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An example of a hierarchical LSP is shown in Figure 9.18. Assume that a number of IP routers are connected to a SONET/SDH network, which in turn is connected to
Figure 9.17 The hierarchy of the four types of interfaces.
WAVELENGTH ROUTING OPTICAL NETWORKS
Figure 9.18 An example of hierarchical LSPs.
a backbone wavelength routing network. The LSP starts at IP router A and ends at IP router C. As can be seen, IP router A is connected to IP router B via a 1-GbE link, and IP router B is connected to DCS A via an OC-48/STM-16 SONET/SDH link. DCS A is connected to OXC A via an OC-192/STM-64 SONET/SDH link. OXCs A and B are part of a wavelength routing network, and are connected by a single fiber that has 32 wavelengths - with each wavelength carrying an OC-192/STM-64 SONET/SDH stream. At the other side of the wavelength routing optical network, OXC B is connected to DCS B via an OC-192/STM-64 SONET/SDH link, and DCS B is connected to IP router C via a 1-GbE link.
The interfaces along the path of the LSP from IP router A to IP router C can be easily deduced. The 1-GbE links between IP routers A and B, and DCS B and IP router C have PSC interfaces. The SONET/SDH links between IP router B and DCS A, DCS A and OXC A, and OXC B and DCS B have TDM interfaces. Finally, the link between OXCs A and B has an LSC interface.
As we move towards the wavelength routing optical network, the capacity of the links increase. (This is indicated in Figure 9.18 by using thicker lines). On the other side of the wavelength routing optical network, the link capacities decrease as we move towards the edge, and this is indicated by decreasing the thickness of the lines. The increase in the link capacity as we move closer to the backbone network is normal, since the links carry more traffic than those in the edge of the network.
In Figure 9.18, the LSP between IP routers A and C is labeled as packet LSP1. As can be seen, this LSP is nested together with other LSPs in the TDM LSP2, which in turn is nested in the lambda LSP3. When LSP1 is being established, DCS A will try to allocate bandwidth within its TDM LSP2. If this is not possible, DCS A will establish a new TDM LSP2 to DCS B. The new TDM LSP2 will be nested within the lightpath lambda LSP3, if bandwidth is available. Otherwise, OXC A will establish a new lightpath to OXC B. If LSPs 2 and 3 do not exist at the time when IP router A is attempting to establish LSP1, then the establishment of LSP1 will trigger DCS A to establish TDM LSP2, and OXC A to establish lambda LSP3.
The generalized label request
The generalized label request is used to communicate characteristics required to support the establishment of an LSP. The information required in a generalized label request is shown in Figure 9.19. The following fields have been defined:
GENERALIZED MPLS (GMPLS)
0 12 3
LSP enc. type
Figure 9.19 The information carried in a generalized label request.
• LSP encoding type: This 8-bit field indicates how the data to be transmitted over the LSP will be encoded. The following values have been defined:
2 Ethernet V2/DIX
3 ANSI PDH
4 ETSI PDH
5 SDH ITU-T G.707
6 SONET ANSI T1.105
7 Digital wrapper
8 Lambda (photonic)
10 Ethernet 802.3
11 Fiber Channel
• Switching type: An 8-bit field used to indicate the type of switching that should be performed on a particular link. This field is used on links that advertise more than one type of switching capability.
• Generalized payload identifier (G-PID): A 16-bit filed used to identify the payload carried by an LSP. It is used by the endpoints of the LSP. The following are some of the values specified:
Value Type Technology
0 Unknown All
14 Byte synchronous mapping of E1 SONET/SDH
17 Bit synchronous mapping of DS1/T1 SONET/SDH
28 PoS- No scrambling, 16 bit CRC SONET/SDH
32 ATM mapping SONET,SDH
33 Ethernet Lambda, Fiber
34 SDH Lambda, Fiber
35 SONET Lambda, Fiber
36 Digital wrapper Lambda, Fiber
37 Lambda Fiber
The generalized label
Since the scope of MPLS was widened into the optical and TDM domains, several new forms of labels are required. The generalized label not only allows for the MPLS-type label that travels in-band with the associated packet, but also allows for labels that identify time
WAVELENGTH ROUTING OPTICAL NETWORKS
slots, wavelengths, or a fiber. These new forms of labels, which are collectively referred to as the generalized label, can carry a label that represents: