Ch 5. Wireless ATM - Penn Engineeringtcom510/AdobeFiles_pdf/ch5.pdf · Ch 5. Wireless ATM n Introduction to Broadband ISDN and ATM n What is wireless ATM? n Protocol Reference Model

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Magda El Zarki - Dept. of EE., University of Pennsylvania
Ch 5. Wireless ATM

n Introduction to Broadband ISDN and ATM

n What is wireless ATM?

n Protocol Reference Model

n What is mobile ATM?

n Protocol extensions to support mobility

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N

n Control


n 5.1 Broadband ISDN (BISDN) and ATM

n What is an Integrated Network - Broadband ISD

n Asynchronous Transfer Mode (ATM)

n ATM and BISDN

n ATM Transport

n AAL

n ATM Layer

n Traffic Management, Admission and Congestio

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vices via a single interface:

network:

Access Loop (NISDN)

s


n 5.1.1 What is an Integrated Network?

l It is a network that can support a wide variety of servideo, audio, voice, images, data, etc.

l Integration can be performed at different levels in a

• Level 1 - User to Network Interface (UNI) and the

• Level 2 - Network Trunks or transmission facilitie

• Level 3 - Network switches (BISDN).

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are reserved and there is no

dwidth usage (i.e., no. of ection).

n a slot by slot basis.

ns, access control m. They are used to guaran-., as agreed upon in the con-

and increase processing

ite controversial:

packets had to be small.

y the different interest n: bytes!


n 5.1.2 Asynchronous Transfer Mode

l It is a time slotted system but none of the time slots framing structure.

l At connection set-up time, a contract is signed for banslots that may be used per unit of time by the conn

l User data is packetized and transmitted in the slots o

l As slots are not specifically assigned to user connectioschemes must be used to provide for a ‘‘fair’’ systetee that users do not use more than their share (i.enection’s contract).

l The slots are of a fixed size to simplify switch design speed.

l Deciding on the appropriate slot/packet size was qu

• For low volume real-time services such as voice,

• For data, small packet sizes meant high overhead.

l Packet sizes that were considered (or put forward bgroups): 32, 64, 128 bytes -> compromised solutio 48

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tes and also bursty or vari-esign.

ys as congestion can occur d access control schemes and slot must carry the connec-

.........


l Pros of ATM: 1) Very versatile, can support all bit raable bit streams, 2) one switch and one interface d

l Cons of ATM: 1) No timing structure, 2) variable dela(simultaneous user peaks), 3) requires sophisticatecall admission control, 4) higher overhead as eachtion information (addressing!).

........... Full Empty Full Full Empty Empty

Slot

Transmission Trunk

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ATM because of its versatil-ate (data, compressed voice,

ated slightly from the OSI

nagement.

nnections.

aring down of connections,

network operations.

ata from all three planes.

tion Layer (AAL). Its e ATM packet structure.

network .


n 5.1.3 BISDN and ATM

l Despite its disadvantages it was decided to go withity and the fact that most services are variable bit rvideo, images, etc)

l The BISDN reference model based on ATM has devimodel.

l There are now 3 planes: 1) user, 2) control, and 3) ma

l The user plane is responsible for the data of user co

l The control plane is responsible for setting up and tei.e., all network signaling functions.

l The management plane is used for maintenance and

l The data link layer is now the ATM layer. It carries d

l A new sub-layer was introduced, called the ATM Adaptasole purpose being to adapt the data streams to th

l The AAL and ATM layers constitute the ATM transport

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ome argue that no net-e used (i.e., IP over ATM).

s layer 3.

such as Simple Network

emand switched services ns are required. These func-

ent


l No network layer has been defined for the user plane. Swork layer is needed, others argue that IP should b

l The control plane uses a signaling protocol Q.93B a

l The management plane uses one of many protocolsManagement Protocol (SNMP).

l An ATM network, unlike Frame Relay, provides on dand so routing and connection management functiotions are the responsibility of the control plane.

