by which we mean a glossary which is structured to lead to some conclusion or other...!
With thanks to the authors of draft-ietf-qosr-framework-00.txt
and draft-ietf-rsvp-spec-14.txt.
An Adspec is an object in a Path message that carries
a package of OPWA advertising information. See OPWA.
A routing technique where multiple paths, rather
than just the shortest (typically opportunistic) path, between
a source and a destination are utilized to
route traffic. One of the objectives of alternate path routing might
be to distribute load among multiple paths in the network (or,
conversely to reduce dependence on single mode/path failure).
PHB for Differentiated Service that allows multiple forwarding classes
with (orthoganally) multiple drop priorities. Aimed at supported mixes
of RTP/UDP and TCP traffic. Might use RED
Virtual Circuit Identifier - Path Identifier - used
as a 2-level tag for a flow.
Un-specified, Variable, Avaialble and Constant Bit Rate
service classes
Mean, Peak, Sustainable Cell Rate
Cell Delay Variation, Burst Tolerance
Resource Management
Private Network Network Interface - signaling and QoS
routing from the ATM Forum
A routing domain which has a common intradomain routing
protocol and administrative authority.
A traffic class is a contract _type_ - a contract is a contract type,
plus a set of vvalues for the paraemters for that type - the contract
type specifieds the parameters of the admission control....for
example:
has no parameters (beyond soruce+destiantio naddress and ToS
and precedence!)
Specifies a contract which looks to the source(sink)
like a lightly loaded network with the specified mean rate...
borrowing of capacity between a flow that has a burst at a
higher rate and ones that are currently lower rate is
possible....the control of this over
the short time frame is a factor in selecting a packet
scheduling algorithm. (c.f. schedule)
This is very like the ATM CBR contract....but it is
also like the VBR rt service - it specifies delay
bounds as well as throughput parameters - these are actually
implemented end to end and hop by hop, so are somewhat
different from the CDV parameter which is a traffic behaviour
specification rather than a contract request!
A term in RSVP for how to divvy up varioation along
the hops of a path
Blockade state helps to solve a "killer reservation" problem.
Address Aggreagation - currently used to compact destination
based forwarding tables - could be used for sources or even for
logical (e.g. multicast class D or mobile) addresses, but isn't yet.
A sate of the network and its offered load where traffic is
partially or largely not being carried usefully - e.g. traffic flows
across a link to a bottleneck only to be dropped. Also, in
multiservice networks with reservations, can refer to high call
blocking probability - actually, this is simply scarcity of
resource.
A technique where a flow setup is recursively backtracked along the
partial flow path up to the first node that can determine an alternative path
to the destination.
Current standard way that route is chosen for each and every
packet in the Internet - the destination address is used to look up
the "shortest" (by some metric, whetehr hop count, highest throughput,
lowest delay or what) path out of the graph that is the network mesh
map, which may have multiple potential different paths. To select more
than one path, one could use external state (e.g. random number,
traffic load from other sources) but this might lead to high degrees
of packets arriving out of order at a destination - to use more than a
single path, one needs to distinguish flows based on other information
- e.g. source, or source + ToS (+Precendence(+signaled QoS)) or
generalized port information. Alternatively, a fast lookup key associated
with this information ,whatever it is, culd be installed - e.g. by the
signaling protocol, or by implicit recoginition of the existence of a
"flow", by a "tag" or "flow label" installation protocol.
such tags might be hop specific.
Class of Service rather than Quality of Service. Uses edge devices and
Per Hop Behaviours instead of hop-by-hop and end to end services.
Typicaly, subscription based rather than signaled. Allows aggregation
by class.
Traffic policing done at the first RSVP- (and policing-) capable
router on a data path. aka ingress policing
A PHB for diff serve designed to achieve virtual leased line. typically,
uses priority queue.
A (reservation) style attribute; all reserved senders are to be
listed explicitly in the reservation message. See also "wildcard
sender selection".
An IP packet stream from a source to a destination
(unicast or multicast) with an associated Quality of Service (QoS) (see below)
and higher level demultiplexing information. The associated QoS could be
"best-effort".
Fixed Filter reservation style in RSVP, which has explicit sender selection
and distinct attributes.
Together with the session information, in RSVP
defines the set of data
packets to receive the QoS specified in a flowspec. The filterspec
is used to set parameters in the packet classifier function.
A sequence of packets from a source to a destiantion (possible a
group) consittuging a single activity (e.g. transfer of a file, a web
page, a audio/video stream etc etc) that are usefully temporally as
well as spatially correlated!
A shortcut key for looking up a flow ratehr than the set of typical IP
(TCP and UDP) protocol fields that routers seem poor at loking at
(though hosts seem to manage somehow:-)
An IPv6 fields that might serve as a globlly allocated flow id, or
might not...
