RE: A telephony carrier industry perspective
- To: "'Roy Bynum'" <RBYNUM/0004245935@MCIMAIL.COM>
- Subject: RE: A telephony carrier industry perspective
- From: Andrew Smith <andrew@extremenetworks.com>
- Date: Tue, 18 May 1999 11:23:57 -0700
- Cc: IEEE HSSG <stds-802-3-hssg@ieee.org>
- Sender: owner-stds-802-3-hssg@majordomo.ieee.org
Roy,
This is very similar territory to that explored recently in the IEEE802
QoS/Flow-control study group (see
http://grouper.ieee.org/groups/802/QOSFC/index.html).
Congestion is usually separated into 2 types: short-term, due to unforeseen
traffic peaks, and long-term, due to sustained levels of traffic in excess
of provisioned capacity. I think you are merging the two types in your
message. The latter type of congestion is what is usually known as
"over-subscription" and requires what you term "subscription control".
Queue buffering can be used to handle short-term congestion but is not a
solution for the second type. It can be used to absorb peaks that occur
naturally due to well-behaved data flows traversing switching nodes but
should not be thought of as a good mechanism for handling uncontrolled
bursty sources. In your scenario, with persistent overload and using
per-link flow control, "flow-control will continue to cascade back" until
the whole network becomes equivalent to a shared network segment with an
*aggregate* bandwidth equivalent to that of the congested link: this is
likely not going to be popular with your customers.
In the presence of data sources that react to congestion feedback (through
packet dropping or ECN), the offered load can be throttled at the sources to
match the provisioned capacity: this is how the best-effort Internet works
today using TCP. There are well-understood packet-dropping mechanisms e.g.
RED that are commonly implemented these days in routers in the Internet core
that lead to efficient and fair overall network utilisation for TCP sources:
in the Internet architecture, dropping data to signal congestion is
considered a Good Thing (tm). Uncontrolled (open-loop) data sources are a
potential problem in such a network and must be controlled by shaping at or
near the source and suitable provisioning if they produce enough traffic to
cause problems.
At the IP layer, mechanisms are being standardised (see
http://www.ietf.org/html.charters/diffserv-charter.html and RFC 2475 in
particular) that are widely deployed today in routers for providing
differential services for different traffic classes on a link and within
switching nodes: this model assumes the presence of traffic shapers at
inputs that enforce a per-class contract ("SLA") with the data source that
can take account of the burstiness of the sources and allows a provider to
provision appropriately for such pre-agreed peaks without reliance on
flow-control - in fact, per-link flow control would make it difficult for a
provider to meet such SLAs. The SLAs provide the financial controls to make
this model work.
It is unclear today (to me at least) what added benefit link-layer flow
control can offer on top of TCP in such networks: any economically viable
form of flow control is likely to offer, at best, per-class control, rather
than the more desirable per-microflow control. Per-class control penalises
all microflows that share the class, even those that are well behaved.
Per-microflow control is expensive and would, in any case, duplicate in many
ways functions that are already provided at the transport layer. Certainly
there is scope for some mathematical modelling of such scenarios and there
are also demonstrable scenarios where such detailed flow control is
worthwhile, particularly those using low-speed, expensive transmission
lines: I'm not sure that 10G Ethernet falls into that category.
Persistent over-subscription of WAN links for todays enterprise networks is
a solved problem: you either buy a larger SLA or you use bandwidth
management solutions such as class-based queueing to ensure that the right
traffic gets through. I really don't hear a lot of people asking for
link-level flow control to solve this problem.
But we digress ...
Andrew
****************************************************************
Andrew Smith tel: +1 (408) 579-2821
Extreme Networks fax: +1 (408) 579-3000
3585 Monroe St. http://www.extremenetworks.com
Santa Clara CA 95051-1450 em: andrew@extremenetworks.com
****************************************************************
> -----Original Message-----
> From: Roy Bynum [mailto:RBYNUM/0004245935@MCIMAIL.COM]
> Sent: Tuesday, May 18, 1999 7:46 AM
> To: Andrew Smith
> Cc: IEEE HSSG
> Subject: RE: A telephony carrier industry perspective
>
>
> Andrew,
>
> I have been designing and implementing all sorts of data networking
> environments, LAN/MAN/WAN, for some time. One of the headaches is
> understanding the business application requirements and cost trade-off
> on link circuit bandwidth. Because intermediate/gateway systems
> historically do not have the ability to signal back when an output
> circuit becomes overloaded (the new term is "over-subscribed"), queue
> buffering has been a major issue. The problem is a network that has
> circuits that consistently become overloaded and do so for extended
> lengths of time, such that the queues become overloaded. Data network
> architects tend to design large enterprise WAN networks based on a
> consistent loading with an attempt to limit the peaks to close to the
> maximum circuit bandwidth.
