Network Working Group Rajendra Damle
Internet Draft Young Lee
Expiration Date: December 2001 Iris Labs
Eric Brendel
Coree Networks
Riad Hartani
Caspian Networks
Vishal Sharma
Metanoia
June 2001
Optical Channel Concatenation -- Need and Requirements
draft-damle-optical-channel-concatenation-00.txt
Status of this Memo
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Abstract
This contribution identifies the need and requirements for
concatenating optical channels to create multiple high bandwidth
payload channels. To maximize the benefits of standardization, the
concatenation methodolgy should be independant of framing protocols
e.g., SONET, GFP, OCh etc.) as well as payload types (e.g., Packet,
Cell, Byte Stream).
A contribution for the need to concatenate optical channels was made
at the T1X1.5 meeting in March 2001 and was accepted for further
proposals. This contribution is based on the T1X1.5 contribution and
is presented herein for information only.
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1. Introduction
Historically, port speeds on routers and switches used in the backbone
network were lower than the bandwidths used and needed for efficient
transport over optical fibers. This required devices such as SONET Add
Drop Multiplexers (ADMs) to multiplex multiple lower data rate sources
to higher data rates for transport.
Today the bandwidth requirements between the core routers/switches have
increased from 2.5 Gb/s (OC-48) to 10 Gb/s (OC-192) in some cases.
Routers with OC-48 or OC-192 capable port cards and a transport
system that can carry that data rate over a single wavelength have
supported these increases.
In the future, data bandwidth demands between core switch sites are
projected to quickly grow to 100s of Gb/s. To meet this demand service
providers have to deploy multiple routers per switch site. This results
in using multiple ports at 2.5 Gb/s or 10 Gb/s for inter router
connections within a site as well as between sites [Figure 1].
----------------------------- ---------------------------
WDM Channels | |
| | |
router/switch v mux | Regen |demux
____ ____ ____ ___ |\ | Site | /| ___ ____ ____ ____
| || || |->| |->| | | ---- | | |->| |-| || || |
---- | |---- --- | |_ |_|\_| |_|\_|_| | --- ---- | |----
____ | |____ ___ | | | |/ | | |/ | | | ___ ____ | |____
| || || |->| |->| | | ---- | | |->| |-| || || |
---- | |---- --- | | | optical | | | --- ---- | |----
| X | ->|/ |amplifier | \|-- | X |
: | | : | | | | : | | :
: | | : \ | | | / | : | | :
____ | |____ \_|____________________|__/ | ____ | |____
| || || | | | WDM System | | | || || |
---- ---- ---- | | | | ---- ---- ----
| | | |
| | | |
router/switch | | | |
____ ____ ____ | | | | ____ ____ ____
| || || |------| | | | | || || |
---- | |---- | | | ---- | |----
____ | |____ | | | ____ | |____
| || || | | | ----->| || || |
---- | |---- <--- router/ | | ---- | |----
| X | switch port| | | X |
: | | : | | : | | :
: | | : | | : | | :
____ | |____ | | ____ | |____
| || || | | | | || || |
---- ---- ---- | | ---- ---- ----
| |
------------------------------ ---------------------------
Switch Site A Switch Site B
Figure 1: Multiple router ports connected across multiple WDM channels
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Internet Draft draft-damle-optical-channel-concatenation-00.txt Jul 2001
To eliminate inter router connections within a site, routers are scaling
up capacity per router by developing switch fabric that can support
several thousands of ports at 2.5 Gb/s or 10 Gb/s. Routers with large
numbers of low-speed ports make the network difficult to manage and
hence expensive.
2. Discussion
For carriers to deploy manageable and stable data networks that meet the
projected growth in bandwidth demands, new requirements on router
designs and WDM transmission system designs are emerging.
Switch Fabric Port Speed
/\
||
||
------------
| 100 Gbps |
------------
||
|| WDM Transponder
|| Date Rate Per Lambda
|| /\
|| ||
------------ ------------
| 10 Gbps | | 10 Gbps |
------------ ------------
|| ||
|| ||
------------ ------------
| 2.5 Gbps | | 2.5 Gbps |
------------ ------------
|| || > 1000 km w/o regeneration
Router/Switch --- ____ ------> ____ ---
----- ------- ----- __\ | |--|>|___|--|\ /|--|___|->| |
| || || | \| | | ____ | | | | ____ | |_\
| || || |__ /| |--|>|___|--| | | |--|___|->| | \
----- | |----- / | | | ____ | |--|\--|\--| | ____ | |_ /
| | ^ | |--|>|___|--| | |/ |/ | |--|___|->| | /
: | | : | | | | ____ | | | | ____ | |
: | X | : | | |--|>|___|--|/ \|--|___|->| |
: | | : | --- ---
----- | |----- | ^
| || || | | |__ concatenated channels
| || || | |
----- ------- ----- |___________ High Bandwidth Channels
Figure 2: Need for transparently concatenating multiple optical channels
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Internet Draft draft-damle-optical-channel-concatenation-00.txt Jul 2001
The router designs have to change from large number of 2.5 Gb/s or 10
Gb/s switch fabric ports to a small number of 40 Gb/s and higher
capacity ports. Advances in semiconductor technology and high speed
packet processing are key to enabling high speed router ports at 40 Gb/s
and beyond. The semiconductor technology available today is already
capable of supporting aggregates of more than 40 Gb/s throughput per
port.
