Network Working Group J. Ash Request for Comments: 4126 AT&T Category: Experimental June 2005 Max Allocation with Reservation Bandwidth Constraints Model for
Diffserv-aware MPLS Traffic Engineering & Performance Comparisons Status of This Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document complements the Diffserv-aware MPLS Traffic Engineering (DS-TE) requirements document by giving a functional specification
for the Maximum Allocation with Reservation (MAR) Bandwidth
Constraints Model. Assumptions, applicability, and examples of the
operation of the MAR Bandwidth Constraints Model are presented. MAR performance is analyzed relative to the criteria for selecting a
Bandwidth Constraints Model, in order to provide guidance to user
implementation of the model in their networks.
Table of Contents
1. Introduction (2)
1.1. Specification of Requirements (3)
2. Definitions (3)
3. Assumptions & Applicability (5)
4. Functional Specification of the MAR Bandwidth
Constraints Model (6)
5. Setting Bandwidth Constraints (7)
6. Example of MAR Operation (8)
7. Summary (9)
8. Security Considerations (10)
9. IANA Considerations (10)
10. Acknowledgements (10)
A. MAR Operation & Performance Analysis (11)
B. Bandwidth Prediction for Path Computation (19)
Normative References (20)
Informative References (20)
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1. Introduction
Diffserv-aware MPLS traffic engineering (DS-TE) requirements and
protocol extensions are specified in [DSTE-REQ, DSTE-PROTO]. A
requirement for DS-TE implementation is the specification of
Bandwidth Constraints Models for use with DS-TE. The Bandwidth
Constraints Model provides the ’rules’ to support the allocation of
bandwidth to individual class types (CTs). CTs are groupings of
service classes in the DS-TE model, which are provided separate
bandwidth allocations, priorities, and QoS objectives. Several CTs
can share a common bandwidth pool on an integrated, multiservice
MPLS/Diffserv network.
This document is intended to complement the DS-TE requirements
document [DSTE-REQ] by giving a functional specification for the
Maximum Allocation with Reservation (MAR) Bandwidth Constraints
Model. Examples of the operation of the MAR Bandwidth Constraints
Model are presented. MAR performance is analyzed relative to the
criteria for selecting a Bandwidth Constraints Model, in order to
provide guidance to user implementation of the model in their
networks.
Two other Bandwidth Constraints Models are being specified for use in DS-TE:
1. Maximum Allocation Model (MAM) [MAM] - the maximum allowable
bandwidth usage of each CT is explicitly specified.
2. Russian Doll Model (RDM) [RDM] - the maximum allowable bandwidth
usage is done cumulatively by grouping successive CTs according to priority classes.
MAR is similar to MAM in that a maximum bandwidth allocation is given to each CT. However, through the use of bandwidth reservation and
protection mechanisms, CTs are allowed to exceed their bandwidth
allocations under conditions of no congestion but revert to their
allocated bandwidths when overload and congestion occurs.
All Bandwidth Constraints Models should meet these objectives:
1. applies equally when preemption is either enabled or disabled
(when preemption is disabled, the model still works ’reasonably’
well),
2. bandwidth efficiency, i.e., good bandwidth sharing among CTs under both normal and overload conditions,
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3. bandwidth isolation, i.e., a CT cannot hog the bandwidth of
another CT under overload conditions,
4. protection against QoS degradation, at least of the high-priority CTs (e.g., high-priority voice, high-priority data, etc.), and
5. reasonably simple, i.e., does not require additional IGP
extensions and minimizes signaling load processing requirements.
In Appendix A, modeling analysis is presented that shows the MAR
Model meets all of these objectives and provides good network
performance, relative to MAM and full-sharing models, under normal
and abnormal operating conditions. It is demonstrated that MAR
simultaneously achieves bandwidth efficiency, bandwidth isolation,
and protection against QoS degradation without preemption.
In Section 3 we give the assumptions and applicability; in Section 4 a functional specification of the MAR Bandwidth Constraints Model;
and in Section 5 we give examples of its operation. In Appendix A,
MAR performance is analyzed relative to the criteria for selecting a Bandwidth Constraints Model, in order to provide guidance to user
implementation of the model in their networks. In Appendix B,
bandwidth prediction for path computation is discussed.
1.1. Specification of Requirements
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 [RFC2119].
2. Definitions
For readability a number of definitions from [DSTE-REQ, DSTE-PROTO]
are repeated here:
Traffic Trunk: an aggregation of traffic flows of the same class (i.e., treated equivalently from the DS-TE
perspective), which is placed inside a Label
Switched Path (LSP).
Class-Type (CT): the set of Traffic Trunks crossing a link that is governed by a specific set of bandwidth
constraints. CT is used for the purposes of link bandwidth allocation, constraint-based routing,
and admission control. A given Traffic Trunk
belongs to the same CT on all links.
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Up to 8 CTs (MaxCT = 8) are supported. They are referred to as CTc, 0 <= c <= MaxCT-1 = 7. Each CT is assigned either a Bandwidth Constraint, or a set of Bandwidth Constraints. Up to 8
Bandwidth Constraints (MaxBC = 8) are supported
and they are referred to as BCc, 0 <= c <=
MaxBC-1 = 7.
TE-Class: A pair of: a) a CT, and b) a preemption priority allowed for that CT. This means that an LSP,
transporting a Traffic Trunk from that CT, can
use that preemption priority as the set-up
priority, the holding priority, or both.
MAX_RESERVABLE_BWk: maximum reservable bandwidth on link k specifies the maximum bandwidth that may be reserved; this may be greater than the maximum link bandwidth,
in which case the link may be oversubscribed
[OSPF-TE].
BCck: bandwidth constraint for CTc on link k =
allocated (minimum guaranteed) bandwidth for CTc on link k (see Section 4).
RBW_THRESk: reservation bandwidth threshold for link k (see
Section 4).
RESERVED_BWck: reserved bandwidth-in-progress on CTc on link k
(0 <= c <= MaxCT-1), RESERVED_BWck = total amount of the bandwidth reserved by all the established LSPs that belong to CTc.
UNRESERVED_BWk: unreserved link bandwidth on link k specifies the amount of bandwidth not yet reserved for any CT, UNRESERVED_BWk = MAX_RESERVABLE_BWk - sum
[RESERVED_BWck (0 <= c <= MaxCT-1)].
UNRESERVED_BWck: unreserved link bandwidth on CTc on link k
specifies the amount of bandwidth not yet
reserved for CTc, UNRESERVED_BWck =
UNRESERVED_BWk - delta0/1(CTck) * RBW-THRESk
where
delta0/1(CTck) = 0 if RESERVED_BWck < BCck
delta0/1(CTck) = 1 if RESERVED_BWck >= BCck
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A number of recovery mechanisms under investigation in the IETF take advantage of the concept of bandwidth sharing across particular sets of LSPs. "Shared Mesh Restoration" in [GMPLS-RECOV] and "Facility-
based Computation Model" in [MPLS-BACKUP] are example mechanisms that increase bandwidth efficiency by sharing bandwidth across backup LSPs protecting against independent failures. To ensure that the notion
of RESERVED_BWck introduced in [DSTE-REQ] is compatible with such a
concept of bandwidth sharing across multiple LSPs, the wording of the definition provided in [DSTE-REQ] is generalized. With this
generalization, the definition is compatible with Shared Mesh
Restoration defined in [GMPLS-RECOV], so that DS-TE and Shared Mesh
Protection can operate simultaneously, under the assumption that
Shared Mesh Restoration operates independently within each DS-TE
Class-Type and does not operate across Class-Types. For example,
backup LSPs protecting primary LSPs of CTc also need to belong to
CTc; excess traffic LSPs that share bandwidth with backup LSPs of CTc also need to belong to CTc.
3. Assumptions & Applicability
In general, DS-TE is a bandwidth allocation mechanism for different
classes of traffic allocated to various CTs (e.g., voice, normal
data, best-effort data). Network operation functions such as
capacity design, bandwidth allocation, routing design, and network
planning are normally based on traffic-measured load and forecast
[ASH1].
