Thursday, September 13, 2007

How to Detect Slow Link with a formula



Here is the scenario; you have connected to the client PC, who is complaining about seeing big Christmas balloon "Exchange is retrieving information from ExchangeServer". The outlook freezes up client cannot do anything, the windows are not responding to anything, task manager is the only way to kill the outlook and get back to a desktop. As soon as outlook opens up the problem arises.16000 ms (number miniseconds per minute) divided by /average millisecond on the extended ping. Slow link detection is accomplished with consecutive ICMP pings that are sent to the Authenticated Domain Controller. IF the response from any of the pings is less than 10 Millisecond (ms) the link considered to be a fast link.

If the response from any of the pings is higher than 10 Millisecond, this indicates latency. Here is the magic formula as below

Link Speed = 16000 / (average ping for 2048 byte packet)

Now we will do troubleshoot and find out the culprit. The message may cause for several reasons, including

  • Poor Network Connection (Not enough bandwidth) this is what the cause in most of the cases. If VPN is being used, even WORST, Because now every traffic is going inside of VPN tunnel which is encrypted, so implement RPC/HTTPS or recommend to use
  • Exchange server is performing poor
  • I/O issues, CPU, HD, Memory Bottleneck
  • GC is performing poor, when Exchange does the queries, this is Chocking exchange down.
  • Local PC related issues (NIC speed, HD, CPU, Memory)

Now let's get to a work and show you the use a formula and find out the speed of the client

  • Click Start, Run, CMD

You need to know the IP address of the Exchange server, so in this example the IP Address of the Exchange server is 10.74.0.41

In the CMD windows type below

  • -l is resizing the ICMP Packet Size
  • -t (Extended ping, Ping the specified host until stopped.)

C:\>ping 10.74.0.41 -l 2048 -t

Pinging 10.74.0.41 with 2048 bytes of data:

Reply from 10.74.0.41: bytes=2048 time=570ms TTL=126

Reply from 10.74.0.41: bytes=2048 time=253ms TTL=126

Reply from 10.74.0.41: bytes=2048 time=397ms TTL=126

Reply from 10.74.0.41: bytes=2048 time=216ms TTL=126

Reply from 10.74.0.41: bytes=2048 time=322ms TTL=126

Reply from 10.74.0.41: bytes=2048 time=405ms TTL=126

Reply from 10.74.0.41: bytes=2048 time=708ms TTL=126

Reply from 10.74.0.41: bytes=2048 time=157ms TTL=126

Reply from 10.74.0.41: bytes=2048 time=217ms TTL=126

Reply from 10.74.0.41: bytes=2048 time=207ms TTL=126

Ping statistics for 10.74.0.41:

Packets: Sent = 10, Received = 10, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

Minimum = 157ms, Maximum = 708ms, Average = 345ms


Average is 345 so the formula will be

16000 / divide into 345 = 46Kbpc

The link would be considered slow, the trash hold round-trip time for a fast link (default = 500 Kbps) is 32 ms. This is great way to see the link speed and make some assumptions and recommendations. If you remember on 100meg LAN connection the Speed would be less than 1ms, if you perform the same test within the LAN.

From Experience if these ms go above 200 and up, good luck even opening up Outlook. The bandwidth is the culprit and client must get better conection.

Best Regards,

Oz ozugurlu

1 comment:

AL said...

if exchange client connect to exchange server from long distance/different country? how it take 1024? result around 73ms
i try use 2048, result rto ....