Driving Optical Network Evolution
Overview
Over the years, advancement in technologies has improved transmission
limitations, the number of wavelengths we can send down a piece of fiber,
performance, amplification techniques, and protection and redundancy of the
network. When people have described and spoken at length about optical
networks, they have typically limited the discussion of optical network technology
to providing physical-layer connectivity. When actual network services are
discussed, optical transport is augmented through the addition of several
protocol layers, each with its own sets of unique requirements, to make up a
service-enabling network. Until recently, transport was provided through specific
companies that concentrated on the core of the network and provided only point-
to-point transport services. A strong shift in revenue opportunities from a service
provider and vendor perspective, changing traffic patterns from the enterprise
customer, and capabilities to drive optical fiber into metropolitan (metro) areas
has opened up the next emerging frontier of networking. Providers are now
considering emerging lucrative opportunities in the metro space. Whereas
traditional or incumbent vendors have been installing optical equipment in the
space for some time, little attention has been paid to the opportunity available
through the introduction of new technology advancements and the economic
implications these technologies will have.
Specifically, the new technologies in the metro space provide better and more
profitable economics, scale, and new services and business models. The current
metro infrastructure comprises this equipment, which emphasizes voice traffic; is
limited in scalability; and was not designed to take advantage of new
technologies, topologies, and changing traffic conditions. Next-generation
equipment such as next-generation Synchronous Optical Network (SONET),
metro core dense wavelength division multiplexing (DWDM), metro-edge
DWDM, and advancements in the optical core have taken advantage of these
limitations, and they are scalable and data optimized; they include integrated
DWDM functionality and new amplification techniques; and they have made
improvements in the operational and provisioning cycles.
This tutorial provides technical information that can help engineers address
numerous Cisco innovations and technologies for Cisco Complete Optical
Multiservice Edge and Transport (Cisco COMET). They can be broken down into
five key areas: photonics, protection, protocols, packets, and provisioning.
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Network Flexibility
Networks today must support a variety of traffic types, including legacy traffic
based on regional SONET ring structures that require multiple traffic adds/drops
(that is, voice, asynchronous transfer mode [ATM], frame relay) but must also
support high-speed Internet backbones that are typically express lanes that
require little add/drop multiplexing. Deploying the hybrid Raman amplifier and
erbium-doped fiber amplifier (EDFA) amplification application in the L-band
enables extended long-haul reach for this express Internet traffic, while still
allowing deployment of the C-band as traditional long haul for legacy-type traffic,
a deployment that requires multiple traffic add/drop sites. This mix of traditional
long haul in the C-band and extended long haul in the L-band allows for better
network flexibility.
Amplification Extended to Metro, Long Haul
The key drivers for this application include a reduction in the cost of bandwidth
(that is, a reduction in price/performance and distance, an increase in network
capacity, higher network availability, and better network flexibility).
Reduction in Cost of Bandwidth
In conventional long-haul (EDFA) technology, the transmission signals must be
regenerated every 500 km or so to overcome signal distortion due to dispersion
and nonlinear effects and to overcome the build-up of noise generated within the
EDFA amplifiers. This regeneration is accomplished through optical-to-electrical-
to-optical (O E O) conversion, the signal being regenerated during the electrical
phase. This regeneration equipment is required on a per-channel basis and is,
therefore, very expensive, and it also requires a large equipment footprint and
high electrical power consumption and subsequent site climatic control. If a
hybrid distributed Raman amplifier plus EDFA technology is used, the
regeneration-site spacing can be extended from 500 km to 2,000 km. This
extended long-haul application, therefore, introduces significant cost savings
and reduces the dollar cost of transmission capacity for digital signal (DS3) per
kilometer.
Network Capacity
A limiting factor in DWDM systems that restricts the minimum channel spacing
and, therefore, the capacity of the system lies in pulse distortions and
interference that arises from nonlinear effects. Four-wave mixing (FWM) and
cross-phase modulation (XPM) are two such nonlinear effects that are channel-
spacing dependent and, therefore, restrict the minimum channel spacing and
ultimate fiber capacity. However, the efficiency of these nonlinear effects is
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dependent on the channel signal power. Using the Raman amplification
effectively reduces the "apparent" loss of the transmission fiber that the signal
sees. Therefore, the "per-channel" power launched by the EDFA can be reduced,
and this reduction in per-channel power reduces nonlinear effects in the fiber
and allows closer channel spacing and greater system capacity.
Network Availability
The network availability is determined from the failure in time (FIT) rates of the
components that make up the network. The regeneration sites that are placed
every 500 km in conventional EDFA based networks are "heavy" in high-speed
electronics and optical components and, therefore, have the highest FIT rate and
thus the highest failure rate in the network. Using hybrid distributed Raman
amplifiers plus EDFA amplification in extended long-haul systems dramatically
reduces the number of regeneration sites, yielding significantly higher network
availability.
Channel Spacing
With enhancements in demultiplexing technology, it is now possible to deploy
DWDM systems with 50-GHz channel spacing at 10-Gbps rates. This scenario
allows for greater channel counts and, therefore, higher capacities. Previously in
the C-band with 100-GHz spacing, it was possible to deploy 40 channels; with
50-GHz spacing, this figure has been doubled to 80 channels.
Improved transmitter wavelength stability is required to achieve 50-GHz channel
spacing. "Wavelength locking" of transponder transmitter lasers has been
introduced to achieve improved wavelength stability. The local feedback loop
ensures long-term accuracy of the transmitter laser wavelength over the
operating temperature range of the system.
With the closer channel spacing, multichannel, nonlinear effects such as FWM
and XPM become more critical. To control these nonlinear effects, automatic
power provisioning (APP) of the amplifiers is required to control and maintain
channel launch powers below nonlinear thresholds. To maintain span distances
with the greater channel counts and with the requirement to maintain per-
channel launch power below nonlinear thresholds, greater sensitivity is required
in the receivers. This (change increased to greater) increased sensitivity has been
achieved through the introduction of out-of-band forward error correction (OOB
FEC) transponders. The 7-dB FEC gain, in fact, allows for enhanced span
distances, even with this increased capacity.
