Multi Protocol Labeled Switching



Multi Protocol Labeled Switching(MPLS) is the best and new way of heeding the fast growing communication network.It enhances the performance of network by increasing the speed and other capabilities.It plays a major role in the betterment of next generation.Transmission resources can be optimized as MPLS carries different services thtrough internet with the help of labeled packets.In this paper we have discussed the basics of MPLS.It discusses the technology used by MPLS networks.Problems related to the previously existing technologies are also a part of this paper.We have thrown light on advantages and some the disadvantages as well.The working operation of the MPLS networks are also discussed with the help of figures.



MPLS is a technique to provide which emphasizes on the management of traffic and connection oriented quality of service, that is basically found in ATM networks .It maintains the flexibility of an IP based network and speeds up the process of IP packet forwarding [1].


MPLS is basically an improved method for forwarding the packets through a network with the help of labels which are being attached with the packets. These labels are actually inserted or attached between the layer 2 and layer 3 header in the case of frame-based layer 2 technologies and they are inserted in two type of the fields and these fields are Virtual channel identifier (VCI) and virtual path identifier (VPI) in the case technologies like ATM.MPLS uses layer 2 and layer 3 combined routing technologies[1].The basic objective of MPLS is to build special network that provides betterment in stability and performance. It includes things like traffic engineering and VPN capacities providing better quality of service.

2.3 SCOPE:

Internet has become a impressing source of entertainment, user interaction, learning and e-commerce. Service providers currently provides services like ATM, frame relay ,voice and internet services. ATM is very popular because they are very versatile and reliable, but ATM does not interact with IP properly and as a result we have to face different problems. A lot of efforts have been made to combine best features of ATM and IP and finally this led to the development of MPLS (multi protocol label switching) in 1998 which basically includes the different implementations of IP switching and which actually uses labels to speed up the forwarding of packets without making any change in the existing IP routing protocol[2].


The background of MPLS goes back to the various efforts that were made in middle of 1990's to combine the IP and ATM technologies. First effort made in this regard was IPO IP switching. After that, some of other companies like IBM, Cisco systems, Cascade introduced their products. IBM introduced (aggregate route based IP switching), Cisco introduced tag switching and Cascade introduced IP navigator. The basic theme of of all these efforts was to improve the delay and throughput of IP. All these companies put their emphasis on the approach to use a standardardized protocol like open shortest path first (OSPF) to define a path between the source end point and destination end point, packets are assigned as they approach the network and then ATM switches are used to move these packets along the specified paths. When these products were introduced ATM switches were much more better than IP routers and then efforts were made at large extent to improve the performance by putting a large traffic on to the ATM level with the help of ATM switching hardware[1].

As a response to the above mentioned effrorts,the internet engineering force( IETF) introduced a working group on MPLS to have a standardized approach. First set of standard protocols was introduced by this group in 2001.It did not put any positive impact on the market. In late 1990's many routers were introduced in the market, which


MPLS basically works on the principle of ATM and frame relay technologies. These two technologies are the back bone of MPLS , so in order to get the basics of MPLS , we should have enough knowledge of ATM and frame relay.


Frame relay is basically a connection oriented layer to transport protocol. In case of frame relay it is assumed that frame relay will run over clean digital line, so an extensive error connection is not needed. Further more reduces the need for more and more leased lines. Many of these lines are required to increase the network capacity. These lines were used to create point to point networks between corporate data centers and offices. Many of these sites had more leased lines that needed or require ensuring redundancies. Because of these facts, frame relay was developed and was introduced in 1980's. With the help of frame relay , it was made possible to considerate the requirement of multiple lines between every location .

Frame relay is basically a very high speed packet switching technology. The maximum link speed of the frame relay is 2Mbps, and it has surprisingly evolved as part of narrow band ISDN. As mentioned above multiplexing of the channels is actually a function of layer 2 which reduces the need of any layer 3 processing at the nodes. Further more in comparison with X.25 only a subset of function of layer 2 subset are implemented at this stage in the network [3] . It is significant network technology and because its inherent advantages frame relay is specially best suited to LAN's . In these networks, we have a very dominating advantages for the users because these networks are cost effective and have much better performance [3] . Flow control is another important factor of frame relay networks . Routing and store forward functions are performed by the intermediate nodes. The nodes discards the frame when there is a case of error. Better through put can be gained with the help of tuned dynamic flow control[4].


ATM is a cell relay protocol designed by the ATM forum and adopted by the IUTO-T. Its combination with the SOFNET and it will allow high speed interaction of all the world network. It can be said that ATM is the “high way” of the information super highway[5].ATM was basically designed for the transmission of voice, graphical data like images etc on local as well as wide networks. Before the introduction of ATM technology networks were designed depending upon the data to transmitter . At that time

Circuit switched network were used to transport delay sensitive information such as video and voice.

