Scholarly article on topic 'Greenness Link State Advertisement Extension for WDM Networks'

Greenness Link State Advertisement Extension for WDM Networks Academic research paper on "Computer and information sciences"

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Procedia Computer Science
OECD Field of science
{"link state advertisements" / greenness / "OSPF extension" / "traffic engineering" / "Co2 emission"}

Abstract of research paper on Computer and information sciences, author of scientific article — Alireza Nafarieh, Yashar Fazili, Mohammad Raza, William Robertson

Abstract This paper introduces a new Link State Advertisement (LSA) for a new link characteristic to be used with Constrained Open Shortest Path (CSPF) routing mechanism. The new LSA is to be exploited for building a topology database based on realistic energy and Co2 emission data about each link and the sections of the network. The energy-aware CSPF mechanism can use this topology database to incorporate energy and emission information in routing data traffic form greener sections of network.

Academic research paper on topic "Greenness Link State Advertisement Extension for WDM Networks"



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Procedía Computer Science 94 (2016) 310 - 317

The 11th International Conference on Future Networks and Communications

(FNC 2016)

Greenness Link State Advertisement Extension for WDM Networks

Alireza Nafarieh* ,Yashar Fazili, Mohammad Raza, William Robertson

Internetworking Program at Dalhousie University 1360 Barrington Street, A Wing, 2nd Floor, Room A208


This paper introduces a new Link State Advertisement (LSA) for a new link characteristic to be used with Constrained Open Shortest Path (CSPF) routing mechanism. The new LSA is to be exploited for building a topology database based on realistic energy and Co2 emission data about each link and the sections of the network. The energy-aware CSPF mechanism can use this topology database to incorporate energy and emission information in routing data traffic form greener sections of network.

© 2016PublishedbyElsevier B.V. Thisisanopenaccess article under the CC BY-NC-ND license


Peer-reviewunderresponsibility of the ConferenceProgram Chairs

Keywords: link state advertisements; greenness, OSPF extension; traffic engineering;Co2 emission;

1. Introduction

Routing within optical networks relies on knowledge of network topology and resource availability. This information may be gathered and used by a centralized system, or by a distributed link state routing protocol. In either case, the first step towards network-wide link state determination is the discovery, by each route, of the status of local links to all neighbors. To disseminate TE information among entire nodes of a network, the information should be propagated inside and outside the autonomous system, along the path from source to destination. For intra-domain TE-information dissemination, OSPF-TE opaque LSAs with newly proposed extensions are used in this paper.

In a multi-homed network topology, link attribute information can be communicated using dynamic SLA negotiation mechanisms. The customer side of the network is exposed to SLA information from all the service

* Corresponding author. Tel.:+1-902-494-2058. E-mail address:

1877-0509 © 2016 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license


Peer-review under responsibility of the Conference Program Chairs


providers to which it is connected. The customer has the choice to pick the service provider that is the most suitable for satisfying the requested connection.

This paper presents a dynamic SLA negotiation mechanism considering intra-domain communications over shared mesh optical networks. The intra-domain negotiation mechanism propagates the link attribute as SLA parameters while an inter-domain mechanism advertises the proposed SLA-based traffic engineering path constraints. The paper shows how SLA negotiation protocols together with the proposed traffic engineering attributes improve the performance of energy-aware algorithms.

In some cases, the requested parameters in an SLA are beyond the capacity of the network, and the connection is easily rejected or blocked. To give the customer a chance to choose another provider, or in case of having only one provider, to comply with the provider's network capacity as much as possible, an automatic, bidirectional, and dynamic mechanism for SLA parameters negotiation between service providers and customers is required. This mechanism helps service providers to control the network resource assignment in WDM networks. This is the motivation for proposing a dynamic mechanism to negotiate specific SLA parameters or any other metrics which may be desirable. Some paradigms of the desirable SLA parameters, such as TE path/link attributes will be introduced in the following sections.

