Significant Speed loss in TCP

**McKenzie!** · 05-07-2011

Recently I have been facing troubleshoot with my TCP speed. I have Roger's router.My speed was D: 21mb/s and U: 0.5mb/s, recently the speed decreased to 2 & 0.3mb/s respectively. My statistics that I have got from MLab are
Your system: Windows 7 version 6.1
Java version: 1.6.0_20 (x86)

TCP receive window: 1240832 current, 1575424 maximum
6.98812E-4 packets lost during test
Round trip time: 120 msec (minimum), 575 msec (maximum), 305.31 msec (average)
Jitter: 455 msec
0 seconds spend waiting following a timeout
TCP time-out counter: 608
108 selective acknowledgement packets received

No duplex mismatch condition was detected.
The test did not detect a cable fault.
Network congestion may be limiting the connection.
No network addess translation appliance was detected.

0.9388% of the time was not spent in a receiver limited or sender limited state.
84.46000000000001% of the time the connection is limited by the client machine's receive buffer.
Optimal receive buffer: 1613234176 bytes
Bottleneck link: Cable/DSL modem
0 duplicate ACKs set

--------------------------------------------------------------------------

WEB100 Kernel Variables:
Client: localhost/127.0.0.1
CurMSS: 1382
X_Rcvbuf: 87380
X_Sndbuf: 258912
SumRTT: 152960
Timeouts: 0
TimestampsEnabled: 0
WinScaleRcvd: 8
WinScaleSent: 7
DupAcksOut: 0
StartTimeUsec: 878458
Duration: 10195052
c2sData: 2
c2sAck: 2
s2cData: 8
s2cAck: 3
half_duplex: 0
link: 0
congestion: 1
bad_cable: 0
mismatch: 0

minCWNDpeak: 11056
maxCWNDpeak: 136818
CWNDpeaks: 1

The theoretical network limit is 1.31 Mbps
The NDT server has a 126.0 KByte buffer which limits the throughput to 6.46 Mbps
Your PC/Workstation has a 1538.0 KByte buffer which limits the throughput to 39.36 Mbps
The network based flow control limits the throughput to 3.41 Mbps

Client Data reports link is 'T1', Client Acks report link is 'T1'
Server Data reports link is 'OC-48', Server Acks report link is 'Ethernet'
What should I do? Please give your advices.

**Amie** · 05-07-2011

As you have mentioned in the question that your speed is 21mb/s / 0.5mb/s i.e. 21 Mbps / 500 Kbps. After seeing your speed it seems your line latency is high. Let me consider that you have a router in the mix, if yes and if you have connected it directly to the modem to eliminate the router then the issue lies there. Do as I recommend, open the command prompt application and type: tracert google.com. After doing that the tracert will show where, your pings spike high at. Check whether its in control or not. Also check the ISP or the actual Internet Cloud peering networks.

**HiSpeed** · 05-07-2011

According to me your modem must be getting 96% of packet loss as you have connected it directly and because of it can’t even run the tests properly.
Your tests results should be like the below:

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.

C:\Users\Corey>tracert google.com

Tracing route to google.com [74.125.91.106]
over a maximum of 30 hops:

1 8 ms 10 ms 17 ms 192.168.1.1
2 23 ms 27 ms 22 ms 10.45.208.1
3 24 ms 31 ms 25 ms 67.231.220.169
4 31 ms 21 ms 20 ms 69.63.248.181
5 147 ms 30 ms 20 ms 69.63.251.142
6 24 ms 21 ms 115 ms 72.14.216.14
7 26 ms 20 ms 29 ms 216.239.47.114
8 60 ms 99 ms 104 ms 216.239.46.170
9 134 ms 101 ms 208 ms 72.14.239.93
10 122 ms 202 ms 204 ms 209.85.248.75
11 136 ms 100 ms 101 ms 209.85.254.237
12 123 ms 103 ms 97 ms 209.85.240.57
13 107 ms 123 ms 61 ms qy-in-f106.1e100.net [74.125.91.106]

Trace complete.

**BiGMaCHiNe** · 05-07-2011

I have seen you MLab stats for high latency. Round trip time: 120 msec (minimum), 575 msec (maximum), 305.31 msec (average)Jitter: 455 msec. According to the tracert everything is going within your home. You First hop latency should be hovering between 1-3ms. Your Roger's router should be not more than 3-6ms, at most. I think you should directly connect to the modem and then run the tests. In the signal level page identify the snooping around. Post the downstream, upstream, and signal-to-noise ratio (SNR) numbers for signals. If the signal levels are poor then, definitely the packet loss resulting to speed degradation. Use the command prompt application for ping and see to it the background applications does not utilize your bandwidth.

**Connect_Me** · 05-07-2011

I have a simple way to check whether your packet data loss. In your command prompt type command: ping -n 30 10.45.208. After doing that if you get the following below result.

command: ping -n 30 10.45.208.1
----------------------------------
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.

ping -n 30 10.45.208.1

Pinging 10.45.208.1 with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Request timed out….

Ping statistics for 10.45.208.1:
Packets: Sent = 30, Received = 0, Lost = 30 (100% loss),
In this way you will get confirmation what is happening.

**Wguy2008** · 05-07-2011

I am confused with the latency of your 10.45.208.1. The reason is that it seems that its not responding in your ping stats to ICMP requests. I just want to let you know that whenever you switch network devices from the modem it needs to be rebooted. Its because it remembers the sync with the last MAC address, in your case it was router. This goes for all routers, hubs, etc network devices.

**teenQ** · 06-07-2011

If your latency stats is solved then you will get the results like below. You will get the results from command: ping-n 30 192.168.100.

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.

ping -n 30 192.168.100.1

Pinging 192.168.100.1 with 32 bytes of data:
Reply from 192.168.100.1: bytes=32 time=19ms TTL=63
Reply from 192.168.100.1: bytes=32 time=20ms TTL=63
Reply from 192.168.100.1: bytes=32 time=43ms TTL=63
Reply from 192.168.100.1: bytes=32 time=64ms TTL=63
Reply from 192.168.100.1: bytes=32 time=87ms TTL=63……..

Ping statistics for 192.168.100.1:
Packets: Sent = 30, Received = 30, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 3ms, Maximum = 87ms, Average = 12ms

Your problem is solved. And you can see that the there is no Loss now.