In IP routing each packet travels from one router to the next, each router makes an independent forwarding decision for that packet. That is each router analyses packet header, and each router runs a network layer routing algorithm. Each router independently chooses a next hop for the packet, based on its analysis and the results of running the routing algorithm.
In conventional IP forwarding a particular router will typically consider two packets to be in the same FEC(forward equivalence class) if there is some address prefix X in that router's routing table such that X is the largest match for each packets destination address. As the packet traverses the network each hop in turn reexamines the packet and assigns it to the FEC.
Almost all protocols deployed today are based on algorithms designed to obtain the shortest path in the network for packet traversal and do not make into account of additional metrics (such as delay and congestion), which can further decreases the network performance. To speed up the forwarding scheme, a GMPLS device uses labels rather than address matching to determine the next hop for the received packet.
GMPLS is an extended framework of MPLS protocol. Generalized MPLS provides not also the packet switching but also switching in time slot domain(TDM), wavelength domain(DWDM),and space domain(fiber). In
MPLS the assignment of a particular packet to a particular FEC is done just once, as the packet enters the network. The FEC to which the packet is assigned and is encoded as a short fixed length value known as a label. When a packet is forwarded to its next hop, the label is sent along with it that is the packets are labeled before they are forwarded. GMPLS is a significant and challenging concept for next generation data and optical networks. By eliminating the two layers, ATM and SONET/SDH, GMPLS provides interoperable, scalable and parallel development of IP over DWDM network architecture.
INTRODUCTION TO GMPLS
The emergence of optical transport systems has dramatically increased the raw capacity of optical networks and has enabled new sophisticated applications. For example, network-based storage, bandwidth leasing, data mirroring, add/drop multiplexing [ADM], dense wavelength division multiplexing [DWDM], optical cross-connect [OXC], photonic cross-connect [PXC], and multiservice switching platforms are some of the devices that may make up an optical network and are expected to be the main carriers for the growth in data traffic.
Multiple Types of Switching and Forwarding Hierarchies
Generalized MPLS (GMPLS) differs from traditional MPLS in that it supports multiple types of switching, i.e. the addition of support for TDM, lambda, and fiber (port) switching. The support for the additional types of switching has driven GMPLS to extend certain base functions of traditional MPLS and, in some cases, to add functionality. These changes and additions impact basic LSP properties, how labels are requested and communicated, the unidirectional nature of LSPs, how errors are propagated, and information provided for synchronizing the ingress and egress LSRs.
1. Packet Switch Capable (PSC) interfaces:
Interfaces that recognize packet boundaries and can forward data based on the content of the packet header. Examples include interfaces on routers that forward data based on the content of the IP header and interfaces on routers that forward data based on the content of the MPLS "shim" header.
2 . Time-Division Multiplex Capable (TDM) interfaces:
Interfaces that forward data based on the data's time slot in a repeating cycle. An example of such an interface is that of a SDH/SONET Cross-Connect (XC), Terminal Multiplexer , or Add-Drop Multiplexer (ADM).
3 . Lambda Switch Capable (LSC) interfaces:
Interfaces that forward data based on the wavelength on which the data is received. An example of such an interface is that of a Photonic Cross-Connect (PXC) or Optical Cross-Connect (OXC) that can operate at the level of an individual wavelength. Additional examples include PXC interfaces that can operate at the level of a group of wavelengths, i.e. a waveband.
4. Fiber-Switch Capable (FSC) interfaces:
Interfaces that forward data based on a position of the data in the real world physical spaces. An example of such an interface is that of a PXC or OXC that can operate at the level of a single or multiple fibers.
The diversity and complexity in managing these devices have been the main driving factors in the evolution and enhancement of the MPLS suite of protocols to provide control for not only packet-based domains, but also time, wavelength, and space domains. GMPLS further extends the suite of IP-based protocols that manage and control the establishment and release of label switched paths (LSP) that traverse any combination of packet, TDM, and optical networks. GMPLS adopts all technology in MPLS.
