<s>
Content	B-Protocol
delivery	I-Protocol
network	I-Protocol
interconnection	I-Protocol
(	O
CDNI	B-Protocol
)	O
is	O
a	O
set	O
of	O
interfaces	O
and	O
mechanisms	O
required	O
for	O
interconnecting	O
two	O
independent	O
content	B-Operating_System
delivery	I-Operating_System
networks	I-Operating_System
(	O
CDNs	O
)	O
that	O
enables	O
one	O
to	O
deliver	O
content	O
on	O
behalf	O
of	O
the	O
other	O
.	O
</s>
<s>
Among	O
its	O
many	O
use	O
cases	O
,	O
it	O
allows	O
small	O
CDNs	O
to	O
interconnect	B-Architecture
and	O
provides	O
services	O
for	O
CSPs	O
that	O
allows	O
them	O
to	O
compete	O
against	O
the	O
CDNs	O
of	O
global	O
CSPs	O
.	O
</s>
<s>
The	O
CDNI	B-Protocol
targets	O
at	O
leveraging	O
separate	O
CDNs	O
to	O
provide	O
end-to-end	O
delivery	O
of	O
content	O
from	O
CSPs	O
to	O
end	O
users	O
,	O
regardless	O
of	O
their	O
location	O
or	O
attachment	O
network	O
.	O
</s>
<s>
Let	O
's	O
consider	O
an	O
interconnection	B-Architecture
of	O
two	O
CDNs	O
as	O
presented	O
in	O
the	O
below	O
figure	O
.	O
</s>
<s>
thumb|none|600px|alt	O
=	O
An	O
example	O
of	O
end-to-end	O
content	O
delivery	O
using	O
CDNI.	O
|An	O
example	O
of	O
end-to-end	O
content	O
delivery	O
using	O
CDNI	B-Protocol
.	O
</s>
<s>
In	O
this	O
example	O
,	O
all	O
four	O
parties	O
can	O
benefit	O
from	O
the	O
interconnection	B-Architecture
:	O
the	O
end	O
users	O
can	O
benefit	O
from	O
better	O
quality	O
of	O
service	O
(	O
QoS	O
)	O
;	O
the	O
CSP	O
benefits	O
because	O
it	O
has	O
to	O
make	O
only	O
one	O
business	O
and	O
technical	O
arrangement	O
with	O
uCDN	O
;	O
the	O
uCDN	O
benefits	O
because	O
it	O
does	O
not	O
have	O
to	O
deploy	O
such	O
an	O
extensive	O
CDN	O
;	O
and	O
the	O
dCDN	O
will	O
receive	O
some	O
compensation	O
for	O
the	O
delivery	O
.	O
</s>
<s>
Below	O
is	O
an	O
incomplete	O
list	O
of	O
use	O
cases	O
for	O
which	O
CDNI	B-Protocol
was	O
presented	O
.	O
</s>
<s>
An	O
interconnection	B-Architecture
may	O
be	O
attractive	O
to	O
a	O
large	O
CDN	O
provider	O
who	O
possesses	O
many	O
CDNs	O
in	O
various	O
locations	O
and	O
who	O
may	O
want	O
to	O
make	O
them	O
interoperable	O
.	O
</s>
<s>
A	O
CDNI	B-Protocol
footprint	O
extension	O
is	O
also	O
beneficial	O
for	O
cases	O
in	O
which	O
CDN	O
providers	O
deliver	O
a	O
lot	O
of	O
popular	O
content	O
to	O
networks	O
of	O
a	O
few	O
ISPs	O
.	O
</s>
<s>
If	O
so	O
,	O
interconnection	B-Architecture
of	O
such	O
CDNs	O
would	O
offer	O
improved	O
QoS	O
and	O
QoE	O
to	O
end	O
users	O
,	O
reduce	O
and	O
allow	O
control	O
of	O
ingress	O
traffic	O
in	O
the	O
ISP	O
's	O
network	O
,	O
reduce	O
