Switch

In the previous tutorial we saw that hubs did not segment networks. Indeed, due to the excessive traffic they made the networks almost inoperable. A means was required that would forward the frames originating from the source only to its destination instead of being forwarded to all the hosts on the network. Since on an Ethernet CSMA/CD (Carrier sense multiple access with collision detection algorithms block other senders for a certain amount of time if one device is already transmitting on the network. It reduces collisions) network only one host can transmit at a given time, if the network can be segmented the collisions and traffic would reduce allowing access to higher bandwidths than was previously available. All of these can be accomplished by a switch.  

Working principle of device:

Switch is layer 2 device. In other words, it works at the Data link layer of the OSI model. Thus switches are aware of the Physical or MAC (Media Access Control) layer of the frame that it receives. Therefore, they segment the network on the basis of the MAC address. A switch will identify the MAC address of the sender, receiver and the port on which it was received. Depending upon the MAC address of the destination host the switch will send the frame out only to the port on which the destination host is located reducing broadcast traffic. This increases the usable bandwidth. However, if the destination host cannot be located the frame will be passed on to every port on the switch except the one on which the frame was received. This is the only time when the network performance will be adversely affected.

Each port on a switch represents its own collision domain (it is the section of network connected by common means where data packets can collide if more than one device transmits at the same time). This greatly reduces the number of collisions taking place on a network as the network can be broken up into as many collision domains as the number of ports on the switch. Reduction in collision increases the response time and network throughput.

There are basically two drawbacks of switches. One is that it will forward broadcast frames to all the hosts present on the network (or it will replicate the frame to all the ports/collision domains present on the switch). This means that switches don’t break up broadcast domains (It is a logical network segment in which all hosts receive the broadcast frame sent by a host at the data link layer). All segments connected to a switch represent a single broadcast domain. And second issue is that a switch will not be able to route between different networks and forward packets to the hosts that are not present on the network on which the switch resides. In such cases, the switch will simply drop/discard the packet and report the same to the host that had transmitted the packet. If broadcast domains need to be broken up or if routing and connecting different networks together in order to build an internetwork for communicating with distant hosts is desired a router is the device of choice.

Device installation: Connect the various segments to the RJ-45 ports on the switch using patch cables. Power on the switch and Bingo! The network will in no time will start humming sweetly!

Manufacturer of device, its models and prices:

1.      Cisco – Cisco WS-C3550-24-SMI 24 PORTS 3550 (Rs. 10,500)

2.      D-Link – D-Link 8-Port Gigabit (Rs. 4,374)

3.      Digisol – Digisol DG-GS1008DG Gigabit Ethernet Unmanaged (Rs. 1,634)

4.      Netgear – Netgear GS105NA Prosafe 5-Port Gigabit Switch (Rs. 4,012)

5.      TP-Link - TP-LINK 24-Port Gigabit Ethernet Rackmount Switch (TL-SG1024D) (Rs. 14,498)

Standard Configuration of device: Switches can vary from being a small box having a few RJ-45 ports to a colossal rack-mounted dragon having hundreds of ports. Features that depend on the IP address such as telnet, VoIP, VLANs, SNMP etc are not available on unmanaged switches. However more advanced switches such as that of Cisco allow us to access these features on selected ports by adding IP address functionality to those ports. These advanced switches are called managed switches. Strictly speaking switches are layer 2 devices and hence cannot inherently support IP address which is a layer 3 concept. Unmanaged switches have no configuration information (almost everything is rigid and pre-determined) and plug-and-play while managed switches can be configured (are more flexible). 

Cost: Cost increases with the increase in the number of ports present and the maximum Ethernet speed supported by the switch. Also managed switches are costlier than their unmanaged counter parts.

Market share of different models (Standard companies only):

l  Cisco

l  D-Link

l  Digisol

l  Netgear

l  TP-Link