are the same as LSP Encoding as defined in [GMPLS-SIG].
An interface may have more than one Interface Switching Capability
Descriptor. This is used to handle interfaces that support multiple
switching capabilities, for interfaces that have Max LSP Bandwidth
values that differ by priority level, and for interfaces that support
discrete bandwidths.
Depending on a particular Interface Switching Capability, the
Interface Switching Capability Descriptor may include additional
information, as specified below.
2.4.1. Layer-2 Switch Capable
If an interface is of type L2SC, it means that the node receiving
data over this interface can switch the received frames based on the
layer 2 address. For example, an interface associated with a link
terminating on an ATM switch would be considered L2SC.
2.4.2. Packet-Switch Capable
If an interface is of type PSC-1 through PSC-4, it means that the
node receiving data over this interface can switch the received data
on a packet-by-packet basis, based on the label carried in the "shim"
header [RFC3032]. The various levels of PSC establish a hierarchy of
LSPs tunneled within LSPs.
For Packet-Switch Capable interfaces the additional information
includes Maximum LSP Bandwidth, Minimum LSP Bandwidth, and interface
MTU.
For a simple (unbundled) link, the Maximum LSP Bandwidth at priority
p is defined to be the smaller of the unreserved bandwidth at
priority p and a "Maximum LSP Size" parameter which is locally
configured on the link, and whose default value is equal to the Max
Link Bandwidth. Maximum LSP Bandwidth for a bundled link is defined
in [LINK-BUNDLE].
The Maximum LSP Bandwidth takes the place of the Maximum Link
Bandwidth ([ISIS-TE], [OSPF-TE]). However, while Maximum Link
Bandwidth is a single fixed value (usually simply the link capacity),
Maximum LSP Bandwidth is carried per priority, and may vary as LSPs
are set up and torn down.
Although Maximum Link Bandwidth is to be deprecated, for backward
compatibility, one MAY set the Maximum Link Bandwidth to the Maximum
LSP Bandwidth at priority 7.
The Minimum LSP Bandwidth specifies the minimum bandwidth an LSP
could reserve.
Typical values for the Minimum LSP Bandwidth and for the Maximum LSP
Bandwidth are enumerated in [GMPLS-SIG].
On a PSC interface that supports Standard SDH encoding, an LSP at
priority p could reserve any bandwidth allowed by the branch of the
SDH hierarchy, with the leaf and the root of the branch being defined
by the Minimum LSP Bandwidth and the Maximum LSP Bandwidth at
priority p.
On a PSC interface that supports Arbitrary SDH encoding, an LSP at
priority p could reserve any bandwidth between the Minimum LSP
Bandwidth and the Maximum LSP Bandwidth at priority p, provided that
the bandwidth reserved by the LSP is a multiple of the Minimum LSP
Bandwidth.
The Interface MTU is the maximum size of a packet that can be
transmitted on this interface without being fragmented.
2.4.3. Time-Division Multiplex Capable
If an interface is of type TDM, it means that the node receiving data
over this interface can multiplex or demultiplex channels within an
SDH payload.
For Time-Division Multiplex Capable interfaces the additional
information includes Maximum LSP Bandwidth, the information on
whether the interface supports Standard or Arbitrary SDH, and Minimum
LSP Bandwidth.
For a simple (unbundled) link the Maximum LSP Bandwidth at priority p
is defined as the maximum bandwidth an LSP at priority p could
reserve. Maximum LSP Bandwidth for a bundled link is defined in
[LINK-BUNDLE].
The Minimum LSP Bandwidth specifies the minimum bandwidth an LSP
could reserve.
Typical values for the Minimum LSP Bandwidth and for the Maximum LSP
Bandwidth are enumerated in [GMPLS-SIG].
On an interface having Standard SDH multiplexing, an LSP at priority
p could reserve any bandwidth allowed by the branch of the SDH
hierarchy, with the leaf and the root of the branch being defined by
the Minimum LSP Bandwidth and the Maximum LSP Bandwidth at priority
p.