Until recently, the EDFA gain bandwidth was restricted to the so-called C-band, a
wavelength band of about 35 nm spanning from just below 1530 nm to just over
1560 nm. However, by optimizing the erbium fiber doping composition and fiber
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design and implementing an improved pumping scheme, it has been possible to
extend the gain bandwidth out past 1600 nm, the L-band.
The introduction of amplifiers for the L-band has allowed for increased system
capacity over the installed fiber plant. This additional bandwidth allows for
growth of up to 80 additional long-haul channels at 50-GHz spacing.
Alternatively, this bandwidth can be used with a hybrid of L-band EDFA
amplifiers and Raman amplification for extended-long-haul applications,
allowing greater reach between costly regeneration sites.
Topics
1. Error Correction, Threshold Control
2. Protection
3. Protocols and Packets
4. Provisioning
5. Provisioning Services
6. Summary
Self-Test
Correct Answers
Glossary
1. Error Correction, Threshold Control
Transmission fiber dispersion, fiber nonlinear effects, and amplifier noise limit
the number of channels and the unregenerated transmission distance of DWDM
systems. These factors can be overcome with OOB FEC transponders to enable a
70 percent increase in the number of channels or a 60 percent increase in the
transmission distance. Additionally, the OOB FEC allows an improvement in the
quality of service (QoS) by guaranteeing a received data channel bit-error rate
(BER) of better than 1.0E 15 OOB FEC coding relies on Reed-Solomon
algorithms to add redundancy bits to the data stream, enabling the identification
and correction of corrupted data bits. These redundant bits take the optical
carrier (OC) 192 data rate from 9.953 Gbps to 10.663 Gbps and yield a 7-dB
improvement in optical signal-to-noise ratio (OSNR) margin compared to non-
FEC transmission. This 7-dB OSNR improvement allows for the improved
channel capacity, transmission distance, and QoS.
To further enhance performance, the 10-Gbps OOB FEC transponders utilize
optimized threshold crossing control in the receiver side of the transponder to set
the decision circuit threshold to the in the received data "eye." When multiple
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traces of the data stream are superimposed on top of each other, the 0s and 1s
form an "eye." The more open the eye, the more reliably the 0s and 1s will be
detected and the better the BER. However, amplitude noise from the EDFA
amplifiers and electronics, phase noise, dispersion effects, and interference
resulting from conversion of phase into amplitude modulation start to close the
eye. As the eye closes, the decision circuit that determines if a bit is a 0 or 1 gives
fewer bit errors if the decision threshold level can adaptively change to the
optimum level. The optical receiver of the OOB FEC line extender modules
(LEMs) and receive transponders (RXTs) feature adaptive threshold crossing
control driven by the number of errored 0s and 1s determined in the bit stream.
The result is improved receiver sensitivity and a resultant improvement in BER
performance.
2. Protection
As mentioned previously, traditional networks have been optimized for voice
traffic, from both transport and protection levels. Many network topologies exist,
from point-to-point, ring, and hub-and-spoke to fully meshed networks.
Meshed networks fall outside the common Telcordia specified protection
schemes of Bidirectional Line-Switched Ring (BLSR) and Universal Path-
Switched Ring (UPSR). As a result, legacy SONET equipment manufacturers
have not offered viable solutions for meshed networks. With its path-protected
meshed network (PPMN) capability, Cisco has extended the simple concept of
path protection on a SONET ring to meshed networks, offering service providers
a new degree of flexibility in designing their networks.
Meshed Networks
"Meshed networks" refers to any number of sites arbitrarily connected together
with at least one loop. For this discussion, the connections between sites are
SONET, at various line rates. Sites within the meshed network that can be
reached from other sites through at least two distinct routes form the mesh,
whereas the remaining sites are spurs off of this mesh. Meshed networks are
often large rings with numerous sub-rings, as shown in Figure 1.
Figure 1. Sample Meshed Network
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With PPMN, a network planner can design the mesh shown in Figure 1 with
unprotected spans and various line rates. If a failure occurs on a route,
connection is re-established through another path in the mesh within the well-
known SONET restoration time of 50 milliseconds. By designing PPMN
consistent with SONET standards, Cisco offers network planners flexibility they
can use today.
Practical PPMN Networks
Good ideas are usually simple, and this one is no different. By using path
protection, PPMN simply extends the UPSR beyond the basic ring topology to the
meshed architecture. The software locates two diverse routes in the network
between the source and destination of a circuit. These two routes form a logical
ring for the path of that circuit, and they behave exactly as UPSR. The source
bridges its traffic onto each of the diverse paths, and the destination selects
between the two paths. With a failure on the active path, the destination simply
switches to the standby path within 50 ms. Again, because of the strict adherence
to SONET standards, PPMN applied to the logical ring is no different from the
standard, Telcordia-specified UPSR.
The real benefit of PPPN, however, lies not in the development of PPMN itself,
but in the user interface. Cisco's Java-based graphical user interface (GUI), the
Cisco Transport Controller, makes provisioning within a meshed network as
simple as clicking a mouse button. All the nodes on the network, as soon as they
are turned up, begin the process of autodiscovery. Within minutes, each node has
a full description and status of the other nodes and connections throughout the
network. (This scenario is possible because Cisco uses Internet protocol [IP] and
Open Shortest Path First [OSPF] for SONET Data Country Code [DCC]
communications). Creating a circuit is then accomplished by simply specifying
the source and destination, another Cisco innovation called A-Z Provisioning.
Software then determines the shortest path through the network and establishes
all the intermediate cross-connections. A check box determines whether the
circuit is to be protected or not. When checked, PPMN is provisioned. A protect
circuit is established on the second-shortest path through the network between
the source and destination, and a second set of cross-connections is created. With
this capability, turn-up and provisioning of circuits can be done in a matter of
hours rather than days.
