Gateways can perform all of the functions of switches and routers as well as accomplish protocol conversion at all seven layers of the OSI Reference Model. (As shown in Figure 13). Generally consisting of software residing in a host computer equivalent in processing power to a midrange or mainframe, gateway technology is expensive but highly functional.
Protocol conversion, rather than encapsulation, can serve to fully convert from Ethernet to Token Ring or any other standard or proprietary protocol. Additionally, protocol conversion can address higher layers of the OSI model, perhaps through Layer 7, the Application Layer. As the process of protocol conversion is complex, gateways tend to operate rather slowly as compared to switches and routers. As a result, they impose additional latency on packet traffic and may create bottlenecks of congestion during periods of peak usage. In a large and complex network routers tend to be positioned at the edges of the network where they can be used to full advantage. Therefore, they make complex and time-consuming decisions and invoke complex and time-consuming processes only where required. Switches tend to be positioned within the core of the network because they can operate with greater speed.
|Figure 13: Networking devices and OSI model|
Now we can conclude that switch creates separate collision domains and router creates separate broadcast domains. All ports of hub are one collision domain.
A collision domain is defined as a single CSMA/CD network segment in which there will be a collision if two computers attached to the system both transmit at the same time.
A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcast at the data link layer. (Figure 14)
|Figure 14: Collision Domain and Broadcast Domain|