Internet Engineering Task Force F. Le Faucheur, Ed.
Internet-Draft Cisco Systems
Intended status: Standards Track G. Bertrand, Ed.
Expires: September 3, 2016 I. Oprescu, Ed.
Orange
R. Peterkofsky
Skytide, Inc.
March 2, 2016
CDNI Logging Interface
draft-ietf-cdni-logging-22
Abstract
This memo specifies the Logging interface between a downstream CDN
(dCDN) and an upstream CDN (uCDN) that are interconnected as per the
CDN Interconnection (CDNI) framework. First, it describes a
reference model for CDNI logging. Then, it specifies the CDNI
Logging File format and the actual protocol for exchange of CDNI
Logging Files.
Status of This Memo
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. CDNI Logging Reference Model . . . . . . . . . . . . . . . . 5
2.1. CDNI Logging interactions . . . . . . . . . . . . . . . . 5
2.2. Overall Logging Chain . . . . . . . . . . . . . . . . . . 8
2.2.1. Logging Generation and During-Generation Aggregation 9
2.2.2. Logging Collection . . . . . . . . . . . . . . . . . 10
2.2.3. Logging Filtering . . . . . . . . . . . . . . . . . . 10
2.2.4. Logging Rectification and Post-Generation Aggregation 11
2.2.5. Log-Consuming Applications . . . . . . . . . . . . . 12
2.2.5.1. Maintenance/Debugging . . . . . . . . . . . . . . 12
2.2.5.2. Accounting . . . . . . . . . . . . . . . . . . . 13
2.2.5.3. Analytics and Reporting . . . . . . . . . . . . . 13
2.2.5.4. Content Protection . . . . . . . . . . . . . . . 13
2.2.5.5. Notions common to multiple Log Consuming
Applications . . . . . . . . . . . . . . . . . . 14
3. CDNI Logging File . . . . . . . . . . . . . . . . . . . . . . 16
3.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2. CDNI Logging File Structure . . . . . . . . . . . . . . . 17
3.3. CDNI Logging Directives . . . . . . . . . . . . . . . . . 20
3.4. CDNI Logging Records . . . . . . . . . . . . . . . . . . 24
3.4.1. HTTP Request Logging Record . . . . . . . . . . . . . 25
3.5. CDNI Logging File Example . . . . . . . . . . . . . . . . 35
3.6. Cascaded CDNI Logging Files Example . . . . . . . . . . . 37
4. Protocol for Exchange of CDNI Logging File After Full
Collection . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.1. CDNI Logging Feed . . . . . . . . . . . . . . . . . . . . 41
4.1.1. Atom Formatting . . . . . . . . . . . . . . . . . . . 41
4.1.2. Updates to Log Files and the Feed . . . . . . . . . . 41
4.1.3. Redundant Feeds . . . . . . . . . . . . . . . . . . . 42
4.1.4. Example CDNI Logging Feed . . . . . . . . . . . . . . 42
4.2. CDNI Logging File Pull . . . . . . . . . . . . . . . . . 44
5. Protocol for Exchange of CDNI Logging File During Collection 45
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
6.1. CDNI Logging Directive Names Registry . . . . . . . . . . 46
6.2. CDNI Logging File version Registry . . . . . . . . . . . 47
6.3. CDNI Logging record-types Registry . . . . . . . . . . . 47
6.4. CDNI Logging Field Names Registry . . . . . . . . . . . . 48
6.5. CDNI Logging MIME Media Type . . . . . . . . . . . . . . 49
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7. Security Considerations . . . . . . . . . . . . . . . . . . . 50
7.1. Authentication, Authorization, Confidentiality, Integrity
Protection . . . . . . . . . . . . . . . . . . . . . . . 50
7.2. Denial of Service . . . . . . . . . . . . . . . . . . . . 51
7.3. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 51
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 52
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 53
9.1. Normative References . . . . . . . . . . . . . . . . . . 53
9.2. Informative References . . . . . . . . . . . . . . . . . 54
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56
1. Introduction
This memo specifies the CDNI Logging interface between a downstream
CDN (dCDN) and an upstream CDN (uCDN). First, it describes a
reference model for CDNI logging. Then, it specifies the CDNI
Logging File format and the actual protocol for exchange of CDNI
Logging Files.
