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HIPER LAN

SEMINAR REPORT

BACHELOR OF TECHNOLOGY

IN

COMPUTER SCIENCE AND ENGINEERING

Submitted by

(G. Sundeep kumar)

Register No: 08501A0538

Department of Computer Science and Engineering

PRASAD V POTLURI SIDDHARTHA INSTITUTE OF TECHNOLOGY

(Affiliated to JNTU: Kakinada, Approved by AICTE)

(An ISO certified institution)

Kanuru, Vijayawada - 520007

January, 2012

MARKS AWARDED: / 50

Signature of the coordinator Signature of the HOD

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ABSTRACT

Recently, demand for high-speed Internet access is rapidly increasing

and a lot of people enjoy broadband wired Internet access services using

ADSL (Asymmetric Digital Subscriber Line) or cable modems at home. On the

other hand, the cellular phone is getting very popular and users enjoy its

location-free and wire -free services. The cellular phone also enables people

to connect their laptop computers to the Internet in location-free and wire-

free manners.

However, present cellular systems like GSM (Global System for Mobile

communications) can provide much lower data rates compared with those

provided by the wired access systems, over a few Mbps (Mega bit per

second).Even in the next generation cellular system, UMTS (Universal Mobile

Telecommunications System), the maximum data rate of its initial service is

limited up to 384 kbps; therefore even UMTS cannot satisfy users’

expectation of high-speed wireless Internet access. Hence, recently, Mobile

Broadband System (MBS) is getting popular for its higher data rates even for the Wire free

manner which are comparable to the wired broadband internet. This Mobile Broadband system

puts forward a service called Hiper LAN to help the users to access the internet at higher data

rates.

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CONTENTS

Acknowledgement 3

Introduction 5

History 5

H/2 System Architecture 6

H/2 Service Model 8

Data Link Control Layer 9

Physical Layer 9

Convergence Layer 11

Protocol Data Unit 13

Linking Process 13

Properties 14

Coexistence and Resource Sharing 16

Collision Resolution 17

Conclusion 17

References 18

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ACKNOWLEDGEMENT

The satisfaction that accompanies the successful completion of any task would be

incomplete without a mention of the people, who made it possible and whose guidance and

encouragement crown all the efforts with success.

I reckon to a distant pleasure to endorse out indebtedness and deep sense of gratitude to

Dr. K. Nageswara Rao, Head, Department of Computer Science and Engineering, for his

encouragement in all endeavors.

In addition, I would like to thank all staff members of CSE department and all my friends

of B.Tech 4th semester for their suggestions and constructive criticism.

G. Sundeep kumar

(08501A0538)

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1. INTRODUCTION

Recently, demand for high-speed Internet access is rapidly increasing and a lot of people

enjoy broadband wired Internet access services using ADSL (Asymmetric Digital Subscriber

Line) or cable modems at home. On the other hand , the cellular phone is getting very popular

and users enjoy its location-free and wire-free services. The cellular phone also enables people to

connect their laptop computers to the Internet in location-free and wire-free manners. However,

present cellular systems like GSM (Global System for Mobile communications) can provide

much lower data rates compared with those provided by the wired access systems, over a few

Mbps (Mega bit per second).Even in the next generation cellular system, UMTS (Universal

Mobile Telecommunications System), the maximum data rate of its initial service is limited up to

384 kbps; therefore even UMTS cannot satisfy users’ expectation of high-speed wireless Internet

access. Hence, recently, Mobile Broadband System (MBS) is getting popular and important and

wireless LAN (Local Area Network) such as ETSI (European Telecommunication

Standardization Institute) standard HIPERLAN (High Performance Radio Local Area Network)

type2 (denoted as H/2) is regarded as a key towards providing high speed wireless access in

MBS. H/2 aims at providing high speed multimedia services, security of services , handover

when roaming between local and wide area as well as between corporate and public networks. It

also aims at providing increased throughput of datacom as well as video streaming applications.

It operates in the 5 GHz band with a 100 MHz spectrum. WLAN is W-ATM based and is

designed to extend the services of fixed ATM networks to mobile users. H/2 is connection

oriented with a connection duration of 2 ms or multiples of that. Connections over the air are

time-division multiplexed . H/2 allows interconnection into virtually any type of fixed network

technology and can carry Ethernet frames, ATM cells and IP packets Follows dynamic frequency

allocation. Offers bit rates of 54 Mbps.

