Subject Name: Computer Communication Networks Subject Code: 10EC71 Prepared By: Kala H S & Megha Gupta Department: ECE Date: 9/21/2018

Connecting LANs, Backbone Networks, and Virtual LANs Unit 5 Connecting LANs, Backbone Networks, and Virtual LANs 9/21/2018

Connecting Devices Backbone Networks Virtual LANs TOPICS COVERED 9/21/2018

CONNECTING DEVICES We divide connecting devices into five different categories based on the layer in which they operate in a network. Fig. Five categories of connecting devices 9/21/2018

The five categories contain devices which can be defined as Those which operate below the physical layer such as a passive hub. Those which operate at the physical layer (a repeater or an active hub). Those which operate at the physical and data link layers (a bridge or a two-layer switch). Those which operate at the physical, data link, and network layers (a router or a three-layer switch). Those which can operate at all five layers (a gateway). 9/21/2018

PASSIVE HUBS A passive hub is just a connector. It connects the wires coming from different branches. In a star-topology Ethernet LAN, a passive hub is just a point where the signals coming from different stations collide; the hub is the collision point. This type of a hub is part of the media; its location in the Internet model is below the physical layer. 9/21/2018

A repeater is a device that operates only in the physical layer. REPEATERS A repeater is a device that operates only in the physical layer. Signals that carry information within a network can travel a fixed distance before attenuation endangers the integrity of the data. A repeater receives a signal and, before it becomes too weak or corrupted, regenerates the original bit pattern. The repeater then sends the refreshed signal. A repeater can extend the physical length of a LAN. 9/21/2018

Fig. A repeater connecting two segments of a LAN 9/21/2018

Fig. Function of a repeater 9/21/2018

ACTIVE HUBS An active hub is actually a multipart repeater. It is normally used to create connections between stations in a physical star topology. Hubs can also be used to create multiple levels of hierarchy, as shown in below Figure. 9/21/2018

A bridge operates in both the physical and the data link layer. BRIDGES A bridge operates in both the physical and the data link layer. As a physical layer device, it regenerates the signal it receives. As a data link layer device, the bridge can check the physical (MAC) addresses (source and destination) contained in the frame. 9/21/2018

Fig. A bridge connecting two LANs 9/21/2018

Transparent Bridges A transparent bridge is a bridge in which the stations are completely unaware of the bridge's existence. If a bridge is added or deleted from the system, reconfiguration of the stations is unnecessary. According to the IEEE 802.1 d specification, a system equipped with transparent bridges must meet three criteria: Frames must be forwarded from one station to another. The forwarding table is automatically made by learning frame movements in the network. Loops in the system must be prevented. 9/21/2018

Solution of looping problem - use the spanning tree algorithm to create a loopless topology. 9/21/2018

Fig. A system of connected LANs and its graph representation 9/21/2018

Fig. Finding the shortest paths and the spanning tree in a system of bridges 9/21/2018

Fig. Forwarding and blocking ports after using spanning tree algorithm 9/21/2018

Dynamic Algorithm In the spanning tree algorithm we discussed was as though it required manual entries. This is not true. Each bridge is equipped with a software package that carries out this process dynamically. The bridges send special messages to one another, called bridge protocol data units (BPDUs), to update the spanning tree. The spanning tree is updated when there is a change in the system such as a failure of a bridge or an addition or deletion of bridges. 9/21/2018

Source Routing Bridges Another way to prevent loops in a system with redundant bridges is to use source routing bridges. A transparent bridge's duties include filtering frames, forwarding, and blocking. In a system that has source routing bridges, these duties are performed by the source station and, to some extent, the destination station. In source routing, a sending station defines the bridges that the frame must visit. The addresses of these bridges are included in the frame. In other words, the frame contains not only the source and destination addresses, but also the addresses of all bridges to be visited. The source gets these bridge addresses through the exchange of special frames with the destination prior to sending the data frame. 9/21/2018

A backbone network allows several LANs to be connected. BACKBONE NETWORKS A backbone network allows several LANs to be connected. In a backbone network, no station is directly connected to the backbone; the stations are part of a LAN, and the backbone connects the LANs. 9/21/2018

Bus Backbone In a bus backbone, the topology of the backbone is a bus. Bus backbones are normally used as a distribution backbone to connect different buildings in an organization. Each building can comprise either a single LAN or another backbone (normally a star backbone). A good example of a bus backbone is one that connects single- or multiple-floor buildings on a campus. Each single-floor building usually has a single LAN. Each multiple-floor building has a backbone (usually a star) that connects each LAN on a floor. A bus backbone can interconnect these LANs and backbones. 9/21/2018

In a star backbone, the topology of the backbone is a star. Star Backbone(Collapsed/Switched) In a star backbone, the topology of the backbone is a star. In this configuration, the backbone is just one switch (that is why it is called, erroneously, a collapsed backbone) that connects the LANs. In this configuration, the switch does the job of the backbone and at the same time connects the LANs. 9/21/2018

VIRTUAL LANs We can roughly define a virtual local area network (VLAN) as a local area network configured by software, not by physical wiring. 9/21/2018

Fig. A switch using VLAN software 9/21/2018

Fig. Two switches in a backbone using VLAN software 9/21/2018

Communication Between Switches Membership Port Numbers MAC Addresses IP Addresses Multicast IP Addresses Combination Configuration Manual Configuration Automatic Configuration Semiautomatic Configuration Communication Between Switches Table Maintenance Frame Tagging Time-Division Multiplexing (TDM) 9/21/2018

Advantages Cost and Time Reduction VLANs can reduce the migration cost of stations going from one group to another. Physical reconfiguration takes time and is costly. Instead of physically moving one station to another segment or even to another switch, it is much easier and quicker to move it by using software. Creating Virtual Work Groups VLANs can be used to create virtual work groups. For example, in a campus environment, professors working on the same project can send broadcast messages to one another without the necessity of belonging to the same department. This can reduce traffic if the multicasting capability of IP was previously used. Security VLANs provide an extra measure of security. People belonging to the same group can send broadcast messages with the guaranteed assurance that users in other groups will not receive these messages. 9/21/2018

Acknowledgement : MY SINCERE THANKS TO By Kala H S & Megha Gupta THE AUTHOR PROF.BEHROUZ A FOROUZAN. BECAUSE THE ABOVE PRESENTATION MATERIALS ARE HEAVILY BORROWED FROM HIS TEXTBOOK “DATA COMMUNICATION & NETWORKING” 4TH EDITION, PUBLISHER TATA MCGRAW HILL SURESHA V. PROFESSOR, DEPT. OF E&C, KVG COLLEGE OF ENGINEERING. SULLIA, D.K - 574 327 By Kala H S & Megha Gupta Assistant Professor 9/21/2018