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Semester 1Semester 1

CHAPTER 6CHAPTER 6

Le Chi TrungLe Chi Trung

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ContentContent

• LAN Standards.

• Hexadecimal Numbers.

• MAC Addressing.

• Framing.

• Media Access Control (MAC).

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ScheduleSchedule

No Name Est time No Name22-May Chapter 5 Online Exam

6.1 LAN Standards 0:40:006.2 Hexadecimal numbers 0:20:00

24-May 6.3 MAC Addressing 0:30:006.4 Framing 0:30:006.5 Media access control (MAC) 0:30:00

Summary Chapter 6 0:30:0026-May Chapter 6 Online Exam

Lesson LabDay

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LAN STANDARDSLAN STANDARDS

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Limitations of Layer 1Limitations of Layer 1

• Cannot organize streams of bits.

• Cannot name or identify computers.

• Cannot communicate with the upper-level layers.

• Cannot decide which computer will transmit binary data.

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Layer 2Layer 2

• Layer 2 uses framing to organize or group the bits.

• Layer 2 uses an addressing process to identify computers.

• Layer 2 uses Logical Link Control (LLC) to communicate with the upper-level layers.

• Layer 2 uses Media Access Control (MAC) to decide which computer will transmit.

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OSI and various LAN standardOSI and various LAN standard

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IEEEIEEE

• The Institute of Electrical and Electronic Engineers.

• LAN standards:

– 802.1d: Spanning tree.

– 802.2: LLC.

– 802.3: MAC ~ Ethernet.

– 802.5: MAC ~ Token ring.

– 802.11: Wireless LAN.

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IEEE LAN StandardIEEE LAN Standard

• Logical Link Control (LLC): Transitions up to the network layer.

• Media Access Control (MAC): Transitions down to media.

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Two Sub-layers Two Sub-layers WHYWHY ? ?

• LLC serves to communicate upward to Network layer, independent of the specific LAN technology used and Upper layer.

• MAC serves to access and communicate downward to the technology-specific Physical layer.

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LLCLLC

• PDU: Protocol data unit

• DSAP: Destination service access point

• SSAP: Source service access point

Packet

Packet

Packet

LLC PDU

Frame

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MACMAC

• Naming.

• Framing.

• Media access control rules.

Packet

Packet

Packet Packet

802.3 802.5

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4 Concepts of Layer 24 Concepts of Layer 2

1. Layer 2 uses framing to organize or group the data.

2. Layer 2 uses a flat addressing convention.

3. Layer 2 communicates with the upper-level layers through LLC.

4. Layer 2 uses MAC to choose which computer will transmit binary data, from a group in which all computers are trying to transmit at the same time.

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ReviewReview

• 2 sub-layers of data link layer.

• Functions of LLC.

• Functions of MAC.

• 4 concepts of layer 2.

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HEXADECIMAL NUMBERSHEXADECIMAL NUMBERS

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Base 16 systemBase 16 system

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Conversion algorithmsConversion algorithms

Homework

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Exercise: Exercise: DEC – HEX – BIN DEC – HEX – BIN

203

CB

11001011

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Exercise: Exercise: DEC – HEX – BIN DEC – HEX – BIN

159

9F

10011111

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Exercise: Exercise: DEC – HEX – BIN DEC – HEX – BIN

95

5F

01011111

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Exercise: Exercise: HEX – BIN – DECHEX – BIN – DEC

FA

250

11111010

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Exercise: Exercise: HEX – BIN – DECHEX – BIN – DEC

A1

161

10100001

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Exercise: Exercise: HEX – BIN – DECHEX – BIN – DEC

B9

185

10111001

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Exercise: Exercise: BIN – DEC – HEXBIN – DEC – HEX

10101011

171

AB

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Exercise: Exercise: BIN – DEC – HEXBIN – DEC – HEX

11101001

233

E9

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Exercise: Exercise: BIN – DEC – HEXBIN – DEC – HEX

00101101

45

2D

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ReviewReview

• Conversion algorithms.

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MAC ADDRESSINGMAC ADDRESSING

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MAC AddressMAC Address

• Every computer has a unique way of identifying itself : MAC address or physical address.

• The physical address is located on the Network Interface Card (NIC).

• MAC addresses have no structure, and are considered flat address spaces.

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MAC address formatMAC address format

The first six hexadecimal digits, which are administered

by the IEEE, identify the manufacturer or vendor.

The remaining six hexadecimal digits comprise the interface serial number.

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MAC addressMAC address

• MAC addresses are sometimes referred to as burned-in addresses (BIAs) because they are burned into read-only memory (ROM) and are copied into random-access memory (RAM) when the NIC initializes.

• 0000.0c12.3456 or 00-00-0c-12-34-56.

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Using MAC addressesUsing MAC addresses

A DData A DData A DDataA DData

Source Address

Destination Address

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EncapsulationEncapsulation

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Limitation of MACLimitation of MAC

• Flat, does not work well in internetwork.

• Hardware dependent.

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ReviewReview

• MAC address structure.

• Limitation of MAC.

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FRAMINGFRAMING

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EncodingEncoding

• Encoding is the process of converting information into a form that can travel on a physical link.

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Why framing is necessary?Why framing is necessary?

• Which computers are communicating with one another.

• When communication between individual computers begins and when it terminates.

• A record of errors that occurred during the communication.

• Whose turn it is to “talk” in a computer “conversation”.

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Frame format diagramFrame format diagram

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Frame format diagramFrame format diagram

• The frame format diagram shows different groupings of bits (fields) that perform other functions.

• Read them from left to right.

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Generic frame formatGeneric frame format

• There are many different types of frames described by various standards.

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Start frame fieldStart frame field

• The Start Frame field tells other devices on the network that a frame is coming down the wire.

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Address fieldAddress field

• The Address field stores the source and destination MAC addresses.

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Length/Type fieldLength/Type field

• The Type/Length field is an optional field used by some protocols to either state what type of data is coming or possibly the length of the frame.

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Data fieldData field

• The Data field is the actual information being sent by the upper layer protocols. Therefore, it will be all upper layer data.

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Stop frame fieldStop frame field

• The Stop Frame field, also called the Frame Trailer, is an optional field that is used when the length of the frame was not specified in the Type/Length field.

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ReviewReview

• Generic frame format.

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MEDIA ACCESS CONTROLMEDIA ACCESS CONTROL

MACMAC

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Definition MACDefinition MAC

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Definition MACDefinition MAC

• Specified by the technology being used.

• Determine who can transmit and when.

• Two types:

– Deterministic: “Let’s take turns”.

• Token-Ring, FDDI.

– Non-deterministic: “First come, first serve”.

• Ethernet : CSMA/CD.

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Deterministic MAC protocolDeterministic MAC protocol

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Non-deterministic MAC protocolNon-deterministic MAC protocol

• Carrier Sense Multiple Access with Collision Detection (CSMA/CD). 

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CSMA/CDCSMA/CD

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LAN TechnologiesLAN Technologies

• Ethernet: logical broadcast topology

• Token Ring: logical token ring topology

• FDDI: logical token ring topology

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ReviewReview

• Function of MAC layer.

• Type of MAC protocols.

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