On an interface having Arbitrary SDH multiplexing, an LSP at priority
p could reserve any bandwidth between the Minimum LSP Bandwidth and
the Maximum LSP Bandwidth at priority p, provided that the bandwidth
reserved by the LSP is a multiple of the Minimum LSP Bandwidth.
Interface Switching Capability Descriptor for the interfaces that
support sub VC-3 may include additional information. The nature and
the encoding of such information is outside the scope of this
document.
A way to handle the case where an interface supports multiple
branches of the SDH multiplexing hierarchy, multiple Interface
Switching Capability Descriptors would be advertised, one per branch.
For example, if an interface supports VC-11 and VC-12 (which are not
part of same branch of SDH multiplexing tree), then it could
advertise two descriptors, one for each one.
2.4.4. Lambda-Switch Capable
If an interface is of type LSC, it means that the node receiving data
over this interface can recognize and switch individual lambdas
within the interface. An interface that allows only one lambda per
interface, and switches just that lambda is of type LSC.
The additional information includes Reservable Bandwidth per
priority, which specifies the bandwidth of an LSP that could be
supported by the interface at a given priority number.
A way to handle the case of multiple data rates or multiple encodings
within a single TE Link, multiple Interface Switching Capability
Descriptors would be advertised, one per supported data rate and
encoding combination. For example, an LSC interface could support
the establishment of LSC LSPs at both STM-16 and STM-64 data rates.
2.4.5. Fiber-Switch Capable
If an interface is of type FSC, it means that the node receiving data
over this interface can switch the entire contents to another
interface (without distinguishing lambdas, channels or packets).
I.e., an interface of type FSC switches at the granularity of an
entire interface, and can not extract individual lambdas within the
interface. An interface of type FSC can not restrict itself to just
one lambda.
2.4.6. Multiple Switching Capabilities per Interface
An interface that connects a link to an LSR may support not one, but
several Interface Switching Capabilities. For example, consider a
fiber link carrying a set of lambdas that terminates on an LSR
interface that could either cross-connect one of these lambdas to
some other outgoing optical channel, or could terminate the lambda,
and extract (demultiplex) data from that lambda using TDM, and then
cross-connect these TDM channels to some outgoing TDM channels. To
support this a Link State Advertisement may carry a list of Interface
Switching Capabilities Descriptors.
2.4.7. Interface Switching Capabilities and Labels
Depicting a TE link as a tuple that contains Interface Switching
Capabilities at both ends of the link, some examples links may be:
[PSC, PSC] - a link between two packet LSRs
[TDM, TDM] - a link between two Digital Cross Connects
[LSC, LSC] - a link between two OXCs
[PSC, TDM] - a link between a packet LSR and Digital Cross Connect
[PSC, LSC] - a link between a packet LSR and an OXC
[TDM, LSC] - a link between a Digital Cross Connect and an OXC
Both ends of a given TE link has to use the same way of carrying
label information over that link. Carrying label information on a
given TE link depends on the Interface Switching Capability at both
ends of the link, and is determined as follows:
[PSC, PSC] - label is carried in the "shim" header [RFC3032]
[TDM, TDM] - label represents a TDM time slot [GMPLS-SONET-SDH]
[LSC, LSC] - label represents a lambda
[FSC, FSC] - label represents a port on an OXC
[PSC, TDM] - label represents a TDM time slot [GMPLS-SONET-SDH]
[PSC, LSC] - label represents a lambda
[PSC, FSC] - label represents a port
[TDM, LSC] - label represents a lambda
[TDM, FSC] - label represents a port
[LSC, FSC] - label represents a port
2.4.8. Other Issues
It is possible that Interface Switching Capability Descriptor will
change over time, reflecting the allocation/deallocation of LSPs.
For example, assume that VC-3, VC-4, VC-4-4c, VC-4-16c and VC-4-64c
LSPs can be established on a STM-64 interface whose Encoding Type is
SDH. Thus, initially in the Interface Switching Capability
Descriptor the Minimum LSP Bandwidth is set to VC-3, and Maximum LSP
Bandwidth is set to STM-64 for all priorities. As soon as an LSP of
VC-3 size at priority 1 is established on the interface, it is no
longer capable of VC-4-64c for all but LSPs at priority 0.
