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![](MPLSRC - Acronym Dictionary_files/placeholder.gif) |
MPLS Acronym Dictionary
Courtesy of Addison Wesley Publishing, reprinted
from "MPLS: Implementing the Technology", by Eric W.
Gray
Acronym Expansions
AAL |
ATM Adaptation Layer |
AF |
Assured Forwarding |
AFI |
Address Family Identifier |
APN |
actual private network |
ARIS |
Aggregate Route-based IP Switching |
ARP |
Address Resolution Protocol |
AS |
Autonomous System |
ATM |
Asynchronous Transfer Mode |
BA |
Behavior Aggregate |
BGP |
Border Gateway Protocol |
BOF |
Birds of a Feather |
CAC |
Call (or Connection) Admission Control |
CE |
customer edge (or customer equipment) |
CLIP |
Classical IP and ARP over ATM |
CLP |
Cell Loss Priority |
CPCS |
Common Part Convergence Sublayer |
CPE |
Customer premises (or provided) equipment |
CR-LDP |
Constraint-based Routing Label Distribution Protocol |
CSR |
cell switching router |
DE |
Discard Eligibility |
DLCI |
Data Link Connection Identifier |
DLL |
data link layer (L2) |
DoD |
downstream on-demand label distribution (mode) |
DSCP |
Differentiated Services Code (Control) Point |
DU |
downstream unsolicited label distribution (mode) |
ECN |
Explicit Congestion Notification |
EF |
Expedited Forwarding |
EGP |
exterior gateway protocol |
E-LSP |
EXP-inferred-PSC LSP |
EXP |
Experimental bits |
FANP |
Flow Attribute Notification Protocol |
FEC |
forwarding equivalence class |
FF |
Fixed Filter |
FIB |
forwarding information base |
FR |
Frame Relay |
FTN |
FEC-to-NHLFE map |
GSMP |
General (or Generic) Switch Management Protocol |
ICMP |
Internet Control Message Protocol |
IEEE |
Institute of Electrical and Electronics Engineers |
IETF |
Internet Engineering Task Force |
IFMP |
Ipsilon's Flow Management Protocol |
IGP |
interior gateway protocol |
ILM |
Incoming Label Map |
ION |
Internetworking over NBMA |
IP |
Internet Protocol |
I-PNNI |
Integrated PNNI |
IPv4 |
IP version 4 |
IPv6 |
IP version 6 |
ISP |
Internet service provider |
LAN |
local area network |
LANE |
LAN emulation |
LC-ATM |
label switching controlled-ATM |
LC-FR |
label switching controlled-Frame Relay |
LDP |
Label Distribution Protocol1 |
LER |
label edge router |
LIS |
logical IP subnet |
L-LSP |
Label-only-inferred-PSC LSP |
LSP |
label-switched path |
LSR |
label switching (switched or switch) router |
MIB |
Management Information Base |
MPLS |
Multiprotocol Label Switching |
MPOA |
Multi-Protocol over ATM |
NBMA |
nonbroadcast multiple access (networks) |
NHLFE |
Next Hop Label Forwarding Entry |
NHRP |
Next Hop Resolution Protocol |
NHS |
Next Hop Server |
NLRI |
network layer reachability information |
OA |
Ordered Aggregate |
OSI |
Open Systems Interconnection |
OSPF |
Open Shortest Path First |
PAR |
PNNI augmented routing |
PDU |
protocol data unit |
PE |
provider edge |
PHB |
per-hop behavior |
PHP |
penultimate hop pop |
PNNI |
Private Network-to-Network Interface |
POS |
Packet over (on) SONET |
PPP |
Point-to-Point Protocol |
PSC |
PHB scheduling class |
PSTN |
Public Switched Telephone (Telephony) Network |
PVC |
permanent virtual circuit |
QoS |
quality of service |
RD |
route distinguisher |
RFC |
Request for Comments |
ROLC |
Routing Over Large Clouds |
RSVP |
Reservation Protocol |
SAFI |
Subsequent Address Family Identifier |
SE |
Shared Explicit |
SITA |
Switching IP Through ATM |
SNPA |
Subnetwork Points of Attachment |
SONET |
Synchronous Optical Network |
STII |
Internet Stream Protocol version II |
SVC |
switched virtual circuit |
TDP |
Tag Distribution Protocol |
TE |
traffic engineering |
TLV |
type-length-value |
TM |
traffic management |
TTL |
Time to Live |
VC |
virtual circuit |
VCI or VCID |
virtual circuit identifier |
VP |
virtual path |
VPCI |
virtual path and circuit identifier |
VPI |
virtual path identifier |
VPN |
virtual private network |
Definitions
- abstract node
- An abstraction used in describing an explicit route. An
abstract node may be a network element, a group of network
elements sharing an address prefix, or an Autonomous System. An
abstract node consisting of exactly one network element is called
a simple abstract node.