The reader should be familiar with the following documents:
o CDNI problem statement [RFC6707] and framework [RFC7336] identify
a Logging interface,
o Section 8 of [RFC7337] specifies a set of requirements for
Logging,
o [RFC6770] outlines real world use-cases for interconnecting CDNs.
These use cases require the exchange of Logging information
between the dCDN and the uCDN.
As stated in [RFC6707], "the CDNI Logging interface enables details
of logs or events to be exchanged between interconnected CDNs".
The present document describes:
o The CDNI Logging reference model (Section 2),
o The CDNI Logging File format (Section 3),
o The CDNI Logging File Exchange protocol (Section 4).
1.1. Terminology
In this document, the first letter of each CDNI-specific term is
capitalized. We adopt the terminology described in [RFC6707] and
[RFC7336], and extend it with the additional terms defined below.
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Intra-CDN Logging information: logging information generated and
collected within a CDN. The format of the Intra-CDN Logging
information may be different to the format of the CDNI Logging
information.
CDNI Logging information: logging information exchanged across CDNs
using the CDNI Logging Interface.
Logging information: logging information generated and collected
within a CDN or obtained from another CDN using the CDNI Logging
Interface.
CDNI Logging Field: an atomic element of information that can be
included in a CDNI Logging Record. The time an event/task started,
the IP address of an End User to whom content was delivered, and the
Uniform Resource Identifier (URI) of the content delivered, are
examples of CDNI Logging fields.
CDNI Logging Record: an information record providing information
about a specific event. This comprises a collection of CDNI Logging
fields.
CDNI Logging File: a file containing CDNI Logging Records, as well as
additional information facilitating the processing of the CDNI
Logging Records.
CDN Reporting: the process of providing the relevant information that
will be used to create a formatted content delivery report provided
to the CSP in deferred time. Such information typically includes
aggregated data that can cover a large period of time (e.g., from
hours to several months). Uses of Reporting include the collection
of charging data related to CDN services and the computation of Key
Performance Indicators (KPIs).
CDN Monitoring: the process of providing or displaying content
delivery information in a timely fashion with respect to the
corresponding deliveries. Monitoring typically includes visibility
of the deliveries in progress for service operation purposes. It
presents a view of the global health of the services as well as
information on usage and performance, for network services
supervision and operation management. In particular, monitoring data
can be used to generate alarms.
1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
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"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119].
2. CDNI Logging Reference Model
2.1. CDNI Logging interactions
The CDNI logging reference model between a given uCDN and a given
dCDN involves the following interactions:
o customization by the uCDN of the CDNI Logging information to be
provided by the dCDN to the uCDN (e.g., control of which CDNI
Logging fields are to be communicated to the uCDN for a given task
performed by the dCDN or control of which types of events are to
be logged). The dCDN takes into account this CDNI Logging
customization information to determine what Logging information to
provide to the uCDN, but it may, or may not, take into account
this CDNI Logging customization information to influence what CDN
logging information is to be generated and collected within the
dCDN (e.g., even if the uCDN requests a restricted subset of the
logging information, the dCDN may elect to generate a broader set
of logging information). The mechanism to support the
customization by the uCDN of CDNI Logging information is outside
the scope of this document and left for further study. Until such
a mechanism is available, the uCDN and dCDN are expected to agree
off-line on what exact set of CDNI Logging information is to be
provided by the dCDN to the uCDN, and to rely on management plane
actions to configure the CDNI Logging functions in the dCDN to
generate this information set and in the uCDN to expect this
information set.
o generation and collection by the dCDN of the intra-CDN Logging
information related to the completion of any task performed by the
dCDN on behalf of the uCDN (e.g., delivery of the content to an
End User) or related to events happening in the dCDN that are
relevant to the uCDN (e.g., failures or unavailability in dCDN).
This takes place within the dCDN and does not directly involve
CDNI interfaces.
o communication by the dCDN to the uCDN of the Logging information
collected by the dCDN relevant to the uCDN. This is supported by
the CDNI Logging interface and in the scope of the present
document. For example, the uCDN may use this Logging information
to charge the CSP, to perform analytics and monitoring for
operational reasons, to provide analytics and monitoring views on
its content delivery to the CSP or to perform trouble-shooting.