MPLS BACKGROUND AND OPERATION
MPLS network consists of two types of devices. One is label switch router and another is label edge router. Label switch router is a high speed router in the core of the network. Label edge router separates the MPLS network and access network. Access network may be frame relay, ATM networks. A label is a short fixed length word which has local significance only. LER checks the IP header and inserts the label stack before the header in the IP packet. Label stack is a stack of labels each LSR only looks the topmost label in the stack, and switch the packet to the appropriate router. MPLS extended the suite of IP protocols to expedite the forwarding scheme used by IP routers. Routers have used complex and time-consuming route lookups and address matching schemes to determine the next hop for a received packet, primarily by examining the destination address in the header of the packet. MPLS has greatly simplified this operation by basing the forwarding decision on a simple label. Another major feature of MPLS is its ability to place IP traffic on a defined path through the network. This capability was not previously possible with IP traffic. In this way, MPLS provides bandwidth guarantees and other differentiated service features for a specific user application (or flow). Current IP based MPLS networks are capable of providing advanced services such as bandwidth-based guaranteed service, priority-based bandwidth allocation, and preemption services.
For each specific service, a table for a forwarding equivalence class (FEC) is created to represent a group of flows with the same traffic-engineering requirements. A specific label is then bound to an FEC. At the ingress of an MPLS network, incoming IP packets are examined and assigned a "label" by a label edge router (LER). The labeled packets are then forwarded along an LSP, where each label-switched router (LSR) makes a switching decision based on the packet's label field. An LSR does not need to examine the IP headers of the packets to find an output port (next hop). An LSR simply strips off the existing label and applies a new label for the next hop. The label information base (LIB) provides an outgoing label (to be inserted into the packet) and an outgoing interface (based on an incoming label on an incoming interface).
Signaling to establish a traffic-engineered LSP is done using a label distribution protocol that runs on every MPLS node. There are a number of different label-distribution protocols. The two most popular are RSVP traffic engineering (RSVP-TE) and CR-LDP. RSVP-TE is an extended version of the original RSVP to piggyback and distribute labels on its messages and to provide traffic-engineering capability. CR-LDP was designed specifically for this purpose. Figure 1 shows the flow of label distribution that is carried out by the downstream LER (in this case LER2) while the LSP flow is the reverse.
MPLS ACTIONS DESCRIPTION
Label created and distributed before any traffic begins the routers make the decision to bind a label to a specific FEC and build their tables. In LDP, downstream routers initiate the distribution of labels and the label/FEC binding. A reliable and ordered transport protocol should be used for the signaling protocol. LDP uses TCP. Table creation is done on receipt of label bindings each LSR creates entries in the label information base (LIB). The contents of the table will specify the mapping between a label and an FEC. Mapping between the input port and input label table to the output port and output label table. The entries are updated whenever renegotiation of the label bindings occurs.
Label switched path creation As shown by the dashed blue lines in Figure 1, the LSPs are created in the reverse direction to the creation of entries in the LIBs. Label insertion/table-lookup The first router (LER1 in Figure 1) uses the LIB table to find the next hop and request a label for the specific FEC. Subsequent routers just use the label to find the next hop. Once the packet reaches the egress LSR (LER4), the label is removed and the packet is supplied to the destination. Packet forwarding With reference to Figure 1 let us examine the path of a packet as it to its destination from LER1, the ingress LSR, to LER4, the egress LSR. LER1 may not have any labels for this packet as it is the first occurrence of this request. In an IP network, it will find the longest address match to find the next hop. Let LSR1 be the next hop for LER1. LER1 will initiate a label request toward LSR1.This request will propagate through the network as indicated by the broken green lines. Each intermediary router will receive a label from its downstream router starting from LER2 and going upstream till LER1. The LSP setup is indicated by the broken blue lines using LDP or any other signaling protocol. If traffic engineering is required, CR-LDP will be used in determining the actual path setup to ensure the QoS/CoS requirements are complied with.LER1 will insert the label and forward the packet to LSR1.Each subsequent LSR, i.e., LSR2 and LSR3, will examine the label in the received packet, replace it with the outgoing label and forward it. When the packet reaches LER4, it will remove the label because the packet is departing from an MPLS domain and deliver it to the destination. The actual data path followed by the packet is indicated by the broken red lines.
It is interesting to consider the example of two streams of data packets entering an MPLS domain: One packet stream is a regular data exchange between servers (e.g., file transfer protocol [FTP]). The other packet stream is an intensive video stream, which requires the traffic engineering parameters of QoS (e.g., videoconferencing). These packet streams are classified into 2 separate FECs at the ingress LSR.
