Sunday, February 28, 2010

See how a lunch in 1989 impacted our life today and for many years to come

For those of you that need introduction “Yakov Rekhter” is one of the fathers of BGP and MPLS Architecture, I hope you will all enjoy this Lecture (disregard the Juniper logo :-))

[ OFF TOPIC ] Wet iPhone

Few days ago I have been driving my motorcycle back from work to my home, there was at the time an unexpected pouring rain, needless to say I was wet to my bones When I have arrived home I saw that my iPhone suffered a wet shower, I didn’t know if it damaged my iPhone as it was functioning, so I went to sleep. the next day I tried to open my phone and my precious iPhone refused to function properly, the screen was really dark, I started to cry (not really) then I went to my friend to search for a solution, I saw that someone had saved his blackberry using a bawl of rice, I was skeptic and started to plan the funeral but I have inserted my precious to a bawl of rice (Persian rice), then after almost 2 nights I have opened my iPhone and like magic it started speaking to me again.

conclusion:

  • driving in motorcycle in the rain can damage your iPhone!
  • A bawl off rice can be more then a Chinese side dish

Friday, February 26, 2010

[ OFF TOPIC ] VMWARE ESX Clone

Ok, I wish to share with you a tool I created and is helping me in my day to day work. for thouse of you that are using ESX or ESXi (especialy the ESXi as it is free) without the Virtual Center you probebly noticed that there is no clone option, now it is no problem for us tech people to overcome this problem, but some times we are lazy (dont tell that to anyone). I have done a simple shell script that run under the ESX or ESXi console (in the ESXi there is the unsupported console) please noice as I written it very fast and for my use it has almost no tolerance for user error so play with care. Get it here

Thursday, February 25, 2010

TCP Over Satellite communications

First I would like to say it has been a very long time since my last article, but now I am in the mode for writing so I would like to share my expireance with TCP and Satellite Communication challanges. I am working at Expand Networks and one of our advantages is in optimizing TCP communication in challanging enviorments such as Satellite, so what is so challanging you ask??
  • The Satellites we use for communication are up in the sky ~35000 kilometer away from ground also called GEO Sat
  • Communication between ground station to the Satellite easly impacted from enviorment (clouds, rain, snow, solar events...)
  • Satellite is a shared resource

All the Satellite set a big challange in TCP communication, one of the main is RTT (round trip time), the other is packet loss due to channel error's the satellite may encounter.

To overcome this challanges we use some of the avilable TCP enhancments avilable such as: proxying the TCP session and in the session over the satelite increasing Window Size using the window scale options. additional to that selecting the congestion control that is most suitable for the enviorment we are in. the congestion control as his name indicate is an algorithem that tells the TCP when to back off because a congestion was detected or when to continue and at what level to send the tcp traffic.

Here are Some of the Congestion Control Algorithems:

Reno - the most common used today by default (linux implement NewReno), basicly during the slow start increasing 1/cwnd for each ACK recived and decrease by 0.5 if a loss was detected

BIC - binary increase congestion as the name imply it uses some binary search algorithem to esitimate the correct cwnd

CUBIC - another algorithem considered some kind of enhancment to the BIC algorithem

Hybla - some kind of a hot topic in congestion control algorithem over satellite communication

Vegas, illinois,Veno, Westwood....

basicly you can see that there are many algorithms out there and all are created due to diffrent challanges sattelite , wireless or even wired communication had brought over the years.

There is no ultimate algorithem that can handle all sitiuations (as of today), each have his advantages and disadvantages, Reno is ok when delay is going +-20ms + RTT but more then that if you had +-100ms + RTT with Reno you would be in a problem as it would often back off the window by half.

Risk Management - Quantitative risk assessment

The name kind of give away the type of assessment we talk about "Quantitative" according to google translate: relating to, meas...