The act of determining the path for a flow, and attempting to
establish state in routers along the flow path to satisfy its QoS requirement.
The combination of a flowspec and a filterspec.
Defines the QoS to be provided for a flow. The flowspec is used to
set parameters in the packet scheduling function to provide the
requested quality of service. A flowspec is carried in a FLOWSPEC
object. The flowspec format is opaque to RSVP, and is defined by
the Integrated Services Working Group.
A process by which it is determined whether a
link or a node has sufficient resources to satisfy the QoS required for a flow.
FAC is typically applied by each node in the path of a flow during flow set-up
to check local resource availability.
RSVP uses this to identify an IPv4 flow.
The component of a session definition that provides further
transport or application protocol layer demultiplexing beyond
DestAddress. See "session".
A process by which it is determined whether or
not a flow set-up should proceed, based on estimates of the overall resource
usage by the flow. Higher-level admission control may result in the failure of
a flow set-up even when FAC at each node along the flow path indicates resource
availability.
The killer reservation problem describes a case where a receiver
attempting and failing to make a large QoS reservation prevents
smaller QoS reservations from being established.
The LIH (Logical Interface Handle) is used to help deal with non-
RSVP clouds.
Allows RSVP to rapidly adapt its reservations to changes in
routing.
When traffic specifies a service contract, it should keep to it
(especially if there are tarrif (whetehr per use or per subscription
based) considerations. To check this, traffic is typically monitored
as it is placed into appropaite wquues for appropriate schedules - if
a contract is exceeded, packets can be treated in a number of ways:
This can be tricky given the lower class may have a policy
associated with it....e.g. maybe it gets an overal minimum share...
This is easy, esp. with RED.
No field currently in IP to do this, unless the packet was in
a class becaudser of priority or precendence, in which case the field
could be overwritrten, but this would invalidate the IP (v4 header)
checksum unless restored after the current piece of network....
Traffic policing that takes place at data merge point of a shared
reservation.
The process of taking the maximum (or more generally the least
upper bound) of the reservations arriving on outgoing interfaces,
and forwarding this maximum on the incoming interface.
A subtree of the network topology in which
all the leaves and zero or more interior nodes are members of the same multicast
group. A multicast path may be per-source, in which case the subtree is rooted
at the source.
An RSVP object that carries the Next Hop information in RSVP control
messages.
Abbreviation for "One Pass With Advertising". Describes a
reservation setup model in which (Path) messages sent downstream
gather information that the receiver(s) can use to predict the
end-to-end service. The information that is gathered is called
an
advertisement. See also "Adspec".
A set of service requirements to be met by the
network while transporting a flow.
Quality of Service or route:
RSVP defines some fields that carry QoS descriptions - the
actual meaning s of these are as per the int-serv classes/templates.
Given a service class, a flow also is covered by:
Information kept in routers and hosts about all RSVP senders.
Path Error RSVP control message.
Path Teardown RSVP control message.
PHB
Per Hop Behaviour - a service description based around behaviour rather than
mechanism, and local, rather than path gobal. See Expedited and
Assured Forwarding groups.
An object that carries the Previous Hop information in RSVP
control
messages.
A routing mechanism under which paths for flows are
determined based on some knowledge of resource availability in the network as
well as the QoS requirement of flows.
Queues exist to smooth traffic in a statistically multiplexed
network. In a TDM multiplexed network, queues don't hard hever
happen.
A technoque for controlling best effort queue lenghts - miught
also e sued on out-of-contract packets within a class better than best
effort.
Describes a set of attributes for a reservation, including the
sharing attributes and sender selection attributes.
Reservation request RSVP control message.
Reservation Confirmation RSVP control message, confirms
successful
installation of a reservation at some upstream node.
Reservation Error control message, indicates that a reservation
request has failed or an active reservation has been preempted.
Reservation Teardown RSVP control message, deletes reservation
state.
The component of a flowspec that defines a desired QoS. The
Rspec
format is opaque to RSVP, and is defined by the Integrated
Services
Working Group of the IETF.
Type of service is a well understood field in the IPv4 header
- some systems even implemnet setting it -some forwarding software
(e.g. slip drivers) use this, but fre routers.
QoS - refers to a route derived from consideration of network
topology, edge costs and traffic conditions. QoR refers to routes
derived soley from edge fixed parameters...
A mechanism to keep a flow path fixed for a duration of time.
The proposed Internet signaling protocol.
Shared Explicit reservation style, which has explicit sender
selection and shared attributes.
An RSVP session defines one simplex unicast or multicast data flow
for which reservations are required. A session is identified by
the destination address, transport-layer protocol, and an optional
(generalized) destination port.