Most of the revenues generated today by the networks is due to the excellent services provided by the ATM.the future carrier networks are going to continue to have their basis on the established technologies like ATM. Mostly this can be done by maintaining by separate ATM and IP core networks.ATM will continue to support guaranteed services like broadband access, private lines and videos development in IP and MPLS based traffic engineering can increase the performance of IP based networks which can support ATM services using MPLS.


Basically MPLS is an extension to the current or existing internet protocol model. The routing used in MPLS facilities balancing the load by splitting the traffic and moving the crowded part of the network to any other part in a very well way. These harmful changing can be avoided by varying the splitting ratios with finer granularity step. By the help of these steps, no of iteration to reach the optimal solution increases. This problem can be avoided by adopting a granularity algorithm for MPLS networks .A special method has been introduce that checks the performance of algorithm and mean delay obtained in no of iteration are very close to the optimal values and with the help of this output has been made better in MPLS network.[6]
Another problem in MPLS is reroute sequence planning for label switch path in multi protocol. This problem occur when set of label switched path is checked by a central path optimization tool to get a much better resource utilization in the network. In this problem, we have to find a sequence of label switched path for their one by one reconfiguration without service interruption , this also involves the constraint that capacity of link should not be violated during the process of rerouting at any time. The problem is related to divergence theory and it is NP complete. Different algorithm are used for solving this problem which examine the existence of any possible reroute sequence .There are some other solution which can be implemented when any other feasible solution does not exist . A last the performance of these algorithm can be evaluated with the help of empirical analysis[7].


As we know that MPLS is an improved method for forwarding

Packets through a network using information contained in label attached to IP packet. Now we are going to discuss different benefit of MPLS(1-6 are based on information from [8]) such as

MPLS uses IP as a way to make ATM run over IP.

MPLS is basically protocol neutral which means that it work with Ethernet at core or we can say it work with ATM frame relay . It can support video, cell phone network and metro Ethernet.

Flexibility is an important factor of MPLS networks. MPLS can support a label stack of different sizes and it easily handle unicast forwarding.

MPLS networks are adoptable which means they can support new application and services.

MPLS require only two new protocol and these protocols are

* Label distribution protocol(LDP)

* Link management protocol(LMP)

MPLS allows an easy measurement of traffic volume using support metrics and it also allows latency for traffic management.

Using MPLS, service providers can create layers VPNs across their back bone network for multiple customers , using a common infrastructure without the need for encryption or end user application.

Using MPLS, quality of service can be maintained , service providers can provide multiple classes of service with hard quality of service to their VPN customers[1].

Most of the carrier networks employ can over lay model in which ATM is used at layer 2 and IP is used at layer 3 ,such implementations have different scalability issues. With the help of MPLS , the carrier can migrate many of the functions of the ATM control plane to layer 3, so with simplifying network management and its complexity as well. This is why we can say that MPLS is scalable network[1].

MPLS networks can efficiently enable the delivery of IP services over ATM switched networks . It creates different routes between a source and a destination on purely route basis . Most of service providers have introduced MPLS in their networks models and have reduced costs, have increased their economy and productivity , provided differentiated services. They also have gained a competitive advantage over those who do not use MPLS[1].


As we know that every thing having advantages has some disadvantages as well . Like wise MPLS having a lot of advantages also has a number of disadvantages as well. Some of them are discuss below


Another disadvantage or drawback of MPLS is resiliency. A modern MPLS enabled network is actually implemented across a nationwide network of Ip switches do not provides any more resiliency than a legacy ATM network having nodes in same locations.The network architecture beneath the MPLS is responsible for resiliency[9].

One should be familiar with the fact that in MPLS VPN,the network cloud could not have access to customer site .If the costumer site has just one connection to the MPLS provider, then there is just one single point of failure. Dual connectivity is possible only in very rare cases and is implemented


One of the major problems now a days is human error , this is increasing day by day as MPLS VPN are always provided with virtual routing and forwarding table as well ,we do not have any tool which can prevent a provisioning engineer making a configuration error and different leaking routes between customers. Most of the manufactures such as Cisco are some how familiar with this issue but still there is no way of prevention up till now. MPLS VPN is not encrypted across the providers and there is always a huge risk of back door access to the customer data. In UK mostly the internet connectivity needs a BTs network that provides last mile connectivity to the customer , this adds more risk of some one whose trying to access in this way .BT is anxious that they do not have sufficient control to their exchanges of the third party[9] .


An important concern is that MPLS will not considerably going to improve throughput in existing IP network. Most of the existing providers networks are based completely upon IP using very high speed layer three switches such devices used special type of hardware known as ASICs[9] .

