BUNDLE]. A typical example is an optical meshed network where adjacent optical cross-connects (LSRs) are connected by several hundreds of parallel wavelengths. In this network, consider the application of link state routing protocols, like OSPF or IS-IS, with suitable extensions for resource discovery and dynamic route computation. Each wavelength must be advertised separately to be used, except if link bundling is used. When a pair of LSRs is connected by multiple links, it is possible to advertise several (or all) of these links as a single link into OSPF and/or IS-IS. This process is called link bundling, or just bundling. The resulting logical link is called a bundled link as its physical links are called component links (and are identified by interface indexes).
The result is that a combination of three identifiers ((bundled) link identifier, component link identifier, label) is sufficient to unambiguously identify the appropriate resources used by an LSP. The purpose of link bundling is to improve routing scalability by reducing the amount of information that has to be handled by OSPF and/or IS-IS. This reduction is accomplished by performing information aggregation/abstraction. As with any other information aggregation/abstraction, this results in losing some of the information. To limit the amount of losses one need to restrict the type of the information that can be aggregated/abstracted. OSPF-TE] and [ISIS-TE], i.e., they must have the same: - Link Type (i.e., point-to-point or multi-access), - TE Metric (i.e., an administrative cost), - Set of Resource Classes at each end of the links (i.e., colors). Note that a FA may also be a component link. In fact, a bundle can consist of a mix of point-to-point links and FAs, but all sharing some common properties. GMPLS-ROUTING]. The liveness of the bundled link is determined by the liveness of each its component links. A bundled link is alive when at least one of its component links is alive. The liveness of a component link can be determined by any of several means: IS-IS or OSPF hellos over the component link, or RSVP Hello (hop local), or LMP hellos (link local), or from layer 1 or layer 2 indications. Note that (according to the RSVP-TE specification [RFC3209]) the RSVP Hello mechanism is intended to be used when notification of link layer failures is not available and unnumbered links are not used, or when the failure detection mechanisms provided by the link layer are not sufficient for timely node failure detection. Once a bundled link is determined to be alive, it can be advertised as a TE link and the TE information can be flooded. If IS-IS/OSPF hellos are run over the component links, IS-IS/OSPF flooding can be restricted to just one of the component links.
Note that advertising a (bundled) TE link between a pair of LSRs does not imply that there is an IGP adjacency between these LSRs that is associated with just that link. In fact, in certain cases a TE link between a pair of LSRs could be advertised even if there is no IGP adjacency at all between the LSR (e.g., when the TE link is an FA). Forming a bundled link consist in aggregating the identical TE parameters of each individual component link to produce aggregated TE parameters. A TE link as defined by [GMPLS-ROUTING] has many parameters; adequate aggregation rules must be defined for each one. Some parameters can be sums of component characteristics such as the unreserved bandwidth and the maximum reservable bandwidth. Bandwidth information is an important part of a bundle advertisement and it must be clearly defined since an abstraction is done. A GMPLS node with bundled links must apply admission control on a per-component link basis.
RFC3473]/[RFC3472], respectively). For a bi-directional LSP, a component link is provided for each direction by the upstream node. This mechanism does not require each component link to have its own control channel. In fact, it does not even require the whole (bundled) link to have its own control channel. RFC3473]/[RFC3472], respectively). This object/TLV carries the component interface ID in the downstream direction for a unidirectional LSP, and in addition, the component interface ID in the upstream direction for a bi-directional LSP. The two LSRs at each end of the bundled link exchange these identifiers. Exchanging the identifiers may be accomplished by configuration, by means of a protocol such as LMP (preferred solution), by means of RSVP-TE/CR-LDP (especially in the case where a component link is a Forwarding Adjacency), or by means of IS-IS or OSPF extensions. This mechanism does not require each component link to have its own control channel. In fact, it does not even require the whole (bundled) link to have its own control channel.
