1. Lab 2 – Hub/Switch Data Link Layer
MPC8360 Computer Networks I
Lab 2 – Hub/Switch Data Link Layer
Semester B, 2010

2. The Open System Interconnection Reference Model (OSI)
Application 1 2 3 4 5 6 7
Presentation
Session
Transport
Network
Data Link
We Are Here
Physical

3. HUB/SWITCH
Multiple access - several stations connected to the same physical medium to share it.
In our case the medium is twisted pair.
How we connecting several stations in order to create LAN?
Using one of this devices HUB/SWITCH.

4. Hub
Hub- is a device that connects multiple twisted pair Ethernet devices together and making them act as a single network segment.
Hubs work at the physical layer (layer 1) of the OSI model.
Hubs do not manage any of the traffic that comes through them, and any packet entering any port is broadcast out on all other ports.
Since every packet is being sent out through all other ports, packet collisions can occur.

5. Switch
Switch- a computer networking device that connects several Ethernet devices and creates network segments.
Switch operates at the data-link layer of the OSI model.
Switch creates a different collision domain per switch port.
It allows you to have dedicated bandwidth on point to point connections with every computer and therefore to run in Full duplex with no collisions.

6. Ethernet SWITCH
Switching technologies are crucial to network design, as they allow traffic to be sent only where it is needed.
Switches uses the media access control address (MAC address) to build and maintain filter tables (also known as MAC address tables).
Using the MAC address tables it decide where to forward frames.

7. Switch MAC Table The MAC table contains three columns
Port (Interface number)
MAC address
Time
Each row contains the following information:
Which MAC is connected to which port and when the Frame was received.
Port
MAC
Time 2 0x
15:30:21

8. MAC Table How the switch builds the MAC table?
For each incoming frame it matches the port (interface) to the source MAC address and to the frame received time.
Port
MAC
Time 2 0x
15:30:21

9. Spanning Tree
Some sites use two or more bridges in parallel between pairs of LANs. This introduces some problems because it creates loops in the topology.
Each bridge, following the normal rules for handling unknown destinations, uses flooding, which in this example just means copying it to LAN 2. Shortly thereafter, bridge 1 sees F2, a frame with an unknown destination, which it copies to LAN 1, generating F3 (not shown). Similarly, bridge 2 copies F1 to LAN 1 generating F4 (also not shown). Bridge 1 now forwards F4 and bridge 2 copies F3. This cycle goes on forever.

10. Spanning Tree
To build the spanning tree, first the bridges have to choose one bridge to be the root of the tree. They make this choice by having each one broadcast its serial number, installed by the manufacturer and guaranteed to be unique worldwide.
The bridge with the lowest serial number becomes the root. Next, a tree of shortest paths from the root to every bridge and LAN is constructed. This tree is the spanning tree. If a bridge or LAN fails, a new one is computed.

11. SWITCH
The End