QoS

1
QoS

• Chapter 8

2
Introduction

• QoS is one of the biggest issue
• A free service
• Paying subscribers
• Service package
• Lower cost than the PSTN
• Voice and data service
• Technical solutions for providing QoS
• Various solutions
• Combined to complement each other

3
The Need for QoS

• A collective measure of the level of service
• For a particular application
• Performance criteria
• Availability, throughput, connection setup time,
  percentage of successful transmissions, speed of
  fault detection and correction
• Bandwidth, packet loss, delay and jitter
• IP is a best-effort service
• Well suited to non-real-time communication
• TCP
• Error-free, in-sequence delivery
• delay

4

• UDP
• Fine for transporting voice
• Provided that
• Low packet loss
• Little congestion on the network
• Traffic in the network can be bursty and
  unpredictable
• A speaker may be forced to repeat what he just
  said
• In case of significant packet loss
• To attract and retain paying subscribers
• Circuit switching has a distinct advantage
• But ill-suited to other forms of communication
• IP network solutions for the QoS are needed
• Resource-reservation techniques

5
End-to-End QoS

• QoS must be end-to-end
• The support of all networks in the chain
• SLAs
• Service-Level Agreements between different
  operators
• Regarding the type and quality of service to be
  offered
• Or the penalties
• VoIP and voice over the Internet
• Are not the same
• SLAs may be possible between certain VoIP carriers

6

• Things will get better
• VoIP for long-distance service
• Connected to the PSTN at each end
• Some VoIP operators
• Begin on IP and terminate on the PSTN
• More VoIP operators
• Over IP from source to destination
• All of the providers embrace the same quality
  objectives and implement similar technical
  solutions
• Voice over the Internet?

7
Its not just the network

• A quality service
• A lot more than just good voice quality
• A potentially high cost associated with acquiring
  a customer
• Means
• Superior customer service, rapid service
  provisioning, 100 percent accurate billing, clear
  and concise product descriptions, etc.

8
Overview of QoS Solutions

• One approach
• Reserve the resource before establishing the
  session
• Has certain similarities to circuit switching
• Another approach
• Categorize traffic into different classes or
  priorities
• Real-time applications with higher-priority
  values
• Require a fair resource-allocation techniques
• The easiest technique
• The provision of more bandwidth

9
More Bandwidth

• Sounds like a simplistic and expensive
• No major system development
• Significant overbuild
• Unused for most of the time
• An inefficient way
• Huge advances in bandwidth
• 9600-baud modem
• 56kbps modem
• DSL
• The core of the network, DWDM

10

• Moores Law
• Doubles roughly every 18 months
• Bandwidth availability and bandwidth demand have
  tended to move almost in lock-step
• New applications to use the available bandwidth

11
QoS Protocols and Architectures

• RSVP, Resource-Reservation Protocol
• RFC 2205
• Part of the IETF integrated-services suite
• Enable resources to be reserved for a given
  session in prior
• The most complex, and closest to circuit
  emulation
• Strong QoS guarantees
• Significant granularity of resource allocation
• Significant feedback to applications
• Two levels of service
• Guaranteed - as close as possible to circuit
  emulation
• Controlled load equivalent to the service in a
  best-effort network under no-load conditions

12

• RSVP

13

• A sender issues a PATH message to the far end
• Contains a traffic specification (TSpec)
• Bandwidth requirement and packet size
• Each RSVP-enabled router along the way
• Establish a path state
• The previous source address
• The receiver of the Path message
• Responds with a Reservation Request (RESV)
• A flowspec a TSpec and the type of reservation
  service
• The RESV message travels back to the sender
• Along the same route
• At each router, the requested resource is
  allocated
• Can accommodate multicast transport

14

• Differentiated Service, DiffServ
• A relatively simple means for prioritizing
  different types of traffic
• RFC 2475
• Makes use of
• The IPv4 Type of Service (TOS) field
• The IPv6 Traffic Class field
• Known as the DS field
• Mark a given stream as requiring a particular
  type of forwarding
• Per-Hop Behavior (PHB)
• Expedited Forwarding (EF)
• Assured Forwarding (AF)