Q.93B IP (?) SNMP, etc.

AAL AAL AAL

ATMPhysical

Control User Managem

1

2

3

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AAL

UpperLayers

ATM

PHY


n 5.1.4 ATM Transport

UpperLayers

AAL

ATM

PHY

ATM ATMATM

PHYPHY PHY

ATM Subnetwork

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ATM based network

on the following 3 basic ser-

tion: synchronous or asyn-

tionless

C Class D

ot required

le

Connectionless


n 5.1.4.1 AAL

l It serves as the interface between the user and the

l Four classes of service have been defined based upvice requirements:

• Timing relationship between source and destinachronous

• Bit rate : constant (CBR) or variable (VBR)

• Connection mode: connection oriented or connec

Requirement/Class Class A Class B Class

Timing

Bit rate

Connection mode

Required N

Constant Variab

Connection Oriented

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5). Most common and

) segments and encapsu-middle of user data message

lexing, timing


l Five AAL layers have been defined so far (AAL 1 - widely used are AAL1 and AAL5.

l The AAL consists of two sublayers:

• Segmentation and Reassembly Sublayer (SAR -lates the user data. Identifies beginning, end or

• Convergence Sublayer (CS) - error control, multip

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vice.

An identifier is used to

t is for all AAL types

VPI

VCI

yload C

Controlpe (PT)

1 bit FEC)


n 5.1.4.2 ATM Layer

l ATM was defined to provide a connection oriented ser

l A virtual connection is used to transport user data. uniquely identify a virtual connection.

l The cell consists of a header and a payload.

l The header was meant to be service independent, and iexcept AAL 5.

Header (5bytes) Payload (48 bytes)

ATM Cell

Generic FlowControl

VPI

VCI

VCI

Pa

Header ErrorTy

Header Format(Detection and

C: Cell discard bitPT: 1) 1 bit to indicate Control or Data,2) Congestion indication bit,3) EOM indication bit for AAL5

8 bits

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s (VCs)

c management. A virtual (VC). Some switches

virtual connections are


n 5.1.4.2.1 Virtual Paths (VPs) and Virtual Circuit

l Virtual paths (VP) are used in ATM to facilitate traffipath provides a conduit for several virtual connectionswill only switch VPs and others will switch VCs.

l Virtual paths are defined over single hops, whereasdefined end to end.

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ell size: -> very small .

ics): on the order of mil-

n long haul trunks:

tes=7K

ntrol nor flow control

ow error rates on fiber

are in transit between source y effect.


n 5.1.4.3 Features of an ATM network:

l High bit rate transmission trunks (155Mbps) and small ctransmission times: 53 bytes/155M = 2.8microsecs

l Propagation delays have not changed (laws of physlisecs (e.g.: NY - SF: 20ms).

l This means that several thousand cells are in transit o

From NY - SF: 155Mx20ms/53by

l Because of this phenomenom ATM uses neither error coon user data streams!

l Error control introduces too many delays and with theloptic trunks it is not worth it.

l Flow control is totally useless as too many packets and destination for a feedback mechanism to have an

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to describe an end user

based upon their Quality of have been identified as

sses of service have been

th timing

iented data

s data


n 5.1.4.4 Traffic Management

l In an ATM network, a traffic source descriptor is usedservice to the network.

l In the ITU these user services have been classifiedService (QoS) requirements.The following parametersbeing important to service provisioning:

• End-to-end delay

• Delay variation (jitter)

• Cell loss ratio

l Given those three parameters the following QoS cladefined by the ITU :

• Class 1 corresponding to Class A - CBR traffic

• Class 2 corresponding to Class B - VBR traffic wi

• Class 3 corresponding to Class C - connection or

• Class 4 corresponding to Class D - connectionles

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ses of service:

with timing

it delay with guaranteed

ranteed delivery service

ry of data traffic, no guar-

y service for a minimumailable the service can use it.


l The ATM Forum has specified a different set of clas

• Constant Bit Rate (CBR) - continuous bit stream

• Real-time Variable Bit Rate (rt-VBR) - low transdelivery service (i.e. low losses) and timing.

