© information & telecommunications technology center (ittc), eecs, university of kansas qos...

© Information & Telecommunications Technology Center (ITTC), EECS, University of Kansas

QoS Scheduling in Cable and Broadband Wireless

Networks

Mohammed Hawa and David W. PetrInformation and Telecommunication

Technology Center (ITTC), University of Kansas

Project Funded by Sprint Corporation

© Information & Telecommunication Technology Center (ITTC), EECS, University of Kansas

Presentation Outline What is QoS and QoS Management? Difference between QoS in wired and

wireless networks. A scheduling architecture to support

QoS in broadband wireless access networks. Infrastructure MAC Protocol Support for UGS, rtPS, nrtPS and BE Traffic

Scheduler Features and Advantages Discussion


Quality of Service (QoS) Packet switched networks (e.g., Internet)

were designed to provide best effort service.

A QoS architecture introduces tools to treat packets differently, thus one flow receives better performance on the expense of others.

Provides guaranteed services to end users (better than best effort).

QoS guarantees can be characterized by: Delay, delay jitter, bandwidth and error rate.


QoS Management Supporting QoS in packet switched networks

requires collaboration of many components: Admission Control: Limits number of flows

admitted into the network so that each individual flow obtains its desired QoS.

Scheduling: Which packet gets transmitted first on the output link significantly impacts QoS guarantees for different flows. Scheduling affects delay, jitter and loss rate. Allows protection against misbehaving flows.


QoS Management (Cont.) Buffer Management: Control the buffer

size and decide which packets to drop. Controls packet loss rate. Many packet drop strategies including

weighted Random Early Detection (RED). Congestion Control: Prevent, handle

and recover from network congestion scenarios. Challenging feedback problem because

Internet traffic shows self-similar behavior.


IETF QoS Architectures IntServ:

Resource reservation per flow using RSVP. Similar to ATM virtual connections. Problems with scalability.

DiffServ: Aggregation of flows into per-hop behavior

groups. Expedited forwarding and Assured forwarding.

A good wireless QoS architecture should integrate with both IETF standards.


Wireless Networks The Internet is expanding to the wireless

realm, specially in recent years: Wireless Local Area Networks (WLANs) based

on the IEEE 802.11 standard, called Wi-Fi™. WLAN Hot Spots by companies such as:

Boingo, Surf and Sip, T-Mobile HotSpot and Wayport.

Broadband Wireless Access Networks (BWAs) based on IEEE 802.16, called WiMAX.

Supported by Intel, Nokia, and Fujitsu. Need to expand QoS to the wireless side.


Wireless QoS Observations Several new technical challenges:

Quality of the wireless channel is typically different for different users, and randomly changes with time (on both slow and fast time scales).

Wireless bandwidth is usually a scarce resource that needs to be used efficiently (can not overprovision the wireless link).

Excessive amount of interference and higher error rates are typical.

Mobility complicates resource allocation.


The MAC Protocol For wireless networks it is natural to integrate

the QoS architecture with the MAC protocol. The MAC protocol coordinates communication

over the shared wireless medium (and the shared HFC cable medium as well).

IEEE 802.16 is the most talked about standard for broadband wireless access (BWA) systems, and is based on DOCSIS.

DOCSIS is the de facto standard for delivering broadband services over HFC networks.


DOCSIS Introduction A Cable Modem Termination System

(CMTS) controls many terminating Cable Modems (CMs).

Upstream and downstream channels are separated using FDD.

Each upstream channel is further divided into a stream of fixed-size time minislots.

DOCSIS MAC utilizes a request/grant mechanism to coordinate transmission between multiple CMs.