Cisco COMET Applications in Meshed Topologies
The following is an example of PPMN in the meshed network shown in Figure 1.
Suppose a protected circuit is specified between nodes C and J. The PPMN
software will determine that the shortest route between the two end nodes passes
through node H and node G. Cross-connections at each of the four nodes (C, H,
G, and J) are then automatically created, and working traffic is initially carried on
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this route. Concurrently, cross-connections are created for the protected traffic
on the second-shortest unique route between nodes C and J, C  B  A  L  J. If
a fiber is cut or other failure occurs on the primary route, node J immediately
switches to the traffic coming in from node L (instead of node G), and service
resumes. Figures 2 and 3 offer graphical descriptions of this scenario and also
show how the ring formed by A  B  C  H  G  J  L is a UPSR ring for this
circuit.
Figure 2. Working and Protecting Traffic Routed through a
Meshed Network
Figure 3. Failure on Primary Path in Meshed Network
Another application for PPMN in meshed Cisco COMET networks is building
what is commonly called "virtual rings." Figure 4 shows nodes A, B, C, and D
forming an existing OC 192 backbone ring. Nodes E, F, G, and H are then added
with OC 48 links to the backbone. The ring formed by E  F  G  H, which uses
some of the bandwidth on the OC 192 backbone, is termed a "virtual ring."
Protecting circuits created in this network topology is no different from the
aforementioned example. Furthermore, PPMN does not care if the OC 192
backbone is UPSR or BLSR, as long as there is protected path from source to
destination.
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Figure 4. Example of a Virtual Ring
Protection for Ethernet MANs
With Ethernet the accepted Local-Area Network (LAN) standard, many
organizations are looking to extend Ethernet into the metropolitan-area network
(MAN). This in turn provides numerous consequences with regard to how the
network will handle this type of traffic from both QoS and protection levels.
Although Ethernet provides a tremendous foundation on which to build this
next-generation network, fully realizing this end-to-end solution requires an
Ethernet with carrier-class robustness. New capabilities are necessary to provide
comprehensive Operations, Administration, Maintenance, and Provisioning
(OAM&P) in a unified Ethernet optical environment. Ethernet must provide
optical performance monitoring to help carriers deliver quality services meeting
committed service-level agreements (SLAs). If an optical failure occurs, Ethernet
must provide alarm indications and failure-protection mechanisms and help with
fiber-failure isolation.
QoS and class-of-service (CoS) capabilities are required to segregate and
differentiate applications in a public services environment. Ethernet must
continue to efficiently transport IP traffic while meeting the additional delay-
sensitive requirements of certain applications. Optimizing this data traffic
requires integrated routing and control for both IP and optical layers to build an
optimal Cisco COMET network.
3. Protocols and Packets
Resilient Packet Ring Technology
As service providers struggle to keep up with the demands of their customer base
in the MAN, packet-based technologies are migrating from the traditional LAN to
the MAN. Enterprise application growth is driving the increased bandwidth
requirements and exceeding the existing capacity limits of the transport
architectures in most provider networks. Until now, providers have generally
deployed TDM technologies such as SONET/Synchronous Digital Hierarchy
(SONET/SDH) for their offerings in this space. Inherent to Time Division
Multiplexing (TDM) architectures, bandwidth is allocated in fixed amounts on
point-to-point style circuits. This technology was successful for transporting
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traditional voice, circuit-switched links, but the growth of pure data transport has
exceeded the capacity in many networks. In addition, providers are finding it very
difficult to provision new services quickly and expensive to upgrade to meet the
demands of their customers. Therefore, providers have been forced to look to
packet-based technologies to scale these needs.
When reviewing the options available to scale this need, one immediately thinks
of Ethernet as the leader for the inexpensive and flexible transport of packet-
based topologies. However, Ethernet relies on the Spanning-Tree Protocol
(802.1d) to provide for loop detection and elimination, generally recovering from
a fault in 5 to 30 seconds.
SONET offers the ability to provide protection from physical and logical failures
in the ring in 50 ms based on the automatic protection switching (APS) standard.
Whereas some proprietary technologies exist for recovery in shorter periods, the
50 ms recovery time was needed for many of the voice services carried over these
networks. In addition to recovery issues, Ethernet is based on point-to-point,
non-meshed physical layouts not conducive to deployment over the existing ring-
based architectures of SONET. These two keys issues left providers with few
options for solving the bandwidth needs of their customers.
Enter packet-ring technologies. Cisco introduced Dynamic Packet Transport
(DPT) in early 1999 based on a new concept called Spatial Reuse Protocol (SRP).
This protocol takes advantage of both the ring-based architecture of SONET and
the packet characteristics of Ethernet. DPT emerged as a new standard for
deployment of these services for many providers seeking a solution without
requiring the replacement of their existing fiber infrastructures. The Institute of
Electrical and Electronics Engineers (IEEE) standards body quickly embraced
this technology; subsequently, a new group was formed to advance the
standardization of the technology. Many participate in this group, and they all
work to make Resilient Packet Ring (RPR) technology more robust and
interoperable.
The working group rapidly adopted numerous objectives set forth to drive the use
of RPR technology into the service-provider market:
" Distributed Access There is no "master node" required in an RPR ring,
allowing for the loss of any node in the ring without affecting ring
operation.
" Destination Stripping for Unicast Frames In other packet-ring
technologies, such as token ring, unicast frames must transit the entire
ring to be removed only by the sending node after the intended receiver
(802.5, Frame Copy Indication [FCI]) copies them. In RPR, the
destination node removes unicast frames as they arrive, thereby freeing
the bandwidth for downstream nodes.
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" "Plug-and-Play" Support This operation allows new nodes to be easily
added to a ring without manual configuration or reconfiguration of other
nodes in that ring.
