Advance Computer Networks Lecture#12 Instructor: Engr. Muhammad Mateen Yaqoob.

Advance Computer NetworksLecture#12

Instructor:

Engr. Muhammad Mateen Yaqoob

MATEEN YAQOOB DEPARTMENT OF COMPUTER SCIENCE

Introduction IEEE 802.16 i.e. WiMAX latest technology for Broadband wireless access

Evolved from 802.16 to 802.16d for fixed wireless access and the new 802.16e for mobility support

The standard specifies the air interface, including the medium access control (MAC) and physical (PHY) layers.

Key development in the PHY layer includes orthogonal frequency-division multiplexing (OFDM), in which multiple access is achieved by assigning a subset of subcarriers to each individual user.

OFDM system, the data is divided into multiple parallel substreams at a reduced data rate, and each is modulated and transmitted on a separate orthogonal subcarrier.

IEEE 802.16 standard specified a frequency range of 10–66 GHz with a theoretical maximum bandwidth of 120 Mb/s and maximum transmission range of 50 km. However, the initial standard only supports line-of-sight (LOS) transmission and thus does not seem to favor deployment in urban areas.

IEEE 802.16a-2003, can support NLOS (non line of sight transmission)


Features Added Mobility support is an advantage like in latest IEEE 802.16e (Mobile WiMAX)

It uses adaptive antenna system (AAS) and multiple input multiple output (MIMO) technologies to improve coverage.

It improves NLOS coverage by utilizing advanced antenna diversity schemes and hybrid automatic repeat request (hARQ).

IEEE 802.16 provides the capability to offer new wireless services such as multimedia streaming, real-time surveillance, voice over IP (VoIP), and multimedia conferencing.

Due to its long-range and high-bandwidth transmission, IEEE 802.16 has also been considered in areas where it can serve as the backbone network with long separation among the infrastructure nodes.


Comparisons between WiMAX and WiFi

Comparisons and confusion between WiMAX and Wi-Fi are frequent because both are related to wireless connectivity and Internet access.

WiMAX is a long range system, covering many kilometers, that uses licensed or unlicensed spectrum to deliver connection to a network, in most cases the Internet.

Wi-Fi uses unlicensed spectrum to provide access to a local network.

Wi-Fi is more popular in end user devices.

Wi-Fi runs on the Media Access Control's CSMA/CA protocol, which is connectionless and contention based, whereas WiMAX runs a connection-oriented MAC.

WiMAX and Wi-Fi have quite different quality of service (QoS) mechanisms:

WiMAX uses a QoS mechanism based on connections between the base station and the user device. Each connection is based on specific scheduling algorithms.

Wi-Fi uses contention access - all subscriber stations that wish to pass data through a wireless access point (AP) are competing for the AP's attention on a random interrupt basis. This can cause subscriber stations distant from the AP to be repeatedly interrupted by closer stations, greatly reducing their throughput.


ITU Definitions Fixed wireless access (FWA)

◦ Wireless access application in which the location of the end-user termination and the network access point to be connected to the end-user are fixed.

Mobile wireless access (MWA)◦ Wireless access application in which the location of the end-user termination is mobile.

Nomadic wireless access (NWA)◦ Wireless access application in which the location of the end-user termination may be in different places

but it must be stationary while in use.

MATEEN YAQOOB DEPARTMENT OF COMPUTER SCIENCE 6

Standards World Interoperability for Microwave Access

There are two main applications of WiMAX:

◦ Fixed WiMAX (IEEE 802.16-2004) - Fixed WiMAX applications are point-to-multipoint enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL for homes and businesses.

◦ Mobile WiMAX (IEEE 802.16e-2005) - Mobile WiMAX offers the full mobility of cellular networks at true broadband speeds.


WiMAXFixed WiMAX Architecture


Fixed and Mobile WiMAX AdoptionFixed WiMAX Adoption

Fixed WiMAX is currently available however the adoption rate is impacted by the high cost of equipment in comparison to cable or DSL.

Fixed WiMAX provides greater benefits for developing countries that do not already have physical infrastructure to support wired broadband access.

Mobile WiMAX Adoption

Mobile equipment testing typically takes between 12 to 18 months before the equipment is introduced to the consumer market.