As such, the following assumptions are made according to the
operation of MAR:
1. Connection admission control (CAC) allocates bandwidth for network flows/LSPs according to the traffic load assigned to each CT,
based on traffic measurement and forecast.
2. CAC could allocate bandwidth per flow, per LSP, per traffic trunk, or otherwise. That is, no specific assumption is made about a
specific CAC method, except that CT bandwidth allocation is
related to the measured/forecasted traffic load, as per assumption #1.
3. CT bandwidth allocation is adjusted up or down according to
measured/forecast traffic load. No specific time period is
assumed for this adjustment, it could be short term (seconds,
minutes, hours), daily, weekly, monthly, or otherwise.
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4. Capacity management and CT bandwidth allocation thresholds (e.g., BCc) are designed according to traffic load, and are based on
traffic measurement and forecast. Again, no specific time period is assumed for this adjustment, it could be short term (hours),
daily, weekly, monthly, or otherwise.
5. No assumption is made on the order in which traffic is allocated
to various CTs; again traffic allocation is assumed to be based
only on traffic load as it is measured and/or forecast.
6. If link bandwidth is exhausted on a given path for a
flow/LSP/traffic trunk, alternate paths may be attempted to
satisfy CT bandwidth allocation.
Note that the above assumptions are not unique to MAR, but are
generic, common assumptions for all BC Models.
4. Functional Specification of the MAR Bandwidth Constraints Model
A DS-TE Label Switching Router (LSR) that implements MAR MUST support enforcement of bandwidth constraints, in compliance with the
specifications in this section.
In the MAR Bandwidth Constraints Model, the bandwidth allocation
control for each CT is based on estimated bandwidth needs, bandwidth use, and status of links. The Label Edge Router (LER) makes needed
bandwidth allocation changes, and uses [RSVP-TE], for example, to
determine if link bandwidth can be allocated to a CT. Bandwidth
allocated to individual CTs is protected as needed, but otherwise it is shared. Under normal, non-congested network conditions, all
CTs/services fully share all available bandwidth. When congestion
occurs for a particular CTc, bandwidth reservation prohibits traffic from other CTs from seizing the allocated capacity for CTc.
On a given link k, a small amount of bandwidth RBW_THRESk (the
reservation bandwidth threshold for link k) is reserved and governs
the admission control on link k. Also associated with each CTc on
link k are the allocated bandwidth constraints BCck to govern
bandwidth allocation and protection. The reservation bandwidth on a link (RBW_THRESk) can be accessed when a given CTc has bandwidth-in- use (RESERVED_BWck) below its allocated bandwidth constraint (BCck). However, if RESERVED_BWck exceeds its allocated bandwidth constraint (BCck), then the reservation bandwidth (RBW_THRESk) cannot be
accessed. In this way, bandwidth can be fully shared among CTs if
available, but is otherwise protected by bandwidth reservation
methods.
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Bandwidth can be accessed for a bandwidth request = DBW for CTc on a given link k based on the following rules:
Table 1: Rules for Admitting LSP Bandwidth Request = DBW on Link k
For LSP on a high priority or normal priority CTc:
If RESERVED_BWck <= BCck: admit if DBW <= UNRESERVED_BWk
If RESERVED_BWck > BCck: admit if DBW <= UNRESERVED_BWk - RBW_THRESk; or, equivalently:
If DBW <= UNRESERVED_BWck, admit the LSP.
For LSP on a best-effort priority CTc:
allocated bandwidth BCck = 0;
Diffserv queuing admits BE packets only if there is available link
bandwidth.
The normal semantics of setup and holding priority are applied in the MAR Bandwidth Constraints Model, and cross-CT preemption is permitted when preemption is enabled.
The bandwidth allocation rules defined in Table 1 are illustrated
with an example in Section 6 and simulation analysis in Appendix A. 5. Setting Bandwidth Constraints
For a normal priority CTc, the bandwidth constraints BCck on link k
are set by allocating the maximum reservable bandwidth
(MAX_RESERVABLE_BWk) in proportion to the forecast or measured
traffic load bandwidth (TRAF_LOAD_BWck) for CTc on link k. That is: PROPORTIONAL_BWck = TRAF_LOAD_BWck/[sum {TRAF_LOAD_BWck, c=0, MaxCT-1}] X MAX_RESERVABLE_BWk
For normal priority CTc:
BCck = PROPORTIONAL_BWck
For a high priority CT, the bandwidth constraint BCck is set to a
multiple of the proportional bandwidth. That is:
For high priority CTc:
BCck = FACTOR X PROPORTIONAL_BWck
where FACTOR is set to a multiple of the proportional bandwidth
(e.g., FACTOR = 2 or 3 is typical). This results in some ’over-
allocation’ of the maximum reservable bandwidth, and gives priority Ash Experimental [Page 7]
to the high priority CTs. Normally the bandwidth allocated to high
priority CTs should be a relatively small fraction of the total link bandwidth, with a maximum of 10-15 percent being a reasonable
guideline.
As stated in Section 4, the bandwidth allocated to a best-effort
priority CTc should be set to zero. That is:
For best-effort priority CTc:
BCck = 0
6. Example of MAR Operation
In the example, assume there are three class-types: CT0, CT1, CT2.
We consider a particular link with
MAX-RESERVABLE_BW = 100
And with the allocated bandwidth constraints set as follows:
BC0 = 30
BC1 = 20
BC2 = 20
These bandwidth constraints are based on the normal traffic loads, as discussed in Section 5. With MAR, any of the CTs is allowed to
exceed its bandwidth constraint (BCc) as long a there are at least
RBW_THRES (reservation bandwidth threshold on the link) units of
spare bandwidth remaining. Let’s assume
RBW_THRES = 10
So under overload, if
RESERVED_BW0 = 50
RESERVED_BW1 = 30
RESERVED_BW2 = 10
Therefore, for this loading
UNRESERVED_BW = 100 - 50 - 30 - 10 = 10
CT0 and CT1 can no longer increase their bandwidth on the link,
because they are above their BC values and there is only RBW_THRES=10 units of spare bandwidth left on the link. But CT2 can take the
additional bandwidth (up to 10 units) if the demand arrives, because it is below its BC value.
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As also discussed in Section 4, if best effort traffic is present, it can always seize whatever spare bandwidth is available on the link at the moment, but is subject to being lost at the queues in favor of
the higher priority traffic.
Let’s say an LSP arrives for CT0 needing 5 units of bandwidth (i.e., DBW = 5). We need to decide, based on Table 1, whether to admit this LSP or not. Since for CT0
RESERVED_BW0 > BC0 (50 > 30), and
DBW > UNRESERVED_BW - RBW_THRES (i.e., 5 > 10 - 10)
Table 1 says the LSP is rejected/blocked.
Now let’s say an LSP arrives for CT2 needing 5 units of bandwidth
(i.e., DBW = 5). We need to decide based on Table 1 whether to admit this LSP or not. Since for CT2
RESERVED_BW2 < BC2 (10 < 20), and
DBW < UNRESERVED_BW (i.e., 5 < 10)
Table 1 says to admit the LSP.
Hence, in the above example, in the current state of the link and in the current CT loading, CT0 and CT1 can no longer increase their
bandwidth on the link, because they are above their BCc values and
there is only RBW_THRES=10 units of spare bandwidth left on the link. But CT2 can take the additional bandwidth (up to 10 units) if the
demand arrives, because it is below its BCc value.
7. Summary
The proposed MAR Bandwidth Constraints Model includes the following:
1. allocation of bandwidth to individual CTs,
2. protection of allocated bandwidth by bandwidth reservation
methods, as needed, but otherwise full sharing of bandwidth,
3. differentiation between high-priority, normal-priority, and best- effort priority services, and
4. provision of admission control to reject connection requests, when needed, in order to meet performance objectives.
