Foundation Summary

Other Functions

Fields That Can

Besides Class and

Be Examined for

Fields That Can

Tool

Mark

Classification

Be Marked*

Policy-based routing

Routing packets based on

ACLs indirectly through

IP ToS field

(PBR)

something besides desti-

route maps

IP Precedence field

nation address

QoS Group

Committed access

Policing

IP ACLs

IP Precedence

rate (CAR)

QoS Group

IP DSCP

IP DSCP

QoS Group

MPLS Experimental

Class-based marking

None

IP ACLs

IP precedence

(CB marking)

Any markable fields

DSCP

Input interface

802.1P CoS

MAC addresses

ISL Priority

All NBAR-enabled fields

ATM CLP

Frame Relay DE

MPLS Experimental

QoS Group

Network based appli-

Statistical information

Extensive list (see Chapter

None; used in con-

cation recognition

about traffic mix; recog-

3, “Classification and

junction with CB

(NBAR)

nition of applications that

Marking”)

marking

use the dynamic port

VoIP dial peers

Call routing for VoIP

None

IP Precedence

Maximum

Queue Service

Number of

Classification

Algorithm/End

Tool

Queues

Capabilities

Result of Algorithm

Priority Queuing

4

IP ACL*

Strict service; always serves

(PQ)

Input interface

higher-priority queue over lower

queue.

Fragments

Custom Queuing

16

IP ACL*

Serves a configured number of

(CQ)

Input interface

bytes per queue, per round-robin

pass through the queues. Result:

Fragments

Rough percentage of the

bandwidth given to each queue

under load.

Weighted Fair

4096

Automatic, based on

Each flow uses a different queue.

Queuing (WFQ)

flows. (Flow identified

Queues with lower volume and

by source/destination

higher IP precedence get more

address and port

service; high volume, low prece-

numbers, plus protocol

dence flows get less service.

type.)

Class-Based

64

IP ACL*

Service algorithm not published;

Weighted Fair

NBAR

results in set percentage band-

Queuing (CBWFQ)

width for each queue under load.

Same as CB marking

Low Latency

N/A

Same as CBWFQ

LLQ is a variant of CBWFQ,

Queuing

which makes some queues

“priority” queues, always getting

served next if a packet is waiting

in that queue. It also polices

traffic.

IP RTP Priority

N/A

Even UDP ports between

An added feature with WFQ or

16384 and 32767 (all

CBWFQ, all VoIP payload is

VoIP payload ports)

placed in a special “priority”

queue, always getting served next

if a packet is waiting in that

queue.

Modified Deficit

8

IP precedence

Similar to CQ, but each queue

Round-Robin

gets an exact percentage of

(MDRR)

bandwidth. Supports LLQ

mechanism as well.

Tool

CAC Type

CAC Decision Is Based on Whether . . .

Physical DS0 limitation

Local

A DS0 channel is available on a trunk

Max-connections

Local

A configured number of maximum connections on the

dial peer used for the call has been exceeded

Voice-bandwidth for Frame

Local

VoFR PVC CIR has been exceeded; VoFR only (not

Relay

VoIP)

Trunk conditioning

Local

Keepalives sent to other end of network keep working or

not; used for “connection trunk” calls only*

Local Voice Busy-Out

Local

One or more local interfaces fail; if they all fail, no IP

(LVBO)

connectivity would exist, so the trunk is placed in busy-

out state

Advanced Busy-Out

Measurement

Probe measurements are better than a configured

Monitor (AVBO)

based

“impairment factor”; if value is higher, the entire trunk

is placed in busy-out

PSTN Fallback

Measurement

Probe measurements are better than a configured

based

“impairment factor”; instead of busying-out the trunk,

calls are allowed or rejected on a call-by-call basis

Resource Availability

Resource

Terminating gateway’s calculation of available DSPs

Indicator (RAI)

based

and DS0s implies it has adequate number of resources or

not

Gatekeeper Zone Band-

Resource

Gatekeeper believes that the bandwidth into the zones in

width (GK Zone

based

question has been oversubscribed or not

Bandwidth)

Resource Reservation

Resource

The RSVP reservation request flow can, both at call

Protocol (RSVP)

based

setup and ongoing throughout the call, reserve the

needed bandwidth on all RSVP-supporting links in the

IP network

Feature

Comments

Flow

A flow is a unidirectional set of packets, sent from one source IP address

and port, to one destination IP address and port, using the same transport

layer protocol.

Flow-based QoS tools

Flow-based tools automatically recognize flows without explicit classifica-

tion configuration. Each flow can be treated differently, providing a great

amount of granularity for QoS.

Class-based QoS tools

Class-based tools treat packets differently based on the category or class to

which they belong. The number of classes chosen in a typical network is

small (typically fewer than 10). Network engineers choose which types of

packets are placed into each class, so class-based QoS tools require explicit

configuration of classification parameters.

QoS tools that are

Some QoS tools operate on all traffic entering or exiting an interface. Other

neither flow or class

tools may work on a predetermined type of traffic. For example, com-

based

pressed RTP only operates on packets with RTP headers. Therefore, some

tools do not need to consider flows or explicitly defined classes.

QoS class planning—

For a single enterprise network, a considered, thorough analysis of the

enterprise

network can yield a relatively small set of useful QoS packet categories.

