Networking

I purchased a server from Dell recently. Want to use it as a test server to play with at home. I have a small LAN at home setup using a Dlink 614+ router. I forwarded some services to the server, so that I can access it remotely. Since the IP address on my cable modem changes every so often, how do I access it remotely? Dynamic DNS from dyndns.org to the rescue :).

Register for an account over here.
Create a Dynamic DNS host on Dyndns.org
Log into the 614+ router
Go to Tools –> Misc.
Enable DDNS
Use members.dyndns.org as the server address
Enter the complete hostname (ex. Samurai.kicks-ass.net)
Enter the username and password that you have registered at dyndns.org
Click on “Apply” and you are all set.

Came across this article on security-protocols.com in which the author discusses DDoS (Distributed Denial of Service). I was particularly interested since we have been experiencing such attacks on our network recently. Unlike DoS (Denial of Service) attacks where the source of attack can be easily identified and blocked, it is very difficult to identify the source of DDoS attacks. The only way we can stop the attack is by blocking all traffic to the destination of the attack. And this is exactly what the attacking party wants. I don’t see a solution to this in the near future. A good point that the author mentions is that all routers should have ingress and egress filtering configured properly. This in effect allows only authorized networks to originate and terminate at a router, thereby minimizing the ability of an attacker to use a spoofed IP address.

As mentioned here, I work in the satellite industry. I am pretty new to it and everyday is a learning experience. Today, I sat down with our in house satellite guru and found out how one calculates the bandwidth occupied by a carrier from the from the data rate on a satellite link. The formula is

Where
BW_AL = Bandwidth allocated for the satellite link in Khz.
S_r = Symbolrate of the link in Ksym/s (Kilo Symbols per second).

S_r in turn is calculated using the following formula

Where
D_r = Datarate in Kbps.
MI = Modulation Index (The values of MI for the different modulations are BPSK=1 | QPSK = 2 | 8PSK = 3 | 16PSK=4 | 16QAM = 4).
FEC = Forward Error Correction.
RS = Reed Solomon value. This can vary depending on what values are being used. Reed Solomon is an external codec as compared to Turbo which is a stand alone codec. If RS is not being used in the link, then a value of 1 is used.

Pretty confusing eh :). As if though this is not enough, there is another value called Information rate (I_r). And the formula for that is

Think that is enough satellite technology for one day :).

I work at a teleport and most of our business is related to providing Internet service to ISPs in South Asia. One of the most frequent complaints that our help desk gets is “My link is slow, you guys are not providing us the complete speed”. Usually it is a case of the customer not understanding the finesse of TCP/IP. I came across this article by Adam Grow III. He uses the following formula to calculate the maximum possible speed per session on a link.

Where
Throughput is measured in Kilobits per seconds (Kbps)
TCPS = Size of the TCP/IP stack in byte (Windows default is 8192)
PropDelay = propogation delay in seconds

Using the above formula, for a geostationary satellite (where the propogation delay is ~540ms), the throughput is ~120Kbps. So even if the client has a 1Mb link and he just has one session, he can only use a fraction of the link. Only multiple sessions can saturate the link.