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Publicly
routable IP address on the external interface of the
AV Edge Server |
Publicly routable IP address on the external interface
of the AV Edge Server
The external interface on the A/V Edge server requires
an IP Address which is public routable.
Why do we need the public IP?
Following are the two reasons which leads an AV edge
server to have routable IP Address on its interfaces.
·
A) The A/V Edge server need to reflect back the IP
Address it observed from an external user’s router
because of the following two reasons.
o
This external user IP address is used to enable the use
of efficient media paths using the ICE protocol.
o
To ensure proper IP permissions are set on the A/V Edge
server’s 50,000 port range. If the A/V Edge external
address was behind a NATed IP, the A/V edge server would
return that address instead of the address of the home
router, leading to less efficient (sometimes broken)
media paths and permission issues on the 50,000 port
range.
·
B)
To
support UDP load balancing: UDP is the preferred
protocol to transfer RTP packets for real time
Audio\Video traffic. However, UDP is a stateless
protocol, so some load balancers distribute UDP packets
to the servers without any context for the current
session. To mitigate this, the A/V edge server returns
its external IP address on the first UDP packet of a
media session, and OC or the Meeting Console client
sends subsequent UDP traffic directly to that IP address
instead of through the load balancer. In order for this
mechanism to work, the external IP must be publicly
routable.
Note:
Due to same reason we need routable IP address on the
internal interface as well of the A/V Edge server.
What is ICE?
ICE is a protocol for Network Address Translator (NAT)
traversal for multimedia session signaling protocols
based on the offer/answer model, such as the Session
Initiation Protocol (SIP). This protocol is called
Interactive Connectivity Establishment (ICE). ICE makes
use of existing protocols, such as Simple Traversal of
UDP through NAT (STUN) and Traversal Using Relay NAT
(TURN). ICE makes use of STUN in peer-to-peer
cooperative fashion, allowing participants to discover,
create and verify mutual connectivity.
http://www.ietf.org/mail-archive/web/ietf-announce/current/msg04231.html
What is STUN protocol?
Simple Traversal of UDP through NATs
(STUN), is a network protocol allowing a client
behind a NAT (Network Address Translator) to find out
its public address, the type of NAT it is behind and the
internet-side port associated by the NAT with a
particular local port. This information is used to set
up UDP (User Datagram Protocol) communication between
two hosts that are both behind NAT routers. The protocol
is defined in
RFC 3489
What Microsoft Says?
http://communicationsserverteam.com/archive/2008/03/25/133.aspx
