| Internet Engineering Task Force | Q. Wang, Ed. |
| Internet-Draft | ZTE |
| Intended status: Informational | R. Valiveti, Ed. |
| Expires: December 1, 2017 | Infinera Corp |
| H. Zheng, Ed. | |
| Huawei | |
| H. Helvoort | |
| Hai Gaoming B.V | |
| S. Belotti | |
| Nokia | |
| May 30, 2017 |
GMPLS Routing and Signaling Framework for B100G
draft-merge-ccamp-otn-b100g-fwk-00
The 2016 revision of G.709 introduces support for OTU links with rates larger than 100G. This document provides a framework to address the GMPLS routing and signalling extensions that enable GMPLS to setup paths through network that contain these newly introduced OTUCn links.
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The current GMPLS routing [RFC7138] and signaling extensions [RFC7139] includes coverage for all the OTN capabilities that were defined in the 2012 version of G.709 [ITU-T_G709_2012].
The 2016 version of G.709 [ITU-T_G709_2012] introduces support for higher rate OTU signals, termed OTUCn (which have a nominal rate of n x 100 Gbps). The newly introduced OTUCn represent a very powerful extension to the OTN capabilities, and one which naturally scales to transport any newer clients with bit rates in excess of 100G, as they are introduced.
This document presents an overview of the changes introduced in [ITU-T_G709_2016] and analyzes them to identify the extensions that would be required in GMPLS routing and signaling to enable the new OTN capabilities.
For the purposes of the B100G control plane discussion, the OTN should be considered as a combination of ODU and OTSi layers. Note that [ITU-T_G709_2016] is deprecating the use of the term "Och" for B100G entities, and leaving it intact only for maintaining continuity in the description of the signals with bandwidth upto 100G. This document focuses on only the control of the ODU layer. The control of the OTSi layer will be addressed in a separate document.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
Detailed description of these terms can be found in [ITU-T_G709_2016].
This section provides an overview of new features in [ITU-T_G709_2016].
In G.709 [ITU-T_G709_2012], the standard mechanism for transporting a client signal is to first map it into an ODU signal (of the appropriate rate), and then switch the resulting ODU signal through the OTN network. In the course of its traversal through the OTN network, the ODU signal generated by the mapper is either (a) multiplexed into higher-order ODU, and then encapsulated to form an OTU or (b) directly encapsulated into an OTU signal that defines the section layer. The option (b), i.e. direct encapsulation into an OTU was possible only for ODU1/ODU2/ODU3/ODU4; ODU signals with other rates (e.g. ODUflex) would first have to be processed per option (a) above. The term "client signal" is generic in the sense that it encompasses both Constant Bit rate (CBR) clients (e.g. 10GBASE-R, SONET OC-768), or packet traffic -- where the goal is to transfer the payload from end-to-end (without regard for bit transparency at the PCS layer). Given that OTU4 was the highest rate section layer signal supported in [ITU-T_G709_2012], the client signal rates were limited to be less than 100G (if ODU-VCAT was not used).
In order to carry client signals with rates greater than 100Gbps, [ITU-T_G709_2016] takes a general and scalable approach that decouples the rates of OTU signals from the client rate evolution. The new OTU signal is called OTUCn; this signal is defined to have a rate of (approximately) n*100G. The following are the key characteristics of the OTUCn signal:
The ODUCn signal [ITU-T_G709_2016] can be viewed as being formed by the appropriate interleaving of content from n ODUC signal instances. The ODUC frames have the same structure as a standard ODU -- in the sense that it has the same Overhead (OH) area, and the payload area -- but has a higher rate since its payload area can embed an ODU4 signal. The ODUCn signal can be formed in one of the following ways:
The ODUCn signals have a rate that is captured in Table 1.
