The Multicast Status web pages provide some
information to describe the growth and general status of the Multicast Enabled Internet,
as seen from the AmericaFree.TV Autonomous System (AS 16517).
There is no one unique measure for the size of the Internet as a whole.
One set of measurements that has proven useful in the past are based on the size of the
unicast (BGP) routing
tables. Estimates of the number of address blocks (prefixes) accessible by BGP
have been available for some years from
Telstra, and more recently
from
KPNQwest, providing a useful
guide to the overall growth of the unicast Internet.
This web pages provides similar
measures describing both the absolute growth in the multicast enabled Internet, and the relative
growth of multicasting compared to that of the Internet as a whole. Currently this information is
updated at least 4 times per day using an automated script.
These graphs are intended to provide a synoptic view of long term changes, and thus
to complement the more detailed short term information available from sources
such as
Mantra.
An Autonomous System (or AS) is a network participating in the Internet but with its own
routing policy.
Each Autonomous System will have a set of address blocks (or prefixes), sets of Internet
addresses assigned to it that are routed in common.
In many ways, the Internet can be viewed as a collection of
Autonomous Systems, and the Border Gateway Protocol (or BGP)
provides the routers of an Autonomous System with the paths required to reach any given address block
in another Autonomous System. (In this context the path is a
list of Autonomous Systems in the order that a packet will have to transit to reach its
destination.) The Multiprotocol extension to BGP (or MBGP) provides this information for
multicast routing. The BGP and MBGP tables thus provide, from any location in the
Internet, complete information about how to route packets to the rest of the Internet.
In this web page we use these tables and other related information as a means of
measuring the size of the multicast-enabled Internet at the Autonomous System level.
For the current list of Autonomous Systems with multicast routing as seen from
AmericaFree.TV, click
here
.
For the master list of all Autonomous Systems with BGP routing as seen from
AmericaFree.TV, including their address and organization name, click
here
.
The oldest archived data available here are from mid-December, 2000. Data logging started
on a weekly basis in February, 2001 and on a daily basis in mid-March. Currently this information is
updated at least 4 times per day using an automated script, with manual updates occurring when
finer time granularity is required.
Note that there is no means of obtaining systematic information about the deployment
of multicast internally on corporate or other closed networks; these graphs only
provide information about the growth of multicast on the Internet.
No one view of the Internet is complete. This is certainly true of the view from AS 16517, and
we encourage others to log and display similar information from their location in the Internet.
It is our hope that others may find this information useful, and
suggestions for other metrics suitable for monitoring on a regular basis would be welcomed.
Any such comments, questions or suggestions
should be directed to Marshall Eubanks at
tme@multicasttech.com
Measures of the Multicast Enabled Internet
Figure 1a : The Number of Prefixes in our MBGP tables - a measure of the extent of the Multicast Enabled Internet
A basic measure of the size of the Multicast Enabled Internet is given by Figure 1a, which shows the
number of address blocks (or prefixes) that have multicast routing as seen
from the AmericaFree.TV Autonomous
System. This number can be expected to grow proportionally to the number of sites that are
Multicast Enabled, as each additional address block will tend to represent a new computer
network (such as a LAN or a WAN) that has become multicast enabled.
Figure 1b : The Number of Prefixes in our BGP tables - a measure of the size of the routable Internet
Figure 1b shows the analogous measure for the growth of the unicast Internet, i.e., the
number of address blocks (or prefixes) that have unicast BGP routing as seen
from the AmericaFree.TV Autonomous
System. This number can be expected to grow proportionally to the number of sites that are
on the Internet, as each additional address block will typically represent a new computer
network (such as a LAN or a WAN) that has become multicast enabled.
Figure 2a : The Number of Autonomous Systems in the Multicast Enabled Internet
The total number of Autonomous Systems with multicast routing, shown in Figure 2a,
provides a different measure of the growth of the multicast enabled Internet. Although
multicast systems represent networks that vary widely in size, each new Autonomous System
with multicast routing represents a new network enabled for multicast. Occasional rapid drops
in the numbers of multicast Autonomous Systems are caused by failure of network links,
and this metric has proven useful as an indicator of network problems.
Click
here
to obtain the current list of Autonomous Systems with multicast routing from
AmericaFree.TV.
For the data used to make this plot, click
here
.
Figure 2b : The Number of Active Autonomous Systems in the Commodity Internet
The total number of Autonomous Systems with BGP routing, shown in Figure 2a,
provides a different measure of the size of the entire commodity Internet.
Again, each new Autonomous System represents a new network, and occasional rapid drops
in the numbers of Autonomous Systems are caused by failure of network links.
Figure 3 a : Useable Addresses in the Internet
with MBGP (Multicast) connectivity
Figure 3 a shows the total number of addresses announced by MBGP (and thus with multicast routing) as
seen from AS 16517.
For the data on domains with active sources used to make this plot, click
here
.
Figure 3 b : Useable Addresses in the Internet
with BGP (Unicast) connectivity.
Figure 3 b shows the total number of addresses announced by BGP (and thus with unicast routing) as
seen from AS 16517.
For the data on domains with active sources used to make this plot, click
here
.