>
> With "flow-control" using GbE I can design WAN data networks closer to
> the consistent loading with less concern for peak traffic. I have set
> up a test WAN network using Native data GbE over Optical DWDM and
> SONET DATS to test this. When the L2/L3 GbE switches are properly
> configured, I can only attempt to overload the network "circuits".
> When the flow-control is applied all the way to the data source
> systems, the flow-control will continue to cascade back such that
> over-subscription does not occur. Unlike a traditional TDM WAN circuit
> based design, no data is lost during peak "overloading", which tends
> to prevent more problems because of re-transmissions. As this is
> better understood and implemented, it will change the bandwidth
> allocation process of designing enterprise networks.
>
> Thank you,
> Roy Bynum
>
>
>
> Date: Mon May 17, 1999 5:27 pm CST
> Source-Date: Mon, 17 May 1999 16:26:58 -0700
> From: Andrew Smith
> EMS: INTERNET / MCI ID: 376-5414
> MBX: andrew@extremenetworks.com
>
> TO: * ROY BYNUM / MCI ID: 424-5935
> CC: IEEE HSSG
> EMS: INTERNET / MCI ID: 376-5414
> MBX: stds-802-3-hssg@ieee.org
> Subject: RE: A telephony carrier industry perspective
> Message-Id: 99051723270571/INTERNETGWDN1IG
> Source-Msg-Id:
> <D0805D3B448BD211A7990008C7B18130142CFC@ftp.extremenetworks.com>
> U-Content-return: allowed
> U-X-Mailer: Internet Mail Service (5.5.2448.0)
>
> Roy,
>
> At the risk of waking some sleeping dogs, could I ask you to
> elaborate a
> little on your statement:
>
> 'In addition to being less expensive, GbE over Native Data
> SONET DATS will
> provide "subscription control" though "flow control" That
> "subscription
> control" will prevent over-subscribing the WAN links, which
> is a big problem
> for enterprise data network designers and architects.'
>
> Andrew
>
> ****************************************************************
> Andrew Smith tel: +1 (408) 579-2821
> Extreme Networks fax: +1 (408) 579-3000
> 3585 Monroe St. http://www.extremenetworks.com
> Santa Clara CA 95051-1450 em: andrew@extremenetworks.com
> ****************************************************************
>
>
>
> > -----Original Message-----
> > From: Roy Bynum [mailto:RBYNUM/0004245935@MCIMAIL.COM]
> > Sent: Monday, May 17, 1999 4:12 PM
> > To: bill.st.arnaud
> > Cc: IEEE HSSG
> > Subject: RE: A telephony carrier industry perspective
> >
> >
> >
> > Bill,
> >
> > Internet IP will continue to be what the market
> requirements reflect.
> > Slow restoration times are acceptable in that environment. The UUNet
> > Long Haul GbE is part of what I am doing. I am the one that put the
> > Long Haul Optical switching/Metro DWDM/SONET DATS evaluation of GbE
> > together.
> >
> > As a bit irony, dependable GbE is turning out to be less expensive
> > than undependable IP over TDM, ATM, or POS. Unless MPLS comes in a
> > respectable price break, GbE over Native Data SONET DATS
> will still be
> > less expensive.
> >
> > In addition to being less expensive, GbE over Native Data SONET DATS
> > will provide "subscription control" though "flow control" That
> > "subscription control" will prevent over-subscribing the WAN links,
> > which is a big problem for enterprise data network designers and
> > architects. Combine that with "priority queueing" and most of what
> > MPLS was supposed to do has already been accomplished by GbE. You
> > guys as IEEE have done a greater job than you knew.
> >
> > Dependable, high quality transport of Native data traffic
> such as GbE
> > and 10GbE is probably going to be a different market, one that "best
> > effort" is unacceptable to. If there is a market that provides the
> > profit margin that will sustain 10GbE, it will not be the
> Internet as
> > it is today.
> >
> > I do know that I have been given the requiement that
> carriers can not
> > support a data service over long haul systems that does not provide
> > "SONET like" functionality. The reason that I joined this
> study group
> > is to provide that insight to the standards developers. If
> that is GbE
> > or 10GbE over SONET then the issue is already resolved. All that
> > remains is to determine what the LAN application requirements are,
> > then the standard can be defined.
