An ISP (Internet Service Provider) is the first link, for users, to the public Internet. AOL.com, PeoplePC.com, Comcast.net, Verizon.net are all examples of ISPs.
Most large ISPs cache popular Web pages, only updating them a few times a day, this lowers the telecommunication costs that the ISP incurs in connecting to its upline provider (often a national telecommunications company that charges by the number of bits of data transmitted). You may have noticed the problem of caching while trying to get the most current scores from ESPN.com. Although I am not an avid sports fan, I have seen the scores delayed not because ESPN was slow to update its site, but because the ISP cached a stale copy of the site, sending the stale copy to users who linked into ESPN.com.
Regarding e-mail, the speed of delivery of e-mail is dependent upon three things:
- The performance of the e-mail server (which is the machine on which the e-mail mailbox is stored and which is not necessarily the same machine on which the site’s Web site is hosted)
- The available bandwidth of the user’s connection to the e-mail server (the slowest point in the connection is the bottleneck, whether it is a public connection on the Internet, the connection from the user to his or her ISP, or the user’s home network). Users who pay extra for a high-speed broadband connection of 16Mbps (Megabits per second), yet have a 10Mbps Wi-Fi network in their home are wasting money. Since the bottleneck is the Wi-Fi network, the extra speed of the broadband connection is never tapped.
- The user’s computer (affected by the amount of RAM, CPU speed, and efficiency of the e-mail application).
Regarding Wi-Fi networks. Users can be duped into thinking that a 10Mbps (802.11g) router provides 10Mbps of one-way bandwidth. Actually, a Wi-Fi router splits the available bandwidth by two, reserving half for upstream and half for downstream traffic, plus there is a bit of overhead involved. So, a single user connecting to a 10Mbps Wi-Fi router will actually only download data at about 4Mbps (I’ve rounded the numbers for clarity). If two users were concurrently downloading data from the same Wi-Fi router, the bandwidth is split again, in half.
However, to access data on most Web sites, dozens of connections must be made, each of which could be a bottleneck.
A traceroute between my home and the Web server in Lansing, Michigan indicates 19 hops were made, this evening. If I were to run this traceroute again, the number of hops may be a bit greater or fewer. There are thousands of routes a request for data can take, that is the essence of packetized data transfer and the inherent strength of the Internet. Files are broken into small packets, each of which is transmitted in the fastest manner to its destination…any given number of packets do not have to each follow the same path.