Agreement to these categories should occur before beginning the classifica-

tion and marking strategy of marking near the edge.

Classification and

Packets should be classified and marked near the edge of the network, as

marking

packets enter the network. By doing so, classification configuration on the

remaining routers in the packets’ path is simplified, reducing processing

overhead, complexity, the risk of misconfiguration.

QoS class planning—

For the Internet, anything more than a handful of general class conventions

Internet

is unlikely to be agreed upon by a large number of ISPs and customers.

Cisco suggests a short list with five categories: VoIP payload, video

payload, voice/video signaling, important data, and not-so-important

important data.

Internet reclassification

Between different autonomous systems, reclassification and re-marking

and re-marking

may need to occur. If the autonomous systems distrust each other, packets

must be matched based on the contents of the various fields in their

headers. If the autonomous systems trust each other, and agree on what

packets belong to each of the traffic classes, all that may be required is to

reclassify and re-mark based on the marked field inside the IP header.

Term

Definition

DS field

The IPv4 header ToS octet or the IPv6 traffic class octet when interpreted

in conformance with the definition given in [DSFIELD]. The bits of the

DSCP field encode the DS code point, whereas the remaining bits are

currently unused.

Dropper

A device that performs dropping.

Marker

A device that performs marking.

Meter

A device that performs metering.

MF classifier

A multifield (MF) classifier that selects packets based on the content of

some arbitrary number of header fields; typically some combination of

source address, destination address, DS field, protocol ID, source port and

destination port.

Per-hop behavior (PHB)

The externally observable forwarding behavior applied at a DS-compliant

node to a DS BA.

Policing

The process of discarding packets (by a dropper) within a traffic stream in

accordance with the state of a corresponding meter enforcing a traffic

profile.

Re-mark

To change the DS code point of a packet, usually performed by a marker in

accordance with a TCA.

Shaper

A device that performs shaping.

Traffic conditioner

An entity that performs traffic-conditioning functions and which may

contain meters, markers, droppers, and shapers. Traffic conditioners are

typically deployed in DS boundary nodes only. A traffic conditioner may

re-mark a traffic stream or may discard or shape packets to alter the

temporal characteristics of the stream and bring it into compliance with a

traffic profile.

Low Drop Probability

Medium Drop

High Drop Probability

Within Class

Probability Within Class

Within Class

Name/Decimal/Binary

Name/Decimal/Binary

Name/Decimal/Binary

Class 1

AF11 / 10 / 001010

AF12 / 12 / 001100

AF13 / 14 / 001110

Class 2

AF21 / 18 / 010010

AF22 / 20 / 010100

AF23 / 22 / 010110

Class 3

AF31 / 26 / 011010

AF32 / 28 / 011100

AF33 / 30 / 011110

Class 4

AF41 / 34 / 100010

AF42 / 36 / 100100

AF43 / 38 / 100110

PHB

Key Components

Names of DSCPs

Best effort (BE)

PHB for getting no specific QoS treatment

DSCP BE (default)

Class selector

Uses 8 DSCPs, all with binary 0s for the last 3 bits.

CS1, CS2, CS3, CS4, CS5,

(CS)

Used for backward compatibility with IP precedence.

CS6, CS7

Uses “bigger-is-better” logic—the bigger the DSCP,

the better the QoS treatment.

Assured

PHB consists of 2 components: queuing to provide a

AF11, AF12, AF13, AF21,

forwarding (AF)

minimum bandwidth to each for 4 different queues,

AF22, AF23, AF31, AF32,

and 3 drop thresholds inside each queue. DSCPs do

AF33, AF41, AF42, AF43

not always follow the “bigger-is-better” logic.

Expedited

PHB also has 2 components: queuing to provide low

EF

forwarding (EF)

delay/jitter/loss and a guaranteed amount of band-

width, and policing to prevent EF from preventing

other types of traffic from getting enough bandwidth.

Traffic Conditioner

Explanation

Metering

The metering function measures the traffic rate to determine whether the

traffic conforms to the stated contract, or exceeds the traffic contract.

Metering typically occurs per class.

Dropping (policing)

If the traffic exceeds the contract, one option is to drop some packets, so

that the packets that are allowed through meet the contract. Most

implementations for this feature are called policing.

Shaping

If the traffic exceeds the contract, one option is to shape the traffic.

Shaping just means to buffer or queue the traffic, slowing it down, so

that the resulting sending rate is within the contract.

Marking

A third option for traffic that exceeds the contract is to re-mark the

DSCP with a different value. For instance, Platinum AF41 (low drop

probability) traffic that exceeds the contract might get re-marked to

AF43. In such a case, if congestion were to occur, this packet would

more likely be dropped than if not re-marked.

Do nothing

Not actually written down in the RFCs; one option is to allow the traffic

to keep moving right along.

Hannah

Server 1

FA0

R1

s0

s0

R2

s1

T1

s0

R3

SW1

SW2

Request 30 kbps,

Request 30 kbps,

Request 30 kbps,

Request 30 kbps,

Low Delay

Low Delay

Low Delay

Low Delay

Reserve 30 kbps,

Reserve 30 kbps,

Reserve 30 kbps,

Reserve 30 kbps,

Low Delay

Low Delay

Low Delay

Low Delay