frame relay
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... Multiprotocol Label Switching Architecture is described in
[ARCH]. It is possible to use Frame Relay switches as Label
Switching Routers. Such Frame Relay ...
... Frame Relay switches as Label
Switching Routers. Such Frame Relay switches run network layer ...
... is based on the results of these routing algorithms. No specific
Frame Relay routing is needed.
...
...
When a Frame Relay switch is used for label switching, the top
(current) label, on which forwarding decisions are based, is carried
...
... (current) label, on which forwarding decisions are based, is carried
in the DLCI field of the Frame Relay data link layer header of a
...
... header of a
frame. Additional information carried along with the top (current)
label, but not processed by Frame Relay switching, along with other
labels, if the packet is multiply labeled, are carried in the generic
MPLS ...
... traffic. The DLCIs would be used as MPLS
Labels and the Frame Relay switches would become Frame Relay Label
Switching Routers ...
... MPLS
Labels and the Frame Relay switches would become Frame Relay Label
Switching Routers, while the MPLS traffic ...
... MPLS encapsulation
(Frame Relay, ATM, Generic) of a packet that determines the
packet's MPLS ...
... Encapsulation is the type of MPLS encapsulation (Frame
Relay, ATM, Generic) of a packet when that packet is received on
an LSR ...
... Encapsulation is the type of MPLS encapsulation (Frame
Relay, ATM, Generic) of a packet when that packet is transmitted
on an LSR ...
... Special characteristics of Frame Relay Switches ...
... frame format imposed by the
Multiprotocol Interconnect over Frame Relay [MIFR], or Frame Relay
...
... Multiprotocol Interconnect over Frame Relay [MIFR], or Frame Relay
standards [FRF], etc.... Because of these constraints ...
... the label swapping function is performed on fields (DLCI) in the
frame's Frame Relay data link header; this dictates the size and
...
...
This document describes ways of applying label switching to Frame
Relay switches, which work within these constraints.
...
... generic label encapsulation as defined in [STACK], using the frame
relay null encapsulation mechanism:
...
...
The use of the frame relay null encapsulation implies that labels
implicitly encode the network protocol ...
... STACK] but not for the label,
which is rather carried in the DLCI field of the Frame Relay data
link header encoded in Q.922 [ITU ...
... Frame Relay Label Switching Processing ...
... MPLS label is carried in the DLCI field
of the Frame Relay data link layer header of the frame. The top
...
... Naturally there will be MPLS networks which contain a combination of
Frame Relay switches operating as LSRs, and other LSRs ...
... LSP.
Such an LSR may swap off a Frame Relay encoded label on an incoming
interface and replace it with a label encoded into a Generic MPLS ...
... Frame Relay Label Switching Loop Prevention and Control ...
... Encapsulation |
+================+=================+=================+=================+
| 0 | Frame Relay | Frame Relay | Frame Relay |
...
... +================+=================+=================+=================+
| 0 | Frame Relay | Frame Relay | Frame Relay |
+----------------+-----------------+-----------------+-----------------+
...
... | 0 | Frame Relay | Frame Relay | Frame Relay |
+----------------+-----------------+-----------------+-----------------+
| 1 | any | Generic MPLS ...
... Encapsulation |
+================+=================+=================+=================+
| 0 | Frame Relay | Frame Relay | Frame Relay |
...
... +================+=================+=================+=================+
| 0 | Frame Relay | Frame Relay | Frame Relay |
+----------------+-----------------+-----------------+-----------------+
...
... | 0 | Frame Relay | Frame Relay | Frame Relay |
+----------------+-----------------+-----------------+-----------------+
| | | Generic MPLS ...
... encapsulation is Generic MPLS, "f" when
it is Frame Relay, "a" when it is ATM, and furthermore considering
the symbols "iIf", "gGf", "fFf", etc... as LSRs ...
... | mpls_ttl = n-5 ^
| |
number of hops 1| Frame Relay |5
| |
V 2 3 4 |
...