A (reservation) style attribute: all reserved senders share the
same reserved resources. See also "distinct style".
Control state in hosts and routers that will expire if not
refreshed within a specified amount of time.
A neat way to think about scheduling ois to take a picture of a
resource share over time and picture how it is _decreased_ by someone
else asking for special circumstances.
First In First Out - a strange, but widespread service
discipline in IP (and multiprotocol) routers
When the queue is full, which packet gets lost?
When there is more than one packet ina queue , which
gets fowarded?
Note priority queueing can starve lower priority
packets of ever seeing service
Priority Queue basedn the preceedence bits i nthe IP
header
A (proprietary, but commonly used if by other names)
scheme to give certain flows a minimum performance
through "hardwired" classsifications and minimumqueue service
rates.
Round robin
Rounder robin (rounding error is to allow for variable
length packets - "weight" in WFQ sometiems used to refer to unfair
share - actually, its the P in PGPS - see GPS and PGPS!).
A service scheme for TDM that still stat muxes.
The theorty of WFQ - fluid flow
The practice of WFQ - packet flow
A neat alternative scheduler for delay bounding
A single packet cannot be said to see a service contract. A flow of
packets can see a statistical properties with distributions such as
interarrival and departure times, drop probabilities, re-ordering probabilities,
erroring probabilities and so on. The difference between
distributions before and after service are the result of the scedulign
discipline, vombined possiblty with the other traffic (especially true
for best effort and priority queueing). The atate mathematics theory
is such that we typically cannot derive anything beyound mean and
bounds (if they exist) for typical service classes and worst case
traffic. The Internet lrgely survicves because of FIFO and drop
tail's amazing ability to survive many traffic arrival patterns and
under engineering. RED appears to improve this.
QoS requires state. State has costs in memory and in messages to
establish it. The state may simply be a constant increase over the
state needed for detaintion routing - however, suually destiantions
are heavily aggregated (e.g. at least by network number, but also by
CIDR etc). Flows are per user, and may be present in much larger
numbers than host ids 9although if the phone net is anything to go by
this is not true - they typically have <1% of numbers active.)
traffic may be wihin contract, but incur extra jitter due to burst s
of other traffic when goign through a switch. THe jury is still out on
whether one should then re-shape the traffic to its mean rate -
typically, if a path has 2* bandwidth* delay of buffering, then it can
sustain any burstiness - however, there may be stat muxing synergy to
haveing a minimum (and maximum) amount of burstiness -there is
probably some statistical thermodynamic theory that could show this
(e.g. diffusion model, or lattice gas occupancy analogy) but its byond
me right now...
A host or router that can be identified by a unique unicast IP address.
A technique for selecting a path out of many at the source - requires
network to deliver choce to the source, and soruce to be able to
indicate choice in packet, or in signaling. Useful for policies (cf.
long haul POTS provider selection) but not for scaling.
Incurred from Route, QoS, QoR and signaled information.
A technique for optinmisign the lookup for forwarding packets -
reduces router memory limits by a constant factor.
See ARIS, flow labeling - can be used on per flow by detection
(autocorrelation of destination and time) or by route (output port) or
by application....
A tarrif structure has a per paraemter, per service class price
structure which may include time of day, or even other-traffic related
factors. The more complexthe service model and the tarrif structure,
the more expensive it is to collect usage based revenue.
A traffic parameter set that describes a flow. The format of a
Tspec is opaque to RSVP and is defined by the Integrated Service
A host or router that can be identified by a unique unicast
IP address.
Not an IP concept......yet.... or ever, if we can help it...
End to end arguments - a control theoretic model based scheme for
limiting traffic going in to the network based on history - given a
delayed feedback loop of what has arrived, what can we say about what
can be sent? hard (but not impossible) to apply to multicast flows.
Van has perpetrated this algorithm no less than 3 times:
Wildcard Filter reservation style, which has wildcard sender
selection and shared attributes.
A (reservation) style attribute: traffic from any sender to a
specific session receives the same QoS. See also "explicit sender
selection".
A way for hosts that cannot use raw sockets to participate in RSVP
by encapsulating the RSVP protocol (raw) packets in ordinary UDP
packets. See Section APPENDIX C for more information.
Controlled Delay
Committed Rate
Predictive
These are three proposed but still under study service
contracts
ATM
RSVP/Q.2931 or PNNI mapping
QoS parameter mapping
802.1q
FR
SMDS
Native
Token Rate
Bucket Depth
The Tspec/Rspec parameters -
Version | Maximum Transmission Unit
Token Bucket Rate | Token Bucket Size
Maximum Transmission Rate | Minimum Delay Noticed
Maximum Delay Variation | Loss Sensitivity
Burst Loss Sensitivity | Loss Interval
Quality of Guarantee |