| ODU Type | ODU Bit Rate |
|---|---|
| ODUCn | n x 239/226 x 99,532,800 kbit/s = n x 105,258,138.053 kbit/s |
The ODUCn is a multiplex section ODU signal, and is mapped into an OTUCn signal which provides the regenerator section layer. In some scenarios, the ODUCn, and OTUCn signals will be co-terminous, i.e. they will have identical source/sink locations. [ITU-T_G709_2016] and [ITU-T_G872] allow for the ODUCn signal to pass through a digital regenerator node which will terminate the OTUCn layer, but will pass the regenerated (but otherwise untouched) ODUCn towards a different OTUCn interface where a fresh OTUCn layer will be initiated. Specifically, the OPUCn signal flows through these regenerators unchanged. That is, the set of client signals, their TPNs, trib-slot allocation remains unchanged. Note however that the ODUCn Overhead (OH) might be modified if TCM sub-layers are instantiated in order to monitor the performance of the repeater hops. In this sense, the ODUCn should not be seen as a general ODU which can be switched via an ODUk cross-connect. [Note: This document doesn't elaborate on other adaptations (e.g. to/from OTSiA) which are required to transport the OTUCn signal.]
The standard OTUCn signal has the same rate as that of the ODUCn signal as captured in Table 1. This implies that the OTUCn signal can only be transported over wavelength groups which have a total capacity of multiples of (approximately) 100G. Modern DSPs support a variety of bit rates per wavelength, depending on the reach requirements for the optical link. With this in mind, ITU-T supports the notion of a reduced rate OTUCn signal, termed the OTUCn-M. The OTUCn-M signal is derived from the OTUCn signal by retaining all the n instances of overhead (one per OTUC slice) and crunching the OPUC tributary slots marked as "unavailable".
[ITU-T_G709_2012] introduced the support for 1.25G granular tributary slots in OPU2, OPU3, and OPU4 signals. With the introduction of higher rate signals such as the OPUCn, it is no longer practical for the optical networks (and the datapath hardware) to support a very large number of flows at such a fine granularity. ITU-T has defined the OPUC with a tributary slot granularity of 5G. This means that the ODUCn signal has 20*n tributary slots (of 5Gbps capacity).
As mentioned above, the OPUCn signal has 20*n 5G tributary slots. The OPUCn contains n PSI structures, one per OPUC instance. The PSI structure consists of the Payload Type (of 0x22), followed by a Reserved Field (1 byte), followed by the MSI. The OPUCn MSI field has a fixed length of 40*n bytes and indicates the ODTU content of each TS of an OPUCn. Two bytes are used for each of the 20*n tributary slots, and each such information structure has the following format ([ITU-T_G709_2016] G.709:Section 20.4.1):
Note that [ITU-T_G709_2016] introduces support for OTUCn signals with rates of n*100G and also introduces support for client signals with rates larger than 100G (e.g. the future 400GBASE-R client being standardized by IEEE, higher packet streams from NPUs). The approach taken by the ITU-T to map non-OTN client signals to the appropriate ODU containers is as follows:
| ODU Type | ODU Bit Rate |
|---|---|
| ODU0 | 1,244,160 Kbps |
| ODU1 | 239/238 x 2,488,320 Kbps |
| ODU2 | 239/237 x 9,953,280 Kbps |
| ODU2e | 239/237 x 10,312,500 Kbps |
| ODU3 | 239/236 x 39,813,120 Kbps |
| ODU4 | 239/227 x 99,532,800 Kbps |
| ODUflex for CBR client signals | 239/238 x Client signal Bit rate |
| ODUflex for GFP-F mapped packet traffic | Configured bit rate |
| ODUflex for IMP mapped packet traffic | s x 239/238 x 5 156 250 kbit/s: s=2,8,5*n, n ≥ 1 |
| ODUflex for FlexE aware transport | 103 125 000 x 240/238 x n/20 kbit/s, where n is total number of available tributary slots among all PHYs which have been crunched and combined. |
Note that this table doesn't include ODUCn -- since it cannot be generated by mapping a non-OTN signal. An ODUCn is always formed by multiplexing multiple LO-ODUs.