" Bandwidth Distribution Bandwidth is dynamically allocated to
competing flows on demand as they enter the ring. Theories specific to this
area abound. Currently, Cisco's DPT technology protects traffic already on
the ring and queues traffic bound for the ring. The standards body has not
reached an agreement on how this area should be handled in the draft
specification.
" Dual-Ring Topology Unlike SONET, which uses one ring to transmit live
traffic and the other for protection, RPR utilizes both directions. By using
both rings, transmitting data in opposite directions at the same time, RPR
substantially increases fiber utilization.
" Rapid Protection Switching RPR offers restoration from ring
interruption in less than 50 ms. This restoration feature is very important
for providers looking to maintain ring stability if a fiber is cut. In many
voice networks, it is critical to the support of circuit-switched traffic. Also,
as more IP traffic is deployed carrying loss-sensitive data, protection
switching will help guarantee that traffic is not lost.
" Multicast Traffic Support Multicast traffic travels around the entire ring
one time. This topology is very different from mesh-based topologies
where multicast traffic must be replicated by each device in the network in
order to reach all destinations.
" Universal Physical-Layer (PHY) Support RPR is a Media Access Control
(MAC) layer specification and, therefore, allows the use of existing PHYs
already available.
" Multi-Gigabit Ethernet Transport RPR can carry 10/100-Mbps Ethernet
as well as 1 Gbps and 10 Gbps.
" QoS Support The goal of RPR is to deliver TDM like QoS offerings to
enable service providers to offer many varying services while maintaining
customer SLA requirements for jitter and guaranteed-bandwidth services.
Structured Design and Architecture for Cisco
COMET Metro Ethernet Networks
Regardless of whether a pure, switched Layer-2 network or an Ethernet-over-
multiprotocol label switching (EoMPLS) network is utilized, careful
consideration of numerous parameters must be made. The following sections
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provide some general guidelines that must be considered before designing and
deploying a metro network.
Failure Domain
A Layer-2 switched domain is considered to be a failure domain because a
misconfigured or malfunctioning workstation can introduce errors that impact or
disable the entire domain. For example, a jabbering network interface card (NIC)
might flood the entire domain with broadcasts or undesirable frames at a very
high rate. A protocol malfunction (for example, spanning-tree error or
misconfiguration) can inhibit a large part of the network. Problems of this nature
can be very difficult to localize in a flat, switched Ethernet environment.
Therefore, care must be taken in terms of how this type of network is deployed.
In this model, it is strongly recommended that each enterprise customer be
mapped to a virtual LAN (VLAN). This set-up affords the service provider the
ability to segment the network by customer. Although it could be possible to have
multiple enterprise customers per VLAN, this set-up is considered undesirable
for numerous reasons. First, an unexpected broadcast storm in one customer's
network could affect the performance of the other customers on that VLAN.
Second, and perhaps more important, the customers will have the ability to
"sniff" the other customers' traffic, providing for massive security breaches.
Finally, because of the inherent ability to sniff Ethernet traffic on the wire, a
malicious individual could cause significant damage to multiple customers'
networks. This scenario could potentially leave the service provider open to
violations in its SLAs to its customers, to say nothing of a poor customer-service
situation.
Service providers can take many steps to limit the failure domain per VLAN.
First, service providers can limit the number of switches that are participating in
that VLAN. Cisco's VLAN trunking protocol (VTP) can enable every switch in the
network to be aware of a new VLAN in the network and to autoconfigure trunk
ports and spanning trees. In an enterprise network, this feature can be very
helpful, but it can be highly detrimental in a service provider's Layer-2 network.
Therefore, VTP should be disabled and VLANs manually configured as needed
per switch. Secondly, Cisco technology can specify VLANs that are enabled on the
802.1Q trunk links. Only the VLANs of interest should be configured on a trunk
link. Finally, the topology of the network should be well known and mapped out,
both generally and specifically, per VLAN. This scenario allows the service
provider to better isolate potential network faults.
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Topology and Spanning-Tree Protocol
Considerations
The topology of the network refers to the way in which the network is physically
connected. It is very important for the service provider to understand the layout
of the network and how to plan for its interconnection. If a service provider is
implementing an Ethernet service over a SONET or Wavelength Division
Multiplexing (WDM) network, then the Ethernet topology is more
straightforward. In this case, the Ethernet network does not need to account for
redundancy because redundancy can (and should) be accounted for at the
transport layer by SONET or WDM. After all, SONET and WDM have
significantly faster convergence times than spanning tree (50 milliseconds versus
50 seconds), meaning that spanning tree may not be necessary and Ethernet can
be run in a simple point-to-point configuration with no loops.
However, if the service provider is building the network based on pure Ethernet
transport, then the Ethernet topology becomes critically important. The first
thing to account for is summarized by the rule: "If some redundancy is good,
more redundancy is not better!" This mistake is one of the major ones made by
network architects utilizing spanning tree and Ethernet. Spanning tree requires
control packets (called bridge protocol data units, or BPDUs) to be sent out and
processed by each switch in the broadcast domain to stabilize the topology and
reroute around failures. The more complicated the network, the more time it will
take for the network to converge. In addition, a large Layer-2 switched network
may enter a state in which the central processing unit (CPU) is so busy processing
BPDUs that some are missed, preventing the spanning tree from ever recovering.
It was not uncommon in the early days of VLANs to have a network in such a
state that all redundancy had to be removed just to stabilize the network.
The network should be designed in such a way that the primary and secondary
root bridges of the spanning tree can be easily and readily identified. These
switches should be located in a central point of presence (POP).
Virtual LANs
A VLAN is essentially an extended Layer-2 switched domain that is, a broadcast
domain that extends as far as the VLAN reaches. If several VLANs coexist across
a set of Layer-2 switches, each individual VLAN has the same characteristics of a
failure domain, broadcast domain, and spanning-tree domain, as described
previously. Therefore, although customers can use VLANs to segment the metro
network, deploying pervasive VLANs throughout the metro introduces
complexity and reduces the deterministic behavior of the network. Avoiding
loops and restricting VLANs to the specific Layer-2 switch where they have a
presence minimizes the complexity.
