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Chapter 4B: Data Link Layer Protocols

Presentation_ID 2 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Chapter 4: Objectives

Upon completion of this chapter, you will be able to:

Describe the data link layer in preparing communication for transmission on specific media.

Compare logical topologies and physical topologies.

Describe the basic characteristics of media control methods on WAN topologies.

Presentation_ID 3 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer The OSI has 7 layers.

The Data Link Layer is the second layer, just above the Physical Layer.

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OSI Data Link Layer

• This layer is the protocol layer. • It transfers data between adjacent network nodes. • It is concerned with local delivery of frames

between devices. • A frame is a digital data transmission unit.

Presentation_ID 5 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer - Media Access Control

The Data Link Layer

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OSI Data Link Layer Framing

• Data are streamed from the network layer to the Data Link Layer.

• These Data are first framed, then delivered. • Framing is a technique performed by the Data Link

layer. • It breaks the bit stream into discrete frames.

Presentation_ID 7 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer A Frame

A frame comprises, • A header • A packet • A trailer

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OSI Data Link Layer - The Data Link Header

A frame consists of a header, data, and a trailer. A header consists of a start frame, address type and control. A trailer consists of a FCS (Frame Check Sequence) and stop frame.

Presentation_ID 9 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer A Frame

The packet contains the actual data to be sent.

Presentation_ID 10 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer The Trailer

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OSI Data Link Layer – Formatting Data for Transmission

• The frame header and trailer must be of a fixed format.

• The header signals start of a packet. • The trailers signals the end of a packet.

Presentation_ID 12 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer Formatting Data for Transmission

• Error Detection is done. If error is detected, the frame will not be transmitted.

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OSI Data Link Layer Ethernet Frame, used for LANs

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OSI Data Link Layer – Point-to-Point Protocol (PPP) Frame, used for WANs

The PPP frame has 6 fields. Each field contains bytes of information.

Presentation_ID 15 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – 802.11 Wireless Frame

The frame for wireless transmission is more complex, with many fields.

Presentation_ID 16 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – Layer 2 Address

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OSI Data Link Layer - LAN and WAN Frames

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OSI Data Link Layer – Data Link Layer Standards

Standard organization Networking Standards

IEEE

• 802.2: Logical Link Control (LLC) • 802.3: Ethernet • 802.4: Token bus • 802.5: Token passing • 802.11: Wireless LAN (WLAN) & Mesh (Wi-Fi certification) • 802.15: Bluetooth • 802.16: WiMax

ITU-T • G.992: ADSL • G.8100 - G.8199: MPLS over Transport aspects • Q.921: ISDN • Q.922: Frame Relay

ISO • HDLC (High Level Data Link Control) • ISO 9314: FDDI Media Access Control (MAC)

ANSI • X3T9.5 and X3T12: Fiber Distributed Data Interface (FDDI)

Transmission of data must follow some standards so that all hardware can communicate.

Presentation_ID 19 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer Data Link Sublayers

This layer has 2 sub-layers: • LLC (Logical Link Control) Layer

interacts with Network Layer • MAC (Media Access Control) Layer

interacts with Physical Layer

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OSI Data Link Layer – Media Access Control (MAC) Sublayer

Data Link Layer controls the transfer of frames.

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OSI Data Link Layer – Summary of data transfer

Data from a source go through the 7 layers (7 to 1) during encapsulation. Bits sent from one source goes through the 7 layers (1 to 7) during de-encapsulation. Device at destination receives data sent.

Presentation_ID 22 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer

Topology

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OSI Data Link Layer Topology

Topology is the way in which constituent parts are interrelated or arranged.

There are two types of network topology:

Physical

Logical

Presentation_ID 24 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer - Physical Topology

Physical topology is the placement of the various components of a network, including device location and cable installation.

Presentation_ID 25 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer - Logical Topology

Logical topology illustrates how data flows within a network, regardless of its physical design.

Presentation_ID 26 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – Common Physical WAN Topologies

Common Physical WAN Topologies include: • Point-to-Point • Hub and Spoke • Full Mesh

Presentation_ID 27 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – WAN Physical Point-to-Point Topology

Point-to-Point Topology is limited to having 2 nodes.

Presentation_ID 28 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer - WAN Logical Point-to-Point Topology

Adding more devices or changing locations do not affect the logical topology of a network.

Presentation_ID 29 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – WAN Half- and Full-Duplex

Half-Duplex – Data can be sent in one direction at any one time.

Full-Duplex – Data can be sent/received in both directions at the same time. Faster data transfer can be achieved.

