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Data Throughput |
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UMTS - HSPA
HSPA has evolved a long way and throughput has been improved greatly according to the evolution. What I will talk about in this note is about general factors determining the maximum throughput of variants of HSPA.
Whenever I have inquiries about HSDPA related throughput problem, I am going through the following check list.
i) Does the Network (or Network Emulator) define TFRI table for max throughput ? ii) Does the TFRI Index has been selected at each transmission for max throughput ? iii) Does UE reflect the proper category information on ‘RRC Connection Setup Complete’ ? iv) Does HARQ memory model is properly configured in Radio Bearer Setup ? (e.g, Implicit vs Explicit, Number HARQ, HARQ Memory Size etc) v) Does PHY layer shows any HARQ Retransmission ? vi) Does RLC shows any retransmission ? vii) Does PC inject the packet which is big enough to fully utilize the data pipe defined by theNetwork? viii) Does PC inject the data packet as frequently to fully utilize the data pipe ?
Now you may understand why I put such a amphasis on having proper logging tools for throughput troubleshoot. Almost none of the list you can check without having proper logging tool. The best option is to have such a logging tool both on Network side and UE side, but if not.. you should have the tools at least on one side (UE or Network).
Now let's look into overall data flow. In HSDPA case, the packet size at the input stage (IP packet size) is similar to the final L1 frame size, even though the final L1 frame size can be a little bit smaller and larger than the input packet size depending on HSDPA Category. But still you have MAC-d is involved in the data path and the MAC-d packet size is much smaller than IP packet size and L1 frame size. It means the IP packet should get splitted into multiple small chunks to go through MAC-d and have to be reassembled before it gets into L1. I don't think this is very efficient process but we would not be able to get rid of MAC-d because of current UMTS network architecture. Technically this kind of split/combine process can be a source of problems.
In HSDPA case, there is another issue that make situation complicated. In R99 case, the most common L1 transmission timing is 10 ms (1 TTI = 10 ms), but in HSDPA case the most common L1 transmission timing is 2 ms (1 TTI = 2 ms). It means that if L1 frame size is similar to one IP packet size, the PC tool should be able to create IP packet 500 times per second and Network's internal layer is operating fast enough to pass all those packets down to L1. It implies that PC performance or PC configuration can be a bottle neck for throughput test (especially HSDPA Category 8, 10 case).
For your reference, I created a table showing you a maximum (near maximum) throughput for most commonly used HSDPA categories. Just for this throughput issues, let's just focus on TTI, TBS, PDU. TTI shows how often a network transmit a chunk through PHY layer. For example, TTI = 2 means the network transmit a PHY layer data chunk every 2 ms. TBS is Transmit Block Size. The unit in 3GPP table is in Bits, but I added another column showing TBS in Bytes just for you to easily compare it with IP packet size which is normally expressed in Bytes. For example, if TTI = 2 and TBS = 3630, the network transmit a data chunk with the size of 3630 (about 453 bytes) bits every 2 ms. PDU is the data chunk of MAC-d. So PDU size is the size of data chunk getting out of MAC-d. If you compare PDU size and TBS, you will notice that TBS (PHY data chunk) is much bigger than PDU size. If you compare PDU size and common IP packet size (1500 Bytes), you will notice IP packet size is much bigger than PDU size. Putting all these together, you will figure out that in this process an IP packet should split into many PDUs and those many PDUs should be reassembled into a single Transport Block(TB) and then get transmitted through antenna. This is the meaning of diagram shown above.
Another important thing you can notice from the table above is that from Category 8, one transport block size gets bigger than one IP packet. It means that PC has to tranmit one or more IP packets every 2 ms. If you see Category 10, you will notice that PC(Data Server) should be able to transmit more than 2 IP packets every 2 ms. So in this case, PC performance greatly influence the overall throughput.
So my recommendation, especially for high data rate category, is for you to check PC setting/performance and see if the PC performance is good enough for this testing. (Connect the client and server PC directly with LAN cable and do the PC-to-PC wireline throughput test and make it sure that the throughput is well higher than the expected UE throughput.
If you fully understood what was explained in HSDPA section, you can easily understand what would be the critical issue for HSPA+. Simply put, in HSPA+ case, you will have much bigger TBS comparing to conventional HSDPA. So you would guess, IP layer performance (e.g, Data Server and Client PC) would be much more important comparing to HSDPA case.
Just to give you clearer idea on this process. I put down the data flow at each layer. Go over these examples with special attention to the data size that I put in ( ).
