FRONT Paper 97
-
Upload
prabhakarelex -
Category
Documents
-
view
214 -
download
0
description
Transcript of FRONT Paper 97
Optical network management with OSC*
Fengqing Liu, Qingji Zeng, Shilin Xiao, Xu Zhu, Jie XuElectronic Engineering Department, Shanghai Jiaotong University,
Shanghai, 200030, P. R. China
ABSTRACT
How to transport the control and management information of optical networking is a major concern these days. We
compare several means and arrive at a conclusion that OSC (optical supervisory channel) is a better choice. The contentof OSC is given and OSC channel wavelength, bit rate and coding method are discussed. An OSC example of WDMmetro network, which demonstrates the processing operation of overheads in OSC, FDI behavior for three types of
failure, and Self-management of OSC subsystem, are illuminated. To fulfill the demand of intelligent and distributedmanagement of optical transport network, an OSC of OC-3 (155Mbps) channel bit rate may be needed in the nearfuture.
Keywords: OSC, OTN (Optical Transport Network), FDI, WDM metro ring.
1. INTRODUCTION
With the unprecedented growth in data traffic, demand for bandwidth is seemly limitless. Optical transport network
(OTN) is being adopted for this purpose. And optical networking technology has been developed to circumvent the datarate bottleneck caused by the electronic device in OEO transition. To implement optical networking, some characteristicinformation of OTN must be transported between network elements and sent to network management system. There are
various means to provide for these and are summarized in the table below.Table 1 several methods
In-fiber Separate network
In-band Optical Channel Overhead Optical Channel
Out of band Optical Supervisory Channel (OSC) Data Communications Network (DCN)
The OSC is a separate channel, which carries overhead information for network management purposes. Managementmessages for the OMS and OTS layers, together with management messages for the Och layer that are transported via a
channel non-associated implementation, may share an OSC1.
Comparing these methods, we can arrive at the conclusion that OSC is a better choice. The advantage of OSC can besummarized as follows:
1. In the equipment without electronic interface, such as line optical amplifiers, the control and managementinformation of them cannot be sent with in-band method. That is why the OSC is presented.
2. OSC (Optical supervisory channel) is physically diverse from the associated data bearing channel. OSC ’s health is
independent from that of data bearing channel (that is optical channel). So when the data bearing channel fails, the
� This paper is supported by National Natural Science Foundation of China. The number is 69990540.� E_mail: [email protected] Tel: 86-21-62932166 Fax: 86-21-62820892.
Fiber Optic Components, Subsystems, and Systems for Telecommunications, Suning Tang,Xiaomin Ren, Editors, Proceedings of SPIE Vol. 4604 (2001) © 2001 SPIE · 0277-786X/01/$15.00 195
control channel may still work and vice versa. For example, communications between nodes is possible if thefailure is specific to the OCH and not the entire fiber or a node.
3. Unlike DCN (Data Communication Network), OSC doesn’t need a separate network. It can utilize the existing fibernetwork. As OTN may transverse some place where there is no existing data networks, it is convenient to use OSC.
4. OSC can transport OTS and OMS overhead, so it has the inherent ability to carry common information of multiple
wavelength, even multiple links. This can reduce the information that needs to be communicated between nodes.As more and more fibers and more available wavelengths in a fiber between adjacent nodes will be provisioned,control and management issues will become complex and error-prone. OSC can make this simple and makes the
OTN more scalable. This is very useful for GMPLS, which extends MPLS to IP/WDM integrated network andneed implementing LSP hierarchy and link bundling for scalability2.
The paper is organized as follows. In section 2 we will discuss the content of Optical Supervisory Channel and both
frame-based and message-based methods will be used. In section 3 an example of using OSC to manage WDM metronetwork is given, which specifies how to process the OSC overhead and describes the scenario of FDI sending over theOSC. In section 4, we mainly deal with the self-management of itself. Finally, we discuss the future trend of OSC,
which will eat up about 100Mbps bandwidth.
2. OSC contents
It has been agreed that OMS (Optical Multiplex Section) and OTS (Optical Transport Section) overhead are carried onthe Optical Supervisory Channel. Some Optical Channel overhead, such as optical channel trace, need to be associated
with Och. However, there are some locations where Och associated overhead are not available, but there are needs forOMS terminations to perform an OCh maintenance function. Otherwise, there must be a standby transmitter to becapable of generating an above-line-rate signal in order to create the byte that houses the OCh maintain information3. In
such an instance, 2.5 Gb/s capable transmitter would be necessary to send a 2 Mb/s signal. It is very expensive and lowcost-effective ratio.
In another view, OSC will need to carry several separate information streams, including control and management
information. Control information has low latency requirement, which includes the signaling for both data bearingchannel and OSC channel itself. Fault management information including FDI and APS is an example of it.Management information is relative time insensitive information, which includes OMS, Och FTFL messages. OTS,
OMS DCC (Data communication channel) may be time-critical or time insensitive according to what are transferred init. Besides these information, there are OTS, OMS order wire bandwidth requirements and some other information.