MAC layer in WiMAX MAC layer consists of three sublayers: the service-specific convergence sublayer (CS), MAC common part sublayer (MAC CPS), and security sublayer.

Main functionality of the CS is to transform or map external data from the upper layers into appropriate MAC service data units (SDUs) for the MAC CPS.

MAC CPS provides the core functionality for system access, allocation of bandwidth, and connection establishment and maintenance.

For the PHY layer, the standard supports multiple PHY specifications, each handling a particular frequency range.

IEEE 802.16d MAC provides two modes of operation: point-to-multipoint (PMP) and multipoint-to-multipoint (mesh).


Point to Multipoint mode PMP operational mode fits a typical fixed access scenario, where multiple service subscribers are served by a centralized service provider.

uplink transmissions from a subscriber station (SS) to a base station (BS) occur in separate timeframes.

In the downlink subframe, the BS can transmit a burst of MAC protocol data units (PDUs).

SS listening to the data transmitted by the BS is only required to process PDUs addressed to itself.

Subscriber stations share the uplink to the BS on a demand basis.

Downlink and uplink subframes are duplexed either using frequency-division duplex (FDD) or time-division duplex (TDD).


MULTIPOINT-TO-MULTIPOINT Mesh mode nodes are organized in an ad hoc fashion.

Each station is able to establish direct communication to a number of other stations

Some certain nodes could provide BS function of connecting mesh network to backhaul links

The key difference is that in mesh mode all SSs may have direct links with other SSs.

IEEE 802.16 defines two mechanisms to schedule data transmission in mesh mode.

In centralized scheduling the BS works like a clusterhead and determines how SSs share the channel in different time slots.

In distributed scheduling every node competes for channel access using a pseudo-random election algorithm based on the scheduling information of its two-hop neighbors.


P2P & P2MP Architecture


Additional features Flexible spectrum allocation in that it is scaled to work in different channelization from 1.25 to 20 MHz complying with diverse requirement in different countries

High data rate with the MIMO antenna techniques and flexible sub-channelization schemes, which can support peak rates of 63 Mb/s in downlink and 28 Mb/s uplink per sector

There are many issues that must be carefully examined, including the deployment of infrastructure, data transmission, service guarantee, and scheduling.


Bandwidth allocation and scheduling for enhanced QoS

In downlink transmissions a BS has sufficient information to perform scheduling, but in uplink transmissions a BS performs the scheduling of various service transmissions based on information gathered from SSs.

SS will request uplink bandwidth from the BS, and the BS will allocate bandwidth on an as needed basis.

Unsolicited grant service (UGS) is designed to support real-time constant bit rate (CBR) traffic such as VoIP; this provides fixed size transmission opportunities at regular time interval without the need for requests or polls.

Real-time polling service (rtPS) is designed to support variable bit rate (VBR) traffic such as MPEG video. In this service the BS offers the SS periodic request opportunities to indicate the required bandwidth.

Non-real-time polling service (nrtPS) is for delay-tolerant data service with a minimum data rate, such as FTP. This service allows an SS to use contention request and unicast request opportunities for bandwidth request. Unicast request opportunities are offered regularly in order to ensure that the SS has a chance to request bandwidth even in a congested network environment.

Best effort (BE) service does not specify any service related requirements. Similar to nrtPS, it provides contention request and unicast request opportunities, but it does not provide bandwidth reservation or regular unicast polls.


Hindrance Factors WiMAX BSs to provide wide coverage for an entire region can still be economically infeasible due to the high cost of setup and maintenance of infrastructure.

With the existing 3G or/and other cellular infrastructure available, cost issues will always remain a major concern hindering the deployment of WiMAX.

The IEEE 802.16j Working Group aims to solve these issues through the use of multihop relay stations in an attempt to extend the coverage area and improve throughput at a feasible economical level.

It is well known that an increase in the number of hops in transmission adversely affects overall throughput; this is further challenged by the potential QoS degradation and scheduling complexity.


WiMAX DeploymentAlternative to cable and DSL


INTEROPERABILITY OF IEEE 802.16 ANDIEEE 802.11

Interoperability between IEEE 802.16 and other wireless technologies is one area that warrants much research interest.

IEEE 802.11 builds on a completely different design at the MAC level.

