cisco ccna module 6

1© 2004, Cisco Systems, Inc. All rights reserved.

Module 6Ethernet Fundamentals


www.pnj.ac.idObjectives


www.pnj.ac.idEthernet

• Ethernet is a bus network in which multiple computers share a single transmission medium. While one computer transmits a frame to another. All other computers must wait.

• Ethernet is the dominant LAN technology in the world.

• Ethernet is not one technology but a family of LAN technologies.( E- FE-GE)


www.pnj.ac.idIntroduction to Ethernet

• Most of the traffic on the Internet originates and ends with Ethernet connections.

• Competing and fighting to access the media -------Original idea for Ethernet was developed in early 1970s at the University of Hawaii .

• 1970’s Alohanet was the basis Ethernet access method known as CSMA/CD.

• DIX-1980 Robert Metcalfe+ The first LAN in the world. That is the original version of Ethernet.

• 1985—IEEE---The Institute of Electrical and Electronics Engineers published standards for LANs. These standards start with the number 802. The standard for Ethernet is 802.3. (IEEE –must be compatible to OSI model). The standard for Ethernet is 802.3.

• Essentially, Ethernet and IEEE 802.3 are the same standards ( some small modification )

• In 1995, IEEE announced a standard for a 100-Mbps Ethernet (called Fast Ethernet).

• In 1998 and 1999 standards for gigabit per second (Gbps, 1 billion bits per second)

• The bandwidth of the network could be increased many times without changing the underlying Ethernet technology


www.pnj.ac.idThe Success of Ethernet

The success of Ethernet is due to the following factors:

• Simplicity and ease of maintenance

• Ability to incorporate new technologies

• Reliability

• Low cost of installation and upgrade

Together, Ethernet and IEEE 802.3 currently maintain the greatest market share of any LAN protocol


www.pnj.ac.id

Inventor of Ethernet – Out of the Ether


www.pnj.ac.idIntroduction to Ethernet

Ethernet was originally developed to operate over radio in the Hawaiian islands


www.pnj.ac.idDefining Standard

• "The nice thing about standards is that there's so many to choose from."


www.pnj.ac.idOSI Model


www.pnj.ac.idThe Physical layer

Layer 1 involves interfacing with:

• media, signals, bit streams that travel on the media

• components that put signals on media, and various topologies.


www.pnj.ac.idData Link Layer

• Data link layer provides reliable transit of data across a physical link by using the Media Access Control (MAC) addresses.

• Data link layer is concerned with physical (as opposed to network, or logical) addressing.


www.pnj.ac.idData link layer– Two Parts (sub-layers)

Logical link Control (LLC) : (IEEE 802.2)

• The Logical Link Control (LLC) sublayer remains relatively independent of the physical equipment

• Provides an interface between the MAC layer and the Network layer which is independent of the hardware

Media Access Control (MAC): (part of IEEE 802.3)

• The MAC sub-layer is concerned with the physical components that will be used to communicate the information..

• WHO can access the network when multiple computers are trying to access it simultaneously.

• physical addressing (MAC addresses) and access control methods.


www.pnj.ac.idEthernet and the OSI Model

• Ethernet operates in two areas of the OSI model, the lower half of the data link layer, known as the MAC sub layer and the physical layer

• Trick question


www.pnj.ac.idIEEE Ethernet Standards

IEEE 802 Committee Standards:

• 802.1 - Standards introduction

• 802.2 - Logical Link Control (LLC)to prevent senders from overwhelming receivers (ACK)

• 802.3 – EthernetCSMA/CD, multiple media access methods, and packet (frame) format.

• 802.4 - Token Bus - 75 ohm CATV coax or Fibre

• 802.5 - Token Ring - physical standard and media access sublayer

• 802.6 - MAN (Metropolitan Area Network) - similar to FDDI

• 802.7 - Broadband

• 802.8 - Fiber Optics

• 802.9 - Integrated Voice and Data

• 802.10 - LAN Security

• 802.11 - Wireless

• 802.12 -100 VG AnyLAN


www.pnj.ac.idNaming – The MAC or Hardware Address

• A 48-bit address burned onto the NIC.

• It is a unique way of identifying each computer on a network.

• Flat Address

All devices that are connected to the Ethernet LAN have MAC addressed interfaces including workstations, printers, routers, and switches.


www.pnj.ac.idNaming – MAC Address Format

The MAC address consists of 12 hex digits (48 bits)

The first six digits (assigned by the IEEE) represent the Organizational Unique Identifier (OUI) which identifies the manufacturer

The last six are assigned by the manufacturer and represent a unique hardware ID number for the NIC


www.pnj.ac.idFraming

• Framing is the Layer 2 encapsulation process.

