25-Oct-15Network Layer Connecting Devices Networks do not normally operate in isolation.They are connected to one another using connecting devices. The need To resolve incompatibility issues between different networks. Approach Hardware Software The result is  a virtual network

25-Oct-15Network Layer Connecting Devices Category Connecting devices can be categorised into: - Networking devices Repeater Bridge Internetworking devices Gateway Router

Figure 16.1 Connecting devices

25-Oct-15Network Layer Repeater An electronic device that operates only in the physical layer. Connects two segments of the same LAN. Needed to correct attenuated or corrupted signals. A repeater receives a signal before it becomes too weak or corrupted, regenerates the original bit pattern and sends the refreshed signal. Therefore, it is capable of extending the physical length of a LAN.

Figure 16.2 Repeater

Figure 16.3 Function of a repeater

25-Oct-15Network Layer Bridge A computer that has its own processor, memory and two NIC cards to connect to two different portions of a network. Operates in both physical and data link layers. Physical layer Regenerates signals received Data link layers Provides filtering capability that checks the destination address of a frame and decide if the frame should be forwarded or dropped. If the frame is to be forwarded, the decision must specify the port, based on its table.

Figure 16.5 Bridge

Figure 16.6 Learning bridge

Figure 16.7 Loop problem

Figure 16.8 Prior to spanning tree application

Figure 16.9 Applying spanning tree

Figure Forwarding ports and blocking ports

25-Oct-15Network Layer Router A host containing: - Software Routing table that enables it to determine the best path for a transmission Operates at the physical, data link and network layers. Connecting two different networks that adopt common transmission protocol.

25-Oct-15Network Layer Figure Routers in an Internet

25-Oct-15Network Layer Gateway A powerful computer. Operates at all layers. Connecting two dissimilar networks that use different transmission protocol. Therefore, it has the ability to translate between two different protocols

Figure A Gateway

25-Oct-15Network Layer The need for a network layer: - To enable data exchange between different networks Responsible for host-to-host delivery and for the routing of packets through the routers of switches These functions are made achievable via: - Addressing and Routing

Figure 19.1 Internetwork

Figure 19.2 Links in an internetwork

Figure 19.3 Network layer in an internetwork

25-Oct-15Network Layer Network Layer (Ctd…) At source Receives data from transport layer, adds the source universal address and destination universal address and make sure the packet is the correct size for delivery At router or switch Find the interface from which the packet must be sent At destination Verify the destination address

Figure 19.4 Network layer at the source

Figure 19.5 Network layer at a router

Figure 19.6 Network layer at the destination