Upstream bitrate per modem in D1.1

Hi!

We're having a bit of a struggle getting high throughput on upstream traffic in a BSR 1000 EuroDOCSIS. Aggregate throughput seems to be OK and as expected by the 3.2 MHz width and 16QAM modulation (we see peaks of 7 Mbps, so there should be headroom to the maximum capacity of 8.8 Mbps with this setup). The problem is the throughput for each modem which maxes out just below 3 Mbps. I'm used to D2.0 where I believe things are handled a bit differently, and I know I have had cases where an SB5101E has used up all 8.8 Mbps of a similar channel.

Downstream is no problem. We get 25 Mbps as configured in the modem file.

Reading through documents on the web, I see that the MAP interval and latency in combination gives a modem 250 opportunities per second to send packets. Using 1518 byte packets this calculates to near 3 Mbps, which is consistent with our results with the BSR 1000 Euro. I have tweaked the MaxTrafficBurst parameter and I can clearly see that a too low value (1522 to 4066) gives less performance than higher values. 60880 as in the config below may be excessive, but doesn't pose a problem.

Here comes the interesting part. Using the exact same modem and Windows 7 PC and directing the modem to an Arris C3 running TDMA and 16QAM/3.2 MHz upstream, we get more than 5.5 Mbps upstream rates per modem. Since the C3 US is running TDMA, I'd say it should behave just like a BSR 1000, which cannot do ATDMA,. but does TDMA of course, even though the C3 is D2.0 capable. They both run in D1.1 mode basically, or is this not true?

Measurements have been made with iperf (tcp and udp), FTP upload and web sites with bandwidth test pages, all with the same result.

My question: Is there an actual limitation of 3 Mbps per modem on upstream in a D1.1 CMTS (or the BSR 1000 specifically)?

Backgrund info:

Modem file:

Main
{
NetworkAccess 1;
DocsisTwoEnable 1;
SnmpMibObject cmDocsis20Capable.0 Integer 1; /* true */
GlobalPrivacyEnable 1;
BaselinePrivacy
{
AuthTimeout 10;
ReAuthTimeout 10;
AuthGraceTime 600;
OperTimeout 10;
ReKeyTimeout 10;
TEKGraceTime 600;
AuthRejectTimeout 60;
}
MaxCPE 2;
UsServiceFlow
{
UsServiceFlowRef 2;
QosParamSetType 7;
MaxRateSustained 6194304;
MaxTrafficBurst 60880;
MaxConcatenatedBurst 60880;
SchedulingType 2;
TrafficPriority 2;
}
DsServiceFlow
{
DsServiceFlowRef 1;
QosParamSetType 7;
MaxRateSustained 26214400;
MaxTrafficBurst 30440;
TrafficPriority 7;
}
}

BSR 1000 Euro config (relevant parts of it):

interface cable 0/0
ip address 172.22.0.1 255.255.254.0
ip address 104.213.6.1 255.255.255.0 secondary
cable helper-address 192.168.1.2 cable-modem
cable helper-address 192.168.1.2 host
no shutdown
cable downstream 0 frequency 5060000000
cable downstream 0 power-level 500
cable downstream 0 rate-limit
no cable downstream 0 shutdown
cable upstream 0 frequency 45000000
cable upstream 0 power-level 70
cable upstream 0 pre-equalization
cable upstream 0 rate-limit
no cable upstream 0 shutdown
cable upstream 1 frequency 45000000
cable upstream 1 power-level 70
cable upstream 1 minislot-size 8 # Just playing around...
cable upstream 1 pre-equalization
cable upstream 1 rate-limit
cable upstream 1 physical-delay automatic
no cable upstream 1 shutdown
cable upstream 2 frequency 45000000
cable upstream 2 power-level 70
cable upstream 2 pre-equalization
cable upstream 2 rate-limit
no cable upstream 2 shutdown
cable upstream 3 frequency 49000000
cable upstream 3 power-level 70
cable upstream 3 pre-equalization
cable upstream 3 rate-limit
no cable upstream 3 shutdown
cable dynamic-service authorization-mode unauthorize
ip dhcp relay information option
no cable flap-list trap-enable
cable downstream schedule priority-wfq
!
packet-cable
dqos shutdown
no em shutdown
!
ipsec
ipsec shutdown
!
enable rdn-process

Version: BSR 1000R(tm) version 2.0.1.08P02.PRRU

#show cable modem detail 5c35.3b4c.7c11
CM Record (index 12) Dump:
Psid 20
Config 0xb
Status regComplete
BPI Enabled Yes
MAC Address 5c35.3b4c.7c11
IP Addr 172.22.0.251
US Chan 1
DS Chan 0
Vendor Id 00 00 00
MAX Classifier 0
MAX CPEs 2
--Ranging State--
State 0x4
Retry 0
NoReqCount 0
Pending 0
Rx Power 92
Freq Offset -16
Timing Offset 846
Last Invited 26648091(ms)
Max Interval 12229(ms)
Max Req Delay 130811(ticks)
Equalization Data:
00 20 ff e0 00 00 00 60 00 20 ff e0 3d c0 00 00
00 a0 ff e0 00 20 ff e0 ff a0 00 20 00 60 00 00
##CM Capability:##
Concatenation: 1
DOCSIS Version: DOCSIS 2.0
Fragmentation: 1
PHS: 1
BPI: 1
DS SAIDs: 15
US SIDs: 16
Transmit Equilizer: 1(Taps/Symbol)
Xmit Equilizer Taps: 24
DCC Support: 0

#show cable modem 5c35.3b4c.7c11 svc-flow-id
Service flow id Interface Flow Direction Flow Max Rate
119 cable 0/0 Upstream 6194304
120 cable 0/0 Downstream 26214400

#show cable modem 5c35.3b4c.7c11 mac
MAC Address MAC Prim Ver Frag Concat PHS Priv DS US
State SID Saids Sids
5c35.3b4c.7c11 online 20 DOC1.1 yes yes yes BPI+ 15 16

The tested modem is a Motorola/Compal CBN CV6181E, but other modems behave exactly the same.

I'd be most grateful for any response!

/Fredrik