IEEE 802.11 the MAC protocol uses contention access, in which each SS has to compete against one another for accessing a wireless access point (AP).

subscriber distant from an AP can suffer performance degradation which makes it difficult to maintain the service requirements for applications like VoIP and streaming video.

one possible IEEE 802.16 deployment is to combine IEEE 802.16 and IEEE 802.11 to form a wireless network for both outdoors and indoors.


INTEROPERABILITY OF IEEE 802.16 ANDIEEE 802.11

not be practical or economically feasible to use WiMAX for providing full coverage of an indoor environment as obstruction and building materials can attenuate outdoor signals to a large extent.

To provide more complete coverage of indoor and outdoor

environments, it seems natural to use a mix of IEEE 802.16 and IEEE 802.11.


Integrated IEEE 802.16e and IEEE 802.11e scenario

An end user performs a handover from an IEEE 802.16e network to an IEEE 802.11e network.

The core network represents the backbone of the overall network, which provides connectivity for BSs and APs.

The network must be able to recognize the handover and reroute packets appropriately such that there is minimum disruption to the traffic routing.


Applications of WiMAX Last mile connectivity : It is cost effective to provide high speed last mile connectivity to areas (remote, isolated & sparsely populated) that are too expensive to serve with wired technology. Hence, alternative to ADSL, DSL, ISDN, cable modems & fiber optics.

Flexibility to accommodate a variety of applications through a scheduling algorithm that assigns data allocations to various SS based on their needs.


Applications of WiMAXClass Description Real Time Application Type Bandwidth

Interactive Gaming YesInteractive Gaming

50-85 kbps

VOIP, Video Conference Yes

VOIP 4 - 64 kbps

Video Phone 32 - 384 kbps

Streaming Media Yes

Music/Speech 5 - 128 kbps

Video Clips 20 - 384 kbps

Movies Streaming >2Mbps

Information Technology No

Instant Messaging <250 byte messages

Web Browsing >500 kbps

Email (with attachments) >500 kbps

Media Content Download (store & Forward)

NoBulk data, Movie Download >1Mbps

Peer-to-peer >500kbps


WiMAX System Components


WiMax Success Factors It is crucial that WiMax becomes an important building block to enable fixed/mobile convergence and to ensure its success.

Ability to offer ease of use is crucial to the success of WiMAX service providers

Success of WiMAX may depend on the ability to combine fixed and mobile access over the same infrastructure


Conclusions It is expected that WiMax becomes the dominant standard for Wireless MAN in the world market, at least, in fixed broadband networks.

WiMax products will have to be delivered to the market needs and those for the end-users will have to be extremely easy to install.

Focus is too often on technologies

Subscribers pay for services, not technologies

Broadband capabilities are important, but bandwidth is not the only meter to assess service

What is mobility?spectrum of mobility, from the network perspective:


no mobility high mobility

mobile wireless user, using same access point

mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone)

mobile user, connecting/ disconnecting from network using DHCP.

wide area network


Mobility: vocabularyhome network: permanent “home” of mobile(e.g., 128.119.40/24)

permanent address: address in home network, can always be used to reach mobilee.g., 128.119.40.186

home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote


Mobility: more vocabulary

wide area network

care-of-address: address in visited network.(e.g., 79,129.13.2)

visited network: network in which mobile currently resides (e.g., 79.129.13/24)

permanent address: remains constant (e.g., 128.119.40.186)

foreign agent: entity in visited network that performs mobility functions on behalf of mobile.

correspondent: wants to communicate with mobile

Mobility: approaches let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange.

◦ routing tables indicate where each mobile located◦ no changes to end-systems

let end-systems handle it: ◦ indirect routing: communication from correspondent to mobile goes through home agent, then

forwarded to remote◦ direct routing: correspondent gets foreign address of mobile, sends directly to mobile


not scalable

to millions of mobiles


Components of cellular network architecture

correspondent

MSC

MSC

MSC MSC

MSC

wired public telephonenetwork

different cellular networks,operated by different providers

Handling mobility in cellular networks

home network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon)◦ home location register (HLR): database in home network containing permanent cell phone #, profile

information (services, preferences, billing), information about current location (could be in another network)

visited network: network in which mobile currently resides◦ visitor location register (VLR): database with entry for each user currently in network◦ could be home network


Advance Computer Networks Lecture#12 Instructor: Engr. Muhammad Mateen Yaqoob.

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