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Traffic Engineering in Multi-Granularity, Heterogeneous,

WDM Optical Mesh Networks Through Dynamic Traffic Grooming

Keyao Zhu, Hongyue Zhu, and Biswanath Mukherjee

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• Introduction

• Node Architecture in Heterogeneous WDM Backbone Networks

• Provisioning connections in Heterogeneous WDM networks

• A Generic Provisioning Model

• Illustrative Numerical Examples

• Future Work

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Introduction

• Traffic engineering： it is an effective solution to control the network congestion and optimize network performance.

• purpose： it is to facilitate efficient and reliable network operations while simultaneously optimizing network resource utilization and traffic performance.

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Traffic Engineering In Optical WDM Networks Through Traffic Grooming

Traffic Grooming• High-bandwidth wavelength channels will be

filled up by many low-speed traffic streams• Efficiently provisioning customer connections

with such diverse bandwidth needs is the traffic-grooming problem.

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Dynamic traffic-grooming problem

• Each such connection needs to be properly routed through the network based on the current network state.

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Optical WDM Network Heterogeneity

Network equipment (NE) may come from different vendors and new equipment has to co-exist with legacy equipment.

For example: • (1) network nodes may have optical crossconnects (OXC

s) employing different architectures and technologies; • (2) not all nodes may have wavelength conversion and tr

affic grooming capabilities• (3) wavelength conversion and traffic grooming may only

be available on certain wavelength channels • (4) different fiber links may support different numbers of

wavelength channels, which may also operate at different speeds.

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Node Architecture in Heterogeneous WDM Backbone Networks

There are transparent and opaque approaches to build these OXCs.

• The transparent approach refers to all-optical (O-O-O) switching

• The opaque approach refers to switching with optical-electronic-optical (O-E-O) conversion.

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Four kinds of OXCs(1/7)

According to their grooming capabilities, OXCs can be divided into four categories

(1)Non-grooming OXC:

• It has wavelength-switching capability.

• There is no low-data-rate port on a non-grooming OXC.

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Four kinds of OXCs(2/7)

(2)Single-hop grooming OXC: • This type of OXC will only switch traffic at wavelength

granularity.• It may have some lower-data-rate ports, which can

directly support low-speed traffic streams.• The traffic from these low-speed ports can be

multiplexed onto a wavelength channel using a TDM scheme, before the traffic enters the switch fabric.

• All of low-speed streams on one wavelength channel at the source node will be switched to the same destination node

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Four kinds of OXCs(3/7)

• Fig. 1(a) shows how a low-speed connection (C1) is carried by a lightpath (L4) from node 1 to node 5 using the single-hop grooming scheme.

• In Fig. 1(a), nodes 1 and 5 are equipped with single-hop grooming OXCs, which can only switch at wavelength granularity.

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Four kinds of OXCs(4/7)

(3)Multi-hop partial-grooming OXC: • the switch fabric of this type of OXC is composed of two

parts: • A wavelength-switch fabric (W-Fabric)• An electronic-switch fabric which can switch low-

speed traffic streams is called grooming fabric (G-Fabric).

• With this hierarchical switching and multiplexing architecture, this type of OXC can switch low-speed traffic streams from one wavelength channel to other wavelength channels and groom them with other low speed streams

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Four kinds of OXCs(5/7)

• Fig. 1(a) also shows how a low-speed connection (C2) can be carried by multiple lightpaths (L1, L2, and L3) from node 1 to node 5.

• nodes 2 and 3 are equipped with multihop partial-grooming OXCs, and only their G-Fabrics are shown in the figure.

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Four kinds of OXCs(6/7)

• In this architecture, only a few of wavelength channels can be switched to the G-Fabric for switching at finer granularity.

• Assuming that the wavelength capacity is OC-N and the lowest input port speed of the electronic switch fabric is OC-M ( M ≤ N ), the ratio between N and M is called the grooming ratio.

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Four kinds of OXCs(7/7)

(4) Multi-hop full-grooming OXC: • Every OC-N wavelength channel arriving

at the OXC will be de-multiplexed into its constituent OC-M streams before it enters the switch fabric.

