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CS6250 Exam 2 - Lesson 12
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CS6250 Exam 2 - Lesson 12
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CS6250 Exam 2 - Lesson 12CDNs - -_______ are 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.
-online content - -The first major shift that impact the evolution of the
internet ecosystem was the increased demand for ______.
-topological flattening - -The second major shift that impact the evolution of
the internet ecosystem was _____.
-topological flattening - -In _____ the traditional topology (hierarchical) has
transitioned to more flat.
-flat - -In topological flattening the traditional topology (hierarchical) has
transitioned to more _____
-Enter Deep - -In the ____ approach of CDN server placement, the CDNs
place many smaller server clusters "deep" into the access networks around
the world.
-server cluster - -With the Enter Deep approach, the goal is to make the
distance between a user and the closest ______ as small as possible, which
reduces the delay and increases the available throughput for each user.
-Bring Home - -In the ____ approach of CDN server placement, the CDNs
place fewer larger server clusters at key points (typically in IXPs, not in
access networks).
-higher delay - -With Bring Home, 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 _____ and lower throughput.
-mapping, selection - -The two main steps of CDN server selection are _____
and server ______.
-geographically - -The simplest approach for selecting a cluster is to pick
the _____ closest cluster.
-performance - -A limitation of picking the geographically closest cluster is
that the cluster which is geographically closest may not be the best choice in
terms of actual end-to-end network ______.
, -LDNS - -Picking the geographically closest cluster is really "picking the
cluster closest to the LDNS" and not "closest to the user." This does not work
well when users use a remote ______.
-active, passive - -The metrics for cluster server selection are obtained
through _____ and ______ measurements.
-select a cluster - -There are various metrics that can be used to _____. For
instance, one could use network-layer metrics such as delay, available
bandwidth or both. A better strategy could be to use application-layer
metrics. For instance, if the content to be delivered is video, metrics such as
re-buffering ratio and average bitrate can be used in cluster selection.
Similarly, for web-browsing, application-layer performance indicators such as
page load time can be used.
-global view - -A coarse-grained global layer operates at larger time scales
(timescale of a few tens of seconds (or minutes)). This layer has a ______ of
client quality measurements. It builds a data-driven prediction model of
video quality.
-decisions - -A fine-grained per-client decision layer that operates at the
millisecond timescale. It makes actual _____ upon a client request. This is
based on the latest (but possibly stale) pre-computed global model and up-
to-date per-client state.
-two-layered system - -A challenge of the _______ is that it needs to have
data for different subnet-cluster pairs. Thus, some of the clients deliberately
need to be routed to sub-optimal clusters.
-subnet-cluster pairs - -A challenge of the two-layered system is that it
needs to have data for different _______. Thus, some of the clients
deliberately need to be routed to sub-optimal clusters.
-server selection - -A simple solution to _______ is to map the requests based
on the content.
-mapping - -One of the challenges of ______ requests based on the content
arises from the fact that the cluster environment is quite dynamic and is
characterized by frequent machine failures and load changes. Now, when
there is a change in the cluster environment such as when a machine fails,
the hash table used to map the content to servers needs to be recomputed.
-consistent hashing - -The main idea behind _______ is that servers and the
content objects are mapped to the same ID space.
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