1. Part III. Data Link Layer
Chapters 13. Wired LANs
Chapter 15. Wireless LANs
Chapter 17. Connecting LANs, ...
COMP 3270 Computer Networks
Computing Science
Thompson Rivers University

2. Course Outline Overview Physical Layer Data Link Layer Network Layer
Digital transmission
Analog transmission
Bandwidth utilization …
Data Link Layer
Error detection
Data link control
Multiple access
Ethernet; Wireless LANs; Connecting LANs
Network Layer
Logical addressing
IPv4, protocols
Delivery, forwarding and routing

3. Learning Objectives Understand the architecture of WLAN.
Understand the architecture of Bluetooth.
Match major layers with hub, bridge, switch, router and gateway.
List advantages of using VLANs.

4. Chapter 13. Wired LANs: Ethernet

5. IEEE STANDARDS
In 1985, the Computer Society of the IEEE started a project, called Project 802, to set standards to enable intercommunication among equipments from a variety of manufacturers. Project 802 is a way of specifying functions of the physical layer and the data link layer of major LAN protocols.

6. IEEE standard for LANs

7. STANDARD ETHERNET
The original Ethernet was created in 1976 at Xerox’s Palo Alto Research Center (PARC). Since then, it has gone through four generations. We briefly discuss the Standard (or traditional) Ethernet in this section.

8. Ethernet evolution through four generations

9. 802.3 MAC frame Post- amble Length or protocol ID CRC-32
Data length: < 1518 = (0x600)
Protocol ID: >= 1536
CRC-32
IEEE 802.3
Ethernet II

10. ☺ What if an IP packet of 40 bytes is stored?
Minimum and maximum lengths
☺ What if an IP packet of 40 bytes is stored?

11. Categories of Standard Ethernet

12. 10Base-T implementation

13. Chapter 15. Wireless LANs

14. 15.2 IEEE
IEEE has defined the specifications for a wireless LAN, called IEEE , which covers the physical and data link layers.

15. A BSS without an AP is called an ad hoc network;
a BSS with an AP is called an infrastructure network.

16. Basic service sets (BSSs)

17. Extended service sets (ESSs)

18. 802.11n – 802.11g with MIMO (multiple input multiple output) antennas
Physical layers
PSK or QAM
802.11n – g with MIMO (multiple input multiple output) antennas

19. Industrial, scientific, and medical (ISM) band

20. 15.3 BLUTOOTH
Bluetooth is a wireless LAN technology designed to connect devices of different functions such as cellphones, tablet computers, notebooks, computers, cameras, printers, coffee makers, and so on. A Bluetooth LAN is an ad hoc network, which means that the network is formed spontaneously.

21. Master/slave (maximum 8 stations)
2.4 GHz ISM band
1Mbps; 3Mbps in the 2nd generation
TDMA

22. Chapter 17. Connecting LANs, ...

23. 17.1 CONNECTING DEVICES Topics discussed in this section:
In this section, we divide connecting devices into five different categories based on the layer in which they operate in a network.
Topics discussed in this section:
Passive Hubs
Active Hubs
Bridges
Two-Layer Switches
Routers
Three-Layer Switches
Gateways

24. Five categories of connecting devices

25. Repeaters and Hubs

26. A repeater forwards every frame; it has no filtering capability.

27. A repeater is a regenerator, not an amplifier.

28. A hierarchy of hubs
☺ Collision domain is ???
Multi-port repeater

29. A bridge has a table used in filtering decisions.
Bridges
A bridge has a table used in filtering decisions.

30. It needs to read the addresses
=> data link layer
☺ Collision domain is ???
Information can be learned.

31. Collision domains in an unbridged network and a bridged network

32. ☺ Could there be packet collisions?
Switches (L2 Switches)
☺ Could there be packet collisions?
No.

33. Routers (L3 Switches)
Routers connecting independent LANs and WANs

34. 17.2 BACKBONE NETWORKS Topics discussed in this section:
A backbone network allows several LANs to be connected. In a backbone network, no station is directly connected to the backbone; the stations are part of a LAN, and the backbone connects the LANs.
Topics discussed in this section:
Bus Backbone
Star Backbone
Connecting Remote LANs

35. Bus Backbone
Old days

36. Star Backbone
These days

37. 17.3 VIRTUAL LANs Topics discussed in this section:
We can roughly define a virtual local area network (VLAN) as a local area network configured by software, not by physical wiring.
Topics discussed in this section:
Membership
Configuration
Communication between Switches
IEEE Standard
Advantages

38. A switch connecting three LANs A
☺ The project in which A has been involved is now completed, and so A needs to move to
another project group, e.g., Group 2. Then does A need to move to another office?
Is there any other easier way to reconfigure logical groups of computers without moving?

39. A switch using VLAN software
VLAN (Virtual LAN) : a local area network configured by software,
not by physical wiring => flexible reconfiguration
(broadcasting
possible)

40. Two switches in a backbone using VLAN software
IEEE 802.1Q
Over a trunk

41. IEEE 802.1Q IEEE 802.1Q Over a trunk Router; Firewall This system
has to know
about VLANs.

42. Logically
Router;
Firewall
LAN3
LAN1
LAN2

43. ☺ Advantages ?
o Easy change/creation of broadcast domains => Flexible reconfiguration; Some software requires broadcast, e.g., Novel NetWare to share printers and files;
o Easy change/creation of IP logical networks;
o Easy implementation of firewall at a central router;
o Less networking devices at a central router;