Performance Evaluation of Traffic Engineering Signal Protocols in IPV6 MPLS Networks ()
1. Introduction
In the last years there have been an enormous growth in the use of Internet, and new real-time connection-oriented services like streaming technologies and missioncritical transaction-oriented services are in use and new ones are currently emerging. The increased number of Internet users made the popular services Television and Telephone to use the Internet as a medium to reach their customers [1]. However providing the Real-time applications on Internet is a challenging task for the conventional IP networks as it uses best-effort services which doesn’t provides guarantee quality of services and Traffic Engineering (TE) [2]. Multi-Protocol Label Switching (MPLS) technology works to solve those shortcomings of IP. MPLS is a new industry development standardized by the IETF from the phrase “multi-protocol” one might imply that MPLS provides support for multiple different protocols. However, the reality is that the emphasis of MPLS has till date been only on supporting the internet protocol. IP is connection less best effort protocol that works effectively in data networks with no QoS requirements, MPLS merges the flexibility of the IP routing protocols with speed that ATM switches provide to introduce fast packet switching in frame-based IP networks [3]. MPLS is not designed to replace IP; it is designed to add a set of rules to IP so that traffic can be classified, marked, and policed. MPLS as a traffic-engineering tool has emerged as an elegant solution to meet the bandwidth management and service requirements for next generation Internet Protocol (IP) based backbone networks [4]. MPLS networks can offer the Quality of Service (QoS) guarantees that data transport services like frame relay (FR) or Asynchronous Transfer Mode Switching (ATM) give, without requiring the use of any dedicated lines. MPLS was devised to convert the Internet and IP backbones from best effort data networks to business-class transport mediums capable of handling traditional real time services [5]. The initial trust was to deliver much needed traffic engineering capabilities and QoS enhancements to the generic IP cloud. The availability of traffic engineering has helped MPLS reach critical mass in term of service provider mind share and resulting MPLS deployments. Advantages accrue primarily to the carriers, User benefits include lower cost in most cases, greater control over networks, and more detailed QoS. The constraint-based routing label distributions protocol (CRLDP) and the resource reservation protocol (RSVP) are the signaling algorithms used for traffic engineering. In this paper, a comparative study of the performance MPLS TE signal protocols is presented. The paper also shows the performance enhancement of MPLS networks over conventional IP networks. MPLS is improved network performance for multimedia type application in heavy load traffic environment. The rest of the paper is organized as follows. In Section 2, a brief reference to related works has been presented. Section 3 describes traditional IP network and MPLS network operation along with the important terms associated with MPLS. In Section 4, traffic engineering signal protocols of MPLS networks have been described. In Section 5, simulation methodology and traffic parameters are described, then simulation results are presented. Section 6 summarizes the main conclusions of the paper.
2. Related Works
In [6], the author made a comparative analysis of MPLS and Non-MPLS networks and shows MPLS networks have a better performance over traditional IP networks. The authors in [7] mainly focuses on the analytical models to measure efficiency of voice over IP network with applications to MPLS network. In [8], the main objective of the paper was to calculate minimum number of VoIP calls that can be established in an enterprise IP network. In [9], the main objective of the paper were performed and compared for a multisite office network for G.723 VOIP communication traffic applied on two network infrastructure models: one for IP and the other for MPLS.
3. MPLS and IP Networks
3.1. Traditional IP Routing
In IP routing, source node sends the packet to the intermediate nodes, if any, and later to destination node based on destination IP address of the packet. Every time the source node has to decide about the next node to forward the packet. To make such decision each node maintains a table called routing table. The node which maintains such routing table is called as router [10].
3.2. MPLS Operation
MPLS is a technology to forward the packets in IP unaware networks. Entire MPLS network can be divided into two parts namely MPLS edge and MPLS core [4]. MPLS edge is the boundary of the MPLS network consisting of ingress and egress routers shown in Figure 1. MPLS core encompasses intermediate Label Switching Routers (LSRs), through which Label Switched Paths (LSPs) are formed. General terms associated with MPLS network and their meaning is specified below:
1) Label Switching Router (LSR): LSR is a type of MPLS router which operates at the boundary and core of the MPLS network. Ingress and egress router are the two types of edge LSR. The ingress router attaches a new label to every incoming packet and forwards it into
MPLS core. On the other hand, the egress router removes the attached label from the incoming MPLS packet and forwards it further to destination;
2) Label Switched Path (LSP): It is a route established between two edge LSRs which act as a path for forwarding labeled packets over LSPs;
3) Label Distribution Protocol (LDP): It is a protocol used by the routers to create a label database. RSVP (Resource Reservation Protocol) and CR-LDP (Constraint-based Routed Label Distribution Protocol) are some type of LDPs.
