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

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

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.

Chapter 13. Wired LANs: Ethernet

13.1 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.

IEEE standard for LANs

13.2 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.

Ethernet evolution through four generations

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

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

Categories of Standard Ethernet

10Base-T implementation

Chapter 15. Wireless LANs

15.2 IEEE 802.11 IEEE has defined the specifications for a wireless LAN, called IEEE 802.11, which covers the physical and data link layers.

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

Basic service sets (BSSs)

Extended service sets (ESSs)

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

Industrial, scientific, and medical (ISM) band

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.

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

Chapter 17. Connecting LANs, ...

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

Five categories of connecting devices

Repeaters and Hubs

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

A repeater is a regenerator, not an amplifier.

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

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

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

Collision domains in an unbridged network and a bridged network

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

Routers (L3 Switches) Routers connecting independent LANs and WANs

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

Bus Backbone Old days

Star Backbone These days

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

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?

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

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

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

Logically Router; Firewall LAN3 LAN1 LAN2

☺ 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;