2. LAN Switching

Improving LAN Performance

The performance of a network can be improved in a shared media LAN such as Ethernet by using one or more of the following solutions:

Segmenting the network using Bridges, Routers, or LAN Switches

Move to full duplex transmitting

Upgrade to the Fast Ethernet Standard

2. LAN Switching

2. LAN Switching

Why Segment LANs?

A Cisco Segment

A network can be divided in smaller units called segments. Each segment uses the (CSMA/CD) protocol and maintains traffic between users on the segment. By using segments in a network less users/devices are sharing the same 10Mbps when communicating to one another within the segment. Each segment is considered its own collision domain.

2. LAN Switching

2. LAN Switching

Why Segment LANs?

In a segmented Ethernet LAN data passed between segments is transmitted on the backbone of the network using a bridge, switch, or router. The backbone network is its own collision domain and uses CSMA/CD to provide a best effort delivery service between segments.

2. LAN Switching

2. LAN Switching

Segmentation with Bridges

Bridges are different than routers because they are Layer 2 devices, independent of Layer 3 protocols they pass on data frames regardless of which Layer 3 protocol is being used and are transparent to the other devices on the network. Bridges increase the latency (delay)in a network by 10-30%. Why?

2. LAN Switching

A bridge is considered a store and forward device because it must examine the destination address (MAC) field in the frame and determine which interface to forward the frame. If there is no match in the table, the frame is flooded out all other interfacesBridges "learn a networks" segmentation by building address tables that contain the (MAC) address of each network device and which segment to use to reach that device. Smaller collision domains are created, not broadcast domains.

2. LAN Switching

2. LAN Switching

Segmentation with LAN Switches

A switch segments a LAN into microsegments creating collision free domains from one larger collision domain, not broadcast domains. With switched ethernet implementation the available bandwidth can reach closer to 100%.

2. LAN Switching

Using Full Duplex

Node mustBe directly attached to a dedicated switched portHave installed network interface card that supports
full duplex

HUB

Full Duplex

Half Duplex

2. LAN Switching

Full-Duplex Ethernet Design

Standard Ethernet normally can only use 50-60% of the 10Mbps available bandwidth. This is due to collisions and latency. Full duplex Ethernet offers 100% of the bandwidth in both directions. This produces a potential 20Mbps throughput 10Mbps TX and 10Mbps RX.

2. LAN Switching

2. LAN Switching

2. LAN Switching

This virtual network circuit exists only when two nodes need to communicate. This is why it is called a virtual circuit it exists only when needed and is established within the switch.Allows multiple users to communicate in parallel via these virtual circuits.

2. LAN Switching

2. LAN Switching

Source MAC address is used to build this table

2. LAN Switching

2. LAN Switching

How a LAN Switch Learns Addresses

This means that as new addresses are read they are learned and stored in Content Address Memory (CAM). Each time an address is stored it is time stamped. This allows addresses to be stored for a set period of time.

2. LAN Switching

But more domains

2. LAN Switching

2. LAN Switching

Segmentation with Routers

Routers operate at the network layer and base all of their forwarding decisions between segments on the Layer 3 protocol address. Because routers perform more functions than bridges they operate with a higher rate of latency. (Higher than other internetworking devices.)

2. LAN Switching

Routers:

Segment broadcast domainsForward packets based on destination network layer addressesSegment collision domains

2. LAN Switching

More collision domains, but more bandwidth for each user

2. LAN Switching