Presentation_ID 30 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – Physical LAN Topologies

WAN Topologies – some are same as LAN Topologies, some are not

Presentation_ID 31 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – Physical LAN Topologies

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OSI Data Link Layer – LAN Logical Topology for Shared Media

There are two methods of sharing media (data) in a LAN: • Contention-based Access Method • Controlled Access Method

Presentation_ID 33 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – LAN Logical Topology for Shared Media

Contention-Based Access Method This method is based on devices contending to send data whenever there is room for traffic in the network.

Characteristics Contention-Based Technologies • Stations can transmit at any time • Collision of frames can take place as there is

no control of transmission • There are mechanisms to resolve contention

for the media

• CSMA/CD for 802.3 Ethernet networks • CSMA/CA for 802.11 wireless networks

Presentation_ID 34 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – LAN Logical Topology for Shared Media

Controlled Access Method This method allows a device to send data only when it is given the right.

Characteristics Controlled Access Technologies

• Only one station can transmit at a time • Devices wanting to transmit must wait their turn • No collisions of frames at all • May use a token passing method

(token passing - a signal called a token is passed between nodes; it authorizes the node to communicate

• Token Ring (IEEE 802.5) • FDDI

Presentation_ID 35 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – LAN Multi-Access Topology Only one device is allowed to transmit data at any one time.

Presentation_ID 36 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – LAN Ring Topology

In a LAN Ring Topology, a frame sent out stops at every device. If it is not meant for the device, the frame is sent to the next, until one device accept the frame. This is time consuming.

Presentation_ID 37 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – Fragile vs Protected Environment

There are two network environments: • Fragile environment

Open air, weather interference, uncontrolled factors, etc.

• Protected environment In a building, all factors controllable

Presentation_ID 38 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer – Fragile Environment

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OSI Data Link Layer – Protected Environment

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Network Access Summary The TCP/IP network access layer is the equivalent of the OSI data link

layer (Layer 2) and the physical layer (Layer 1).

The OSI physical layer provides the means to transport the bits that make up a data link layer frame across the network media.

The physical layer standards address three functional areas: physical components, frame encoding technique, and signaling method.

Using the proper media is an important part of network communications. Without the proper physical connection, either wired or wireless, communications between any two devices will not occur.

Wired communication consists of copper media and fiber cable.

There are three main types of copper media used in networking: unshielded-twisted pair (UTP), shielded-twisted pair (STP), and coaxial cable. UTP cabling is the most common copper networking media.

Presentation_ID 41 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Network Access Summary (cont.) Optical fiber cable has become very popular for interconnecting

infrastructure network devices. It permits the transmission of data over longer distances and at higher bandwidths (data rates) than any other networking media.

Wireless media carry electromagnetic signals that represent the binary digits of data communications using radio or microwave frequencies.

The data link layer is responsible for the exchange of frames between nodes over a physical network media. It allows the upper layers to access the media and controls how data is placed and received on the media.

Among the different implementations of the data link layer protocols, there are different methods of controlling access to the media. These media access control techniques define if and how the nodes share the media.

The actual media access control method used depends on the topology and media sharing. LAN and WAN topologies can be physical or logical.

Presentation_ID 42 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Network Access Summary (cont.) WANs are commonly interconnected using the point-to-point, hub and

spoke, or mesh physical topologies.

In shared media LANs, end devices can be interconnected using the star, bus, ring, or extended star (hybrid) physical topologies.

All data link layer protocols encapsulate the Layer 3 PDU within the data field of the frame. However, the structure of the frame and the fields contained in the header and trailer vary according to the protocol.

Presentation_ID 43 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

1. The OSI has ___ layers.

The Data Link Layer is the ________ layer, just above the Physical Layer.

Presentation_ID 44 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

1. The OSI has 7 layers.

The Data Link Layer is the second layer, just above the Physical Layer.

Presentation_ID 45 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

2. This data link layer is the ________ layer. It _________ data between adjacent network nodes. It is concerned with local delivery of frames between devices. A ______ is a digital data transmission unit.

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Review

3. The Data Link Layer protocols govern how to format a ________.

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Review

3. The Data Link Layer protocols govern how to format a frame.

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Review

4. _________ is a technique performed by the Data Link layer. It _______ the bit stream into discrete frames.

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Review

4. Framing is a technique performed by the Data Link layer. It breaks the bit stream into discrete frames.

Presentation_ID 50 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

5. A frame comprises, • A ______ • A ______ • A trailer

Presentation_ID 51 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

5. A frame comprises, • A header • A packet • A trailer

Presentation_ID 52 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer - The Data Link Header

6. A frame consists of a header, data, and a trailer. A header consists of a ______ frame, address type and control. A trailer consists of a _____ (Frame Check Sequence) and stop frame.

