1. Chapter 6 – Connectivity Devices

2. Types of Connectivity Devices
Repeater
Hubs
Bridges
Switches
Routers
Gateways

3. Repeater Contains one input port and one output port
Suited only to bus topology networks
Allows you to extend the length of the bus network
Serve to amplify an analog or digital signal
Work at the Physical Layer of OSI model
In 10Base2 network, entire bus network cannot exceed 1000 meters, so you can’t use more than 5 repeaters in sequence

4. Hub Contains multiple ports that connect to a group of clients
Can also use hub to connect servers, printers, as well as other hubs
Hub typically supports the star topology
Hubs may be passive or intelligent
Passive – does nothing but repeat signal
Intelligent – Does internal processing such as permit remote management and data filtering

5. Types of Hubs Stand alone hub Stackable hubs Modular hubs
Intelligent hubs

6. Stand Alone Hub Used to connect a small group of clients together
Not connected to other hubs in a tree or daisy-chain fashion
Usually contain 24 or less ports
Should the hub fail, the entire network goes down

7. Stackable Hubs
Physically consist of multiple hubs sitting on top of each other
These are designed for the hubs to be linked together
Stackable hubs linked together logically represent one large hub to the network
Some us proprietary high-speed cabling to link the hubs together
For compatibility, it is best to use the same manufacturer for all the stackable hubs in one unit

8. Modular Hubs More flexible by providing a number of interface optins
Similar to a PC
Contains a system board and slots into which you can insert different adapters which can connect the hub to other hubs, routers, or the backbone
You can attach redundant components to modular hubs
Offer the highest reliability of any of the hubs

9. Intelligent Hubs
Can process data, monitor traffic, provide troubleshooting information
Information generated by hub can be stored in a database
This data can be used to determine problem nodes
Can identify nodes that are generating unnecessary traffic

10. Bridges
Look like repeaters in that bridges have a single input and a single output port
Differ from repeaters in that they can interpret the data
Bridges work a the Data Link Layer (2)
Bridges analyze incoming frames (from one segment) and determine if they should be transmitted out the other segment
The destination MAC address is used to decide whether to retransmit or to discard the packet
Bridge uses a Forwarding Table – See Fig. 6-22

11. Bridges – Continued
Using Figure 6-22, see how the bridge operates when Client #1 sends info to Client #3
What happens when Client #1 sends info to Client # 6?

12. Bridges- Continued
A bridge does not know initially what stations are associated with what ports. The Forwarding Table must be built
Once a bridge is installed, it polls the clients on each of its ports to provide their MAC address
Once the bridge receives this information, it is recorded in its Forwarding Table
The filtering of traffic enhances the network performance because the nodes spend less time listening to packets that are not destined for them

13. Switches These operate at the Data Link Layer (2)
They can interpret MAC address information just like routers
They resemble bridges and may be considered as multiport bridges
Each port on the switch can act like a bridge
If a single device is connected to a port on a switch, then it effectively receives its own dedicated channel without the possibility of a collision
The switch turns the shared channel into several

14. Switches – Continued
Each dedicated channel represents a collision domain
Switches have historically been used to replace hubs
Advantages of switches
Secure because they isolate one device’s traffic from another device’s traffic
Provide separate channel for each device

15. Switches – Continued Disadvantages of switches
Buffers inside switches can be overwhelmed by heavy traffic and data loss can occur. The devices sending the info do not detect this situation. Higher-level protocols such as TCP will detect the loss of data

16. Two Methods of Switching
Cut-Through Mode
Store and Forward

17. Cut-Through Mode
Switch reads the frame header and decides where to forward the data before it receives the entire packet
In this mode the switch begins transmitting the packet before it receives the Frame Check Sequence at the end of the frame, so it can’t verify frame integrity
It can detect packet fragments or runts
Main advantage is its speed
If switch is flooded with traffic, however, this is not an advantage – data must be stored

18. Store and Forward Mode
The switch reads the entire data frame into memory and checks it for accuracy before transmitting the information
These type switches do not propagate data errors
These can transfer data between segments using different transmission speeds
Example – Network printer is attached to a 100 Mbps port while the workstations that are to use the printer may be connected to the switch through 10Mbps ports

19. VLANs
Switches allow you to create virtual local area networks by logically grouping a number of ports into a broadcast domain
The ports grouped together do not have to reside on the same switch
See Figure as a example of a VLAN
To create the VLAN, you must configure the ports correctly

20. Routers
Multiport device that connects dissimilar LANs that use different transmission speeds and a variety of protocols
Operate at the Network Layer (Layer 3)
Slower than switches or bridges because routers use information from Layer 3 such as protocols and logical addresses
Routers are protocol dependent
Keep track of locations of nodes on the network
Determine the best path between two nodes
Protocol being used must be routable (TCP/IP)

21. Routers – Continued All routers can perform the following:
Connect dissimilar networks
Interpret Layer 3 (Network) information
Determine the best path from A to B
Reroute traffic if a particular path is down
Some additional tasks the router might be able to perform
Prevent broadcast transmissions
Prevent certain type of traffic from getting to a network
Router Manufacturers: Cisco, Nortel
See operation of router, figure 6-26

22. Routing Protocols
Routers use routing protocols to determine the best path from node A to node B in a network.
These protocols used to collect data about the current network status . From this data the routers build a Routing Table
Four most common routing protocols:
RIP
OSPF
EIGRP
BGP

23. Gateways Used to connect two completely different networks
Gateways operate at the Application Layer (7) of the OSI model