2. Related Work

Since OSPF and BGP are widely used by service providers as intra-domain and inter-domain routing protocols, respectively, the majority of the work referenced here modifies or adds extensions to these protocols to enhance their ability for serving in traffic engineered environments. The authors in1 describe extensions to the OSPF protocol version 2 to support intra-area TE, using opaque link state advertisements (LSAs)2 Different types of opaque LSAs and their associated format have been discussed in1. The standard track presented in1 talks about LSA payload details in which one of the top-level Type/Length/Value (TLV) triplets is the link TLV which describes a single link, and is constructed of a set of sub-TLVs. The link TLV presented in1 contains sub-TLVs including reservable, used, and unreserved bandwidth, and a traffic engineering metric. The traffic engineering metric sub-TLV in the link TLV of the LSA payload specifies link metrics for traffic engineering purposes. Although this sub-TLV is usually used for propagating the standard OSPF link metrics, it can also be used for other traffic engineering purposes1. In3, extensions to the OSPF routing protocol in support of carrying link state information for Generalized Multiprotocol Label Switching (GMPLS) have been presented. The sub-TLVs for the link TLV in support of GMPLS have been enhanced in3. The link protection type and shared risk link group (SRLG) sub-TLVs presented in3 are the new sub-TLVs added to the link TLV presented in1. The link protection type identifies that the protection scheme is shared. The extensions introduced in1 and3 are considered as the base of the new extensions to OSPF-TE proposed in this paper. Although standards1 and3 have proposed traffic engineering metric extensions, they discuss neither path constraints nor efficient ways of propagation of such constraints inside and/or outside an autonomous system. In Section 3, a new sub-TLV to OSPF-TE extensions are proposed to support intra-domain TE path/link attribute dissemination, and to propagate the link availability inside an autonomous system.

Since traffic engineering information should be able to travel throughout the entire network, an efficient and uncomplicated mechanism is required to propagate TE path attributes between different autonomous systems. In this paper, it is assumed that a BGP-TE attribute which enables BGP to carry TE-information is used4. In4, connection bandwidth at different priority levels and switching capability information were introduced as the attributes added to BGP for traffic engineering. Although the BGP-TE protocol introduced in4 is meant to act as an inter-autonomous TE parameters propagation protocol, it does not discuss how TE path attributes can be disseminated over several autonomous systems while making no changes on the path calculation process.

The idea of disseminating path-related (not domain-related) QoS-metric per destination within an extended TE-attribute has been presented in [5], and the efficiency of BGP-TE extensions under the GMPLS framework has been

evaluated. The proposed path-related TE-attribute in5 is representative of the overall path from a certain node to the destination. In order to provide multiple paths per destination and to map the hop-by-hop BGP into the source-routing requirements of GMPLS, the authors in5 have proposed a behavioral modification of the protocol which consists of using the BGP only as a dissemination protocol, not as a path selection one. Since the proposed mechanism in5 propagates TE-related information without affecting the BGP path selection process, it has been considered as an appropriate model for the mechanism presented in this research. The sub-TLVs proposed in Section 3 facilitate a dynamic mechanism for link/path availability dissemination.

As mentioned above, another challenging issue in propagating, routing, signaling, or managing information over the entire network is control overheads that the flooded information applies to the network. An improved OSPF-TE protocol has been proposed in6 so that rather than disseminating link state information through LSAs, a newly designed path sub-TLV called path state advertisements (PSAs) propagates path attributes. Unlike the traditional OSPF-TE, the proposed protocol in6 does not advertise the absolute value of available link resources. Instead, it only disseminates resources' increments or decrements to cope with control overheads issues. As mentioned earlier, the link and path availabilities are important TE metrics requested by customers through the SLA to guarantee the reliability of the network1. Although6 has proposed a path-related extension to OSPF, it does not propagate link or path availability. In addition, inter-AS communications has not been considered in6.

Several other protocols have already been proposed for SLA parameters negotiation, such as Resource Negotiation and Pricing (RNAP) protocol7, Service Negotiation Protocol (SrNP)8, Common Open Policy Service- Service Level Specification (COPS-SLS)9, and QoS Generic Signaling Layer Protocol (QoS-GSLP)10, to name a few.

