1. Advanced Computer Networks
ECE 466/566
Advanced Computer Networks
Thinh Nguyen
Electrical Engineering and Computer Science
Oregon State University
7: Multimedia Networking

2. Integrated Services and Differentiated Services
7: Multimedia Networking

3. 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

4. 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

5. 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 T-spec to routers (where reservation is required)
RSVP
7: Multimedia Networking

6. Intserv QoS: Service models [rfc2211, rfc 2212]
Guaranteed service:
worst case traffic arrival: leaky-bucket-policed source
simple (mathematically provable) bound on delay [Parekh 1992, Cruz 1988]
Controlled load service:
"a quality of service closely approximating the QoS that same flow would receive from an unloaded network element."
WFQ
token rate, r
bucket size, b
per-flow
rate, R
D = b/R
max
arriving
traffic
7: Multimedia Networking

7. 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

8. Diffserv Architecture
Edge router:
per-flow traffic management
marks packets as in-profile and out-profile r 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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
bits
slope r
b*R/(R-r)
b tokens
slope R
<= R bps
time
regulator
7: Multimedia Networking

16. 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

17. 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
slope r
bits
Arrival curve b d Ba
7: Multimedia Networking

18. 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
(b,r,R,3)
num hops S2 R S
(b,r,R)
(b,r,R,2,D-d1)
(b,r,R,3,D)
worst-case delay S1 S3
(b,r,R,1,D-d1-d2)
(b,r,R,0,0)
7: Multimedia Networking

19. 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
Egress
Ingress
Egress
Edge router
Core router
7: Multimedia Networking

20. Differentiated Service (DS) Field5 6 7
DS Field 4 8 16 19 31
Version
HLen
TOS
Length
Identification
Flags
Fragment offset
TTL
Protocol
Header checksum IP
header
Source address
Destination address
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

21. Examples of Differentiated Services
Two types of service
Assured service
Premium service
Plus, best-effort service
7: Multimedia Networking

22. 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 best-effort
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

23. 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

24. Edge Router Class 1 Marked traffic Class 2 Data traffic Classifier
Ingress
Traffic conditioner
Class 1
Marked traffic
Traffic conditioner
Class 2
Data traffic
Classifier
Scheduler
Best-effort
Per aggregate
Classification
(e.g., user)
7: Multimedia Networking

25. Assumptions Assume two bits Traffic conditioner (TC) implement
P-bit denotes premium traffic
A-bit denotes assured traffic
Traffic conditioner (TC) implement
Metering
Marking
Shaping
7: Multimedia Networking

26. TC Performing Metering/Marking
Used to implement Assured Service
In-profile traffic is marked:
A-bit is set in every packet
Out-of-profile (excess) traffic is unmarked
A-bit is cleared (if it was previously set) in every packet; this traffic treated as best-effort
r bps
User profile
(token bucket)
b bits
assured traffic
Set A-bit
in-profile traffic
Metering
Clear A-bit
out-of-profile traffic
7: Multimedia Networking

27. 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
(token bucket)
b bits
premium traffic
Metering/
Shaper/
Set P-bit
in-profile traffic
out-of-profile traffic
(delayed and dropped)
7: Multimedia Networking

28. 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

29. Scheduler Example Premium traffic sent at high priority
Assured and best-effort traffic pass through RIO and then sent at low priority
yes
P-bit set?
high priority no
yes
A-bit set? no
RIO
low priority
7: Multimedia Networking

30. 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

31. Example Achieve end-to-end bandwidth guarantee BB BB BB 2 3 1 7 5 9 8
profile 6
profile 4
profile
receiver
sender
7: Multimedia Networking

32. Comparison to Best-Effort and Intserv
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
Complexity
No setup
Long term setup
Per flow steup
Scalability
Highly scalable (nodes maintain only routing state)
Scalable
(edge routers maintains per aggregate state; core routers per class state)
Not scalable (each router maintains per flow state)
7: Multimedia Networking

33. 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