Therefore, the node advertises a modified Interface Switching
Capability Descriptor indicating that the Maximum LSP Bandwidth is no
longer STM-64, but STM-16 for all but priority 0 (at priority 0 the
Maximum LSP Bandwidth is still STM-64). If subsequently there is
another VC-3 LSP, there is no change in the Interface Switching
Capability Descriptor. The Descriptor remains the same until the
node can no longer establish a VC-4-16c LSP over the interface (which
means that at this point more than 144 time slots are taken by LSPs
on the interface). Once this happened, the Descriptor is modified
again, and the modified Descriptor is advertised to other nodes.
2.5. Bandwidth Encoding
Encoding in IEEE floating point format [IEEE] of the discrete values
that could be used to identify Unreserved bandwidth, Maximum LSP
bandwidth and Minimum LSP bandwidth is described in Section 3.1.2 of
[GMPLS-SIG].
3. Examples of Interface Switching Capability Descriptor
3.1. STM-16 POS Interface on a LSR
Interface Switching Capability Descriptor:
Interface Switching Capability = PSC-1
Encoding = SDH
Max LSP Bandwidth[p] = 2.5 Gbps, for all p
If multiple links with such interfaces at both ends were to be
advertised as one TE link, link bundling techniques should be used.
3.2. GigE Packet Interface on a LSR
Interface Switching Capability Descriptor:
Interface Switching Capability = PSC-1
Encoding = Ethernet 802.3
Max LSP Bandwidth[p] = 1.0 Gbps, for all p
If multiple links with such interfaces at both ends were to be
advertised as one TE link, link bundling techniques should be used.
3.3. STM-64 SDH Interface on a Digital Cross Connect with Standard SDH
Consider a branch of SDH multiplexing tree : VC-3, VC-4, VC-4-4c,
VC-4-16c, VC-4-64c. If it is possible to establish all these
connections on a STM-64 interface, the Interface Switching Capability
Descriptor of that interface can be advertised as follows:
Interface Switching Capability Descriptor:
Interface Switching Capability = TDM [Standard SDH]
Encoding = SDH
Min LSP Bandwidth = VC-3
Max LSP Bandwidth[p] = STM-64, for all p
If multiple links with such interfaces at both ends were to be
advertised as one TE link, link bundling techniques should be used.
3.4. STM-64 SDH Interface on a Digital Cross Connect with Two Types of
SDH Multiplexing Hierarchy Supported
Interface Switching Capability Descriptor 1:
Interface Switching Capability = TDM [Standard SDH]
Encoding = SDH
Min LSP Bandwidth = VC-3
Max LSP Bandwidth[p] = STM-64, for all p
Interface Switching Capability Descriptor 2:
Interface Switching Capability = TDM [Arbitrary SDH]
Encoding = SDH
Min LSP Bandwidth = VC-4
Max LSP Bandwidth[p] = STM-64, for all p
If multiple links with such interfaces at both ends were to be
advertised as one TE link, link bundling techniques should be used.
3.5. Interface on an Opaque OXC (SDH Framed) with Support for One
Lambda per Port/Interface
An "opaque OXC" is considered operationally an OXC, as the whole
lambda (carrying the SDH line) is switched transparently without
further multiplexing/demultiplexing, and either none of the SDH
overhead bytes, or at least the important ones are not changed.
An interface on an opaque OXC handles a single wavelength, and cannot
switch multiple wavelengths as a whole. Thus, an interface on an
opaque OXC is always LSC, and not FSC, irrespective of whether there
is DWDM external to it.
Note that if there is external DWDM, then the framing understood by
the DWDM must be same as that understood by the OXC.
A TE link is a group of one or more interfaces on an OXC. All
interfaces on a given OXC are required to have identifiers unique to
that OXC, and these identifiers are used as labels (see 3.2.1.1 of
[GMPLS-SIG]).