RNAP protocol enables service negotiation between user applications and the access network. The protocol permits negotiation and communication of QoS specifications, user traffic profiles, admission of service requests, and pricing and charging information for requested services7. The Service Negotiation Protocol (SrNP)8 supports dynamic SLS negotiation using network-level QoS parameters. A unique feature of SrNP is that the protocol is not specific to any particular SLS format or to the context of an SLS. It is general enough to be applied for negotiating any parameters provided the parameter is in the form of attribute-value pairs. The semantics and format of the parameter under negotiation are transparent to the protocol. The objective of the negotiation process is to agree on the value of the attributes included in the parameter under negotiation, rather than the attributes themselves11. COPS-SLS protocol follows a client-server model which provides all operations needed for service level negotiation such as requesting, accepting, rejecting, proposing, or degrading a service level9. A characteristic feature of COPS is that it distinguishes the interactions between a subscriber and the negotiating node into two phases: configuration and negotiation. In the configuration phase, the service provider informs the subscriber how to request a level of service11. However, those protocols have mainly been designed either for wireless networks or for pricing purposes11. They do not use the commonly used traffic engineering IP routing protocols, such as OSPF, BGP, and they are independent and complicated protocols. In addition to the complexity, there are message overhead considerations for the protocols such as RNAP which requires periodic signaling to refresh the negotiated service11. As studied in detail in11, none of the above mentioned negotiating protocols have been widely deployed on real networks since the issues involved in inter-working of these negotiation protocols with other standardized protocols have not been resolved yet. In addition, a dynamic service negotiation should be able to interact with other network components including QoS routing, wavelength assignment, and network provisioning. Therefore, the above discussed protocols have not been considered as the primary means of propagation in this paper although they can be considered as alternative options.

3. New Opaque LSA

An SLA is a common means of communication between customers and service providers through which one of the most important parameters for the customers, connection availability, is requested. The service provider goal is to provide a reliable connection with the minimum allocated resources over a shared-mesh path restoration scheme in WDM networks. It is required to show what type of SLA parameters or path/link metrics can be communicated over

the proposed negotiating mechanism and how the new negotiation mechanism can handle the QoS-based routing and wavelength assignment (RWA) using the new mechanism. To achieve this goal, new path constraints by which network performance is enhanced will be introduced in the following sections. Here, the general communication mechanism of such attributes will be discussed.

To disseminate the SLA parameters inside an area, Type-10 OSPF opaque LSAs are a suitable choice since Type-10 opaque LSAs are not flooded beyond the borders of their associated area. In addition, as defined in10, to disseminate the SLA parameters inside an AS, Type-11 opaque LSAs are a suitable choice. In OSPF-TE, a top-level link TLV in the payload field describes the characteristics of a single link8. The link TLV and its sub-TLVs have a format shown in Table 1. The new sub-TLV, proposed here to carry and propagate link-attribute (LA) inside an AS, is defined in Table 1. Using this new sub-TLV, an important SLA parameter, link availability, can be flooded all through an AS. Although the new TLV is a part of OSPF regular flooding, a solution for controlling the overheads caused by this TLV is introduced in the following sections.

Table 1 Link TLV payload format

Link Type

Link Length

Link Sub-TLV 1

Link Sub-TLV 2

Link Sub-TLV n

Table 2 New link attribute sub-TLV

LA= p Type LA= p Length

LA= p Value

In this paper we denote the Greenness of energy as p, which is a number between 0 and 1. The Greenness of energy is the ratio of amount of Co2 emission that is currently being emitted over the amount of Co2 emission emitted to produce the same wattage of electricity if only non-green source of the energy were to be used. With the maximum amount of emission emitted by generating electricity using non-green sources of energy such as coal and oil. p Can be determined by the information that is publicly presented by the power distribution companies. Summation of product of amount of energy being produced in wattage and corresponding emission value presented in12 (e.g. 350 gCo2 per kwh) gives the total amount of currently emitting emission ET as shown in equation (1). In this paper the Greenness source of energy coal has 880 (gCo2 per kwh) and is denoted by D resulting in total possible emission of DT in equation (2). The calculation of p is presented in equation (3).


