Network Topologies

In computer networking, topology refers to the layout of connected devices. This article introduces the standard topologies of networking.

Topology in Network Design
Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there. 
Network topologies are categorized into the following basic types: 
• bus 
• ring 
• star 
• tree 
• mesh
More complex networks can be built as hybrids of two or more of the above basic topologies.


Bus Topology
 
Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. 
Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

DSL and Cable Broadband Speed Tweaks

So-called broadband speed tweaks are techniques to improve performance of DSL and cable Internet connections. Home networking enthusiasts started experimenting with cable and DSL tweaks many years ago, when broadband Internet services first became popular.

Performance tweaks for low-speed (dialup) Internet often do not work for broadband links. Additionally, while broadband speed tweaks originally focused on increasing the performance of general Web surfing, speed tweaks are now more commonly made to tune specific applications like P2P file sharing systems and games.

Limitations of Broadband Speed Tweaks
First, broadband tweaks should be made only after your network is tested and running reliably. Speed tweaks are performance optimizations only, not designed to fix installation errors or basic network configuration issues.

You should expect broadband tweaks might yield only small speed increases, and then only in certain situations. For example, a tweak to improve the performance of one online game may only benefit that title and then only initially when it is loading. Broadband tweaks may help certain applications (like games) but at the same time slow down others (like Web browsing). In general, assume any performance benefits you obtain may be on the order of 10-20% gain rather than 100-200%.

Finally, speed tweaks also can create instability on some networks. Depending on the type of equipment and Internet service you use, some tweaks will be technically incompatible and need to be avoided.

Types of Broadband Speed Tweaks
The most common broadband tweaks involve adjusting various parameters of the TCP/IP network protocol, typically:
• TCP receive window size
• Maximum Transmission Unit (MTU)
• Maximum Segment Size (MSS)
• Time-To-Live (TTL)

The Microsoft Windows Registry contains default values for TCP/IP parameters. You can apply these speed tweaks to your computers by using a Registry editor or the TCP Optimizer utility (see below) to change some of the default values on each, rebooting the computers each time. Other operating systems like Linux and Mac OS X provide alternative mechanisms to tune TCP/IP parameters.

Another common broadband tweak entails manipulating Web browser settings. For example, suppressing the download of large images saves network bandwidth that can be used instead to download other data faster.

Finally, though less common, a few speed tweaks modify settings on routers and modems. For example, TCP/IP MTU settings can be changed on a broadband router separate from individual computers on the network.



About Web Accelerators for Broadband Tweaks
Speed tweaks have been traditionally applied to the network by an administrator manually, one device at a time, but in recent years software applications have been developed to help automate and maintain tweaks.

So-called Internet download accelerators are pre-packaged software programs that automatically apply speed tweaks to a computer. Installing and running an accelerator program will automatically make the Registry, Web browser and other configuration changes. The more sophisticated applications collect information about your computers and network and apply tweaks intelligently to ensure maximum benefit.

While many Web accelerators are designed specifically for dialup networks, examples of accelerator applications useful for broadband are:
• Download Accelerator Plus
• Google Web Accelerator
• Netfury
• ONSPEED

Making Broadband Tweaks Work
Because speed tweaks can cause computer and network crashes if made improperly, test each change methodically. If possible, use a proven Web accelerator program rather than configuring tweaks manually, and test each change individually before making the next one.

To determine whether a speed tweak is working, use an Internet speed test service to measure your Internet performance before and after making a tweak. In addition, try local file transfers, Web downloads, online games, and other applications you use often to assess whether a tweak makes any noticeable difference. Do not hesitate to undo a change if you cannot observe any benefit.