• Non-real-time Variable Bit Rate (nrt-VBR) - guabut with less stringent delay requirements.

• Unspecified Bit Rate (UBR) - for best effort deliveantees whatsoever.

• Available Bit Rate (ABR) - guaranteed deliverbandwidth requirement. If more bandwidth is av

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TM Networks

n Admission Control

ure to ensure that the admis-connections and also thatis call. If the connection isand buffer will be reservede required quality of serviceg the traffic behavior thehieve the desired QoS.

to monitor and control thek resources from mali-h can affect the QoS of other of negotiated parameter val-her immediately discarded orncountered in the network.


n 5.1.4.5 Admission and Congestion Control in A

l Traffic control incorporates two functions: Connectio(CAC) and Usage Parameter Control (UPC).

• CAC is implemented during the call setup procedsion of a call will not jeopardize the existing enough network resources are available for thadmitted, a certain amount of bandwidth (BW) according to the source traffic descriptor and th(QoS). A service contract is also specified statininput bit stream should conform to in order to ac

• UPC is performed during a connection’s lifetimeinput traffic. Its main purpose is to protect networcious as well as unintentional misbehavior whicestablished connections by detecting violationsues. If excessive traffic is detected, it can be eittagged for selective discarding if congestion is e

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ORK


User Terminal CAC

UPC

BISDNNETW

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and buffer space will be tor and the required Quality

havior that the input

check if the source traffic ation.

iately discarded or tagged d in the network.

implementation of a UPC


n Operation of CAC and UPC

l If a connection is admitted, a certain amount of BWreserved in accordance to the source traffic descripof Service of a source.

l The resultant service contract also specifies the traffic bebit stream should conform to.

l UPC is performed during a connection’s lifetime to characteristics adhere to the service contract specific

l If violating traffic is detected, it can be either immedfor selective discarding if congestion is encountere

l The Leaky Bucket (LB) scheme is a widely acceptedfunction.

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PolicedTraffic

eneration rate)


BLTokenBuffer

InputTraffic

BI

Fn Sn

B = BI+BL

Input Buffer

R (token g

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so is the size of the token

better, less bursty aller BI , i.e., lower

pacing between cells SCR) and Maximum

necessarily the source’s

/PCR)


n Operation of Leaky Bucket

l The choice of R, token generation rate is crucial andbuffer BL

l The higher R the smaller BL . For network, smaller BL issource. However, for a fixed R, a larger BL means a smdelays.

l The user specifies: Peak Cell Rate (PCR) (minimum swhen coming from the source), Sustainable Cell Rate (Burst Size (MBS).

l The token generation rate R = SCR. (Note SCR is notaverage rate)

l The burst tolerance is defined by:

BT = BL = (MBS - 1) (1/SCR + 1

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n air interface between a ing the access point is mobil-ement functions).

(RAL) that include:

dii, power levels, modula-ta format (burst preamble,

oS aware - data format,

acteristics of the wirelessntrol messages, error recov-

anagement - has to inter-


n 5.2 What is wireless ATM (WATM)?

l WATM consists of ATM service that rides on top of aterminal and an access point. The ATM switch servity enhanced (it includes the radio resource manag

l The air interface consists of the Radio Access Layers

• The radio physical layer - frequency bands, cell ration scheme, bit rate, diversity, line coding, dasync., etc.), signal spectrum, equalization, etc..

• The Medium Access Control (MAC) - that is Qframing, algorithms for QoS, etc.

• The Data Link Control (DLC) - hides the charchannel from ATM - frame format, headers, coery, etc., and interface to ATM layer.

• The wireless control protocol for radio resource mface to ATM control plane.

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TM twork

ATMHost

ATM

User appl

AAL

ATM

PHY

SAAL

ATM

AAL

TM

HY PHY

NNI UNI

TM

HY


n 5.2.1 Protocol Architecture

WATMTerminal

WATMAccess Pt.

