IP characteristics for 3G and WiFi links


We are testing protocols on our lab platform and we would like to simulate
communication 2 types of communication :
   - From terminals to service platform using a 3G (HSPA / HSPA+) Access
   - From terminal to service platform using a WiFi Access connection

We are using dummyNet to simulate the links so we are interested in IP
characteristics layers for Packet loss Rate, bandwidth and latency. Values
depends on multiple factors, but we would like to know what mean values are
considered when services are deployed.

Currently we are considering the following values. Packet Lost Rate for L2
seems 7% for Wifi and 5% for 3G. We are wondering how L3 is affected?

Parameter | Wifi (802.11a/g) | 3G (HSDPA)
Latency 100 ms 60 ms
Bandwidth 5 Mbps 3 Mbps
Packet Lost Rate XXX XXX

Any comment links will be appreciated.


TCP retransmits. UDP does not.


WiFi (802.11) uses ARQ to emulate a layer 2 network that has much much lower loss than this (otherwise TCP really wouldn't work over it). I suspect 3G is similar. So both these numbers are highly suspect.

Matthew Kaufman

So, if you want to emulate HSPA you need to understand how it works. If you go from "idle" (30 seconds of not sending data) you will see 1-2 seconds of jitter as radio resources are allocated and brought "online", until you can send packets. There are multiple states, either you have HS resources, or you have regular 384k channel, or you basically have "none". All of these have different characteristics.

Packet loss on 3G is really low as it does re-sends itself, normally you'd see muc less than 1% of packet loss, usually a lot lower than that. There is quite a lot of resending and assuring packets are not lost on multiple layers beneath IP in those networks.

I think you have your latency numbers backwards. In my experience, HSDPA
has higher RTT than WiFi. Why would you limit your Wifi to A/G? If you're using
5Ghz (A), much better to go to N than A. N has slight advantages over G in the
2.4Ghz realm.

Your stated packet loss rates are obscenely high and loss at those rates would
severely degrade user experience. Loss over 1% is enough to cause significant
slow-down in TCP short-lived or interactive flows and 2% is more than enough
to effect even longer continuous data flows.

I have not done comparisons of average loss rates between WiFi and 3G
services where the loss rates were so high because either one would be
basically unusable until the packet loss was reduced.


Nevermind my response; I've been outside in the sun too much pulling
cables through vaults. =P