Quality of Service
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Instruction Manual - NXA-ENET8-POE+
Creating QoS Policies
Use the Traffic > DiffServ (Configure Policy) page to create a policy map that can be attached to multiple interfaces. A policy map is
used to group one or more class map statements (page 125). A policy map can then be bound by a service policy to one or more
interfaces (page 130).
Configuring QoS policies requires several steps. A class map must first be configured which indicates how to match the inbound
packets according to an access list, a DSCP or IP Precedence value, or a member of a specific VLAN. A policy map is then
configured which indicates the boundary parameters used for monitoring inbound traffic. A policy map may contain one or more
classes based on previously defined class maps.
The class of service or per-hop behavior (i.e., the priority used for internal queue processing) can be assigned to matching packets.
Meter Mode
- Defines the committed information rate (maximum throughput).
Policing is based on a token bucket, where bucket depth is the maximum burst before the bucket overflows, and the average
rate tokens that are added to the bucket is by specified by the committed-rate option. Note that the token bucket functions
similar to that described in RFC 2697 and RFC 2698.
The behavior of the meter is specified in terms of its mode and two token buckets, C and E, which both share the common
rate CIR. The maximum size of the token bucket C is BC and the maximum size of the token bucket E is BE.
The token buckets C and E are initially full, that is, the token count Tc(0) = BC and the token count Te(0) = BE. Thereafter,
the token counts Tc and Te are updated CIR times per second as follows:
If Tc is less than BC, Tc is incremented by one, else
if Te is less then BE, Te is incremented by one, else
neither Tc nor Te is incremented.
When a packet of size B bytes arrives at time t, the following happens if srTCM is configured to operate in Color-Blind
mode:
If Tc(t)-B 0, the packet is green and Tc is decremented by B down to the minimum value of 0, else
if Te(t)-B 0, the packets is yellow and Te is decremented by B down to the minimum value of 0,
else the packet is red and neither Tc nor Te is decremented.
When a packet of size B bytes arrives at time t, the following happens if srTCM is configured to operate in Color-Aware
mode:
If the packet has been precolored as green and Tc(t)-B 0, the packet is green and Tc is decremented by B down to the
minimum value of 0, else
If the packet has been precolored as yellow or green and if Te(t)-B 0, the packets is yellow and Te is decremented by B
down to the minimum value of 0, else
the packet is red and neither Tc nor Te is decremented.
The following table lists the options on this page:
Traffic - Diffserv Options
Add
Policy Name
Name of policy map. (Range: 1-32 characters)
Description
A brief description of a policy map. (Range: 1-64 characters)
Add Rule
Policy Name
Name of policy map.
Class Name
Name of a class map that defines a traffic classification upon which a policy can act. A policy map
can contain up to 32 class maps.
Action
This attribute is used to set an internal QoS value in hardware for matching packets. The PHB label
is composed of five bits, three bits for per-hop behavior, and two bits for the color scheme used to
control queue congestion with the srTCM and trTCM metering functions.
• Set CoS - Configures the service provided to ingress traffic by setting an internal CoS value for a
matching packet (as specified in rule settings for a class map. (Range: 0-7)
See the Default Mapping of CoS/CFI to Internal PHB/Drop Precedence table on page 124.
• Set PHB - Configures the service provided to ingress traffic by setting the internal per-hop
behavior for a matching packet (as specified in rule settings for a class map. (Range: 0-7)
See the Default Mapping of DSCP Values to Internal PHB/Drop Values table on page 122.
• Set IP DSCP - Configures the service provided to ingress traffic by setting an IP DSCP value for
a matching packet (as specified in rule settings for a class map). (Range: 0-63)
Meter
Check this to define the maximum throughput.
• Meter Mode (Rate) - Defines the committed information rate. Policing is based on a token
bucket, where the average rate tokens that are removed from the bucket is specified by the Rate
option. The committed rate is in kilobits per second. (Range: 16-1000000 kbps at a granularity
of 64 kbps or maximum port speed, whichever is lower)