Suppose users share a 1 Mbps link. Also suppose that the traffic generation proc

Question

Suppose users share a 1 Mbps link. Also suppose that the traffic generation process of each user alternates (independently of the other users) between periods of activity (active modes), when the user generates data at a constant rate of 100 Kbps and periods of inactivity (inactive mode) when the user generates no data. Suppose further that the user is active (independent of other users) only 10 percent of the time. (1) When circuit switching is used to allocate resources on the shared link, how many users can be supported? (2) Suppose now that users are supported by using accordance with a packet switch- ing method, so that the communications channel is shared on a statistical mul- tiplexing manner (rather than being shared by using the synchronous (fixed) multiplexing techniques employed by the circuit switching system). Assume now that the communications channel is used to support a number of users that is 4 times larger than those supported under the circuit switching oper- ation. What is now the probability that more than 10 simultaneously active users cannot be accommodated at a given point in time? Equivalently, what is the probability that 11 or more users are simultaneously in active mode at a given time? 2

Explanation / Answer

There are hundreds of quality dedicated server providers around the world. Some dedicated server offers come with 10Mbps and some with 100Mbps up link port speed – what should I chose when ordering a dedicated server? In order to understand network speed, let’s look at the following transfer speeds and calculations: 1024Kbps = 1Mbps (316GB per month if used 24/7). 10Mbps used 24/7 can transfer 3164GB per month or 105.4GB per day. 100Mbps can transfer 31640GB per month or that is roughly around 1054GB per day. And that is just in one direction – the server has incoming and outgoing bandwidth. Before you sign-up with a new dedicated server company, ask their sales how they calculate the bandwidth. Is it the highest from incoming or outgoing bandwidth or it’s incoming plus outgoing (in+out). For the web server or ftp hosting, the highest will be the outgoing bandwidth, unless your clients are uploading ftp files to your server all around the clock, or your server is getting a flood (incoming bandwidth). Of course the network latency will be much less and files served much faster with 100Mbps up link, comparing to overloaded 10Mbps up link connectivity in peak times. For example 9 users downloading at around 1024Kbps (1Mbps) files from your server will use the 10Mbps up link around 90% of the total capacity or only 9-10% of 100Mbps uplink capacity. This clearly shows that some of the users (or users who will connect to the server) will get some packet loss and transfer speed will decrease on the 10Mbps port, but not on the 100Mbps up link. We believe in our example that there is no packet loss in the upstream providers. You're probably getting this connection speed from the icon at your task tray, correct? That's the maximum speed of your interface, which is 100MB/s, but that's not your actual internet speed.

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