The modeling results presented in Appendix A show that MAR bandwidth allocation achieves a) greater efficiency in bandwidth sharing while still providing bandwidth isolation and protection against QoS
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degradation, and b) service differentiation for high-priority,
normal-priority, and best-effort priority services.
8. Security Considerations
Security considerations related to the use of DS-TE are discussed in [DSTE-PROTO]. They apply independently of the Bandwidth Constraints Model, including the MAR specified in this document.
9. IANA Considerations
[DSTE-PROTO] defines a new name space for "Bandwidth Constraints
Model Id". The guidelines for allocation of values in that name
space are detailed in Section 13.1 of [DSTE-PROTO]. In accordance
with these guidelines, the IANA has assigned a Bandwidth Constraints Model Id for MAR from the range 0-239 (which is to be managed as per the "Specification Required" policy defined in [IANA-CONS]).
Bandwidth Constraints Model Id 2 was allocated by IANA to MAR.
10. Acknowledgements
DS-TE and Bandwidth Constraints Models have been an active area of
discussion in the TEWG. I would like to thank Wai Sum Lai for his
support and review of this document. I also appreciate helpful
discussions with Francois Le Faucheur.
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Appendix A. MAR Operation & Performance Analysis
A.1. MAR Operation
In the MAR Bandwidth Constraints Model, the bandwidth allocation
control for each CT is based on estimated bandwidth needs, bandwidth use, and status of links. The LER makes needed bandwidth allocation changes, and uses [RSVP-TE], for example, to determine if link
bandwidth can be allocated to a CT. Bandwidth allocated to
individual CTs is protected as needed, but otherwise it is shared.
Under normal, non-congested network conditions, all CTs/services
fully share all available bandwidth. When congestion occurs for a
particular CTc, bandwidth reservation acts to prohibit traffic from
other CTs from seizing the allocated capacity for CTc. Associated
with each CT is the allocated bandwidth constraint (BCc) which
governs bandwidth allocation and protection; these parameters are
illustrated with examples in this Appendix.
In performing MAR bandwidth allocation for a given flow/LSP, the LER first determines the egress LSR address, service-identity, and CT.
The connection request is allocated an equivalent bandwidth to be
routed on a particular CT. The LER then accesses the CT priority,
QoS/traffic parameters, and routing table between the LER and egress LSR, and sets up the connection request using the MAR bandwidth
allocation rules. The LER selects a first-choice path and determines if bandwidth can be allocated on the path based on the MAR bandwidth allocation rules given in Section 4. If the first choice path has
insufficient bandwidth, the LER may then try alternate paths, and
again applies the MAR bandwidth allocation rules now described.
MAR bandwidth allocation is done on a per-CT basis, in which
aggregated CT bandwidth is managed to meet the overall bandwidth
requirements of CT service needs. Individual flows/LSPs are
allocated bandwidth in the corresponding CT according to CT bandwidth availability. A fundamental principle applied in MAR bandwidth
allocation methods is the use of bandwidth reservation techniques.
Bandwidth reservation gives preference to the preferred traffic by
allowing it to seize idle bandwidth on a link more easily than the
non-preferred traffic. Burke [BUR] first analyzed bandwidth
reservation behavior from the solution of the birth-death equations
for the bandwidth reservation model. Burke’s model showed the
relative lost-traffic level for preferred traffic, which is not
subject to bandwidth reservation restrictions, as compared to non-
preferred traffic, which is subject to the restrictions. Bandwidth
reservation protection is robust to traffic variations and provides Ash Experimental [Page 11]
significant dynamic protection of particular streams of traffic. It is widely used in large-scale network applications [ASH1, MUM, AKI,
KRU, NAK].
Bandwidth reservation is used in MAR bandwidth allocation to control sharing of link bandwidth across different CTs. On a given link, a
small amount of bandwidth (RBW_THRES) is reserved (perhaps 1% of the total link bandwidth), and the reservation bandwidth can be accessed when a given CT has reserved bandwidth-in-progress (RESERVED_BW)
below its allocated bandwidth (BC). That is, if the available link
bandwidth (unreserved idle link bandwidth UNRESERVED_BW) exceeds
RBW_THRES, then any CT is free to access the available bandwidth on
the link. However, if UNRESERVED_BW is less than RBW_THRES, then the CT can utilize the available bandwidth only if its current bandwidth usage is below the allocated amount (BC). In this way, bandwidth can be fully shared among CTs if available, but it is protected by
bandwidth reservation if below the reservation level.
Through the bandwidth reservation mechanism, MAR bandwidth allocation also gives preference to high-priority CTs, in comparison to normal- priority and best-effort priority CTs.
Hence, bandwidth allocated to each CT is protected by bandwidth
reservation methods, as needed, but otherwise shared. Each LER
monitors CT bandwidth use on each CT, and determines if connection
requests can be allocated to the CT bandwidth. For example, for a
bandwidth request of DBW on a given flow/LSP, the LER determines the CT priority (high, normal, or best-effort), CT bandwidth-in-use, and CT bandwidth allocation thresholds, and uses these parameters to
determine the allowed load state threshold to which capacity can be
allocated. In allocating bandwidth DBW to a CT on given LSP (for
example, A-B-E), each link in the path is checked for available
bandwidth in comparison to the allowed load state. If bandwidth is
unavailable on any link in path A-B-E, another LSP could be tried,
such as A-C-D-E. Hence, determination of the link load state is
necessary for MAR bandwidth allocation, and two link load states are distinguished: available (non-reserved) bandwidth (ABW_STATE), and
reserved-bandwidth (RBW_STATE). Management of CT capacity uses the
link state and the allowed load state threshold to determine if a
bandwidth allocation request can be accepted on a given CT.
A.2. Analysis of MAR Performance
In this Appendix, modeling analysis is presented in which MAR
bandwidth allocation is shown to provide good network performance,
relative to full sharing models, under normal and abnormal operating conditions. A large-scale Diffserv-aware MPLS traffic engineering
simulation model is used, in which several CTs with different
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priority classes share the pool of bandwidth on a multiservice,
integrated voice/data network. MAR methods have also been analyzed
in practice for networks that use time division multiplexing (i.e.,
TDM-based networks) [ASH1], and in modeling studies for IP-based
networks [ASH2, ASH3, E.360].
All Bandwidth Constraints Models should meet these objectives:
1. applies equally when preemption is either enabled or disabled
(when preemption is disabled, the model still works ’reasonably’
well),
2. bandwidth efficiency, i.e., good bandwidth sharing among CTs under both normal and overload conditions,
3. bandwidth isolation, i.e., a CT cannot hog the bandwidth of
another CT under overload conditions,
4. protection against QoS degradation, at least of the high-priority CTs (e.g., high-priority voice, high-priority data, etc.), and
5. reasonably simple, i.e., does not require additional IGP
extensions and minimizes signaling load processing requirements.
The use of any given Bandwidth Constraints Model has significant
impacts on the performance of a network, as explained later.
Therefore, the criteria used to select a model need to enable us to
evaluate how a particular model delivers its performance, relative to other models. Lai [LAI, DSTE-PERF] has analyzed the MAM and RDM
Models and provided valuable insights into the relative performance
of these models under various network conditions.
In environments where preemption is not used, MAM is attractive
because a) it is good at achieving isolation, and b) it achieves
reasonable bandwidth efficiency with some QoS degradation of lower
classes. When preemption is used, RDM is attractive because it can
achieve bandwidth efficiency under normal load. However, RDM cannot provide service isolation under high load or when preemption is not
used.
Our performance analysis of MAR bandwidth allocation methods is based on a full-scale, 135-node simulation model of a national network,
combined with a multiservice traffic demand model to study various
scenarios and tradeoffs [ASH3, E.360]. Three levels of traffic
priority -- high, normal, and best effort -- are given across 5 CTs: normal priority voice, high priority voice, normal priority data,
high priority data, and best effort data.
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The performance analyses for overloads and failures include a) the
MAR Bandwidth Constraints Model, as specified in Section 4, b) the
MAM Bandwidth Constraints Model, and c) the No-DSTE Bandwidth
Constraints Model.
