[ILUG] Help needed with VOIP & Digital Phone
watty at eircom.net
Fri Mar 6 13:01:52 GMT 2009
Kevin Brennan wrote:
> We made some preliminary tests using vodafone's USB dongle and VoIP
> was perfect.
> USB dongle was connected to a router which accepts USB card which was
> to a Thompson Speedtouch 716 acting as an ATA.
> The far end voip device was a grandstream GXP2000 connected to a BT
> DSL line, codec was G729 - VoIP was peer to peer meaning we did not
> bring RTP stream onto our network.
> As I mention these were very preliminary, we only tested VoIP to VoIP
> calls (and to be honest I was very surprised at quality) we will be
> doing some more rigorous testing to see if we can consistent results.
Did you try calls from DSL without the 3G user explicitly connecting first?
> VoIP phones have built in echo cancellation (as do mobile phones) and
> calls to PSTN are likely to be very echo sensitive unless VoIP/PSTN
> gateways use aggressive hardware echo cancellation (which costs). You
> tend to get echo problems (to analogue phones) when ping times go
> over 50ms, in the TDM world national calls don't need echo
> cancellation as the round trip time would be sub 20ms, international
> destinations normally have echo cancellation as a longer round trip
> time is expected. It's different in the IP world where switches
> introduce delay and local call latency is dependent your hops to the
> ITSP you are using. My point here is that if the VoIP network is
> prepared for high latency then echo should not really be an issue, and
> the only symptom of the large round trip time is some delay in speech.
> Packet loss and jitter are another thing, for the moment you will
> probably find hot-spots which can support VoIP well, but coverage will
> be limited. It's early days for VoIP over mobile broadband and I would
> expect we will see big improvements as demand heightens and networks
> improve with HSUPA, HSOPA etc..
It will get worse as more subscribers added. All my analysis is on HSPA+
aka I-HSPA, which is the next level after HSDPA and HSUPA.
HSOPA is not 3G compatible. It's LTE now, different spectrum, different
handsets/Modems, different Licence and unlike HSPA, HSUPA, HSDPA there
is NO 3G compatibility on the air. You can't support 3G/HSDPA devices on
I've done extensive scientific tests of many Mobile Systems (HSDPA,
EDGE, Flash-OFDM and IPW). You need to know the distance from
mast, the power settings of base that controls cell size, if it's an
isolated cell or has adjoining cells, number of users and what they are
doing and where, or else all you have is an anecdote.
At the minute it's slightly easier to get a workable VOIP call than
throw a six (about 1:5 chance). It only gets worse as customers added.
Since Data application costs x500 the voice for the Operator, the
cell planning and density of subscribers per mast is based on phone
usage not data usage. Voice calls (3G & GSM not VOIP on HSPA/EDGE) have
Your results are anecdotal and not what you can base a strategy or
recommendation because of the variable nature of Mobile compared with
Fixed Wireless, DSL, cable or Fibre broadband.
Yes, VOIP can work on HSDPA/HSUPA/HSPA+/I-HSPA, but with NO reliability
or consistency. Oddly EDGE2 (which we are not likely to see) can do VOIP
a bit better as GSM does not have the evil cell breathe of W-CDMA, the
underlying air interface of UMTS 3G/HSDPA/HSUPA/HSPA+/I-HSPA.
The Mobile companies make a loss or at best break even on Data packages.
The regular phone package pays for it. At best a sector could support 10
VOIP calls, a bit sad compared to 3G voice call capacity, and that
assumes NO voice calls or other data streaming!
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