Ethernet Basics

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• Ethernet Basics 6

Quality of Service/Class of Service (QOS/COS)
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Quality of Service/Class of Service (QOS/COS)

• The problem- You have multiple traffic streams
  using the same ports, but some are more important
  than others
• Solution- Implement QOS/COS
• What is the difference?
• QOS- the level of guarantee that I have that a
  given packet of some importance will make it to
  the end point
• COS- The way you can classify a given traffic
  type so that QOS can take place
• There are 3 ways to provide Class of Service-
• Port based Prority (802.1p)- network centric
• TOS- A field in the IP packet header. The
  contents of this byte specify the kind of
  transmission desired, with respect to delay,
  throughput and reliability- generated by the end
  device, handled by the network

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Quality of Service/Class of Service (QOS/COS)

• Differentiated Service (DIFFSERV)- A replacement
  header field, called the DS field, is defined,
  which is intended to supersede the existing
  definitions of the IPv4 TOS octet RFC791 and
  the IPv6 Traffic Class octet IPv6. Six bits of
  the DS field are used as a codepoint (DSCP) to
  select the per-hop-behavior a packet experiences
  at each node. This is both end user and network
  based mechanism
• Ethernet Direct currently supports Port Based
  802.1p
• 802.1p is also the easiest to implement
• 802.1p has 2 classes of priority- normal and high
• 0-3 Normal
• 4-7 High

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Prioritisation (QoS)

• Original Ethernet standards
• Maximum frame size 1518 bytes
• Recent change to allow Prioritisation
• Maximum frame size 1522 bytes (increase of 4
  bytes)

64 byte - 1518 byte
TPID Tag Protocol Identifier TCI Tag Control
Information CFI Canonical Format Indicator
TPID
TCI
User Priority
Tag Protocol ID
CFI
VLAN ID
16 bit
3 bit
1 bit
12 bit
5
Prioritisation (QoS)
Email Attach

File
Priority
Voice
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Video
5
File
3
Email
0
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Thank You
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