The allocated bandwidth constraints for MAR are described in Section 5 as:
Normal priority CTs: BCck = PROPORTIONAL_BWk,
High priority CTs: BCck = FACTOR X PROPORTIONAL_BWk
Best-effort priority CTs: BCck = 0
In the MAM Bandwidth Constraints Model, the bandwidth constraints for each CT are set to a multiple of the proportional bandwidth
allocation:
Normal priority CTs: BCck = FACTOR1 X PROPORTIONAL_BWk,
High priority CTs: BCck = FACTOR2 X PROPORTIONAL_BWk
Best-effort priority CTs: BCck = 0
Simulations show that for MAM, the sum (BCc) should exceed
MAX_RESERVABLE_BWk for better efficiency, as follows:
1. The normal priority CTs and the BCc values need to be over-
allocated to get reasonable performance. It was found that over- allocating by 100% (i.e., setting FACTOR1 = 2), gave reasonable
performance.
2. The high priority CTs can be over-allocated by a larger multiple
FACTOR2 in MAM and this gives better performance.
The rather large amount of over-allocation improves efficiency, but
somewhat defeats the ’bandwidth protection/isolation’ needed with a
BC Model, because one CT can now invade the bandwidth allocated to
another CT. Each CT is restricted to its allocated bandwidth
constraint BCck, which is the maximum level of bandwidth allocated to each CT on each link, as in normal operation of MAM.
In the No-DSTE Bandwidth Constraints Model, no reservation or
protection of CT bandwidth is applied, and bandwidth allocation
requests are admitted if bandwidth is available. Furthermore, no
queuing priority is applied to any of the CTs in the No-DSTE
Bandwidth Constraints Model.
Table 2 gives performance results for a six-times overload on a
single network node at Oakbrook, Illinois. The numbers given in the table are the total network percent lost (i.e., blocked) or delayed Ash Experimental [Page 14]
traffic. Note that in the focused overload scenario studied here,
the percentage of lost/delayed traffic on the Oakbrook node is much
higher than the network-wide average values given.
Table 2
Performance Comparison for MAR, MAM, & No-DSTE
Bandwidth Constraints (BC) Models
6X Focused Overload on Oakbrook
(Total Network % Lost/Delayed Traffic)
Class Type MAR BC MAM BC No-DSTE BC
Model Model Model
NORMAL PRIORITY VOICE 0.00 1.97 10.30
HIGH PRIORITY VOICE 0.00 0.00 7.05
NORMAL PRIORITY DATA 0.00 6.63 13.30
HIGH PRIORITY DATA 0.00 0.00 7.05
BEST EFFORT PRIORITY DATA 12.33 11.92 9.65
Clearly the performance is better with MAR bandwidth allocation, and the results show that performance improves when bandwidth reservation is used. The reason for the poor performance of the No-DSTE Model,
without bandwidth reservation, is due to the lack of protection of
allocated bandwidth. If we add the bandwidth reservation mechanism, then performance of the network is greatly improved.
The simulations showed that the performance of MAM is quite sensitive to the over-allocation factors discussed above. For example, if the BCc values are proportionally allocated with FACTOR1 = 1, then the
results are much worse, as shown in Table 3:
Table 3
Performance Comparison for MAM Bandwidth Constraints Model
with Different Over-allocation Factors
6X Focused Overload on Oakbrook
(Total Network % Lost/Delayed Traffic)
Class Type (FACTOR1 = 1) (FACTOR1 = 2)
NORMAL PRIORITY VOICE 31.69 1.97
HIGH PRIORITY VOICE 0.00 0.00
NORMAL PRIORITY DATA 31.22 6.63
HIGH PRIORITY DATA 0.00 0.00
BEST EFFORT PRIORITY DATA 8.76 11.92
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Bandwidth Constraints Models for a high-day network load pattern with a 50% general overload. The numbers given in the table are the total network percent lost (i.e., blocked) or delayed traffic.
Table 4
Performance Comparison for MAR, MAM, & No-DSTE
Bandwidth Constraints (BC) Models
50% General Overload (Total Network % Lost/Delayed Traffic)
Class Type MAR BC MAM BC No-DSTE BC
Model Model Model
NORMAL PRIORITY VOICE 0.02 0.13 7.98
HIGH PRIORITY VOICE 0.00 0.00 8.94
NORMAL PRIORITY DATA 0.00 0.26 6.93
HIGH PRIORITY DATA 0.00 0.00 8.94
BEST EFFORT PRIORITY DATA 10.41 10.39 8.40
Again, we can see the performance is always better when MAR bandwidth allocation and reservation is used.
Table 5 illustrates the performance of the MAR, MAM, and No-DSTE
Bandwidth Constraints Models for a single link failure scenario (3
OC-48). The numbers given in the table are the total network percent lost (blocked) or delayed traffic.
Table 5
Performance Comparison for MAR, MAM, & No-DSTE
Bandwidth Constraints (BC) Models
Single Link Failure (2 OC-48)
(Total Network % Lost/Delayed Traffic)
Class Type MAR BC MAM BC No-DSTE BC
Model Model Model
NORMAL PRIORITY VOICE 0.00 0.62 0.63
HIGH PRIORITY VOICE 0.00 0.31 0.32
NORMAL PRIORITY DATA 0.00 0.48 0.50
HIGH PRIORITY DATA 0.00 0.31 0.32
BEST EFFORT PRIORITY DATA 0.12 0.72 0.63
Again, we can see the performance is always better when MAR bandwidth allocation and reservation is used.
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Bandwidth Constraints Models for a multiple link failure scenario (3 links with 3 OC-48, 3 OC-3, 4 OC-3 capacity, respectively). The
numbers given in the table are the total network percent lost
(blocked) or delayed traffic.
Table 6
Performance Comparison for MAR, MAM, & No-DSTE
Bandwidth Constraints (BC) Models
Multiple Link Failure
(3 Links with 2 OC-48, 2 OC-12, 1 OC-12, Respectively)
(Total Network % Lost/Delayed Traffic)
Class Type MAR BC MAM BC No-DSTE BC
Model Model Model
NORMAL PRIORITY VOICE 0.00 0.91 0.92
HIGH PRIORITY VOICE 0.00 0.44 0.44
NORMAL PRIORITY DATA 0.00 0.70 0.72
HIGH PRIORITY DATA 0.00 0.44 0.44
BEST EFFORT PRIORITY DATA 0.14 1.03 1.04
Again, we can see the performance is always better when MAR bandwidth allocation and reservation is used.
Lai’s results [LAI, DSTE-PERF] show the trade-off between bandwidth
sharing and service protection/isolation, using an analytic model of a single link. He shows that RDM has a higher degree of sharing than MAM. Furthermore, for a single link, the overall loss probability is the smallest under full sharing and largest under MAM, with RDM being intermediate. Hence, on a single link, Lai shows that the full
sharing model yields the highest link efficiency, while MAM yields
the lowest; and that full sharing has the poorest service protection capability.
The results of the present study show that, when considering a
network context in which there are many links and multiple-link
routing paths are used, full sharing does not necessarily lead to
maximum, network-wide bandwidth efficiency. In fact, the results in Table 4 show that the No-DSTE Model not only degrades total network
throughput, but also degrades the performance of every CT that should be protected. Allowing more bandwidth sharing may improve
performance up to a point, but it can severely degrade performance if care is not taken to protect allocated bandwidth under congestion.
Both Lai’s study and this study show that increasing the degree of
bandwidth sharing among the different CTs leads to a tighter coupling between CTs. Under normal loading conditions, there is adequate
capacity for each CT, which minimizes the effect of such coupling. Ash Experimental [Page 17]
Under overload conditions, when there is a scarcity of capacity, such coupling can cause severe degradation of service, especially for the lower priority CTs.
Thus, the objective of maximizing efficient bandwidth usage, as
stated in Bandwidth Constraints Model objectives, needs to be
exercised with care. Due consideration also needs to be given to
achieving bandwidth isolation under overload, in order to minimize
the effect of interactions among the different CTs. The proper
tradeoff of bandwidth sharing and bandwidth isolation needs to be
achieved in the selection of a Bandwidth Constraints Model.
