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Transcript
Bandwidth Management and
Optimisation (BMO): Policy
development workshop
Overview of Challenges and Solutions
Objectives
- Discuss challenges and solutions to
bandwidth management and optimisation
- Compare technical and policy-based
solutions
- Determine which policy-based solution
can be used within your institution
TCP/IP reminder
• Understanding basic TCP/IP issues is important in
understanding problems of congested circuits
– IP = Internet Protocol, basic protocol on which the Internet is
built. A “connectionless” and “unreliable” protocol
– TCP = Transmission Control Protocol, adds (among other
things) “flow control” to the IP layer, a connection-oriented,
reliable-transport protocol
• As TCP segments are received so they are
acknowledged, and the sending host knows it can
send more. if a segment is not acknowledged then it
is retransmitted
• Severe congestion can lead to severe degradation in
performance and regressive deterioration of a
circuit’s performance
Traffic graphs
• Volumes of inbound and outbound traffic
• Primary tool for first-line diagnosis of
problems
• They’re an essential tool for effective
bandwidth management
• Network traffic strand of this workshop is
dealing with the practical issues of monitoring
and reporting such issues
- Symmetric circuit
- Maximum traffic load of 12.4 Mbps
- Not overloaded
- The kind of traffic patterns we might all
like to see?
- Symmetric circuit
- Maximum traffic load of 10 Mbps
- Completely saturated during office hours
Dropped packets
- Between a quarter and a third of inbound datagrams are being
dropped
- Catastrophic for everyone
- When TCP is used as a transport protocol it can aggravate the
situation because a router which is experiencing congestion will
drop packets which TCP recognizes as packet loss and sends a
duplicate of each one to fix the problem which not only is not fixed
but it forwards further traffic to the congested router, etc, etc.!
Effects of congestion
•
•
•
•
Packets delivered affected by congestion.
When the offered load is within the packet
handling capacity of the network (no
congestion) every packet is delivered.
When the offered load gets near the
handling capacity of the network, congestion
appears (moderate congestion) and there is
only a small increase on the number of
packets delivered which is not proportional
to the number of packets offered.
When congestion gets worse (severe
congestion) the number of packets delivered
is reduced.
The second picture shows how the offered
load increases delay in packet delivery
when the network cannot handle the
incoming traffic
•
Contents credit: Lancaster University, Vasileios
Asloglou, Advanced Networking and the
Internet Coursework. Tutorial Topic :
Congestion Control techniques
http://www.lancs.ac.uk/postgrad/asloglou/
What can be done
- Buy more bandwidth
- Optimise the efficiency of the circuit
- Charge
- Censor?
- Control the kind of traffic that traverses
the circuit
Buy more
- Expensive
- Often only a short-term solution
- Can make things worse
- Important however to benchmark
- Sometimes no budget is big enough
(example: the University of Helsinki,
2004)
Technical optimisation
- Critically important
- Often provides a basis for further action
- Almost never a complete solution
- What kind of technical issues…?
Examples of technical optimisation
• House-keeping: Microsoft updates, virus definition files,
automated patches of all kinds
• Spam is always a problem – it is valueless traffic that eats a lot
of bandwidth, and it needs to be managed downwards as much
as possible
• Virus outbreaks can consume your bandwidth
• Caching is hugely important: the most effective free technical
solution is Squid delay pools
• Traffic shaping
– Commercial traffic shapers are expensive but are very effective.
But note that there are open source traffic shapers as well, and
these should always be considered before expensive investments
in commercial solutions are considered
• All of these issues are essential and help a lot, but they do not
influence the supply and demand problem for traffic on the
network in question
Charge
- Very effective at controlling or reducing
demand
- Can fund growth of the circuit
- Highly damaging to educational and
research objectives
Censor?
- http://www.sussex.ac.uk
- http://www.expertsexchange.com
- http://196.21.99.105/archive/img097.jpg
Policy-based solution
• Aims to bring about behavioral change
• Treats bandwidth just as any common good that
needs policy management
• Technical solutions can distribute the bandwidth
evenly and make sure that no one user can use a
disproportionate amount
– They can also prioritise and restrict traffic flows or users but
which ones and how?
• Technical solutions do not necessarily ensure that the
traffic that flows is consistent with institutional
purposes
• Policy must be used to support this…
Examples of policy based approaches
• Some simple examples, that we can come
back to later
• A policy that says something about…
– Appropriate and inappropriate use…
• Can be used to reward/punish such behaviour
– Ability to limit traffic by volume…
• Can be used to set quotas
– Ability to shape traffic
• Can be used to throttle non-core online resources or
sped up core ones
– Virus protection and software standards
• Can be used to remove problem computers/users from
the network who do not comply
Thank you
Any questions?