==================================================================
Clients (e.g. SONET/SDH, Ethernet)
+ + +
| | |
+------------------+-------+------+------------------------+
| OPUk |
+----------------------------------------------------------+
| ODUk |
+-----------------------+---------------------------+------+
| OTUk, OTUk.V, OTUkV | OPUk | |
+----------+----------------------------------------+ |
| OTLk.n | | ODUk | |
+----------+ +---------------------+-----+ |
| OTUk, OTUk.V, OTUkV | OPUCn |
+----------+-----------------------+
| OTLk.n | | ODUCn |
+----------+ +------------+
| OTUCn |
+------------+
==================================================================
Figure 1: Digital Structure of OTN interfaces (from G.709:Figure 6-1)
This section introduces various usecases that provide the rationale for the requirements that any solution must satisfy. At a later point in time, it is possible to consolidate these usecases so that all the multiplexing (and demultiplexing) variants are encountered along the path of an end-to-end ODU circuit.
Note-1: These usecases present scenarios in which OTUCn links are depicted. These illustrations do not highlight how the OTUCn is transported between the 3R points. That is, these usecases cover cases in which a standard FlexO interface (e.g. as defined in [ITU-T_G709.1]) is used, or whether a vendor specific mapping of OTUCn to OTSiG (as defined in [ITU-T_G872]) is used. In other words, multiple variants of these usecases based on FlexO usage (or not) are not included in this document.
Note-2: This version of the document covers many usecases in detail. Future versions of this document may combine multiple usecases (e.g. all cases involving ODUflex into one broad category), and retain only the minimal set of usecases.
In the scenario illustrated in Figure 2 a 100GBASE-R client is mapped into an ODU4 at NE1. The resulting ODU4 signal is multiplexed into the ODUC1 server layer (using GMP) and further encapsulated to form the OTUC1 signal. The links NE1-NE2, and NE2-NE3 are both OTUC1 links -- and they can carry one 100GE client mapped into an ODU4 server layer. Actions performed at NE2 are: (a) terminate OTUC1, and ODUC1 towards NE1 (b) demultiplex the ODU4 signal from ODUC1 (c) map the ODU4 signal onto a different ODUC1/OTUC1 towards NE3. NE3 performs the inverse sequence of steps performed at NE1, and recovers the 100GBASE-R client from the ODU4 signal. Note that the ODU4 and ODUC1 signals are not "interoperable" and that the ODUC1 is a server layer to the ODU4 signal.
This illustration is also applicable to the usecase in which members of a FlexE group are transported in a flexe-unaware mode in the transport network. Although this illustration included only OTUC1 signals, any higher rate OTUCn signal can be substituted for these signals. In this particular scenario, there are two adjacent ODUC1 hops, and the NE2 demultiplexs (and multiplexes) the ODU4 onto the ODUC1. It is possible to construct an alternative scenario in the case when NE2 acts as a regenerator, and doesn't terminate the ODUC1 signals in the two hops, and instead repeats the ODUC1 signal; this scenario is specifically discussed in Section 4.6.
==================================================================
+----------+ +----------+
| 100GE | | 100GE |
+----------+ +---------------+ +----------+
| ODU4 | | ODU4 | | ODU4 |
+----------+ +---------------+ +----------+
| ODUC1 | | ODUC1 | ODUC1 | | ODUC1 |
+----------+ +---------------+ +----------+
| OTUC1 +--------+ OTUC1 | OTUC1 +---------+ OTUC1 |
+----------+ +---------------+ +----------+
NE1 NE2 NE3
+-------------> +------------->
Scope of Scope of
OTUC1, ODUC1 OTUC1, ODUC1
==================================================================
Figure 2: 100GE Client service
In the scenario illustrated in Figure 3 a 100GBASE-R client is mapped into an ODU4 at NE1. The resulting ODU4 signal is encapsulated with an OTU layer to form the OTU4 signal. Actions performed at NE2 are: (a) terminate OTU4 layer, and extract the ODU4 signal (b) map the ODU4 signal onto a different ODUC1/OTUC1 towards NE3. NE3 performs the same set of actions that were performed by NE3 in Figure 2. This usecase illustrates a scenario in which an ODU4 signal can span between network elements regardless of whether they support the OTUCn interfaces or not.