- actual private network
- A term invented for comparison with virtual private network
(VPN).
- adjacent
- Having a direct logical link. Either directly connected
physically, or connected using an approach that makes intervening
devices transparent in a logical context-for example,
tunneling.
- aggregation
- Grouping or bundling traffic requiring similar forwarding.
Distinct from merging, generally, because it may be desirable to
separate aggregate traffic at some point without having to resort
to a routing decision at L3 for all packets within the
aggregate.
- Assured Forwarding
- A per-hop behavior (PHB) defined for Differentiated Services
that provides for four classes of PHB, each having three levels of
drop precedence. Assured Forwarding also requires that packets
within a class not be reordered, regardless of the drop
precedence. Assured Forwarding does not define a quantifiable
value for delay or delay variation of packets forwarded.
- Autonomous System
- In interdomain routing, an administrative domain identified
with an AS number.
- Behavior Aggregate
- IP packets that require the same Differentiated Services
behavior at the point where they are crossing a link.
- Border Gateway Protocol
- The only exterior gateway routing protocol. Currently version
4 is in use. A routing protocol used in routing between
administrative domains.
- bridge
- A device used to forward frames at the data-link
layer.
- Cell Loss Priority
- A bit in the AAL5 ATM header indicating that the cell can be
dropped earlier under congested conditions.
- Connection (or Call) Admission Control
- Use of some approach to determine whether or not a requested
service requirement can reasonably expect to be met by a device,
prior to committing to provide the requested service at the
device.
- conservative retention mode
- Labels are requested and retained only when needed for a
specific next hop. Unnecessary labels are immediately
released.
- content addressable memory
- A memory device that allows a key to be compared to the
contents of all memory locations at the same time. Content
addressable memory is roughly a hardware analogue of a software
hashing algorithm.
- control word
- An instruction, index, or key into a table of instructions,
generally at the (virtual) machine level.
- Data Link Connection Identifier
- Used in Frame Relay to identify a circuit connection between
adjacent Frame Relay switches.
- data link layer
- Layer 2 of the OSI model; the layer between the physical and
network layers.
- Differentiated Services (DiffServ)
- An IETF standard for providing different classes of service
based on some common sets of assumptions about queuing behavior on
a hop-by-hop basis. Because the basis for specific treatment is
explicitly carried in packets, rather than requiring local storage
of packet classification information, this approach to providing
quality of ser-vice (QoS) is often referred to as "less
state-full" than, for example, the Integrated Services QoS
model.
- Discard Eligibility
- A bit in the Frame Relay header indicating that the frame can
be discarded under congested conditions.
- domain of (label) significance
- The portion of a network consisting of logically connected
logical interfaces with a common knowledge of the significance
(meaning) of a label. A label only has meaning upon arrival at a
logical interface if that interface was represented in the process
during which the meaning was originally negotiated.
- downstream
- In the direction of expected traffic flow. Applies to traffic
that is part of a specific forwarding equivalence class.
- downstream label allocation
- Label negotiation in which the downstream LSR determines what
label will be used. This is the only currently supported
approach.