GMPLS-ROUTING], the second property could be the Encoding [GMPLS-ROUTING], the third property could be the Administrative Weight (cost), the fourth property could be the Resource Classes and finally links may be correlated based on other metrics such as SRLG (Shared Risk Link Groups). When routing an alternate path for protection purposes, the general principle followed is that the alternate path is not routed over any link belonging to an SRLG that belongs to some link of the primary path. Thus, the rule to be followed is to group links belonging to exactly the same set of SRLGs. This type of sequential sub-division may result in a number of bundles between two adjacent nodes. In practice, however, the link properties may not be very heterogeneous among component links between two adjacent nodes. Thus, the number of bundles in practice may not be large. section 5.2 and the section about signaling with an explicit route).
Conceptually, a difference between UNI and NNI make sense either if both interface uses completely different protocols, or if they use the same protocols but with some outstanding differences. In the first case, separate protocols are often defined successively, with more or less success. The GMPLS approach consisted in building a consistent model from day one, considering both the UNI and NNI interfaces at the same time [GMPLS-OVERLAY]. For that purpose, a very few specific UNI particularities have been ignored in a first time. GMPLS has been enhanced to support such particularities at the UNI by some other standardization bodies (see hereafter). OIF-UNI] defines an interface between a client SONET/SDH equipment and an SONET/SDH network, each belonging to a distinct administrative authority. It is designed for an overlay model. The OIF UNI defines additional mechanisms on the top of GMPLS for the UNI. For instance, the OIF service discovery procedure is a precursor to obtaining UNI services. Service discovery allows a client to determine the static parameters of the interconnection with the network, including the UNI signaling protocol, the type of concatenation, the transparency level as well as the type of diversity (node, link, SRLG) supported by the network. Since the current OIF UNI interface does not cover photonic networks, G.709 Digital Wrapper, etc, it is from that perspective a subset of the GMPLS Architecture at the UNI.
exchanged at the UNI, except maybe the ordered list of LSRs. The only routing information used by the edge node is that list. The edge node sends by default an LSP request to the preferred LSR. ICMP redirects could be send by this LSR to redirect some LSP requests to another LSR connected to the edge node. GMPLS does not preclude that model. - Partial peering: limited routing information (mainly reachability) can be exchanged across the UNI using some extensions in the signaling plane. The reachability information exchanged at the UNI may be used to initiate edge node specific routing decision over the network. GMPLS does not have any capability to support this model today. - Silent listening: the edge node can silently listen to routing protocols and take routing decisions based on the information obtained. An edge node receives the full routing information, including traffic engineering extensions. One LSR should forward transparently all routing PDUs to the edge node. An edge node can now compute a complete explicit route taking into consideration all the end-to-end routing information. GMPLS does not preclude this model. - Full peering: in addition to silent listening, the edge node participates within the routing, establish adjacencies with its neighbors and advertises LSAs. This is useful only if there are benefits for edge nodes to advertise themselves traffic engineering information. GMPLS does not preclude this model. LMP] has been defined to fulfill these operations. LMP has been initiated in the context of GMPLS but is a generic toolbox that can be also used in other contexts.
In GMPLS, the control channels between two adjacent nodes are no longer required to use the same physical medium as the data links between those nodes. Moreover, the control channels that are used to exchange the GMPLS control-plane information exist independently of the links they manage. Hence, LMP was designed to manage the data links, independently of the termination capabilities of those data links. Control channel management and link property correlation procedures are mandatory per LMP. Link connectivity verification and fault management procedures are optional.
Each control channel individually negotiates its control channel parameters and maintains connectivity using a fast Hello protocol. The latter is required if lower-level mechanisms are not available to detect link failures. The Hello protocol of LMP is intended to be a lightweight keep-alive mechanism that will react to control channel failures rapidly so that IGP Hellos are not lost and the associated link-state adjacencies are not removed uselessly. The Hello protocol consists of two phases: a negotiation phase and a keep-alive phase. The negotiation phase allows negotiation of some basic Hello protocol parameters, like the Hello frequency. The keep-alive phase consists of a fast lightweight bi-directional Hello message exchange. If a group of control channels share a common node pair and support the same LMP capabilities, then LMP control channel messages (except Configuration messages, and Hello's) may be transmitted over any of the active control channels without coordination between the local and remote nodes. For LMP, it is essential that at least one control channel is always available. In case of control channel failure, it may be possible to use an alternate active control channel without coordination.
