GMPLS and Automatically Switched Optical Network (1)

1. What is GMPLS?
GMPLS universal Multi-Protocol Label exchange) is a universal Multi-Protocol Label Exchange Technology proposed by IETF for the optical layer. In order to achieve seamless integration of IP and WDM, GMPLS expands MPLS labels so that labels can be used not only to mark traditional data packets, but also to mark TDM time slots, wavelengths, wavelength groups, and optical fibers. To fully utilize the resources of WDM optical networks, to meet the needs of new businesses in the future, such as VPN and optical wavelength leasing, to achieve intelligent optical networks, GMPLS also modifies and supplements signaling and routing protocols; to solve various link management problems in optical networks, GMPLS designs a new LMP Protocol. To ensure the reliability of optical network operations, GMPLS also improves the protection and recovery mechanisms of optical networks.
Ii. GMPLS Technology
1. Interface Type
By adding a 32bit "shim" label to the IP Address Header, MPLS enables connection-oriented IP address transmission, which greatly speeds up IP packet forwarding. GMPLS expands the labels by uniformly marking TDM time slots, optical wavelengths, and optical fibers, so that GMPLS not only supports IP packets and ATM cells, moreover, it can support voice-oriented TDM networks and WDM optical networks that provide large-capacity transmission bandwidth, thus realizing the normalization mark of IP Address data exchange, TDM Circuit Switching mainly SDH) and WDM optical switching.
GMPLS defines five interface types to implement the above normalization labels:
(1) group exchange interface PSCPacket Switch Capable): Performs group exchange. The Group boundary is identified and forwarded to the group based on the information in the group header. For example, the MPLS label exchange router LSR forwards data based on the "shim" label;
(2) L2 switching interface L2SCLayer2 Switch Capable): Performs cell switching. Identify the boundaries of cells and forward the cells according to the information in the cell header. For example, an atm lsr is based on an atm vpi/VCI forwarding cell;
(3) Time Slot Switching interface TDMCTime Division Multiplexing Capable): Forward Services Based on TDM time slots. For example, electrical interfaces of sdh dxc devices can exchange SDH Frames Based on Time slots;
(4) wavelength switching interface LSCLambda Switch Capable): based on the optical wavelength or optical band forwarding service carrying services. For example, OXC is a type of optical wavelength-level device that can be used to make forwarding decisions based on optical wavelength. Further, you can make forwarding decisions based on the optical band. Optical band switching is a further extension of optical wavelength switching. It regards a series of continuous optical wavelengths as a switching unit. The use of optical band switching can effectively reduce waveform distortion caused by single wavelength switching, reduce the number of optical switches, and reduce the interval between optical wavelengths;
(5) optical fiber exchange interface FSCFiber Switch Capable): Based on the service optical fiber, it is forwarded to the actual location in the physical space. For example, an OXC device can connect one or more optical fibers.
The relationships between the above five GMPLS interface types are shown in 1.

Figure 1 GMPLS interface relationship
2. GMPLS label
In contrast to the above interfaces, GMPLS defines that the group switch label corresponds to PSC and L2SC), the circuit switch label corresponds to TDMC), and the optical switch label corresponds to LSC and FSC ). The group switch label is the same as the traditional MPLS label, which is not described in this article. Circuit Switching tags and Optical Switching tags are newly defined by GMPLS, including request tags, General tags, recommended tags, and set tags.
(1) Request tag
The request tag is used to establish the LSP path. It is issued by the upstream node of the LSP and is applied to the downstream node for creating LSP resources. Similar to MPLS, the LSP creation process of GMPLS is to send a "tag request message" and "tag shot message" to the target node ". The difference is that you need to add a description of the LSP to be created in the "tag request message", including the LSP type PSC, TDMC, etc.) and the load type. The format is 2.

Figure 2 GMPLS request tag
LSP Enc. Type: The value is used to indicate the LSP Type. For example, when LSP = 1, LSP indicates group transmission, while LSP = 5 indicates SDH, and LSP = 9 indicates optical fiber;
Reserved: Reserved. The value must be set to "0". The value is ignored during receiving;
G-PID: 16 bits, used to indicate the type of load carried by the LSP. For example, G-PID = 14, represents the SDH E1 load of the byte synchronization ing; G-PID = 17, represents the SDH DS1/T1 load of the Bit Synchronization ing; G-PID = 32, represents the number of encapsulated frames.
(2) General labels
A common label is used to indicate the businesses transmitted along the LSP after the LSP is created. The format of common labels is related to the specific technology used for transmission. The tags used for circuit switching and optical switching are different. SDH circuit switch label format 3.

Figure 3 SDH circuit switch label
Where: S indicates the signal rate level of SDH/SONET. S = N represents the STM-N/STS-N signal; U is used to indicate a specific virtual container VC in a STM-1. U is only valid for SDH. For SONET, the value of U should be ignored. U = 1 indicates a VC-4, U = 2 ~ 4 represents the VC-3; K parameters and U, also only valid for SDH. The K parameter is used to represent a specific branch of a VC-4, K = 1 represents only one VC-4 container in the C-4, K = 2 ~ 4 represents the VC-4 contains TUG-3; L is used to indicate whether TUG-3, the VC-3 or the STS-1 SPE has a branch. L = 1 indicates TUG-3/VC-3/STS-1 SPE can no longer minute. L = 2 ~ 8 indicates a specific TUG-2/VT group in the corresponding high-order signal. M indicates the branches of TUG-2/VT. M = 1 indicates that TUG-2/VT can no longer be divided, contains only one VC-2/VT-6. M = 2 ~ 3 represents a specific VT-3 in the corresponding high-order VT group. M = 4 ~ 6 indicates a specific VC-12/VT-2 in the corresponding higher order TUG-2/VT group, and M = 7 ~ 10 represents a specific VC-11/VT-1.5 in the corresponding higher order TUG-2/VT group. M = 0 represents the VC-4, VC-3 or STS-1 SPE. For example, S> 0, U = 1, K = 1, L = 0, M = 0 indicates the STM-1 of the VC-4.
For OXC devices, one-time switching of a set of continuous optical wavelengths can effectively reduce waveform distortion of a single optical wavelength and improve the transmission quality of services. The optical wavelength group exchange can be expressed by optical band exchange tags, as shown in tag format 4.

Figure 4 optical band switching labels
Waveband Id: used to identify an optical band. The value is set by the OXC device on the sending end;
Start Label: used to represent the minimum optical wavelength of the optical band;
End Label: used to represent the maximum wavelength of the optical band;