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802.1Q Encapsulation
802.1Q encapsulation, often referred to as QinQ, provides a VLAN tunneling
mechanism by encapsulating a frame tagged with an 802.1Q header with another
802.1Q header. (Extreme Networks has similar functionality; its solution is called
Virtual MAN, or VMAN.) This means that an enterprise could transport multiple
VLANs across the service provider's network without interfering with the service
provider's VLAN identifications. For example, Acme, Inc. could send 10 VLANs,
with IDs 1 through 10, into the service-provider cloud. The service provider
would encapsulate those frames with another 802.1Q header with its own VLAN,
let's say VLAN 100. The service provider would transport VLAN 100 across its
own network and, wherever VLAN 100 terminated, out would come the 10
customer VLANs. In theory, this means that a service provider could support
4,096 VLANs, with each VLAN containing 4,096 customer VLANs.
Some practical issues must be considered when implementing a QinQ
encapsulation. First, QinQ assumes that customers want to transport their
VLANs and spanning trees across a MAN or WAN, and, as discussed previously,
this assumption is not true for most enterprise customers. This assumption has
led to the failure of many previous transparent LAN services (TLSs). Second, one
of the main benefits of QinQ is that, in theory, it scales the number of VLANs in
the network from 4,096 to 40,962, or 16,777,216 VLANs. In reality, however, it is
unlikely that an enterprise customer would be willing to put its VLANs in a
service provider's "super-VLAN" with numerous other customers. The risk for
security breaches and spanning-tree events damaging their network is far too
great. Keep in mind that the service provider will still switch frames based on
only the "outer" tag, not both tags.
Ethernet over Multiprotocol Label Switching
Many service providers are looking to expand their metro networks to very large
scales or perhaps to inter-metro areas. A pure Layer-2 solution is limited by the
IEEE 802.1Q specification to 4,096 VLANs. Therefore, a service provider would
be able to support only 4,096 customers within the metropolitan area. To scale
beyond the 4,096 VLAN limit, EoMPLS can be utilized.
Using this technology, a particular VLAN can be mapped to an EoMPLS tunnel.
The provider-edge router will then transport that tunnel through the MPLS
network. It is important to note a few points here regarding MPLS and its
Ethernet type. First, MPLS resides on top of an IP network backbone. This set-up
inherently allows the network to scale as well as provides the mapping between
the MPLS label and some underlying intelligence. Therefore, it is strongly
recommended that the network architect understand the best practices and
guidelines for IP routing deployment on such protocols as OSPF, Intermediate
System-to-Intermediate System (IS-IS) or Border Gateway Protocol (BGP).
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Secondly, EoMPLS is a point-to-point solution only (based on the Martini draft;
there is a follow-up draft that has not been readily adopted called Kompella,
which allows for an Ethernet point-to-multipoint broadcast domain). For
example, if the service provider wants to transport VLAN 100 across an EoMPLS
network, the other side of the MPLS cloud can have only a single exit point. This
issue, however, is not important in network design, because the enterprise will
utilize multiple VLANs, one per destination site exiting the MPLS cloud.
Examples of how to set up this scenario are discussed later in this tutorial.
Cisco COMET UCP Protocols
Perhaps more important than the technology differences between each protocol
is how customers intend to apply each of the protocols. The way service providers
apply unified control plane (UCP) protocols is important later in this section,
where both the specific feature requirements and platforms and relevant
protocols for different opportunity areas are discussed.
Figure 5. O ONI and GMPLS Protocols
Figure 5 illustrates the basic aspects of both Generalized Multiprotocol Label
Switching (GMPLS) and Optical User-to-Network Interface (O UNI) protocols
and how the protocols apply to routing both within a domain and between a user-
(or client)-side interface and that domain. O UNI is illustrated on the right side
of the network, emphasizing that there is a clearly delineated boundary between
which a client-side UNI device (O UNI C) communicates with a network-side
UNI device (O UNI N). The differences between the function of the O UNI C
and the O UNI N is that the O UNI C provides a signaling termination
function, whereas O UNI N provides a signaling pass-through and interworking
function, circuit routing, and reachability information. Between the nodes on this
interface, information about light paths available on the network is presented.
Light paths are illustrated in Figure 5 by the lines above the O UNI interface. If
O UNI is employed, the optical transport network (OTN) can run any kind of
routing, including GMPLS, other standards such as Private Network-to-Network
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Interface (PNNI) or OSPF, or even a proprietary routing protocol can be
employed.
The interface between an edge GMPLS node and a GMPLS label-switched router
(LSR) on the network side can also be referred to as a User Network Interface
(UNI), whereas the interface between two network-side LSRs may be referred to
as a Network-to-Network Interface (NNI). Nonetheless, GMPLS does not specify
separately a UNI and a NNI protocol, an important point to understand when
looking at the requirements. In GMPLS, edge nodes are simply connected to
LSRs on the network side, and these LSRs are in turn connected between them.
There is no delineated boundary over which a distinct protocol function is
introduced such as with O UNI. Of course, the lack of defined boundary and
distinct protocol set does not mean the behavior of an edge node needs to be
exactly the same as the behavior of an LSR on the network side. Specifically, in
the aforementioned case, the edge node might be responsible for signaling paths
across the network. If GMPLS is used, however, the edge node needs to
communicate as a peer to the network-side device. Specifically, the two network
elements will share topology, addressing, and other types of routing information.