2. HISTORY

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Currently WLANs provide wideband wireless connectivity between PCs and other consumer

electronic devices as well as access to the core network and other equipment in corporate, public,

and home environments. The demand for mobile broad-band communication caused the

European Telecommunications Standards Institute (ETSI) to create the Broadband Radio Access

Networks (BRAN) Project. The project makes available various technologies for the access to

wired networks in private as well as in public environments until the year 2000 and offers bit

rates upto 155 Mbps.

The project started with the goal of specifying a W-ATM (Wireless-

Asynchronous Transfer Mode) based air interface for applications. The W-ATM idea has been

strictly followed when specifying the DLC (Data Link Control) layer of H/2 where a user data

packet handled in the MAC (Medium Access Control) layer is one ATM cell. It was planned

from the start that an ATM-based WLAN should be able to support any broad-band network-

based service upto a WLAN’s bandwidth limitations according to the service classes known

from ATM networks.

To be able to establish a wireless system to support any type of transport network, both

connection- and packet-oriented data transmission are taken into account. An earlier initiative of

the ETSI/BRAN project was Hiper LAN/1, a connectionless packet-based broad-band WLAN

standard at 5 GHz in 1996 that has not found acceptance to date owing to the lack of products.

H/2 is connection-oriented high-performance radio technology, specifically suited for operating

in LAN environments. This system operates in the unlicensed 5-GHz frequency band that has

been specifically allocated to WLANs. In contrast to the IEEE 802.11 Ethernet technology H/2 is

connection oriented with connection duration of 2ms or multiples of that. Connections over the air

are time-division multiplexed (TDM). H/2 allows interconnection into virtually any type of fixed

network technology and can carry Ethernet frames, ATM cells and IP packets.

3. H/2 SYSTEM ARCHITECTURE

H/2 system provides wireless access to wired networks for users by a mobile Terminal(MT)

inside buildings , outside in free terrain, or in the proximity of buildings. The system is

cellular.An AP (Access Point) is typically connected to a core network or a distributed system

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consists of an APC (Access Point Controller) and one or more APTs (Access Point Transceiver).

An APT operates one frequency carrier and covers a certain area, called the radio cell. The

APC(AP Controller) is responsible for the management of its APTs.

Two operation modes are defined for the H/2 DLC (Data LinkControl ): centralised mode

and direct mode . In the direct mode , MTs communicate directly over direct links with each

other. In both modes, the AP assigns the radio resources and controls the communcation in the

radio Cell. In HIPERLAN, each communicating node is given a HIPERLAN ID (HID) and a

Node ID (NID). The combination of these two IDs uniquely identifies any station, and restricts

the way it can connect to other HIPERLAN nodes. All nodes with the same HID can

communicate with each other using a dynamic routing mechanism denoted Intra-HIPERLAN

Forwarding.

The HIPERLAN/2 Access Points (APs) have a built-in support for automatic

transmission frequency allocation within the AP's coverage area. This is performed by the

Dynamic Frequency Selection (DFS) function. An appropriate radio channel is selected based on

both what radio channels are already in use by other AP's and to minimize interference with the

environment. Thus, there is no need for manual frequency planning as in cellular networks like

GSM. DFS algorithm is described below, where each AP selects a channel with the least

interference level.

Step 1: APs are randomly ordered.

Step 2: According to the order, select an AP.

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Step 3: The AP estimates total power of interference signals from other APs which have already

selected a channel and selects a channel with the least interference signal power. ( Repeat step 2

and 3 until all APs select their channels.) Interference signals from MHs are not take into

account in this algorithm. And we assume that each AP selects a channel only once and never

changes the channel.

4. H/2 SERVICE MODEL

The H/2 service model comprises the physical and the DLC ( Data Link Control) layer

for both the MT and the AP. Various network types like IP, Ethernet, IEEE1394 and ATM can

be connected to the DLC layer by the Convergence layer that performs the adaptation of the

packet formats to the requirements of the DLC layer. For higher layers other than ATM, the

convergence layer contains a SAR ( Segmentation And Reassembly) function. The physical layer

provides the basic transport functions for the DLC (Data Link Control) PDU (Protocol Data

Unit).The physical layer includes the medium or air interface through which the data is

transmitted.In the physical layer the PDUs are Orthogonal Frequency Division

Multiplexed(OFDM).