DOCSIS Operation


QoS in DOCSIS To support QoS, DOCSIS 1.1 introduces

the concept of a service flow. IEEE 802.16 defines identical upstream

service flow types. Upstream Service Flow Types in DOCSIS

and IEEE 802.16: Unsolicited Grant Service (UGS) Real-Time Polling Service (rtPS) Non Real-Time Polling Service (nrtPS) Best Effort (BE)


Real-Time Service Flows Unsolicited Grant Service (UGS):

Supports real-time traffic (Voice over IP). Offers fixed size unsolicited data grants

(transmission opportunities) on a periodic basis. Real-Time Polling Service (rt-PS):

Supports real-time flows that generate variable size data packets on a periodic basis (MPEG).

Offers periodic unicast request opportunities. The CMs specify the size of the desired data grants.


Non Real-Time Service Flows

Non Real-Time Polling Service (nrt-PS): Supports flows that require variable size data

grants on a regular basis (high bandwidth FTP). Offers infrequent unicast polls plus contention

and piggybacking. Best Effort (BE):

The CM uses contention and piggybacking only. Key service parameters for nrt-PS and BE:

Minimum Reserved Traffic Rate. Traffic Priority.


The New CMTS Scheduler

. . .

S er v er

s em i- p r eem p tiv ep r io r ity

p r io r ity - en h an c edW F Q ( o r a v ar ian t)

F lo w 1

F lo w 2

F lo w N

Blo c k g en er a tin g D ataG r an ts f o r UG S f lo w s

an d u n ic as t R eq u es ts f o rr tP S an d n r tP S f lo w s

F lo w s w ithm in im u m

b an d w id thr es er v a tio n s

F lo w s w ithNO b an d w id th

r es er v a tio n s

F lo w s1 . . . M

T y p e 1 ( F I F O ) Q u eu e

T y p e 2 ( F I F O ) Q u eu es

T y p e 3 ( P r io r ity ) Q u eu e

T r an s la te R eq u es tsin to D ata G r an ts

r tP S , n r tP S an d BE R eq u es ts( e ith er u n ic as t , p ig g y b ac k o r

c o n ten tio n )

F r am in g an dC o n ten tio n /D ata

M in is lo t Allo c a tio n


Scheduler Architecture Requests arrive at the CMTS.

Through contention, unicast requests and piggybacking. Requests are translated into upstream data

grants. Data grants are scheduled on a frame-by-frame

basis by building a corresponding allocation MAP: The hardware block responsible for creating the MAP is

represented by a server. Each data grant (or unicast request opportunity) is

treated as a packet. Actual transmission of the corresponding data packet takes place in the next frame.

Data grants are queued in three types of buffers: Type 1, Type 2 and Type 3 buffers.


Extra Features Dynamic Contention

Minislot Allocation: An appropriate number of contention request minislots is allocated in each frame period to reduce collisions and to shorten contention resolution.

A Buffer Management mechanism based on RED was also suggested.


Scheduler Advantages Easy to implement in hardware thus

gaining a performance advantage over software-based alternatives.

Takes advantage of the Tolerated Jitter parameter for UGS to fit as many packets as possible in the upstream frame thus avoiding fragmentation and being more efficient.

Lends itself to easier and straightforward performance analysis via classical queuing theory techniques.


Future Work

Validation of the analysis and comparing the architecture performance to other architectures will be done through simulation using OPNET.

Stochastic analysis of FQ algorithms have not been given much attention due to difficulty in tracing the dynamics of fair queuing algorithms. 0 1 2 3 4 5 6 7 8

0

0.001

0.002

0.003

0.004

0.005

0.006

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0.009

0.01

Incoming Load of Tagged Flow (Mb/s)

Mea

n W

aitin

g T

ime

(s)

Mean Waiting Time for the Tagged Flow under SCFQ, WFQ and SPFQ

SCFQWFQSPFQ


Summary Introduced QoS concepts in both the

wired and wireless parts of the network. Summary of DOCSIS and IEEE 802.16

standards and their QoS features. Introduced a new scheduling

architecture to integrate QoS within the MAC layer of such protocols.

Discussed the features of the architecture and its advantages.

Suggested possible future work.


Discussion

Thank you!

© information & telecommunications technology center (ittc), eecs, university of kansas qos...

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