Transcript ppt - College of Engineering | Oregon State University

ECE 466/566
Advanced Computer Networks
Thinh Nguyen
Email: [email protected]
Electrical Engineering and Computer Science
Oregon State University
7: Multimedia Networking
7-1
 Integrated Services and Differentiated Services
7: Multimedia Networking
7-2
IETF Integrated Services
 architecture for providing QOS guarantees in IP
networks for individual application sessions
 resource reservation: routers maintain state info
(a la VC) of allocated resources, QoS req’s
 admit/deny new call setup requests:
Question: can newly arriving flow be admitted
with performance guarantees while not violated
QoS guarantees made to already admitted flows?
7: Multimedia Networking
7-3
Intserv: QoS guarantee scenario
 Resource reservation
 call setup, signaling (RSVP)
 traffic, QoS declaration
 per-element admission control
request/
reply

QoS-sensitive
scheduling (e.g.,
WFQ)
7: Multimedia Networking
7-4
Call Admission
Arriving session must :
 declare its QOS requirement
R-spec: defines the QOS being requested
 characterize traffic it will send into network
 T-spec: defines traffic characteristics
 signaling protocol: needed to carry R-spec and Tspec to routers (where reservation is required)
 RSVP

7: Multimedia Networking
7-5
Intserv QoS: Service models [rfc2211, rfc 2212]
Controlled load service:
Guaranteed service:
 "a quality of service closely
 worst case traffic arrival:
approximating the QoS that
same flow would receive
from an unloaded network
element."
leaky-bucket-policed source
 simple (mathematically
provable) bound on delay
[Parekh 1992, Cruz 1988]
arriving
traffic
token rate, r
bucket size, b
WFQ
per-flow
rate, R
D = b/R
max
7: Multimedia Networking
7-6
IETF Differentiated Services
Concerns with Intserv:
 Scalability: signaling, maintaining per-flow router
state difficult with large number of flows
 Flexible Service Models: Intserv has only two
classes. Also want “qualitative” service classes


“behaves like a wire”
relative service distinction: Platinum, Gold, Silver
Diffserv approach:
 simple functions in network core, relatively
complex functions at edge routers (or hosts)
 Don’t define service classes, provide functional
components to build service classes
7: Multimedia Networking
7-7
Diffserv Architecture
Edge router:
r
 per-flow traffic management
 marks packets as in-profile
and out-profile
b
marking
scheduling
..
.
Core router:
 per class traffic management
 buffering and scheduling based
on marking at edge
 preference given to in-profile
packets
 Assured Forwarding
7: Multimedia Networking
7-8
Edge-router Packet Marking
 profile: pre-negotiated rate A, bucket size B
 packet marking at edge based on per-flow profile
Rate A
B
User packets
Possible usage of marking:
 class-based marking: packets of different classes marked
differently
 intra-class marking: conforming portion of flow marked
differently than non-conforming one
7: Multimedia Networking
7-9
Classification and Conditioning
 Packet is marked in the Type of Service (TOS) in
IPv4, and Traffic Class in IPv6
 6 bits used for Differentiated Service Code Point
(DSCP) and determine PHB that the packet will
receive
 2 bits are currently unused
7: Multimedia Networking 7-10
Classification and Conditioning
may be desirable to limit traffic injection rate of
some class:
 user declares traffic profile (e.g., rate, burst size)
 traffic metered, shaped if non-conforming
7: Multimedia Networking
7-11
Forwarding (PHB)
 PHB result in a different observable (measurable)
forwarding performance behavior
 PHB does not specify what mechanisms to use to
ensure required PHB performance behavior
 Examples:


Class A gets x% of outgoing link bandwidth over time
intervals of a specified length
Class A packets leave first before packets from class B
7: Multimedia Networking 7-12
Forwarding (PHB)
PHBs being developed:
 Expedited Forwarding : pkt departure rate of a
class equals or exceeds specified rate

logical link with a minimum guaranteed rate
 Assured Forwarding : 4 classes of traffic
 each guaranteed minimum amount of bandwidth and
buffering.
 each with three drop preference partitions
7: Multimedia Networking 7-13
Traffic and Service Characterization
 To quantify a service one has two know
 Flow’s traffic arrival
 Service provided by the router, i.e., resources reserved
at each router
 Examples:
 Traffic characterization: token bucket
 Service provided by router: fix rate and fix buffer space
7: Multimedia Networking 7-14
Token Bucket
 Characterized by three parameters (b, r, R)



b – token depth
r – average arrival rate
R – maximum arrival rate (e.g., R link capacity)
 A bit is transmitted only when there is an available token

When a bit is transmitted exactly one token is consumed
r tokens per second
b tokens
bits
slope r
b*R/(R-r)
slope R
<= R bps
time
regulator
7: Multimedia Networking 7-15
Characterizing a Source by Token
Bucket
 Arrival curve – maximum amount of bits transmitted by
time t
 Use token bucket to bound the arrival curve
bps
bits
Arrival curve
time
time
7: Multimedia Networking 7-16
Per-hop Reservation
 Given b,r,R and per-hop delay d
 Allocate bandwidth ra and buffer space Ba
such that to guarantee d
slope ra
bits
slope r
Arrival curve
b
d
Ba
7: Multimedia Networking 7-17
End-to-End Reservation
 Source S sends a message containing traffic characteristics


r,b,R
This message is used to computes the number of hops
 Receiver R sends back this information + worst-case delay (D)
 Each router along path provide a per-hop delay guarantee and
forwards the message

