Exampromax - Stuvia US 2025/2026
1
CS 6250 TEST 1 Questions and Answers and
Graded
How does the "narrow waist" allow a large variety of different protocols to
be used on the Internet?
Correct Answer
Standardized traffic routing between networks (all use IP),
opens the way for different protocols to be used at
higher/lower levels.
© 2025 Assignment Expert
IP responsible for moving traffic between networks (level 3),
Exampromax - Stuvia US
each network may network may use tech they choose at lvl
1 and 2 to move traffic within their net. Data can still
traverse internet because IP glues different networks
together.
Higher layers (transport/application) operate strictly end-
to-end. Since IP works in the core of network, any end -to-
end services may be built on top of it.
Discuss how the design principles of the Internet are manifest in the ARP
protocol.
Also discuss how the absence of some points from the design principles
(e.g., security and mobility) has influenced ARP.
Correct Answer
Goals: Connect disparate individual (layer 2) networks by
inter-networking them with IP (layer 3).
, Exampromax - Stuvia US 2025/2026
2
ARP translates between different addressing schemes of IP
(L3) and Ethernet (L2).
E-2-E communication through IP (L3) because src/dest may
not be on same local (L2) network.
Internet comm dependent on local L2 network being able to
deliver within that network using MAC. Thus ARP fills the
need to find MAC address of a machine using the IP (L3)
address.
© 2025 Assignment Expert
Exampromax - Stuvia US
Keep in mind not all L2 networks use MAC -- narrow waist
dictates all networks use IP at L3, but L2 may have other
addressing.
ARP allows for IP→MAC mapping discovery dynamically, on
an as-needed basis. Thus there is no need for a machine's
IP→MAC mappings to be proactively reported to other
hosts on the network.
What are the advantages of using circuit-switched networks instead of
packet-switched networks (like the Internet) for streaming video?
Correct Answer
Guaranteed bandwidth -> sufficient throughput available
for video, throughput won't be effected by other
users'/applications' traffic on the network (dedicated cir cuit
for communication)
, Exampromax - Stuvia US 2025/2026
3
Circuit switched can't prevent all packet loss, but the ability
to reserve sufficient resources for video traffic can eliminate
a major source of packet loss.
Certain video streaming applications (VOIP / video
conference) may benefit from the upper bounds on latency
that circuit switched networks can provide.
In what way are caching HTTP proxies a violation of the end-to-end
argument? Also, what are the consequences of this?
© 2025 Assignment Expert
Correct Answer
Exampromax - Stuvia US
HTTP proxies divert web requests from their stated dest
(web server) to the proxy, which is likely closer to the
requestor (client/browser) and can respond with less
latency, providing the same content.
Desirable for performance gains, however violates E2E
argument. Remote host you end up talking to is not the one
you stated you wanted to talk to.
Can use encryption for proxy-client, however, E2E
encryption between client/original web server not possible.
Original web server cannot identify itself to client while
proxy acts as intermediary. Proxy could identify itself, but
additional mechanisms would be needed to verify proxy is
authorized to act upon web server.
1
CS 6250 TEST 1 Questions and Answers and
Graded
How does the "narrow waist" allow a large variety of different protocols to
be used on the Internet?
Correct Answer
Standardized traffic routing between networks (all use IP),
opens the way for different protocols to be used at
higher/lower levels.
© 2025 Assignment Expert
IP responsible for moving traffic between networks (level 3),
Exampromax - Stuvia US
each network may network may use tech they choose at lvl
1 and 2 to move traffic within their net. Data can still
traverse internet because IP glues different networks
together.
Higher layers (transport/application) operate strictly end-
to-end. Since IP works in the core of network, any end -to-
end services may be built on top of it.
Discuss how the design principles of the Internet are manifest in the ARP
protocol.
Also discuss how the absence of some points from the design principles
(e.g., security and mobility) has influenced ARP.
Correct Answer
Goals: Connect disparate individual (layer 2) networks by
inter-networking them with IP (layer 3).
, Exampromax - Stuvia US 2025/2026
2
ARP translates between different addressing schemes of IP
(L3) and Ethernet (L2).
E-2-E communication through IP (L3) because src/dest may
not be on same local (L2) network.
Internet comm dependent on local L2 network being able to
deliver within that network using MAC. Thus ARP fills the
need to find MAC address of a machine using the IP (L3)
address.
© 2025 Assignment Expert
Exampromax - Stuvia US
Keep in mind not all L2 networks use MAC -- narrow waist
dictates all networks use IP at L3, but L2 may have other
addressing.
ARP allows for IP→MAC mapping discovery dynamically, on
an as-needed basis. Thus there is no need for a machine's
IP→MAC mappings to be proactively reported to other
hosts on the network.
What are the advantages of using circuit-switched networks instead of
packet-switched networks (like the Internet) for streaming video?
Correct Answer
Guaranteed bandwidth -> sufficient throughput available
for video, throughput won't be effected by other
users'/applications' traffic on the network (dedicated cir cuit
for communication)
, Exampromax - Stuvia US 2025/2026
3
Circuit switched can't prevent all packet loss, but the ability
to reserve sufficient resources for video traffic can eliminate
a major source of packet loss.
Certain video streaming applications (VOIP / video
conference) may benefit from the upper bounds on latency
that circuit switched networks can provide.
In what way are caching HTTP proxies a violation of the end-to-end
argument? Also, what are the consequences of this?
© 2025 Assignment Expert
Correct Answer
Exampromax - Stuvia US
HTTP proxies divert web requests from their stated dest
(web server) to the proxy, which is likely closer to the
requestor (client/browser) and can respond with less
latency, providing the same content.
Desirable for performance gains, however violates E2E
argument. Remote host you end up talking to is not the one
you stated you wanted to talk to.
Can use encryption for proxy-client, however, E2E
encryption between client/original web server not possible.
Original web server cannot identify itself to client while
proxy acts as intermediary. Proxy could identify itself, but
additional mechanisms would be needed to verify proxy is
authorized to act upon web server.