==================================================================
+----------+ +----------+
| 100GE | | 100GE |
+----------+ +---------------+ +----------+
| ODU4 | | ODU4 | | ODU4 |
+----------+ +-------+-------+ +----------+
| OTU4 +--------+ OTU4 | ODUC1 | | ODUC1 |
+----------+ +---------------+ +----------+
| OTUC1 +---------+ OTUC1 |
--------+ +----------+
NE1 NE2 NE3
+--------------> +---------------->
Scope of Scope of
OTU4 layer OTUC1, ODUC1
==================================================================
Figure 3: 100GE Client Service with a mix of OTU4, and OTUC1 links
In the scenario illustrated in Figure 4 a 400GBASE-R client is mapped into an ODUflex at NE1. The resulting ODUflex signal is multiplexed into an ODUC4 (using GMP), and then transformed into an OTUC4 signal. The links between NE1-NE2, and NE2-NE3 are OTUC4 and OTUC6 (respectively). Actions performed at NE2 are: (a) terminate OTUC4, and ODUC4 towards NE1 (b) demultiplex the ODUflex signal from ODUC4 (c) map the ODUflex signal onto ODUC6/OTUC6 towards NE3. NE3 performs the inverse sequence of steps performed at NE1, and recovers the 400GBASE-R client from the ODUflex signal.
Although not specifically illustrated in this figure, the 200G of spare capacity in the NE2-NE3 links can be used to carry other client signals.. Although the scenario illustrated in Figure 4 is specific to 400GE, the treatment for packet clients at other rates (e.g. 25G, 50G, 200G) follows a very similar processing sequence. In the case of 25GBASE-R clients , the 25GE client signal will be mapped to an ODUflex, and can be multiplexed into an ODU4 signal, or an ODUCn signal as illustrated here.
==================================================================
+----------+ +----------+
| 400GE | | 400GE |
+----------+ +---------------+ +----------+
| ODUflex | | ODUflex | | ODUflex |
+----------+ +-------+-------+ +----------+
| ODUC4 | | ODUC4 | ODUC6 | | ODUC6 |
+----------+ +---------------+ +----------+
| OTUC4 +--------+ OTUC4 | OTUC6 +---------+ OTUC6 |
+----------+ +-------+-------+ +----------+
NE1 NE2 NE3
<-------------> <------------->
Scope of Scope of
OTUC4, ODUC4 OTUC6, ODUC6
==================================================================
Figure 4: 400GE transport over OTUCn links
In the scenario illustrated in Figure 5 NE1 interfaces to a client equipment which includes the FlexE SHIM functions which originate/terminate a FlexE group. The transport network edge node NE2 is FlexE aware -- but doesn't terminate the FlexE group. NE1 may (as defined in the FlexE draft [I-D.izh-ccamp-flexe-fwk]), crunch the unavailable tributary slots in the FlexE PHY signals, and map the resultant stream to one or more ODUflex signals. The links between NE1-NE2, and NE2-NE3 are OTUC4 and OTUC6 (respectively). Actions performed at NE2 are: (a) terminate OTUC4, and ODUC4 towards NE1 (b) demultiplex the ODUflex signal from ODUC4 (c) map the ODUflex signal onto ODUC6/OTUC6 towards NE3. NE3 recovers the Crunched and combined PHY(s) from the ODUflex signal, re-adds the unavailable calendar slots, and outputs the resulting stream towards the FlexE PHY(s).
In the scenario illustrated in Figure 5 the lowest rate OTUCn link is the OTUC4 link between NE1-NE2. This means that the size of the FlexE group is at most 4. FlexE groups with greater sizes can be handled by utilizing appropriate OTUCn links. Note that at most 400G of the capacity of OTUC6 (or 600G) NE2-NE3 link is occupied by the ODUflex signal; the remaining bandwidth can be allocated to other client signals.