In simplest case routers split the delay D
num hops
S
(b,r,R)
(b,r,R,0,0)
S1
S2
(b,r,R,2,D-d1)
(b,r,R,1,D-d1-d2)
(b,r,R,3)
S3
R
(b,r,R,3,D)
worst-case delay
7: Multimedia Networking 7-18
Diffserv Architecture
 Ingress routers


Police/shape traffic
Set Differentiated Service Code Point (DSCP) in Diffserv (DS)
field
 Core routers


Implement Per Hop Behavior (PHB) for each DSCP
Process packets based on DSCP
DS-2
DS-1
Ingress
Ingress
Egress
Edge router
Egress
Core router
7: Multimedia Networking 7-19
Differentiated Service (DS) Field
0
5 6 7
DS Field
0
4
Version HLen
8
16
TOS
Identification
TTL
19
31
Length
Flags
Fragment offset
Protocol
Header checksum
Source address
Destination address
IP
header
Data
 DS filed reuse the first 6 bits from the former Type
of Service (TOS) byte
 The other two bits are proposed to be used by ECN
7: Multimedia Networking 7-20
Examples of Differentiated Services
 Two types of service
 Assured service
 Premium service
 Plus, best-effort service
7: Multimedia Networking 7-21
Assured Service
[Clark & Wroclawski ‘97]
 Defined in terms of user profile, how much
assured traffic is a user allowed to inject into
the network
 Network: provides a lower loss rate than besteffort

In case of congestion best-effort packets are dropped
first
 User: sends no more assured traffic than its
profile

If it sends more, the excess traffic is converted to
best-effort
7: Multimedia Networking 7-22
Premium Service
[Jacobson ’97]
 Provides the abstraction of a virtual pipe
between an ingress and an egress router
 Network: guarantees that premium packets are
not dropped and they experience low delay
 User: does not send more than the size of the
pipe

If it sends more, excess traffic is delayed, and dropped
when buffer overflows
7: Multimedia Networking 7-23
Edge Router
Ingress
Traffic conditioner
Class 1
Marked traffic
Traffic conditioner
Data traffic
Class 2
Classifier
Best-effort
Scheduler
Per aggregate
Classification
(e.g., user)
7: Multimedia Networking 7-24
Assumptions
 Assume two bits
 P-bit denotes premium traffic
 A-bit denotes assured traffic
 Traffic conditioner (TC) implement
 Metering
 Marking
 Shaping
7: Multimedia Networking 7-25
TC Performing Metering/Marking
 Used to implement Assured Service
 In-profile traffic is marked:

A-bit is set in every packet

A-bit is cleared (if it was previously set) in every packet;
this traffic treated as best-effort
 Out-of-profile (excess) traffic is unmarked
r bps
User profile
b bits (token bucket)
assured traffic
Metering
Set A-bit
in-profile traffic
Clear A-bit
out-of-profile traffic
7: Multimedia Networking 7-26
TC Performing
Metering/Marking/Shaping
 Used to implement Premium Service
 In-profile traffic marked:

Set P-bit in each packet
 Out-of-profile traffic is delayed, and when buffer
overflows it is dropped
r bps
User profile
b bits (token bucket)
premium traffic
Metering/
Shaper/
Set P-bit
out-of-profile traffic
(delayed and dropped)
in-profile traffic
7: Multimedia Networking 7-27
Scheduler
 Employed by both edge and core routers
 For premium service – use strict priority, or weighted fair
queuing (WFQ)
 For assured service – use RIO (RED with In and Out)

Always drop OUT packets first
• For OUT measure entire queue
• For IN measure only in-profile queue
Dropping
probability
1
OUT
IN
Average queue length
7: Multimedia Networking 7-28
Scheduler Example
 Premium traffic sent at high priority
 Assured and best-effort traffic pass through
RIO and then sent at low priority
P-bit set?
yes
high priority
no
yes
A-bit set? no
RIO
low priority
7: Multimedia Networking 7-29
Control Path
 Each domain is assigned a Bandwidth Broker
(BB)

Usually, used to perform ingress-egress bandwidth
allocation
 BB is responsible to perform admission control
in the entire domain
 BB not easy to implement



Require complete knowledge about domain
Single point of failure, may be performance
bottleneck
Designing BB still a research problem
7: Multimedia Networking 7-30
Example
 Achieve end-to-end bandwidth guarantee
3
2
BB
1 9
8 profile
7
BB
6
profile
5
BB
4 profile
receiver
sender
7: Multimedia Networking 7-31
Comparison to Best-Effort and Intserv
Best-Effort
Diffserv
Intserv
Service
Connectivity
No isolation
No guarantees
Per aggregate isolation
Per aggregate
guarantee
Per flow isolation
Per flow guarantee
Service
scope
End-to-end
Domain
End-to-end
Complexity No setup
Long term setup
Per flow steup
Scalability
Scalable
Not scalable (each
(edge routers maintains router maintains
per flow state)
per aggregate state;
core routers per class
state)
Highly scalable
(nodes maintain
only routing
state)
7: Multimedia Networking 7-32
Summary
 Diffserv more scalable than Intserv
 Edge routers maintain per aggregate state
 Core routers maintain state only for a few traffic classes
 But, provides weaker services than Intserv, e.g.,
 Per aggregate bandwidth guarantees (premium service)
vs. per flow bandwidth and delay guarantees
 BB is not an entirely solved problem
 Single point of failure
 Handle only long term reservations (hours, days)
7: Multimedia Networking 7-33