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Generic MPLS label, frame relay label, ATM label
A set of time slots within a SONET/SDH frame
A single wavelength within a waveband or fiber
A single waveband within a fiber
A single fiber in a bundle
Since the node using GMPLS knows the type of link used, the generalized label does not contain a type field. The generalized label is not hierarchical. When multiple level of labels are required, each LSP must be established separately. The information carried in the generalized label is shown in Figure 9.20. The interpretation of the label field depends on the type of the link over which the label is used.
The suggested label
GMPLS permits the use of a suggested label. This label is used to provide a downstream node with the upstream nodes label preference. This permits the upstream node to start configuring its hardware with the proposed label before the label is communicated by the downstream node. This a useful option, if the configuration time is non-trivial. A suggested label can be over-ridden by the downstream node. The suggested label format is the same as the generalized label format.
The label set
The label set is used to limit the label choice of a downstream node to a set of acceptable labels. This limitation applies on a per-hop basis. The receiver of the label set must restrict its choice of labels according to the label set. A label set might be present over many hops, in which case each node generates its own label set possibly based on the incoming label set and the nodes hardware capabilities.
A label set is useful in the optical domain in the following four cases:
Case 1: The end equipment is only capable of transmitting or receiving on a small, specific set of wavelengths.
Case 2: There is a sequence of interfaces that cannot support wavelength conversion, and require the same wavelength to be used over a sequence of hops or even the entire path.
Case 3: Limit the number of wavelength conversions along the path.
Case 4: Two ends of a link support different sets of wavelengths.
The information carried in a label set is shown in Figure 9.21. A label set is composed of one or more elements of the label set. Each element is referred to as a subchannel, and
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Figure 9.20 The information carried in the generalized label.
GENERALIZED MPLS (GMPLS)
Figure 9.21 The information carried in the label set.
has the same format as the generalized label. The following fields have been defined in addition to the subchannel:
Action: This 8-bit field indicates how the label set is to be interpreted. The following values have been defined:
? Inclusive list (value set to 0): Indicates that the label set contains one or more subchannel elements that should be included in the label set.
? Exclusive list (value set to 1): Indicates that the label set contains one or more subchannel elements that should be excluded from the label set.
? Inclusive range (value set to 2): Indicates that the label set contains a range of labels. The object/TLV contains two subchannel elements: the first one indicates the start of the range, and the second one indicates the end of the range. A value of 0 indicates that there is no bound on the corresponding portion of the range.
? Exclusive range (value set to 3): Indicates that the label set contains a range of labels that should be excluded from the label set. As above, the object/TLV contains two subchannel elements: the first one indicates the start of the range, and the second one indicates the end of the range. A value of 0 indicates that there is no bound on the corresponding portion of the range.
Label type: A 14-bit field that is used to indicate the type and format of the labels that are carried in the object/TLV.
In MPLS, a bidirectional LSP is established by setting up separately two unidirectional LSPs. GMPLS, unlike MPLS, supports the establishment of a bidirectional LSPs. That is, both directions of the LSP are established using a single set of signaling messages.
For a bidirectional LSP, two labels must be allocated over the same hop. Bidirectional setup is indicated by the presence of an upstream label object/TLV in the appropriate signaling message. An upstream label has the same format as the generalized label presented above.
Protection information is used to indicate the protection type - dedicated 1 + 1, dedicated 1:1, shared 1:N, or unprotected - desired by the requested LSP on a link. Protection
WAVELENGTH ROUTING OPTICAL NETWORKS
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