ECE 6160: Advanced Computer Networks Gigabit Ethernet

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ECE 6160 Advanced Computer NetworksGigabit
Ethernet

• Instructor Dr. Xubin (Ben) He
• Email Hexb_at_tntech.edu
• Tel [phone]
• Course web http//www.ece.tntech.edu/hexb/616f05

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Prev

• HIPPI
• FC

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GBE borrows from FC and Ethernet

• Ethernet
• Frame format
• CSMA/CD
• Link layer technology

• FC
• Physical specifications, fibre optics
• 8b/10b data encoding
• Ordered sets for link commands and delimiters

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GBE objectives

• 1000 Mb/s MAC
• 802.3 Ethernet Frame format
• Meet all 802 requirements except possibly Hamming
  distance
• Preserve min and max frame size of 802.3
• Full and half-duplex operation
• Support star-wired topologies
• Use CSMA/CD with at least 1 repeater
• Support Fiber and, if possible, copper
• At least 500 m over multimode fiber, At least 25
  m over copper
• Þ Wiring-closet or data center backbone 100 m
  desirable
• At least 2 km on single mode fiber
• Collision domain diameter of 200 m
• Accommodate 802.3x flow control
• Cost effective

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GBE(802.3z)/Ethernet(802.3) and FC
802.2 LLC
CSMA/CD or full full duplex MAC
802.2 LLC
8b/10b
802.3 CSMA/CD
SerDes
FC-1
Connector
802.3 Physical
FC-0
Media
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GBE Layers
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MAC issue

• Carrier Extension
• Frame Bursting
• Buffered Distributor

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Carrier extension

• Slot time (or slot size)A signal propagates from
  one end to the other. Minimum time to detect a
  collision.
• Carrier Extension is a way of maintaining 802.3
  minimum and maximum frame sizes with meaningful
  cabling distances.

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Slot-Time

• The MAC Layer of Gigabit Ethernet uses the same
  CSMA/CD protocol as Ethernet. The maximum length
  of a cable segment used to connect stations is
  limited by the CSMA/CD protocol. If two stations
  simultaneously detect an idle medium and start
  transmitting, a collision occurs.
• Ethernet has a minimum frame size of 64 bytes.
• The reason for having a minimum size frame is to
  prevent a station from completing the
  transmission of a frame before the first bit has
  reached the far end of the cable, where it may
  collide with another frame. Therefore, the
  minimum time to detect a collision is the time it
  takes for the signal to propagate from one end of
  the cable to the other.
• This minimum time is called the Slot Time. ( A
  more useful metric is Slot Size, the number of
  bytes that can be transmitted in one Slot Time.
  In Ethernet, the slot size is 64 bytes, the
  minimum frame length.)

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Gigabit Ethernet Slot Time

• The maximum cable length permitted in Ethernet is
  2.5km (allowing up to 4 repeaters in a single
  network path). As the bit rate increases, the
  sender transmits the frame faster. As a result,
  if the same frames sizes and cable lengths are
  maintained, then a station may transmit a frame
  too fast and not detect a collision at the other
  end of the cable. So, one of two things has to be
  done
• Keep the maximum cable length and increase the
  slot time ( and therefore, minimum frame size) OR
• keep the slot time same and decrease the maximum
  cable length
• OR both. In Fast Ethernet, the maximum cable
  length is reduced to only 100 meters, leaving the
  minimum frame size and slot time intact.
• Gigabit Ethernet maintains the minimum and
  maximum frame sizes of Ethernet. Since, Gigabit
  Ethernet is 10 times faster than Fast Ethernet,
  to maintain the same slot size, maximum cable
  length would have to be reduced to about 10
  meters, which is not very useful. Instead,
  Gigabit Ethernet uses a bigger slot size of 512
  bytes.
• To maintain compatibility with Ethernet, the
  minimum frame size is not increased, but the
  "carrier event" is extended. If the frame is
  shorter than 512 bytes, then it is padded with
  extension symbols. These are special symbols,
  which cannot occur in the payload. This process
  is called Carrier Extension.

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Frame bursting

• Carrier Extension wastes bandwidth. Up to 448
  padding bytes may be sent for small packets. This
  results in low throughput. In fact, for a large
  number of small packets, the throughput is only
  marginally better than Fast Ethernet.
• Packet Bursting is "Carrier Extension plus a
  burst of packets". When a station has a number of
  packets to transmit, the first packet is padded
  to the slot time if necessary using carrier
  extension. Subsequent packets are transmitted
  back to back, with the minimum Inter-packet gap
  (IPG) until a burst timer (of 1500 bytes)
  expires. Packet Bursting substantially increases
  the throughput.

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Buffered distributor (Full Duplex Repeater or
Buffered Repeater)

• A Buffered Distributor is a multi-port repeater
  with full-duplex links. It provides hub
  functionality with full duplex mode of operation.
  Each port has an input FIFO queue and an output
  FIFO queue. A frame arriving to an input queue is
  forwarded to all output queues, except the one on
  the incoming port.
• It provides full duplex connectivity, just like a
  switch, yet it is not so expensive, because it is
  just an extension of a repeater.

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Full Duplex Operation

• Half Duplex Ethernet Fast Ethernets is based on
  CSMA/CD
• IEEE ratified 802.3x in 1995 Full Duplex can
  send send and receive frames simultaneously
• Requires point-to-point environment, stations
  connected to HUBS or ROUTERS will work at Half
  Duplex
• Stations connected back to back or to Layer-2
  Switches will work at Full Duplex
• Full Duplex devices are NOT interoperable with
  Half Duplex devices mismatch errors

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GMII
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Physical media

• Copper
• Unshielded Twisted Pair (UTP-5) 4-pairs
• Shielded Twisted Pair (STP)
• Fibre optics
• Multimode Fiber 50 mm and 62.5 mm
• Single-Mode Fiber 10 mm
• Bit Error Rate better than 10-12

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GBE Physical Layer
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Fast Ethernet vs. 1000base-T
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Summary

• Ethernet is running at 1000Mbps, and 10Gbps is
  available
• Is competing with ATM and FC
• Both shared and full-duplex links
• Fully compatible with current Ethernet

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VLAN Virtual LAN

• Virtual LANs (VLANs) can be viewed as a group of
  devices on different physical LAN segments which
  can communicate with each other as if they were
  all on the same physical LAN segment.
• Switches using VLANs create the same division of
  the network into separate broadcast domains but
  do not have the latency problems of a router.
• IEEE 802.1Q

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Traditional LAN routers segment the network and
provide logical structure, but are slow,
complicated and expensive.
Picture is from Intel
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Standard switches are much faster than routers
and provide dedicated bandwidth where needed, but
are vulnerable to broadcast storms.
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VLANs allow highly flexible, efficient network
segmentation, enabling users and resources to be
grouped logically, without regard to physical
location.
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Pros and Cons

• PROs
• Flexible network segmentation logical
• Simple management management console
• Increased performance limiting broadcast traffic
• Better use of server resources member of
  multiple VLANs
• Enhanced network security virtual bounderis can
  only be crossed through a router.
• CONs
• Broadcast limitations
• Device limitations
• Port constraints