Ch. 12 Ethernet

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Ch. 12 Ethernet

• Data Communications
• By
• Stallings

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12.1 Traditional Ethernet

• IEEE 802.3 Medium Access Control
• Carrier Sense Multiple Access with Collision
  Detection (CSMA/CD)
• The most commonly used medium access control
  technique for bus/tree and star topologies.
• Original baseband version was developed by Xerox
  and formed the basis IEEE 802.3 CSMA/CD standard.

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12.1 Ethernet (p.2)

• ALOHA
• Developed for packet radio networks (Abrahamson,
  1970).
• If a station has something to send, it does so.
• Then the station listens for an ACK.
• If no ACK is received, then a collision is
  assumed and the frame is retransmitted.
• Simple but maximum efficiency is only 18.

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12.1 Ethernet (p.3)

• Slotted ALOHA
• Stations always wait for the beginning of a
  slot--this reduces collisions.
• Improves the performance --37 maximum
  efficiency.

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12.1 Ethernet (p.4)

• Carrier Sense Multiple Access (CSMA)
• Suppose propagation delays are small relative to
  frame transmission times--then stations usually
  know when the line is being used.
• With CSMA, a station first listens--if the medium
  is in use it will wait.

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12.1 Ethernet (p.5)

• 1-persistent CSMA (Fig. 12.2)
• 1. If the medium is idle, transmit otherwise,
  go to step 2.
• 2. If the medium is busy, continue to listen
  until the channel is sensed idle then transmit
  immediately.
• Other Approaches
• Nonpersistent--if busy, wait a random amount of
  time.
• p-persistent--if idle, transmit with probability
  p.

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16.1 Ethernet (p.6)

• CSMA/CD (Fig. 12.3)
• 1. If the medium is idle, transmit otherwise, go
  to step 2.
• 2. If the medium is busy, continue to listen
  until the channel is idle, then transmit
  immediately.
• 3. If a collision is detected during
  transmission, transmit a brief jamming signal to
  assure that all stations know that there has been
  a collision and then cease transmission.
• 4. After transmitting the jamming signal, wait a
  random amount of time, then attempt to transmit
  again (repeat from step 1).

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16.1 Ethernet (p.7)

• How long does it take to detect a collision?
• Frames should be long enough to allow collision
  detection prior to the end of transmission
  (distance and speed are factors also.)
• How long can segments be?
• The signal is attenuated and long segments will
  cause problems in CD algorithm.
• IEEE standards recommend maximum lengths.

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12.1 Ethernet (p.8)

• IEEE 802.3 MAC Frame--Fig. 12.4
• Preamble--7-octet pattern of alternating 0s and
  1s.
• Start frame delimiter--pattern 10101011.
• Destination address--48 bit address.
• Source address--48 bit address.
• Length--length of the LCC data field--2 bytes.
• Pad--octets added to ensure that the frame is
  long enough for proper CD operation.
• Frame check sequence--32-bit cyclic redundancy
  check (does not cover preamble and SFD.)

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12.1 Ethernet (p.9)

• Three types of MAC Frames
• Basic (original Ethernet format.)
• Q-tagged framesupports 802.1 Q VLAN
• Envelope frameallows additional prefixes and
  suffixes to the data field (Provider Bridges and
  MAC SecurityIEEE 802.1 Working group) also
  ITU-T, and IETF (MPLS or multiprotocol label
  switching)

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16.1 Ethernet (p.10)

• IEEE 802.3 10-Mbps Specification (Ethernet)
• 10BROAD36rarely used today
• 10BASE5
• 10BASE2
• 10BASE-T
• 10BASE-F (3 options)
• Table 12.1 summarizes the 10Mbps alternatives.

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12.2 High Speed Ethernet

• IEEE 802.3 100-Mbps (Fast Ethernet)
• Generic designation is 100BASE-T.
• All options use IEEE 802.3 MAC protocol and frame
  format.
• 100BASE-X (TX and FX)
• Set of options that use a signal encoding scheme
  defined for FDDI--4B/5B NRZI.
• 100BASE-T4
• Uses four twisted pair lines between nodes.

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12.2 High Speed Ethernet (p.2)

• Gigabit Ethernet
• Uses the IEEE 802.3 MAC protocol and frame
  format.
• A new medium and transmission specification is
  defined.
• Fig. 12.6 illustrates a typical Gigabit Ethernet
  application.

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12.2High Speed Ethernet (p.3)

• Gigabit Ethernet--Media Access Layer (1995)
• Two enhancements for shared medium hub.
• Carrier extension--appends a set of special
  symbols to the end of short MAC frames so that
  the resulting block is as least 4096 bit-time in
  duration--this makes the transmission time longer
  than the propagation time.
• Frame bursting--allows for multiple short frames
  to be transmitted consecutively--avoids the
  overhead of carrier extension when a number of
  small frames are ready for transmission.
• The above are not needed in switching hubs.

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12.2 High Speed Ethernet (p.4)

• Gigabit Ethernet--Physical Layer
• 1000BASE-SX--supports duplex links of up to 275
  meters and 550 meters depending on multimode
  fiber diameter--wavelengths are 770 to 860 nm.
• 1000BASE-LX--supports duplex links from 550 m to
  5km depending on fiber diameter--wavelengths are
  1270 to 1355 nm.
• 1000BASE-CX--2 shielded twisted pair (25m.)
• 1000BASE-T--4 CAT 5 unshielded twisted pair
  (100m).

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12.2 High Speed Ethernet (p.5 )

• 10-Gbps Ethernet
• Satisfies increased bandwidth demand.
• Initially used for backbone connectivity.
• Provides for connectivity between ISPs and NSPs
  co-located facilities.
• Allows MANs to be constructed, and begins to
  compete with ATM.

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12.2High Speed Ethernet (p.6)

• 10-Gbps Ethernet (p.2)
• 10GBASE-S--(up to 300 meters).
• 10GBASE-L--(up to 10 kilometers)
• 10GBASE-E--(up to 40 kilometers)
• 10GBASE-LX4--(up to 10 kilometers uses WDM)
• Figure 12.7.

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12.2 High Speed Ethernet(p.7)

• 100 G bps Ethernet (fig. 12.8)
• IEEE 802.3ba standard was finalized in 2010.
• 40G bps and 10 G bps (on the edges of fig. 12.8)
• Expected to be deployed in switch uplinks inside
  the data center as well as inter-building,
  intercampus, MAN, and WAN connections.

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12.3 IEEE 802.1 Q VLAN Standard

• (2005) Defines the operation VLAN bridges and
  switches that permits the definition, operation
  and administration of VLAN topologies. (see Fig.
  12.11)
• Fig. 12.10 shows the tagged IEEE 802.3 MAC
  Frame Format.