According to information that belongs to different layers (OTS, OMS, Och) and used for data bearing channel or optical
supervisory channel, the contents of OSC can be depicted as figure 1. FDI/BDI is used to suppress the downstream orupstream alarming messages in the corresponding layer, respectively. FTFL (Fault Type and Fault Location) messagesare used to determine the fault type and fault location of corresponding layer. Data communication channel has multiple
usages, which can be used to transport wavelength provision information, control information of the OXC and OADM,even they can be used to download software between nodes. The overhead for OSC mainly includesprotection-switching signaling for OSC subsystem, the states and commands that OSC subsystem and network manager
want to exchange. There are also some bits that are reserved for national and carrier use.
There are two different means to transport these separate streams, frame-based and message-based. We use both, forthey have different advantages for different information. Fixed bit assignments of a frame are used to carry the low
latency information, which can be easily examined and has the advantage of low latency. An OSC of 2Mbps, usingPCM30/32 frame structure is used in our implementation�of Metro ring. Message-based protocols, a simplified TCP/IP
Proc. SPIE Vol. 4604196
protocol stacks, are used for those time insensitive information. A fixed amount of transport capacity in a frame isreserved for the message-based protocol and variable contents can be defined in it. That is, some information will be
packaged and transported though the fixed amount of bandwidth, such as DCC.
OTS OH
OMS OH_P
OMS OH_S
OCH unassociated OH_P
OCH unassociated OH_S
Figure 1 Content of the OSC
OMS OH_P means OMS overhead for OMS payload. OMS OH_S means OMS overhead for OSC channel. So is forother similar expression. OSC states and commands from network manager are defined in OMS DCC as a type of
message.
3. An OSC example of WDM metro network
We will illuminate an OSC implementation of WDM metro network. It is a three-nodes 4-fiber BLSR Ring with 16
wavelengths per fiber. Two of three nodes are OADMs. Another is OXC. Using of OXC is just for scalable purpose tointerconnect with other future WDM rings. It functions like an OADM at present. All these three nodes fulfill mainlyOTS and OMS layer function as defined by ITU-T. They can Add/Drop and switch wavelength channels, but they don’t
have the ability to process the associated overhead of OCH layer. In this architecture, there is no optical line amplifier.So this network includes a very simplified OTS layer, including just FAS series to delimiter the frame. The overhead ofOMS and OCH layer is just like figure 1. Someone may argue that reserving a fixed bandwidth for the FTFL message is
too bandwidth consuming for three-node network. We keep it in our frame structure for the compatible and scalableconsideration. Figure 2 (Two fibers are pictured, another two is similar and omitted) shows the node structure, thestructure of OSC controller and segregation of OSC subsystem (control plane) and WDM network (data plane).
OSC is a physically independent subsystem. OSC and WDM data network just share fibers and 1510/1550 multiplexerand demultiplexer, which are passive and reliable. But they operate in different wavelength and have different internalstructure. To make the failure of data channel not infect the control channel, OSC channel wavelength should be chosen
to be different from data channel wavelength band, which is near 1550nm. OSC channel wavelength, data bit rate andchannel coding is not yet standardized. For channel wavelength, there are several choices. It can be selected in 1510nm,1310nm or 1480nm. Corning corporation, which OA operates in 1400nm, select 1625nm wavelength as OSC channel
wavelength. We use 1510±�10 nm, for it is normally used and has a compatible advantage in interoperability with othercarriers. To a three-node WDM metro ring, 2Mbps is enough. CMI (Coded Mark Inversion) is adopted for OSC in ourmetro ring. And a PCM30/32 frame structure is used. Some bytes of the frame are assigned to transport the time crucial
information. Another bytes are used to transport message-based variable contents, such as DCC.We demonstrate the processing operation of overheads in OSC when a fault happens.
OSC APSOMS OSC FDI/BDI
FAS OTS TTI OTS OW OTS DCC OTS Reserved
OMS TTI OMS OW OMS FDI/BDI OMS ReservedOMS APS OMS DCC OMS FTFL
OCH1 FDI/BDI OCH1 FTFL • • • OCHn FTFLOCHn FDI/BDI
OCH Reserved
OCH1 OSC FDI/BDI OCHn OSC FDI/BDI• • •
OSC APS
Proc. SPIE Vol. 4604 197
Prior to the fault the OSC OH will be processed as follows:1). OTS OH and OMS OH will terminate at the OMS layer. A new OTS OH and OMS OH will be generated.
2). OCH unassociated OH-p and OCH unassociated OH_S will be passed through unchanged. Their contents will
(C) Physically separation of OSC
subsystem and WDM optical network
OSC control plane
(1510 nm band)
Data plane
(1550nm band)
Figure 2 OSC node structure and segregation of OSC network and WDM optical network
OADM
OADM
OXC
Add/Drop
module
OSC controller
Device
interface
OSC
controller
O/E E/O
O/EE/O
NE
Manager
OW
1550/1510Demultiplexer
1550/1510Multiplexer
(a) OADM Node structure (b) OSC controller
NEManager
DATA BEARING CHANNEL
OMS OH OTS OH
NO FAULT
OCH un. OH-P
Figure 3 the overhead processing operation in a node
OTS OH
OCH un. OH-P
OCH Fault detection (OCH LOS-P)
OSC channel Fault Detection( OCH LOS_S)
OTS/OMS
OH Rev.
