Add'l Reading: QoS classification and marking

Some notes that perhaps didn't get clearly stated in my first posts about marking traffic with ACLs versus using the match command. If you use an extended ACL, you get all the options that format presents for matching traffic. This includes IP traffic (Source/Destination IP address, ToS, IP precedence), ICMP, IGMP, TCP, UDP, and of course DSCP.

Using the match command allows you to directly specify the IP Precedence and DSCP fields without using an extended ACL. However, other syntax options give you the flexibility to identify traffic based on source/destination MAC address, MPLS experimental bit, CoS, input interface, RTP UDP port numbers, QoS group, NBAR protocol types, NBAR Citrix applications, and hostname/URL strings.

IP Precedence and DSCP Values
I looked back at my notes and realized I have not yet transcribed these. This table is excerpted from the Cisco QoS Exam Certification Guide. The key to remembering these is of course the binary value arrangement. If you try and use the decimal, you're missing the structure of the design!

Note that under the original IP Precedence design, larger decimal numbers got better QoS treatment. This isn't the case with DSCP values (notably EF) due to the binary value assignments. Also, below you'll see CS values- the meaning of this is "Class Selector"which is the DiffServ name for the backwards-compatible values that match up to IP Precedence.

Field & Value (Decimal)                  Binary         Name                                    
Precedence 0                                   000            Routine
Precedence 1                                   001            Priority
Precedence 2                                   010            Immediate
Precedence 3                                   011            Flash
Precedence 4                                   100            Flash Override
Precedence 5                                   101            Critical
Precedence 6                                   110            Internetwork Control
Precedence 7                                   111            Network Control

DSCP 0                                           000000      Best Effort/default
DSCP 8                                           001000      CS1          
DSCP 16                                         010000      CS2
DSCP  24                                        011000      CS3
DSCP 32                                         100000      CS4
DSCP 40                                         101000      CS5
DSCP 48                                         110000      CS6
DSCP 56                                         111000      CS7
DSCP 10                                         001010      AF11
DSCP 12                                         001100      AF12
DSCP 14                                         001110      AF13
DSCP 18                                         010010     AF21
DSCP 20                                         010100     AF22
DSCP 22                                         010110     AF23
DSCP 26                                         011010     AF31
DSCP 28                                         011100     AF32
DSCP 30                                         011110     AF33
DSCP 34                                         100010     AF41
DSCP 36                                         100100     AF42
DSCP 38                                         100110     AF43
DSCP 46                                         101110     EF

Notes from the Cisco Enterprise QoS SRND
Cisco's text excellently defines QoS as being a combination of 3 items: delay (latency), jitter (variation in the amount of latency), and packet loss. One excellent way to get a real life insight into jitter is to grab a packet capture of RTP and examine it in Wireshark (www.pcapr.net has several). Under Telephony -> RTP -> Show All Streams you will get a window with various statistics on max and mean jitter.