IP over WDM network

1
IP over WDM network

• Fang Yu
• 294 Class Presentation

2
Outline

• History of WDM networks
• Current Internet Multi-layer protocol stack
  between IP and WDM layers
• Future IP directly over WDM
• Challenge
• Virtual Topology Reconfiguration
• Multi-layer routing
• One proposal Optical Burst Switching technologies

3
History

• In the late 70s
• First fiber based optical transmission system
• Before 1995
• Mostly a single high-speed optical channel
• All multiplexing done in electrical domain(TDM)
• 50Mb/s to 10Gb/s data services
• After 1995
• WDM allows simultaneously transmitting multiple
  high-speed channels on different frequencies (Up
  to 160 wavelengths today)
• 40G per l (OC768)
• Total link capacity 160 l 40G 6.4 Tbps

4
Current Typical Protocol Stacks
IP
ATM
SONET
WDM
WDM
5
Transport Layer Model
Service Layers
Packet
Packet
Packet
Packet
DS1 (1.5 Mb/s)
3/1 DCS Layer
DS3 (45 Mb/s)
Core ATM/IPLayers
3/3 DCS Layer (DACS III)
DS3 (45 Mb/s)
SONET ADM Layer
ADM
ADM
ADM
ADM
ADM
ADM
ADM
OC48 (2.5 Gb/s)
Media Layer
Fiber Conduit/ Sheath
6
Disadvantage of Current Multi-layer Protocol Stack

• Inefficient
• In IP over ATM over SONET over WDM network, 22
  bandwidth used for protocol overhead
• Layers often do not work in concert
• Every layer now runs at its own speed. So, low
  speed devices cannot fill the wavelength
  bandwidth.
• When detecting of failure, different layers
  compete for protection
• Optical layer detects failure almost immediately,
  restores error in 2us to 60ms
• SONET layer detects failure in 2.3100 us,
  restores error in 60 ms

7
Disadvantage of Current Multi-layer Protocol
Stack (Cont)

• Functional overlap So many layers are doing the
  same thing
• Routing
• Protections
• Slow speed
• Electronic devices can not catch the transmission
  speed available at optical layer
• Latencies of connection

8
Historical Reason for Multi-layer

• SONET over WDM
• Conventional WDM deployment is using SONET as
  standard interface to higher layers
• IP over ATM
• IP packets need to be mapped into ATM cells
  before transporting over WDM using SONET frame
• OEO conversions at every node is easier to build
  than all optical switch

9
Simplified Protocol Stacks?
IP
IP
Frame Relay
WDM-aware Electronic layer
ATM
SONET
WDM
WDM
Current Typical Protocol Stack
Simplified Protocol Stack
10
IP Directly Over WDM?

• Establish high-speed optical layer connections
  (lightpaths)
• IP routers connected through lightpaths rather
  than fiber

11
Challenge for IP over WDM network

• WDM-aware Electronic layer
• Reconfiguration and load balancing
• Protection and restoration
• Optical flow switching
• Network management/control
• Cross-layer optimization
• Reconfigurable (within milli-seconds) OXC
• Wavelength Converters

12
Virtual Topology Reconfiguration

• Physical topology
• Seen by optical layer
• Virtual topology a set of nodes interconnected
  by light-paths (wavelength)
• Seen by electronic layer
• Reconfigure of light-paths in WDM network by
• Changing the light path connectivity between
  electronic switches
• Tuning of the transmitter wavelength and the
  frequency-selective-switches

A
A
B
B
C
D
C
D
13
Virtual Topology Reconfiguration(Cont.)

• Enable network to dynamically response to
  changing of traffic pattern
• Load balancing
• Efficiency
• Issues
• Time scale of changes
• Triggered by what mechanisms
• IP routing properties (e. g. stability)

14
Multi-layer Routing

• IP layer routing is the bottleneck of present
  Internet
• Solution Routing long duration flows at lower
  layers
• Conventional packet routing
• Optical bypass of intermediate routers for high
  volume traffic
• End-to end (user-to-user) flow of entire file
  bypassing routers

LIDS
15
Multi-layer Routing(Cont.)

• Routing in higher layer
• No bandwidth reservation needed
• More knowledge of application requirements
• Routing in lower layer
• Faster routing
• Faster error detection and restoration

16
Switching all the packets in optical layer?

• Requires intelligence in the optical layer
• Need to store packet during header processing
• Optical buffers are extremely hard to implement
• 1 pkt 12 kbits _at_ 10 Gbps requires 1.2 ?s of
  delay gt 360 m of fiber)
• Optical Packet Switch still has a long way to
  go

17
Various Optical Switching Technologies
18
Optical Burst Packet Switching

• Retrospect the goal of IP over WDM
• Avoid electronic bottlenecks
• Decrease the cost by simplifying the multiple
  layer architecture
• OBS is one proposal of how to realize such a
  network

19
Optical Burst Switching

• Resources are allocated using one way reservation
• Sender sends a request
• Sender sends burst without waiting for an
  acknowledgement of its reservation request
• Switch does preparation for the burst when
  getting the request
• Bursts can have variable lengths
• Burst switching does not necessarily require
  buffering

20
Various OBSs

• The schemes differ in the way bandwidth release
  is triggered.
• In-band-terminator (IBT) header carries the
  routing information, then the payload followed by
  silence (needs to be done optically).
• Tell-and-go (TAG) a control packet is sent out
  to reserve resources and then the burst is sent
  without waiting for acknowledgement. Refresh
  packets are sent to keep the path alive.

21
Main Characteristics of Optical Burst Switching

• There is a time separation(offset time) between
  header and data
• Header and data are usually carried on different
  channels
• Header goes through sophisticated electronic
  processing
• Data is kept in optical domain

22
Conclusion

• Current IP over ATM over SONET over WDM network
  is inefficient and redundant
• Future IP directly over WDM network
• Advantages
• Less latency
• Automatic provisioning
• Higher bandwidth utilization
• Challenge of packet directly over WDM network
• Optical buffer
• Optical burst switch is one of the proposed
  techniques to IP over WDM network

23
Reference

• John Strand, Optical Networking and IP over
  Optical, Feb 4, 2002
• Kumar N. Sivarajan, IP over Intelligent Optical
  Networks, Jan 5, 2001
• Gaurav Agarwal, A Brief Introduction to Optical
  Networks, 2001
• Yang Lihong, Optical Burst Switching, CMU
  networking seminar presentation
• Vincent W. S. Chan, Optical Networks Technology
  and Architecture
• Eytan Modian, WDM-Based Packet Networks, IEEE
  Communication Magazine, March 1999
• Ornan (Ori) Gerstel, Rajiv Ramaswami,, Optical
  Layer SurvivabilityAn Implementation
  Perspective, IEEE Journal on selected areas in
  communications, October 2000
• Eytan Modiano, Aradhana Narula-Tam, Survivable
  lightpath routinga new approach to the design of
  WDM-based networks, IEEE JSAC,April 2002
• R. Ramaswami and K. N. Sivarajan, Optical
  Networks A Practical Perspective, San
  Francisco Morgan Kaufmann, 1998.