15

• RFC 3246 specifies EF
• A given traffic stream is assigned a minimum
  departure rate from a given node
• If the arrival rate lt a pre-agreed maximum
• Queuing delays are removed
• Ensures that delay and jitter are minimized
• Equivalent to a virtual leased line
• RFC 2597 specifies AF
• Packets from a given source are forwarded with a
  high probability
• Provided that source does not exceed pre-agreed
  max

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• Four classes
• An amount of resources (buffer space and
  bandwidth)
• If there is congestion within the resources
  allocated
• Packets with the highest drop-rate values will be
  discarded first
• Label Switching
• Has gained significant interest
• MPLS, Multi-Protocol Label Switching
• Mark traffic at the entrance to the network
• To determine the next router in the path from the
  source to destination
• A short label to a packet in front of the IP
  header
• A new layer below the IP layer

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• To look up the next hop in the path
• The match is exact enable a faster routing
  decisions
• FEC, a Forwarding Equivalence Class
• All packets of a given FEC are treated equally
  all packet from A to B follow exactly the same
  path
• Bandwidth can be allocated at the start of a
  session
• A traffic-engineering protocol as well
• Analogous to the establishment of virtual
  circuits in ATM

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QoS Policies

• Which QoS levels?
• QoS policies specify how those mechanisms are
  used
• Pay more to get better service
• Authentication functions
• Rules to specify which circumstances lead to
  which actions
• COPS, Common Open-Policy Service Protocol
• Policy Enforcement Point (PEP)
• Policy Decision Point (PDP)

19
RSVP

• Functions in routers and host
• Policy control
• Admission control
• Whether sufficient resources exist
• Packet classifier
• Determine the QoS
• Packet scheduler
• Traffic control
• Admission control, packet classifier and packet
  scheduler

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• RSVP within host and routers

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RSVP Syntax

• The syntax of RSVP messages
• RFC 2215
• General Characterization Parameters for
  Integrated Service Network Elements
• Services are identified by particular numbers
• Service number 2 the Guaranteed Service
• Service number 5 the Controlled-load Service
• Service number 1 common to a number of services
• A number of parameters
• Parameter numbers
• TLV (Type-Length-Value) format

22
Establishing Reservations

• Reserve resources from the receiver back to the
  sender
• With multicast in mind
• In the reverse direction, the path merges
• The maximum of the merged requests
• Deal with unidirectional data transfer only
• A PATH message
• TSpec
• An RESV message
• Flowspec
• Merging flowspecs the flowspec is modified

23

• TSpec
• Also included in a RESV message
• A token bucket specification
• bucket size, b
• token rate, r
• the packet is transmitted onward only if the
  number of tokens in the bucket is at least as
  large as the packet
• peak rate, p
• p gt r
• maximum packet size, M
• minimum policed unit, m
• All packets less than m bytes are considered to
  be m bytes

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• The overhead to process each packet
• Bound the bandwidth overhead of link-level
  headers
• The Token Bucket TSpec has parameter number 127

25

• Flowspec
• An indication of the QoS control service
  requested
• Controlled-load service and Guaranteed service
• For Controlled-load service
• Simply a Tspec
• For Guaranteed service
• A Rate (R) term, the bandwidth required
• R ? r, extra bandwidth will reduce queuing delays
• A Slack (S) term
• The difference between the desired delay and the
  delay that would be achieved if rate R were used
• Used to reduced the resource reserved

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• Filter Spec
• An RSVP session
• A destination IP address and protocol ID
• An optional destination port number
• No information about the sender
• A problem to determine the specific data flow of
  a reservation
• Define the flow to which a particular QoS is to
  be applied
• A sender IP address and an sender port number
  (optional)
• For a video conference
• A different QoS requirement for each stream

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• A router in the path must examine the header
• IP datagrams in the flow must not be fragmented
• Use path MTU discovery
• IP security might encrypt the header
• RSVP must include security functions
• IPv6 header is of variable length
• A greater processing effort
• Included in a PATH message
• A Sender template