(1) (2) (3)

Where Wi is the amount of power being generated by ilh source of energy such as wind, coal, biomass etc. and Ei is the corresponding emission value (e.g. 350 gCo2 per kwh) based on information in12.

4. Analysis

Figure 1 shows the infrastructure of the testbed for this experiment. The number on the links are the node distances in units of km. Links are assigned an availability of 0.9999 to 0.99999 which is constant for the entire duration of simulation. Traffic or routing request is simulated with Poisson process with arrival rate of 20 connections and duration of 10 hours on average. Lambda assignment is performed without continuity constraint. Energy powering each section of the network is a mixture of green and non-green resources and is changed every 3 hour of the simulated time. Parameters for analysis comes next.

Fig1. NSFNet Network

4.1. Performance Metrics

For our analysis section we introduce three performance metrics. The first metric is the amount of GHG emission per unit resource Lambda. This is the GHG emitted to establish a unit of Lambda. The lower number is better and shows how much a routing mechanism is successful in terms or reducing the emission. The second metric as introduced in13 is the amount of satisfaction for a green route request. This is called green SLA and nodes can ask for a route that is powered ON by minimum certain percentage of green energy. The higher number is better for this metric as more connections are served with a route that met their green SLA. The third metric is the average amount of resources or Lambda assigned to a connection. The lower the number for this metric the better performance of the routing mechanism. The lower number for this metric means on average less number of Lambdas were assigned to all of the connections of the simulation and a routing mechanism is more resource efficient. The next section details the results of our analysis by means of simulation performed in Matlab.

4.2. Analysis

As we can see in Figure 2a, EE14, 15 mechanism using the new LSA is capable of reducing the emission of the network by about 10 percent when compared to the traditional non-green mechanism of shortest path denoted as SP. It may come to as a surprise that why another non-green mechanism of SB also analysed in16 has lower emission than EE method; but the answer is lower average emission for this method is due to very long routes and poor resource efficiency of the method as we will see in Fig3 when emission is divided by a larger resource number it yields to a smaller number for an emission per unit resource; however as we can see in Fig 2b EE has the higher green SLA satisfaction which means it server more connection requests with routes that met their requested greenness therefore the routes that were computed and served by EE mechanism were greener by about 2 percent compared to SB method that seemed to be greener in the previous graph. By combining the analysis for these two graphs one can say that EE successfully reduced the emission of the network.

Fig2. (a) Average emission per unit resource ;(b) Green SLA

In terms of resource efficiency, EE shows about 9 percent increase compared to SP method but the reason is EE is trying to bypass the non-green or less green sections of the network therefore the routes are 9 percent longer on average compared to SP. EE is about 22 percent more resource efficient when compared to SB method. Therefore as we mentioned the higher denominator or divider for emission results in lower average emission for SB in Fig 2a. EE shows and over acceptable resource efficiency when compared to SB.

Fig3. Average Lambda per connection/route

5. Conclusion

This paper has presented a dynamic SLA negotiation mechanism for shared mesh optical networks. The proposed TE extensions applied to OSPF protocol consider both intra-domain communications. Link attributes as an SLA parameter have been negotiated via intra-domain mechanism and any new proposed SLA-based TE path attributes can be advertised through the inter-domain negotiation mechanism. The paper has shown how an SLA parameter negotiation mechanism together with the proposed TE metric can improve the performance of different protection schemes or algorithms. The energy-aware CSPF mechanism has been introduced to incorporate energy and emission information in routing data traffic form greener sections of network.

The Performance analysis has shown that the proposed mechanism can be easily scalable using the path state advertisement concept, and also verifies that the scheme introduced in this paper has a better network performance.


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