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4.1. DATA LINK CONTROL (DLC) LAYER

The DLC layer is vertically sub-divided into the control plane and the user plane. In the user

plane , the data transport function is fed with user data packets from the higher layers via the U-

SAP ( User Service Access Point). This part contains the Error control that applies the ARQ

( Automatic Repeat reQuest) protocol. The control plane consists of the RLC (Radio Link

Control ) protocol that includes the DCC ( DLC Connection Control), the RRC (Radio Resource

Control), and the ACF (Association Control Function). Both the user plane and the control plane

access the physical medium via the MAC ( Medium Access Control ) protocol.

4.2. PHYSICAL LAYER

H/2 systems are meant to operate as private or public systems in the license exempt spectrum in

the 5-6 GHz band. The channel grid is 20 MHz. The H/2 sampling frequency is chosen equal to

20 MHz at the output of a typically used 64-point Inverse Fourier Transformation. 52 subcarriers

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are used per channel to facilitate implementation of filters and to achieve sufficient adjacent

channel suppression. 48 subcarriers carry the actual data and 4 are pilots that facilitate phase

tracking for coherent demodulation. A key feature of the physical layer is to provide several

PHYSICAL modes with different coding and modulation schemes that are selected by a link

adaptation mechanism. The channeling is implemented by Orthogonal Frequency Division

Multiplexing (OFDM) due to its excellent performance on highly dispersive channels. The basic

idea of OFDM is to transmit broadband, high data rate information by dividing the data into

several interleaved, parallel bit streams, and let each bit stream modulate a separate sub-carrier.

The channel spacing is 20 MHz , which allows high bit rates per channel yet has reasonable

number of channels. The independent frequency sub-channels are used for one transmission link

between the AP(Access Points) and the MTs.

MAC ( Medium Access Control): MAC protocol functions are used for organising access to

and transmission of data on the radio link. The control is centralised to the AP (Access Point)

that informs the MTs (Mobile Terminal) at what point in time in the MAC Frame they are

allowed to transmit their so- called PDU ( Protocol Data Units ) trains. The length of the PDU

trains vary depending on the Resource Requests (RRs) received at the AP from the MTs. The air

interface is based on time-division duplex (TDD) and dynamic time-division multiple access

( TDMA ), which allows for simultaneous communication in both downlink and uplink within

the same time frame, i.e. the MAC frame.

The MAC frame format consists of four elements: Broadcast Channel (BCH), Down Link

(DL), Up Link ( UL ), and Random Access (RA) . Except for the broadcast control, the duration

of the fields is dynamically adapted to the current traffic situation. The whole DLC is based on

scheduling efficiently MAC frame. The MAC frame and the transport channels form the

interface between the DLC and the physical layer. The broadcast phase carries the BCCH

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(Broadcast Control Channel), the FCCH (Frame Control Channel) and the RFCH (Random

Access Feedback Channel). The BCCH ( downlink only ) transmits control information in each

MAC frame and to all MTs. It provides information about transmission power levels, starting

point and length of the Frame channel & Random channel. It also transmits the AP identifier and

the wakeup indicator. The FCCH ( downlink only) transmitted in the Frame Channel (FCH)

contains an exact description of how the current MAC Frame resources have been allocated in

the downlink , uplink and the direct link phases. The downlink phase carries user-specific

control information and the user data,transmitted from an AP to one or more MTs. The uplink

phase carries control and user data from the MTs to the AP. The direct link phase carries user

data from the MTs to the AP.

In the random access phase (RAP) the MTs that do not have capacity allocated in the current uplink phase may use the Random channel (RCH) to transmit a resource request.Non-associated MTs first get in contact with a AP via the Random channel that is also used by MTs during handover to have access to a new AP.

4.3. CONVERGENCE LAYER

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The Convergence Layer(CL) adapts the core network to the H/2 DLC layer.For each network

supported a specific convergence layer has been defined. The convergence layer provides all

functions needed for connection setup and mobility support.