28

• ADSpec
• PATH(TSpec)
• RESV(flowspec)
• The receiver to be informed about the network
• The receiver does not request what the network
  cannot provide
• The sender and routers
• Indicate their QoS capabilities advertising
• The sender constructs an initial ADSpec
• Each router update the ADSpec
• Also indicate that one or more routers
  RSVP-incapable

29

• Figure 8-9
• Service number 1
• X a non-IS hop is involved in the path
• Not integrated Service capable lacking RSVP
  support
• 1, the rest of ADSpec is no longer relevant
• The number of hops between IS-capable nodes
• The path MTU
• The minimum path latency
• If no queuing delay

30
RSVP Messages

• Path (1), Resv (2), PathErr (3), ResvErr(4),
  PathTear (5), ResvTear (6), RsevConf (7)
• A common header, Fig. 8-10
• Send_TTL the IP TTL value of the message
• To determine that a non-RSVP hop has been
  involved
• IP TTL --, but not Send_TTL
• A number of objects
• Sender Tspec, ADSpec, etc.
• Class-num identifies the object itself
• C-Type identifies the different version
• e.g., IPv4 or IPv6

31

• SESSION Class
• Class-num 1
• C-Type 1, IPv4 2, IPv6
• IP destination address, the protocol ID and
  (optional) the destination port
• FLOWSPEC Class
• Class-num 9
• C-Type 2
• SENDER_TEMPLATE Class
• Class-num 11
• C-type 1, IPv4 2, IPv6
• e.g., a filter spec in a Path message

32

• RSVP_HOP Class
• The IP address of the interface through which the
  last RSVP-capable node passed this message
• Used in the Path message and saved at each node
• Ensure that the RESV message use the same path
  back
• Class-num 3
• C-type 1, IPv4 2, IPv6
• TIME_VALUES Class
• A timeout period in milliseconds for the message
• Class-num 5

33

• ERROR_SPEC Class
• In a RSVP error message
• the IP address of the node where the error was
  detected
• An error code plus additional cause information
• Class-num 6
• C-type 1, IPv4 2, IPv6
• STYLE Class
• Select different reservation styles
• Multiple receivers and/or multiple senders
• Fixed-filter style a receiver uniquely
  identifies a sender
• Wildcard-filter for all data streams from all
  senders
• Shared-filter lists specific senders
• Class-num 8 C-type 1

34
Example Reservations

• Successful reservation for a single sender and
  receiver

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• For a single sender and two receivers
• QoS requirement of Receiver 1 is stronger
• Receiver 2 requests a confirmation Receiver 1
  does not
• May lead to false confirmation
• e.g., the reservation request fails later

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Reservation Errors

• A given resource reservation fails
• An error message is returned
• PathErr messages simply sent back to the sender
• ResvErr messages are sent to a receiver
• Only to the receiver whose request fails

39
Guaranteed Service

• RFC 2212
• Two elements
• No packet loss
• Is a function of the token bucket depth (b) and
  the token rate (r)
• Ensuring minimal delay
• A fixed delay due to processing
• The queuing delay lt b/R C/R D
• C and D are maximum deviations from an ideal
  fluid model
• The ADSpec includes
• Ctot and Dtot

40
Controlled-Load Service

• A close approximation to
• A network that is lightly loaded
• A high percentage of packet will be delivered
• And will not exceed the minimum delay
• Does not identify specific characteristics of
  network elements that needs to be minimized
• Offer the the necessary bandwidth and buffer
  space to support the TSpec
• flowspec is just a TSpec

41
Removing Reservations

• Explicitly by a sender or receiver
• PathTear
• Travels towards all receivers
• Deletes path states and reservation states
• ResvTear
• Do the same thing in reverse
• Only to the receivers own reservation states
• As a result of a timeout a soft-state approach
• Reservations need to be refreshed on a regular
  basis
• A refresh period (R) within the TIME-VALUES
• Within each node, a timer L gtgt R
• If the node does not receive refreshing message
  within L seconds

