Content Distribution
Internetworking
IETF BOF
December 12, 2000
Phil Rzewski
Gary Tomlinson
Content Networking
• Using IETF “application layer” protocols as
transport
– e.g. HTTP, RTSP
• Routing & forwarding of requests &
responses instead of packets
Example Content Network:
Hierarchical caching
“parent”
cache(s)
ISP
bar.com
foo.com
“edge” / “access”
caches
• Typically static forwarding rules
– HTTP parenting
– ICP
• Example request forwarding
– Single path
– Redundant
– URL partitioning
client
Example Content Network:
Content Distribution Network (CDN)s
“request-routing”
system(s)
CDN
“surrogates”
• Request routing systems map a
client to a surrogate
– e.g. DNS
Local DNS
• Example request forwarding
– Ask another surrogate
– Seek origin
client
Content Distribution
Internetworking
CDN
ISP
• Interconnect Content Networks
• Different administrative domains
• Different technologies
Content Distribution
Internetworking
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• Area of CDI interest lies in communication across these boundaries
• Details within each Content Network should be irrelevant
Key Terms
&
Concepts
Surrogate
“A delivery server, other than
the origin. Receives a mapped
request and delivers the
corresponding content.”
Delivery
“The activity of presenting a
publisher’s content for
consumption by a client.”
origin
Content Network
surrogate
delivery
client
Distribution
“The activity of moving a publisher’s content from
its origin to one or more surrogates.
Injection
origin
CN
(aka “origin distribution peering”)
“Publishing of content into one-or-more
Content Networks by origins.”
CN
CN
Content Signal
“A message delivered through a distribution system
that specifies information about an item of content.”
e.g. to indicate the origin has a new version of
some piece of content
Request-Routing
“The activity of steering or directing a request from a
client to a suitable surrogate.”
CN
CN
client
Accounting
“Measurement and recording of distribution and delivery activities,
especially when the information recorded is ultimately used as a
basis for the subsequent transfer of money, goods, or obligations”
CN
CN
CN
Drafting teams
• Two design teams produced 8 of the 9 drafts
• The two teams were aligned with Content
Bridge & Content Alliance
• Sharing and cooperation developed late so
there is some overlap
Understanding
the Strawman
Drafts
draft-day-cdnp-model-04.txt
• Introduction, background, & vocabulary on
CDNs
– CDN examples provided
• Introduction & vocabulary on developing
CDN interconnection technology
– CDN peering examples provided
– Content Peering Gateways (CPG) defined
• Some high-level operational considerations
included
draft-day-cdnp-scenarios-02.txt
• Used to collect the communities of interest
requirements
• Describes representative configurations that
can be realized when internetworking
CDNs.
• Framed by the concepts:
– CONTENT has value
– DISTRIBUTION has value
– CLIENTS have value
draft-green-cdnp-gen-arch-02.txt
• Presents three main architectural elements
– Request-Routing Peering System
– Distribution Peering System
– Accounting Peering System
• For each architectural element, presents:
– Known requirements
– Problems that need further investigation
• Security considerations
draft-green-cdnp-gen-arch-02.txt
Conceptual View of Peered CDNs
CDN A
CDN B
Request-Routing
Request-Routing
Distribution
CPG
CPG
Distribution
Accounting
Accounting
CPG
surrogates
surrogates
CDN C
Request-Routing
Distribution
Accounting
surrogates
clients
draft-green-cdnp-gen-arch-02.txt
Request-Routing Peering System Architecture
client
Authoritative
Request-Routing
System
Inter-CDN Request-Routing
(1stdraft-cain-cdnp-known-request-routing-00.txt
Level)
Request-Routing
Request-Routing
• Presents known
mechanisms
to
direct
client
CPG
CPG
requests to surrogate servers.
Request-Routing
draft-deleuze-cdnp-dnsmap-peer-00.txt
– DNS
CDN
A request-routing
CDN B Request-Routing
System
System
• Proposes a DNS-based Mapping
– Transport-layer request-routing
System
– Application-layer
Request-Routing request-routing
Surrogates
Surrogate
Surrogates
CPG
• Discusses measurements, metrics, and feedback• Focused on determining the next hop
Inter-CDN Recursive Request-Routing
toward the appropriate surrogate
Request-Routing
(2nd Level)
• Describes an approach using CNAME
CPG
• Proposes naming criteria to describe
CDN C Request-Routing
– Delivery service
System
Surrogate
– Delivery Footprint
Surrogates
draft-green-cdnp-gen-arch-02.txt
Distribution Peering System Architecture
Origin
Origin Distribution Peering
Distribution
CPG
CDN A
Distribution
CPG
Distribution
System
Surrogates
CDN B
Distribution
CPG
Distribution
System
Distribution
CPG
Inter-CDN Distribution Peering
Distribution
CPG
CDN C
Distribution
System
Surrogate
Surrogates
Surrogates
draft-green-cdnp-gen-arch-02.txt
Accounting Peering System Architecture
Billing
Organization
Origin
Billing Accounting Peering
Origin Accounting Peering
Accounting
CPG
CDN A
Accounting
CPG
Accounting
System
Surrogates
CDN B
Accounting
CPG
•
Accounting
System
draft-gilletti-cdnp-aaa-reqs-00.txt
Accounting
Surrogates
Requirements
for
CDN
Accounting
Peering
CPG
– Framed against ongoing work of AAA WG
Inter-CDN Accounting Peering
Accounting
• Details
CPG
CDN C
on CDN Accounting Peering models
– Additional terminology
Accounting
– Transaction models
System
– Accounting messaging
• Lists
problems to be solved
Surrogate
Surrogates
draft-rzewski-oacp-00.txt
• Origin/Access Content Peering for HTTP
• Specific (“vertical”) implementation proposal of a
way to pass control & accounting between origin
& access endpoints.
– Roles described for specific types of content networks
(Hoster/CDN, Operator, Access Provider)
• Note Request- Routing is a “null case” in the
implementation
draft-rzewski-oacp-00.txt
Hoster/CDN
Access Provider (ISP)
Operator
Origin
www.
com