> >
> >
> > Date: Mon May 17, 1999 3:23 pm CST
> > Source-Date: Mon, 17 May 1999 17:17:51 -0400
> > Fromm: bill.st.arnaud
> > EMS: INTERNET / MCI ID: 376-5414
> > MBX: bill.st.arnaud@canarie.ca
> >
> > TO: * ROY BYNUM / MCI ID: 424-5935
> > Subject: RE: A telephony carrier industry perspective
> > Message-Id: 99051721234042/INTERNETGWDN1IG
> > Source-Msg-Id:
> > <NBBBJIMEPHPGCNGAHPMFIEIJELAA.bill.st.arnaud@canarie.ca>
> > U-Importance: Normal
> > U-X-Mailer: Microsoft Outlook IMO, Build 9.0.2212 (4.71.2419.0)
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> > U-X-MSMail-priority: Normal
> > U-X-Priority: 3 (Normal)
> >
> > Roy:
> >
> > Again no disagreement. I don't think traditional SONET or
> > ATM networks will
> > disappear. The model we advocate is the same that Frontier is
> > now deploying:
> > IP/DWDM for best efforts, slow restoral traffic on one set of
> > wavelengths,
> > IP over SONET on another set of wavelengths for those
> > services that need
> > fast restoral and security of SONET, and IP over ATM over
> > SONET on another
> > set of wavelengths for fine grained QoS services.
> >
> > I agree with you that the driving force for GbE is cost. It makes a
> > dramatic difference to the overall cost of the network.
> >
> > But I believe GbE can also make an equal dramatic difference on the
> > transport side on medium, long haul links up to 1000 km.
> Your sister
> > company UUNet has already demonstrated that on some long haul
> > GbE systems.
> > But I agree with you this type of link is probably only
> good for best
> > efforts IP traffic.
> >
> > Bill
> >
> > -------------------------------------------
> > Bill St Arnaud
> > Director Network Projects
> > CANARIE
> > bill.st.arnaud@canarie.ca
> > http://tweetie.canarie.ca/~bstarn
> >
> >
> >
> >
> >
> >
> >
> > > -----Original Message-----
> > > From: Roy Bynum [mailto:RBYNUM/0004245935@MCIMAIL.COM]
> > > Sent: Monday, May 17, 1999 4:54 PM
> > > To: bill.st.arnaud
> > > Cc: IEEE HSSG
> > > Subject: RE: A telephony carrier industry perspective
> > >
> > >
> > > Bill,
> > >
> > > I have an IP base video conferencing demonstration
> > application that is
> > > full motion, full resolution. It uses MPEG2 compression and
> > drives the
> > > IP data at 7Mbs bidirectional. Part of the demonstration of the
> > > reliability of GbE over optical and SONET Native Data
> > systems is to do
> > > a simulated fiber break. Over a normal IP network, there
> is a major
> > > loss of data and thus video synchronization, sometimes
> the "call" is
> > > even dropped. Over a Native data network, optical or
> SONET DATS, if
> > > you blink, you miss the cut. It is that kind of traffic path
> > > restoration quality that will be required by future, real time,
> > > visual, and virtual applications. This is the quality of
> > traffic path
> > > restoration that needs to be implemented in Metro/MAN and WAN
> > > environments. I do not believe that any one protocol and/or
> > system can
> > > do that and still be cost effective.
> > >
> > > Fromm looking at Cisco's DPT description, it looks a lot like a
> > > SONET/SDH BLSR ring. In duplicating the alternate path coupled
> > > architecture of SONET/SDH, Cisco could well duplicate the
> > restoration
> > > functionality of SONET/SDH. Although what value it will
> > have over long
> > > haul systems that are geared for very high bandwidth, I
> am not sure.
> > > Within a LAN environment, that type of restoration is probably not
> > > required. Within a Metro MAN environment, we have found that GbE
> > > combined with optical path protected DWDM is very cost effective.
> > > Cisco will have to come in at a VERY "cheep" cost in order
> > to justify
> > > the deployment of their systems. I expect to have some
> test systems
> > > before too long. I am looking forward to finding out.
> > >
> > > The bottom line to this is cost. Preliminary evaluations
> are showing
> > > that GbE already is so cost effective that it is less expensive to
> > > have 10 GbE interfaces on a router than it is to have 4 OC48 POS
> > > interfaces. Combine that with the less expensive interfaces on the
> > > DWDM and SONET DATS equipment it becomes even more attractive. The
> > > capital cost of IP over "Ethernet" or what I am now calling
> > Native IP
> > > is less expensive over a MAN or WAN environment than the
> > existing TDM
> > > WAN systems. 10GbE must compete in this environment. In
> order for it
> > > to be deployed, it must provide high native data bandwidth,
> > very cost
> > > effectively with the specific service, maintenance, and operations
> > > support that each very different environment requires.
> > >
> > >
> > > Thank you,
> > > Roy Bynum
> > >
> > >
<much good stuff chopped from below here>