This document exclusively specifies non-real-time exchange of
Logging information. Closer to real-time exchange of Logging
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information (say sub-minute or sub-second) is outside the scope of
the present document and left for further study. This document
exclusively specifies exchange of Logging information related to
content delivery. Exchange of Logging information related to
operational events (e.g., dCDN request routing function
unavailable, content acquisition failure by dCDN) for audit or
operational reactive adjustments by uCDN is outside the scope of
the present document and left for further study.
o customization by the dCDN of the CDNI Logging information to be
provided by the uCDN on behalf of the dCDN. The mechanism to
support the customization by the dCDN of CDNI Logging information
is outside the scope of this document and left for further study.
o generation and collection by the uCDN of Intra-CDN Logging
information related to the completion of any task performed by the
uCDN on behalf of the dCDN (e.g., serving of content by uCDN to
dCDN for acquisition purposes by dCDN) or related to events
happening in the uCDN that are relevant to the dCDN. This takes
place within the uCDN and does not directly involve CDNI
interfaces.
o communication by the uCDN to the dCDN of the Logging information
collected by the uCDN relevant to the dCDN. For example, the dCDN
might potentially benefit from this information for security
auditing or content acquisition troubleshooting. This is outside
the scope of this document and left for further study.
Figure 1 provides an example of CDNI Logging interactions (focusing
only on the interactions that are in the scope of this document) in a
particular scenario where four CDNs are involved in the delivery of
content from a given CSP: the uCDN has a CDNI interconnection with
dCDN-1 and dCDN-2. In turn, dCDN-2 has a CDNI interconnection with
dCDN-3, where dCDN-2 is acting as an upstream CDN relative to dCDN-3.
In this example, uCDN, dCDN-1, dCDN-2 and dCDN-3 all participate in
the delivery of content for the CSP. In this example, the CDNI
Logging interface enables the uCDN to obtain Logging information from
all the dCDNs involved in the delivery. In the example, the uCDN
uses the Logging information:
o to analyze the performance of the delivery performed by the dCDNs
and to adjust its operations after the fact (e.g., request
routing) as appropriate,
o to provide (non-real-time) reporting and monitoring information to
the CSP.
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For instance, the uCDN merges Logging information, extracts relevant
KPIs, and presents a formatted report to the CSP, in addition to a
bill for the content delivered by uCDN itself or by its dCDNs on the
CSP's behalf. The uCDN may also provide Logging information as raw
log files to the CSP, so that the CSP can use its own logging
analysis tools.
+-----+
| CSP |
+-----+
^ Reporting and monitoring data
* Billing
,--*--.
Logging ,-' `-.
Data =>( uCDN )<= Logging
// `-. _,-' \\ Data
|| `-'-'-' ||
,-----. ,-----.
,-' `-. ,-' `-.
( dCDN-1 ) ( dCDN-2 )<== Logging
`-. ,-' `-. _,-' \\ Data
`--'--' `--'-' ||
,-----.
,' `-.
( dCDN-3 )
`. ,-'
`--'--'
===> CDNI Logging Interface
***> outside the scope of CDNI
Figure 1: Interactions in CDNI Logging Reference Model
A downstream CDN relative to uCDN (e.g., dCDN-2) integrates the
relevant Logging information obtained from its own downstream CDNs
(i.e., dCDN-3) in the Logging information that it provides to the
uCDN, so that the uCDN ultimately obtains all Logging information
relevant to a CSP for which it acts as the authoritative CDN. Such
aggregation is further discussed in Section 3.6.
Note that the format of Logging information that a CDN provides over
the CDNI interface might be different from the one that the CDN uses
internally. In this case, the CDN needs to reformat the Logging
information before it provides this information to the other CDN over
the CDNI Logging interface. Similarly, a CDN might reformat the
Logging information that it receives over the CDNI Logging interface
before injecting it into its log-consuming applications or before
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providing some of this Logging information to the CSP. Such
reformatting operations introduce latency in the logging distribution
chain and introduce a processing burden. Therefore, there are
benefits in specifying CDNI Logging formats that are suitable for use
inside CDNs and also are close to the intra-CDN Logging formats
commonly used in CDNs today.