Content
Injector


Access
Caches


Content
Relay
Content Relay
Content
Relay
Surrogate
Access
Clients
 New Content Published by Content Provider
draft-rzewski-cndistcs-00.txt
 Content signals for changed URLs sent to Content Relay at Hoster/CDN
Proposes
specific content signals
 Content• signals
for changed URLs forwarded to Content Relay at Operator
– HTTP DELETE method for
 Content signals
for changed URLs forwarded to Content Relay Surrogate at Access
“invalidation”
– Also
additional “CND: GET” header
 Changed content
may be retrieved by Content Relay at Access Provider (HTTP GET)
to kick off pre-load
Provider
 Content signals for changed URLs forwarded to Access Caches
 Access clients request content from Access Caches, if it is not in Access Cache, content is
pulled from Content Gateway Surrogate (parent cache)
draft-rzewski-oacp-00.txt
Hoster/CDN
Access Providers (ISPs)
Operator
Accounting
Relay
Origin
ISP 1

Access
Caches


Accounting
Relay
Settlement
& Billing
Accounting
Relay
ISP 2

Summary
Logging
Access
Caches
draft-rzewski-cnacct-00.txt
 Log info is collected
and summarized at Access
Proposes
SQUID-like
Caches in•regular
intervals
summary log
 Access log infoformat
is collated at Accounting Relay at
Access Provider
• Proposes
using HTTP POST to pass
 Access log information
centralized
& passed
log information
between
networks
through Operator for settlement and billing
 Near real-time summaries are forwarded to
Accounting Gateway at Hoster/CDN
Accounting
Relay
Summary
Logging

Access
Clients

Organization
Going Forward
Possible Informal Structure
Models
Scenarios
Architecture
Framework
Other WGs
A
A
A
W
E
B
I
D
N
S
e
x
t
“umbrella”
.
.
.
“communities
of interest”
Accounting
Distribution
Request-Routing
Known methods
Requirement specifications
Proposed protocols
Implementation debate
Known methods
Requirement specifications
Proposed protocols
Implementation debate
Known methods
Requirement specifications
Proposed protocols
Implementation debate