- downstream on-demand label distribution mode
- Labels are allocated and provided to the upstream peer only
when requested. This mode is most useful when the upstream LSR is
using conservative label retention or is not merge capable (or, as
is likely, both).
- downstream unsolicited label distribution mode
- Labels are allocated and provided to the upstream peer at any
time (typically in conjunction with advertisement of a new route).
Most useful when the upstream neighbor is using liberal retention
mode.
- egress
- Point of exit from an MPLS context or domain. The egress of an
LSP is the logical point at which the determination to pop a label
associated with an LSP is made. The label may actually be popped
at the LSR making this determination or at the one prior to it (in
the penultimate hop pop case). Egress from MPLS in general is the
point at which the last label is removed (resulting in removal of
the label stack).
- Expedited Forwarding
- A per-hop behavior defined for Differentiated Services that
requires a network node to provide a well-defined minimum
departure rate service for a configurable departure rate such that
if incoming traffic is conditioned not to exceed this minimum
departure rate, packets are effectively not queued within the
node. Expedited Forwarding ensures that, for conditioned traffic,
the delay at any node is bounded and quantifiable.
- explicit route
- A route specified as a nonempty list of hops that must be part
of the route used. If an explicit route is strict, only specified
hops may be used. If an explicit route is loose, all specified
hops must be included, in order, in the resulting path, but the
path is otherwise unrestricted.
- extranet
- From the perspective of a private network, any other network,
including all other networks.
- filtering database
- Used in some bridging technologies to determine what
interfaces an L2 frame will not be forwarded on.
- Fixed Filter
- A reservation style that is useful in establishing a
point-to-point LSP from one ingress to one egress LSR.
- flooding
- The process of forwarding data on all, or most, interfaces in
order to ensure that the receiver gets at least one copy.
- forwarding database
- Information used to make a forwarding determination.
- forwarding determination
- The process used to determine the interface to be used to
forward data. This process may or may not be directly driven by a
route determination.
- forwarding equivalence class
- A description of the criteria used to determine that a set of
packets is to be forwarded in an equivalent fashion (along the
same logical LSP). Forwarding equivalence classes are defined in
the base LDP specification and may be extended through the use of
additional parameters (such as is the case with CR-LDP). FECs are
also represented in other label distribution protocols.
- frame
- A message encapsulation generally consisting of a DLL header,
a payload-frequently consisting of at least part of a
network-layer packet-and (possibly) a trailer. Normally
encapsulated by physical-layer framing.
- FTN
- FEC-to-NHLFE map, used to insert unlabeled packets onto an
LSP.
- hard state
- State information that remains valid until explicitly
invalidated.
- implicit null label
- A label value given to an upstream neighbor when it is
desirable to have that LSR pop one label prior to forwarding the
packet. This behavior is commonly referred to as penulitimate hop
pop (PHP).
- Incoming Label Map
- Used to find the NHLFE for determining forwarding information
for a labeled packet.
- independent control mode
- Mode in which an LSR allocates and provides labels to upstream
peers at any time. This mode may be used, for instance, when
routing is used to drive label distribution and it is desirable to
supply applicable labels to routing peers at about the same time
as new routes are advertised.
- ingress
- Point at which an MPLS context or domain is entered. The
ingress of an LSP is the point at which a label is pushed onto the
label stack (possibly resulting in the creation of the label
stack).
- Integrated Services (IntServ)
- An IETF quality-of-service standard. In essence, QoS is
assured based on signaling end-to-end service requirements using a
common signaling protocol. (RSVP is the only common end-to-end
protocol currently defined for this purpose.) These service
requirements are then mapped to specific queuing parameters for
each specific medium type that may be present in such an
end-to-end service. The use of CAC and traffic disciplining
techniques allows this approach to effectively guarantee a
requested service requirement. Because packets are classified to
determine what level of service they require, and the
classification information must be retained at each node, this QoS
approach is often referred to as the "state-full" QoS
model.