MobilityEnhanced ATM switch

ANe

WATM WATM ATM

User appl

AAL

ATM

RAL

S

A

SAAL

ATM

AAL

ATM

RAL

SAAL

ATM

RAL PHY PHY P

UNI +MUNI +M NNI +M

W -

Con

trol

W - C

ontrol

ATM ATM A

PHY PPHYRAL

U - Plane

C - Plane

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topologically, the current

to maintain an active con-e infrastructure.


n 5.3 Mobile ATM

l Mobile ATM has two major components:

• Location Management: the ability to determine,location of the mobile terminal.

• Mobility Management: the ability of the network, nection as the mobile terminal moves through th

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aintain several databases nt location.

stration. Registration e terminal.

system address that y location. The databases n changes to the routing ID.


n 5.3.1 Location Management

l To support location management, a network must mthat contain subscriber information and their curre

l Location of a subscriber can only be maintained viaregiupdates inform the sytsem of the new location of th

l To support mobility, two addresses will be used: 1) endnever changes, and 2) routing address that changes bwill carry both, and registration updates will result i

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n 5.3.2 Mobility Management

l Consists of 2 major components:

• Hand-offs -> maintaining QoS

• Routing -> based on routing IDs

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d switch negotiate a set of

be involved in the negotia-

l connected, it will want to be possible given the load at

have to occur.

l of resources, however

of buffering and re-routing ust be done.

dle hand-offs.


n 5.3.2.1 Hand-Offs

l When a call is set-up across a network, the user anQoS parameters.

l In a wireless environment, a BS (access point) will tions (radio resource management)

l When a mobile moves to another location whilst stilmaintain the same levels of service. That may not the new location.

l Renegotiation of the QoS parameters will most likely

l Reservation of bandwidth for hand-offs is very wastefuconnection dropping rates should be low.

l During hand-off, no cells should be lost, some formof packets in transit during a hand-off procedure m

l The network will need special signaling/control to han

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M:

twork

n for hand-offs (routeh discovery, new path set-up,

naling changes necessary to


n 5.3.2.2 Routing

l There are two considerations that arise in mobile AT

• mapping of mobile routing IDs to a path in the ne

• route indentification, re-routing and optimizatioextensions -> removal of loops, crossover switcetc.)

l The NNI will have to be upgraded to support the sighandle hand-offs.

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ed by WATM.

s responsible for flow and

nments, error control is a

emes are used to support ose and discuss their abili-


n 5.4 Current WATM Implementations

l The focus of this section is on the data link layer us

l The data link layer consists of a link controller that ierror control and a media access control scheme.

l Because of the high bit error rates in wireless enviromust. Two major classes of error control are:

• Forward Error Correction (FEC)

• Automatic Repeat Request (ARQ)

l Different Types of Media Access Control (MAC) schQoS over a WATM link. We shall look at some of thties and how they meet their goals.

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on error patterns - high over-

s


n 5.4.1. Error Control Techniques

n Forward error correction (FEC)

l Low constant delay

• an important feature for real-time services

l Stationary

• capability of the error correction code - depends head if designed for worst case!

n Automatic repeat request (ARQ)

l Adaptive

• only retransmit data that was received with error

l Variable delay

• not appropriate for real-time services

n Hybrid ARQ - Combination of FEC and ARQ

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error control

nnel quality. When channel is ARQ is used.


n 5.4.1.1. Hybrid ARQ

l The combination of the above two basic classes of

l FEC is used to combat bit errors for reasonable chavery poor FEC overhead would be too high and so

l Two types exist: Type I and Type II

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packet.

correct errors.

el conditions

t contain some useful infor-

2 C

I 2 C

ut


n Type-I Hybrid ARQ:

Advantages:

l Information can be recovered from each transmitted

l Error correction code in the transmitted packet can

• reducing the frequency of retransmissions

• higher throughput than pure ARQ for poor chann

Disadvantages:

l Packets with errors are discarded even if they mighmation.