OTS/OMS
OH Trans.
OMS OH
OCH un. OH-S
OCH OH-P Trans.
OCH un. OH-SOCH OH-S Trans.
DROP ADD
Proc. SPIE Vol. 4604198
be changed only if a data channel failure or OSC channel failure occurs.
A special device (such as OSA, Optical spectrum Analyzer) will detect the data bearing channel failure, and notify the
OSC controller through internal mechanism. OSC controller will detect failure of the OSC channel. OCH FDI-P orOCH FDI-S and associated FTFL messages will be inserted into OSC OCH overhead. PD (Photonical Detector) willfind fiber cut. It will make OMS FDI, OMS FTFL transmitted. Figure 3 shows the overhead processing operation in a
node.
Figure 4 demonstrates the way to deal with three possible failure of the WDM metro ring. As there is no node with Ochassociated overhead accessing capability, OCH FDI and OCH FTFL are transported in OSC channel and processed byOSC controller. Optical transmitter/receiver communicate with OSC through internal mechanism. Although there areonly three nodes, we use the backward indication of failure for future consideration.
4. Self-management of OSC subsystem
OSC is a subsystem of OTN network. It has its own management information to transport. We defined dedicated bytes
for them in OSC frame. Alarm, self-protection signaling, command/state are the information that need to becommunicated in the OSC channel.
OSC is a lower bit rate channel, so it can be monitored in electrical domain to get more details to decide protection or
not. Separation of data channel and control channel protection has some other advantages.
OSC channel failure may be caused by OSC channel failure, OSC optical transmitter/receiver or OSC controller failure.We consider only the former two failures. There are two signals to indicate it. One is LOL (Loss Of Light), detected byoptical transmitter/receiver. The other is LOF (Loss Of frame), detected by OSC controller.
Topology of OSC ring in normal conditions is as figure 5(a). When any OSC work channel between two nodes fails,
protection switching will be activated. To reduce the information that needs to be transported we use the sate-commandmodel. States of OSC channel (just refer to the channel between upstream node and it) are kept in the node. OnlyProtection request (or ACK) are sent in APS bytes. According to its states and the signaling in OSC channel, each node
decides whether it initiate protection.
When protection actions are finished, the topology of OSC subsystem is like figure 5 (b). Besides the work channel ring,
OTS_TT
OMS_TT
OTS_TT
OMS_TT
OMS BDI, OMS
FTFL via OSC
OTS_TT
OMS_TT
OTS_TT
OMS_TT
Figure 4 FDI Behavior for three types of failure in WDM metro ring
c) OSC channel failure
OCHi channelfaiure
OTS_TT
OMS_TT
OTS_TT
OMS_TT
OCHi FDI, OCHi FTFL
via OSC
OCHi FTFL
via OSC
b) payload channel failure
OADM
OADM OADM
Fiber cut
OTS_TT
OMS_TT
OMS FDI_P, OMS FDI_S ,
OMS FTFL via OSC
a) Fiber cut
OADM
OADM OADM
OSC channelfailure
OTS_TT
OMS_TT
OMS FDI_S, OCHi
FTFL via OSC
OMS FTFLvia OSC
OADM
OADM OADM
OTS_TT
OMS_TT
Proc. SPIE Vol. 4604 199
Failure
another ring will be formed as soon as the failure is repaired. So these two nodes can detect signal of frame sync andone of them will activate restoration back to the normal states.
5. Conclusion and future trend
In this paper, we compare the advantage and disadvantage of in-band and out of band methods. OSC contents arediscussed. Both frame-based and message-based methods are used to transport them. Finally, an example of metroWDM ring is given, including self-protection of OSC subsystem, OSC overhead processing process and FDI behavior
for three types of failure.
To manage a big intelligent and distributed optical network, there is a lot more information to be transported. Theseinformation include OTS Layer Alarm messaging, OMS Layer Data Control, Network Topology Probing, Trouble
Shooting, Maintenance, OSC Protection and others, which will eat up about 100Mbps bandwidth3. So a 2Mbps channelis not enough and an OC-3 link may be used to transport them. To interface with internal devices, Ethernet or fastEthernet technology may be used.
REFERENCES
1. G.9591 Optical transport network physical layer interfaces
2. A. Banerjee et al., “Generalized Multiprotocol Lable Switching: An Overview of Routing and ManagementEnhancements” IEEE Comm. Mag., Vol. 39, no1., Jan. 2001.”
3. Laszio I. Szerenyi, Optical networking – OSC requirements, T1X1.5/2000-138
Node 1
work ring
protection ring
O/E E/O
O/EE/O
Node 2O/E E/O
O/EE/O
Node 3O/E E/O
O/EE/O
a) Topology of OSC ring in
normal conditions
Figure 5 protection of OSC subsystem.
Node 1
work ring
protection ring
O/E E/O
O/EE/O
Node 2O/E E/O
O/EE/O
Node 3O/E E/O
O/EE/O
b) Topology of OSC ring after
protection has been finished
Proc. SPIE Vol. 4604200