Mobile Skype: Quality Issues?
Skype's introduced a PDA version that will work with 802.11b-enabled Pocket PC handhelds with more than 40 Mbytes of memory onboard (see Skype Me? Skype You! on the regular Skype client).
In theory, this is an application that enables users to -- at least partially -- bypass wireless carriers: If users live in an area with plentiful WiFi hotspot access and all their friends and family use Skype.
That's a big if, if you consider the nature of hotspot coverage when compared with traditional mobile networks: It's spotty, at best...
How spotty? Get all the details on Unstrung.
— Dan Jones, Site Editor, Unstrung
1) Skype use Voice codec from Global IP sound that supposed to be able to tolerate 30% packet loss with no loss in voice quality. I do nto know whether it is true
iLBC is a very good compression codec but the voice quality does drop off significantly if you have sustained packet loss. For those who aren't familiar, the iLBC codec from Global IP Sound supports basic frame sizes of 20 and 30 mSec. It's toll quality at relatively low complexity compared to, say, G.728. It's quite good at dealing with dropped packets.
Given that Wifi, DSL, Cable Modem has a lot more bandwidths than it is required for voice. Waste bandwidth so it can works in a low quality transport situation looks more reasonable that required QOS in all networks. Bandwidth is cheap in those scenerio
For voice over cable service offered by the MSOs, they're going to eventually phase in compression codecs. Bandwidth is cheap until you do the analysis on running multiple simultaneous G.711 VoIP streams on a single DOCSIS upstream frequency. DOCSIS has big pipes on the downstream and small pipes on the upstream. DOCSIS 2.0 repairs this somewhat but there's no DOCSIS 2.0 plant deployed yet and cable modems are mostly at DOCSIS 1.0 and 1.1.
The 'bandwidth is cheap' argument works great on a PowerPoint slide deck but when you do the real traffic analysis on the access network, VoIP ends up being a real hog if you have 30% market penetration on homes passed and are traffic engineering using traditional telco erlang numbers. You end up having to double your DOCSIS cable modem plant if you assume a 10% take rate on cable modem and 30% take rate on telephony. 2x the number of fiber nodes. Twice the fiber. 2x the number of CMTSs. Truck rolls to partition the network and move amplifiers around.