hardware	O
capacity	O
and	O
footprint	O
of	O
uCDN	O
and	O
allow	O
the	O
ISP	O
to	O
derive	O
some	O
revenue	O
.	O
</s>
<s>
A	O
CDNI	B-Protocol
can	O
be	O
very	O
useful	O
in	O
overload	O
handling	O
because	O
it	O
allows	O
the	O
unexpected	O
spikes	O
in	O
traffic	O
,	O
e.g.	O
</s>
<s>
Additionally	O
,	O
a	O
CDNI	B-Protocol
provides	O
means	O
for	O
resiliency	O
against	O
content	O
delivery	O
and	O
acquisition	O
failure	O
.	O
</s>
<s>
Similarly	O
,	O
with	O
a	O
deployed	O
CDNI	B-Protocol
,	O
if	O
a	O
default	O
acquisition	O
source	O
fails	O
,	O
other	O
sources	O
within	O
the	O
interconnection	B-Architecture
,	O
e.g.	O
</s>
<s>
This	O
,	O
in	O
turn	O
,	O
provides	O
load	B-Application
balancing	I-Application
between	O
content	O
acquisition	O
sources	O
.	O
</s>
<s>
A	O
CDNI	B-Protocol
can	O
be	O
a	O
means	O
of	O
extending	O
a	O
supported	O
range	O
of	O
devices	O
and	O
network	O
technologies	O
if	O
a	O
CDN	O
is	O
not	O
able	O
to	O
support	O
them	O
or	O
if	O
its	O
provider	O
is	O
not	O
willing	O
to	O
provide	O
them	O
.	O
</s>
<s>
Similarly	O
,	O
an	O
interconnection	B-Architecture
may	O
enable	O
a	O
fixed-line	O
CDN	O
provider	O
to	O
extend	O
its	O
services	O
to	O
mobile	O
devices	O
.	O
</s>
<s>
When	O
a	O
CDN	O
provider	O
runs	O
many	O
networks	O
in	O
different	O
technologies	O
,	O
has	O
a	O
multi-vendor	O
strategy	O
or	O
deploys	O
separate	O
networks	O
for	O
many	O
CSPs	O
an	O
interconnection	B-Architecture
can	O
ease	O
its	O
establishing	O
technology	O
and	O
vendor	O
interoperability	O
by	O
simplification	O
or	O
automatisation	O
of	O
some	O
inter-CDN	O
operations	O
.	O
</s>
<s>
Another	O
use	O
case	O
would	O
be	O
an	O
improvement	O
of	O
QoS	O
and	O
QoE	O
for	O
a	O
CDN	O
provider	O
if	O
an	O
interconnection	B-Architecture
option	O
with	O
a	O
network	O
of	O
surrogates	O
closer	O
to	O
end	O
users	O
existed	O
.	O
</s>
<s>
The	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
(	O
see	O
Standardisation	O
status	O
section	O
)	O
defines	O
five	O
interfaces	O
required	O
to	O
interconnect	B-Architecture
a	O
pair	O
of	O
CDNs	O
from	O
a	O
technical	O
perspective	O
,	O
as	O
depicted	O
in	O
Figure	O
2	O
.	O
</s>
<s>
This	O
model	O
of	O
the	O
CDNI	B-Protocol
does	O
not	O
define	O
content	O
acquisition	O
,	O
delivery	O
,	O
request	O
interfaces	O
and	O
mechanisms	O
because	O
today	O
CDNs	O
already	O
use	O
standardised	O
protocols	O
for	O
them	O
,	O
e.g.	O
</s>
<s>
The	O
interconnection	B-Architecture
allows	O
a	O
number	O
of	O
CDNs	O
to	O
be	O
connected	O
in	O
various	O
topologies	O
,	O
such	O
as	O
line	O
,	O
