How Fast?
So a key question is how much throughput or bandwidth do you need? The answer depends on what you are doing on your network.
These terms are generally used interchangeably to refer to the "Mbps" number that you can find somewhere in wireless LAN products' specifications. They are all ways of referring to the amount of data ("Mb" or megabits) per unit time ("ps" or per second) that can be handled by the product.
Speed and Throughput actually can be used interchangeably. But think of them as describing the maximum rate that data can be handled for a single user.
Bandwidth, on the other hand, is more a description of maximum capacity and implies multiple users.
Said differently, a single user has all the capacity (bandwidth) of a network at his or her disposal. So that connection should run at the maximum speed (throughput). But as more users connect to the same network, that bandwidth is now shared among the users, so the per user speed will drop. If the user's speed drops below what the user's application requires, then problems can result.
Most network applications are designed to handle this basic fact of network life and respond by just slowing down. This is why web browsing is slower during evenings or when school lets out. Same bucket o' bandwidth; more users drawing from the bucket; less bandwidth per user.
But "real time" applications such as audio and video have less of an ability to deal with a slowdown in the delivery of bits. If bits don't arrive in time for audio, then voice gets garbled or drops out entirely. Video is even more sensitive and it doesn't take much to start to see pixelation and picture breakup as available bandwidth drops below what is needed.
Note that manufacturers have headed away from playing up the "Mbps" in wireless networking product advertising and marketing materials due, in part, to some quiet (and not so quiet) lawsuits alleging false speed and range claims for wireless LAN products. So you now find relative performance claims such as "10x speed" and "20x coverage", which are supposedly less misleading, but completely unhelpful in determining whether a wireless product is going to provide the speed or bandwidth that you require.
Table 1 summarizes common network activities, the size of the data involved, and the duration of the activity. The Bandwidth Used column combines the Data Size and Duration into a subjective measure of the required bandwidth.
The Variation Sensitivity column is different because it indicates how much an activity is affected by changes in bandwidth. Video's sensitivity is high, because it requires a lot of data to arrive at a high rate in order to produce a problem-free picture. Web browsing's sensitivity is low, because even on a slow connection a web page will still completely load...eventually!
| Activity | Data Size | Duration | Bandwidth Used | Variation Sensitivity |
|---|---|---|---|---|
| Web Browsing / Email / Text IM | Small | Short | Low | Low |
| Local folder copy - non-media | Small - Medium | Short | Low - Medium | Low |
| Backup - Incremental | Small - Medium | Short - Medium | Low - Medium | Low |
| Web Video | Small | Short - Medium | Low - Medium | Low |
| VoIP or Voice IM | Small | Medium | Medium | Medium |
| Backup - Full | Large | Long | High | Low |
| BitTorrent, P2P filesharing, downloading | Large | Long | High | Low |
| Local folder copy - media | Large | Long | High | Low |
| Standard Definition Video Stream | Large | Long | High | High |
| HD Video Stream | Very Large | Long | Very High | Very High |
Table 1: Bandwidth of Common Home Network Activities
It's important to note that the table is per user. So more simultaneous users means that available bandwidth will be divided more ways. If you have only one or two users using the network at a time and they are just web browsing, doing email and IMing, then your bandwidth requirements will be relatively low. On the other hand, one HD Video stream requires a relatively high bandwidth.
Since it's important to know whether the technology that you are considering can support these unforgiving media applications, Table 2 is a summary of the actual bandwidth ranges required by common multimedia application types.
| Type | Required Bandwidth |
|---|---|
| VoIP, Voice IM | 24 - 128 kbps |
| Streaming Music | 64 - 128 kbps |
| Web Video | 0.5 - 1.5 Mbps |
| Uncompressed Standard Definition MPEG 2 (DVD VOB file) | 5-7 Mbps (average) 10-12 Mbps (peak) |
| HD Video (H.264) | 7-10 Mbps (average) 20+ Mbps (peak) |
Table 2: Bandwidth requirements of multimedia applications
Video bandwidths are frustratingly difficult to deal with in terms of throughput planning. This is due to the wide array of compression formats, display resolutions and bit rates in use. Needless to say, if you are planning on using a wireless LAN to support streaming video, more throughput is always better.
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