Mobile Computing over the Internet

Upkar Varshney
Computer Information Sciences
Washburn University of Topeka
Topeka, KS 66621
E-mail: zzvars@acc.wuacc.edu

Abstract the network and is allowed to roam around from one place
There has been a trend to support ‘computing on move’ to the other [3]. The mobile user is provided with a
or mobile computing, where a user is free to roam and he wireless connection to a fixed part of the network and
or she still expects an uninterrupted access to the Internet. possibly to other mobile users. The mobile computing
To support mobile computing over the Internet, two environment can be described by the following attributes:
possible approaches can be considered. One is to use (a) mobile hosts (MHs), (b) mobile support stations
mobile version of IP (Internet Protocol), which could (MSSs) or base stations serving an area (a cell), (c) a
support typical Internet applications. The second approach wireless interface, (d) wireless medium with varying
is to use Wireless ATM (Asynchronous Transfer Mode), channel characteristics (due to fading, noise, interference,
an emerging technology where ATM cells are transmitted etc.), and (e) various applications running on MHs
over wireless links and part of the ATM connection lies in requiring different quality of service (QoS).
the wireless network. Wireless ATM has received Mobile computing environment creates several
attention due to the need to support mobile multimedia interesting addressing and network routing challenges. The
services and also because of an increasing deployment of mobility can affect various layers of protocols including
ATM technology in the Internet and other networks. The data link layer (loss due to wireless medium and link-by-
paper discusses the challenges and issues that must be link retransmission issues), network layer (addressing and
considered before Wireless ATM can be widely deployed in routing issues) and transport layer (end-to-end congestion,
the Internet environment. flow control and retransmission issues).
IETF (Internet Engineering Task Force) has introduced
1. Introduction Mobile IP (Internet Protocol) to support forwarding of IP
datagrams to the current location of a mobile user [4]. The
Mobile Computing refers to a distributed environment functioning of mobile IP is shown in Figure 1, which
where a user does not have to maintain a fixed position in includes all the necessary steps.

Subnetwork 1 Subnetwork 3

Sending
host Registration
Checking/verifying Foreign completed Current location
agent of mobile host
Registration
request
Routing Home Forwarding
agent

Subnetwork 2
Former location
of mobile host
Figure 1. Functioning of mobile IP

1060-3425/98 $10.00 (C) 1998 IEEE

 two users is established using a series of VPI/VCI
Routing to (Virtual Path Identifiers/Virtual Circuit Identifiers). ATM
home agent cells can be transported using SONET (Synchronous
Home
Fixed host Optical Network), a standard for transmitting a large
agent
number of bits over fiber. SONET specifies bit rates of
optical carriers including OC-1 (Optical Carrier at 51.84
Direct routing
Mbps), OC-3 (155.52 Mbps), OC-12 (622.08 Mbps) and
Tunneling to
to fixed host
so on.
mobile host
The ATM cell format at the user-network interface
Mobile host (between a user and the switch) is shown in Figure 3. In
this format, the GFC field was to be used for flow
control (not actually used in practice), VPI field to identify
Figure 2. Triangular routing in mobile IP virtual paths, VCI field to identify virtual circuits, PT
field to indicate the type of information in the information
field, CLP field to make a decision about cell dropping in
Each mobile user is permanently registered with a case of network congestion, and, HEC field for error
home agent. As the mobile user moves to a new location, detection in the rest of the header.
it registers with a host (called foreign agent) in the new The ATM cell format at the network-network interface
subnetwork. The packets to the mobile user are still (between two switches) is shown in Figure 4. The only
routed to its previous location and from there packets are difference between these two formats is the replacement of
rerouted to the current location of mobile user by its home GFC by adding more bits for VPI. The reason behind this
agent. is that the number of virtual paths between switches is
The routing and forwarding of packets to the current expected to be much higher than between a user and a
location of mobile users may cause two different routes switch.
between the fixed and mobile users (Figure 2). This is
termed as triangular routing and it can create different
delays for packets going in two different directions. The
triangular routing can be avoided using route
optimization, where the sending host is informed of the bits
current location of mobile host. 1 2 3 4 5 6 7 8
Mobile IP is designed to support typical Internet
applications such as e-mail, ftp, web etc. However, due to GFC VPI 1
growing demand for multimedia and other real time VPI VCI 2
services and quality of service requirements, one possible VCI 3
b
way to support mobile computing over the Internet is to 4
VCI PT CLP y
use “Wireless ATM (Asynchronous Transfer Mode)” 5
HEC t
technology. 6
e
The organization of this paper is as follows. In section .
s
2, we overview ATM and then in section 3, we introduce DATA (48 bytes) .
“Wireless ATM”. In section 4, we discuss issues related to 5
3
wireless ATM, and then in section 5, we survey the work
done in connection re-routing. In section 6, we introduce
the concept of triangular and loop routing in wireless
ATM and finally in section 7, we make some concluding GFC: Generic Flow Control
remarks. VPI: Virtual Path Identifier
VCI: Virtual Channel Identifier
2. Asynchronous Transfer Mode (ATM) PT: Payload Type
CLP: Cell Loss Priority
ATM is a connection-oriented cell switching technique HEC: Header Error Control
where 53 bytes long cells (small and fixed size packets)
can be prepared, transmitted and switched at very high Figure 3. ATM cell format at the user-
speeds. 53 bytes of an ATM cell are divided into 5 bytes network interface
of overhead and 48 bytes of data. A connection between