2.2. Overall Logging Chain
This section discusses the overall logging chain within and across
CDNs to clarify how CDN Logging information is expected to fit in
this overall chain. Figure 2 illustrates the overall logging chain
within the dCDN, across CDNs using the CDNI Logging interface and
within the uCDN. Note that the logging chain illustrated in the
Figure is obviously only an example and varies depending on the
specific environments. For example, there may be more or fewer
instantiations of each entity (e.g., there may be 4 Log consuming
applications in a given CDN). As another example, there may be one
instance of Rectification process per Log Consuming Application
instead of a shared one.
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Log Consuming Log Consuming
App App
^ ^
| |
Rectification----------
^
|
Filtering
^
|
Collection
^ ^
| |
| Generation
|
| uCDN
CDNI Logging ---------------------------------------------------
exchange dCDN
^
| Log Consuming Log Consuming
| App App
| ^ ^
| | |
Rectification Rectification---------
^ ^
| |
Filtering
^
|
Collection
^ ^
| |
Generation Generation
Figure 2: CDNI Logging in the overall Logging Chain
The following subsections describe each of the processes potentially
involved in the logging chain of Figure 2.
2.2.1. Logging Generation and During-Generation Aggregation
CDNs typically generate Logging information for all significant task
completions, events, and failures. Logging information is typically
generated by many devices in the CDN including the surrogates, the
request routing system, and the control system.
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The amount of Logging information generated can be huge. Therefore,
during contract negotiations, interconnected CDNs often agree on a
retention duration for Logging information, and/or potentially on a
maximum volume of Logging information that the dCDN ought to keep.
If this volume is exceeded, the dCDN is expected to alert the uCDN
but may not keep more Logging information for the considered time
period. In addition, CDNs may aggregate Logging information and
transmit only summaries for some categories of operations instead of
the full Logging information. Note that such aggregation leads to an
information loss, which may be problematic for some usages of the
Logging information (e.g., debugging).
[RFC6983] discusses logging for HTTP Adaptive Streaming (HAS). In
accordance with the recommendations articulated there, it is expected
that a surrogate will generate separate Logging information for
delivery of each chunk of HAS content. This ensures that separate
Logging information can then be provided to interconnected CDNs over
the CDNI Logging interface. Still in line with the recommendations
of [RFC6983], the Logging information for per-chunk delivery may
include some information (a Content Collection IDentifier and a
Session IDentifier) intended to facilitate subsequent post-generation
aggregation of per-chunk logs into per-session logs. Note that a CDN
may also elect to generate aggregate per-session logs when performing
HAS delivery, but this needs to be in addition to, and not instead
of, the per-chunk delivery logs. We note that aggregate per-session
logs for HAS delivery are for further study and outside the scope of
this document.
2.2.2. Logging Collection
This is the process that continuously collects Logging information
generated by the log-generating entities within a CDN.
In a CDNI environment, in addition to collecting Logging information
from log-generating entities within the local CDN, the Collection
process also collects Logging information provided by another CDN, or
other CDNs, through the CDNI Logging interface. This is illustrated
in Figure 2 where we see that the Collection process of the uCDN
collects Logging information from log-generating entities within the
uCDN as well as Logging information coming from the dCDNs through the
CDNI Logging interface.
2.2.3. Logging Filtering
A CDN may be required to only present different subsets of the whole
Logging information collected to various log-consuming applications.
This is achieved by the Filtering process.
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In particular, the Filtering process can also filter the right subset
of Logging information that needs to be provided to a given
interconnected CDN. For example, the filtering process in the dCDN
can be used to ensure that only the Logging information related to
tasks performed on behalf of a given uCDN are made available to that
uCDN (thereby filtering out all the Logging information related to
deliveries by the dCDN of content for its own CSPs). Similarly, the
Filtering process may filter or partially mask some fields, for
example, to protect End Users' privacy when communicating CDNI
Logging information to another CDN. Filtering of Logging information
prior to communication of this information to other CDNs via the CDNI
Logging interface requires that the downstream CDN can recognize the
subset of Logging information that relate to each interconnected CDN.
The CDN will also filter some internal scope information such as
information related to its internal alarms (security, failures, load,
etc).