< Example 1 > Cat 14, Ping Test
TE -> RLC : (60 Bytes) 45 00 00 3c 00 e5 00 00 80 01 b6 88 c0 a8 01 02 c0 a8 01 01 08 00 48 5c 03 00 02 00 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e 6f 70 71 72 73 74 75 76 77 61 62 63 64 65 66 67 68 69
RLC -> MAC : (82 Bytes = 656 Bits) 80 0d 79 fe 45 00 00 3c 00 e5 00 00 80 01 b6 88 c0 a8 01 02 c0 a8 01 01 08 00 48 5c 03 00 02 00 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e 6f 70 71 72 73 74 75 76 77 61 62 63 64 65 66 67 68 69 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
MAC->L1 : (3372 Bytes = 26976 Bits) 00 40 1c 00 6b cf f2 28 00 01 e0 07 28 00 04 00 0d b4 46 05 40 08 16 05 40 08 08 40 02 42 e0 18 00 10 03 0b 13 1b 23 2b 33 3b 43 4b 53 5b 63 6b 73 7b 83 8b 93 9b a3 ab b3 bb 0b 13 1b 23 2b 33 3b 43 48 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ..... 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
In terms of throughput perspective, you can think of HSPA+ Dual Carrier as two HSPA+ running in parallel. So the IP layer tool performance will be almost critical factor. In this case, Data Server should be able to transmit almost 9 IP packets every 2 ms. In the same token, this means Client PC to which UE is connected to is working fast enough to receive all of these data and process. So the client PC performance is important as well
< Example 1 > Cat 24, Iperf UDP
TE -> RLC : (1498 Bytes) 45 00 05 da bf b5 00 00 80 11 f2 09 c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4c f0 00 00 00 41 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ff e8 90 ..... 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39
TE -> RLC : (1498 Bytes) 45 00 05 da bf b8 00 00 80 11 f2 06 c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4c ed 00 00 00 44 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ff e8 90 ..... 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39
TE -> RLC : (1498 Bytes) 45 00 05 da bf b8 00 00 80 11 f2 06 c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4c ed 00 00 00 44 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ff e8 90 ..... 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39
TE -> RLC : (1498 Bytes) 45 00 05 da bf b8 00 00 80 11 f2 06 c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4c ed 00 00 00 44 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ff e8 90 ..... 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39
RLC -> MAC : (1500 Bytes) 81 de 45 00 05 da bf af 00 00 80 11 f2 0f c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4c f6 00 00 00 3b 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ff ... 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39
RLC -> MAC : (1500 Bytes) 81 de 45 00 05 da bf af 00 00 80 11 f2 0f c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4c f6 00 00 00 3b 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ff ... 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39
RLC -> MAC : (1500 Bytes) 81 de 45 00 05 da bf af 00 00 80 11 f2 0f c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4c f6 00 00 00 3b 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ff ... 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39
RLC -> MAC : (1500 Bytes) 81 de 45 00 05 da bf af 00 00 80 11 f2 0f c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4c f6 00 00 00 3b 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ff ... 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39
MAC-> L1 : Primary Channel (5274 Bytes) eb b8 f4 eb b8 eb b8 e5 fb 81 1a 45 00 05 da bf 97 00 00 80 11 f2 27 c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 74 2d 00 00 00 23 4d cc 77 da 00 06 7e 63 00 00 00 00 00 00 00 01 00 00 13 89 00 ..... 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 81 22 45 00 05 da bf 98 00 00 80 11 f2 26 c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 74 2c 00 00 00 24 4d cc 77 da 00 06 7e 63 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 ..... 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 81 2a 45 00 05 da bf 99 00 00 80 11 f2 25 c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 74 2b 00 00 00 25 4d cc 77 da 00 06 7e 63 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ..... 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 81 32 45 00 05 da bf 9a 00 00 80 11 f2 24 c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4d 0b 00 00 00 26 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ff e8 90 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 ...... 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34
MAC-> L1 : Secondary Channel (5274 Bytes) e5 be fa eb b8 eb b9 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 ...... 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 81 3e 45 00 05 da bf 9b 00 00 80 11 f2 23 c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4d 0a 00 00 00 27 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ff ff e8 90 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 ...... 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 81 42 45 00 05 da bf 9c 00 00 80 11 f2 22 c0 a8 01 02 c0 a8 01 01 04 61 13 89 05 c6 4d 09 00 00 00 28 4d cc 77 da 00 06 a5 82 00 00 00 00 00 00 00 01 00 00 13 89 00 00 00 00 02 9f 63 00 ...... 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 36 37 38 39 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...... 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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