... segment, and
"ingress LSR" in Frame Relay segment and calculates: mpls_ttl=n-6
"fGa" "egress LSR ...
... segment and calculates: mpls_ttl=n-6
"fGa" "egress LSR" from Frame Relay segment, and
"ingress LSR ...
... segment, and
"ingress LSR" in Frame Relay segment and calculates: mpls_ttl=n-13
"fGg" is "egress LSR ...
... segment and calculates: mpls_ttl=n-13
"fGg" is "egress LSR" from Frame Relay segment, and
ingress LSR ...
... MPLS label stack [STACK]
with at least one entry. The frame relay null encapsulation will
carry information about the network layer protocol ...
... MPLS TTL SHOULD be decremented with the
number of hops of the Frame Relay LSP (homogeneous), or Frame Relay
...
... Next, the MPLS encapsulated packet is passed down to the Frame Relay
data link driver with the top label as output DLCI ...
... data link driver with the top label as output DLCI. The Frame Relay
frame carrying the MPLS encapsulated packet ...
... LSR, the current (top) MPLS label is carried in the DLCI
field of the Frame Relay data link layer header of the frame. Just
...
... data link layer header of the frame. Just
as in conventional Frame Relay, for a frame arriving at an interface,
the DLCI ...
... stack. In the top-level entry, all fields except the label
information, which is carried and switched in the Frame Relay frame
data link-layer header ...
... Label Switching Control Component for Frame Relay ...
...
To support label switching a Frame Relay Switch MUST implement the
control component of label switching, which consists primarily of
...
... BGP) to
distribute label bindings. In these cases, a Frame Relay LSR should
participate in these protocols.
...
... LDP, or
RSVP, or others, with no involvement from traditional Frame Relay
mechanisms, it is assumed that circuit establishing contractual
...
... done by the FR-LSRs in a similar fashion as for traditional Frame
Relay circuits. With the goal of emulating a best-effort router as
...
...
Support of label switching on a Frame Relay switch requires
conformance only to [FRF] (framing, bit-stuffing ...
... signaling may be used for non-MPLS (standard Frame Relay) PVCs and/or
SVCs when both are running on the same interface ...
...
The existence of the label switching control component on a Frame
Relay switch does not preclude the ability to support the Frame Relay
control component defined by the ITU ...
... The existence of the label switching control component on a Frame
Relay switch does not preclude the ability to support the Frame Relay
control component defined by the ITU and Frame Relay ...
... Frame Relay
control component defined by the ITU and Frame Relay Forum on the
same switch and the same interfaces ...
... components, label switching and those defined by ITU/Frame Relay
Forum, would operate independently.
...
... VC merging) may be restricted in
case the frame traffic requires Frame Relay fragmentation. The issue
is that Frame Relay ...
... Frame Relay fragmentation. The issue
is that Frame Relay fragments must be transmitted in sequence, i.e.,
fragments ...
... LDP messages specific to Frame Relay ...
... Label Distribution Protocol [LDP] messages exchanged between two
Frame Relay "LDP-peer" LSRs may contain Frame Relay ...
...
"Frame Relay Label Range":
...
... to 0.
"Frame Relay Merge":
0 1 2 3 4 5 6 7
...
... and must be ignored on receipt.
and "Frame Relay Label":
0 1 2 3
...
... DLCI
The binary value of the Frame Relay Label. The significant number
of bits (10 or 23) of the label value are to be encoded into the
...
... Data Link Connection Identifier (DLCI) field when part of the
Frame Relay data link header (see Section 4.).
...
... forgery an existent label in the DLCI field
of the Frame Relay data link layer header of a frame or one or more
...
... Also thanks to Nancy Feldman and Bob Thomas for their collaboration
in including the LDP messages specific to Frame Relay LSRs.
...
... Bradley, T., Brown, C. and A. Malis, "Multiprotocol Interconnect over Frame Relay", RFC 2427std55, September 1998. ...