form a network of networks. |
| What is the primary characteristic of a Digital Subscriber Line (DSL) access network? | It uses existing telephone lines to provide a dedicated connection to the telephone company's central office. |
| What does the term 'HFC' stand for in the context of cable access networks? | Hybrid Fiber Coax. |
| Why are cable internet connections typically asymmetric? | They provide a much higher downstream transmission rate (to the user) than upstream transmission rate (from the user). |
| What technology provides symmetric, high-speed internet access directly to a residence using optical signals? | Fiber to the Home (FTTH). |
| What is a major disadvantage of geosynchronous satellite internet service compared to terrestrial services? | High propagation delay (e.g., 270 msec end-to-end) due to the great distance to the satellite. |
| Within a local area, a _____ connects end systems to a router. | base station or access point |
| What is the term for breaking down a large application message into smaller chunks for network transmission? | Packetization, where the chunks are known as packets. |
| What is the formula for calculating packet transmission delay? | $Transmission_Delay = L / R$, where L is packet length in bits and R is the link transmission rate in bits per second. |
| Signals propagating in solid media like copper or fiber are known as _____ media. | guided |
| What is the local action a router performs to move an arriving packet from an input link to the correct output link? | Forwarding (or switching). |
| What is the global action of determining the end-to-end paths that packets take through the network? | Routing. |
| What fundamental principle of packet-switching dictates that a router must receive an entire packet before it can begin sending it on the next link? | Store-and-forward. |
| When does packet queueing occur at a router's output link? | Queueing occurs when the packet arrival rate to the link exceeds the link's transmission rate. |
| What happens to a packet that arrives at a router when the output buffer for its destination link is already full? | The packet is dropped (lost). |
| What is the core principle of circuit switching? | End-to-end resources (e.g., bandwidth) are allocated to and reserved for a 'call' for its entire duration. |
| What does FDM stand for, and how does it work? | Frequency Division Multiplexing; it divides the electromagnetic spectrum into narrower frequency bands, allocating one band to each call. |
| What does TDM stand for, and how does it work? | Time Division Multiplexing; it divides time into slots and allocates periodic time slots to each call. |
| Packet switching is particularly well-suited for _____ data, where users have data to send only some of the time. | bursty |
| What are the four sources of total nodal delay for a packet at a router? | Processing delay, queueing delay, transmission delay, and propagation delay. |
| Term: Nodal Processing Delay (`d_proc`) | The time required for a router to check a packet's header for bit errors and determine its output link. |
| What is the formula for calculating propagation delay? | $Propagation_Delay = d / s$, where d is the length of the physical link and s is the propagation speed. |
| In the context of network performance, what is traffic intensity? | A ratio, calculated as $La/R$, that represents the relationship between the average packet arrival rate and the link's transmission capacity. |
| What happens to the average queueing delay as the traffic intensity ($La/R$) approaches 1? | The average queueing delay grows very large, approaching infinity. |
| What networking utility provides delay measurements from a source to each router along an end-to-end Internet path? | The traceroute program. |
| Term: Throughput | The rate, in bits per time unit, at which bits are actually being transferred from a sender to a receiver. |
| What is a 'bottleneck link'? | The link on an end-to-end path that has the minimum capacity, thus constraining the overall throughput. |
| What is 'packet sniffing'? | A network attack where an attacker uses a promiscuous network interface to read and record all packets passing through a broadcast medium. |
| Term: IP Spoofing | An attack where a malicious actor injects a packet into the network with a false source IP address. |
| What is the goal of a Denial of Service (DoS) attack? | To make network resources, like a server or bandwidth, unavailable to legitimate users by overwhelming them with bogus traffic. |
| The primary benefit of using a layered architecture in networking is _____ which eases maintenance and updating of the system. | modularization |
| What is the function of the Application Layer in the Internet protocol stack? | To support network applications and their specific protocols, such as HTTP for the web or SMTP for email. |
| What is the primary function of the Transport Layer? | To provide for process-to-process data transfer, using protocols like TCP and UDP. |
| Which layer is responsible for routing datagrams from a source host to a destination host across multiple networks? | The Network Layer, using the IP protocol. |
| What is the function of the Link Layer? | To handle data transfer between neighboring network elements (e.g., from a host to a router). |
| The _____ layer is responsible for the physical transmission of bits over a wire or wireless medium. | Physical |
| Term: Encapsulation | The process of adding a layer's header information to the data unit received from the layer above it as data moves down the protocol stack. |
| What is the PDU (Protocol Data Unit) called at the Application Layer? | Message. |
| An application-layer message encapsulated by the Transport Layer is called a _____. | segment |
| A transport-layer segment encapsulated by the Network Layer is called a _____. | datagram |
| A network-layer datagram encapsulated by the Link Layer is called a _____. | frame |
| In an HTTP request message, what indicates the end of the header lines? | A blank line, consisting of a carriage return and line feed character (\r\n). |
| An HTTP response with status code `301 Moved Permanently` means the requested object has moved and its new address is in the _____ field. | Location: |
| What does the HTTP status code `404 Not Found` signify? | The requested document could not be found on the server. |
| What is the primary purpose of web caching? | To reduce response time for client requests and reduce traffic on an institution's access link by storing copies of objects closer to the client. |
| In Python socket programming, what function is used to create a new socket? | The `socket()` function from the socket library. |
| For a UDP server in Python, which socket method is used to associate the socket with a specific port number? | The `bind()` method. |
| In Python, which socket type constant is used to create a UDP socket? | `SOCK_DGRAM`. |
| In Python, which socket type constant is used to create a TCP socket? | `SOCK_STREAM`. |
| Which method must a TCP client call to initiate a connection with a server? | The `connect()` method. |
| A TCP server uses a 'welcoming socket'. Which method does it call on this socket to wait for and accept an incoming connection request? | The `accept()` method. |
| When a TCP server's `accept()` method returns, what does it provide? | A new connection socket dedicated to communicating with the specific client that just connected, and the client's address. |
Created by:
sethr06