8x+2y...

just for completeness and so i don't appear completely invested in the method i developed to understand dscp and the corresponding af decimal values (even though i am)

here it is...


af31

8 x 3 + 2 x 1 = 26

af22

8 x 2 + 2 x 2 = 20

simply multiply the first af digit by 8 and add the second digit multiplied by 2...

or my way...

cs 0                                   0

cs1                                    8
  af11                                10
  af12                                12
  af13                                14
    
   

cs2                                    16

  af21                                18
  af22                                20
  af23                                22

so what's the decimal value of cs3? right...

my way is better... based on the cs values you can map the whole thing out on paper in 30 seconds...

dscp school...

i posted this to the ccie r&s forum on cln in response to a post where someone was having difficulty understanding dscp... i'm hoping someone attempts to refute it...

no takers yet...

here is a copy of the text larger... i wrote that in a couple of minutes from off the top of my head in the forum... this is the way dscp should be taught...


here is a chart that helped me make sense of it... the key is the class selector... the ip precedence simply follows the class selector, in other words it's the same for each cs... there are three af values per class selector... the classes are 0 to 7 or 8 total... class zero is zero, class 1 is decimal 8 and each selector increments by 8 there after... so 8x5 is 40 or class selector 5, whose decimal value is 40... the binary values simply follow the decimal values...  for each af value within each class selector the af values increment by 2 until they reach the next class selector... so class selector 2 = 16 and it's first af value is 18... the afs' themselves are described 1, 2 and 3for each class selector, so for class selector 2, they are 21 22 and 23, class selector 4 is 41, 42 and 43... see the chart below... ef breaks the pattern with a value of 46, but that's phone and you just remember that one...  6 and 7 are easy, just multiply by 8...

dscp...

because a good table is hard to find...




you don't even have to memorize the table...

the class selector starts at 0 and thereafter it's decimal value increments by 8...
the binary value equals the decimal value, duh...

each corresponding class selector has 3 af's whose first number is the class selector and whose second number increments by 1...

0

8            cs1
    10      af11
    12
    14      af13
16          cs2
     18
     20
     22      af23

ip precedence equals the class selector and is maintained with the af...

8X5 is 40 = cs5

ef is easy because it breaks the pattern

child's play... just ask chucky...

i love what he's done with his hair...

gns3 is way better than xbox... my routes can kick your routes' ass...

dscp/ip precedence...

even easier still... thanks to this guy   http://www.dasblinkenlichten.com/?p=376

just great... ordered so well.... barely have to remember afxy(8x + 2y)

the class selector and the ip precedence follow each other... binary and decimal at cs1 (8) always increment by two, until voice... sheer genius...

thank you dasblinkerlicker... he did what i was shooting for yesterday...

3 QoS models...

best effort delivery
   (BE) what it says, no guarantees, all traffic treated equally, the lack of QoS

integrated services
   (IntServ) rfc 1633, end-to-end QoS for real-time applications such as voice and     video; explicit management of network resources for specific user packet streams

differentiated services
   (DiffServ) unlike IntServ, no advance reservations required. preferred

see below for ToS evolution (this is a great intro which quickly goes deep; take human bites)

 http://fengnet.com/book/ios_mpls/ch13lev1sec1.html

Figure 13-1 shows the IPv4 packet header with an 8-bit type of service (ToS) field. The ToS field was conventionally used to provide QoS in IP networks. However, since the advent of the Diff-Serv model, it has been replaced by the implementation of IP Precedence or DSCP values.

Figure 13-1. IP Packet Header

The higher order 3 bits in the TOS field, shown in Figure 13-1, map to the IP Precedence value assigned to the IP packet. The predefined values used to identify the IP Precedence are shown in Table 13-1.

Table 13-1. IP Precedence Values

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

dscp...

otherwise known as diffserv

this was originally the type of service (ToS) field in an ipv4/ipv6 header, redefined by  http://www.rfc-editor.org/rfc/rfc2474.txt for differentiated services... real time data streaming technologies have emerged like voice over ip that make use of this field...

diffserv or differentiated services code point should not be confused with mpls (more on that later)... it is used to carry information about ip packet service requirements and operates only at layer 3

traffic is treated by intermediate systems based on priorities of the type of service