1060-3425/98 $10.00 (C) 1998 IEEE

 bits backbone speed uses ATM at OC-12 (Optical Carrier 12
1 2 3 4 5 6 7 8 or 622.08 Mbps) and may soon be increased to OC-48
(2.4 Gbps).
VPI VPI1 With increasing proliferation of ATM in local and wide
VPI VCI2 area networks, the author envisions that future Internet
VCI 3 b will have even higher ATM penetration. To support
VCI PT CLP 4 y emerging mobile and multimedia computing applications
HEC 5 t in that environment, the use of wireless ATM technology
6 e should be considered. In the next section, we discuss
. s issues that must be resolved before wireless ATM can be
DATA (48 bytes) . considered for deploying in the future Internet.
53
3. Wireless ATM

VPI: Virtual Path Identifier “ATM everywhere” is an interesting and important idea
VCI: Virtual Channel Identifier in the sense that it could lead to simple and high speed
PT: Payload Type interfaces to connect different networks together. Also the
CLP: Cell Loss Priority advantages of ATM such as support for real time delivery
HEC: Header Error Control can be extended to other networks. These reasons along
with the desire to support mobile multimedia computing
Figure 4. ATM cell format at the network- have motivated researchers to introduce the ATM
network interface technology in wireless environment also [1, 2, 7, 9].
Wireless ATM is an emerging technology where ATM
cells are transmitted over wireless channels and part(s) of
In the last few years, there has been an increasing the ATM connection lies in the wireless network. This
deployment of ATM (Asynchronous Transfer Mode) introduction of ATM in wireless environment creates
technology in the local as well as wide area environments. many interesting challenges. These include how to
Many campus based ATM LANs (Local Area Networks) maintain the end-to-end ATM connection as the user
have been designed and implemented. The backbone of the moves from one location to the other, how to provide
Internet, termed vBNS (very high speed Backbone quality of service, and the choice of transport protocol if
Network Service), interconnects 5 major NSF needed to support mobile computing environment.
supercomputing centers as shown in Figure 5. The current

Cornell Theory
Center

National Center for

Atmospheric Research Pittsburg
Supercomputing Center
National Center for
Supercomputing Applications

San Diego
Supercomputing Center

Figure 5. vBNS (very high speed Backbone Network Service)