In some use cases described in [RFC6770], the interconnected CDNs do
not want to disclose details on their internal topology. The
filtering process can then also filter confidential data on the
dCDNs' topology (number of servers, location, etc.). In particular,
information about the requests served by each Surrogate may be
confidential. Therefore, the Logging information needs to be
protected so that data such as Surrogates' hostnames are not
disclosed to the uCDN. In the "Inter-Affiliates Interconnection" use
case, this information may be disclosed to the uCDN because both the
dCDN and the uCDN are operated by entities of the same group.
2.2.4. Logging Rectification and Post-Generation Aggregation
If Logging information is generated periodically, it is important
that the sessions that start in one Logging period and end in another
are correctly reported. If they are reported in the starting period,
then the Logging information of this period will be available only
after the end of the session, which delays the Logging information
generation. A simple approach is to provide the complete Logging
Record for a session in the Logging Period of the session end.
A Logging rectification/update mechanism could be useful to reach a
good trade-off between the Logging information generation delay and
the Logging information accuracy.
In the presence of HAS, some log-consuming applications can benefit
from aggregate per-session logs. For example, for analytics, per-
session logs allow display of session-related trends which are much
more meaningful for some types of analysis than chunk-related trends.
In the case where aggregate logs have been generated directly by the
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log-generating entities, those can be used by the applications. In
the case where aggregate logs have not been generated, the
Rectification process can be extended with a Post-Generation
Aggregation process that generates per-session logs from the per-
chunk logs, possibly leveraging the information included in the per-
chunk logs for that purpose (Content Collection IDentifier and a
Session IDentifier). However, in accordance with [RFC6983], this
document does not define exchange of such aggregate logs on the CDNI
Logging interface. We note that this is for further study and
outside the scope of this document.
2.2.5. Log-Consuming Applications
2.2.5.1. Maintenance/Debugging
Logging information is useful to permit the detection (and limit the
risk) of content delivery failures. In particular, Logging
information facilitates the detection of configuration issues.
To detect faults, Logging information needs to report success and
failure of CDN delivery operations. The uCDN can summarize such
information into KPIs. For instance, Logging information needs to
allow the computation of the number of times, during a given time
period, that content delivery related to a specific service succeeds/
fails.
Logging information enables the CDN providers to identify and
troubleshoot performance degradations. In particular, Logging
information enables tracking of traffic data (e.g., the amount of
traffic that has been forwarded by a dCDN on behalf of an uCDN over a
given period of time), which is particularly useful for CDN and
network planning operations.
Some of these maintenance and debugging applications only require
aggregate logging information highly compatible with use of
anonymization of IP addresses (as supported by the present document
and specified in the definition of the c-groupid field under
Section 3.4.1). However, in some situations, it may be useful, where
compatible with privacy protection, to access some CDNI Logging
Records containing full non-anonymized IP addresses. This is allowed
in the definition of the c-groupid (under Section 3.4.1), with very
significant privacy protection limitations that are discussed in the
definition of the c-groupid field. For example, this may be useful
for detailed fault tracking of a particular end user content delivery
issue. Where there is a hard requirement by uCDN or CSP to associate
a given enduser to individual CDNI Logging Records (e.g., to allow
a-posteriori analysis of individual delivery for example in
situations of performance-based penalties), instead of using
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aggregates containing a single client as discussed in the c-groupid
field definition, an alternate approach is to ensure that a client
identifier is embedded in the request fields that can be logged in a
CDNI Logging Record (for example by including the client identifier
in the URI query string or in a HTTP Header). That latter approach
offers two strong benefits: first, the aggregate inside the c-groupid
can contain more than one client, thereby ensuring stronger privacy
protection; second, it allows a reliable identification of the client
while IP address does not in many situations (e.g., behind NAT, where
dynamic IP addresses are used and reused,...). However, care SHOULD
be taken that the client identifiers exposed in other fields of the
CDNI Records cannot themselves be linked back to actual users.
2.2.5.2. Accounting
Logging information is essential for accounting, to permit inter-CDN
billing and CSP billing by uCDNs. For instance, Logging information
provided by dCDNs enables the uCDN to compute the total amount of
traffic delivered by every dCDN for a particular Content Provider, as
well as, the associated bandwidth usage (e.g., peak, 95th
percentile), and the maximum number of simultaneous sessions over a
given period of time.
