Ethernet Basics – 6 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

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

Original Ethernet standards –Maximum frame size – 1518 bytes Recent change to allow Prioritisation –Maximum frame size – 1522 bytes (increase of 4 bytes) Prioritisation (QoS) PreambleSFD Destination- Address Source Address FCSData Length/ Type TPIDTCI TPID = Tag Protocol Identifier TCI = Tag Control Information CFI = Canonical Format Indicator Tag Protocol ID User Priority CFIVLAN ID 16 bit3 bit1 bit12 bit PreambleSFD Destination- Address Source Address FCSData Length/ Type TAG 64 byte byte

Prioritisation (QoS) File Video Voice + Attach Voice Video File Priority

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