This procedure should be performed initially when a data-bearing link is first established, and subsequently, on a periodic basis for all unallocated (free) data-bearing links. The verification procedure consists of sending Test messages in-band over the data-bearing links. This requires that the unallocated links must be opaque; however, multiple degrees of opaqueness (e.g., examining overhead bytes, terminating the payload, etc.), and hence different mechanisms to transport the Test messages, are specified. Note that the Test message is the only LMP message that is transmitted over the data-bearing link, and that Hello messages continue to be exchanged over the control channel during the link verification process. Data-bearing links are tested in the transmit direction as they are unidirectional. As such, it is possible for LMP neighboring nodes to exchange the Test messages simultaneously in both directions. To initiate the link verification procedure, a node must first notify the adjacent node that it will begin sending Test messages over a particular data-bearing link, or over the component links of a particular bundled link. The node must also indicate the number of data-bearing links that are to be verified; the interval at which the test messages will be sent; the encoding scheme, the transport mechanisms that are supported, the data rate for Test messages; and, in the case where the data-bearing links correspond to fibers, the wavelength over which the Test messages will be transmitted. Furthermore, the local and remote bundled link identifiers are transmitted at this time to perform the component link association with the bundled link identifiers.
LMP provides a fault localization procedure that can be used to rapidly localize link failures, by notifying a fault up to the node upstream of that fault (i.e., through a fault notification procedure). A downstream LMP neighbor that detects data link failures will send an LMP message to its upstream neighbor notifying it of the failure. When an upstream node receives a failure notification, it can correlate the failure with the corresponding input ports to determine if the failure is between the two nodes. Once the failure has been localized, the signaling protocols can be used to initiate link or path protection/restoration procedures. LMP-WDM] defines extensions to LMP for use between an OXC and an OLS. These extensions are intended to satisfy the Optical Link Interface Requirements described in [OLI-REQ]. Fault detection is particularly an issue when the network is using all-optical photonic switches (PXC). Once a connection is established, PXCs have only limited visibility into the health of the connection. Although the PXC is all-optical, long-haul OLSs typically terminate channels electrically and regenerate them optically. This provides an opportunity to monitor the health of a channel between PXCs. LMP-WDM can then be used by the OLS to provide this information to the PXC. In addition to the link information known to the OLS that is exchanged through LMP-WDM, some information known to the OXC may also be exchanged with the OLS through LMP-WDM. This information is useful for alarm management and link monitoring (e.g., trace monitoring). Alarm management is important because the administrative state of a connection, known to the OXC (e.g., this information may be learned through the Admin Status object of GMPLS signaling [RFC3471]), can be used to suppress spurious alarms. For example, the OXC may know that a connection is "up", "down", in a "testing" mode, or being deleted ("deletion-in-progress"). The OXC can use this information to inhibit alarm reporting from the OLS when a connection is "down", "testing", or being deleted.
It is important to note that an OXC may peer with one or more OLSs and an OLS may peer with one or more OXCs. Although there are many similarities between an OXC-OXC LMP session and an OXC-OLS LMP session, particularly for control management and link verification, there are some differences as well. These differences can primarily be attributed to the nature of an OXC-OLS link, and the purpose of OXC-OLS LMP sessions. The OXC-OXC links can be used to provide the basis for GMPLS signaling and routing at the optical layer. The information exchanged over LMP-WDM sessions is used to augment knowledge about the links between OXCs. In order for the information exchanged over the OXC-OLS LMP sessions to be used by the OXC-OXC session, the information must be coordinated by the OXC. However, the OXC-OXC and OXC-OLS LMP sessions are run independently and must be maintained separately. One critical requirement when running an OXC-OLS LMP session is the ability of the OLS to make a data link transparent when not doing the verification procedure. This is because the same data link may be verified between OXC-OLS and between OXC-OXC. The verification procedure of LMP is used to coordinate the Test procedure (and hence the transparency/opaqueness of the data links). To maintain independence between the sessions, it must be possible for the LMP sessions to come up in any order. In particular, it must be possible for an OXC-OXC LMP session to come up without an OXC-OLS LMP session being brought up, and vice-versa. RFC3471]. 2. RSVP-TE extensions [RFC3473]. 3. CR-LDP extensions [RFC3472]. In addition, independent parts are available per technology: 1. GMPLS extensions for SONET and SDH control [RFC3946]. 2. GMPLS extensions for G.709 control [GMPLS-G709].