I I 1 C

I 1 C

I 2 C

I 2 C

ITransm itter

R eceiver

C: FEC code

T im eo

A C K

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discarded.

s

acket alone.

orrection capability.

C 2

I C 1 C 2

u t


n Type-II Hybrid ARQ:

Advantages:

l Erroneous packet is kept for future use rather than

l Redundancy increased incrementally

• provides the ability to adapt to channel condition

Disadvantages:

l Cannot recover information from the retransmitted p

l Requires more retransmissions to get a high error c

II I

I

I

C 1 C 2 C 1

I C 1

C 2

C 1

Transm itte r

R ece iver

In fo rm ation R ecovery

T im eou t T im eo

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smission alone.

nsmitted packet.

th the previous transmissionled for the individual trans-

sty errors.


n Concatenated Hybrid ARQ (CH-ARQ) Scheme

n Combine type-I and type-II hybrid ARQ

n Use the Strengths of both schemes

l Recover information from each transmission or retran

l Error correction capability is provided in each (re)tra

• reduces the frequency of retransmissions

• enhances the throughput

l Retransmitted packet consists of parity bits.

• forms a more powerful code when combined wito recover information if error correction has faimissions.

• information in errored packets is not discarded

l Very flexible and effective against both random and bur

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(I) P(I)I

P(I)

Timeout

P(I) C

Q

P(I) C

Q


n Operation of CH-ARQ Scheme

Receiver

Information Recovery

TimeoutTransmitter

Timeout

P(I)I

P(I)I

I

PI

Error Correction

I P(I)

I C

J

I C

J

I C

J

I C

J

P(I) C

Q

P(I) C

Q

C: FEC bits (RCPC)

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P(I) C

type-II

type-I


D1

Dλ

D1

Dλ

P1(D)

Pλ(D)

I

Rate 1/2 Code

SymbolInterleaver

CRC

FEC bits

Bit Interleaver

C

J Q

Encoding

C: FEC bits

I P(I)

Flow of Data

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access techniques, e.g.:

: random access, fixeded and decentralised).

TDD.

and TDMA.

e classification as most of guarantees use a mix of the

emand assignment can be used se proposed use narrowband


n 5.4.2 Media Access Control (MAC) Schemes

l There are different ways in which we can classify media

• By the method in which the resource is acquiredassignment, and demand assignment (centralis

• By the duplexing methodology used, i.e., FDD or

• By the multiplexing methodology: FDMA, CDMA,

l We shall use the duplexing method for access schemthe MACs used over a wireless link that require QoSother approaches, e.g., both random access and dby a scheme to provide service. And so far all of thoTDMA as the multiplexing scheme.

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.

sal by the team at WINLAB


n 5.4.2.1 FDD MAC Schemes

l We shall look at two schemes:

• DQRUMA: proposed by researchers at Bell Labs

• PRMA/DA: an enhancement to the original propo(Rutgers Univ.)

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ess (DQRUMA)

similar to ATM) with no

er access request (uplink) or

quests.

permit that indicates to a transmission.

piggybacked access request.

ach time slot uses a random at become active (have a data ission.


n DQRUMA (Karol et al.)

l Distributed Queueing Request Update Multiple Acc

l It is based on TDMA, it uses a time slotted system (frame structure.

l Time slots are of two types:

• Carry data traffic with a small time alotted to eithACK of access request (downlink).

• Carry only access requests or ACK of access re

l In addition each uplink time slot includes a transmitwaiting mobile that it can use the next time slot for

l The downlink data carrying time slots also include aThese requests are contention free.

l Whereas the access request minislot contained in eaccess technique. This allows registered mobiles thpacket to transmit) to demand a time slot for transm

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gister with the base station hich is used from then on to nsmit permits.

ansmit permits based upon the mobile for a particular session.

d or some other form of alg.

ack to the mobile (FDD!).

tly more complex than a


l Each mobile wanting to set-up a connection must re(BS). The BS then assigns a local ID to the mobile widentify the mobile, either for access requests or tra

l The BS queues all access requests and gives out trstatus of the queues and the QoS demanded by a

l The random access mechanism can be Aloha basethat does allow for backoff schemes.

l DQRUMA is an elegant MAC that gives quick feedb

l However because of FDD the mobile design is slighTDD system.