Label request:- Using this mechanism, an LSR requests a label from its downstream neighbor so that it can bind to a specific FEC. This mechanism can be employed down the chain of LSRs up until the egress LER (i.e., the point at which the packet exits the MPLS domain).
Label mapping:- In response to a label request, a downstream LSR will send a label to the upstream initiator using the label mapping mechanism. The above concepts for label request and label mapping are explained in Figure 2.
Figure 2. Signaling Mechanisms
TUNNELING IN MPLS
A unique feature of MPLS is that it can control the entire path of a packet without explicitly specifying the intermediate routers. It does this by creating tunnels through the intermediary routers that can span multiple segments.
Consider the scenario in Figure 3. LERs (LER1, LER2, LER3, and LER4) all use BGP and create an LSP between them (LSP 1). LER1 is aware that its next destination is LER2, as it is transporting data for the source, which must go through two segments of the network. In turn, LER2 is aware that LER3 is its next destination, and so on. These LERs will use the LDP to receive and store labels from the egress LER (LER4 in this scenario) all the way to the ingress LER (LER1).
Figure 3. Tunneling in MPLS
MPLS EVOLUTION TO GMPLS
Within the past year, the International Engineering Task Force (IETF) has extended the MPLS suite of protocols to include devices that switch in time, wavelength, (e.g., DWDM) and space domains (e.g., OXC) via GMPLS. This allows GMPLS based networks to find and provision an optimal path based on user traffic requirements for a flow that potentially starts on an IP network, is then transported by SONET, and then is switched through a specific wavelength on a specific physical fiber. GMPLS protocols are extended framework of MPLS protocol. It adopts all technology in MPLS.
Table 2. gives a summary of the GMPLS framework.
Switching domain Traffic type Forwarding
Scheme Example of
Packet, cell IP,ATM Label as shim header IP router
ATM switch Packet switch
time TDM/SONET Time slot in repeating cycle Digital cross
(DCS) TDM capable
lambda DWDM capable (LSC) Lambda switching
space Transparent fiber OXC Fiber switching
The basic challenge for an all-encompassing control protocol is the establishment, maintenance, and management of traffic-engineered paths to allow the data plane to efficiently transport user data from the source to the destination. A user flow starting from its source is likely to travel several network spans, for example, an access or edge network that aggregates the flows from multiple users (e.g., enterprise applications) to feed into a metro network that is SONET-based or ATM-based that itself aggregates multiple flows from various edge networks to feed into a long-haul network that uses lambdas to transport the aggregated flow of multiple metro networks. The reverse path is used to deliver data to its destination. These networks and the typical devices used are shown in Figure 3.
Figure 4. Dissimilar Networks That Carry End-User Traffic
Summary of the GMPLS Protocol Suite
Table 1. GMPLS Protocols
Routing OSPF-TE,IS-IS-TE routing protocols for the auto discovery of network topology,
Advertise resource availability (eg., bandwidth or protection type)
The major enhancement are as follows:
Advertising of link-protection type.
Implementing derived links for improved scalability. Accepting and advertising links with no IP address-link ID ,incoming and outgoing interface ID.
signaling RSVP-TE,CR-LDP signaling protocols for the establishment of traffic-engineered LSPs. The major enhancement are as follows: Label exchange to include non-packet networks (generalized label)
Establishment of bidirectional LSPs.
Signaling for the establishment of a back-up path (protection Information)
Waveband switching support set of contiguous wavelengths switched together
Link Management (LMP) Control-channel Management: Established by negotiating link parameters and ensuring the health of a link(hello protocol)
Link â€œconnectivity verification: ensures the physical connectivity of the link between the neighboring nodes using a
PING â€œlike test message.
Link-property correlation: Identification of the link properties of the adjacent nodes(eg., protection mechanism)
Fault isolation: Isolates a single or multiple faults in the optical domain
Figure 5 .MPLS protocol stacks
Note that the IS-IS-TE routing protocol stack is similar to OSPF-TE with the exception that, instead of IP, connectionless network protocol (CLNP) is used to carry IS-IS-TE's information.