The following is an example of an interface switching capability
descriptor on an SDH framed opaque OXC:
Interface Switching Capability Descriptor:
Interface Switching Capability = LSC
Encoding = SDH
Reservable Bandwidth = Determined by SDH Framer (say STM-64)
3.6. Interface on a Transparent OXC (PXC) with External DWDM That
Understands SDH Framing
This example assumes that DWDM and PXC are connected in such a way
that each interface (port) on the PXC handles just a single
wavelength. Thus, even if in principle an interface on the PXC could
switch multiple wavelengths as a whole, in this particular case an
interface on the PXC is considered LSC, and not FSC.
_______
| |
/|___| |
| |___| PXC |
========| |___| |
| |___| |
\| |_______|
DWDM
(SDH framed)
A TE link is a group of one or more interfaces on the PXC. All
interfaces on a given PXC are required to have identifiers unique to
that PXC, and these identifiers are used as labels (see 3.2.1.1 of
[GMPLS-SIG]).
The following is an example of an interface switching capability
descriptor on a transparent OXC (PXC) with external DWDM that
understands SDH framing:
Interface Switching Capability Descriptor:
Interface Switching Capability = LSC
Encoding = SDH (comes from DWDM)
Reservable Bandwidth = Determined by DWDM (say STM-64)
3.7. Interface on a Transparent OXC (PXC) with External DWDM That Is
Transparent to Bit-Rate and Framing
This example assumes that DWDM and PXC are connected in such a way
that each interface (port) on the PXC handles just a single
wavelength. Thus, even if in principle an interface on the PXC could
switch multiple wavelengths as a whole, in this particular case an
interface on the PXC is considered LSC, and not FSC.
_______
| |
/|___| |
| |___| PXC |
========| |___| |
| |___| |
\| |_______|
DWDM (transparent to bit-rate and framing)
A TE link is a group of one or more interfaces on the PXC. All
interfaces on a given PXC are required to have identifiers unique to
that PXC, and these identifiers are used as labels (see 3.2.1.1 of
[GMPLS-SIG]).
The following is an example of an interface switching capability
descriptor on a transparent OXC (PXC) with external DWDM that is
transparent to bit-rate and framing:
Interface Switching Capability Descriptor:
Interface Switching Capability = LSC
Encoding = Lambda (photonic)
Reservable Bandwidth = Determined by optical technology limits
3.8. Interface on a PXC with No External DWDM
The absence of DWDM in between two PXCs, implies that an interface is
not limited to one wavelength. Thus, the interface is advertised as
FSC.
A TE link is a group of one or more interfaces on the PXC. All
interfaces on a given PXC are required to have identifiers unique to
that PXC, and these identifiers are used as port labels (see 3.2.1.1
of [GMPLS-SIG]).
Interface Switching Capability Descriptor:
Interface Switching Capability = FSC
Encoding = Lambda (photonic)
Reservable Bandwidth = Determined by optical technology limits
Note that this example assumes that the PXC does not restrict each
port to carry only one wavelength.
3.9. Interface on a OXC with Internal DWDM That Understands SDH Framing
This example assumes that DWDM and OXC are connected in such a way
that each interface on the OXC handles multiple wavelengths
individually. In this case an interface on the OXC is considered
LSC, and not FSC.
_______
| |
/|| ||\
| || OXC || |
========| || || |====
| || || |
\||_______||/
DWDM
(SDH framed)
A TE link is a group of one or more of the interfaces on the OXC.
All lambdas associated with a particular interface are required to
have identifiers unique to that interface, and these identifiers are
used as labels (see 3.2.1.1 of [GMPLS-SIG]).
The following is an example of an interface switching capability
descriptor on an OXC with internal DWDM that understands SDH framing
and supports discrete bandwidths:
Interface Switching Capability Descriptor:
Interface Switching Capability = LSC
Encoding = SDH (comes from DWDM)
Max LSP Bandwidth = Determined by DWDM (say STM-16)
Interface Switching Capability = LSC
Encoding = SDH (comes from DWDM)
Max LSP Bandwidth = Determined by DWDM (say STM-64)
3.10. Interface on a OXC with Internal DWDM That Is Transparent to
Bit-Rate and Framing
This example assumes that DWDM and OXC are connected in such a way
that each interface on the OXC handles multiple wavelengths
individually. In this case an interface on the OXC is considered
LSC, and not FSC.