Bandwidth reservation supports greater efficiency in bandwidth
sharing, while still providing bandwidth isolation and protection
against QoS degradation.
In summary, the proposed MAR Bandwidth Constraints Model includes the following: a) allocation of bandwidth to individual CTs, b)
protection of allocated bandwidth by bandwidth reservation methods,
as needed, but otherwise full sharing of bandwidth, c)
differentiation between high-priority, normal-priority, and best-
effort priority services, and d) provision of admission control to
reject connection requests, when needed, in order to meet performance objectives.
In the modeling results, the MAR Bandwidth Constraints Model compares favorably with methods that do not use bandwidth reservation. In
particular, some of the conclusions from the modeling are as follows:
o MAR bandwidth allocation is effective in improving performance over methods that lack bandwidth reservation; this allows more bandwidth sharing under congestion.
o MAR achieves service differentiation for high-priority, normal-
priority, and best-effort priority services.
o Bandwidth reservation supports greater efficiency in bandwidth
sharing while still providing bandwidth isolation and protection
against QoS degradation, and is critical to stable and efficient
network performance.
Ash Experimental [Page 18]
Appendix B. Bandwidth Prediction for Path Computation
As discussed in [DSTE-PROTO], there are potential advantages for a
Head-end when predicting the impact of an LSP on the unreserved
bandwidth for computing the path of the LSP. One example would be to perform better load-distribution of multiple LSPs across multiple
paths. Another example would be to avoid CAC rejection when the LSP no longer fits on a link after establishment.
Where such predictions are used on Head-ends, the optional Bandwidth Constraints sub-TLV and the optional Maximum Reservable Bandwidth
sub-TLV MAY be advertised in the IGP. This can be used by Head-ends to predict how an LSP affects unreserved bandwidth values. Such
predictions can be made with MAR by using the unreserved bandwidth
values advertised by the IGP, as discussed in Sections 2 and 4:
UNRESERVED_BWck = MAX_RESERVABLE_BWk - UNRESERVED_BWk -
delta0/1(CTck) * RBW-THRESk
where
delta0/1(CTck) = 0 if RESERVED_BWck < BCck
delta0/1(CTck) = 1 if RESERVED_BWck >= BCck
Furthermore, the following estimate can be made for RBW_THRESk:
RBW_THRESk = RBW_% * MAX_RESERVABLE_BWk,
where RBW_% is a locally configured variable, which could take on
different values for different link speeds. This information could
be used in conjunction with the BC sub-TLV, MAX_RESERVABLE_BW sub-
TLV, and UNRESERVED_BW sub-TLV to make predictions of available
bandwidth on each link for each CT. Because admission control
algorithms are left for vendor differentiation, predictions can only be performed effectively when the Head-end LSR predictions are based on the same (or a very close) admission control algorithm used by
other LSRs.
LSPs may occasionally be rejected when head-ends are establishing
LSPs through a common link. As an example, consider some link L, and two head-ends H1 and H2. If only H1 or only H2 is establishing LSPs through L, then the prediction is accurate. But if both H1 and H2
are establishing LSPs through L at the same time, the prediction
would not work perfectly. In other words, the CAC will occasionally run into a rejected LSP on a link with such ’race’ conditions. Also, as mentioned in Appendix A, such a prediction is optional and outside the scope of the document.
Ash Experimental [Page 19]
Normative References
[DSTE-REQ] Le Faucheur, F. and W. Lai, "Requirements for Support
of Differentiated Services-aware MPLS Traffic
Engineering", RFC 3564, July 2003.
[DSTE-PROTO] Le Faucheur, F., Ed., "Protocol Extensions for Support of Diffserv-aware MPLS Traffic Engineering," RFC 4124, June 2005.
[RFC2119] Bradner, S., "Key words for Use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[IANA-CONS] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, RFC
2434, October 1998.
Informative References
[AKI] Akinpelu, J. M., "The Overload Performance of
Engineered Networks with Nonhierarchical & Hierarchical Routing," BSTJ, Vol. 63, 1984.
[ASH1] Ash, G. R., "Dynamic Routing in Telecommunications
Networks," McGraw-Hill, 1998.
[ASH2] Ash, G. R., et al., "Routing Evolution in Multiservice Integrated Voice/Data Networks," Proceeding of ITC-16, Edinburgh, June 1999.
[ASH3] Ash, G. R., "Performance Evaluation of QoS-Routing
Methods for IP-Based Multiservice Networks," Computer
Communications Magazine, May 2003.
[BUR] Burke, P. J., Blocking Probabilities Associated with
Directional Reservation, unpublished memorandum, 1961. [DSTE-PERF] Lai, W., "Bandwidth Constraints Models for
Differentiated Services-aware MPLS Traffic Engineering: Performance Evaluation", RFC 4128, June 2005.
[E.360] ITU-T Recommendations E.360.1 - E.360.7, "QoS Routing & Related Traffic Engineering Methods for Multiservice
TDM-, ATM-, & IP-Based Networks".
[GMPLS-RECOV] Lang, J., et al., "Generalized MPLS Recovery Functional Specification", Work in Progress.
Ash Experimental [Page 20]
With的用法全解 with结构是许多英语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 一、 with结构的构成 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without-名词/代词+形容词； 2. with或without-名词/代词+副词； 3. with或without-名词/代词+介词短语； 4. with或without-名词/代词 +动词不定式； 5. with或without-名词/代词 +分词。 下面分别举例： 1、 She came into the room，with her nose red because of cold.（with+名词+形容词，作伴随状语）
2、 With the meal over ， we all went home.（with+名词+副词，作时间状语） 3、The master was walking up and down with the ruler under his arm。（with+名词+介词短语，作伴随状语。） The teacher entered the classroom with a book in his hand. 4、He lay in the dark empty house，with not a man ，woman or child to say he was kind to me.（with+名词+不定式，作伴随状语）He could not finish it without me to help him.（without+代词 +不定式，作条件状语） 5、She fell asleep with the light burning.（with+名词+现在分词，作伴随状语） Without anything left in the with结构是许多英 语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 二、with结构的用法 with是介词，其意义颇多，一时难掌握。为帮助大家理清头绪，以教材中的句子为例，进行分类，并配以简单的解释。在句子中with结构多数充当状语，表示行为方式，伴随情况、时间、原因或条件（详见上述例句）。 1.带着，牵着…… (表动作特征)。如： Run with the kite like this.
with用法归纳 （1）“用……”表示使用工具，手段等。例如： ①We can walk with our legs and feet. 我们用腿脚行走。 ②He writes with a pencil. 他用铅笔写。 （2）“和……在一起”，表示伴随。例如： ①Can you go to a movie with me? 你能和我一起去看电影'>电影吗？ ②He often goes to the library with Jenny. 他常和詹妮一起去图书馆。 （3）“与……”。例如： I’d like to have a talk with you. 我很想和你说句话。 （4）“关于，对于”，表示一种关系或适应范围。例如： What’s wrong with your watch? 你的手表怎么了？ （5）“带有，具有”。例如： ①He’s a tall kid with short hair. 他是个长着一头短发的高个子小孩。 ②They have no money with them. 他们没带钱。 （6）“在……方面”。例如： Kate helps me with my English. 凯特帮我学英语。 （7）“随着，与……同时”。例如： With these words, he left the room. 说完这些话，他离开了房间。 [解题过程] with结构也称为with复合结构。是由with+复合宾语组成。常在句中做状语，表示谓语动作发生的伴随情况、时间、原因、方式等。其构成有下列几种情形： 1.with+名词(或代词)+现在分词 此时，现在分词和前面的名词或代词是逻辑上的主谓关系。 例如:1)With prices going up so fast, we can't afford luxuries. 由于物价上涨很快，我们买不起高档商品。（原因状语） 2)With the crowds cheering, they drove to the palace. 在人群的欢呼声中，他们驱车来到皇宫。（伴随情况） 2.with+名词(或代词)+过去分词 此时，过去分词和前面的名词或代词是逻辑上的动宾关系。
独立主格篇 独立主格，首先它是一个“格”，而不是一个“句子”。在英语中任何一个句子都要有主谓结构，而在这个结构中，没有真正的主语和谓语动词，但又在逻辑上构成主谓或主表关系。独立主格结构主要用于描绘性文字中，其作用相当于一个状语从句，常用来表示时间、原因、条件、行为方式或伴随情况等。除名词/代词+名词、形容词、副词、非谓语动词及介词短语外，另有with或without短语可做独立主格，其中with可省略而without不可以。*注：独立主格结构一般放在句首，表示原因时还可放在句末；表伴随状况或补充说明时，相当于一个并列句，通常放于句末。 一、独立主格结构： 1. 名词/代词+形容词 He sat in the front row, his mouth half open. Close to the bank I saw deep pools, the water blue like the sky. 靠近岸时，我看见几汪深池塘，池水碧似蓝天。 2. 名词/代词+现在分词 Winter coming, it gets colder and colder. The rain having stopped, he went out for a walk.
