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?