• Then, the switched streams will be multiplexed back onto different wavelength channels.

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Provisioning Connections in Heterogeneous WDM Networks

There are three important components in

WDM network control, which determine how

connections of different bandwidth

granularities are provisioned.

(1) resource-discovery protocol

(2) route-computation algorithm.

(3) signaling protocol

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Resource Discovery:Four types of lightpaths(1/4)

Multi-hop un-groomable lightpath: • It is not connected with a finer-granularity

switching element at its end nodes.

• This lightpath can only be used to carry the traffic directly between node pair (i, j).

• Lightpath L4 in Fig. 1(a) is a multihop-ungroomable lightpath.

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Resource Discovery: Four types of lightpaths(2/4)

Source-groomable lightpath: • It is only connected with a finer-granularity

switching element at its source node.

• All traffic on this lightpath has to terminate at node j, but the traffic may originate from any other network node as well.

• Lightpath L3 in Fig. 1(a) is a source-groomable lightpath.

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Resource Discovery: Four types of lightpaths(3/4)

Destination-groomable lightpath: • it is only connected with a finer-granularity switc

hing element at its destination node. • All traffic on this lightpath has to originate from n

ode i. At the lightpath destination node j, the traffic on lightpath (i, j) can either terminate at j or be groomed to other lightpaths and routed towards other nodes.

• Lightpath L1 in Fig. 1(a) is a destination-groomable lightpath.

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Resource Discovery: Four types of lightpaths(4/4)

Full-groomable lightpath:

• It connects to finer-granularity switching elements at both end nodes.

• Lightpath L2 in Fig. 1(a) is a full-groomable lightpath.

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Resource Discovery: Link type(1/3)

we present the link state of each network link type as follows.

Fiber Link: The representation of a fiber link (in a full wavelength-

convertible network) can be denoted as f (m, n, t, w, c)• m and n : the end nodes of the fiber link• t : fiber index (for numbering multiple fibers between the

same node pair)• w : the available (free) wavelength channels on that fiber• c : the administrative link cost.

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Resource Discovery: Link type(2/3)

• If there are multiple fibers between the same node pair, they may be further bundled.

• The purpose of link bundling is to improve routing scalability by reducing the amount of information that has to be handled by the network control plane.

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Resource Discovery: Link type(3/3)

Virtual Link: The representation of a lightpath can be denoted as l (i, j, v,

t, m1, m2, c)• i and j : the end nodes of the lightpath• v : the lightpath type• t : the lightpath id• m1:the minimal reservable bandwidth on this lightpath, w

hich is determined by the grooming ratio of the end nodes

• m2 : the maximal reservable bandwidth on this lightpath,which is bounded by the total available (free) capacity on the lightpath

• C: denotes the administrative link cost.

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Route Computation(1/2)

The route of a connection request will be

computed either by the source node of the request

or by the network control and management system.

Let Req(s, d, r) denote a connection request

s : the source node

d : the destination node

r : the capacity requirement of the connection.

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Route Computation(2/2)

• Carry Req using an existing lightpath l(s, d, v, t, m1, m2, c) between nodes s and d, if m1≤r ≤m2 .

• Carry Req using multiple existing groomable lightpath.

• Carry Req by establishing a new lightpath (either groomable or non-groomable) between node pair (s, d) if enough resources exist.

• Carry Req using a combination of both existing groomable lightpaths and setting up new groomable lightpaths using available wavelength channels in fiber links and grooming resources in network nodes.

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Signaling

• After a route is successfully computed, every intermediate node along the route needs to be informed through appropriate signaling protocols.

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A Generic Provisioning Model (1/10)

• A generic bandwidth-provisioning model, which can incorporate various network elements and accommodate different grooming policies, will enable network operators to manage their transport networks easily and efficiently

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A Generic Provisioning Model(2/10)

The graph is divided into four layers, namely access layer, mux layer, grooming layer, and wavelength layer.

• The access layer : the access point of a connection request, i.e., the point where a customer’s connection starts and terminates. It can be an IP router, an ATM switch, or any other client equipment.

