CS 6250 Quiz 12 (All Quizzes) 2026/2027 Latest Update | Verified Questions and Correct Answers | Complete Study Guide – Georgia Institute of Technology

CS 6250 Quiz 12 (All Quizzes) 2026/2027 Latest Update | Verified Questions and Correct Answers | Complete Study Guide – Georgia Institute of Technology 2026/2027 | GRADED A+ | 100 out of 100 Question: When streaming stored multimedia applications, the user must download first the entire content before it can start playing. (T/F) Answer False Question: With streaming stored multimedia applications, the user can pause, fast forward, skip ahead the audio/video. (T/F) Answer False Question: Which of the following applications is the least sensitive to network delays? Streaming video VoIP Interactive games File Transfer Answer File Transfer Question: Which of the following applications is the least tolerant to packet losses? Streaming video VoIP Interactive games File Transfer Answer File Transfer Question: What are the consequences of using TCP instead of UDP for VoIP applications? Select all that apply. Less packet loss More packet loss Less end-to-end delay. More end-to-end delay Answer Less packet loss More end-to-end delay Question: Which of the following are QoS metrics for VoIP applications? Select all that apply. End-to-end delay Jitter Packet loss Available bandwidth Answer End-to-end delay Jitter Packet loss Question: In VoIP applications, increased packet jitter results in increased end-to-end delay. (T/F) Answer True Question: Which of the following has an impact on packet jitter? Encoding delay Decoding delay The type of multimedia application Network conditions such as buffer sizes, queueing delays, network congestion levels Answer Network conditions such as buffer sizes, queueing delays, network congestion levels Question: In VoIP applications, we have a harsher definition for packet loss, as we consider a packet to be lost if it never arrives or if it arrives after its scheduled playout. (T/F) Answer True Question: With Forward Error Concealment we also transmit redundant data that can be used for reconstructing the stream at the receiver's side. This approach to error recovery can lead to more bandwidth consumption. (T/F) Answer True Question: With interleaving we mix chunks of audio together so we avoid scenarios where consecutive chunks are lost. This approach can lead to increased latency. Answer True Question: Which transport-level protocol is preferred for video content delivery? Answer TCP Question: What are the characteristics of good quality of experience from the user's perspective? Select that apply. Low or zero re-buffering High video quality Low video quality variations Low start up latency Low or zero re-buffering Answer High video quality Low video quality variations Low start up latency Question: With throughout-based rate adaption, our goal is to have a buffer-filling rate that is greater than the buffer-depletion rate. Answer True Question: With rate-based adaption, when the bandwidth changes rapidly, the player takes some time to converge to the right estimate of the bandwidth, which can lead to overestimation of the future bandwidth. (T/F) Answer True Question: Having a single server for providing Internet content has the following disadvantages: Single point of failure. Bandwidth waste in high demand for the same content. Scalability issues. Potentially big geographic distance between Internet hosts/users and the server. Answer Bandwidth waste in high demand for the same content. Scalability issues. Potentially big geographic distance between Internet hosts/users and the server. Question: One of the advantages of using CDNs is that the routing protocols they use take important aspects into consideration, such as congestion, latency, etc., in order to best deliver the content to the Internet users. (T/F) Answer False Question: There are several factors that can make a CDN network unreliable, such as misconfigured routers, power outages, malicious attacks or natural disasters. (T/F) Answer True As the Internet evolves, the topology of the ISPs has become flatter, and the number of IXPs increases as the time progresses due to the services they offer and the lower costs for the ISPS. (T/F) Answer True The major drawback of the "Enter Deep" approach is that, if one server is lost, that geographic area will experience a higher delay and lower throughput. (T/F) Answer False When using CDN servers for content delivery, there is more overhead than when using the traditional approach. (T/F) Answer True For a CDN to deliver content to an Internet user, a cluster is mapped to a client first and then a server within that cluster is selected. (T/F) Answer True Picking the geographically closest cluster location for a user is always the best choice in terms of performance for content delivery. (T/F) Answer False By using consistent hashing for server selection, in the case of a server failure, the objects that the server was responsible for can be taken care of by a random server within the same ID space. (T/F) Answer False When using DNS caching, what would happen if a host A makes a request for a domain that was just previously queried by another host? Answer The local DNS server will send the request to the appropriate DNS server to fetch the IP address. The local DNS server will immediately answer the host with the IP address. The request