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IP Bandwidth Sharing. Paul Ferguson Consulting Engineer Internet Architecture Office of the CTO [email protected] 1. What exactly is “bandwidth sharing”?. Bandwidth sharing:.

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Ip bandwidth sharing

IP Bandwidth Sharing

Paul Ferguson

Consulting Engineer

Internet Architecture

Office of the CTO

[email protected]


What exactly is bandwidth sharing

What exactly is “bandwidth sharing”?

Bandwidth sharing
Bandwidth sharing:

  • It can be called the “thing” that TCP/IP does to allow bits of information originating from (and destined to) various sources to utilize the same pathways.

  • IP has been this doing this since Day 1.

Well there actually might not be a problem
Well, there actually might not be a problem:

  • Is there congestion?

  • If “Yes”, then there’s definitely a problem. This is where “bandwidth management” comes into the picture.

  • If “No”, then there might be a perception or expectation problem (more on that later).

Bandwidth management
Bandwidth Management:

  • Ensure that the network provides an adequate “appropriate environment” for applications, some of which may have “special” requirements.

  • Ensure that the network doesn’t melt down.

Problem objective

  • Avoid congestion, or

  • Provide an “appropriate environment” for applications which have “special” requirements -- “traffic protection”.

  • Provide an environment which provides the least amount of end-to-end delay.

In all cases
In all cases….

  • Ongoing capacity monitoring and planning is required.

  • If you do not know how much traffic is in your network, then this is a problem (e.g. peak/avg. rates, traffic source/dest.)

Avoiding congestion
Avoiding congestion…

  • Over-build. Throw bandwidth at it.

  • Limit aggregate incoming traffic to bandwidth of smallest link.

  • Neither of these are necessarily realistic.

Dealing with congestion
Dealing with congestion…

  • Allow queues to tail-drop packets.

  • Or do something else. Several options are available here. More on this later….

Do nothing
Do nothing...

  • Tail-dropping packets can have an adverse impact on all traffic traversing the router, resulting in poor performance for a larger percentage of traffic.

  • No control for which packets get dropped during congestion events.

So something
So something…..

  • …which provides traffic differentiation in the face of congestion, and/or

  • ….partition bandwidth to allow protection for a subset of traffic.

A brief note on the most common denominator
A brief note on “The most common denominator”

  • The End-to-End KISS theory of working within the Most Common Denominator -- IP.

  • “An IP packet may traverse any number of link-layer mediums (e.g. Ethernet, FDDI), so any differentiation done at the link-layer is lost in the end-to-end problem.”

Congestion we all know what happens when you do nothing
Congestion: We all know what happens when you do nothing…..

  • It just gets worse.

  • And people complain.

  • And sometimes, heads roll when the performance is intolerable.

Ip differentiation two options

Stateful nothing…..

IETF Integrated Services (Intserv)/RSVP


IETF Differentiated Services (Diffserv)

IP Differentiation: Two options

The building blocks

Diffserv: nothing…..












Resource Reservation

The Building Blocks:

Building blocks 2
Building blocks (2): nothing…..

  • Classifier: Classifies packets individually, or as belonging to a flow.

  • Shaper: Compares incoming traffic to a profile and drops/remarks packets which exceed a threshold.

  • Policer: Compares incoming traffic to a profile and drops/remarks packets which exceed a threshold.

Building blocks 3
Building blocks (3): nothing…..

  • Scheduler: A (non-FIFO) queuing strategy.

  • Dropper: A (non-taildrop) packet discarding scheme.

  • Resource Reservation: RSVP

Major differences intserv diffserv
Major differences: Intserv & Diffserv nothing…..

  • State, or no state.

  • RSVP has some minor scaling concerns, when individual flows using RSVP grow beyond a few hundred (or perhaps a few thousand). This concern may be somewhat alleviated in the near future with an RSVP reservation aggregation scheme.

Diffserv ef phb major points
Diffserv EF PHB: Major points nothing…..

  • Strict use of shaping to conform incoming EF traffic to available capacity.