mesh	O
or	O
start	O
topology	O
.	O
</s>
<s>
It	O
is	O
important	O
to	O
note	O
that	O
in	O
order	O
to	O
deploy	O
a	O
CDNI	B-Protocol
,	O
additional	O
business	O
arrangements	O
have	O
to	O
be	O
established	O
between	O
the	O
CSP	O
and	O
the	O
uCDN	O
and	O
between	O
the	O
uCDN	O
and	O
the	O
dCDN	O
.	O
</s>
<s>
thumb|none|400px|alt	O
=	O
A	O
CDNI	B-Protocol
model	O
as	O
defined	O
by	O
the	O
IETF.	O
|A	O
CDNI	B-Protocol
model	O
as	O
defined	O
by	O
the	O
IETF	O
.	O
</s>
<s>
The	O
CI	O
is	O
designed	O
to	O
initiate	O
an	O
interconnection	B-Architecture
across	O
two	O
CDNs	O
and	O
bootstrap	O
the	O
other	O
CDNI	B-Protocol
interfaces	O
.	O
</s>
<s>
The	O
collected	O
metadata	O
is	O
used	O
later	O
for	O
CDNI	B-Protocol
redirection	O
and	O
user	O
content	O
request	O
responses	O
.	O
</s>
<s>
Enables	O
content	O
distribution	O
and	O
delivery	O
activity	O
details	O
to	O
be	O
exchanged	O
via	O
interconnection	B-Architecture
.	O
</s>
<s>
There	O
is	O
another	O
DNS	O
redirection	O
method	O
in	O
which	O
the	O
authoritative	O
server	O
returns	O
a	O
CNAME	B-Protocol
response	O
.	O
</s>
<s>
Both	O
redirection	O
methods	O
,	O
HTTP	O
and	O
DNS	O
based	O
,	O
can	O
be	O
performed	O
in	O
the	O
CDNI	B-Protocol
,	O
either	O
iteratively	O
or	O
recursively	O
.	O
</s>
<s>
The	O
recursive	O
redirection	O
is	O
more	O
transparent	O
for	O
the	O
end	O
user	O
because	O
it	O
involves	O
only	O
one	O
UE	O
redirection	O
,	O
but	O
it	O
has	O
other	O
dependencies	O
on	O
the	O
interconnection	B-Architecture
realisation	O
.	O
</s>
<s>
The	O
sequence	O
diagram	O
presented	O
in	O
the	O
figure	O
below	O
provides	O
some	O
details	O
on	O
CDNI	B-Protocol
and	O
the	O
iterative	O
DNS	O
redirection	O
operation	O
.	O
</s>
<s>
thumb|none|400px|alt	O
=	O
An	O
example	O
of	O
iterative	O
DNS	O
redirection	O
of	O
content	O
request	O
in	O
CDNI.	O
|An	O
example	O
of	O
iterative	O
DNS	O
redirection	O
of	O
content	O
request	O
in	O
CDNI	B-Protocol
.	O
</s>
<s>
If	O
the	O
dCDN	O
is	O
able	O
to	O
handle	O
the	O
request	O
,	O
the	O
request	O
router	O
in	O
uCDN	O
returns	O
a	O
DNS	O
CNAME	B-Protocol
response	O
.	O
</s>
<s>
If	O
addressed	O
in	O
CDNI	B-Protocol
specifications	O
,	O
support	O
of	O
HTTP	O
adaptive	O
streaming	O
(	O
HAS	O
)	O
is	O
particularly	O
realised	O
.	O
</s>
<s>
In	O
order	O
to	O
reduce	O
the	O
CDNI	B-Protocol
load	O
,	O
specifications	O
either	O
allow	O
relative	O
Uniform	O
Resource	O
Locators	O
(	O
URLs	O
)	O
or	O
modify	O
absolute	O
URLs	O
in	O
the	O
manifest	O
file	O
of	O
a	O
resource	O
distributed	O
via	O
HAS	O
.	O
</s>
<s>
The	O
security	O
