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CS 6250 – Class 7 – 9.10.2002 Ethernet (IEEE 802.3) News Get project description Form groups (no later than today!) Design report is due on Oct 1 We will be discussing the project in each class (ask many questions!) Homework #3: chapter-2: 18, 25, 29 Ethernet evolution

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Cs 6250 class 7 9 10 2002 l.jpg

CS 6250 – Class 7 – 9.10.2002

Ethernet (IEEE 802.3)


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News

  • Get project description

  • Form groups (no later than today!)

  • Design report is due on Oct 1

  • We will be discussing the project in each class (ask many questions!)

  • Homework #3: chapter-2: 18, 25, 29


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Ethernet evolution

  • Developed in mid-70s at XEROX PARC

  • Standardized by IEEE (802.3 10Base2/5/T standards)

  • Initially, a multiple-access shared-bus local area network technology running at 10Mbps

  • Well known for its “Carrier Sense Multiple Access with Collission Detect” (CSMA-CD) algorithm

  • Recent extensions to 100Mbps (“Fast Ethernet” 100BaseT/F), 1Gbps (“Gig-E” 1000BaseSX/LX/CX/T), and 10Gbps (“10Gig-E”)

    • Normally used as a framing protocol for full-duplex point-to-point links, and as L2 protocol in switched networks

    • Rest of this class focuses on 10Mbps Ethernet (and 802.3 standard)


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Physical properties


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Segments and repeaters

  • No more than 4 repeaters between two hosts

  • Maximum distance from host to host: 2500m

  • Maximum round-trip delay in 10Base5 Ethernet network: 51.2 microseconds

  • Up to 1024 hosts in network

Repeater

Host


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Collision domain

  • Ethernet hubs vs Ethernet switches

  • The concept of a “collision domain”

  • Only one host can transmit a frame at a time in the entire Ethernet collision domain

  • Half-duplex vs full-duplex Ethernet networks


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Ethernet frame format

  • Preample + 14B header + CRC (Manchester encoding)

  • Max frame-body size: 1500B

  • Min frame-body size: 46B

  • Header field for frame size?

    • IEEE 802.3 standard: replaces Type with Size

  • Ethernet address format: 8:0:2b:e4:b1:2

    • Each Ethernet card has a different address (e.g., all 00-00-0C-xyz addresses are allocated to Cisco NICs)

    • Address types: unicast, multicast, broadbast

    • Promiscuous receiving mode

64

48

48

16

32

Src

Dest

Preamble

Type

Body

CRC

addr

addr


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Media Access Control (MAC) protocol

  • If line is idle, transmit frame; else wait for line to become idle

  • If transceiver detects frame collision, transmit 32b “jamming” sequence, and abort rest of frame

  • After first collision, wait for k*51.2microseconds (k=0,1,2,3 – selected randomly) before trying again

  • If line is still busy after third collision, choose randomly k between 0 and 2n-1 (n: number of collisions) and wait for k*51.2 microseconds

    • Exponential backoff

    • Adapters typically abort after 16 collisions


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Minimum frame size: 64 bytes

A

B

(a)

  • Frame size is at least 512b (14B for header, 46B for data, and 4B for CRC): Why?

  • We must guarantee that a collision will be detected while sender is still transmitting the frame

  • RTT at 2500m 10Base5 network: 51.2 microseconds (or, 512bits at 10Mbps)

  • How can you maintain the same min frame size requirement in 100Mbps Ethernet?

A

B

(b)

A

B

(c)

A

B

(d)