There are two types of convergence layers defined: Cell based and packet based.The

packet based convergence layer(CL) is defined to integrate H/2 into existing packet-based

networks and support IP, IEEE 802.3 and point-to-point protocol. It provides among others a

SAR ( Segmentation And Reassembly) function to fit IP packets into the fixed length payload of

the H/2 Long transport channel PDUs ( Protocol Data Unit ). The cell based convergence

layer(CL) provides the mapping between ATM connection setup procedures and the

corresponding H/2 functions.A SAR is not necessary as the ATM cell payload and all the

necessary fields of ATM cell header fit into the 54-byte H/2 packet. Nevertheless a compression

of the ATM cell header is necessary.

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5. PROTOCOL DATA UNIT

Two kinds of PDU (Protocol Data Units) are defined: Short transport channel PDU and Long

transport channel PDU.A long transport channel PDU is 54 bytes long and contains 48 byte

payload, a 24 bit CRC ( Cyclic Redundancy Check) for error correction, 12 bits for convergence

layer(CL) information and a 10 bit sequence number for the ARQ ( Automatic Repeat reQuest )

protocol. A short channel PDU is 9 bytes long. In order to reduce overhead, all the long transport

channel and short transport channel PDUs in an MAC frame belonging to connections of the

same MT are combined to a PDU train. In the Ethernet CL , we have to consider three kinds of

over-heads. First overhead is an overhead of Ethernet headers. In the Ethernet CL, IP packet is

handled as a payload of an Ethernet frame. SSCS-PDU (Service Specific Convergence Sublayer

Protocol Data Unit) is constructed by 6 bytes of the destination address field, 6 bytes of the

source address field and 2 bytes of the type/length field. These fields are added to each payload.

The second overhead is the padding ( PAD ) field and the trailer field for SAR

( Segmentation And Reassembly ) function. And the third overhead is the SAR header whose

length is 12 bits . In DLC layer, DLC header and CRC ( Cyclic Redundancy Code ) field are

added to each SAR-PDU. The DLC header is 12 bits length and the CRC field is 24 bits length.

Therefore the overhead of DLC layer is 4.5 bytes length and the total length of DLC-PDU

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becomes 54 bytes. In the MAC layer, BCH ( Broadcast CHannel), FCH ( Frame Channel ), ACH

( Access feedback CHannel) and Random channel do not convey any user data therefore these

channels also decrease the system performance.

6. LINKING PROCESS

The Mobile Terminal (MT) has to scan for the Beacon signal sent in the Broadcast control

channel of every MAC Frame containing among others the AP-ID and the NET-ID of the APT

( Access Point Transceiver ). The MT waits for the NETWORK-OPERATOR -ID broadcast

periodically in theRLC broadcast channel to check whether access to this particular network is

feasible or not and then continues the association procedure by transmitting a request for a

MAC-ID. A MAC-ID is assigned by the AP used for addressing the MT during the whole

session at this AP and is valid only in the radio cell of one APT.

During the link capability procedure , the MT sends its own parameters to the AP containing:

a)The Data Link Control version running in the MT. b)A flag set,if the MT supports the direct

mode. c)The Convergence Layer services supported. d)Authentication and encryption procedures

supported. The AP will respond with its own set of parameters and select the (CL)Convergence

layer services and Encryption&Authentication procedures for the session. The disassociation

procedure may be initiated by either the AP(Access P) or the MT.During explicit disassociation

the AP and the MT discuss the disassociation shortly. Implicit disassociation occurs when the

MT and AP lose their radio link completely.

DCC ( Data Link Control Connection Control ) functions are responsible for setting up ,

maintaining , renegotiating and closing a DUC (DLC User Connection) at the DLC (Data Link

Control) layer and may be initiated by either the AP or the MT. An MT requesting the

establishment of a DUC, will propose the connection characteristics but the AP will decide upon

the DUCs characteristics and attribute a unique ID that together with the MAC ID uniquely

identifies a connection in a radio cell.