In fact, the boundaries between devices are not only divided along protocol
layers, but they are also divided between different operations management
groups. Indeed, service providers typically have two or more distinct operations
groups specific to either data service or transport layers. Typically one group
owns the provisioning, operations, and management of the transport and another
is responsible for the functions for data services. Communications between the
data-services and transport organizations are defined by a workflow process
whereby orders are submitted by the data-services group and then subsequently
filled by the transport group. This group distinction has a major impact on the
choice of protocols. Service providers with distinct groups where one supports
data services and the other supports transport services are more inclined to
desire strict adherence to a non-routing enabled boundary between the two
administrative functions of these groups. Here O UNI is a preferred method
because it separates the roles of each operations department.
4. Provisioning
One new technology that will simplify provisioning is called the unified control
plane, or UCP. UCP represents a common set of control functions and
interconnection mechanisms that allow unified communication, routing, and
control across disparate types of underlying transport technologies (for example,
IP, ATM, SONET/SDH, and DWDM). Traditionally, each specific technology has
its own control protocols and, as a result, cannot communicate directly with the
others. Networks are layered one on top of the other, creating overlays at each
layer to collectively provide end-user services. Obviously, this process requires
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knowledge of each technology domain, provisioning of each layer, and separate
management of per-domain operations functions.
Cisco's UCP uses a set of industry-standard common addressing, routing, and
signaling protocols that uniformly communicate and control across different
transport technologies. Quick deployment of IP applications and services results
from flow-through provisioning of services at single touch points of service
access. No longer will providers need to configure connectivity over each
technology domain separately and manually correlate cross-layer connectivity as
they do today. Figure 6 depicts an abstraction of the IP based control plane over
different types of transport networks.
Figure 6. Unified Control Plane
To address the determination of the appropriate control-plane architecture, the
industry has embraced extending MPLS for integrating data and optical network
technologies. MPLS provides an attractive foundation for the optical control-
plane architecture, because MPLS has natural separation between its data and
control planes. Hence, the Internet Engineering Task Force (IETF) has extended
the MPLS label-switching concept to include other types of forwarding planes.
For example, if we extend the definition of a label, MPLS can be applied to
wavelengths, and the wavelength acts as its own label. The extended MPLS
protocols considered a superset of MPLS are called Generalized MPLS, or
GMPLS.
It is important to note that GMPLS does not define separately edge nodes
connected to the network that imply boundaries between user and network
planes. The interface between an edge GMPLS node and a GMPLS LSR on the
network side is often referred to as a user-to-network interface, or UNI. To
support the UNI case specifically, the Optical Internetworking Forum has
extended several GMPLS components and defined a set of UNI protocols
explicitly. The protocols are known as Optical User-to-Network Interface, or O
UNI, whereby the client-side device runs O UNI C protocols and the network-
side device runs O UNI N protocols. O UNI provides a user-to-network
bidirectional signaling interface between the service requester and service-
provider control-plane entry point and does not share routing information across
these domains.
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UCP will include both O UNI and GMPLS protocols under the Cisco UCP
umbrella to provide essential flexibility in addressing a variety of service and
network models. Providers can select, apply, and deploy the UCP protocol that
best meets their situation, given their own specific organizational, architectural,
or other requirements or constraints.
5. Provisioning Services
The historical context around how optical networks have been designed and
deployed provides much appreciation for why new requirements (for example,
efficient and timely provisioning and management) and services (for example,
on-demand services, CoS, communities of interest) are prevailing challenges
today. New network requirements invalidate the assumptions upon which legacy
networks were founded. Indeed, the communications networks that exist today
were designed primarily for private-line and voice service using circuit switching.
Capacity was portioned out in 64-kbps pieces (the size of an uncompressed voice
channel) using multiple layers of hierarchy. Typically these networks required
several months to deploy a service. This time frame met requirements then
because the traffic demand was quite predictable and assumed to remain static
for years at a time. As the business case for providing data services became
attractive, service providers retrofitted their network typically by yet another
layering of protocols to support multiple data-service interfaces and networks,
including ATM, Frame Relay, and IP.
Layering became an issue as data services became the predominant service
relative to voice and private-line services. The unpredictable nature of data traffic
as well as its flow-direction uncertainty and continual changes invalidated initial
assumptions for voice networks. Procedures to provision services, reserve new
bandwidth, or change network parameters to address growing traffic volumes or
meet customer demands across the network over multiple protocol layers are
time consuming, administratively difficult, and workforce intensive. Overlay
networks require management of their different layers, such as the IP and ATM
layers, as though they are separate networks. Intelligence can be implemented for
some layers but is limited to the specific layers where it is implemented. Layers
do not communicate with each other, so management and scalability of the
network are compromised. Disparate technology layers also limit the ability to
engineer traffic to maximize network and resource efficiency and avoid points of
congestion. Functions are often duplicated, and network management and
control algorithms can even work against each other in a layered protocol
network, creating conflicts and oscillations. And restoration, performed in
varying time scales across multiple layers, is uncoordinated and in most cases
resource inefficient. Additionally, complications of tunneling the protocols of one
technology over another results in inefficiencies due to framing and packet
overhead, multiple instances of sometimes-conflicting functions, and the inability
to optimize based on desired service granularity.
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Obviously, a more dynamic and cost-effective network model that provides on-
demand set-up of a wide range of differentiated Cisco COMET services and the
ability for each class of traffic to be defined and treated appropriately is needed.
To help service providers sustain profitability though automated provisioning
and optimized delivery of optical services, Cisco UCP technology offers a means
to address this overarching need for a more dynamic and cost-effective network-
control model. UCP can help carriers to increase profitability by specifically
addressing the operational expenditures (OPEX) associated with the deployment
and management of services over multiple technology networks. Not only will
UCP technologies help carriers reduce their OPEX cost, but UCP will also
enhance profitability for high-capacity traffic transport by enabling carriers to
deploy new, value-added Cisco COMET services and do so very quickly to market.
The new UCP enabled optical network needs to provide the foundation for
delivering an emerging, yet-to-be-defined portfolio of optical services.
