LAN Wiring & Physical Interfaces

1. LAN Wiring & Physical Interfaces Lecture 6

2. Network Interfaces • Every device has some form of a network interfaces. • A PC has a Network Interface Card (NIC). • The Cisco 2501 routers have an Attachment Unit Interface (AUI) connection.

3. NICs • NICs are dependent on what type of topology exists in the LAN. • For example, an Ethernet NIC can’t be used with a Token Ring NIC, and vice-versa.

4. NICs (cont.) • A NIC performs most of the network-level operations in order to reduce CPU overhead. • Receives incoming packets • Storage of frames • Actively listens on the network • A NIC is exactly the same as any other I/O device to the CPU. Read and write from the data bus with certain addressing.

5. NIC (cont.) • Ethernet NIC • RJ-25 • BNC (British Naval Connector) • AUI • ST/SC for fiber • The NICs pictured at the right have RJ-45 (top) and ST (bottom) connectors.

6. NIC (cont.) • In addition to providing the physical connection to the network, the NIC also deals with hardware addressing. • All LAN traffic ultimately deals with hardware addresses. The NIC will only read (copy) packets destined for it’s own address. • Broadcasted packets are also read.

7. Physical Hardware Addressing • Three separate types of addressing occur: • Static – hardware manufacture specifies the address, and it is unchangeable. • Advantages: Ease of use, and permanence. • Disadvantages: manufactures must keep track of usage. • Configurable – the end user can modify the address through software or switches on the card. • Advantages & Disadvantages: A mix of above and below. • Dynamic – random numbers are tried until one is found that is unused. • Advantages: smaller HW addresses! • Disadvantages: lack of permanence, potential conflict.

8. Broadcasting • Broadcasting refers to the concept that a certain type of packet can be generated that is received by all hardware attached on the network. • Useful for finding printers, file shares, etc. • Broadcasting usually uses a specific broadcast address for such schemes.

9. Thick Ethernet Wiring

10. Thick Ethernet Specifications • 50 Ohm coaxial cable, 0.4” thick. • 10base5 – 10Mbps, 500m segments. • Ends must be terminated. • AUI connectors. • “Vampire” taps / Transceivers.

11. Thin Ethernet Wiring

12. Thin Ethernet Specifications • 50 Ohm coaxial cable, 0.2” thick. • 10base2 – 10Mbps, 185m segments. • Ends must be terminated. • BNC connectors. • Transceivers are integrated into the NIC.

13. Twisted-Pair Ethernet Wiring

14. Twisted-Pair Ethernet Specifications • Twisted-pair cable. • 10baseT- 10Mbps, 100m segments. • 100baseT – 100Mbps, 100m segments. • RJ-45 connectors. • Hubs/Switches required.

16. Extending the LAN • Hardware has been developed that “boosts” the signal so you can create larger LAN segments. • Fiber Extensions • Repeaters • Bridges • Switches • Hubs

17. Why Extend the LAN? • Distance limitation is the most common hurdle for LAN design. • You always want more. More computers, more people, more access to shared resources. • Users want access to shared resources. It doesn’t make economical sense to have a single printer for each segment, for example.

18. Fiber Modems • Fiber modems are used to connect a single remote computer to an established LAN. • Effective, since fiber is low latency, high bandwidth.

19. Repeaters • Repeaters are just as they sound. They connect two segments together as one, and just repeat the traffic of one segment and forward it on to the second. • Repeaters are unintelligent. What you get on one segment is what you get on the other. No more, no less.

20. Repeaters (cont.) • A repeater as it’s commonly used. Hubs and switches have repeaters built-in, so you can connect multiple segments together. • IEEE designates how many segments may be connected together.

21. Repeaters (cont.) • Repeaters have several drawbacks: • They expand the collision domain. • Noise from one segment flows on to the second segment. • Any electrical problems that occur on one segment will be sent to the second segment!

22. Another Common Use of Repeaters

23. Bridges • Bridges are smarter repeaters. • Main difference: bridges verify that the frame is intact and valid before it is forwarded on to the second segment. • This provides a higher quality of service. Problems on one segment do not affect the other segment.

24. Bridges (cont.) • Bridges also have the attractive feature of “frame filtering.” • A frame will only be forwarded to the second frame if the destination computer is not on the first frame. This reduces chatter on the combined segments. • Bridges that learn which computers are on which segments are called “adaptive” or “learning” bridges.

25. Adaptive Bridges • When a bridge boots, it does not have any information about computers on the segments that it connects. • After a long time, the bridge reaches a steady-state where it has developed a mapping of which computers are on which segments. • At this steady-state, extra frames on the segments is cut to a minimum. In this state, maximum parallelism is achieved.

26. Bridging Between Buildings

27. Switching

28. Switches (cont.) • Switches allow for independent, parallel communications between ports on the switch. • Switches are combined with hubs for a cost-effective method of providing equal-access for all users.