Wireless ATM raviteja motaparthi ATM (Asynchronous Transfer Mode) It has been advocated as an important technology for all types of services and networks. Most people believe that ATM will be the standard for the future B-ISDN (Broadband Integrated Services Digital Networks). Due to the success of ATM wired networks , Wireless
ATM can be viewed as a solution for next-generation personal communication networks, or a wireless extension of the B-ISDN networks, which will support integrated data transmission (data, voice, video) with guaranteed QoS. Wireless ATM? WATM consists of ATM service that rides on top of an air interface between a terminal and an access point. Companies will no longer need to buy extra
equipment. Reduces complexity and improves flexibility in traffic performance. ATM cell-relay Paradigm be adopted as basis for next generation. WATM adopts ATM to provide the data communications services so where the overall architecture is based on the ATM protocol stack. WATM Protocol Architecture
Factors to favor the use of ATM cell transport for PCN: Flexible Bandwidth Allocation Efficient multiplexing of traffic End-to-End provisioning of broadband services Suitability of available ATM switching equipment Improved service reliability with packet switching techniques. Ease of interfacing
Key Issues: Architecture: Each Pico cell is served by a base station. To avoid hard boundaries between Pico-cells, the base stations can operate on same frequency. Provides the flexibility of using same frequency and avoids running out of bandwidth. Virtual Circuit Management and Packet Routing: Each processor attaches to ATM switch maintains
a VC to each other processor which it passes data packets, and use a second VC for routing updates. The standard hop-by-hop routing method for datagrams is not adequate with wireless systems, which need to store the location of every mobile system. Physical Layer:
A bit rate ranging 5-10 Mpbs can be achieved using existing wireless technologies. CDMA provides an efficient solution for frequency reuse and achieve bandwidth 2-4 times. In a Pico-cellular environment we can achieve bit range of 8-16Mb/s using narrow band approach(TDMA). Overall with a good physical layer design it should be possible for macro(5-10km),micro(0.5km) and Pico(100m) cells to support baud rates.
. Physical layer Media access control(MAC) WATM MAC is responsible for providing functionally point to point links for the higher protocol layer to use. Each station registers it's address to it's hub during
a hub initiated slotted-ALOHA content period for new registration so that make itself know by others. In a shared environment, there must be some control over the usage of the medium to guarantee QoS. An extended TDMA, which satisfies PCR (Peak Cell Rate), SCR (Sustainable Cell Rate), and MBS (Maximum Burst Size) requests, is suggested. Another design issue of MAC layer is to support multiple PHY layers. Data Link Control (DLC):
Data Link Control is responsible for providing service to ATM layer . Mitigating the effect of radio channel errors should be done in this layer before cells are sent to the ATM layer. In order to fulfill this requirement, error detection or retransmission protocols and forward error correction methods are recommended.
Handover: In WATM networks, a mobile end user establish a virtual circuit (VC) to communicate with another end user . When the mobile end user moves from one AP (access point) to another AP, proper handover is required. To minimize the interruption to cell transport, an efficient switching of the active VCs from the old data path to new data path is needed. When the handover occurs, the current QoS may not be supported by the new data path. Since a mobile user
may be in the access range of several APs, it will select the one which can provides the best QoS. During the handover, an old path is released and a new path is then re-established. Buffering Techniques: Cell buffering consists of Uplink Buffering and Downlink Buffering. If VC is broken when the mobile user is sending
cells to APs, Uplink Buffering is required. The mobile user will buffer all the outgoing cells. Downlink Buffering is performed by APs to preserve the downlink cells for sudden link interruptions, congestion, or retransmissions. It may also occur when handover is executed. Location Management: There are two basic location management schemes: mobile PNNI scheme
location register scheme. In the mobile PNNI scheme, when a mobile moves, the reachability update information only propagates to the nodes in a limited region , if a call is originated by a switch in this region, it can use the location information to directly establish the connection. If a call is originated by a switch outside this region, a connect is established between this switch and the mobile's Home Agent, which then forward the cells to the mobile.
Routing: Due to the mobility feature of mobile ATM, routing signaling is a little bit different from that for the wired ATM network. First, mapping of mobile terminal routing-id's to paths in the network is necessary. Also rerouting is needed to re-establish connection when the mobiles move around. Addressing:
Addressing issue of WATM focuses on the addressing of the mobile terminal. Solution is that each mobile terminal has a name and a local address.. It's constant and doesn't change while the terminal moves. When a terminal is up, it's name is advertised by the switch it attaches to other switches. An local (or temporary) address is assigned when the mobile terminal attaches to a different switch
during roaming where it assign a local significant address to the terminal. Traffic and QoS Control : The mobility feature puts additional impact on traffic control and QoS control. Currently a reference model for resource allocation in WATM is still unavailable. Wireless Network Management :
In wireless networks, the topology is changing in time. A specific methods must be designed to maintain the dynamic nature of the network topology. Other issues, like network and user administration, fault identification and isolation, and performance management, are also need to be considered. Conclusion
Finally, I have tried to analyze different issues pertaining to Wireless ATM, and discussed some of the ideas of different researchers working on it. No standards have been set for Wireless ATM. QUESTIONS??
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