On the transport side of providers, UCP is seen initially as a means to tie together
multivendor domains through the use of O UNI. Desired here is one method of
access to provision across the entire optical transport network, despite having
multiple domains of different vendor equipment. Figure 7 illustrates this concept
of provisioning across multiple-vendor domains within the transport network.
Longer-term, transport architects realize that UCP has a broader and more
significant meaning to service providers.
Here, GMPLS represents a standard protocol for optical transport network
elements. Providers welcome the move from proprietary protocols to open,
standards-based protocols. Standards-based protocols will allow providers
substantial cost savings by enabling them to introduce any vendor equipment
into any given domain. A best-of-breed strategy traditionally has not been
available and has been denied by those trying to "lock in" the provider in using its
equipment at great cost to the provider. GMPLS is also sought in the transport
because of its IP like features, such as self-discovery and dynamic optimization
and provisioning. Transport providers see the combination of the O UNI and
GMPLS protocols as a way to facilitate a seamless evolution to next-generation
technologies without having to upgrade or replace network equipment. Service
providers understand that GMPLS may not exist in all Cisco SONET/SDH
products from the start. They are, however, interested in seeing the path toward
GMPLS, because this represents to them Cisco's commitment toward standards-
based technologies.
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Figure 7. Provisioning Across OTN with Multiple Vendor
Domains
6. Summary
This document has discussed how photonics, protection, protocols, packets, and
provisioning insert into the metro edge, metro core, and long-haul and extended-
long-haul segments. It is important to remember that the Cisco innovations are
ongoing and that legacy equipment will not disappear over night. The enterprise
and service providers still need to protect and provide existing services when
migrating or evolving their current architecture offerings. In addition, service
providers will need to take advantage of the existing infrastructure. The focus on
network evolution is paramount to profitability of providers with existing
network and operations management infrastructure.
Figure 8. Cisco's Coment Technical Innovations
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Self-Test
1. In conventional long-haul (EDFA) technology, the transmission signals must
be regenerated every ______ or so to overcome signal distortion due to
dispersion and nonlinear effects.
a. 2 km
b. 10 km
c. 100 km
d. 500 km
e. 5,000 km
2. In DWDM systems, channel spacing is limited by nonlinear effects such as
four-wave mixing (FWM) and ____________.
a. Attenuation
b. Cross-phase modulation (CPM)
c. Bit-error rate (BER)
d. Failure in time (FIT)
e. Wavelength division multiplexing (WDM)
3. The network availability is determined from the _____________ rates of
the components that make up the network.
a. Attenuation
b. Cross-phase modulation (CPM)
c. Bit-error rate (BER)
d. Failure in time (FIT)
e. Wavelength division multiplexing (WDM)
4. With its __________________ capability, Cisco has extended the simple
concept of path protection on a SONET ring to meshed networks, offering
service providers a new degree of flexibility in designing their networks.
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a. Bidirectional line-switched ring (BLSR)
b. Unidirectional path-swtiched ring (UPSR)
c. Sub-network connections protection (SNCP)
d. Path-protected meshed network (PPMN)
e. Optical signal-to-noise ratio (OSNR)
5. Cisco uses IP and _______________ for SONET data communications
channel (DCC) communications.
a. RIP
b. EIGRP
c. BGP
d. IS IS
e. OSPF
6. ________ application growth is driving the increased bandwidth
requirements and exceeding the existing capacity limits of the transport
architectures in most provider networks.
a. Enterprise
b. Service provider
c. Home user
d. Government
e. Small office
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7. A jabbering network interface card (NIC) might flood the entire domain with
__________ or undesirable frames at a very high rate.
a. Unicast
b. Mulitcast
c. Broadcast
d. Simulcast
e. Duocast
8. 802.1Q encapsulation, often referred to as _____, provides a VLAN
tunneling mechanism by encapsulating a frame tagged with an 802.1Q header
with another 802.1Q header.
a. VLAN
b. MPLS
c. LRE
d. QinQ
e. O E O
9. Cisco introduced dynamic packet transport (DPT) in early 1999 based on a
new concept called spatial reuse protocol (SRP). This protocol takes
advantage of both the ring-based architecture of SONET and the packet
characteristics of ________.
a. ATM
b. Frame relay
c. Ethernet
d. X.25
e. Appletalk
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10. The interface between an edge GMPLS node and a GMPLS label-switched
router (LSR) on the network side can also be referred to as a _________,
whereas the interface between two network-side LSRs may be referred to as a
__________.
a. OPEX, CAPEX
b. UNI, NNI
c. LSR NS, LSR NBS
d. EGMPLS, NGMPLS
e. NE, FE
11. Transport providers see the combination of the O UNI and GMPLS protocols
as a way to facilitate a seamless evolution to next-generation technologies
without having to upgrade or replace network equipment. Service providers
understand that GMPLS may not exist in all.
a. true
b. false
12. GMPLS defines separately edge nodes connected to the network that imply
boundaries between user and network planes.
a. true
b. false
13. UCP will include both O UNI and GMPLS protocols under the Cisco UCP
umbrella to provide essential flexibility in addressing a variety of service and
network models.
a. true
b. false
14. A VLAN is essentially an extended Layer-2 collision domain.
a. true
b. false
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15. Ethernet relies on the spanning-tree protocol (802.1d) to provide for loop
detection and elimination, generally recovering from a fault in five to 30
seconds. SONET offers the ability to provide protection from physical and
logical failures in the ring in 50 ms based on the automatic protection
switching (APS) standard.
a. true
b. false
Correct Answers
1. In conventional long-haul (EDFA) technology, the transmission signals must
be regenerated every ______ or so to overcome signal distortion due to
dispersion and nonlinear effects.
a. 2 km
b. 10 km
c. 100 km
d. 500 km
e. 5,000 km
2. In DWDM systems, channel spacing is limited by nonlinear effects such as
four-wave mixing (FWM) and ____________.