of	O
the	O
CDNI	B-Protocol
is	O
optional	O
,	O
and	O
its	O
support	O
is	O
introduced	O
as	O
a	O
capability	O
of	O
a	O
CDN	O
.	O
</s>
<s>
Security	O
of	O
the	O
CDNI	B-Protocol
involves	O
content	O
confidentiality	O
protection	O
,	O
authenticated	O
peers	O
communication	O
and	O
data	B-Error_Name
origin	I-Error_Name
authentication	I-Error_Name
.	O
</s>
<s>
The	O
data	B-Error_Name
origin	I-Error_Name
authentication	I-Error_Name
is	O
of	O
high	O
importance	O
if	O
the	O
trust	O
of	O
the	O
link	O
between	O
CDN	O
is	O
questioned	O
.	O
</s>
<s>
The	O
security	O
is	O
enforced	O
by	O
switching	O
to	O
secure	O
versions	O
of	O
protocols	O
deployed	O
in	O
the	O
CDNI	B-Protocol
,	O
e.g.	O
</s>
<s>
Usually	O
,	O
if	O
a	O
CDNI	B-Protocol
is	O
established	O
via	O
secure	O
protocols	O
,	O
secure	O
protocols	O
are	O
also	O
used	O
for	O
content	O
acquisition	O
and	O
distribution	O
.	O
</s>
<s>
Further	O
issues	O
related	O
to	O
security	O
could	O
be	O
various	O
end	O
user	O
privacy	O
requirements	O
in	O
relation	O
to	O
the	O
exchanged	O
logs	O
across	O
different	O
countries	O
or	O
authenticity	B-Error_Name
of	O
logs	O
for	O
delivery	O
charging	O
across	O
CDNs	O
.	O
</s>
<s>
IETF	O
,	O
European	O
Telecommunications	O
Standards	O
Institute	O
(	O
ETSI	O
)	O
,	O
Alliance	O
for	O
Telecommunications	O
Industry	O
Solutions	O
(	O
ATIS	O
)	O
and	O
Open	O
ContEnt	O
Aware	O
Networks	O
(	O
OCEAN	O
)	O
,	O
have	O
been	O
working	O
or	O
are	O
working	O
on	O
the	O
standardisation	O
of	O
CDNI	B-Protocol
interfaces	O
and	O
methods	O
.	O
</s>
<s>
describe	O
three	O
CDNI	B-Protocol
interfaces	O
.	O
</s>
<s>
The	O
first	O
one	O
,	O
the	O
interconnection	B-Architecture
control	O
,	O
seems	O
to	O
map	O
on	O
the	O
union	O
of	O
ETSI	O
's	O
control	O
and	O
logging	O
interfaces	O
.	O
</s>
<s>
The	O
OCEAN	O
framework	O
exhaustively	O
specifies	O
the	O
open	O
interfaces	O
and	O
processes	O
of	O
the	O
proposed	O
CDNI	B-Protocol
.	O
</s>
<s>
The	O
paid	O
ATIS	O
standards	O
and	O
technical	O
reports	O
define	O
specification	O
of	O
use	O
cases	O
and	O
high-level	O
requirements	O
for	O
a	O
CDNI	B-Protocol
.	O
</s>
<s>
According	O
to	O
the	O
freely	O
available	O
abstracts	O
these	O
specifications	O
cover	O
,	O
among	O
other	O
aspects	O
,	O
the	O
interconnection	B-Architecture
of	O
two	O
CDN	O
providers	O
as	O
a	O
foundation	O
for	O
using	O
multicast	O
as	O
a	O
means	O
for	O
distributing	O
content	O
across	O
two	O
CDN	O
providers	O
and	O
for	O
joining	O
together	O
a	O
multiple	O
of	O
CDN	O
providers	O
to	O
form	O
a	O
CDN	O
federation	O
.	O
</s>
