The Data Link Layer

Chapter 2

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Data Link Layer Design Issues

• Services Provided to the Network Layer• Framing• Error Control• Flow Control

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Functions of the Data Link Layer

• Provide service interface to the network layer• Dealing with transmission errors• Regulating data flow• Slow receivers not swamped by fast senders

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Functions of the Data Link Layer

Relationship between packets and frames.

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Services Provided to Network Layer

(a) Virtual communication.(b) Actual communication.

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Services Provided to Network Layer

Placement of the data link protocol.

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Framing

A character stream. (a) Without errors. (b) With one error.

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Framing

(a) A frame delimited by flag bytes.(b) Four examples of byte sequences before and after stuffing.

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Framing

Bit stuffing(a) The original data.(b) The data as they appear on the line.(c) The data as they are stored in receiver’s memory after destuffing.

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Error Detection and Correction

• Error-Correcting Codes• Error-Detecting Codes

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Error-Correcting Codes

Use of a Hamming code to correct burst errors.

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Error-Detecting Codes

Calculation of the polynomial code checksum.

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Elementary Data Link Protocols

• An Unrestricted Simplex Protocol• A Simplex Stop-and-Wait Protocol• A Simplex Protocol for a Noisy Channel

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Sliding Window Protocols

• A One-Bit Sliding Window Protocol• A Protocol Using Go Back N• A Protocol Using Selective Repeat

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Sliding Window Protocols

A sliding window of size 1, with a 3-bit sequence number.(a) Initially.(b) After the first frame has been sent.(c) After the first frame has been received.(d) After the first acknowledgement has been received.

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A One-Bit Sliding Window Protocol

Two scenarios for protocol 4. (a) Normal case. (b) Abnormal case. The notation is (seq, ack, packet number). An asterisk indicates where a network layer accepts a packet.

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A Protocol Using Go Back N

Pipelining and error recovery. Effect on an error when(a) Receiver’s window size is 1.(b) Receiver’s window size is large.

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A Sliding Window Protocol Using Selective Repeat

(a) Initial situation with a window size seven.(b) After seven frames sent and received, but not acknowledged.(c) Initial situation with a window size of four.(d) After four frames sent and received, but not acknowledged.

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Protocol Verification

• Finite State Machined Models• Petri Net Models

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Finite State Machined Models

(a) State diagram for protocol 3. (b) Transmissions.

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Example Data Link Protocols

• HDLC – High-Level Data Link Control• The Data Link Layer in the Internet

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High-Level Data Link Control

Frame format for bit-oriented protocols.

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High-Level Data Link Control

Control field of (a) An information frame.(b) A supervisory frame.(c) An unnumbered frame.

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The Data Link Layer in the Internet

A home personal computer acting as an internet host.

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PPP – Point to Point Protocol

The PPP full frame format for unnumbered mode operation.

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PPP – Point to Point Protocol

A simplified phase diagram for bring a line up and down.

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PPP – Point to Point Protocol

The LCP frame types.

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The Medium Access ControlSublayer

Chapter 3

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The Channel Allocation Problem

• Static Channel Allocation in LANs and MANs• Dynamic Channel Allocation in LANs and MANs

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Dynamic Channel Allocation in LANs and MANs

1. Station Model.

2. Single Channel Assumption.

3. Collision Assumption.

4. (a) Continuous Time.(b) Slotted Time.

5. (a) Carrier Sense.(b) No Carrier Sense.

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Multiple Access Protocols• ALOHA• Carrier Sense Multiple Access Protocols• Collision-Free Protocols• Limited-Contention Protocols• Wavelength Division Multiple Access Protocols• Wireless LAN Protocols

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Pure ALOHA

In pure ALOHA, frames are transmitted at completely arbitrary times.

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Pure ALOHA

Vulnerable period for the shaded frame.

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Pure ALOHA

Throughput versus offered traffic for ALOHA systems.1/4/2017 Mr Satyendra Mohan, JIT Barabanki 34

Persistent and Nonpersistent CSMA

Comparison of the channel utilization versus load for various random access protocols.

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CSMA with Collision Detection

CSMA/CD can be in one of three states: contention, transmission, or idle.

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Collision-Free Protocols

The basic bit-map protocol.

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Collision-Free Protocols

The binary countdown protocol. A dash indicates silence.

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Limited-Contention Protocols

Acquisition probability for a symmetric contention channel.

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Adaptive Tree Walk Protocol

The tree for eight stations.

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Wavelength Division Multiple Access Protocols

Wavelength division multiple access.

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Wireless LAN Protocols

A wireless LAN. (a) A transmitting. (b) B transmitting.

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Wireless LAN Protocols

The MACA protocol. (a) A sending an RTS to B.(b) B responding with a CTS to A.

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Ethernet• Ethernet Cabling• Manchester Encoding• The Ethernet MAC Sublayer Protocol• The Binary Exponential Backoff Algorithm• Ethernet Performance• Switched Ethernet• Fast Ethernet• Gigabit Ethernet• IEEE 802.2: Logical Link Control• Retrospective on Ethernet1/4/2017 Mr Satyendra Mohan, JIT Barabanki 44

Ethernet Cabling

The most common kinds of Ethernet cabling.