- interdomain routing
- Routing between administrative domains. Supported currently by
BGP version 4.
- interface
- Physical or logical end point of a link between
devices.
- Internet service provider (ISP)
- Provider of an access service to the Internet, usually for a
charge. Access service charges may be flat rate or based on either
rate or usage. Service providers make up the Internet through
complex tiering and peering relationships.
- intranet
- A private network.
- L1, L2, L3
- physical, data link, and network layers
(respectively).
- label
- A fixed-size field contained in a message header that may be
used as an exact-match key in determining how to forward a
protocol data unit.
- label distribution
- Process by which labels are negotiated between peer
LSRs.
- label edge router
- A term often used to indicate an LSR that is able to provide
ingress to and egress from an LSP. In individual implementations,
this tends to be a function of the capabilities of device
interfaces more than of the overall device. In theory, it is
possible for a device to be an LER and not an LSR (if it is not
able to swap labels, for instance); however, it is unlikely that
such an LER would be generally useful or make any particular sense
in a cost-benefit analysis.
- label stack
- Successive labels in an MPLS shim header in order from the top
to the bottom of the stack.
- label swapping
- Replacing an input label with a corresponding output
label.
- label-switched path
- Path along which labeled packets are forwarded. Packets
forwarded using any label are forwarded along the same path as
other packets using the same label.
- label switching
- Switching based on use of labels.
- label switching router
- A device that participates in one or more routing protocols
and uses the route information derived from routing protocol
exchanges to drive LSP setup and maintenance. Such a device
typically distributes labels to peers and uses these labels (when
provided as part of data presented for forwarding) to forward
label-encapsulated L3 packets. In general, an LSR may or may not
be able to forward non-label-encapsulated data and provide
ingress/egress to LSPs (that is, to perform what is frequently
referred to as the label edge router, or LER, function).
- liberal retention mode
- Labels are retained whenever received. This mode is useful
when the ability to change quickly to a new LSP is desirable;
however, it may result in unacceptable memory consumption for LSRs
with many interfaces.
- link
- Physical or logical connection between two end points.
- logical interface
- An interface associated with a specific encapsulation. Data
arriving at the corresponding physical (or lower-level logical)
interface that is encapsulated for a specific logical interface is
de-encapsulated and delivered to that logical interface.
- merging
- A key function in making MPLS scalable in the number of labels
consumed at each LSR. Merging is the process by which packets from
multiple sources are typically delivered to a single destination
or destination prefix. It is distinct from aggregation in that (in
most cases) the decision to merge traffic implies that the
possibility of being required to separate the merged traffic at a
later point is not significant at the point where merging is being
done.
- network layer
- Layer 3 of the OSI model; the layer between the data-link and
transport layers. Normally encapsulated in one or more data-link
layer frames.
- Next Hop Label Forwarding Information Entry
- Contains all of the information needed to forward a labeled
packet to the next hop. This information includes push, pop, or
swap instructions; the new label (or labels in the event that
multiple pushes are called for); the output interface; and other
information that may be needed to forward the packet to the next
hop.
- Ordered Aggregate
- The set of Behavior Aggregates that share an ordering
constraint. For example, a set of PHB values that can be ordered
relative to one another, such as AF drop precedences within an AF
class.
- ordered control mode
- Mode in which an LSR only allocates and provides labels to an
upstream peer when it is either the egress for the resulting LSP
or it has received a label from downstream for the resulting LSP.
- packet
- A message encapsulation consisting of a network-layer header
and payload.
- packet switching
- An approach used to forward L3 packets from an input L3
logical interface to an output L3 logical interface that may
reasonably be optimized for hardware switching-similar to
switching at the data-link layer.
- penultimate hop pop
- A process by which the peer immediately upstream of the egress
LSR is asked to pop a label prior to forwarding the packet to the
egress LSR. Using LDP, this is done by assigning the special value
of the implicit Null label. This allows the egress to push the
work of popping the label to its upstream neighbor, possibly
allowing for a more optimal processing of the remaining packet.