The question having been settled, we wound up the meeting. 也可以The question settled, we wound up the meeting. 但含义稍有差异。前者强调了动作的先后。 We redoubled our efforts, each man working like two. 我们加倍努力，一个人干两个人的活。 3. 名词/代词+过去分词 The job finished, we went home. More time given, we should have done the job much better. *当表人体部位的词做逻辑主语时，不及物动词用现在分词，及物动词用过去分词。 He lay there, his teeth set, his hands clenched, his eyes looking straight up. 他躺在那儿，牙关紧闭，双拳紧握，两眼直视上方。 4. 名词/代词+不定式 We shall assemble at ten forty-five, the procession to start moving at precisely eleven. We divided the work, he to clean the windows and I to sweep the floor.
with用法小结 一、with表拥有某物 Mary married a man with a lot of money . 马莉嫁给了一个有着很多钱的男人。 I often dream of a big house with a nice garden . 我经常梦想有一个带花园的大房子。 The old man lived with a little dog on the lonely island . 这个老人和一条小狗住在荒岛上。 二、with表用某种工具或手段 I cut the apple with a sharp knife . 我用一把锋利的刀削平果。 Tom drew the picture with a pencil . 汤母用铅笔画画。 三、with表人与人之间的协同关系 make friends with sb talk with sb quarrel with sb struggle with sb fight with sb play with sb work with sb cooperate with sb I have been friends with Tom for ten years since we worked with each other, and I have never quarreled with him . 自从我们一起工作以来，我和汤姆已经是十年的朋友了，我们从没有吵过架。 四、with 表原因或理由 John was in bed with high fever . 约翰因发烧卧床。 He jumped up with joy . 他因高兴跳起来。 Father is often excited with wine . 父亲常因白酒变的兴奋。 五、with 表“带来”，或“带有,具有”，在…身上，在…身边之意
with[wIT] prep.1.与…(在)一起，带着：Come with me. 跟我一起来吧。/ I went on holiday with my friend. 我跟我朋友一起去度假。/ Do you want to walk home with me? 你愿意和我一道走回家吗 2.(表带有或拥有)有…的，持有，随身带着：I have no money with me. 我没有带钱。/ He is a man with a hot temper. 他是一个脾气暴躁的人。/ We bought a house with a garden. 我们买了一座带花园的房子。/ China is a very large country with a long history. 中国是一个具有历史悠久的大国。3.(表方式、手段或工具)以，用：He caught the ball with his left hand. 他用左手接球。/ She wrote the letter with a pencil. 她用铅笔写那封信。4.(表材料或内容)以，用：Fill the glass with wine. 把杯子装满酒。/ The road is paved with stones. 这条路用石头铺砌。5.(表状态)在…的情况下，…地：He can read French with ease. 他能轻易地读法文。/ I finished my homework though with difficulty. 虽然有困难，我还是做完了功课。6.(表让步)尽管，虽然：With all his money, he is unhappy. 尽管他有钱，他并不快乐。/ With all his efforts, he lost the match. 虽然尽了全力，他还是输了那场比赛。7.(表条件)若是，如果：With your permission, I’ll go. 如蒙你同意我就去。8.(表原因或理由)因为，由于：He is tired with work. 他工作做累了。/ At the news we all jumped with joy. 听到这消息我们都高兴得跳了起来。9.(表时间)当…的时候，在…之后：With that remark, he left. 他说了那话就离开了。/ With daylight I hurried there to see what had happened. 天一亮我就去那儿看发生了什么事。10. (表同时或随同)与…一起，随着：The girl seemed to be growing prettier with each day. 那女孩好像长得一天比一天漂亮。11.(表伴随或附带情况)同时：I slept with the window open. 我开着窗户睡觉。/ Don’t speak with your mouth full. 不要满嘴巴食物说话。12.赞成，同意：I am with you there. 在那点上我同你意见一致。13.由…照看，交…管理，把…放在某处：I left a message for you with your secretary. 我给你留了个信儿交给你的秘书了。/ The keys are with reception. 钥匙放在接待处。14 (表连同或包含)连用，包含：The meal with wine came to ￡8 each. 那顿饭连酒每人8英镑。/ With preparation and marking a teacher works 12 hours a day. 一位老师连备课带批改作业每天工作12小时。15. (表对象或关系)对，关于，就…而言，对…来说：He is pleased with his new house. 他对他的新房子很满意。/ The teacher was very angry with him. 老师对他很生气。/ It’s the same with us students. 我们学生也是这样。16.(表对立或敌对)跟，以…为对手：The dog was fighting with the cat. 狗在同猫打架。/ He’s always arguing with his brother. 他老是跟他弟弟争论。17.(在祈使句中与副词连用)：Away with him! 带他走！/ Off with your clothes! 脱掉衣服！/ Down with your money! 交出钱来！ 【用法】1.表示方式、手段或工具等时(=以，用)，注意不要受汉语意思的影响而用错搭配，如“用英语”习惯上用in English，而不是with English。2.与某些抽象名词连用时，其作用相当于一个副词：with care=carefully 认真地/ with kindness=kindly 亲切地/ with joy=joyfully 高兴地/ with anger=angrily 生气地/ with sorrow=sorrowfully 悲伤地/ with ease=easily 容易地/ with delight=delightedly 高兴地/ with great fluency =very fluently 很流利地3.表示条件时，根据情况可与虚拟语气连用：With more money I would be able to buy it. 要是钱多一点，我就买得起了。/ With better equipment, we could have finished the job even sooner. 要是设备好些，我们完成这项工作还要快些。4.比较with 和as：两者均可表示“随着”，但前者是介词，后者是连词：He will improve as he grows older. 随着年龄的增长，他会进步的。/ People’s ideas change with the change of the times. 时代变了，人们的观念也会变化。5.介词with和to 均可表示“对”，但各自的搭配不同，注意不要受汉语意思的影响而用错，如在kind, polite, rude, good, married等形容词后通常不接介词with而接to。6.复合结构“with+宾语+宾语补足语”是一个很有用的结构，它在句中主要用作状语，表示伴随、原因、时间、条件、方式等；其中的宾语补足语可以是名词、形容词、副词、现在分词、过去分词、不定式、介词短语等：I went out with the windows open. 我外出时没有关窗户。/ He stood before his teacher with his head down. 他低着头站在老师面前。/ He was lying on the bed with all his clothes on. 他和衣躺在床上。/ He died with his daughter yet a schoolgirl. 他去世时，女儿还是个小学生。/ The old man sat there with a basket beside her. 老人坐在那儿，身边放着一个篮子。/ He fell asleep with the lamp burning. 他没熄灯就睡着了。/ He sat there with his eyes closed. 他闭目坐在那儿。/ I can’t go out with all these clothes to wash. 要洗这些衣服，我无法出去了。这类结构也常用于名词后作定语：The boy with nothing on is her son. 没穿衣服的这个男孩子是她儿子。 （摘自《英语常用词多用途词典》金盾出版社） - 1 -
