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SonicOS Enhanced 4.0 Administrator Guide
Glossary
• 802.1p – IEEE 802.1p is a Layer 2 (MAC layer) Class of Service mechanism that tags
packets by using 3 priority bits (for a total of 8 priority levels) within the additional 16 bits of
an 802.1q header. 802.1p processing requires compatible equipment for tag generation,
recognition and processing, and should only be employed on compatible networks.
• Bandwidth Management (BWM) – Refers to any of a variety of algorithms or methods
used to shape traffic or police traffic. Shaping often refers to the management of outbound
traffic, while policing often refers to the management of inbound traffic (also known as
admission control). There are many different methods of bandwidth management, including
various queuing and discarding techniques, each with their own design strengths.
SonicWALL employs a Token Based Class Based Queuing method for inbound and
outbound BWM, as well as a discard mechanism for certain types of inbound traffic.
• Class of Service (CoS) – A designator or identifier, such as a layer 2 or layer 3 tag, that
is applied to traffic after classification. CoS information will be used by the Quality of
Service (QoS) system to differentiate between the classes of traffic on the network, and to
provide special handling (e.g. prioritized queuing, low latency, etc.) as defined by the QoS
system administrator.
• Classification – The act of identifying (or differentiating) certain types (or classes) of
traffic. Within the context of QoS, this is performed for the sake of providing customized
handling, typically prioritization or de-prioritization, based on the traffic’s sensitivity to
delay, latency, or packet loss. Classification within SonicOS Enhanced uses Access Rules,
and can occur based on any or all of the following elements: source zone, destination zone,
source address object, destination address object, service object, schedule object.
• Code Point – A value that is marked (or tagged) into the DSCP portion of an IP packet by
a host or by an intermediate network device. There are currently 64 Code Points available,
from 0 to 63, used to define the ascending prioritized class of the tagged traffic.
• Conditioning – A broad term used to describe a plurality of methods of providing Quality
of Service to network traffic, including but not limited to discarding, queuing, policing, and
shaping.
• DiffServ – Differentiated Services. A standard for differentiating between different types or
classes of traffic on an IP network for the purpose of providing tailored handling to the traffic
based on its requirements. DiffServ primarily depends upon Code Point values marked in
the ToS header of an IP packet to differentiate between different classes of traffic. DiffServ
service levels are executed on a Per Hop Basis at each router (or other DiffServ enabled
network device) through which the marked traffic passes. DiffServ Service levels currently
include at a minimum Default, Assured Forwarding, and Expedited Forwarding. Refer
to the
“DSCP Marking” section on page 473 for more information.
• Discarding – A congestion avoidance mechanism that is employed by QoS systems in an
attempt to predict when congestion might occur on a network, and to prevent the
congestion by dropping over-limit traffic. Discarding can also be thought of as a queue
management algorithm, since it attempts to avoid situations of full queues. Advanced
discard mechanisms will abide by CoS markings so as to avoid dropping sensitive traffic.
Common methods are:
–
Tail Drop – An indiscriminate method of dealing with a full queue wherein the last
packets into the queue are dropped, regardless of their CoS marking.
–
Random Early Detection (RED) – RED monitors the status of queues to try to
anticipate when a queue is about to become full. It then randomly discards packets in
a staggered fashion to help minimize the potential of Global Synchronization. Basic
implementations of RED, like Tail Drop, do not consider CoS markings.