Question

Q1 : In your own words, compare between the earliest switches with static switching tables and the learning switches. What kind of a problem we might face in a network that uses learning switches and how can we solve that problem?

Q2: In your own words, discuss the three major differences between a router and a repeater or a switch.

Please I want text written answer, not on a paper thank you!

Answer 1

Answer:-

Q1)

LAN switching is a technology that promises to increase the efficiency of local area networks and solve the current bandwidth problems. This paper covers switch features, switching architectures, protocol support and management functions provided in switches and provides some guidelines for switch shopping. It also touches on how switches can be used to implement virtual LANs and ease management functions.

Static and Dynamic Switching

• Static Switching

  The functionality is similar to that of a hub as the traffic goes to all other ports in the group. Since individual hubs are cheaper, they are normally preferred.

• Dynamic Switching

  These switches learn on which port a station is attached by studying the frames that station transmits. Once learned, the frames are transmitted only to the destination station, saving the bandwidth of other stations. Stations are relearned everytime, so any change of station from one port to another is automatically reconfigured.

Cut-Through Versus Store-and-Forward Switching

Cut-through switching

Marked by low latency, these switches begin transmission of the frame to the destination port even before the whole frame is received. Thus frame latency is about 1/20th of that in store-and-forward switches (explained later). Cut-through switches with runt (collision fragments) detection will store the frame in the buffer and begin transmission as soon as the possibility of runt is eliminated and it can grab the outgoing channel. Filtering of runts is important as they seriously waste the bandwidth of the network. The delay in these switches is about 60 microseconds. Compare this with store-and-forward switches where every frame is buffered (delay: 0.8 microsecond per byte). The delay thus for 1500 byte frame is 1200 microsecond. No Cyclic Redundancy Check (CRC) verification is done in these switches. Figure 1 shows a frame being forwarded from port 1 to port 4 without being stored in buffer.

Figure 1.: Cut through Switching

Store-and-forward switching

This type of switches receive whole of the frame before forwarding it. While the the frame is being received, processing is done. Upon complete arrival of the frame, CRC is verified and the frame is directly forwarded to the output port. Even though there are some disadvantages of store-and-forward switches, in certain cases they are essential. For example when we have a slow port transmitting to a fast port. The frame must be buffered and transmitted only when it is completely received. Another advantage would be in high traffic conditions, when the frames have to be buffered since the output port may be busy. As traffic increases the chances of a certain output port being busy obviously increase, so even cut-through switches may need to buffer the frames. Thus, in some cases store-and-forward switching has its obvious advantage.

Address Resolution

To allow forwarding and filtering of packets at wire speed, LAN switches should be able to decode MAC addresses very quickly. Since Central Processing Unit (CPU) based lookups are expensive, hardware solutions may be used. Switches maintain address tables just like transparent bridges. They learn the addresses of their neighbors, and when a frame is to be forwarded, they first look up the address table and broadcast only if no entry corresponding to that destination is found. Stations that have not transmitted recently are aged out. This way a small address table can be maintained and the switch can relearn if a station starts transmitting again.

Q2)

Explanation:

Repeater:-

• The repeater is used to link the LAN segments.
• A repeater fronts any packet that has no sporting ability.
• Repeaters don't recognize frames, files, or headers. They recognize the signs that represent bits like voltage.
• There are analog devices that use signals on the wires to whom they are attached.

Router:-

• Routers are machines that link to two or more networks. This functions on a network layer.
• They are made up of a mixture of hardware and software.
• The network address helps routers to determine the best route to a computer or a device.
• Routers use the conceptual and practical address to link two or more technically different networks.