RE: [Diffserv-interest] Re: draft-baker-diffserv-basic-classes-01 .txt

Dimitry Haskin <> Mon, 03 November 2003 16:15 UTC

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From: Dimitry Haskin <>
To: "'John H. Shuler'" <>, Jozef Babiarz <>, Brian E Carpenter <>
Subject: RE: [Diffserv-interest] Re: draft-baker-diffserv-basic-classes-01 .txt
Date: Mon, 3 Nov 2003 11:12:12 -0500
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Since the jitter level is bound by latency, your AF4 service class seems to
be incongruous and can be safely removed from the list. What would remain
appears to be a reasonable grouping of services.

-----Original Message-----
From: John H. Shuler []
Sent: Sunday, November 02, 2003 5:30 PM
To: Jozef Babiarz; Brian E Carpenter
Subject: Re: [Diffserv-interest] Re: draft-baker-diffserv-basic-classes-01

Here is my take on the examples you gave below:

Total of 5 service classes, ever, for any service:
Control Class: Highest absolute priority. Never used for anything but
control. Period.

EF for TDM-like services such as IP telephony, circuit em, and possibly
(depending on your attitude) interactive video services. Engineered such
that it is never oversubscribed under even the most extreme conditions.
Yields low latency and jitter.

AF4 for latency-sensitive (but not particularly jitter-sensitive) traffic
such as unidirectional audio-video streaming, TV broadcast, etc. Jitter is
buffered by end systems. Also available for people who want to pay through
the nose for transactional data service (banks may). Very conservatively
engineered w.r.t. CIR... Should never block.

AF1 for guaranteed CIR services with some (but not much) delay sensitivity,
such as SNA, VPN, etc. This class - even CIR - will typically be
oversubscribed, based on statistical analysis of network traffic. 

BE for everything else - Best Effort internet services, etc.  No distinction
between "standard" and "low priority". This is both. BE is subject to
complete blocking under extreme conditions, but these conditions should
almost never occur with proper network engineering. In fact, the apps that
use it should not even know when they are blocked even for several seconds,
since they are totally elastic. Service providers will price and
differentiate based on their performance on this class as well as the
others. If someone is intense about blocking, they can pay to up their
service to AF1 or even AF4.

Why do you need more? All services can be addressed using these basic
classes, plus policy-based tweaks on policers and shapers and queuing
systems (WFQ or CBQ). If a customer wants a better quality than is "typical"
of a particular service, they can pay to bump up a class (except to the
control class). CIR on EF and AF4 will not be oversubscribed. The payback
from excessive attention to detail in management is negligible at best. Any
problems that occur will be due to failure to properly engineer the network
bandwidth or access policies.

Please explain to me why I am wrong.



From: Jozef Babiarz <>
Date: Sun, 02 Nov 2003 16:52:18 -0500
To: Brian E Carpenter <>om>, "John H. Shuler"
Subject: RE: [Diffserv-interest] Re: draft-baker-diffserv-basic-classes-01

Brian E Carpenter wrote: 
John, I guess your comment refers to the draft so I changed the subject. 

If you want to be sure the authors see your comments, you might want to 
write to them directly. My reactions inserted below. 


"John H. Shuler" wrote: 
> Why make a distinction between "Standard Service Class" and "Low Priority 
> Data"? 

There is a kitchen sink aspect to this draft that worries me. Rather than 
starting simple, with three or four generic service classes, the authors 
have chosen to present the union of a number of diffserv deployment models. 
I think that risks confusing operators by giving them too much complexity 
to choose from. 

[[Joe] The draft tries to address the service differentiation that is needed
in carriers and enterprise networks including access networks. I agree that
network administrators both in carrier and enterprise should start off with
only the service differentiation level (service classes) that are required
for their business. Let me provide some examples that I worked on so that
you can understand why we have defined the number of service classes.

Carriers wanted to use IP technology for provide telephony service, plus
provide IP VPN service with CIR as well basic Internet connectivity service.
This scenario can be address by configuring the network using the following
service classes define in the draft.

- Standard service class for Internet connectivity 
- High Throughput Data service class of IP VPN and collection of network
data for billing 
- Telephony service class for VoIP and signaling between voice gateways 
- Network Control service classes for routing, etc. 

This simple example used four of the defined service classes. 

A different operator is deploying the services listed above plus new
multimedia IP services like desktop video conferencing to go along with
telephony, instant massaging plus other "workflow" applications.

This operator needs: 
- Standard 
- High Throughput Data 
- Low Latency Data 
- Multimedia Conferencing 
- Telephony 
- Network Control 

Another operator has plans to offer broadcast TV service, pay-per-view,
telephony, two different SLAs for IP VPN services and basic Internet
connectivity. They will need:

- Standard 
- High Throughput Data 
- Low Latency Data 
- Multimedia Streaming 
- Telephony 
- Network Control 

A large enterprise is currently configuring their network to support the
flowing service classes (using the drafts terminology). Most location will
have a subset of services available with migration to network wide service
transparency in the future. 

- Standard 
- High Throughput Data 
- Low Latency Data 
- Multimedia Streaming 
- Multimedia Conferencing 
- Telephony 
- Network Control 
- Administration 

I can go through more scenarios that I have come across over the years. 
I agree that two or three user service classes is what many operators start
off with, however they are not always the same three and they always like to
know how they can evolve in the future.]

Regards, Joe. 
Jozef Babiarz 
QoS and Network Architecture 
Nortel Networks 
Tel: (613) 763-6098 ESN:393-6098