Figure 4 : The Relative Size of the Multicast Enabled Internet :
Addresses, Prefixes (Address Blocks) and Autonomous System Ratios
Although Figures 1a and 2a show
that the multicast enabled Internet has grown in the last few months,
the entire Internet has also grown during that time.
Figure 4 shows the relative size of the multicast enabled Internet for
both address blocks (or prefixes), and for Autonomous
Systems (i.e., the ratio of the number of multicast enabled Autonomous Systems to the
total number active), in order to provide two independent estimates for
the growth of the multicast enabled Internet. Both measures are growing, although the
address block ratio tends to be higher; a reasonable estimate is that the actual
penetration of multicast into the Internet lies somewhere between these two lines.
For the ASN ratio data used to make this plot, click
here
.
For the prefix ratio data used to make this plot, click
here
.
For the Address ratio data used to make this plot, click
here
.
Figure 5 : Autonomous Systems in the Multicast Enabled Internet :
Totals and Those With Active Sources
Figure 5 shows numbers of Autonomous Systems with multicast routing, together with the number
of Autonomous Systems with active multicast groups. Figures 4, 5 and 6 thus provide an indication of
the use of multicast in the Internet.
For the data on domains with active sources used to make this plot, click
here
.
Figure 6 a : Number of Sources and Groups Sending MSDP SA Messages
Figure 6 a shows the number of active multicast groups and sources with MSDP Source-Active (SA) messages,
and thus provides a complementary measure of
the use of multicast in the Internet. A group may have more than one source either
because it is a many to many application, such as a videoconference, or because the receivers
of a one to many broadcast are sending control information, such as the Receiver Reports
sent under the Real Time Transport Control Protocol (RTCP) protocol.
Figure 6 b : Difference Between the # of Sources and the # of Groups
Figure 6 b shows the difference between the number of Multicast sources and the total
number of groups.
As multicast receivers should send out RTCP packets, and therefore should appear as
MSDP sources, this provides a rough estimate of the number of multicast receivers. This
estimate is only a lower bound as
it cannot measure receivers that do not participate in RTCP like control traffic, or
which use unicast control traffic.
Figure 6 c : Average Number of ASM Sources Per Group
Figure 6 c shows the ratio of the number of Multicast sources and the total
number of groups. This plot thus represents an estimate of the number of sources for each ASM group.
More information about the status of MSDP at AS 16517 is available
from the
MSDP status web page.
Figure 7 : Results from the Multicast Test Button
Figure 7 shows a completely different estimate of the size of the multicast Internet :
results from the Multicast Test Button.
This java applet developed by AmericaFree.TV attempts to join the
NLANR
Multicast Beacon, and the resulting success or failure is used as a proxy for Multicast enablement.
As anyone can attempt to try the button, the results serve as a (non-scientific) sample of the Internet,
and thus provide a usage-based estimate of Multicast deployment. Figure 7 shows weekly averages of the
results from the Multicast Test Button from two series, Series 1 (based on manual inspection of the original
Multicast Tech web logs) and Series 2 (compiled automatically from a more detailed system of web logging).
During the period of overlap, the two Series agree reasonably well.
Figure 8a : Histogram of the Number of Autonomous Systems versus the Number of AS Hops to reach them.
Figure 8b : Histogram of the Number of Prefixes Announced versus the Number of AS Hops to reach them.
Figure 8c : Histogram of the Number of Unique Addresses Announced versus the Number of AS Hops to reach them.
Figures 8 a, b and c show histograms of the numbers of Autonomous Systems, Prefixes and Unique Addresses versus
their distance from AS 16517 (AmericaFree.TV) in terms of the number of AS hops, for
both unicast (upper) and multicast (lower).
The histogram for unicast BGP prefixes peaks at 3 hops, while for multicast the peak is at 4 hops.
(In other words, the most typical BGP path from
AmericaFree.TV for
unicast traffic goes through 2 other Autonomous Systems to get to the destination, while
the most typical path for multicast requires traversing 3 other Autonomous Systems.)
This may be a symptom of a less dense mesh of interconnections for multicast, with
fewer multicast enabled links between Autonomous Systems.
Figure 9a : Histogram of the Number of Prefixes Announced versus the Length of the Prefix.
Figure 9b : Histogram of the Number of Addresses Announced versus the Length of the Prefix.
Figure 9c : Histogram of the Number of CIDR Holes versus the Prefix Length of the Hole.
Figures 9 a and b show histograms of the numbers of Prefixes and Unique Addresses
announced to AS 16517 (AmericaFree.TV) versus the Length of the
Prefix, expressed in Classless Interdomain Internet Routing (CIDR) terminology.
(Remember than the longer the prefix, the shorter the address block, all the way to a /32,
which is a single address.) Classful address blocks have been converted to their equivalent
CIDR length.
Figure 9 c shows the number of holes in CIDR address blocks, as a function of the Prefix length
of the hole. (A hole in a CIDR block is when a smaller prefix is announced from the middle of
a larger one.)
More information about the status of CIDR routing at AS 16517 is available
from the
CIDR status web page.
Please be advised that AmericaFree.TV makes no representation or
warranty (either express or implied) as to the accuracy or completeness of this report, and the reader
assumes all responsibility for any conclusions they may derive from the Report. Multicast
Technologies hereby expressly disclaims any and all liability relating to this report, including
without limitation any errors therein or omissions therefrom.
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