GMPLS ISSUES AND THEIR RESOLUTIONS
Data forwarding is not limited to that packet forwarding. The general solution must be able to retain the simplicity of forwarding using a label for a variety of devices that switch in time or wavelength, or space (physical ports).
Not every type of network is capable of looking into the contents of the received data and of extracting a label. For instance, packet networks are able to check the headers of the packets, check the label, and carry out decisions for the output interface (forwarding path) that they have to use. This is not the case for TDM or optical networks. The equipments in these types of networks are not designed to have the ability to examine the content of the data that is fed into them.
Unlike packet networks, in TDM, LSC, and FSC interfaces, bandwidth allocation for an LSP can be performed only in discrete units. For example, a packet-based network may have flows of 1 Mbps to 10 or 100 Mbps. When a 10 Mbps LSP is initiated by a PSC device and must be carried by optical connections with fixed bandwidths e.g., an OC-12 line-it would not make sense to allocate an entire 622M line for a 10M flow.
Scalability is an important issue in designing large networks to accommodate changes in the network quickly and gracefully. The resources that must be managed in a TDM or optical network are expected to be much larger in scope than in a packet-based network. For optical networks, it is expected that hundreds to thousands of wavelengths (lambdas) will be transporting user data on hundreds of fibers.
Configuring the switching fabric in electronic or optical switches may be a time-consuming process. For instance, in a DCS that is capable of switching tens of thousands of digital signal (DS)-1 physical ports, identifying the connection between the input/output ports could be time consuming as fewer ports become available to accommodate incoming user traffic. Latency in setting up an LSP within these types of networks could have a cumulative delaying effect in setting up an end-to-end flow.
SONET networks have the inherent ability to perform a fast switchover from a failed path to a working one (50 milliseconds). GMPLS' control plane must be able to accommodate this and other levels of protection granularity. It also needs to provide restoration of failed paths via static (pre-allocated) or dynamic reroute, depending on the required class of service (CoS).
To be able to support devices that switch in different domains, GMPLS introduces new additions to the format of the labels. The new label format is referred to as a "generalized label" that contains information to allow the receiving device to program its switch and forward data regardless of its construction (packet, TDM, lambda, etc.). A generalized label can represent a single wavelength, a single fiber, or a single time-slot. Traditional MPLS labels e.g., ATM, VCC, or IP shim are also included. The information that is embedded in a generalized label includes the following:
LSP encoding type that indicates what type of label is being carried (e.g., packet, lambda, SONET, etc.) Switching type that indicates whether the node is capable of switching packets, time-slot, wavelength, or fiber . A general payload identifier to indicate what payload is being carried by the LSP (e.g., ATM, Ethernet, etc.)
Similar to MPLS, label distribution starts from the upstream LSR requesting a label from the downstream LSR. GMPLS takes this further by allowing the upstream LSR to suggest a label for a LSP that can be overridden by the downstream LSR.
LSP Creation in GMPLS-Based Networks
Establishing an LSP in a GMPLS network is similar to that of MPLS networks. Figure 6 shows a packet network (PSC) connected via an OC-12 pipe to DCS1 in the upper TDM network. Both of the TDM networks shown use a SONET UPSR OC-48 ring architecture. The two TDM networks are connected via two OXCs capable of delivering multiple OC-192 lambdas. The goal is to establish an LSP (LSPpc) between LSR1 and LSR4.
To establish the LSPpc between LSR1 and LSR4, other LSPs in the other networks must be established to tunnel the LSPs in the lower hierarchy. For example, per Figure 6, LSP1T1 will carry LSP1, LSP2, and LSP3 if the sum of the traffic-engineering requirements of the packet LSPs can be accommodated by it.
This is done by sending a PATH/Label Request message downstream to the destination that will carry the lower hierarchy LSP. For example, DSCi sends this message to
Figure 6. Establishing an LSP through Heterogeneous Networks with GMPLS
OXC1, destined for DSCe. When received by OXC1, it will then create an LSP between it and OXC2. Only when this LSP (LSPl) is established will an LSP between DSCi to DSCe be established (LSPtdi).