  • aggregate EF ingress <= % of link capacity set aside for this “service” in core

  • Packets marked as EF get priority transmission.

  • Fairly good data protection

Diffserv af phb major points
Diffserv AF PHB: Major points nothing…..

  • Packets are simply marked with relative priority.

  • The service provider can interpret handling at-will.

  • Provides soft or “squishy” differentiation.

What acronym have i thus far avoided
What acronym have I, thus far, avoided? nothing…..

  • QoS, or Quality of Service. I suggest that “QoS” and “bandwidth management” are intrinsically one and the same in the world of IP.

  • Further….

What about hard guarantees on end to end delay and jitter
What about “hard guarantees” on end-to-end delay and jitter?

  • Well, RSVP gives you a bound on end-to-end maximal queuing times which basically bound delay for flows. But it really doesn’t provide for jitter control. It does, however, “protect” flows and guarantee bandwidth.

  • Diffserv’s EF PHB, I believe, parallels the Intserv controlled-load service.

What about hard guarantees on end to end delay and jitter 2
What about “hard guarantees” on end-to-end delay and jitter? (2)

  • Remember: TDM and Packet technologies are fundamentally and intrinsically different. Jitter is an issue within the packet world that is generally uncontrollable at an absolute level. (Think: RTP)

What about hard guarantees on end to end delay and jitter 3
What about “hard guarantees” on end-to-end delay and jitter? (3)

Comparison note:

  • TDM -- Remember what TDM stands for? There really is no delay or jitter in a TDM world -- everything is timing and timing rates. Basically, this has become an unrealistic (my opinion) standard for VoIP -- hard delay & jitter “guarantees”.

What about hard guarantees on end to end delay and jitter 4
What about “hard guarantees” on end-to-end delay and jitter? (4)

  • RSVP: Fairly hard guarantee on end-to-end “maximal queuing delay”. No guarantees on jitter, although probabilistically good.

What about hard guarantees on end to end delay and jitter 5
What about “hard guarantees” on end-to-end delay and jitter? (5)

  • Diffserv EF & AF PHB: No guarantees on delay or jitter. Semi-soft and squishy “guarantees” on delay, respectively. Jitter still elusive insofar as guarantees are concerned, but with EF jitter is less of a concern. AF jitter probability is directly related to priority ordering.

Jitter: jitter? (5)

  • There are no real control mechanisms within the network to control end-to-end jitter. Sure, a consistent queuing scheme might help to make it predictable, but it can never guarantee it.

Jitter message 2
Jitter message (2): jitter? (5)

  • Probably the most effective method of dealing with jitter is to adapt at the end-system (e.g. RTP-based monitoring).

Topological significance
Topological significance jitter? (5)

  • Tools (components) used at only the nodes they are needed.

  • Classify/Mark/Shape packets close to the “edge”, not in the network core.

Where s the architecture
Where’s the architecture? jitter? (5)

  • That’s it.

  • Before you can effectively design the architecture, you must define it.

  • Once that is done, you can look at applications and topologies, and decide which method is appropriate.

Perception problems
Perception problems jitter? (5)

  • What happens when there is no congestion, and you want to differentiate traffic? What happens, and what would you do? Huge problem.

  • There is also the problem of UDP (and other non-responsive traffic).

Summary jitter? (5)

  • Remember: There are two worlds. One is the global Internet, and the other is private organizational networks.

  • PATH and RESV state are not always evil, depending on what you really want.

  • Jitter control is an extremely hard problem to solve in the network.

Summary 2
Summary (2): jitter? (5)

  • Jitter is sometimes more easily dealt with by the host, who can readily adapt when using a real-time protocol (e.g. RTP).

  • Voice is very sensitive to delay & jitter.

  • Jitter is sometimes very difficult (if not altogether impossible) to remove from packet networks.

Summary 3
Summary (3): jitter? (5)

  • It’s generally not practical (or possible) to over-build the network.

  • Low or No Delay and Jitter are very important for some applications, not for others.

  • It’s generally very difficult to maintain a balance of economies of scale and sustain network performance.

Fin. jitter? (5)

Thank you.

[email protected]