The following MPLS profile expressed in terms of MPLS features [RFC3031] applies to GMPLS: - Downstream-on-demand label allocation and distribution. - Ingress initiated ordered control. - Liberal (typical), or conservative (could) label retention mode. - Request, traffic/data, or topology driven label allocation strategy. - Explicit routing (typical), or hop-by-hop routing. The GMPLS signaling defines the following new building blocks on the top of MPLS-TE: 1. A new generic label request format. 2. Labels for TDM, LSC and FSC interfaces, generically known as Generalized Label. 3. Waveband switching support. 4. Label suggestion by the upstream for optimization purposes (e.g., latency). 5. Label restriction by the upstream to support some optical constraints. 6. Bi-directional LSP establishment with contention resolution. 7. Rapid failure notification extensions. 8. Protection information currently focusing on link protection, plus primary and secondary LSP indication. 9. Explicit routing with explicit label control for a fine degree of control. 10. Specific traffic parameters per technology. 11. LSP administrative status handling. 12. Control channel separation. These building blocks will be described in more details in the following. A complete specification can be found in the corresponding documents. Note that GMPLS is highly generic and has many options. Only building blocks 1, 2 and 10 are mandatory, and only within the specific format that is needed. Typically, building blocks 6 and 9 should be implemented. Building blocks 3, 4, 5, 7, 8, 11 and 12 are optional.
A typical SONET/SDH switching network would implement building blocks: 1, 2 (the SONET/SDH label), 6, 9, 10 and 11. Building blocks 7 and 8 are optional since the protection can be achieved using SONET/SDH overhead bytes. A typical wavelength switching network would implement building blocks: 1, 2 (the generic format), 4, 5, 6, 7, 8, 9 and 11. Building block 3 is only needed in the particular case of waveband switching. A typical fiber switching network would implement building blocks: 1, 2 (the generic format), 6, 7, 8, 9 and 11. A typical MPLS-IP network would not implement any of these building blocks, since the absence of building block 1 would indicate regular MPLS-IP. Note however that building block 1 and 8 can be used to signal MPLS-IP as well. In that case, the MPLS-IP network can benefit from the link protection type (not available in CR-LDP, some very basic form being available in RSVP-TE). Building block 2 is here a regular MPLS label and no new label format is required. GMPLS does not specify any profile for RSVP-TE and CR-LDP implementations that have to support GMPLS - except for what is directly related to GMPLS procedures. It is to the manufacturer to decide which are the optional elements and procedures of RSVP-TE and CR-LDP that need to be implemented. Some optional MPLS-TE elements can be useful for TDM, LSC and FSC layers, for instance the setup and holding priorities that are inherited from MPLS-TE.
If the LSP is a bi-directional LSP, an Upstream Label is also specified in the Path/Label Request message. This label will be the one to use in the upstream direction. Additionally, a Suggested Label, a Label Set and a Waveband Label can also be included in the message. Other operations are defined in MPLS-TE. The downstream node will send back a Resv/Label Mapping message including one Generalized Label object/TLV that can contain several Generalized Labels. For instance, if a concatenated SONET/SDH signal is requested, several labels can be returned. In case of SONET/SDH virtual concatenation, a list of labels is returned. Each label identifying one element of the virtual concatenated signal. This limits virtual concatenation to remain within a single (component) link. In case of any type of SONET/SDH contiguous concatenation, only one label is returned. That label is the lowest signal of the contiguous concatenated signal (given an order specified in [RFC3946]). In case of SONET/SDH "multiplication", i.e., co-routing of circuits of the same type but without concatenation but all belonging to the same LSP, the explicit ordered list of all signals that take part in the LSP is returned.