==================================================================
FlexE +----------+ +----------+ FlexE
group | Crunched | | Crunche | Group
+------> and | | and +-------->
| Combined | | Combined | Add
| PHY(s) | | PHY(s) | unavailable
+----------+ +---------------+ +----------+ Calendar
| ODUflex | | ODUflex | | ODUflex | slots
+----------+ +-------+-------+ +----------+
| ODUC4 | | ODUC4 | ODUC6 | | ODUC6 |
+----------+ +---------------+ +----------+
| OTUC4 +---+ OTUC4 | OTUC6 +---+ OTUC6 |
+----------+ +-------+-------+ +----------+
NE1 NE2 NE3
<---------> <----------->
Scope of Scope of
OTUC4, ODUC4 OTUC6, ODUC6
==================================================================
Figure 5: FlexE aware transport over OTUCn links
This use case (see Figure 6) concerns the scenario in which a FlexE group is terminated at the transport network edge node (via the FlexE SHIM function), and the FlexE clients are demultiplexed, and independently transported through the OTN network. In the scenario illustrated in Figure 6 the lowest rate OTUCn link is the OTUC4 link between NE1-NE2. This means that the maximum bit rate of the FlexE client is at most 400G. FlexE clients with greater sizes can be handled by utilizing appropriate OTUCn links. This figure illustrates the case in which one FlexE client is transported between NE1 and NE3. Other FlexE clients recovered at NE1 can routed independently to NE3, or to other network elements.
==================================================================
+-----------------+ +---------------+
| FlexE | | FlexE |
| Client | | Client |
+-----------------+ +---------------+
| FlexE | | +---------------+ | | Flex |
| SHIM | ODUflex | | ODUflex | |ODUflex| SHIM |
+-----------------+ +---------------+ +---------------+
| FlexE | ODUC4 | | ODUC4 | ODUC6 | | ODUC6 | FlexE |
+----+ PHY(s +---------+ +---------------+ +-------+ PHY(s)+---->
FlexE | | OTUC4 +---+ OTUC4 | OTUC6 +---+ OTUC6 | | FlexE
Group +-----------------+ +---------------+ +---------------+ Group
NE1 NE2 NE3
<------------> <----------->
Scope of Scope of
OTUC4, ODUC4 OTUC6, ODUC6
==================================================================
Figure 6: FlexE client transport over OTUCn links
As mentioned in the introductory section, the ODUCn is not a switchable entity. The ODUCn layer is a server layer, which more-or-less occupies the position of a section layer in OTN networks. As such, the ODUCn signal must be terminated and the contained low-order ODU flows can be switched independently to other OTN interfaces. G.709 and G.872 however allow for digital regenerators to terminate the OTUCn layer, and reinject the ODUCn layer towards another interface (where a new OTUCn section layer is started). This scenario is illustrated in Figure 7. In this figure, NE3 is the regenerator. The ODUC2 signal is terminated at NE2, and NE4. At the regeneration points, all the clients embedded inside the ODUCn signal are not touched (i.e. no TS changes can occur). More specifically, the OPUC2 signal is not modified in any way. However, the ODUC2 OH may be modified if intrusive TCM monitoring points are applied to the ODUC2 signal at NE3. It is for this reason that the ODUC2 entity must be visible at NE3.
In scenarios involving multi-hop ODUCn links, GMPLS signalling will be required to setup multiple ODUCn LSPs, each covering a regenerator section (since an end-to-end ODUCn LSP is not possible except in very simple configurations). A LO-ODU can then be switched across multiple ODUCn LSPs (possibly with different rates).
==================================================================
+----------+ +----------+
| 100GE | | 100GE |
+----------+ +---------------+ +----------+
| ODU4 | | ODU4 | | ODU4 |
+----------+ +-------+-------+ +---------+ +----------+
| ODUC1 | | ODUC1 | ODUC2 | | ODUC2 | | ODUC2 |
+----------+ +---------------+ +---------+ +----------+
| OTUC1 +-----+ OTUC1 | OTUC2 +-------+ OTUC2 +-------+ OTUC2 |
+----------+ +-------+-------+ +---------+ +----------+
NE1 NE2 NE3 NE4
<-------------> <-------------> <------------->
Scope of OTUC2 OTUC2
OTUC1, ODUC1
<--------------------------------->
ODUC2
==================================================================
Figure 7: Multihop ODUCn link
The scenario illustrated in Figure 8 is a variant of the basic usecase presented in Figure 2. The only difference is that the second hop of the ODU4 connection makes use of a OTUC2-30 link which has a capacity of 150G.