1060-3425/98 $10.00 (C) 1998 IEEE

 There has been some progress towards adapting where ATM was treated as a data link layer). The stacks
wireless ATM for mobile computing environment. ATM are shown in Figure 6.
Forum has started a working group on wireless ATM to Two possible configurations have been proposed for
discuss and debate some of these issues. Some of the wireless ATM networks. They are termed as Ad-Hoc
issues under consideration are mobility management, Configuration and Infrastructure based Configuration. In
location management, and radio and MAC layer Ad-Hoc Configuration, the topology of wireless network
requirements definition. is not fixed and base stations are portable and can be
Currently ATM protocols do not support any mobility. moved around as needed. The communication is possible
Therefore, to support mobile computing, mobility between users by the co-operation of these portable base
management and signaling functions must be added in stations. This configuration is shown in Figure 7. In
ATM protocol stacks. Wireless ATM may lead to a more Infrastructure based Configuration, the topology of the
efficient implementation of protocol stacks as now the network is fixed and so are the base stations. This
mobility enhanced ATM layer (or W-ATM layer) can be configuration is shown in Figure 8.
treated as a network layer (unlike mobile IP over ATM,

Fixed User ATM Network Base Station Mobile User

Higher
Higher
Layers
Layers
AAL AAL
W-ATM Layer W-ATM Layer
ATM Layer ATM Layer LLC LLC
ATM Layer
MAC Layer MAC Layer
Wired Wired Wired Wireless Wireless
Physical Layer Physical Layer Physical Layer Physical Layer Physical Layer

Figure 6. Protocol stacks for wireless ATM

PBS

PBS
PBS

PBS

Mobile Users

Figure 7. Ad-Hoc configuration for wireless ATM

1060-3425/98 $10.00 (C) 1998 IEEE

 ATM
Switch
ATM ATM
Switch Switch
ATM
Switch

Wireless network with hexagon ATM network

cells and base stations

Figure 8. Infrastructure based configuration for wireless ATM

4. Issues in wireless ATM 4.2. Dealing with lossy wireless links

The introduction of ATM in wireless environment ATM technology is primarily designed for low error
presents many interesting challenges such as how to rate and high bandwidth communication environment.
maintain end-to-end ATM connection when the two ends This is why ATM cell does not employ error control for
of the connection are not stationary any more, how to deal the entire cell as the HEC (Header Error Control) field
with poor wireless links, how to guarantee quality of covers possible errors in the cell header only. So the data
service (QoS) if needed by a mobile computing part of ATM cell is not covered be a error control field.
application, how to resequence misordered ATM cells, and However, wireless links are known for high and variable
what MAC and transport protocols be used. error rates, so when ATM cells are transmitted over
wireless links, a high rate of cell loss may occur. There
4.1. Supporting user mobility could be several different ways to deal with this cell loss.
One way to counteract this loss is the use of forward error
ATM technology is designed to support connections correction (FEC) algorithms to allow receiver to detect and
between fixed end points, where VPI (Virtual Path correct communication errors. Another possible approach
Identifier) and VCI (Virtual Circuit Identifier) are allocated to make this cell loss transparent to the applications/users
to a virtual path involving switches and links. But in is to use an error detection scheme (e.g. CRC) followed
wireless networks, a mobile user moves from a cell to the by buffering and selective retransmission of ATM cells.
other, thus causing a change in its access point. Therefore, The retransmission will require the use of sequence
the issue of maintaining an end-to-end ATM connection number in ATM cells. One more reason behind the need
between a mobile user in the wireless network and a fixed for sequence number is the fact that ATM cells may be
user in ATM network arises. misordered in wireless network. The addition of sequence
Some researchers have started to address the user numbers (2-4 bytes long) would certainly add some
mobility problem [1, 2, 9]. These schemes involve overhead, which may be in addition to overhead caused by
rerouting or rearrangement of end-to-end ATM connection FEC. It may be possible to package sequence number,
using following approaches: (a) by providing multiple FEC overhead and 53 bytes long ATM cell together in a
paths for communications in the wireless network (virtual larger envelope (e.g. 64 bytes or smaller) for transmission
connection tree approach) [1], where the mobile user in wireless ATM environment [7].
chooses one of many paths based on its current location, If efficiency is an issue then some of the ATM header
(b) forwarding of ATM cells by a designated source base fields may have to be removed (or compressed) to give
station to the current location of the mobile user (homing way to wireless specific error correction and sequence
algorithm) [2], (c) rerouting the connection in wireless number fields. For example, if FEC field is being used for
network as the mobile user moves from one location to the entire ATM cell then HEC (Header Error Correction)
the other [9]. These schemes are discussed in more detail field, which covers only the cell header, may not be needed
in section V, where a qualitative comparison of in the ATM cell. A possible cell format for wireless ATM
connection rerouting schemes is presented. environment is shown in Figure 9.

