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Transcript
OSI Data Link Layer
Network Fundamentals – Chapter 7
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1
Objectives

Explain the role of Data Link layer protocols in data transmission.

Describe how the Data Link layer prepares data for transmission
on network media.

Describe the different types of media access control methods.

Identify several common logical network topologies and describe
how the logical topology determines the media access control
method for that network.

Explain the purpose of encapsulating packets into frames to
facilitate media access.

Describe the Layer 2 frame structure and identify generic fields.

Explain the role of key frame header and trailer fields including
addressing, QoS, type of protocol and Frame Check Sequence.
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2
Context Index
 7.1 Data Link Layer – Accessing the Media
 7.2 Media Access Control Techniques
 7.3 Media Access Control Addressing and Framing Data
 7.4 Putting it All Together
 7.5 Labs and Activities
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3
7.1 Data Link Layer –
Accessing the Media
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7.1.1 Data Link Layer – Supporting &
Connecting to Upper Layer Services
 The Data Link layer performs two basic services:
-Allows the upper layers to access the media using techniques
such as framing
-Controls how data is placed onto the media and is received from
the media using techniques such as media access control and
error detection
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7.1.1 Data Link Layer – Supporting &
Connecting to Upper Layer Services
 Data Link Layer Terms
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7.1.1 Data Link Layer – Supporting &
Connecting to Upper Layer Services
 Numerous Data Link layer protocols are being used
over various types of LANs and WANs.
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7.1.2 Data Link Layer – Controlling Transfer
across Local Media
 Layer 2 protocols specify the encapsulation of a packet
into a frame .
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7.1.3 Data Link Layer – Creating a Frame
 Data Link layer frame includes:
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7.1.3 Data Link Layer – Creating a Frame
 The role the Data Link layer plays in linking the
software and hardware layers
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7.1.4 Data Link Layer – Connecting Upper
Layer Services to the Media
 Data Link layer is often divided into two sub-layers:
-Logical Link Control
-Media Access Control
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7.1.5 Data Link Layer – Standards
 Standards for the Data Link layer
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7.2 Media Access Control Techniques
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7.2.1 Placing Data on the Media
 Explain the necessity for controlling access to the
media
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7.2.2 Media Access Control for Shared Media
 There are two basic media access control methods for
shared media:
-Controlled - Each node has its own time to use the medium
-Contention-based - All nodes compete for the use of the medium
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7.2.2 Media Access Control for Shared Media
 There are two basic media access control methods for
shared media:
-Controlled - Each node has its own time to use the medium
-Contention-based - All nodes compete for the use of the medium
思科网络技术学院理事会.
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7.2.2 Media Access Control for Shared Media
 There are two basic media access control methods for
shared media:
-Controlled - Each node has its own time to use the medium
-Contention-based - All nodes compete for the use of the medium
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7.2.3 Media Access Control for Non-Shared
Media
 Define Full Duplex and Half Duplex as it relates to
Media Access Control for non-shared media
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7.2.3 Media Access Control for Non-Shared
Media
 Define Full Duplex and Half Duplex as it relates to
Media Access Control for non-shared media
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7.2.3 Media Access Control for Non-Shared
Media
 Define Full Duplex and Half Duplex as it relates to
Media Access Control for non-shared media
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7.2.4 Logical Topology vs Physical Topology
 The representation of how the media is used to
interconnect the devices is the physical topology.
 A logical topology is the way a network transfers frames
from one node to the next.
 Topologies used in networks
are:
-Point-to-Point
-Multi-Access
-Ring
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7.2.5 Point-to-Point Topology
 A point-to-point topology connects two nodes directly
together.
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7.2.5 Point-to-Point Topology
 A virtual circuit is a logical connection created within a
network between two network devices.
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7.2.5 Point-to-Point Topology
 A virtual circuit is a logical connection created within a
network between two network devices.
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7.2.6 Multi-Access Topology
 Data from only one node can be placed on the medium
at any one time.
 Every node sees all the frames that are on the medium,
but only the node to which the frame is addressed
processes the contents of the frame.
 A Data Link media access control method is required to
regulate the transmission of data.
 The media access control methods are typically
CSMA/CD or CSMA/CA.
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7.2.6 Multi-Access Topology
 How nodes access the media in a multi-access
topology
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7.2.7 Ring Topology
 In a logical ring topology, each node in turn receives a
frame. If the frame is not addressed to the node, the
node passes the frame to the next node.
 If there is no data being transmitted, a signal (known
as a token) may be placed on the media and a node
can only place a data frame on the media when it has
the token.
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7.2.7 Ring Topology
 How nodes access the media in a logical ring topology
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7.3 Media Access Control Addressing
and Framing Data
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7.3.1 Data Link Layer Protocols – The Frame
 The structure of the frame and the fields contained in
the header and trailer vary according to the protocol.
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7.3.2 Framing – Role of the Header
 The role of the frame header in the Data Link layer
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7.3.3 Addressing – Where the Frame Goes
 Data Link layer addressing is contained within the
frame header and specifies the frame destination node
on the local network.
 If the device is moved to another network or subnet,
physical addresses will still function with the same
Layer 2 physical address.
 The intermediate device - a router - will decapsulate the
original frame, create a new frame for the packet.
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7.3.3 Addressing – Where the Frame Goes
 Addressing Requirements
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7.3.4 Framing – Role of the Trailer
 The role of the frame trailer in the Data Link layer
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7.3.5 Data Link Layer Protocol – The Frame
 Given the wide range of physical media used in
networking, there are a correspondingly high number of
Layer 2 protocols in use.
802.11 Wireless
Frame
802.11 Wireless
Frame
HDLC
Frame Relay
PPP frame
Ethernet Frame
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7.3.5 Data Link Layer Protocol – The Frame
 Ethernet Protocol for LANs
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7.3.5 Data Link Layer Protocol – The Frame
 Point-to-point Protocol for WANs
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7.3.5 Data Link Layer Protocol – The Frame
 Wireless Protocol for LANs
From
Retry
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思科网络技术学院理事会.
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7.4 Putting it All Together
思科网络技术学院理事会.
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39
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
40
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
41
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
42
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
43
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
44
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
45
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
46
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
47
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
48
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
49
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
50
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
51
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
52
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
53
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
54
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
55
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
56
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
57
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
58
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
59
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
60
7.4.1 Follow Data Through an Internetwork
 A simple data transfer between two hosts across an
internetwork.
思科网络技术学院理事会.
http://www.catc.edu.cn
61
Summary
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思科网络技术学院理事会.
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