A link may support a set of encoding formats, where support means that a link is able to carry and switch a signal of one or more of these encoding formats. The Switching Type indicates then the type of switching that should be performed on a particular link for that LSP. This information is needed for links that advertise more than one type of switching capability. Nodes must verify that the type indicated in the Switching Type is supported on the corresponding incoming interface; otherwise, the node must generate a notification message with a "Routing problem/Switching Type" indication. The LSP payload type (G-PID) identifies the payload carried by the LSP, i.e., an identifier of the client layer of that LSP. For some technologies, it also indicates the mapping used by the client layer, e.g., byte synchronous mapping of E1. This must be interpreted according to the LSP encoding type and is used by the nodes at the endpoints of the LSP to know to which client layer a request is destined, and in some cases by the penultimate hop. Other technology specific parameters are not transported in the Generalized Label Request but in technology specific traffic parameters as explained hereafter. Currently, two set of traffic parameters are defined, one for SONET/SDH and one for G.709. Note that it is expected than specific traffic parameters will be defined in the future for photonic (all optical) switching. RFC3946] specify a powerful set of capabilities for SONET [ANSI-T1.105] and SDH [ITUT-G.707]. The first traffic parameter specifies the type of the elementary SONET/SDH signal that comprises the requested LSP, e.g., VC-11, VT6, VC-4, STS-3c, etc. Several transforms can then be applied successively on the elementary Signal to build the final signal being actually requested for the LSP. These transforms are the contiguous concatenation, the virtual concatenation, the transparency and the multiplication. Each one is optional. They must be applied strictly in the following order: - First, contiguous concatenation can be optionally applied on the Elementary Signal, resulting in a contiguously concatenated signal.
- Second, virtual concatenation can be optionally applied either directly on the elementary Signal, or on the contiguously concatenated signal obtained from the previous phase. - Third, some transparency can be optionally specified when requesting a frame as signal rather than a container. Several transparency packages are defined. - Fourth, a multiplication can be optionally applied either directly on the elementary Signal, or on the contiguously concatenated signal obtained from the first phase, or on the virtually concatenated signal obtained from the second phase, or on these signals combined with some transparency. For RSVP-TE, the SONET/SDH traffic parameters are carried in a new SENDER_TSPEC and FLOWSPEC. The same format is used for both. There is no Adspec associated with the SENDER_TSPEC, it is omitted or a default value is used. The content of the FLOWSPEC object received in a Resv message should be identical to the content of the SENDER_TSPEC of the corresponding Path message. In other words, the receiver is normally not allowed to change the values of the traffic parameters. However, some level of negotiation may be achieved as explained in [RFC3946]. For CR-LDP, the SONET/SDH traffic parameters are simply carried in a new TLV. Note that a general discussion on SONET/SDH and GMPLS can be found in [SONET-SDH-GMPLS-FRM]. ITUT-G.709] based network is decomposed in two major layers: an optical layer (i.e., made of wavelengths) and a digital layer. These two layers are divided into sub-layers and switching occurs at two specific sub-layers: at the OCh (Optical Channel) optical layer and at the ODU (Optical channel Data Unit) electrical layer. The ODUk notation is used to denote ODUs at different bandwidths. The GMPLS G.709 traffic parameters [GMPLS-G709] specify a powerful set of capabilities for ITU-T G.709 networks. The first traffic parameter specifies the type of the elementary G.709 signal that comprises the requested LSP, e.g., ODU1, OCh at 40 Gbps, etc. Several transforms can then be applied successively on the elementary Signal to build the final signal being actually requested for the LSP.
These transforms are the virtual concatenation and the multiplication. Each one of these transforms is optional. They must be applied strictly in the following order: - First, virtual concatenation can be optionally applied directly on the elementary Signal, - Second, a multiplication can be optionally applied, either directly on the elementary Signal, or on the virtually concatenated signal obtained from the first phase. Additional ODUk Multiplexing traffic parameters allow indicating an ODUk mapping (ODUj into ODUk) for an ODUk multiplexing LSP request. G.709 supports the following multiplexing capabilities: ODUj into ODUk (k > j) and ODU1 with ODU2 multiplexing into ODU3. For RSVP-TE, the G.709 traffic parameters are carried in a new SENDER-TSPEC and FLOWSPEC. The same format is used for both. There is no Adspec associated with the SENDER_TSPEC, it is omitted or a default value is used. The content of the FLOWSPEC object received in a Resv message should be identical to the content of the SENDER_TSPEC of the corresponding Path message. For CR-LDP, the G.709 traffic parameters are simply carried in a new TLV.