2.2.5.3. Analytics and Reporting
The goals of analytics include gathering any relevant information in
order to be able to develop statistics on content download, analyze
user behavior, and monitor the performance and quality of content
delivery. For instance, Logging information enables the CDN
providers to report on content consumption (e.g., delivered sessions
per content) in a specific geographic area.
The goal of reporting is to gather any relevant information to
monitor the performance and quality of content delivery and allow
detection of delivery issues. For instance, reporting could track
the average delivery throughput experienced by End Users in a given
region for a specific CSP or content set over a period of time.
2.2.5.4. Content Protection
The goal of content protection is to prevent and monitor unauthorized
access, misuse, modification, and denial of access to a content. A
set of information is logged in a CDN for security purposes. In
particular, a record of access to content is usually collected to
permit the CSP to detect infringements of content delivery policies
and other abnormal End User behaviors.
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2.2.5.5. Notions common to multiple Log Consuming Applications
2.2.5.5.1. Logging Information Views
Within a given log-consuming application, different views may be
provided to different users depending on privacy, business, and
scalability constraints.
For example, an analytics tool run by the uCDN can provide one view
to an uCDN operator that exploits all the Logging information
available to the uCDN, while the tool may provide a different view to
each CSP exploiting only the Logging information related to the
content of the given CSP.
As another example, maintenance and debugging tools may provide
different views to different CDN operators, based on their
operational role.
2.2.5.5.2. Key Performance Indicators (KPIs)
This section presents, for explanatory purposes, a non-exhaustive
list of Key Performance Indicators (KPIs) that can be extracted/
produced from logs.
Multiple log-consuming applications, such as analytics, monitoring,
and maintenance applications, often compute and track such KPIs.
In a CDNI environment, depending on the situation, these KPIs may be
computed by the uCDN or by the dCDN. But it is usually the uCDN that
computes KPIs, because the uCDN and dCDN may have different
definitions of the KPIs and the computation of some KPIs requires a
vision of all the deliveries performed by the uCDN and all its dCDNs.
Here is a list of important examples of KPIs:
o Number of delivery requests received from End Users in a given
region for each piece of content, during a given period of time
(e.g., hour/day/week/month)
o Percentage of delivery successes/failures among the aforementioned
requests
o Number of failures listed by failure type (e.g., HTTP error code)
for requests received from End Users in a given region and for
each piece of content, during a given period of time (e.g.,
hour/day/week/month)
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o Number and cause of premature delivery termination for End Users
in a given region and for each piece of content, during a given
period of time (e.g., hour/day/week/month)
o Maximum and mean number of simultaneous sessions established by
End Users in a given region, for a given Content Provider, and
during a given period of time (e.g., hour/day/week/month)
o Volume of traffic delivered for sessions established by End Users
in a given region, for a given Content Provider, and during a
given period of time (e.g., hour/day/week/month)
o Maximum, mean, and minimum delivery throughput for sessions
established by End Users in a given region, for a given Content
Provider, and during a given period of time (e.g., hour/day/week/
month)
o Cache-hit and byte-hit ratios for requests received from End Users
in a given region for each piece of content, during a given period
of time (e.g., hour/day/week/month)
o Top 10 most popularly requested contents (during a given day/week/
month)
o Terminal type (mobile, PC, STB, if this information can be
acquired from the browser type inferred from the User Agent
string, for example).
Additional KPIs can be computed from other sources of information
than the Logging information, for instance, data collected by a
content portal or by specific client-side application programming
interfaces. Such KPIs are out of scope for the present document.
The KPIs used depend strongly on the considered log-consuming
application -- the CDN operator may be interested in different
metrics than the CSP is. In particular, CDN operators are often
interested in delivery and acquisition performance KPIs, information
related to Surrogates' performance, caching information to evaluate
the cache-hit ratio, information about the delivered file size to
compute the volume of content delivered during peak hour, etc.
Some of the KPIs, for instance those providing an instantaneous
vision of the active sessions for a given CSP's content, are useful
essentially if they are provided in a timely manner. By contrast,
some other KPIs, such as those averaged on a long period of time, can
be provided in non-real-time.
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3. CDNI Logging File
3.1. Rules
This specification uses the Augmented Backus-Naur Form (ABNF)
notation and core rules of [RFC5234]. In particular, the present
document uses the following rules from [