Note that this can be done because once the label has been used to
determine the next-hop information for the last hop, the label is
no longer useful. Using PHP is helpful because it allows the
packet to be treated as an unlabeled packet by the last hop. Using
PHP, it is possible to implement an "LSR" that never uses
labels.
- per-hop behavior
- A Differentiated Services behavioral definition. A PHB is
defined at a node by the combination of a Differentiated Services
Code Point (DSCP) and a set of configured behaviors.
- PHB scheduling class
- The nonempty set of per-hop behaviors that apply to the
Behavior Aggregates belonging to a given Ordered
Aggregate.
- piggyback
- Intuitive term for the use of routing, or routing-related,
protocols to carry labels.
- pop
- In a label-switching context, the process of removing the
top-level label (the label at the head of the label stack) from
the label stack.
- protocol data unit
- A unit of data used in specific protocol interactions. It may
be generically described as a format for encapsulation and
forwarding of protocol messages between protocol entities.
Messages may span multiple PDUs, a single PDU may contain multiple
messages, and PDUs may be nested.
- push
- In a label-switching context, the process of adding a new
top-level label (which becomes the new label at the head of the
label stack) to the label stack.
- quality of service
- Specific handling or treatment of packets, often in an
end-to-end service. Best-effort (also sometimes referred to as
"worst-effort") is currently the lowest level of packet treatment,
other than an "unconditional drop" service. Currently, there are
two models for providing QoS in an IP network: Integrated Services
(IntServ) and Differentiated Services (DiffServ).
- route computation
- The process by which routers compute entries for a route
table. Route table entries are subsequently used in route
determination.
- route determination
- The process of selecting a route based on header information
in packets and route table entries established previously via
route computation. Typically, a route is determined using the
longest match of the network-layer destination address in L3
packets against a network address prefix in the route
table.
- router
- A device used to forward packets at the network (L3)
layer.
- routing
- A scheme for selecting one of many possible paths.
- scalability
- A reflection of the way in which system complexity grows as a
function of some system parameter, such as size. If growth in
system complexity is approximately linear with respect to growth
in system size, for instance, the size scalability of the system
is generally considered to be good.
- Shared Explicit
- Reservation style in which path resources are explicitly
shared among multiple senders and receivers. Useful when it is
desirable to increase reservation resources or establish a new
reservation without double-booking resources.
- shim header
- An encoding of the MPLS label stack. Present for all media
when a label stack is in use. (The presence of the label stack is
indicated either by protocol numbers or connection identifiers in
the L2 encapsulation.)
- slow-path forwarding
- Used to refer to processing of exception packets in which the
packet is handled via direct intervention of a system CPU resource
that is not normally used in fast-path (optimized)
forwarding.
- soft state
- State information that becomes out of date if not
refreshed.
- source route
- An explicit route specified from the source toward the
destination.
- switching
- Ushering input data or messages more or less directly to an
output; typically based on a simplistic recognition mechanism
(such as an exact match of a fixed-length field).
- traffic engineer
- An operator or automaton with the express purpose of
minimizing congestion in a network. Traffic engineering is an
application of a traffic engineer.
- traffic engineering
- An application of constraint-based routing in which a traffic
engineer uses a set of link characteristics to select a route and
assigns specific traffic to that route.
- type-length-value
- An object description with highly intuitive meaning; that is,
the object consists of three fields: type, length, and value. Type
gives the semantic meaning of the value, length gives the number
of bytes in the value field (which may be fixed by the type), and
value consists of length bytes of data in a format consistent with
type. This object format is used in LDP and several other
protocols.
- upstream
- Direction from which traffic is expected to arrive. Applies to
a specific forwarding equivalence class.
- upstream label allocation
- A scheme by which the upstream peer is allowed to select the
label that will be used in forwarding labeled traffic for a
specific forwarding equivalence class. Not currently supported in
MPLS.
- virtual X
- Pseudo-X. Not quite or really an X. A small white
lie.
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