voip calls using cisco

hi
i have a question..
in order to place a VOIP call and actually achieve very good quality,
is it necessary to use RSVP based resource reservation?? what is the
normal way in which a VOIP call is treated in any IP network?
Does Cisco make use of rsvp mandatory?
are there any other companies that make VoIP gateways?
thanks
t

tease12p

"shido" <> wrote in message
news:8gCPa.4887$ .rogers.com...
> You might want to take a look at www.asterisk.org.

Sort of OT...
>
> -Greg
>
> "tease12p" <> wrote in message
> news: om...
> > hi
> > i have a question..
> > in order to place a VOIP call and actually achieve very good quality,
> > is it necessary to use RSVP based resource reservation??

No - its necessary to have enough bandwidth available for the call, and
latency and drop %age to suit the call quality required.

Many private networks have Voip added using simple priority schemes - but
you need to be able to limit the amount of voip traffic to avoid starving
others uses of the bandwidth of service. Some IP Telephony systems have ways
to limit numbers of calls or amount of bandwidth over particular paths - or
you limit the number of calls within the design.

If there is just one path with limited bandwidth, then limiting the codec
type and number of calls is enough. More complex topologies benefit more
from RSVP, since you reserve bandwidth for calls in progress, and you can
load balance the usage and so on.

RSVP is not ideal - many WAN links are low bandwidth and use compression,
and since RSVP works at layer 3 and header / IP / link layer compression may
be "inivisble" to Voip, the reservations sometimes dont correspond to
bandwidth actually used.

what is the
> > normal way in which a VOIP call is treated in any IP network?

It depends. In a LAN it is usually "so much bandwidth" that voip just gets
absolute priority. Or if the LAN runs at low load ignore priorty all
together - it can work (until something in the traffic profile changes).

The more complex schemes tend to get used where bandwidth is scarce - the
payback is worth the complexity.

> > Does Cisco make use of rsvp mandatory?

No.

> > are there any other companies that make VoIP gateways?
> > thanks

Loads - but compatibility is voip / IP Telephony is not a given. You need
compatible codecs, signalling, and sometimes more subtle stuff still gets in
the way.

> > t
>
--
Regards

Stephen Hope - remove xx from email to reply