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Ethernet Cabling

Three kinds of Ethernet cabling. (a) 10Base5, (b) 10Base2, (c) 10Base-T.

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Ethernet Cabling

Cable topologies. (a) Linear, (b) Spine, (c) Tree, (d) Segmented.

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Ethernet Cabling (4)

(a) Binary encoding, (b) Manchester encoding, (c) Differential Manchester encoding.

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Ethernet MAC Sublayer Protocol

Frame formats. (a) DIX Ethernet, (b) IEEE 802.3.

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Ethernet MAC Sublayer Protocol

Collision detection can take as long as 2 .

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Ethernet Performance

Efficiency of Ethernet at 10 Mbps with 512-bit slot times.

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Switched Ethernet

A simple example of switched Ethernet.

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Fast Ethernet

The original fast Ethernet cabling.

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Gigabit Ethernet

(a) A two-station Ethernet. (b) A multistation Ethernet.

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Gigabit Ethernet

Gigabit Ethernet cabling.

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IEEE 802.2: Logical Link Control

(a) Position of LLC. (b) Protocol formats.

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Wireless LANs

• The 802.11 Protocol Stack• The 802.11 Physical Layer• The 802.11 MAC Sublayer Protocol• The 802.11 Frame Structure• Services

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The 802.11 Protocol Stack

Part of the 802.11 protocol stack.

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The 802.11 MAC Sublayer Protocol

(a) The hidden station problem.(b) The exposed station problem.

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The 802.11 MAC Sublayer Protocol

The use of virtual channel sensing using CSMA/CA.

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The 802.11 MAC Sublayer Protocol

A fragment burst.

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The 802.11 MAC Sublayer Protocol

Interframe spacing in 802.11.

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The 802.11 Frame Structure

The 802.11 data frame.

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802.11 Services

• Association• Disassociation• Reassociation• Distribution• Integration

Distribution Services

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802.11 Services

• Authentication• Deauthentication• Privacy• Data Delivery

Intracell Services

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Broadband Wireless• Comparison of 802.11 and 802.16• The 802.16 Protocol Stack• The 802.16 Physical Layer• The 802.16 MAC Sublayer Protocol• The 802.16 Frame Structure

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The 802.16 Protocol Stack

The 802.16 Protocol Stack.

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The 802.16 Physical Layer

The 802.16 transmission environment.

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The 802.16 Physical Layer

Frames and time slots for time division duplexing.

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The 802.16 MAC Sublayer Protocol

Service Classes• Constant bit rate service• Real-time variable bit rate service• Non-real-time variable bit rate service• Best efforts service

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The 802.16 Frame Structure

(a) A generic frame. (b) A bandwidth request frame.

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Bluetooth

• Bluetooth Architecture• Bluetooth Applications• The Bluetooth Protocol Stack• The Bluetooth Radio Layer• The Bluetooth Baseband Layer• The Bluetooth L2CAP Layer• The Bluetooth Frame Structure

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Bluetooth Architecture

Two piconets can be connected to form a scatternet.

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Bluetooth Applications

The Bluetooth profiles.

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The Bluetooth Protocol Stack

The 802.15 version of the Bluetooth protocol architecture.

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The Bluetooth Frame Structure

A typical Bluetooth data frame.

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Data Link Layer Switching• Bridges from 802.x to 802.y• Local Internetworking• Spanning Tree Bridges• Remote Bridges• Repeaters, Hubs, Bridges, Switches, Routers, Gateways• Virtual LANs

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Data Link Layer Switching

Multiple LANs connected by a backbone to handle a total load higher than the capacity of a single LAN.

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Bridges from 802.x to 802.y

Operation of a LAN bridge from 802.11 to 802.3.

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Bridges from 802.x to 802.y

The IEEE 802 frame formats. The drawing is not to scale.

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Local Internetworking

A configuration with four LANs and two bridges.

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Spanning Tree Bridges

Two parallel transparent bridges.

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Spanning Tree Bridges

(a) Interconnected LANs. (b) A spanning tree covering the LANs. The dotted lines are not part of the spanning tree.

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Remote Bridges

Remote bridges can be used to interconnect distant LANs.

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Repeaters, Hubs, Bridges, Switches, Routers and Gateways

(a) Which device is in which layer.(b) Frames, packets, and headers.

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Repeaters, Hubs, Bridges, Switches, Routers and Gateways

(a) A hub. (b) A bridge. (c) a switch.

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Virtual LANs

A building with centralized wiring using hubs and a switch.

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Virtual LANs

(a) Four physical LANs organized into two VLANs, gray and white, by two bridges. (b) The same 15 machines organized into two VLANs by switches.

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The IEEE 802.1Q Standard

Transition from legacy Ethernet to VLAN-aware Ethernet. The shaded symbols are VLAN aware. The empty ones are not.

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The IEEE 802.1Q Standard

The 802.3 (legacy) and 802.1Q Ethernet frame formats.

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Summary

Channel allocation methods and systems for a common channel.

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References

[1] A. S. Tanenbaum, “Computer Network”, Pearson Education

[2] Forouzen, “Data Communication and Networking”, TMH

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