Conor Daly wrote:
>> I get
>> 3g in most urban areas, in rural areas it's GPRS (and crap).
>>>> How crap is GPRS? Could I use it to collect email from the home server
> and to indulge in things like chat? I could set up a webfilter to block
> all of the ads and flash to reduce browsing load and download limit
>GPRS is about Dialup Speed. About 50k, but variable depending on load.
GSM bases (900/1800MHz, Nationwide Coverage):
GSM, 1 slot = 14.4k (no less, no more)
GSM, 2 slot = 28.8k (no less, no more)
GPRS = UP TO 50kbps ish
EDGE = UP TO about 240 kbps (O2 & Meteor ONLY, Nokia Siemens Networks
have a SW based upgrade just released that slightly more than doubles
speed to UP TO about 569kbps) Not Nationwide.
3G bases (2100MHz, maybe 70% coverage?)
3G = UP TO 380kbps approx
HSDPA = UP TO 1800, 3600, 7200 kbps depending on base/operator (12, 24,
48 max users respectively) 50kbps to 200kbps approx upload depending on
operator. I doubt any 7.2Mbps cells active. Since the HSDPA top speed
is the entire sector capacity of 3G spectrum, it is the most affected
by any other traffic.
3G, unlike GSM uses a CDMA protocol/spread spectrum air interface
upload and download , so adding clients increases everyones noise
(lower SNR) hence cell can shrink to one third leaving people
disconnected. CDMA is cheap simple technology, but scales very badly. A
higher speed version of GSM would have been better, but USA/Qualcomm won
out on specs, an example like MSDOS and original IBM PC of tech going
backwards. 3G's replacement is LTE & HSOPA, not WiMax or Flash-OFDM as
they are more ISP data solutions. HSUPA is a variant of 3G's HSDPA.
HSDPA is just a protocol for data on the 3G signal to use capacity of
multiple calls, up to entire sector capacity. Calls get priority :-)
Backhaul is an issue as many masts only have TDM and some only 2.048
primary ISDN. Only some newer upgrades are native IP based backhaul. A
lot of TDM/ATM used.
Capacity is per sector and is shared with voice calls.
You may not have enough upload for G.711 codec VOIP on any of above.
G.729 is much lower overhead and in theory could run on 2 slot GSM. (In
practice not likely). But packet loss can be high and G.729 does not
cope at all with packet loss. iLBC unlike G.729 is designed for Internet
IP connections with some loss. VOIP uses UDP.
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