QSpiders - Dod Model

DOD MODEL

The DoD Model•The Process / Application Layer

•The Host-to-Host Layer

•The Internet Layer

•The Network Layer

The DoD & OSI

Application

Application

PresentationSession

TransportNetwork

Data Link

Physical

Host-to-HostInternet

Network Access

DoD Model OSI Model

Process/Application Layer

• The Process / Application layer defines protocols for node-to-node application communication and also controls user-interface specification.•A vast array of protocols combine at this layer of DoD’s Model to integrate the activities and duties of upper layer of OSI.• Examples for this layer are :Telnet, FTP, TFTP, NFS, SMTP, SNMP, DNS DHCP, BootP etc.

Host-to-Host Layer• The Host-to-Host layer parallels the functions of the OSIs Transport layer• It performs the following:• Defining protocols for setting up the level of transmission service for Applications• It tackles issues like creating reliable ene-to-end communication.• It ensures the error free delivery of data• It handles packet sequencing and maintains data integrity.

Internet Layer• Internet Layer corresponds to the OSI’s Network Layer.• It performs the following:•Designating the protocols relating to the logical transmission of packets over the entire network.• It takes care of the addressing of hosts by giving them an IP address.• It handles routing of packets among multiple networks.

Network Access Layer

•This layer is equivalent of the Data Link and Physical Layer of OSI model.•It performs the following• It monitors the data exchange between

the host and the network.• Network Access Layer overseas

hardware addressing and defines protocols for the physical transmission of the Data.

Lets have a look on how TCP/IP Protocol suit relates to the DoD model layers.

TCP/IP Protocol Suit at DoD

DoD Model

Process /Application

Host-to-Host

Internet

Network Access

TCP/IP Protocol Suit

Telnet FTP LPD SNMP

X WindowNFSSMTPTFTP

TCP UDP

ICMP

Ethernet

ARP RARP

IP

FastEthernet

TokenRing FDDI

BootP

LOWER LAYERS PROTOCOLS

Common LAN Technologies

• Ethernet

• Token Ring

• FDDI FDDIDual Ring

TokenRing

Ethernet

© 1999, Cisco Systems, Inc. www.cisco.com

Introduction• Ethernet is a methodology for accessing a media• It allows all hosts on a network to share the same

bandwidth of a link.• It is popular because :

• It is easy to implement & Troubleshoot• It is easy to add new technologies like Fast

Ethernet and Gigabit Ethernet to existing infrastructure.

• Ethernet uses Data Link Layer and Physical Layer Specification• It uses something called CSMA/CD

Ethernet Operation

AA BB CC DD

Ethernet OperationAA BB CC DD

D

Data LinkNetworkTransportSessionPresentationApplication

Physical

Ethernet Operation

AA BB CC DD

D


Physical

B and C


Physical

Ethernet LANs:How do they work?

• Multiple workstations are connected to a “segment”

• Each station has to take turns sending traffic

• All stations listen to all traffic on their segment

• Stations can only send data (Ethernet Frames) when no one else is sending

Ethernet LANs: MAC Addresses

• Every workstation has a Network Interface Card (NIC)

• Every NIC has a unique MAC address

• Stations use MAC addresses to send Ethernet Frames to a specific station

0000.0c12.3456

0000.0c12.11110000.1018.321a

Ethernet LANs: Unicast Frames

• Ethernet frames contain the MAC address of the station that the frame was sent to

• These are called “unicast” frames

• All stations receive the Ethernet frame, but ignore the frames that are not addressed to their MAC address

0000.0c12.3456

0000.0c12.11110000.1018.321a

FrameTo: 0000.0c12.3456

Ethernet LANs: Broadcast Frames

• Some Ethernet frames are sent to all stations

• These are called “broadcast” frames

• All stations process this frame

0000.0c12.3456

0000.0c12.11110000.1018.321a

FrameTo: FFFF.FFFF.FFFF

Flow Control Mechanism on Ethernet

•CSMA/CD is the mechanism that regulates the segment•Each station listens for other traffic before they transmit

PacketFrame

Ethernet Collisions• Sometimes

stations transmit simultaneously

• Two frames on the same segment collide

• Collisions require each station to wait and resend

Collision!