1060-3425/98 $10.00 (C) 1998 IEEE

 MAC FEC Seq. Compressed
Specific or Number ATM cell ATM Data
Header CRC Header

2 - 4 bytes 2 - 4 bytes 2 - 4 bytes 4 bytes 48 bytes

Figure 9. A possible cell format for wireless ATM environment

MAC specific header will vary based on the type of of resources in the neighboring wireless cells so that the
media access control used for sharing of wireless QoS can be supported when the mobile user has moved to
bandwidth. FEC (or error correction) should be chosen one of the neighboring cells.
over CRC (or error detection) if the propagation delay Another approach involves using admission control
between two users is high (e.g. ATM-based satellite algorithms by base stations in wireless cells so that a
network) making error detection and subsequent sudden movement of many mobile users into a wireless
retransmission very inefficient as far as the throughput is cell does not severely impact the QoS of existing users
concerned. For smaller network (or networks with lower [1]. If a wireless cell is overloaded (more users than it can
propagation delay), the choice of using error detection support), then some ATM cells can be discarded. This
versus correction does depend on several factors such as discarding may be random, or can be made selective if
the amount of complexity added by FEC, amount of certain mobile users, which can tolerate higher cell loss,
buffering available at intermediate base stations etc. It’s may be identified by the base station.
the old debate of amount of processing overhead versus Wireless ATM introduces some more requirements on
bandwidth overhead. Length of sequence number field MAC protocol such as reduced access delay for real time
depends on the number of ATM cells in the pipeline traffic (CBR: constant bit rate, and VBR: variable bit rate)
before a retransmission is requested. As the network speed and acceptable bandwidth for non real time traffic (ABR:
goes up, the sequence number field has to be increased to available bit rate) to allow the transmission of ATM cells
give unique number to at least each ATM cell between the over wireless channels. The sharing of wireless bandwidth
source and the receiver. The standard ATM cell header may has to be efficient to support more customers and or
be compressed to 4 bytes by removing HEC as other error application requirements. In reality, reducing access delay
detecting or correcting schemes are already there in the cell may not lead to the most effective utilization of the
to cover the entire cell. wireless bandwidth. So a MAC protocol should give
priority to real time traffic as non real time traffic can wait
4.3. Supporting quality of service & MAC for longer duration. Some efforts have been made in
protocol designing MAC protocols for wireless ATM environment
[2, 6]. In [6], a TDMA (Time Division Multiple Access)
In (wired) ATM networks, QoS may include CTD approach is suggested where the channel bandwidth is
(Cell Transfer Delay), CDV (Cell Delay Variation) and divided into frames of slots and these slots are dynamically
CLR (Cell Loss Ratio). Even if the loss of ATM cells be allocated based on the priority and the amount of traffic.
counteracted using FEC or retransmission schemes, One other way to solve the problem is to redefine the
wireless network may still not support or guarantee QoS whole concept of QoS by dividing the it into two classes,
as defined in ATM standards due to the limited and shared Hard QoS and Soft QoS [9]. The Hard QoS is
radio bandwidth. guaranteeing the negotiated parameters, while the Soft
However, there are several ways which can be helpful QoS implies a prioritized probabilistic service based on
in supporting QoS. These are (a) advance resource available resources. If the end-to-end connection lies
reservation in neighboring cells [5], (b) admission control mostly or completely within the wireline ATM network,
[1], (c) design of suitable MAC protocols [2, 6], and (d) then a user’s request for Hard QoS can be supported.
redefining the whole concept of QoS [9]. However, if a part of the end-to-end connection uses
There has been some work in designing resource wireless link(s), then user should be informed that only a
management schemes for wireless environment to provide Soft QoS may be supported.
some QoS [5]. This scheme involves advance reservation