will be forward to the root servers first. None of the above. The local DNS server will immediately answer the host with the IP address. What is the type of the following resource record: (, , ?, TTL)? A NS CNAME MX NS IP Anycast assigns the same IP address to multiple servers in order to deliver content from CDNs by using the closest server to a client based on BGP path length. (T/F) True HTTP redirection can only be used in order to share the load of content requests among servers. (T/F) False Having a single server for providing Internet content has the following disadvantages: SELECT ALL THAT APPLY Single point of failure Bandwidth waste in high demand for the same content Scalability issues Potentially big geographic distance between Internet hosts/users and the server Single point of failure Bandwidth waste in high demand for the same content Scalability issues Potentially big geographic distance between Internet hosts/users and the server There are several factors that can make a CDN network unreliable, such as misconfigured routers, power outages, malicious attacks or natural disasters. True False True The network topology of ISPs has become flatter over time, and the number of Internet Exchange Points (IXPs) has increased. True False True The major drawback of the "Enter Deep" approach is that if one server is lost, that geographic area will experience a higher delay and lower throughput. True False False When using CDN servers for content delivery, there is more overhead than when using the traditional approach. True False True For a CDN to deliver content to an Internet user, a cluster is mapped to a client first and then a server within that cluster is selected. True False True Picking the geographically closest cluster location for a user is always the best choice in terms of performance for content delivery. True False False When utilizing consistent hashing for server selection, in the event of a server failure, the responsibility for managing the objects originally handled by the failed server is transferred to a randomly chosen server within the same ID space. True False False When using DNS caching, what would happen if a host A makes a request for a domain that was just previously queried by another host? The local DNS server will send the request to the appropriate DNS server to fetch the IP address. The local DNS server will immediately answer the host with the IP address. The request will be forward to the root servers first. None of the above. The local DNS server will immediately answer the host with the IP address. What is the purpose of an NS record in DNS? To translate domain names in IP addresses To specify the mail server responsible for accepting email messages on behalf of the domain To redirect one domain to another domain To denote the authoritative name server for a domain To denote the authoritative name server for a domain IP Anycast assigns the same IP address to multiple servers in order to deliver content from CDNs by using the closest server to a client based on BGP path length. True False True HTTP redirection can only be used in order to share the load of content requests among servers. True False False 3 drawbacks to the traditional approach of providing content on the internet 1. Users are located everywhere 2. Can be popular resulting in a spike in demand and requests for same thing 3. Can be single point of failure Content distribution network Networks of multiple, geographically distributed servers and/or data centers, with copies of content (videos, but also many other types of Web content), that direct users to a server or server cluster that can best serve the user's request. Internet application challenges 1. Peering point congestion 2. Inefficient routing protocols 3. Unreliable networks. 4. Inefficient communication protocols. 5. Scalability 6. Application limitations and slow rate of change adoption. 2 major shifts that have changed the evolution of internet ecosystems 1. Large scale content delivery demand 2. Topological flattening CDN server placement approaches Deploying lots of small clusters to get as close as possible to the users, or deploying fewer but larger clusters to critical areas CDN server selection steps Cluster selection and server selection Limitations to choosing the closest geographically located cluster 1. Users may use remote LDNS 2. May not be the best choice in terms of actual end-to-end network performance. This can happen because of multiple reasons. What metric should be used for cluster selection? Network-layer metrics such as delay, available bandwidth or both. Also, application-layer metrics. Active measurements LDNS could probe multiple clusters, such as by sending a ping request to multiple clusters for monitoring the RTT and then use the "closest" server. Passive measurements The name server system in the CDN could keep a track of the performance metrics based on the current traffic conditions. What is the distributed 2 layer system? 1. coarse-grained global layer operates at larger time scale. This layer has a global view of client quality measurements. It builds a data-driven prediction model of video quality. 