42
DiffServ

• RSVP
• The most comprehensive QoS mechanism
• Closest to circuit emulation
• RSVP-enabled routers maintain state
• Significant overhead and difficulty to scale up
• QoS in terms of bandwidth
• To increase the QoS is to increase the bandwidth
• RSVP reserve the resources
• DiffServ offers one application greater QoS at
  the expense of another application
• If the second one will not notice a big difference

43
DiffServ Architecture

• IPv4 has a TOS field and IPv6 has a Traffic Class
  field
• Diffserv renames the fields the DS field
• The least-significant six bits
• DSCP, DS Codepoint
• PHB, per hop behavior
• The packet is handled according to the DSCP
• RFC 2475
• An Architecture for Differentiated Services

44

• The packets of a given stream
• Marked with the appropriate DSCP value
• The routers provide the correct PHB
• The edge of the network ensures
• Only qualified packets are marked
• Metering to measure the packet rate
• The traffic meets an agreed-upon profile
• Traffic shaping and dropping
• These functions are called traffic conditioning

45

• Classifying and conditioning traffic
• The functions are pushed to the edge
• The changes in the core of the network is minimal
• Does not change with the number of applications
• Scales extremely well

46
The Need for SLAs

• A given network domain and packet source must
  agree on
• Packet classification
• Traffic conditions
• The functions can be implemented
• At the source, or
• In an edge router
• SLAs between the customer and operator
• A definition of the traffic profile
• A token bucket specification

47

• The classification and marking rules
• Based on combinations of source address,
  destination address, source port, destination
  port, protocol ID, time of delay
• The behaviors for specific DSCP values
• Also specify for traffic outside the traffic
  profile
• Dropping of packets, the marking of
  non-conformant packets, traffic shaping,
  additional charges
• SLAs between different network operators
• A common set of policies and PHB definitions
• The rules related to the service

48
Per-Hop Behaviors

• The treatment that a DS router applies to a
  packet with a given DSCP value
• An aggregate
• The set of flows from one node to the next that
  share the same DSCP codepoint
• PHB configuration is established w.r.t.
  aggregate, rather than to specific flows
• Two PHBs are defined
• Expedited Forwarding
• Assured Forwarding

49
Expedited Forwarding

• EF PHB
• A service that is low loss, low delay
  approximates a virtual leased line
• By minimizing the queuing delay of each node
• The rate of departure of packets is a
  well-defined min
• And the arrival rate is always less
• The traffic-conditioning functions at the edge
  are important
• The DSCP value is 101110

50

• The EF PHB implementations
• Unlimited preemption of other traffic
• Unacceptably low performance for non-EF traffic
• Does not inflict enormous damage to other traffic
• Using a token bucket limiter, or
• Weighted round-robin scheduler
• The share is equal to a configured rate
• The specific implementation can have an impact on
  jitter
• Appendix of RFC 2598
• A comparison for a priority queue implementation
  versus a weighted round-robin

51

• The Virtual Wire Behavior Aggregate
• An Internet draft
• Discusses the traffic conditioning for the EF PHB
• The aggregate should have a well-defined minimum
  departure rate
• Strict shaping at the ingress to the DiffServ
  network can ensure the traffic is carried jitter
  free
• As soon as the last bit of a packet is received,
  the router starts send the packet
• The last bit of the next packet arrives before
  the last bit of the first packet has departed
• No perceived jitter

52
Assured Forwarding

• The AF PHB
• RFC 2597
• High-priority packet are forwarded with a greater
  reliability
• The traffic into a DiffServ network from a source
  should conform a particular traffic profile
• Certain resources are allocated to certain
  behavior aggregates
• Different levels of forwarding assurances

53

• Packets are marked with different AF classes
• Within each class, packets are marked with
  different drop-precedence values
• If the resources allocated to a given class
  become congested
• The router drops packets with higher
  drop-precedence
• Four classes and three drop-precedence levels