The PATH/Label Request message contains a Generalized Label Request with the type of LSP (i.e., the layer concerned), and its payload type (e.g., DS-3, VT, etc.). Specific parameters such as type of signal, local protection, bidirectional LSP, and suggested labels are all specified in this message. The downstream node will send back a RESV/Label Mapping message including one generalized label that may contain several generalized labels.
When the generalized label is received by the initiator LSR, it can then establish an LSP with its peer via RSVP/PATH messages per network domain. In Figure 4, the following sequence has taken place: LSP is established between OXC1 and OXC2 (LSPl) and capable of delivering OC-192 wavelength to tunnel in TDM LSPs. LSP is established between DSCi and DSCe (LSPtdi). LSP is established between DS-1 and DS-2 (internal LSPs within the two TDM networks are established prior to the establishment of this LSP). LSP is established between LSR2 and LSR3 (LSPpi). LSPpc is established between LSR1 and LSR4.
MPLS devices are capable of discerning the contents-of-information unit that is passed between them. e.g., a packet or a cell that has header information. They need to examine the label (e.g., shim header) to determine the output port and the output label for an incoming packet. The label-swapping paradigm logically separates the data and the control planes.
GMPLS extends this paradigm to those devices that are designed to lookup any headers when they receive the user data. In this case, GMPLS allows the data plane and the control plane to be physically, or logically, separate. For example, the control path between two devices could travel an external line such as an Ethernet connection, or other types of physical links. GMPLS does not mandate how the control information is to be transported between two nodes.
The selection of a medium to carry the control information between the two GMPLS nodes can impact the economics of the network operator. Clearly, a single fiber should not be used to carry this information between two geographically separate devices. e.g., two DCSes in a SONET ring network. Other connection types may be costly to use e.g., an X.25 connection. One approach is to take a logical slice of a line. These bytes are comprised of section and line overhead (three and nine bytes, respectively) and can both be used for this purpose. Together they provide a 768 kbps channel for the exchange of control messages. They can be used in each direction between two adjacent nodes. This is a highly efficient method that does not take away bandwidth that could be used for user data traffic.
When an LSP is being established starting from the access network, it may require the establishment of several other LSPs along its end-to-end path. These intermediate LSPs may be established on TDM and/or LSC based devices. These devices have different internal characteristics, and, therefore, GMPLS must accommodate these differentials in such a way as to expedite the establishment of the end-to-end LSPs. Two important new concepts that are introduced in GMPLS to address these differences are as follows.
As mentioned in an earlier section, an upstream node can optionally suggest a label to its downstream node. The downstream node has the right of refusal and may propose its own. Recall that a label in this case is used to quickly find the internal path between an input and an output port. A suggested label allows the DCS to configure itself with the proposed label, instead of waiting to receive a label from the downstream node, and then configure its hardware. Suggested labels are also important in expediting the set-up of back-up paths (LSPs) for a failed LSP. However, if the downstream device rejects the suggested label and offers its own, the upstream device must re-configure itself with the new label.
Network protection e.g., against fiber cuts in optical networks is provided with back-up fibers, such as four-wire BLSR or two-wire BLSR architectures. Similarly, LSPs in an optical network need to be protected. This is accomplished by establishing two unidirectional LSPs one LSP to protect the other. Bidirectional LSPs must have the same traffic-engineering and restoration requirements.
GMPLS supports the setup of bidirectional LSPs via one set of signaling protocol messages (e.g., RSVP/PATH and RESV). This helps to avoid the extraneous exchange of control messages, race conditions, additional route look-ups, and configuration-latency in setting up the internal input/output paths in an optical switch.
Scalability (forwarding adjacency LSPS)
A FA LSP is a GMPLS based LSP to carry other LSPs. An FA LSP established between two GMPLS nodes can be viewed as a virtual link with its own traffic-engineering characteristics and can be advertised into the OSPF/IS-IS as a normal link like any other physical link. An FA LSP may be incorporated into the link-state database and used in routing-path calculation to carry other LSPs. This can reduce the size of the database, and, consequently, the time that is spent in the table look-up operation.
Figure 7 shows how a TDM LSP (LSPtdm) can be viewed as a link that connects two packet-based networks. This LSP can be viewed as a single link in the packet-based LSRs of the two PSC networks, instead of all of the physical links in the TDM network.