with复合结构 一. with复合结构的常见形式 1.“with+名词/代词+介词短语”。 The man was walking on the street, with a book under his arm. 那人在街上走着，腋下夹着一本书。 2. “with+名词/代词+形容词”。 With the weather so close and stuffy, ten to one it’ll rain presently. 天气这么闷热，十之八九要下雨。 3. “with+名词/代词+副词”。 The square looks more beautiful than even with all the light on. 所有的灯亮起来，广场看起来更美。 4. “with+名词/代词+名词”。 He left home, with his wife a hopeless soul. 他走了，妻子十分伤心。 5. “with+名词/代词+done”。此结构过去分词和宾语是被动关系，表示动作已经完成。 With this problem solved, neomycin 1 is now in regular production. 随着这个问题的解决，新霉素一号现在已经正式产生。 6. “with+名词/代词+-ing分词”。此结构强调名词是-ing分词的动作的发出者或某动作、状态正在进行。 He felt more uneasy with the whole class staring at him. 全班同学看着他，他感到更不自然了。 7. “with+宾语+to do”。此结构中，不定式和宾语是被动关系，表示尚未发生的动作。 So in the afternoon, with nothing to do, I went on a round of the bookshops. 由于下午无事可做，我就去书店转了转。 二. with复合结构的句法功能 1. with 复合结构，在句中表状态或说明背景情况，常做伴随、方式、原因、条件等状语。With machinery to do all the work, they will soon have got in the crops. 由于所有的工作都是由机器进行，他们将很快收完庄稼。（原因状语） The boy always sleeps with his head on the arm. 这个孩子总是头枕着胳膊睡觉。（伴随状语）The soldier had him stand with his back to his father. 士兵要他背对着他父亲站着。（方式状语）With spring coming on, trees turn green. 春天到了，树变绿了。（时间状语） 2. with 复合结构可以作定语 Anyone with its eyes in his head can see it’s exactly like a rope. 任何一个头上长着眼睛的人都能看出它完全像一条绳子。 【高考链接】 1. ___two exams to worry about, I have to work really hard this weekend.（04北京） A. With B. Besides C. As for D. Because of 【解析】A。“with+宾语+不定式”作状语，表示原因。 2. It was a pity that the great writer died, ______his works unfinished. (04福建) A. for B. with C. from D.of 【解析】B。“with+宾语+过去分词”在句中作状语，表示状态。 3._____production up by 60%, the company has had another excellent year. (NMET) A. As B.For C. With D.Through 【解析】C。“with+宾语+副词”在句中作状语，表示程度。
with结构是许多英语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 一、with结构的构成 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without-名词/代词+形容词； 2. with或without-名词/代词+副词； 3. with或without-名词/代词+介词短语； 4. with或without-名词/代词+动词不定式； 5. with或without-名词/代词+分词。 下面分别举例： 1、She came into the room，with her nose red because of cold.（with+名词+形容词，作伴随状语） 2、With the meal over ，we all went home.（with+名词+副词，作时间状语） 3、The master was walking up and down with the ruler under his arm。（with+名词+介词短语，作伴随状语。）The teacher entered the classroom with a book in his hand. 4、He lay in the dark empty house，with not a man ，woman or child to say he was kind to me.（with+名词+不定式，作伴随状语）He could not finish it without me to help him.（without+代词+不定式，作条件状语） 5、She fell asleep with the light burning.（with+名词+现在分词，作伴随状语） 6、Without anything left in the cupboard，she went out to get something to eat.（without+代词+过去分词，作为原因状语） 二、with结构的用法 在句子中with结构多数充当状语，表示行为方式，伴随情况、时间、原因或条件（详见上述例句）。
【With的基本用法与独立主格】 with结构是许多英语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。 一、with结构的构成 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without-名词/代词+形容词； 2. with或without-名词/代词+副词； 3. with或without-名词/代词+介词短语； 4. with或without-名词/代词+动词不定式； 5. with或without-名词/代词+分词。 下面分别举例： 1、She came into the room，with her nose red because of cold.（with+名词+形容词，作伴随状语） 2、With the meal over, we all went home.（with+名词+副词，作时间状语） 3、The master was walking up and down with the ruler under his arm。（with+名词+介词短语，作伴随状语。） 4、He could not finish it without me to help him.（without+代词+不定式，作条件状语） 5、She fell asleep with the light on.（with+名词+现在分词，作伴随状语） 二、with结构的用法 with是介词，其意义颇多，一时难掌握。为帮助大家理清头绪，以教材中的句子为例，进行分类，并配以简单的解释。在句子中with结构多数充当状语，表示行为方式，伴随情况、时间、原因或条件（详见上述例句）。 1. 带着，牵着……(表动作特征)。如： Run with the kite like this. 2. 附加、附带着……(表事物特征)。如： A glass of apple juice, two glasses of coke, two hamburgers with potato chips, rice and fish. 3. 和……(某人)一起。 a. 跟某人一起(居住、吃、喝、玩、交谈……) 。如： Now I am in China with my parents. Sometimes we go out to eat with our friends. He / She's talking with a friend. b. 跟go, come 连用，有"加入"到某方的意思。如： Do you want to come with me? 4. 和play一起构成短语动词play with 意为"玩耍……，玩弄……" 如： Two boys are playing with their yo-yos. 5. 与help 一起构成help...with...句式，意为"帮助(某人) 做(某事)"。如： On Monday and Wednesday, he helps his friends with their English. 6. 表示面部神情，有“含着……，带着……”如： "I'm late for school," said Sun Y ang, with tears in his eyes. 7. 表示"用……" 如：
介词with的用法 1.表示人与人的协同关系，意为“一起”“和” go with 与..一起去 play with 与...一起玩 live with 与...一起住/生活 work with 与...一起工作 make friends with 与....交朋友 talk with sb = talk to sb fight with 与...打架/战斗 cooperate with 与...一起合作 2.表示“带有”“拥有” tea with honey 加蜂蜜的茶 a man with a lot of money 一个有很多钱的人 a house with a big garden 一个带有大花园的房子 a chair with three legs 一张三条腿的椅子 a girl with golden hair 金发的女孩 3.表示“用”某种工具或手段 write with a pencil 用铅笔写字 cut the apple with a knife 用刀切苹果 4.表示“在...身边”“在...身上” I don’t have any money with me. 我身上没带钱。 Take an umbrella with you in case it rains 带把伞以防下雨。 5.表示“在...之下” With the help of sb = with one’s help 在某人的帮助下 6.表示“随着” with the development of ... 随着...的发展 float with the wind 随风飘动
7.常见带有with的动词短语 agree with sb/sth 同意某人或某事deal with sth = do with sth 处理某事 help sb with sth 在...上帮助某人 fall in love with sb/sth 爱上某人/某物 get on with sb 与某人相处 get on well with sb 与某人相处得好 have nothing to do with sb 与某人无关compare A with B 将A和B作比较communicate with sb 与某人交流 argue with sb = quarrel with sb 与某人吵架Have fun with sth 玩的开心 Get away with sth 做坏事不受惩罚 Chat with sb 跟某人闲谈 Charge sb with sth 指控某人。。。 Put up with sth 忍受 8.常见带with的形容词固定搭配 be satisfied with 对...满意 be content with sth 对...满足 be angry with sb 生某人的气 be strict with sb 对某人严格 be patient with sb 对某人有耐心 be popular with sb 受某人欢迎 be filled with sth 装满... 充满..... = be full of sth What’s wrong/the matter with sb/sth be familiar with sb/sth 熟悉某人或某物 be connected with sb/sth 与....有关 Be decorated with 被。。。装饰 Be impressed with/by