PacketFrame PacketFrame

Packet

PacketFrameFrame

Ethernet Reliability

B C DA

B C DAFigure 1

Figure 2

Collision


Collision

C

B C DA

BA D

JAMJAMJAMJAMJAM JAM


B C DA

CollisionB C DA

JAMJAMJAMJAMJAM JAM

• Carrier sense multiple access with collision detection (CSMA/CD)

CSMA/CD

• CSMA/CD stands for Carrier Sense Multiple Access / Collision Detect.

• It is used by all NICs in Ethernet Networking

• In this method all NICs first sense whether the cable is free or not.

• If it is free the request is sent otherwise it waits.

Half Duplex Ethernet

• It is defined in 802.3 Ethernet specifications• It uses only one wire pair for signals running in both direction.• CSMA/CD is used to prevent collision.•Half Duplex typically 10base T is 50-60 % efficient. (Depends on network size)• In a large 10 base T network you only get 3 to 4 MBPS at most.

Full Duplex

• Full Duplex Ethernet uses two pairs of wires.• It uses Point-to-Point connection• There is no collision in Full Duplex• Full Duplex is suppose to offer 100% efficiency in both direction•Means you can get 20 MBPS in 10 MBPS or 200 MBPS in Fast Ethernet running Full Duplex.

Auto Detect Mechanism

•When a Full Duplex port is powered on, it first checks with remote end and decides whether it can run on 10 or 100 MBPS.

• Then it checks to see whether it can run Full duplex or half duplex.

• This is called Auto Detect Mechanism.

Ethernet Addressing

• Ethernet Addressing uses MAC Address• MAC addresses are burned on every

NIC• It is a 48-bit address• It is written in the same format even if

different LAN Technologies are used.

OrganizationallyUnique Identifier (OUI)(Assigned by IEEE)

Vender Assigned

24 bits 24 bits

Ethernet Addressing using MAC Addresses

Ethernet and IEEE 802.3

• Benefits and background• Ethernet is the most popular physical layer LAN

technology because it strikes a good balance between speed, cost, and ease of installation

• Supports virtually all network protocols• Xerox initiated, then joined by DEC & Intel in

1980 • Revisions of Ethernet specification

• Fast Ethernet (IEEE 802.3u) raises speed from 10 Mbps to 100 Mbps

• Gigabit Ethernet is an extension of IEEE 802.3 which increases speeds to 1000 Mbps, or 1 Gbps

• Ethernet and IEEE 802.3

• Several framing variations exist for this common LAN technology

Ethernet Frames

• Frames are used at the Data Link Layer to encapsulate packets coming down for transmission on a type of Media Access• Types of Media Access• Contention (Ethernet)• Token Passing (Token Ring or FDDI)

We will be covering only “Contention”, as rest all are beyond the scope of our course.

DataSource add FCSLengthDest add

Variable266 4

0000.0C xx.xxxx

Vendor assigned

IEEE assigned

MAC Layer - 802.3

MAC SUB-LAYER

Preamble

Ethernet II uses “Type” here and does not use 802.2.

MAC Address

8# Bytes

Ethernet Local Area Network

• Ethernet was first created and implemented by a group called DIX (Digital, Intel and Xerox).• The first Ethernet specification was modified

by IEEE and IEEE 802.3 was created.• This was a 10Mbps network running on co-

axial, twisted pair and fiber physical media.• IEEE 802.3 was further modified by IEEE only

and 802.3u (Fast Ethernet) and 802.3z (Gigabit Ethernet) was created.• 802.3u and 802.3z are specified only on

twisted pair and fiber physical media.

QSpiders - Dod Model

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