home 
wiki
wiki
Spelling: QualityOfService
Quality Of Service or QoS [1] (colloquial/everyday use). used to
regulate traffic over ATM network devices, over Ethernet networks,
using QoS [2] Protocols and/or the IEEE 802.1P standard.
* Introduction [3]
* Implementation [4]
* Protocols [5]
* Hardware [6]
* Wireless [7]
-------------------------
INTRODUCTION
Standard Internet [8] Protocol (IP)-based networks provide "best
effort" data delivery by default. Best-effort IP allows the complexity
to stay in the end-hosts, so the network can remain relatively simple.
This scales well, as evidenced by the ability of the Internet [9] to
support its phenomenal growth. As more hosts are connected, network
service demands eventually exceed capacity, but service is not denied.
Instead it degrades gracefully. Although the resulting variability in
delivery delays (jitter) and packet loss do not adversely affect
typical Internet applications--email, file transfer and Web
applications- other applications cannot adapt to inconsistent service
levels. Delivery delays cause problems for applications with real-time
requirements, such as those that deliver multimedia, the most
demanding of which are two-way applications like telephony.
Let's say a client on the network is experiencing poor audio quality
with IP telephony. If there isn't enough raw capacity, you could just
throw bandwidth at the problem. But many problems are more complex.
For example, acceptable IP telephony requires a maximum 300-ms
end-to-end delay. If you have seven 50-ms router hops from origin to
destination, all the bandwidth in the world won't make the packets
travel faster.
In order to deliver QoS [10], you'll need to remove some hops, make
the routers handle all packets faster or give those telephony packets
some form of priority that gets them through the system faster.
So in an effort to 'deliver' a certain standard of availability,
there are specific protocols that can be used to restrict traffic flow
or give specific network protocols priority over other traffic.
-------------------------
IMPLEMENTATION
The primary selection criteria for a good network is available
bandwidth. Bandwidth, of course, is measured in how many bits per
second (usually measured in Mbits) are available for a connection.
Quality of Service is implemented in order to sustain the performance
of the network.
Performance is typically measured in metrics like maximum end-to-end
response time (how long it takes a packet to go from node A through
all the switches, routers, firewalls and cables to node B); allowable
packet-loss rate (how many packets can be dropped before the
connection is deemed unacceptable), and jitter (variance in packet
delivery delays). Once those QoS [11] criteria are defined, then you
can go to work to meet those needs.
QoS [12] does not create bandwidth, but manages it so it is used more
effectively to meet the wide range or application requirements. The
goal of QoS [13] is to provide some level of predictability and
control beyond the current IP "best-effort" service.
The prospect of such a potentially drastic change makes many of the
Internet's architects very nervous. To avoid these potential problems
as QoS [14] protocols are applied to the Net, the end-to-end principle
is still the primary focus of QoS [15] architects. As a result, the
fundamental principle of "Leave complexity at the `edges' and keep the
network `core' simple" is a central theme among QoS [16] architecture
designs. This is not as much a focus for individual QoS [17]
protocols, but in how they are used together to enable end-to-end QoS
[18].
-------------------------
PROTOCOLS
Applications, network topology and policy dictate which type of QoS
[19] is most appropriate for individual 'flows' or aggregates. To
accommodate the need for these different types of QoS [20], there are
a number of different QoS [21] protocols and algorithms. such as:
* Resource Reservation Protocol [22] (RSVP [23]) : Provides the
signaling to enable network resource reservation (otherwise known as
Integrated Services). Although typically used on a per-flow basis,
RSVP is also used to reserve resources for aggregates.
* Differentiated Services [24] (DiffServ) : Provides a coarse and
simple way to categorize and prioritize network traffic (flow)
aggregates.
* Multi Protocol Labeling Switching [25] (MPLS) : Provides bandwidth
management for aggregates via network routing control according to
labels in (encapsulating) packet headers.
* Subnet Bandwidth Management [26] (SBM) : Enables categorization
and prioritization at Layer 2 (the data-link layer in the OSI model)
on shared and switched IEEE 802 networks.
* 802.11e [27]
* 802.15.3 [28]
-------------------------
HARDWARE
ATM [29], commonly used in wide-area networks and enterprise
backbones, but too expensive and complicated for most LANs, has
outstanding built-in QoS [30] features, but some of these features are
not used extensively, only as required.
To implement QoS [31] over Ethernet, you need an additional protocol
called Resource Reservation Protocol [32] (RSVP). Although RSVP
doesn't offer all the QoS [33] features of ATM, it does help reserve
bandwidth to support real-time jitter-intolerant applications. The
challenge is that RSVP is still new, and many devices and applications
don't know how to use it yet.
-------------------------
WIRELESS
Wireless networks, with a good response time, unreliable bandwidth,
and unreliable latency and unreliable packet-loss prevention have a
lower standard of QoS [34] goals in comparison to ATM or ethernet.
Goals to provide an acceptable jitter and routing response over
PointToMultiPoint [35] access.
Links:
------
[1] http://melbournewireless.org.au/?QoS
[2] http://melbournewireless.org.au/?QoS
[3] http://melbournewireless.org.au/#introduction
[4] http://melbournewireless.org.au/#implementation
[5] http://melbournewireless.org.au/#protocols
[6] http://melbournewireless.org.au/#hardware
[7] http://melbournewireless.org.au/#wireless
[8] http://melbournewireless.org.au/?Internet
[9] http://melbournewireless.org.au/?Internet
[10] http://melbournewireless.org.au/?QoS
[11] http://melbournewireless.org.au/?QoS
[12] http://melbournewireless.org.au/?QoS
[13] http://melbournewireless.org.au/?QoS
[14] http://melbournewireless.org.au/?QoS
[15] http://melbournewireless.org.au/?QoS
[16] http://melbournewireless.org.au/?QoS
[17] http://melbournewireless.org.au/?QoS
[18] http://melbournewireless.org.au/?QoS
[19] http://melbournewireless.org.au/?QoS
[20] http://melbournewireless.org.au/?QoS
[21] http://melbournewireless.org.au/?QoS
[22] http://melbournewireless.org.au/?ResourceReservationProtocol
[23] http://melbournewireless.org.au/?RSVP
[24] http://melbournewireless.org.au/?DifferentiatedServices
[25] http://melbournewireless.org.au/?MultiProtocolLabelingSwitching
[26] http://melbournewireless.org.au/?SubnetBandwidthManagement
[27] http://melbournewireless.org.au/?802.11e
[28] http://melbournewireless.org.au/?802.15.3
[29] http://melbournewireless.org.au/?AsynchronousTransferMode
[30] http://melbournewireless.org.au/?QoS
[31] http://melbournewireless.org.au/?QoS
[32] http://melbournewireless.org.au/?ResourceReservationProtocol
[33] http://melbournewireless.org.au/?QoS
[34] http://melbournewireless.org.au/?QoS
[35] http://melbournewireless.org.au/?PointToMultiPoint
[EditText] [Spelling] [Current] [Raw] [Code] [Diff] [Subscribe] [VersionHistory] [Revert] [Delete] [RecentChanges]