7. PROPERTIES

1. High speed transmission: H/2 has a transmission rate of 54 Mbps. To achieve this,

H/2 makes use of a modulation method called OFDM(Orthogonal Frequency Division

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Multiplexing) for transmission harmonised with IEEE 802.11. OFDM is particularly

efficient in time-dispersive environments, i.e. where the radio signals are reflected from

many points, e.g. in offices. The basic idea of OFDM is to transmit broadband, high data

rate information by dividing the data into several interleaved, parallel bit streams, and let

each bit stream modulate a separate subcarrier. The channel spacing is 20 MHz, which

allows high bit rates per channel yet has reasonable number of channels: 52 subcarriers

are used per channel (48 subcarriers for data, 4 subcarriers tracking the phase for

coherent demodulation). The independent frequency subchannels are used for one

transmission link between the AP and the MTs.

2. Connection oriented: Data are transmitted on connections between the MT(Mobile

Terminal ) and the AP ( Access Point ) that have been established prior to the

transmission, using signaling functions of the H/2 control plane. Point-to- point

connections are bidirectional , point-to-multipoint and broadcast connections are

unidirectional from the AP toward the MTs in the radiocell. Connections are realised by

means of logical channels.

3. QoS support: The connection orientation of H/2 is a prerequisite for the support of

QoS.An H/2 WLAN is able to support all the QoS classes defined for ATM networks and

thus is ideally suited to also support the QoS requirements of IP networks that are less

stringent than those of ATM networks. The IP convergence layer provides the functions

needed for mapping the IP QoS requirements to the QoS parameters available from H/2

for its DLC connections.Each connection may be assigned a specific QoS parameter

set,in terms of throughput ,delay, delay variation , bit error rate etc. In an environment

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where the connection characteristics are not available ,QoS is supported by assigning a

priority level relative to other connections.

4. Automatic frequency allocation: H/2 does not need a manual frequency planning like

conventional cellular networks.The APs in H/2 automatically select an appropriate radio

channel for the transmission within each AP’s coverage area by DFS (Dynamic

Frequency Selection). An AP listens to neighbour APs as well as to other radio sources in

the environment and selects a radio channel based on its current load aiming to minimise

interference with other radio cells.

5. Security support: H/2 supports authentication and encryption.The AP and MT may

authenticate each other to ensure autherised access.The user traffic on established

connections may be encrypted to protect against eavesdropping and man-in-middle

attacks.Authentication relies on a supporting function ,such as directory service that is

outside the scope of H/2.

6. Mobility support: The MT uses the AP with the best radio signal performance as

measured by the SNR .Thus, as the MT moves it may detect an alternative AP with better

radio performance than current AP. The MT will then initiate a handover to this AP and

all its connections will be moved to the new AP.

7. To allow MTs to save power, an MT may at any time request the AP to enter a low

power state,and may request a specific sleep period.At the end of the sleep period the MT

searchs for the presence of any wakeup indication from the AP. An AP will delay any

pending data to an MT until the corresponding sleep period has expired.If no wake-up

indication is received, the MT returns to its low power state for the next sleep period.

8. COEXISTANCE AND RESOURCE SHARING

The guarantee of a certain QoS for wireless multimedia services if WLANs are sharing the

spectrum rather than operating in their own frequency bands.H/2 is likely to share the spectrum

with other system types like IEEE802.11a.H/2 specifies a centrally controlled air interface with a

2 ms MAC frame, IEEE 802.11a in contrast, applies CSMA/CA ( Carrier Sense Multiple

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Access/Collision Avoidance), a network contention protocol that listens to a network in order to

avoid collisions, unlike CSMA/CD that deals with network transmissions once collisions have

been detected. CSMA/CA contributes to network traffic because, before any real data is

transmitted, it has to broadcast a signal onto the network in order to listen for collision scenarios

and to tell other devices not to broadcast), an LBT (Listen-Before-Talk) scheme with variable

packet lengths.The use of a distributed MAC makes IEEE 802.11a more suitable for ad hoc

networking and non-real-time applications. For the coexistence the following points have to be

noted namely that H/2 applies DFS (Dynamic Frequency Selection) and supports

TPC(Transmitter Power Control).

