6 Feb 2015 - Chap 4 Review

Review Topics:

Which layer is responsible for encapsulation
Describe signaling
Why does the physical later use frame encoding
Through put vs goodput
copper cabling issues
cancellation
termination issues
rollover vs straight through vs cross over
fiber multi mode - full duplex
copper vs fiber
wireless concerns when designing a network
802.11 standards
data link's job
sending frames - start and stop bits
physical vs logical topologies
802.11 - CSMA/CA
CSMA/CD
purpose of FCS
Data Link sublayers



Test has been activated.

6 Feb 2015 CCNA - Chapter 4: 4.4 Media Access Control

4.4 Media Access Control

4.4.1.1

The Media Access Control sublayer determines how data frames are put on the media.

The actual media access control method depends on;

Topology - the connection between nodes

Media Sharing - how the nodes share the media - Point to Point (WAN) or LAN

4.4.1.2 / 4.4.3.1

Review the difference between physical and logical topologies

4.4.2.1

Common WAN topologies:  Point to Point, Hub and Spoke, Mesh

4.4.2.2

Physical Point to Point directly connects 2 nodes (the serial connection between routers)

4.4.2.3

In a logical Point to Point a virtual (logical) connection is made between the nodes, but the physical connection may contain intermediary devices.

4.4.2.4

Data can flow using either Half or Full Duplex communication in a point to point topology

4.4.3.2 / 4.4.3.3

Logical topology is closely tied to how data is is sent and received on the network media.

There are two basic media access control methods for shared media:

• Contention-based access: All nodes compete for the use of the medium but have a plan if there are collisions. Figure 1 shows contention-based access.

CMSA/CD Wired  802.3 Eithernet

CMSA/CA Wireless 802.11

• Controlled access: Each node has its own time to use the medium. Figure 2 shows controlled access.

The data link layer protocol dictates which media access control method will provide the appropriate balance between frame control, frame protection and network overhead

New Term:  non-deterministic contention based - a device can attempt to access the medial whenever it has data to send.  CSMA (Carrier Sensing Media Access) prevents chaos.

CD - Collision Detection listens for the presence of a data signal.  No signal - it sends.

CA - Collision Avoidance listens for the presence of a data signal.  No signal - sends an notificaiton of intent to send. Once it receives a clear to transmit, it sends the data.

4.4.3.5

Controlled access method - devices take turns to access the medium.

Token Ring (IEEE 802.5)

Fiber Distributed Data Interface (FFDI)

Both now obsolete

Review the Ring Topology and do Activity 4.4.3.7

4.4.4 Data Link Frame

Please Read the Section

A Data Link Frame has 3 basic parts:  Header, Data and Trailer

But they are formatted differently depending on the protocol used:  Ethernet, PPP or 802.11

Complete Activity 4.4.4.9