Router Technology

Interconnecting devices

• HUB
•  
• BRIDGES
•  
• SWITCHES
•  
• ROUTERS

Hub

Hubs are used to build a LAN by connecting different computers in a star/hierarchal network topology, the most common type on LANs now a day. A hub is a very simple (or dumb) device, once it gets bits of data sent from computer A to B, it does not check the destination, instead, it forwards that signal to all other computers (B, C, D…) within the network. B while other nodes discard it. This amplifies that the traffic is shared.

There are mainly two types of hubs:

1. Passive: The    signal    is    forwarded   as    it    is   (so     it   doesn’t   need   power    supply).

1. Active: The signal is amplified, so they work as repeaters. In fact they have been called multiport repeaters. (Use power supply) .Hubs can be connected to other hubs using an uplink port to extend the network.

OSI Model: Hubs work on the physical layer (lowest layer). That’s the reason they can’t deal with addressing or data filtering.

Fig Hub

Switch

Switches on the other hand are more advanced. Instead of broadcasting the frames everywhere, a switch actually checks for the destination MAC address and forward it to the relevant port to reach that computer only. This way, switches reduce traffic and divide the collision domain into segments, this is very sufficient for busy LANs and it also protects frames from being sniffed by other computers sharing the same segment.

They build a table of which MAC address belongs to which segment. If a destination MAC address is not in the table it forwards to all segments except the source segment. If the destination is same as the source, frame is discarded.

Switches have built-in hardware chips solely designed to perform switching capabilities, therefore they are fast and come with many ports. Sometimes they are referred to as intelligent bridges or multiport bridges. Different speed levels are supported. They can be 10 Mb/s, 100 Mb/s, 1 Gb/s or more.

Like hubs, switches are the connectivity points of an Ethernet network. Devices connect to switches via twisted-pair cabling, one cable for each device. The difference between hubs and switches is in how the devices deal with the data that they receive. Whereas a hub forwards the data it receives to all of the ports on the device, a switch forwards it only to the port that connects to the destination device. It does this by learning the MAC address of the devices attached to it, and then by matching the destination MAC address in the data it receives. Data is forwarded only to the destination node.

By forwarding data only to the connection that should receive it, the switch can improve network performance in two ways. First, by creating a direct path between two devices and controlling their communication, it can greatly reduce the number of collisions on the network. Collisions occur on Ethernet networks when two devices attempt to transmit at exactly the same time.

Fig Switch

In a full-duplex configuration, devices can send and receive data from the switch at the same time. Contrast this with half-duplex communication, in which communication can occur in only one direction at a time. Full-duplex transmissions speeds are double that of a standard, half-duplex, connection. So, a 10Mbps connection becomes 20Mbps, and a 100Mbps connection becomes 200Mbps.

The net result of these measures is that switches can offer significant performance improvements over hub-based networks, particularly when net-work use is high.

Irrespective of whether a connection is at full or half duplex, the method of switching dictates how the switch deals with the data it receives. The following is a brief explanation of each method:

• Cut- through—In a cut-through switching environment, the packet begins to be forwarded as

soon as it is received. This method is very fast, but creates the possibility of errors being propagated through the net- work, as there is no error checking.

• Store-and-forward: Unlike cut-through, in a store-and-forward switching environment, the

entire packet is received and error checked before being forwarded. The upside of this method is that errors are not propagated through the network. The downside is that the error checking process takes a relatively long time, and store-and-forward switching is considerably slower as a result.

• Fragment Free: To take advantage of the error checking of store-and forward switching, but

still offer performance levels nearing that of cut through switching, Fragment Free switching can be used. In a Fragment Free-switching environment, enough of the packet is read so that the switch can determine whether the packet has been involved in a collision. As soon as the collision status has been determined, the packet is forwarded.

OSI: Switches are on the data link layer (just above physical layer) that’s why they deal with frames instead of bits and filter them based on MAC addresses. Switches are known to be used for their filtering capabilities.

VLANs (Virtual LANs) and broadcast domains: Switches do not control broadcast domains by default, however, if a VLAN is configured in a switch it will has its own broadcast domain.

VLAN is a logical group of network devices located on different LAN physical segments.

However they are logically treated as if they were located on a single segment.

BRIDGES

Bridges are used to divide larger networks into smaller sections. They do this by sitting between two physical network segments and managing the flow of data between the two. By looking at the MAC address of the devices connected to each segment, bridges can elect to forward the data (if they believe that the destination address is on another interface), or block it from crossing .

Bridges are used to extend networks by maintaining signals and traffic.

Types of Bridges

Three types of bridges are used in networks:

• Transparent Bridge: derives its name from the fact that the devices on the network are

unaware of its existence. A transparent bridge does nothing except block or forward data based on the MAC address.

• Source route bridge: Used in Token Ring networks. The source route bridge derives its

name from the fact that the entire path that the packet is to take through the network is embedded within the packet.

• Translational bridge: Used to convert one networking data format to another; for example, from Token Ring to Ethernet and vice versa.

OSI: Bridges are on the data link layer so in principle they are capable to do what switches do like data filtering and separating the collision domain, but they are less advanced. They are known to be used to extend distance capabilities of networks.

In a comparison with switches, they are

Impressum

Verlag: BookRix GmbH & Co. KG

Tag der Veröffentlichung: 13.11.2018
ISBN: 978-3-7438-8632-2

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