The MPLS operation is clearly shown in Figure 2. Initially each of the MPLS routers creates a table. LDP uses the routing table information to establish label values among neighboring LSRs and created LSPs. As soon as a packet arrives at ingress router, it assesses the QoS and bandwidth requirements of the packet and assigns a suitable label to the packet and forwards it into MPLS core. The labeled packet is transmitted over several LSRs inside the MPLS core till it reaches the egress router. Egress router takes off the label and reads the packet header and forwards it to appropriate destination node.
4. Traffic Engineering and Signal Protocols
Traffic Engineering is the process of selecting network paths so the traffic patterns can be balanced across the various route choices. The use of LSPs in MPLS can help balance the traffic on network link event [3]. It allows a network administrator to make the path deterministic and bypass the normal routed hop-by-hop paths. An administrator may elect to explicitly define the path between stations to ensure QoS or have the traffic follow a specified path to reduce traffic loading across certain hops. In other words, the network administrator can reduce congestion by forcing the frame to travel around the overloaded segments. Traffic engineering, then, enables an administrator to define a policy for forwarding frames rather than depending upon dynamic routing protocols, traffic engineering is similar to source-routing in that an explicit path is defined for the frame to travel, however, unlike source-routing, the hop-by-hop definition is not carried with every frame [11].
Signaling is a way in which routers exchange relevant information. In an MPLS network, the type of information exchanged between routers depends on the signaling protocol being used. At a base level, labels must be dis-
tributed to all MPLS enabled routers that are expected to forward data for a specific FEC (Forwarding Equivalent Class) and LSPs created. The MPLS architecture does not assume any single signaling protocol. The power of MPLS depends on its TE capabilities and the efficiency of control plane i.e. routing and signaling. The routing protocols are basically reused from the IP system. Consequently, the design of signaling protocols is something that brings new functionalities and thus is very important for general operation as well as for TE. In this way Constraint based routed Label Switched Path CR-LSPs are used for TE in MPLS [10]. Two protocols are used to set CR-LSPs in MPLS that are:
• Constraint based routed LDP (CR-LDP);
• Resource Reservation Protocol (RSVP-TE).
4.1. Constraint Based Routed LDP (CR-LDP)
CR-LDP is an extension of LDP to support constraint based routed LSPs. The term constraint implies that in a network and for each set of nodes there exists a set of constraint that must be satisfied for the link or links between two nodes to be chosen for an LSP [13]. CRLDP is capable of establishing both strict and loose path setups with setup and holding priority, path Preemption, and path re-optimization [6]. CR-LDP and LDP protocols are hard state protocols that means the signaling message are sent only once, and don’t require periodic refreshing of information. In CR-LDP approach, UDP is used for peer discovery and TCP is used for session advertisement, notification and LDP messages. CR-LSPs in the CR-LDP based MPLS network are set by using Label Request message. The Label Request message is the signaling message which contains the information of the list of nodes that are along the constraint-based route. In the process of establishing the CR-LSP the Label Request message is sent along the constraint-based route towards the destination.
If the route meet the requirements given by network operator or network administrator, all the nodes present in route distribute the labels by means of Label Mapping message. Figure 3 summarizes the CR-LDP signal protocol operation.
4.2. Resource Reservation Protocol (RSVP-TE)
RSVP-TE is an extension of RSVP that utilizes the RSVP mechanisms to establish LSPs, distribute labels and perform other label-related duties that satisfies the requirements of TE [12]. The revised RSVP protocol has been proposed to support both strict and loose explicit routed LSPs (ERLSP). For the loose segment in the ER-LSP, the hop-by hop routing can be employed to determine where to send the PATH message [13].
RSVP is a soft state protocol. It uses Path and RSVP commands to establish path.
The CR-LSPs established by RSVP signaling protocol in MPLS network is described by the following steps:
• The Ingress router in the MPLS network selects a LSP and sends the Path message to every LSR along that LSP, describing that this is the desired LSP used to establish as CR-LSP.
• The LSRs along the selected LSP reserve the resources and that information is send to Ingress router using the RSVP message.
• In this process the Path and RSVP messages are send periodically to refresh the state maintained in all LSRs along the CR-LSP [7].
Figure 4 summarizes the RSVP signal protocol operation.