One of the disadvantages of MPLS is that it is not compatible with MPLS/IP networks because MPLS/IP networks do not use extra bit for drop precedence. The overhead is very much necessary for the routing in MPLS network will make the traffic slowdown, It creates latency concerns for the costumers.[2]

Another disadvantage of MPLS is that MPLS port and the loop rates are higher. The host sites requires a large bandwidth than a T1 to guarantee that the host will not over utilized, this directly affects the cost[2].

MPLS has a drawback MPLS require greater IT overhead to to manage all the routers at each site, customers are basically trying to increase the burden of IT, not to increase it. This thing can be solved by having a properly managed network solution.


We are going to discuss the methods or technique followed by MPLS networks. Basically MPLS networks have a set of nodes or switches which are known as labeled switched routers (LSR)[1] , these labels have the capability of switching and the packets and then routing them on the basis of a label which has been attached to a particular

Packet. These labels define a pattern or flow of packets between two systems or in technical way we can say flow of packets between two end points. If we considered multicast case, then it defines a flow of packets between service end point and multicast group of destination end points. A specific path through the network Of LSR's for each distinct flow known as forwarding equilance class (FEC)[1] is already defined so we can say that MPLS is a connection oriented technology. Traffic characterization is associated with every FEC which defines the quality of service for specific flow. The LSR's do not need to examine or process the IP header, they just simply forward the packet according to the label attached to it, so this forwarding method is far simple as compared to the IP router.

The above shown figure shows the methodology followed by the MPLS networks based on [10]

The base and key elements of the whole operation can be summarized as

Firstly it is important to define a path between network known as LABLED SWITCHED PATH. These tasks are performed with the help of two protocols and these two protocols are

1.1 An interior routing protocol like OSPF, it is use to transfer or exchange the routing information along with reach ability.

1.2 For a specific FEC label must be attached to the packets. As the number of useable labels become limited by the use of globally unique labels that would create management load as well. An explicit router is used by the network operator which manually route and assign accordingly label values. Another protocol is used to route and establish label between opposite LSR's. Either of these protocols can be used for this known as LDP (label distribution protocol). This is basically new and improved form of RSVP.

A packet enters the MPLS with the help of an ingress edge LSR(label switch routers), the packet is then processed to check which network layer is required by the packet. The LSR assigns this packet to a specific LSP , this attaches a particular label to packet and forward the packets . In case there is no LSP yet for this FEC , the LSR at the edge must interact with the other LSR so to define a new LSP.

As each LSR receives a labeled packet with in the MPLS domain. It actually remove the incoming label and then attached the appropriate outgoing label to the packet . It also forward the particular packet to the next LSR along the LSP.

The label is checked by the ingress edge LSR and then read the IP header and then it forward the packet finally to its destination.

The figure below describes the whole scenario discussed above . It elaborates the packet forwarding procedure of MPLS networks based on[10]

The figure shows that each of the LSR maintains its own label for the forwarding of LSP. After the arrival of packet, LSR checks label in order to determine the next hop. As mentioned earlier that the LSR detaches the incoming label from the packet and then it attaches the appropriate label before forwarding the packet. The FEC for incoming unlabeled packet is determined by the ingress edge. LSR and on the basis of FEC it assigns the packet to specific LSP, attaches the corresponding label and then forward the packet.


From the above discussion we have concluded that MPLS is a vast networking field having a lot of advantages. Though it has a few problems and disadvantages as well but they can be ignored because of its huge advantages. Most of the organizations are using MPLS as core of their networks. MPLS is basically an improved method for forwarding the packets through a network with the help of labels which are being attached with the packets. Organizations are trying their best for making the network traffic better and for the development networking field from very long time and MPLS is the result of these efforts. The basic objective of MPLS is to build special network that provides betterment in stability and performance. It includes things like traffic engineering and VPN capacities providing better quality of service.


[1] “The Internet Protocol Journal , William Stallings, Volume 4, June 2004

[2] "Advance MPLS design data,Vivek Alwayn,2002".

[3]Some aspects of traffic management in frame relay network,Teletraffic symposiun, Beesyon,April 1994.

[4]"Frame relay in public networks, IEEE,volume 30, March 1992".

[5] Data Communication And Networking, Behroz A Farozan

[6] "Adaptive Granularity Algorithm For Effective Distributive Load and Balancing in MPLS, Advanced computing And Commuminication, Guwahati Assam, November 2007."

[7] “The international journal of computer and telecommunication networking, volume 42, June 2003".

[8] “Selected areas in communication,IEEE, volume 23, March 2005".

[9] Simon Hill, MPLS Misconceptions, White Paper, September 2008

[10] Figure: [1,2] Redford R., "Enabling the Business IP Services with Multiprotocol Label Switching,"White Paper, July 2000

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