54

• The AF implementation
• Must detect and respond to long-term congestion
  by dropping packets
• Respond to short-term congestion by queuing
• A function
• Monitors short-term congestion
• Derives a smoothed long-term congestion level
• Drop packets if necessary
• Must treat all packets within a given class and
  precedence level equally
• All flows experience the same drop rate
• Must not reorder AF packets within a given AF
  class

55

• RSVP
• reserve resource on a session-by-session basis
• end-to-end
• Diffserv
• sharing resources according to priority
• hop-by-hop
• MPLS
• ensure end-to-end resource availability for a
  large number of sessions

56
Multi-Protocol Label Switching

• MPLS is not primarily a QoS solution
• A new switching architecture
• An IP router analyze the IP header to determine
  the next hop
• The longest matched entry in the routing table
• MPLS attaches a label to the packet
• According to a FEC (Forwarding Equivalence Class)
• At the ingress to the network
• The label is examined in the next node and the
  FEC is determined
• Via a simple table lookup
• A new label is attached, and the packet is
  forwarded

57

• The difference from the IP routing
• The FEC is determined at the point of ingress
• Where more information might be available
• e.g., QoS requirements
• A given FEC can force a packet to take a
  particular route without having to cram a list of
  specific routers
• The label doest not necessarily imply a new layer
  between layer 2 and 3
• The label can be carried at layer 2
• e.g., ATM VPI or VCI fields Frame Relay DLCI
  field

58
MPLS Architecture

• Multiprotocol Label Switching Architecture
• RFC 3031
• The ingress point A packet -gt an FEC -gt a label
• At the next router the label -gt the FEC
• In addition, a table lookup -gt the next hop and a
  new label
• The value of the label can be changed
• The FEC doe not change

59

• An example
• R1 is a label edge router
• label switching router

60

• LSPs Label-Switched Paths
• an FEC -gt a path through a network
• a label-switched path
• Label Distribution
• to establish and maintain LSPs
• the routers share FEC/label binding - label
  distribution protocol
• the downstream LSR decides on the particular
  binding
• An upstream router must know the binding of the
  router downstream
• Packets with the same label from different
  routers may have different FECs

61

• Label Assignment and Distribution
• The downstream LSR decides on the particular
  binding
• Then communicates the binding to the upstream LSR
• Through a label-distribution protocol
• RSVP has the extension
• LDP (Label-Distribution Protocol) has been
  developed
• Constraint-Based LDP
• Two ways
• Downstream-on-demand
• Unsolicited downstream

62
FEC and Labels

• An FEC can represent many things
• In reality
• The FEC takes the form of one or more IP
  addresses or IP address prefixes
• LDP sepcifies
• An FEC is composed of a number of FEC elements
• Each element is either a host address or address
  prefix
• Fig. 8-18

63

• A label can be an ATM VPI/VCI or a Frame Relay
  DLCI
• Or, a shim layer between layer 2 and the network
  layer
• 32-bit label, shown in Fig. 8-19
• The label, 20 bits
• Time-to-live, 8 bits
• Experimental use, 3 bits
• S, 1 bit, indicates the label is the last in the
  stack

64

• ATM VPI/VCI, Fig. 8-20
• V-bits
• 00 both VPI and VCI are significant
• 01 only VPI
• 10 only VCI
• Frame Relay, Fig. 8-21
• Len indicates the number of bits in the DLCI
• 0 10 bits long
• 2 23 bits long
• 1,3 reserved

65

• The Label Stack
• A packet can have more than one label
• A label stack contains several labels
• An LSR bases its actions on the first (top) label
• Why might we need a label stack? Tunneling
• An tunneling example
• FEC F LSP R1, R2, R3, and R4
• R2 and R3 are not directly connected
• Form a two ends of the tunnel R2, R2A, R2B, R2C
  and R3
• R2 replaces the first label and place a new label
  on top
• R2C recognizes it is the next-to-last LSR in the
  tunnel