_______
| |
/|| ||\
| || OXC || |
========| || || |====
| || || |
\||_______||/
DWDM (transparent to bit-rate and framing)
A TE link is a group of one or more of the interfaces on the OXC.
All lambdas associated with a particular interface are required to
have identifiers unique to that interface, and these identifiers are
used as labels (see 3.2.1.1 of [GMPLS-SIG]).
The following is an example of an interface switching capability
descriptor on an OXC with internal DWDM that is transparent to bit-
rate and framing:
Interface Switching Capability Descriptor:
Interface Switching Capability = LSC
Encoding = Lambda (photonic)
Max LSP Bandwidth = Determined by optical technology limits
4. Example of Interfaces That Support Multiple Switching Capabilities
There can be many combinations possible, some are described below.
4.1. Interface on a PXC+TDM Device with External DWDM
As discussed earlier, the presence of the external DWDM limits that
only one wavelength be on a port of the PXC. On such a port, the
attached PXC+TDM device can do one of the following. The wavelength
may be cross-connected by the PXC element to other out-bound optical
channel, or the wavelength may be terminated as an SDH interface and
SDH channels switched.
From a GMPLS perspective the PXC+TDM functionality is treated as a
single interface. The interface is described using two Interface
descriptors, one for the LSC and another for the TDM, with
appropriate parameters. For example,
Interface Switching Capability Descriptor:
Interface Switching Capability = LSC
Encoding = SDH (comes from WDM)
Reservable Bandwidth = STM-64
and
Interface Switching Capability Descriptor:
Interface Switching Capability = TDM [Standard SDH]
Encoding = SDH
Min LSP Bandwidth = VC-3
Max LSP Bandwidth[p] = STM-64, for all p
4.2. Interface on an Opaque OXC+TDM Device with External DWDM
An interface on an "opaque OXC+TDM" device would also be advertised
as LSC+TDM much the same way as the previous case.
4.3. Interface on a PXC+LSR Device with External DWDM
As discussed earlier, the presence of the external DWDM limits that
only one wavelength be on a port of the PXC. On such a port, the
attached PXC+LSR device can do one of the following. The wavelength
may be cross-connected by the PXC element to other out-bound optical
channel, or the wavelength may be terminated as a Packet interface
and packets switched.
From a GMPLS perspective the PXC+LSR functionality is treated as a
single interface. The interface is described using two Interface
descriptors, one for the LSC and another for the PSC, with
appropriate parameters. For example,
Interface Switching Capability Descriptor:
Interface Switching Capability = LSC
Encoding = SDH (comes from WDM)
Reservable Bandwidth = STM-64
and
Interface Switching Capability Descriptor:
Interface Switching Capability = PSC-1
Encoding = SDH
Max LSP Bandwidth[p] = 10 Gbps, for all p
4.4. Interface on a TDM+LSR Device
On a TDM+LSR device that offers a channelized SDH interface the
following may be possible:
- A subset of the SDH channels may be uncommitted. That is, they
are not currently in use and hence are available for allocation.
- A second subset of channels may already be committed for transit
purposes. That is, they are already cross-connected by the SDH
cross connect function to other out-bound channels and thus are
not immediately available for allocation.
- Another subset of channels could be in use as terminal channels.
That is, they are already allocated by terminate on a packet
interface and packets switched.
From a GMPLS perspective the TDM+PSC functionality is treated as a
single interface. The interface is described using two Interface
descriptors, one for the TDM and another for the PSC, with
appropriate parameters. For example,
Interface Switching Capability Descriptor:
Interface Switching Capability = TDM [Standard SDH]
Encoding = SDH
Min LSP Bandwidth = VC-3
Max LSP Bandwidth[p] = STM-64, for all p