Figure 7. Forwarding Adjacency
The network hierarchy (access, metro, and long haul) shown in Figure 8 provides an increasing bandwidth capacity per hierarchy. When an end-to-end flow is to be establish for a particular enterprise application, that flow will traverse networks that use devices that may not be designed to configure connections with flexible bandwidth levels i.e., only discrete bandwidth are available. In this case, a single OC-192 physical link between two optical switches should not be expected to carry a traffic that is only 100M or even 2.5G, as it would be wasteful and highly inefficient. It is better to aggregate lower-speed flows into higher-speed ones. This brings the notion of hierarchical LSP.
A natural hierarchy is established wherein a group of PSC-LSPs are nested within TDM-LSPs that are then nested within a LSC that is part of a group of LSCs within an FSC. The link multiplex capability parameter introduced in GMPLS specifies this ordering when an LSP is being established. Clearly, bandwidth that remains within each LSP can and should be used to accept and include additional LSPs from lower-hierarchy LSPs.
Figure 8. Hierarchical LSPs
It is expected that an optical network will deploy tens to hundreds of parallel fibers, each carrying hundreds to thousands of lambdas between two nodes. To avoid a large size for the link database and provide better scaling of the network, GMPLS has introduced the concept of link bundling.
Link bundling allows the mapping of several links into one and advertising that into the routing protocol i.e., OSPF, IS IS. Although, with the increased level of abstraction, some information is lost, this method greatly lowers the size of the link-state database and the number of links that need to be advertised. A bundled link needs only one control channel, which further helps to reduce the number of messages exchanged in signaling and routing protocols.
GMPLS flexibly allows the bundling of both point-to-point (PTP) links and LSPs that were advertised as links to OSPF (forward adjacency). There are restrictions in bundling links. These are as follows: All links that comprise a bundled link must begin and end on the same pair of LSRs. All links that comprise a bundled link must be of the same link type (e.g., PTP or multicast). All links that comprise a bundled link must have the same traffic metric (e.g., protection type or bandwidth). All links that comprise a bundled link must have the same switching capability PSC, TDMC, LSC, or FSC.
Bundled links result in loss of granularity in the network resources. Nevertheless, the gain in the reduction of link-state database entries and the speed gain in table look-ups far outweigh the lost information.
A key attribute of GMPLS suite of protocols is the ability to enable automated fault management in network operation. A fault in one type of the network must be isolated and resolved separately from other networks. This is a very important feature for end-to-end LSPs that are tunneled in other LSPs that require higher degrees of reliability along the hierarchy. A common control plane that spans dissimilar networks must be able to address the varying degrees of reliability requirements within each network span.
Figure 9. Fault-Management Process in GMPLS
GMPLS provides protection against failed channels (or links) between two adjacent nodes (span protection) and end-to-end protection (path protection). The OSPF and IS-IS extensions for GMPLS advertise the link-protection-type parameter to include span protection while the route is being computed. After the route is computed, signaling to establish the backup paths is carried out via RSVP-TE or CR-LDP. Figure 9 depicts span and path protections.
For end-to-end path protections, the primary and secondary paths are computed and signaled to indicate that the two paths share reservations. Shared-risk link group is an optional mechanism that allows the establishing of back-up LSPs that do not have any links in common with the primary LSP. This is achieved in the routing extension of OSPF/IS-IS.
The restoration of a failed path refers to the dynamic establishment of a back-up path. This process requires the dynamic allocation of resources and route calculation. Two different restoration methods are given: line and path. Line restoration finds an alternate route at an intermediate node. Path restoration is initiated at the source node to route around a failed path anywhere within the path for the specific LSP. In Figure 9, node 1 can initiate this new path. In general, restoration schemes take longer to switch to the back-up path, but they are more efficient in bandwidth usage, as they do not pre-allocate any resource for an LSP.
Figure 10. Protection Schemes Supported in GMPLS
Efficient Resource Usage
The inclusion and management of resources in TDM and optical devices, via an IP-based control plane, requires new levels of optimization. Link bundling was discussed earlier as a method to reduce the size of the link-state database per TDM and optical networks. Another major issue in TDM and optical networks is their potential usage of IP addresses. This is discussed next.