• The mux layer : the OXC ports from which low-speed traffic streams are directly multiplexed (de-multiplexed) onto (from) wavelength channels without going through the grooming fabric.

• The grooming layer : the grooming component of the network node.

• The wavelength layer : the wavelength-switching capability and the link state of wavelength channels.

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A Generic Provisioning Model(3/10)

• A network node is divided into two vertices at each layer.

• These two vertices represent the input and output ports of the network node at that layer.

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A Generic Provisioning Model(4/10)

The links in this graph model are named and work as follows.

1. Grooming switching link connects the input port of the grooming layer to the output port of the grooming layer at a given node i, when node i has multi-hop traffic-grooming capability.

2. Wavelength switching link connects the input port of the wavelength layer to the output port of the wavelength layer at a given node i. It represents the wavelength-switching capability of the network node.

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1

2

1

2 2

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A Generic Provisioning Model(5/10)

3.Mux link connects the output port of the access layer to the output port of the mux layer at a given node i.

It represents that the traffic starting from node i can be packed to some wavelength channels and transmitted to other network node together without going through any grooming fabric.

4.Demux link connects input port of the mux layer to the input port of the access layer at a given node i.

It represents that the traffic on a wavelength channel has been de-multiplexed and terminated at this node without going through any grooming fabric.

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A Generic Provisioning Model(6/10)

5. Mux to wavelength transmitting link connects the output port of the mux layer to the output port of the wavelength layer at a given node i.

6. Wavelength to mux receiving link is the link which connects the input port of the wavelength layer to the input port of the mux layer at a given node i.

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A Generic Provisioning Model(7/10)

7. Grooming link connects the output port of the access layer to the output port of the grooming layer at a given node i, when node i has multi-hop grooming capability

It represents that the traffic starting from node i can be groomed with other traffic streams to the same wavelength channel and transmitted to the next network node together.

8. De-grooming link connects the input port of the grooming layer to the input port of the access layer at a given node i, when node i has multi-hop grooming capability.

It represents that the traffic on a wavelength channel have been de-multiplexed, and then they may be either terminated at node i or switched to other lightpaths.

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A Generic Provisioning Model(8/10)

9. Grooming to wavelength transmitting link connects the output port of the grooming layer to the output port of the wavelength layer at a given node i, when node i has multi-hop grooming capability .

It denotes that a multi-hop groomable lightpath (i.e., either a source-groomable lightpath or a multi-hop full-groomable lightpath) can be originated at node i.

10. Wavelength to grooming receiving link connects the input port of the wavelength layer to the input port of the grooming layer at a given node i, when node i has multi-hop grooming capability .

It denotes that a multi-hop groomable lightpath (i.e., either a destination-groomable lightpath or a multi-hop full-groomable lightpath) can be terminated at node i.

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A Generic Provisioning Model(9/10)

11. Wavelength link connects the output port of the wavelength layer at node i to the input port of the wavelength layer at node j.

It denotes the availability of the wavelength channels between node pair (i, j).

12.Lightpath link can start at the output port of the mux layer (grooming layer) at node i, and terminate at the input port of the mux layer (grooming layer) at node j.

The four combinations of the end points represent the four possible lightpath types between node pair (i, j)

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A Generic Provisioning Model(10/10)

• A link is removed if the corresponding network resource is not available (e.g., deleting a wavelength link),

• A link is added if the corresponding network resource becomes available from unavailable state (e.g., adding a lightpath link).

• A customer’s connection request will always originate from the output port of the access layer at the source node and terminate at the input port of the access layer at the destination node.

• After adjusting the administrative link cost, suitable routes can be found according to different grooming policies for a request by simply applying standard shortest path route-computation algorithms.

• This strategy provides a platform for network operators to realize different grooming policies, and eventually improve the provisioning flexibility and network resource efficiency.

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A sample network state and the graph representation(1/3)

• Figures 2(a) and 2(b) show the network state for a simple three-node network.

• The shaded node (node 0) is the node which employs a multi-hop partial-grooming OXC and the un-shaded nodes (nodes 1 and 2) are equipped with single-hop grooming OXCs.

