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Ch. 12 Ethernet

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Title: Ch. 12 Ethernet


1
Ch. 12 Ethernet
  • Data Communications
  • By
  • Stallings

2
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.

3
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.

4
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.

5
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.

6
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.

7
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).

8
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.

9
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.)

10
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)

11
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.

12
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.

13
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.

14
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.

15
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).

16
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.

17
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.

18
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.

19
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.
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