The IEEE 802.11a system ( Which is commensurate to H/2 system ) keeps operating the same

carrier once it has selected it and does not apply DFS nor TPC.Both systems use the same

Physical layer protocols,carrier bandwidth and apply LA(Link Adaptation),a flexible

interference-dependent selection of a Physical layer mode. Based on these schemes an

FSR(Frequency Sharing Rule) may allow operation in a common spectrum. An FSR defines

techniques for radio channel management for the systems operating in a common

spectrum.HiperLAN/2 achieves higher throughput as compared to IEEE 802.11a. This is due to

the use of centrally controlled medium access. This MAC protocol is also more suitable for time-

bounded applications.

9. COLLISION RESOLUTION

The number of concurrently receivable signals is restricted by the antenna system and is

interfernce limited. With the number of simultaneously transmitting MTs ( Mobile Terminals )

increasing , the carrier to interference ratio decreases and a correct reception of a burst becomes

less likely . The present interference situation depends on the number of simultaneous

transmissions taking place,MTs’ positions and the channel characteristics. Since no further

restrictions can be imposed on the initial access to RCH(Random Channel) that is the

interference situation could not be taken into account,some MTs might not succeed in

transmitting via the RCH. To control the retransmission attempts of these collides MTs, a

collision resolution algorithm has to be applied that can make use of the enhanced reception

capabilities.In H/2, the MTs may use the Random Channel (RCH) to transmit their Resource

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request to the Access Point(AP).Especially for delay sensitive devices, this access should be

carried out as fast as possible.

10. CONCLUSION

H/2 system supports IP(Internet Protocol) over wireless ATM(Asynchronous Transfer Mode)

with a guaranteed QoS ( Quality of Service ). H/2 also provides a convergence layer(CL) to

connect directly wireless IP based applications to an IP network without involving any ATM

related signalling(User Network Interfacing) or ATM fixed infrastructure.H/2 has the ability to

support any ATM class of services with less stringent requirements of QoS (Quality of Service).

To be able to rate the system completely H/2 has to be compared with IEEE 802.11a

system. The physical layer of HiperLAN/2 is very similar to the one that 802.11a defines. While

802.11a uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) to transmit

packets, HiperLAN/2 uses Time Division Multiple Access (TDMA). With CSMA/CA, all

stations share the same radio channel and contend for access. For example when an 802.11

station (client) needs to send a packet, the station first listens for other transmissions and then

attempts to send frames when no other station is transmitting. If another station happens to be

transmitting , all other stations will wait until the channel is free.

The use of TDMA in HiperLAN/2, however , offers a regular time relationship for network

access. TDMA systems dynamically assign each station a time slot based on the station's need

for throughput. The stations then transmit at regular intervals during their respective time slots,

making more efficient use of the medium and improving support of voice and video applications.

The true usable maximum throughput of HiperLAN/2,however, is 42Mbps, while the maximum

usable throughput of 802.11a is only around 18 Mbps (based on Ethernet packets with an

average size of 512 bytes). This puts HiperLAN/2 well ahead of 802.11a in terms of throughput

capacity of each Access Point(AP). HiperLAN/2 is presumably more cost effective than 802.11a.

While the initial HiperLAN/2 products will probably cost more than 802.11a counterparts,

supporters say that the better throughput will outweigh the slight price difference.

REFERENCES

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1.”IP OVER WIRELESS MOBILE ATM-GUARANTEED WIRELESS QoS BY Hiper

LAN/2”-Published in the 89th volume of Proceedings of the IEEE. Authors: Bernhard .H. Walke,

Norbert Esseling, Jorg. H, A.Hettich Stephan Mangold and Ulrich Vornefeld.

2. ETSI Project BRAN-Jamshid Khun Jush (Ericsson) & Gilles Straub(THOMSON Multimedia).

3. B.Walke, D.Petras and D.Plassmann, “wireless ATM:Air interface and network protocols of

the mobile broadband system” IEEE Communication.

4.D.Raychaudhari, “Wireless ATM networks:Technology status and future directions”,

Procceedings of the IEEE.

5. Evaluation of HiperLAN/2 scalability for mobile broadband systems-By

Ken’ichi ishii(Networking Laboratories,NEC,Japan) and A.H. Aghvami(Center for

Telecommunications research,King’s College,London).

6. HiperLAN/2-Janne Korhonen,Dept of computer science and engineering,Helsinki University

of technology.

7. HiperLAN/2-An efficient high speed WLAN by Jim Geier.