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llocation (PRMA/DA)

many variants have been pro-asses.

ntion free environment.

e is dedicated to at traffic ots)).

active it does not use up any

ived packets in its buffer, it ansmission. If its attempt is e reserve some slots for the

st by the BS.

es that two or more stations the number of available slots.


n PRMA/DA (Kim et al)

l Packet Reservation Multiple Access with Dynamic A

l PRMA was first proposed by Goodman, since then posed that are better able to handle mixed traffic cl

l It is a time slotted system with a frame structure.

l Fully under the control of the BS it provides a conte

l Each frame consists of 4 sub frames. Each sub framclass (CBR, VBR, data and available slots (open sl

l When a mobile has registered with the BS but is notof the resource.

l When a mobile becomes active because it has recetries to use one of the available slots for a packet trsuccessful the BS will let it know and at the same timmobile in the appropriate sub frame.

l The number of available slots in a frame is broadca

l If a collision occurs in these slots then the BS assumwere trying to gain access and it can then increase

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quick response to their

rawbacks and advantages. A if successful, there is a gain in long time slot is wasted.


l Like DQRUMA, because it uses FDD, mobiles get aaccess attempt.

l Using large time slots for access requests has its dmobile sends data long with its access request. So efficiency. However if there is a collision, then one

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es:

AND system


n 5.4.2.2. TDD MAC schemes

l We shall look at two different multiple access schem

• MASCARA - the MAC for the European Magic W

• DTDMA/TDD - the NEC proposal

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eservation for ATM

d down link (UL)

the down traffic channels.

d a contention period.

biles the status of the current nd the slot allocation for

transmissions (i.e., a train of

s get slots when. Cell delay nsmissions. Token buffers are an consist of.

t a connection. With every delay time. The token buffers ons with full token buffers


n MASCARA (Bauchot et al.)

l Mobile Access Scheme based on Contention and R

l Consists of a variable length frame.

l Each frame consists of 2 subframes: uplink (UL) an

l The DL subframe consists of the frame header and

l The UL subframe consists of up traffic channels an

l Frame header is used by BS to broadcast to all motime frame, the results from the contention period aeach mobile.

l A traffic channel can consist of several data packetcells can be sent consecutively).

l A QoS scheduler is used to determine which mobilebounds are used to determine the scheduling of traused to determine how many cells a transmission c

l The contention period is used by mobiles to requesconnection is associated a SCR, a PCR and a cell are filled with tokens with a rate R=SCR. Connecti

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osition of the transmission

if collisions occur frequently.


get priority and the cell delay time determines the ptime slot.

l The contention slots are large and can be wasteful

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ontrol and 2) data traffic.

ini slots for requests and 2) art for ABR and UBR traffic,

es must be used to deter-ses of traffic.

e drawback is that you have .


n DTDMA/TDD (Raychaudhuri et al.)

l Dynamic TDMA with Time Division Duplex Protocol

l Uses a fixed length frame.

l The down link consists of two parts: 1) ACKs and c

l The uplink consists of two parts too: 1) a group of mthe data traffic part which consists of 3 parts. One pone part for VBR and one part for CBR. CAC schemmine the allocation of slots across the different clas

l Using mini slots for requests is more efficient but thto wait awhile to get feedback for your transmission

l Does ATM header compression.

Documents

Ch 5. Wireless ATM - Penn Engineeringtcom510/AdobeFiles_pdf/ch5.pdf · Ch 5. Wireless ATM n Introduction to Broadband ISDN and ATM n What is wireless ATM? n Protocol Reference Model