Presentation_ID 53 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer - The Data Link Header

6. A frame consists of a header, data, and a trailer. A header consists of a start frame, address type and control. A trailer consists of a FCS (Frame Check Sequence) and stop frame.

Presentation_ID 54 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

7. _____ Detection for the frame is done. If error is detected, the frame will _______ be transmitted.

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Review

7. Error Detection for the frame is done. If error is detected, the frame will not be transmitted.

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Review

8. PPP stands for __________ The PPP frame has ___ fields. Each field contains bytes of information.

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Review

8. PPP stands for Point-to-Point Protocol. The PPP frame has 6 fields. Each field contains bytes of information.

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Review

9. A multi-access frame has ______ destinations, while A point-to-point access frame has ____ destination.

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Review

9. A multi-access frame has many destinations, while A point-to-point access frame has only one destination.

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Review

10. The Data Link layer has 2 _________: • LLC (Logical Link Control) Layer

interacts with Network Layer • MAC (Media Access Control) Layer

interacts with Physical Layer

Presentation_ID 61 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

10. The Data Link layer has 2 _________: • LLC (Logical Link Control) Layer

interacts with Network Layer • MAC (Media Access Control) Layer

interacts with Physical Layer

Presentation_ID 62 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

11. The Data Link Layer controls the transfer of ______.

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Review

11. The Data Link Layer controls the transfer of frames.

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OSI Data Link Layer – Summary of data transfer

Data from a source go through the 7 layers (7 to 1) during encapsulation. Bits sent from one source goes through the 7 layers (1 to 7) during de-encapsulation. Device at destination receives data sent.

Presentation_ID 65 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

OSI Data Link Layer

Topology

Presentation_ID 66 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

12. Topology is the way in which constituent parts are interrelated or arranged.

There are two types of network topology:

______

_______

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Review

12. Topology is the way in which constituent parts are interrelated or arranged.

There are two types of network topology:

Physical

Logical

Presentation_ID 68 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

13. _______ _____ is the placement of the various components of a network, including device location and cable installation.

Presentation_ID 69 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

13. Physical topology is the placement of the various components of a network, including device location and cable installation.

Presentation_ID 70 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

14. _________ _______ illustrates how data flows within a network, regardless of its physical design.

Presentation_ID 71 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

14. Logical topology illustrates how data flows within a network, regardless of its physical design.

Presentation_ID 72 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

15. Common Physical WAN Topologies include: • Point-to-Point • ___________ • Full Mesh

Presentation_ID 73 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

15. Common Physical WAN Topologies include: • Point-to-Point • Hub and Spoke • Full Mesh

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Review

16. Point-to-Point Topology is limited to having ____ nodes.

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Review

16. Point-to-Point Topology is limited to having 2 nodes.

Presentation_ID 76 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review 17. Adding more devices or changing locations do not affect the ________ topology of a network.

Presentation_ID 77 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review 17. Adding more devices or changing locations do not affect the logical topology of a network.

Presentation_ID 78 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

18. Half-Duplex – Data can be sent in ____ direction at any one time.

Full-Duplex – Data can be sent/received in ____ directions at the same time. Faster data transfer can be achieved.

Presentation_ID 79 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

18. Half-Duplex – Data can be sent in one direction at any one time.

Full-Duplex – Data can be sent/received in both directions at the same time. Faster data transfer can be achieved.

Presentation_ID 80 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review 19. The 4 physical WAN topologies are Star, ______, ______ and Ring.

Presentation_ID 81 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review 19. The 4 physical WAN topologies are Star, Extended, Bus and Ring.

Presentation_ID 82 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

20. There are two methods of sharing media (data) in a LAN: • ___________ Access Method • ___________ Access Method

Presentation_ID 83 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

20. There are two methods of sharing media (data) in a LAN: • Contention-based Access Method • Controlled Access Method

Presentation_ID 84 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

21. In a LAN Ring Topology, a frame sent out stops at ________ device.

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Review

21. In a LAN Ring Topology, a frame sent out stops at every device.

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Review

22. There are two network environments: • _______ environment

• ________ environment

Presentation_ID 87 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

Review

22. There are two network environments: • Fragile environment

Open air, weather interference, uncontrolled factors, etc.

• Protected environment In a building, all factors controllable

Presentation_ID 88 © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

End of Review