Local Area Networks

Satisfactory Essays
Topics: Ethernet
IT 548
Telecommunications & Networking
Local Area Networks

Hood College Dept. of Computer Science Spring 2013

Layer 2: The Datalink Layer



2

Datalink layer provides a reliable communications link between devices. Breaks a data stream into chunks called frames, or cells.
Three key functions: • error detection • error correction • flow control





In LANs DL can be broken down into two sub-layers: • media access control (MAC)‫‏‬ • logical link control (LLC). • flow and error control

Datalink Layer Addressing

3

• Frame transmitted

Datalink Layer Addressing

4

• Frame received • Note MAC addresses

LAN Architecture Model
• A network’s architecture consists of:
• Access methodology • Network Logical topology • Network Physical topology

5

No single architecture is best in all circumstances.

Access Methodology-CSMA/CD
1 4

6

2

5

3

6

Access Methodology-Token Passing

7

CSMA/CD vs. Token Passing

8

• CSMA/CD becomes less efficient at high bandwidth demand.

Network Topology
• Logical topology
• Sequential • Broadcast

9

• Physical topology
• Ring • Bus • Star

LAN Components
• • • • A central wiring concentrator Media Network Interface Cards Network interface card drivers.

10

A local area network, regardless of network architecture, requires the following components:

LAN Technology Architecture

11

NOS? What is that?

LAN Technology Choices & Implications

12

13

NIC Technology Analysis Grid

Ethernet
• Traditional Ethernet can be defined as follows:
• Access methodology: CSMA/CD • Logical topology: Broadcast • Physical Topology: Historically—bus, currently—star

14

Ethernet Frame Layout

15

• •

IEEE 802.3 is commonly referred to as “Ethernet”. There are differences as noted here.

LAN Architecture

16

• Typical Fast Ethernet Implementation

Gigabit Ethernet (aka 1000BaseX)‫‏‬
• An upgrade to Fast Ethernet,

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