• Bit streams (data) 010101 alone can not be sent between devices.

• We must divide the data up and add:

a bit pattern to flag the start of each frame

relevant MAC addresses

a block of data

some bits for error detection

a bit pattern to flag the end of the frame

• A frame is the Layer 2 protocol data unit (PDU).


www.pnj.ac.idLayer 2 Framing


www.pnj.ac.idEthernet Frame Structures


www.pnj.ac.idEthernet Frame Structure


www.pnj.ac.idIEEE 802.3 Frame Structure


www.pnj.ac.idIEEE 802.3 Preamble (Start Frame Field)


www.pnj.ac.idEthernet - IEEE802.3 Frame Field Comparison


www.pnj.ac.id Layer 2 Technologies

• Token Ring - logical ring topology (in other words, information flow is controlled in a ring) and a physical star topology (in other words, it is wired as a star)

• FDDI - logical ring topology (information flow is controlled in a ring) and physical dual ring topology (wired as a dual ring)

• Ethernet - logical bus topology (information flow is on a linear bus) and physical star or extended star (wired as a star)


www.pnj.ac.idMedia Access Control (MAC)

• MAC refers to Protocols that determine which computer on a shared-medium environment, or collision domain, is allowed to transmit the data.

• MAC, with LLC, comprises the IEEE version of the OSI Layer 2.

• There are two broad categories of Media Access Control

1. Deterministic

taking turns

2. Non-deterministic

first come, first served).


www.pnj.ac.idEthernet

•Ethernet performs three functions:

• Transmitting and receiving data packets

• Decoding data packets and checking them for valid MAC addresses before passing them to the upper layers of the OSI model

• detecting errors within data packets or on the network

In the CSMA/CD access method, networking devices with data to transmit over the networking media work in a listen-before-transmit mode.


www.pnj.ac.idMAC Rules and Collision Detection/Backoff


www.pnj.ac.id

CSMA/CDNon-Deterministic

1. Listen then transmit

1 2

3 4

2. Collision occurs

3. Broadcast jam signal

4. Devices back off appropriate amount of time, goes back to listen then transmit and then retransmit

Ethernet is a broadcast transmission medium. This means that all devices on a network can see all data that passes along the networking media.

When a device has verified the destination MAC address carried by the data, it then checks the data packet for transmission errors. If the device detects errors, the data packet is discarded.

The destination device will not notify the source device, regardless of whether the packet arrived successfully.

Ethernet is a connectionless network architecture and is referred to as a best-effort delivery system.


www.pnj.ac.idEthernet Timing


www.pnj.ac.idInterframe Spacing and Backoff


www.pnj.ac.idEthernet Timing

• Slot time – the longest time taken to do a round trip of the largest legal network

– 512 Bits = 64 Bytes

• Interframe spacing

– 96 bit times for 10, 100, 1000 Mbps networks


www.pnj.ac.idError Handling


www.pnj.ac.idTypes of Collisions

• What is a Runt frame ?


www.pnj.ac.idAnswer

• Any frame which is received and which is less than 64 bytes is illegal, and is called a "runt".

(14 bytes + 46+ 4)

• A receiver must discard all runt frames


www.pnj.ac.idTypes of Collisions


www.pnj.ac.idEthernet Errors


www.pnj.ac.idFCS Errors


www.pnj.ac.idTransmission Errors

Collision or runt – Simultaneous transmission occurring before slot time has elapsed

Late collision – Simultaneous transmission occurring after slot time (512 bits = 64 Bytes)has elapsed

Jabber, long frame and range errors – Excessively or illegally long transmission (jabber 20000-50000 octets)

Short frame, collision fragment or runt – Illegally short transmission

FCS error – Corrupted transmission


www.pnj.ac.idEthernet Auto-Negotiation

• NLP – Network Link Pulses (10 Mbps)Pulses sent by NIC every 16 ms

Convey information about the capabilities of the card or device

• FLP (100Mbps-1000Mbps)Mandatory

Made up of NLPs so 10 Mbps cards can exist with 100 and 1000 Mbps


www.pnj.ac.idTransmission Priority Rank


www.pnj.ac.idIEEE Ethernet Naming Rules


www.pnj.ac.idWhy was Ethernet Successful

• Ethernet has been the most successful LAN technology largely because of its simplicity of implementation compared to other technologies.

• Ethernet has also been successful because it has been a flexible technology that has evolved to meet changing needs and media capabilities

cisco ccna module 6

Technology