Data Throughput





UMTS - Rlease 99

As I implied in questions listed above and as I experienced, the types of throughput test (I would call this "Failure Mode") differs depending on what kind of radio technology you are using.


In case of R99, I don't see many issue about the problem of "low throughput". The failure mode seems to be more like "All or None", most common problem seems that it started working with full throughput (All) as specified in Radio Bearer Setup and all of the sudden the data path stop working (No throughput).


Let's look into overall data path of R99. I illustrated as follows but it may not be exact in terms of data packet size and number of data packets in each layer.. but I just wanted to give you overall path and relative packet size comparison across the multiple layers.

(This is transmitter side data path and the reciever side data path would be almost same, but just in reverse path).


Normally I look at the first input and the last output at the first step. In most case, the first input is an "IP packet" from the server PC (e.g, "UDP packet" generated by iperf). The size of the data would be around 1500 bytes or just a little less.

Then what is the last output of the data path ? It is L1 output. What is the size of the data frame at L1 ? It gets different depending on the radio bearer setup and even with the same radio bearer each radio frame may carry different data size depending of TFCI selection for each transmission. So I cannot specify any fixed frame size, but I can say it is much less than one IP packet. It means that the input data size is much bigger than the final output data size. It implies that somewhere in the data path, there should be some steps where the input data (IP packet) is get splitted into multiple chunks each of which can be fit into final output data size.

Then you would guess what should be done on reciever side. The reciever should recombined all those fragmented chunk into the orignal IP packet and push up to IP tools.


One of the common problem that may happen in R99 case would be

i) problems at the split and recombine process

ii) problems at selected proper frame size at L1 (selecting proper TFCI)


If any problem happens in these step, it normally lead to total data throughput stop (not just a small throughput drop). But recently I don't see many of throughput problem in R99. It is now very mature technology.