wavelength label. Exception is that semantically the waveband can be subdivided into wavelengths whereas the wavelength can only be subdivided into time or statistically multiplexed labels. In the context of waveband switching, the generalized label used to indicate a waveband contains three fields, a waveband ID, a Start Label and an End Label. The Start and End Labels are channel identifiers from the sender perspective that identify respectively, the lowest value wavelength and the highest value wavelength making up the waveband.
The receiver of a Label Set must restrict its choice of labels to one that is in the Label Set. A Label Set may be present across multiple hops. In this case, each node generates its own outgoing Label Set, possibly based on the incoming Label Set and the node's hardware capabilities. This case is expected to be the norm for nodes with conversion incapable interfaces. RFC3209] or CR-LDP [RFC3212] two unidirectional paths must be independently established. This approach has the following disadvantages: 1. The latency to establish the bi-directional LSP is equal to one round trip signaling time plus one initiator-terminator signaling transit delay. This not only extends the setup latency for successful LSP establishment, but it extends the worst-case latency for discovering an unsuccessful LSP to as much as two times the initiator-terminator transit delay. These delays are particularly significant for LSPs that are established for restoration purposes. 2. The control overhead is twice that of a unidirectional LSP. This is because separate control messages (e.g., Path and Resv) must be generated for both segments of the bi-directional LSP. 3. Because the resources are established in separate segments, route selection is complicated. There is also additional potential race for conditions in assignment of resources, which decreases the overall probability of successfully establishing the bi- directional connection.
4. It is more difficult to provide a clean interface for SONET/SDH equipment that may rely on bi-directional hop-by-hop paths for protection switching. Note that existing SONET/SDH equipment transmits the control information in-band with the data. 5. Bi-directional optical LSPs (or lightpaths) are seen as a requirement for many optical networking service providers. With bi-directional LSPs both the downstream and upstream data paths, i.e., from initiator to terminator and terminator to initiator, are established using a single set of signaling messages. This reduces the setup latency to essentially one initiator-terminator round trip time plus processing time, and limits the control overhead to the same number of messages as a unidirectional LSP. For bi-directional LSPs, two labels must be allocated. Bi- directional LSP setup is indicated by the presence of an Upstream Label in the appropriate signaling message.
2. Expedited notification: Extensions to RSVP-TE enable expedited notification of failures and other events to determined nodes. For CR-LDP, there is not currently a similar mechanism. The first extension identifies where event notifications are to be sent. The second provides for general expedited event notification with a Notify message. Such extensions can be used by fast restoration mechanisms. Notifications may be requested in both the upstream and downstream directions. The Notify message is a generalized notification mechanism that differs from the currently defined error messages in that it can be "targeted" to a node other than the immediate upstream or downstream neighbor. The Notify message does not replace existing error messages. The Notify message may be sent either (a) normally, where non-target nodes just forward the Notify message to the target node, similar to ResvConf processing in [RFC2205]; or (b) encapsulated in a new IP header whose destination is equal to the target IP address. 3. Faster removal of intermediate states: A specific RSVP optimization allowing in some cases the faster removal of intermediate states. This extension is used to deal with specific RSVP mechanisms.
Six link protection types are currently defined as individual flags and can be combined: enhanced, dedicated 1+1, dedicated 1:1, shared, unprotected, extra traffic. See [RFC3471] section 7.1 for a precise definition of each.
This can also be used when it is desirable to "splice" two LSPs together, i.e., where the tail of the first LSP would be "spliced" into the head of the second LSP. When used together with an optimization algorithm, it can provide very detailed explicit routes, including the label (timeslot) to use on a link, in order to minimize the fragmentation of the SONET/SDH multiplex on the corresponding interface.
studies are required to understand the impact of dynamically changing some SONET/SDH circuit characteristics such as the bandwidth, the protection type, the transparency, the concatenation, etc.