==================================================================
+----------+ +-----------+
| 100GE | | 100GE |
+----------+ +------------------+ +-----------+
| ODU4 | | ODU4 | | ODU4 |
+----------+ +-------+----------+ +-----------+
| ODUC1 | | ODUC1 | ODUC2 | | ODUC2 |
+----------+ +------------------+ +-----------+
| OTUC1 +--------+ OTUC1 | OTUC2-30 +------+ OTUC2-30 |
+----------+ +-------+----------+ +-----------+
NE1 NE2 NE3
+-------------> +------------->
Scope of Scope of
OTUC1, ODUC1 OTUC2-30
ODUC2
==================================================================
Figure 8: 100GE Client service over OTUCn-M links
The ODUCn links have a tributary slot granularity of 5G -- and this makes it a bit inefficient if a small number of ODU0 flows have to be switched across an ODUCn links. In these cases, it is conceivable that the intermediate nodes may offer the convenience of a intermediate-stage multiplexing, whereby multiple ODU0 flows are first multiplexed into a higher rate container (e.g. ODU2), and then multiplexed into an ODUCn signal. This however assumes that all these ODU0 flows are co-routed in the network. If this assumption cannot be made, the only solution is to multiplex these ODU0 flows into higher rate flows, from the source of the traffic. This usecase isn't elaborated in this document. We can add details if required.
As described in [ITU-T_G872], the digital layers of the OTN are divided into the OTU layer and a hierarchy of one or more ODU layers. As an ODUCn cannot be used to support non-OTN client signals, the OTN client signals (e.g. ODU0, ODU1, ODU2, ODU2e, ODU3, ODU4, ODUflex) are first multiplexed into an ODUCn container, then the ODUCn container is then mapped into OTUCn (see Figure 1). The signal hierarchy supported by the ODUCn and OTUCn needs to be taken into consideration in control plane Routing and Signaling.
ODUCn based connection management is concerned with controlling the connectivity of ODUCn paths. According to [ITU-T_G872], the intermediate nodes with ODUCn do not support the switching of ODUCn tributary slot. Intermediate ODUCn points are only considered as a forwarding node. Once an ODUCn path is used to transport client signal, the TS occupied will not change across the ODUCn network.
[RFC7139] extends the base RSVP-TE signaling specification [RFC4328] to define RSVP-TE signaling extensions that can used to control OTN networks built in accordance with [ITU-T_G709_2012]. [ITU-T_G709_2016] introduced some new containers, such as OPUCn, ODUCn, and OTUCn. The mechanisms defined in [RFC7139] do not support these new OTN features. Therefore, GMPLS signaling protocols MUST be extended to support this new functionality. The following summarizes key aspects that should be considered for GMPLS signaling extensions:
The path computation process needs to select a suitable route for an ODUCn/OTUCn/OTUCn-M connection request. In order to perform the path computation, it needs to evaluate the available bandwidth/slots available on one or more candidate links. The routing protocol SHOULD be extended to carry sufficient information to represent ODU Traffic Engineering (TE) topology.
The Interface Switching Capability Descriptors defined in [RFC4203] present a new constraint for LSP path computation. [RFC4203] defines the Switching Capability, related Maximum LSP Bandwidth, and Switching Capability specific information. [RFC7138] updates the ISCD to support ODU4, ODU2e and ODUflex. The new Switching Capability specific information provided in [RFC7138] have to be adapted to support new features contained in [G709-2016]. The following requirements should be considered:
This memo includes no request to IANA.
None.
| [I-D.izh-ccamp-flexe-fwk] | Hussain, I., Valiveti, R., Pithewan, K., Wang, Q., Andersson, L., Zhang, F., Chen, M., Dong, J., Du, Z., zhenghaomian@huawei.com, z., Zhang, X., Huang, J. and Q. Zhong, "GMPLS Routing and Signaling Framework for Flexible Ethernet (FlexE)", Internet-Draft draft-izh-ccamp-flexe-fwk-00, October 2016. |