2. A fine-grained per-client decision layer that operates at the millisecond timescale. It makes actual decisions upon a client request. This is based on the latest (but possibly stale) pre-computed global model and up-to-date per-client state. Consistent hashing Balances load by assigning roughly the same number of content IDs, and requires relatively little movement of these content IDs when nodes join and leave the system. Servers and the content objects are mapped to the same ID space. 3 network protocols for server selection DNS HTTP redirection IP Anycast Why do we need DNS? The identifiers we have for an Internet host is the IP address and the hostname. The advantage of using hostnames is that they can be easily remembered by humans. The main disadvantage of hostnames is that they are consisting of variable characters and thus it's difficult for routers to process them. Using this system can help us translate hostnames to IP addresses. How does DNS work? 1. It provides a distributed database implemented over a hierarchy of servers. 2. It is an application layer protocol that allows hosts to query this database and provide the translation of hostnames to IP addresses. Main steps that a host takes to use DNS 1. The user host runs the client side of the DNS application 2. The browser extracts the hostname (Links to an external site.) and passes it to client side of the DNS application. 3. DNS Client sends a query containing the hostname of DNS 4. DNS Client eventually receives a reply which included IP address for the hostname 5. As soon as the host receives the IP addresses, it can initiate a TCP connection to the HTTP server located at that port at that IP What are some other services offered by DNS? Mail server/host aliasing and load distribution Why would a centralized model for DNS be bad? 1. It introduces a single point of failure. 2. It would be very difficult for a single server to handle all the volume of the querying traffic. 3. This model is based on a centralized database which cannot be close to all querying clients. This model would cause significant delays and slow performance for the clients which are geographically distant 4. Maintaining this centralized database would be a big problem as we would have to update a huge database with updates for every single host in the Internet. DNS hierarchy consists of the following servers Root DNS servers Top level domain (TLD) Servers Authoritative servers Local DNS servers DNS caching Caches the responses. This helps reduce performance delay and make it more efficient. After a server receives the DNS reply of mapping from any host to IP address, it stores this information in the Cache memory before sending it to the client. DNS Records Mappings between hostnames and IP addresses. They are contained in the DNS reply messages 4 DNS Record fields Name, value, Type, and TTL Most common type of DNS Record TYPE=A TYPE=NS TYPE=CNAME TYPE=MX: the name is the alias hostname of a mail server, and the Value is the canonical name of the email server. (, , MX) Type A DNS Record The name is a domain name and value is the IP address of the hostname. Type NS DNS Record The name is the domain name, and the value is the appropriate authoritative DNS server that can obtain the IP addresses for hosts in that domain. Type CName DNS Record The name is the alias hostname, and the value is the canonical name Type MX DNS Record The name is the alias hostname of a mail server, and the Value is the canonical name of the email server. IP Anycast Route a client to the "closest" server, as determined by BGP (Border Gateway Protocol), a routing protocol used for inter-AS routing. This is achieved by assigning the same IP address to multiple servers belonging to different clusters. Now, each of these servers will use the standard BGP to advertise this IP address. Thus multiple BGP routes for the same IP address corresponding to different cluster locations will propagate in the public Internet. HTTP Redirection Protocol Essentially, when a client sends a GET request to a server, say A, it can redirect the client to another server, say B, by sending an HTTP response with a code 3xx and the name of the new server. Enter deep CDNs place many smaller server clusters "deep" into the access networks around the world. The goal is to make the distance between a user and the closest server cluster as small as possible, which reduces the delay and increases the available throughput for each user. However, the downside to this highly distributed approach is that it is much more difficult to manage and maintain so many clusters. Bring home CDNs place fewer larger server clusters at key points (typically in IXPs, not in access networks). There's not as many server clusters to manage or maintain, so those tasks are easier, but the downside is that the users will experience higher delay and lower throughput. What role does DNS play in CDNs? Notice the interplay of the DNS request/responses, and what the user's perspective of the whole exchange is. By intercepting the requests with DNS, CDNs have the opportunity to choose where to direct users, based on location and/or current conditions. How are the metrics for cluster selection obtained? Active and passive measurements Why does DNS use a hierarchical scheme? To solve the scalability problem Iterative query process DNS The querying host is referred to a different DNS server in the chain, until it can fully resolve the request. Recursive query process DNS The querying host, and each DNS server in the chain queries the next server and delegates the query to it.