At the core of any
carrier class Voice over IP
service, a Session
Border Controller will be
found. The Session Border
Controller or SBC is powerful device
that allows for the separation of
core components such as SIP
Proxies, Soft Switches and
Class 5 VoIP switches from
their high density
subscribers. A
Session
Border Controller is a
device used in some VoIP
networks to exert control
over the signaling and
usually also the media
streams involved in setting
up, conducting, and tearing
down calls.
The unique
problems associated with
Network Address Translation
(NAT) and Firewalls with
respect to VoIP traffic can
present a multitude of
issues that a session border
controller can solve. In its worst form a
subscriber may be completely
blocked from service, in
other cases unreliable
connections and audio
problems will plague support
personnel. The Session
Border Controller provides
this function without having
to add a multitude of
servers to your core
components.
Within the
context of
VoIP, the
word
"Session" in
Session
Border
Controller
(SBC) refers
to a call.
Each call
consists of
one or more
call
signaling
streams that
control the
call, and
one or more
call media
streams
which carry
the call's
audio,
video, or
other data
along with
information
concerning
how that
data is
flowing
across the
network.
Together,
these
streams make
up a
session, and
it is the
job of a
Session
Border
Controller
(SBC) to
exert
influence
over the
data streams
that make up
one or more
sessions.
The word
"Border" in
Session
Border
Controller
(SBC) refers
to a point
of
demarcation
between one
part of a
network and
another. As
a simple
example, at
the edge of
a corporate
network, a
firewall
demarcs the
local
network
(inside the
corporation)
from the
rest of the
Internet
(outside the
corporation).
A more
complex
example is
that of a
large
corporation
where
different
departments
have
security
needs for
each
location and
perhaps for
each kind of
data. In
this case,
filtering
routers or
other
network
elements are
used to
control the
flow of data
streams. It
is the job
of a Session
Border
Controller
(SBC) to
assist
policy
administrators
in managing
the flow of
session data
across these
borders.
The word
"Controller"
in Session
Border
Controller
refers to
the
influence
that Session
Border
Controllers
have on the
data streams
that
comprise
Sessions, as
they
traverse
borders
between one
part of a
network and
another.
Additionally,
Session
Border
Controllers
often
provide
measurement,
access
control, and
data
conversion
facilities
for the
calls they
control.
When thousands of
subscribers equipment
must re-register to your
core VoIP components at the
same time, this can severely
cripple servers and proxies
that are under powered. With
the threat of hackers,
viruses and Denial of
Service (DoS) the Session
Border Controller can
protect a network.
With the transition
from carrier based H.323
networks to the growing
and popular SIP protocol,
the Session Border
Controller allows
transparent conversion from
legacy H.323 networks and
interoperability with SIP
based networks.
These are just a few of
the important functions a
Session Border Controller
performs. Please see our
Ncite product line of
Session Border Controllers
for more information and
specifications.