• Each link in Fig. 2(a) represents a free wavelength channel between a node pair

• Each link in Fig. 2(b) represents an established lightpath. The lightpath (0, 2) is a source-groomable lightpath

• The lightpath (1, 0) is a destination-groomable lightpath The lightpath (2, 1) is a multi-hop un-groomable lightpath.

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A sample network state and the graph representation(2/3)

• A low-speed connection request from node 1 to node 2 can be carried by lightpaths (1, 0) and (0, 2).

• On the other hand, a request from node 2 to node 0 cannot traverse lightpaths (2, 1) and (1, 0) since node 1 does not have multi-hop grooming capability.

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A sample network state and the graph representation(3/3)

• By assigning proper weights to each link in the graph in Fig. 2(c), the corresponding routes will be computed through standard shortest-path computation algorithms according to different grooming policies.

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A sample network 2(1/3)

• Figure 4 shows an example on how to achieve different traffic-engineering objectives through different grooming policies by using our generic graph model.

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A sample network 2(2/3)

• Assuming that there is a new traffic request from node 1 to node 2, Fig. 4 shows two possible routes (in thick links) for this connection request.

• The route shown in Fig. 4(a) traverses two existing lightpath links,

• The route shown in Fig. 4(b) will employ two new wavelength channels

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A sample network 2(3/3)

• If the connection requires full wavelength-channel capacity, or if the overall bandwidth requirement of the future traffic demands between the node pair is estimated to be close to full wavelength-channel capacity, the route in Fig. 4(b) is preferred since the wavelength channels are fully utilized and no grooming is needed at node 0;

• The route in Fig. 4(a) may be preferred if enough free capacity is available in the existing lightpaths.

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Computational Complexity(1/2)

• The auxiliary graph will consist of 2x4xN nodes and at most links.

• The computation complexity for a standard shortest-path algorithm in a N-node network is

• The computational complexity to provision a connection request using this model in a full wavelength-convertible WDM network is

242 N

)( 2NO

)( 2NO

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Computational Complexity(2/2)

• If the WDM network does not have full wavelength-conversion capability, there will be

nodes and at most links in the auxiliary graph, where W is the number of wavelength channels a fiber supports in the network.

• The computational complexity to provision a connection request using this model will be in such a wavelength-continuous WDM network

NW *)3(*2 2*)3(*2 NW

)( 22NWO

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Illustrative Numerical Examples(1/6)

• Figure.5 represents a typical operator’s optical backbone network topology, which has 24 nodes and 43 bi-directional links.

• The capacity of each wavelength channel is OC-192.

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Illustrative Numerical Examples(2/6)

• The bandwidth requirements of the connection requests follow an uniform distribution between OC-3, OC-12, OC-48, OC-192 (i.e., OC-3 : OC-12 : OC-48 : OC-192 = 1 : 1 : 1 : 1)

• Connection requests are uniformly distributed among all node pairs;

• The cost of a fiber link is modeled as unity;

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Illustrative Numerical Examples(3/6)

• We employ two metrics to evaluate the network performance, namely Traffic Blocking Ratio (TBR), Connection Blocking Probability (CBP). Traffic Blocking Ratio represents the percentage of the amount of blocked traffic over the amount of bandwidth requirement of all traffic requests during the entire simulation period.

• Connection Blocking Probability represents the percentage of the total number of blocked connection requests over the number of all traffic requests during the entire simulation period.

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Illustrative Numerical Examples(4/6)

• In Configuration 1, all network nodes are only equipped with single-hop grooming OXCs.

• In Configurations 2, 3, and 4, the shaded nodes in Fig. 5 are equipped with multi-hop partial-grooming OXCs. The numbers of grooming ports in multi-hop partial-grooming OXCs are 4, 8, and 16 in Configurations 2, 3, and 4, respectively.

• In Configuration 5, all shaded nodes in Fig. 5 are equipped with multi-hop full-grooming OXCs

• Each bi-directional link in Fig. 5 contains two uni-directional fibers and each fiber supports eight wavelength channels

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Future work

• We observed that the unfairness problem can become more severe when a network has more grooming capability.

• This may lead to an interesting research topic in our future work.