wｉth用法归纳 (１)“用……”表示使用工具,手段等。例如: ①We caｎｗaｌｋwith ｏｕｒleｇｓａnｄfｅet. 我们用腿脚行走。 ②Heｗriｔes withａpenｃiｌ。她用铅笔写。 (2)“与……在一起”,表示伴随。例如: ①Ｃan ｙou gｏｔoａｍovie with ｍe？您能与我一起去瞧电影’>电影不？ ②He often ｇoｅs to ｔheｌibrarｙwiｔｈＪenny、她常与詹妮一起去图书馆。 (3)“与……"。例如: I'd ｌike ｔo ｈave a talk wｉth you、我很想与您说句话、 (4)“关于,对于”,表示一种关系或适应范围。例如: Wｈat’s wroｎg with yoｕｒwaｔｃｈ？您得手表怎么了？ (５)“带有,具有"。例如: ①He'ｓ a ｔalｌkｉd ｗitｈｓhoｒt hair. 她就是个长着一头短发得高个子小孩。 ②Tｈeｙhaｖｅno monｅy with them、她们没带钱。 (6)“在……方面”。例如: Ｋate helpｓｍe wiｔh mｙEｎglｉsｈ. 凯特帮我学英语。 (7)“随着,与……同时”、例如: Ｗｉth thesｅwｏｒdｓ, ｈe leftｔｈｅｒooｍ、说完这些话,她离开了房间。［解题过程］ ｗiｔh结构也称为wｉtｈ复合结构。就是由wｉth+复合宾语组成。常在句中做状语,表示谓语动作发生得伴随情况、时间、原因、方式等。其构成有下列几种情形: 1。with+名词(或代词)+现在分词 此时,现在分词与前面得名词或代词就是逻辑上得主谓关系。 例如:1)Ｗitｈprｉcｅs goｉng ｕp ｓo fａｓt, we ｃan’t afford ｌuxuriｅｓ、由于物价上涨很快,我们买不起高档商品。(原因状语) 2)Ｗitｈthe crowds cheerｉnｇ, they drｏve to tｈｅｐalaｃe。 在人群得欢呼声中,她们驱车来到皇宫、(伴随情况) 2、wiｔh+名词(或代词)＋过去分词
with 结构 一：with结构的形式 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without 名词/代词 例句：Yesterday I saw Mary with a gun. 2. with或without 名词/代词+ 形容词 例句：He is used to sleeping with the windows open. 3. with或without 名词/代词+ 副词 例句：She left the room with all the lights on. 4. with或without 名词/代词+ 介词短语 例句：He walked into the dark street with a stick in his hand. 5. with或without 名词/代词+ 动词不定式 例句：With so much work to do, I have no time for a holiday. 6. with或without 名词/代词+ Ving 例句：We found the house easily with the little boy leading the way.(现在分词表示主动动作，即分词所表示的动作是由with后的宾语发出来的) 7. with或without 名词/代词+ Ved With all the things bought, she went home happily.(过去分词表示被动，with后面的宾语与过去分词之间是被动关系) 8. with或without 名词/代词+ 补语 例句：Possibly this person died without anyone knowing where the coins were hidden. He wondered if he could slide out of the lecture hall without anyone noticing (him). 9. with或without 名词/代词+ 动词不定式和+ Ving/Ved的区别 加不定式是指将要进行的动作,加分词是指主动或被动动作. 10. with+名词/代词+名词 例句：He died with his daughter a schoolgirl. 他在他女儿是个小学生的时候死了 二：with复合结构的句法功能 1. with 复合结构，在句中表状态或说明背景情况该结构常做伴随、方式、原因、条件等状语。 例句：With machinery to do all the work, they will soon have got in the crops. 由于所有的工作都是由机器进行，他们将很快收完庄稼。（原因状语） The boy always sleeps with his head on the arm. 这个孩子总是头枕着胳膊睡觉。（伴随状语） The soldier had him stand with his back to his father. 士兵要他背对着他父亲站着。（方式状语）With spring coming on, trees turn green. 春天到了，树变绿了。（时间状语） 2. with复合结构可以作定语 Anyone with its eyes in his head can see it’s exactly like a rope. 任何一个头上长着眼睛的人都能看出它完全像一条绳子。
with的用法大全 with结构是许多英语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 一、with结构的构成 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without-名词/代词+形容词; 2. with或without-名词/代词+副词; 3. with或without-名词/代词+介词短语; 4. with或without-名词/代词+动词不定式; 5. with或without-名词/代词+分词。 下面分别举例： 1、She came into the room，with her nose red because of cold.(with+名词+形容词，作伴随状语) 2、With the meal over ，we all went home.(with+名词+副词，作时间状语)
3、The master was walking up and down with the ruler under his arm。(with+名词+介词短语，作伴随状语。) The teacher entered the classroom with a book in his hand. 4、He lay in the dark empty house，with not a man ，woman or child to say he was kind to me.(with+名词+不定式，作伴随状语) He could not finish it without me to help him.(without+代词+不定式，作条件状语) 5、She fell asleep with the light burning.(with+名词+现在分词，作伴随状语) 6、Without anything left in the cupboard，she went out to get something to eat.(without+代词+过去分词，作为原因状语) 二、with结构的用法 在句子中with结构多数充当状语，表示行为方式，伴随情况、时间、原因或条件(详见上述例句)。 With结构在句中也可以作定语。例如： 1.I like eating the mooncakes with eggs. 2.From space the earth looks like a huge water-covered globe with a few patches of land sticking out above the water. 3.A little boy with two of his front teeth missing ran into the house. 三、with结构的特点 1. with结构由介词with或without+复合结构构成。复合结构中第一部分与第二部分语法上是宾语和宾语补足语关系，而在逻辑上，却具有主谓关系，也就是说，可以用第一部分
Wiｔｈ得用法 1.Wｉｔh sｂ/stｈdoing 表主动且进行 2.Witｈsｔh bｅing donｅ表被动且进行 3.wiｔｈsth done表被动且完成 4.with sth tｏdo表示将来 1.从语法角度瞧: wｉｔh 就是介词,所以后面跟得就是宾语;宾语后面得可以被称为就是宾补。 1.Wiｔhouｔanyone ｎoticing, Ｉsｔoｌ e into tｈe room、 With so many cｈildren talking and laｕghｉng, Ｉcouldｎ’ｔｓｅtｔle ｄｏwn to my work、 2.Wｉｔh so much ｗork beinｇdone, I can’t spaｒe any minute。 3.With ｓo ｍucｈｗoｒｋdone, Ｉhad a nicｅday。 4.Witｈ a lｏt ｏf problems to sｅｔtlｅ, the newｌy elｅcted ｐreｓideｎt ｉs ｈaving a haｒｄtime。 Lie 说谎-ｌiｅd－lieｄ—ｌyinｇ Ｌie躺;存在;位于-lａy－ｌaiｎ—lyiｎg
Lay 放置;产卵下蛋-laiｄ—ｌaid-ｌaｙｉｎg Ｈe lied说谎to me ｔhat he ｈａdｎ't ｓeen the ｂag ｔhat I had laｉd 放置on the cｏunteｒ、Iｎfａct iｔwasｌyｉng存在bｅsｉde ｈim on the grounｄ。 Hiｓsｕggestion aimｉnｇ(aｉm) ｔo ｒemov ｅyouｒｂａｄhabit ｉs acceptａble。 Ｈis suggeｓtion ａiｍed(aiｍ) aｔｒemoｖing your bad habit iｓacceptａbｌe. 迎合caｔer for 做出调整ｍake adjusｔments 在这之前previoｕs to this 协商negotiａte 为…而准备ｂｅｍeant fｏr／be ｉnｔeｎｄeｄfor 明年将被开展得建造工程不就是很容易被及时完成、The buｉｌdinｇpｒｏｊeｃt to be ｃａrrieｄouｔｎｅxt yｅar is ｎｏt ｅasｙto ｃｏmplｅtｅ. Ｒｅｑｕiｒe dｏiｎg＝need ｄoｉng = ｗant d ｏｉｎg以主动表被动 All cars requirｅtesting／to be tｅsｔed。 Pｕｌl ｔhrougｈ康复;完成十分困难得事情