a. Attenuation
b. Cross-phase modulation (CPM)
c. Bit-error rate (BER)
d. Failure in time (FIT)
e. Wavelength division multiplexing (WDM)
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3. The network availability is determined from the _____________ rates of
the components that make up the network.
a. Attenuation
b. Cross-phase modulation (CPM)
c. Bit-error rate (BER)
d. Failure in time (FIT)
e. Wavelength division multiplexing (WDM)
4. With its __________________ capability, Cisco has extended the simple
concept of path protection on a SONET ring to meshed networks, offering
service providers a new degree of flexibility in designing their networks.
a. Bidirectional line-switched ring (BLSR)
b. Unidirectional path-swtiched ring (UPSR)
c. Sub-network connections protection (SNCP)
d. Path-protected meshed network (PPMN)
e. Optical signal-to-noise ratio (OSNR)
5. Cisco uses IP and _______________ for SONET data communications
channel (DCC) communications.
a. RIP
b. EIGRP
c. BGP
d. IS IS
e. OSPF
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6. ________ application growth is driving the increased bandwidth
requirements and exceeding the existing capacity limits of the transport
architectures in most provider networks.
a. Enterprise
b. Service provider
c. Home user
d. Government
e. Small office
7. A jabbering network interface card (NIC) might flood the entire domain with
__________ or undesirable frames at a very high rate.
a. Unicast
b. Mulitcast
c. Broadcast
d. Simulcast
e. Duocast
8. 802.1Q encapsulation, often referred to as _____, provides a VLAN
tunneling mechanism by encapsulating a frame tagged with an 802.1Q header
with another 802.1Q header.
a. VLAN
b. MPLS
c. LRE
d. QinQ
e. O E O
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9. Cisco introduced dynamic packet transport (DPT) in early 1999 based on a
new concept called spatial reuse protocol (SRP). This protocol takes
advantage of both the ring-based architecture of SONET and the packet
characteristics of ________.
a. ATM
b. Frame relay
c. Ethernet
d. X.25
e. Appletalk
10. The interface between an edge GMPLS node and a GMPLS label-switched
router (LSR) on the network side can also be referred to as a _________,
whereas the interface between two network-side LSRs may be referred to as a
__________.
a. OPEX, CAPEX
b. UNI, NNI
c. LSR NS, LSR NBS
d. EGMPLS, NGMPLS
e. NE, FE
11. Transport providers see the combination of the O UNI and GMPLS protocols
as a way to facilitate a seamless evolution to next-generation technologies
without having to upgrade or replace network equipment. Service providers
understand that GMPLS may not exist in all.
a. true
b. false
12. GMPLS defines separately edge nodes connected to the network that imply
boundaries between user and network planes.
a. true
b. false
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13. UCP will include both O UNI and GMPLS protocols under the Cisco UCP
umbrella to provide essential flexibility in addressing a variety of service and
network models.
a. true
b. false
14. A VLAN is essentially an extended Layer-2 collision domain.
a. true
b. false
15. Ethernet relies on the spanning-tree protocol (802.1d) to provide for loop
detection and elimination, generally recovering from a fault in five to 30
seconds. SONET offers the ability to provide protection from physical and
logical failures in the ring in 50 ms based on the automatic protection
switching (APS) standard.
a. true
b. false
Glossary
APP
Automatic Power Provisioning
APS
Automatic Protection Switching
ATM
Asynchronous Transfer Mode
BER
Bit-Error Rate
BGP
Border Gateway Protocol
BLSR
Bidirectional Line-Switched Ring
BTDU
Bridge Protocol Data Units
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COMET
Complete Optical Multiservice Edge and Transport
CoS
Class of Service
CPU
Central Processing Unit
DCC
Data Communications Channel
DPT
Dynamic Packet Transport
DS
Digital Signal
DWDM
Dense Wavelength Division Multiplexing
EDFA
Erbium-Doped Fiber Amplifier
EoMPLS
Ethernet-over MPLS
FCI
Frame Copy Indication
FEC
Forward Error Correction
FIT
Failure In Time
FWM
Four-Wave Mixing
GHz
Gigahertz
GMPLS
Generalized Multiprotocol Label Switching
GUI
Graphical User Interface
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IEEE
Institute of Electrical and Electronic Engineers
IETF
Internet Engineering Task Force
IP
Internet Protocol
IS IS
Intermediate System to Intermediate System
LAN
Local-Area Network
LEM
Line Extender Module
LSR
Label-Switched Router
MAC
Media Access Control
MAN
Metro-Area Network
MPLS
Multiprotocol Label Switching
NIC
Network Interface Card
NNI
Network-to-Network Interface
O E O
Optical-to-Electrical-to-Optical
O UNI
Optical User-to-Network Interface
O UNI C
Optical User-to-Network Interface Client
O UNI N
Optical User-to-Network Interface Network
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OAM&P
Operations, Administration, Maintenance, and Provisioning
OC
Optical Carrier
OOB FEC
Out-of-Band Forward Error Correction
OSNR
Optical Signal-to-Noise Ratio
OSPF
Open Shortest Path First
OTN
Optical Transport Network
PHY
Universal Physical-Layer
PNNI
Private Network-to-Network Interface
POP
Point of Presence
PPMN
Path Protected Meshed Network
QoS
Quality of Service
RPR
Resilient Packet Ring
RXT
Receive Transponders
SDCC
SONET Data Communications Channel
SDH
Synchronous Digital Hierarchy
SLA
Service-Level Agreement
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SONET
Synchronous Optical Network
SRP
Spatial Reuse Protocol
TDM
Time Division Multiplexing (T1, T3, E1, etc.)
TLS
Transparent LAN Services
UCP
Universal Control Plane
UNI
User-to-Network Interface
UPSR
Unidirectional Path-Switched Ring
VLAN
Virtual LAN
VTP
VLAN Trunking Protocol
WAN
Wide-Area Network
WDM
Wavelength Division Multiplexing
XPM
Cross-Phase Modulation
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