In transmission systems, the WDM systems requirements are changing to
ultra long reach between terminals in order to make transport as
economical as possible. The ultra long reach requirement over existing
fiber plant is limiting the maximum data rate per wavelength that can be
transported economically. Economical ways to mitigate fiber non-
linearities, advances in optical amplification, laser modulation and
optical mux/demux technologies will enable higher data rates per lambda.
The semiconductor technology is already enabling router/switch fabric
ports at 40 Gb/s and greater. However deployable transmission systems
are far from being ready to transport 40 Gb/s and greater per wavelength
over ultra long reach distances. Therefore there is a clear need to
concatenate lower speed WDM optical channels (sub-channels) that use any
framing protocol to form one or more higher bandwidth interfaces (super
channels) to the routers/switches.
In the future semiconductor technologies are expected to develop
faster than high speed optical transmission technologies creating a
sustained need for concatenating multiple optical channels to create
high bandwidth channels.
Standardizing a methodology to concatenate multiple optical channels
that is agnostic to the transport framing protocols and payload types
will have a significant impact on the both the equipment manufacturers
and the carriers. The standardized methodology will completely de-couple
the router/switch equipment from the transmission equipment. This
de-coupling will allow the development of new equipment in both domains
such that carriers can extract huge savings by deploying large but
manageable routers/switches directly over a cost effective ultra long
haul WDM system.
3. Requirements
There are proposals at T1X1 and ITU [1]-[3] to virtually concatenate VTs
and STSs to make efficient use of SONET based transport for bursty
traffic. However, they do not cover the emerging applications and
requirements described in this document. These requirements for
concatenating optical channels to enable a carrier grade backbone data
network are as follows:
A. In order for the concatenation to be truly transparent today and in
the future, it should be agnostic to:
- Payload types: work with Cell/Packet/TDM or byte stream as the input.
- Framing protocols used on the optical channels (sub-channels) -
capability to concatenate optical channels that use any of the
standardized framing protocols (SONET, OCh, GFP etc.) into one or more
higher bandwidth super channels.
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B. The concatenation should be truly scalable by being independent of:
- Payload data rates
- Transmission data rates - capability to concatenate a set of channels
at any data rate as long as the data rate is the same within a set.
Variation in optical channel data rate within a concatenated set is
unlikely in a real network hence the added complexity to accommodate a
set of variable data rate channels would not be necessary
C. Keep the overhead to the minimum by optimizing for point-to-point
network topology since the data traffic demands are essentially
point-to-point. Low overhead also ensures that there is minimal penalty
for the concatenation function.
D. Should have all the carrier class survivability features required to
make the high bandwidth channels ultra reliable across the long haul
transmission system and have graceful degradation. We believe the
following features support carrier class survivability:
- Capability to uniquely identify a concatenated channel as well as
optical sub-channels contained within the concatenated channel
- Capability to monitor degradation per concatenated optical channel
through BER monitoring and CRCs
- Generalized arrival-time variation compensation
- Capability to add/remove sub-channels automatically without disrupting
the super channel
- Capability to communicate individual optical channel status to the
transmit end without the use of separate messages so as to minimize the
delay in this critical communication
- Capability to de-couple individual optical channel errors from the
concatenated superchannels and evenly distribute the available bandwidth
amongst all the payload streams
- Provide capability for extended burn-in testing of individual
sub-channels
- Provide hooks to support concatenated channel level protection schemes
under the control of a higher layer
- Capability to guarantee payload arrival sequence (e.g., packet order)
E. Should have the capability to allow the carriers to easily manage and
service the concatenated super channel and the sub-channels through
automatic as well as manual provisioning features.
5. References
[1] T1X1.5/2000-157R1 "A Justification for a Variable Bandwidth
Allocation Methodology for SONET Virtually Concatenated SPEs"
[2] T1X1.5/2000-156 "A Proposal for Variable Bandwidth Allocation (VBA)
Methodology for SONET Virtually Concatenated SPEs"
[3] T1X1.5/2000-199 "A Proposed Link Capacity Adjustment Scheme (LCAS)
for SONET Virtually Concatenated SPEs"
[4] T1X1.5/2001-090 "Need for Concatenating Optical Channels to Create a
Transparent High Bandwidth Channels"
[5] T1X1.5/2001-103 "Clarification of T1X1.5/2001-090"
Damle, et. al. [Page 5]
Internet Draft draft-damle-optical-channel-concatenation-00.txt Jul 2001
5. Security Considerations
This draft does not introduce any new security issues.
6. Authors' Addresses
Rajendra Damle
Iris Labs Inc.
101 E. Park Blvd 855
Plano, TX 75025
Phone: 972 943 2963
Email: rdamle@irislabs.com
Young Lee
Iris Labs Inc.
101 E. Park Blvd 855
Plano, TX 75025
Phone: 972 943 2964
Email: ylee@irislabs.com
Eric Brendel
Coree Networks
56 Park Road
Tinton Falls, NJ 07724
Phone: 732 380 2800
Email: brendel@coreenetworks.com
Riad Hartani
Caspian Networks
170 Baytech Drive
San Jose, CA 95143
Phone: 408 382 5216
Email: riad@caspiannetworks.com
Vishal Sharma
Metanoia, Inc.
335 Elan Village Lane Unit 203
San Jose, CA 95134-2539
Phone: 408-943-1794
Email: v.sharma@ieee.org
Lee, et. al. [Page 6]
Internet Draft draft-ylee-optical-channel-concatenation-00.txt July 2001
Expiration Date: January 2002