why 9,584,640,000 is excellent
- To: stds-802-3-hssg-speed@xxxxxxxx
- Subject: why 9,584,640,000 is excellent
- From: pbottorf@xxxxxxxxxxxxxxxxxx (Paul Bottorff)
- Date: Fri, 25 Jun 1999 13:38:17 -0700
- Sender: owner-stds-802-3-hssg-speed@xxxxxxxxxxxxxxxxxx
Here is my action item to provide a speed position statement.
9,584,640,000 bps is the best choice for the data rate of the next Ethernet
1) it is the exact rate of the available capacity in the installed base of
lit wide area networks worldwide. Ethernet has a hallmark of supporting the
installed base. It is this aspect of Ethernet which has allowed rapid
uptake in the market of new Ethernet versions. The exact same principle
which Ethernet applied in the past for LANs is also the key for rapid
uptake and market acceptance of Ethernet as the preferred data transport in
the WAN. By building a standard which can operate over the existing
infrastructures the entire wide area market will be open.
Compatibility with the installed base is a deciding factor in the wide
acceptance of Ethernet as the data transport technology of choice for the
wide area. Without installed base support Ethernet will be isolated to
greenfield applications. Since the turnover in the wide area is relatively
slow due to the huge investment in infrastructure components this will keep
Ethernet out of the mainstream for many years.
Compatibility with the installed base is highly advantageous even for
greenfield applications. Many environments which have dark fiber or
frequency independent optical networks will still need to use the installed
base of lit fiber for a portion of their networks. Without easy interface
between the installed base and the greenfield environment these
environments will be forced to make trade-offs between deploying some other
compatible technology, limiting their scope, or making less optimal networks.
2)Matching the installed base data rate allows a smooth migration from TDM
multiplexing equipment to direct transmission of 9.584640 GigE on DWDM
wavelengths. The installed base of DWDM equipment includes frequency
sensitive regenerator components. In the transition from TDM networking to
photonic networking the regenerators will be retained in the networks core.
The regenerators operate on all the wavelengths of the DWDM network some
carrying TDM traffic and others carrying 9.584640 GigE.
3)A 4% difference in speed will be un-noticeable to the operation of the
traditional LAN environments. Ethernet LANs have traditionally operated at
loads much below their maximum capacity. A rule of thumb is to keep the
average network utilization below 10% of
the network capacity. The low average utilization level allows the network
very high on demand burst rates and provides high quality service
throughout the campus.
4)An exact rate match from 9.584640 Gig Ethernet and 10,100,1000 Ethernets
is unimportant. Ethernet always has used packet multiplexed not TDM.
Ethernet uses switches and routers to perform aggregation to and from
different speed links. Switched Ethernet networks are designed to support
highly imbalanced data rates by providing congestion control protocols at
the edges of the networks and switches which contain sufficient buffers to
handle transient imbalances. These two techniques are pervasive in switched
Ethernet networks today allowing the networks to rate adapt to any link speed.
5)The IEEE can easily specify the maximum packet rate for 9.584640 GigE for
reference by test labs and customers evaluating 9.584640 GigE. It is not
important for 9.584640 GigE to represent the data carrying capacity since
previous 10, 100, and 1000 Mbit Ethernets do not indicate the data carrying
capacity of the links. The bit rate specified includes many overhead areas
including the Preamble, IFG, SA, DA, Type, and FCS. The actual data rate
received from previous Ethernets is dependent on the type and size of
6)The decision to use 9.584640 does not determine the PHY coding system or
any characteristics of the optical system. This data rate can be supported
with any coding technology.
7)The use of a 9.584640 Gbps data rate allows a simple scalable interface
between the installed base of lit fiber and 10 GigE. Regardless of the code
system chosen it will be possible to perform a synchronous transform at the
edge of an existing WAN using a small fixed size buffer. The transform may
be as simple as a short retiming queue or in the worst case a code
translation queue. These solutions can be performed completely at the PHY
layers without using a MAC.
8)The decision to use a 10.000000 Gbps data rate will limit 10 GigE to
campus LAN applications. The interfaces required for adaption to the
installed base of lit wide area networks will make Ethernet more expensive,
more complex, and less scalable than competing solutions which are taylored
to wide area networks. Ethernet at 10.000000 Gbps will unable to compete in
the wide area.
Paul A. Bottorff, Director Switching Architecture
Bay Architecture Laboratory
Nortel Networks, Inc.
4401 Great America Parkway
Santa Clara, CA 95052-8185
Tel: 408 495 3365 Fax: 408 495 1299 ESN: 265 3365