66

• LSP tunnel

67
ROUTE AT EDGE, SWITCH IN CORE
IP
IP
IP Forwarding
IP Forwarding
LABEL SWITCHING
68
Actions at LSRs

• Depend on the value of the label
• The Next Hop-Level Forwarding Entry (NHLFE)
• Indicates the next hop, the operation to perform
  on the label stack, and the encoding to be used
• e.g., replace the label at the top, pop the label
  stack, or replace the top label, then add
  additional labels on top
• The next hop might be the same LSR
• The LSR pop the top-level label and forwards the
  packet to itself
• The packet might still have a label, or it might
  be a native IP packet

69

• A given label might map to more than one NHLFE
• For load sharing across multiple paths
• The LSR chooses one of the NHLFEs to use
• If a router knows it is the next-to-last LSR in a
  given path
• It should remove any labels and pass the packet
  to the final LSR without a label
• To minimize the amount of effort that the
  ultimate LSR need to undertake
• Otherwise, the final LSR examines the label
• The next hop is itself, pop the stack and forward
  to itself

70

• How a particular LSR determines
• It is the next-to-last LSR for a given path
• A function of label distribution and the
  distribution protocol used

71
Label-Switched Paths

• Label switching will be introduced
• In the form of islands within IP network
• There will be points of ingress and egress to the
  MPLS network
• A point of ingress
• Choose the FEC for a given packet
• A point of egress
• Determine a label/FEC binding and passing that
  information upstream

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LABEL SWITCHED PATH (vanilla)
- A Vanilla LSP is actually part of a tree from
every source to that destination
(unidirectional). - Vanilla LDP builds that tree
using existing IP forwarding tables to route the
control messages.
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• An egress LSR w.r.t. a particular FEC
• If the FEC refers to the LSR,
• If the next hop for the FEC is outside of the
  MPLS network, or
• If the next hop means traversing a boundary
• An LSP
• A path for a given FEC
• From an ingress LSR to the egress LSR
• Many points of ingress might exist
• The LSPs forms a tree with the egress LSR at the
  root
• LDP establishes and maintains the LSPs

74
MPLS Traffic Engineering

• One of the most important applications of MPLS
• Modeling, characterization, and control of
  traffic to meet specific performance objectives
• Might be traffic oriented or resource oriented
• The two objectives are not necessarily mutually
  exclusive
• e.g., congestion avoidance is a common goal

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• Congestion is primarily caused in two ways
• A lack of sufficient resources on the network
• Expand capacity
• Congestion-control techniques
• The steering to traffic towards loaded area
• Good traffic engineering
• OSPF (Open Shortest Path First)
• Tends to force traffic down the shortest route
• May promote congestion
• ATM traffic engineering functions at layer 2
• Enable virtual circuits to be easily rerouted

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Traffic Trunks

• A traffic trunk
• A set of flows that share specific attributes
• The ingress and egress LSRs, the FEC, and other
  traffic characteristics
• Can explicitly specify the LSP that a traffic
  trunk should use
• Steer traffic away from the shortest path
• Adapt to changing load conditions by changing the
  LSP

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• Three main aspects of traffic engineering
• Mapping packets to FECs
• Mapping FECs to traffic trunks
• Mapping traffic trunks onto the physical network
  topology through label-switched paths
• 1st and 2nd are functions at the ingress
• 3rd ensures that the network
• Provides the quality that is needed
• Can involve constraint-based routing
• Match the traffic and the available resources of
  the network

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Constraint-Based Routing and LDP

• Constraint-Based LSP Setup Using LDP
• CR-LDP, RFC 3212
• Offers a routing capability
• The path is chosen according to certain
  constraints
• Based on LDP
• LDP
• The establishment of LSPs with which particular
  FECs are associated
• Discovery messages
• Announce and maintain the presence of an LSR

79

• Session messages
• Establish, maintain, and terminate sessions
  between LDP peers
• Advertisement messages
• Create, change, and delete label mapping for FECs
• e.g., set up the actual LSPs
• Notification message
• Provide advisory information and signal error
  information

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MPLS HOW DOES IT WORK
TIME
TIME
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• The advertisement messages
• Label Request message
• An upstream LSR requests a downstream LSR to
  assign and advertise a label for a given FEC
• Fig. 8-26
• Two optional parameters
• The Hop Count specifies the running total of the
  number of LSR hops along the LSP
• Too many hops
• The Path Vector is a list of LSRs in the path
• For loop detection
• Label Mapping message
• Advertise a given label/FEC mapping
• Fig. 8-27

