|Document ID:1998121012190112 |
Network bandwidth and pcAnywhere
|Situation:||You would like to know how much of the available network bandwidth that pcAnywhere uses.|
|Solution:||There are two ways to divide network bandwidth - fixed channels and packet-based protocols. Each method provides capabilities that the other method does not. A feature that works well under one method may not work well under the other. pcAnywhere, as well as most network-capable applications (Web browsers, file servers, application servers, and so on), use packet-based protocols. This method allows pcAnywhere to use as much bandwidth as can be acquired.|
A majority of the pcAnywhere data that is sent is host screen information. The amount of host screen data depends on the amount of change to the host screen, the host's screen resolution, and the number of colors displayed by the host. The higher the host's resolution and the higher the number of colors the host displays, the more bytes are involved in displaying the host's screen, the more information pcAnywhere sends back to the remote and the more bandwidth is required to send that data.
The following are general explanations of the two types of bandwidth division:
- Packet based protocol
With this technique, individual applications packetize the data they send into the network channel. If only one application is sending data, and it needs to send large amounts of data, it can use all of the available bandwidth. If multiple applications are sending data into the channel, the applications dynamically adjust the amount of data they send so that the bandwidth is distributed to all of the applications. If an application is sending a small amount of data, it will only use a small amount of the bandwidth. If an application is not sending data, then it does not use any bandwidth at all.
For example, you have four computer pairs connected via routers and a 56K leased telephone line. At both ends of the line, you have four computers connecting to a router. The routers connect to each other over a 56K leased telephone line. If only one computer pair is sending data its top bandwidth would be the entire line - 56K. If all four computer pairs are sending as much data as possible, then each pair would have a top bandwidth of 14K. If two computer pairs were sending as much data as possible, and the other two pairs were sending just a little bit of data, the two large data senders would have a top bandwidth of about 24K. The two small data senders could have an effective throughput that is higher.
Packet based protocol has several advantages over fixed channels. There is very little bandwidth wastage. All applications share the bandwidth between them. If there is only a small amount of traffic, then a specific application can use a larger amount of bandwidth. The disadvantage is that individual applications will sometimes transfer their data fast, and other times slow.
- Fixed channels
This method divides the bandwidth into fixed channels. Each channel has a specific amount of the total bandwidth. A channel can not use more bandwidth then has been allocated to it. If one of the channels is not making full use of its bandwidth, the unused bandwidth can not be used by another channel. Multiplexer (MUX) connections are an example of this type of division.
For example, you have four computers that are connected to a MUX using each computer's serial port. The MUX is connected to another MUX over a 56K leased telephone line. The second MUX is connected to four computers using each computer's serial port.. Each computer pair has been allocated 14K of the 56K bandwidth. If you are using one computer pair, your top bandwidth is 14K. If you are using all four computer pairs, each pair has a guaranteed 14K pipeline.
The advantages of fixed channels are that the users will always see the same bandwidth between the computer pair. The disadvantages are that users will not be able to use unused bandwidth, they always see the same bandwidth, and only specific users will have access to the bandwidth.
|Document ID:1998121012190112 |