Instead of assigning a different IP address to each TDM or optical link, the concept of "unnumbered links" is used to keep track of these types of links. This is necessary because of the following: The number of TDM channels, wavelengths, and fibers can easily reach a point where their management, per IP address, will become very time-consuming. IP addresses are considered scarce resources. An unnumbered link is a link that has no IP address instead, a combination of a unique router ID and link number is used to represent it. These links carry traffic-engineering information and can be specified in the signaling plane, just like a regular link with an IP address.
RSVP-TE and CR-LDP have both been extended to carry this information in the signaling plane. The same has been done in the routing protocols (OSPF-TE, IS-IS-TE).
GMPLS OUTSTANDING ISSUES
Traditional IP routing examines the contents of the header of a received packet to determine the next hop for it. While time-consuming, this step allows the establishment of firewalls, as the necessary information is available in the packet header e.g., the source and the destination addresses that are globally unique. In contrast, MPLS/MPLS labels are used to speed up the forwarding scheme and only have local significance i.e., the label is only understood and used internally by the GMPLS device itself. As such, these labels cannot be used for access-control or network-security purposes. One way to establish security in a GMPLS network is to enforce access security during the connection set-up time, like other connection-oriented networks e.g., X.25 or ATM.
The success of GMPLS will partially depend on its ability to communicate with the many existing ATM or Frame Relay network infrastructures. Interworking with ATM and Frame Relay networks will allow transport of control and data plane information exchanged between two similar networks (e.g., two ATM networks) through a dissimilar network (e.g., GMPLS). The implementation of interworking functions between these networks face these issues: Interworking in the control plane is very complicated as different suites of protocols are used in each network (e.g., routing, private network-to-network interface [PNNI] in ATM versus OSPF-TE in GMPLS networks). The maintenance of end-to-end service quality as usage data travels through dissimilar network types is essential. GMPLS switching can be packet-based, TDM-based, wavelength-based, waveband-based, or fiber-based. This creates quite a few combinations in the data-plane interworking context between GMPLS networks and ATM or frame-relay (FR) networks, which carry data in cells or frames, respectively.
When a new resource is deleted or added in a GMPLS network, the set of control information that is exchanged is larger than that of a traditional IP network. GMPLS uses traffic-engineering models that include introducing a set of traffic parameters, associated with data links, performing constraints-based routing, LMPs, etc. While not tested, theoretically, an MPLS/GMPLS network would take a relatively longer time to achieve an equilibrium state than would a traditional IP network when the network is disrupted.
Network management System
The most important parameter in managing a traditional IP network e.g., the Internet is address reachability. In contrast, the GMPLS network-management system needs to keep track of several thousands (even millions) of LSPs for their operational status, routing paths, traffic engineering, etc. This renders the GMPLS network-management system more complex relative to the management of the traditional Internet.
GMPLS will be an integral part of deploying the next generation network. It provides necessary bridges between IP and photonic dimensions. GMPLS provides interoperable,scalable and common control plane networks. Distributed network topology and resource availability advertisement. GMPLS protocol provides neighbor discovery and link management. Link management protocol provides fault detection and restoration of the network. GMPLS protocol provides high performance networks. GMPLS mainly focus on control plane (the management of connection) rather than the data plane(actual data traffic). GMPLS protocol replace SONET,ATM layer from the architecture. It provides two tier network layer architecture.
1. Computer networks. Tenebaum.
4. Internet Engineering Task Force (IETF) framework for GMPLS.
5. IEEE communication magazine.
6. J. P Lang Link management protocol.
1. Introduction to GMPLS 2
2. MPLS background and operation 3
3. MPLS action description 4
4. Signalling mechanism 6
5. Tunneling 7
6. MPLS evolution to GMPLS 9
7. GMPLS protocols 11
8. GMPLS protocol stack 12
9. GMPLS Issues and Resolution 13
10. GMPLS Outstanding Issues 25
11. Conclusion 28
12. References 29
I express my sincere thanks to Prof. M.N Agnisarman Namboothiri (Head of the Department, Computer Science and Engineering, MESCE), Mr. Sminesh (Staff incharge) for their kind co-operation for presenting the seminars.
I also extend my sincere thanks to all other members of the faculty of Computer Science and Engineering Department and my friends for their
co-operation and encouragement.
DAISE ANTONY K