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MPLS Label Distribution
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
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Label Switched Path (LSP)
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
84

• CR-LDP enhances LDP
• Traffic parameters, resource requirements and
  other characteristics can be incorporated in the
  establishment of LSPs
• Enable the establishment of explicit routes
• A subset of constraint-based routes
• Explicit Routes
• A CR-LSP is an LSP that is established subject to
  a number of criteria
• Based on information that is available at the
  edge of the network

85

• An ER (Explicit Route) is one type of
  constraint-based LSP where some or all of the
  nodes to be used are specified
• A strict ER, all the nodes in the path are
  specified
• A loose ER, several nodes in the path are
  specified, but other nodes can also be used
• CR-LDP enables explicit route information to be
  included in the LDP Label Request message
• Define specific paths for traffic that has
  specific char

86
EXPLICITLY ROUTED OR ER-LSP
B
C
A
- ER-LSP follows route that source chooses. In
other words, the control message to establish the
LSP (label request) is source routed.
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EXPLICITLY ROUTED LSP ER-LSP
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
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• Traffic Characteristics
• Be specified through the use of traffic parameter
• Fig. 8-28
• The peak rate the Peak Data Rate and the Peak
  Burst Size
• A token bucket specification
• The committed rate the Committed Data Rate and
  the Committed Burst Size
• The Excess Burst Size
• Used at the edge of the MPLS domain for traffic
  conditioning
• The token bucket size is EBS and the token rate
  is CDR

89

• The Frequency
• How often the CDR should be made available
• 1 average at least the CDR over any short
  interval (a small number of the shortest packet
  times)
• 2 Very frequent, average at least the CDR over
  any packet interval
• The Weight determines
• The CR-LSPs share of any possible excess
  bandwidth above the committed rate

90

• Resource Classes
• To specify what links can be used in a given
  CR-LSP
• To limit the set of possible links
• Could indicate OC-48, ADSL, etc.
• Known as colors
• CR-LDP provides a means form indicating a
  resource class in LDP messages
• Preemption
• If a CR-LSP cannot be established due to a lack
  of available resources
• It is possible to reroute other traffic in order
  to make room
• The assignment of two priority levels to a given
  CR-LSP

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• setupPriority
• The authority to preempt another
• hodlingPriority
• How much authority is required by another CR-LSP
  to bump the CR-LSP
• The value 0 is most important, 7 the least
• For a given CR-LSP
• setupPriority lt holdingPriroity
• Modified LDP messages for CR-LDP
• The Label Request and Label Mapping messages are
  modified
• Figs. 8-30 and 8-31
• The Pinning parameter is used with loose explicit
  routes

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• Indicating whether or not a path can be changed
  at a given LSR if a better next hop becomes
  available later
• The LSPID is a unique identifier for a CR-LSP
• End-to-End QoS
• How the traffic is classified and conditioned at
  the edge of the MPLS network

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CR-LDP

• CR Constraint based Routing
• eg USE (links with sufficient resources AND
  (links of type someColor) AND
  (links that have delay less than
  200 ms)

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Combining QOS Solutions

• The QoS solutions
• Each has its advantages and disadvantages
• RSVP
• Powerful
• Each router maintains path states
• DiffServ
• Simpler
• More of a prioritization techniques than a
  resource-guarantee mechanism

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• MPLS
• Great promise as an overall solution
• Significant changes to all routers
• Combining the solutions in smart ways
• Be used in different parts of the network
• e.g., RSVP in one domain and DiffServ in another
• Map an RSVP service request to an appropriate
  DiffServ PHB
• Map a DiffServ behavior aggregate to an MPLS FEC

96

• An example of combining QoS techniques

97
Further Information

• QoS is of major importance to the future of IP
  networks
• Further Information
• IETFs Web site
• QOS Forum
• Not a standards-setting body