1060-3425/98 $10.00 (C) 1998 IEEE

4.4. Choosing transport protocol for wireless BAHAMA is an ad hoc wireless ATM LAN (Local
ATM Area Network), where portable base stations (PBS) are
employed and connected in an arbitrary topology. Mobile
The transport protocol for such an environment must users locally registers with PBS and a paging scheme is
be able to deal with reliable (wireline ATM) and unreliable used to locate the corresponding PBS of the called mobile
(wireless ATM) links of an internetwork. It is not clear user. The concept of Wireless ATM VP/VC (Virtual
whether or not the AALs (ATM adaptation layers) can be Path/Virtual Circuit) has been introduced by allocating
treated as transport layer. For example, AAL 5 is VPI (virtual Path Identifier) corresponding to a base
functionally similar to UDP (User Datagram Protocol), a station rather than to a virtual path. The technique
transport protocol, but none of the AALs provide any employs designated “Source Home” and “Destination
reliable end-to-end service [8]. It appears that some Home” base stations to reroute ATM cells to new
transport protocol needs to be used on top of wireless locations of mobile user(s). After a handoff the traffic is
ATM to support mobile computing applications. still routed through their original source and destination
The transport protocol to be employed could be a home base stations. However, it has been suggested that
modified version of TCP as some researchers have these home base stations be slowly updated to reduce the
proposed using TCP with some changes over wireless bandwidth waste. To maintain the ATM cell sequence
networks. However, such proposed changes are also valid integrity, sequence numbers are used for ATM cells in
for wireless ATM environment. One point that must be parts of the network.
noted here is that since TCP assumes that underlying A scheme to reduce handoff overhead to ATM network
network layer protocol is IP, TCP can not be directly call processor is proposed using a virtual connection tree
employed on top of mobility enhanced ATM layer (or W- approach [1]. The scheme involves allocating multiple
ATM layer). This would require either building another Virtual Connection Numbers (VCNs) per call. Each VCN
AAL (ATM Adaptation Layer) or making required changes defines a path between the root of a connection tree and a
in TCP to handle underlying W-ATM layer. Some other distinct base station. A mobile user selects a base station
researchers have argued that new transport protocols, during handoff by choosing one of these numbers. The
which are aware of a underlying wireless link(s), be network call processor comes into picture to set up a new
designed to support mobile computing over wireless ATM connection through ATM network only when the mobile
environment [9]. user leaves a certain geographic area covered by a
connection tree. This paper also addresses the issues of
5. Work in connection rerouting admission control required for maintaining QoS.
Two schemes termed RAC (Rearrange ATM
One significant problem to overcome before wireless Connection) and EAC (Extend ATM Connection), based
ATM deployment is how to reconfigure or reroute the on connection rerouting through ATM network and
ATM connection as the user moves from one location to connection extension in wireless network, respectively,
the other. There has been few schemes proposed in the have been proposed [9]. RAC places the processing
literature based on setting up new connection every time requirement for rerouting in ATM network, and if NCP
the mobile user moves from one location to the other, or (Network Call Processor) is unable to process the request,
allowing multiple connections or dynamic rerouting of then EAC (to extend the connection to the new location of
connection etc. We first briefly overview some of the the mobile user) is performed in wireless network using
proposed schemes for connection management in wireless base stations. These schemes can be used in isolation or
ATM and then we will perform a qualitative comparison in conjunction to support connection management in
of these schemes. wireless ATM networks. The choice to use any one or
An ATM based wireless network using ATM switches both could be based on the desired criteria such as
to interconnect PCN (Personal Communications Network) utilization of bandwidth, implementation complexity, or
microcells has been proposed [7]. This paper presents amount of rerouting load. The choice can also be made
various issues in interconnecting ATM and wireless based on the type of signaling employed in ATM
networks together including issues related to the physical, network. If it uses centralized signaling system, then
media access control and data link layers of ATM-based RAC can be executed by Network Call Processor (NCP)
wireless networks, however it does not address how an and EAC by the base stations of wireless networks. In a
end-to-end ATM connection will be maintained with user distributed signaling environment, rearrangement of a
mobility. WATMnet [6] is a wireless ATM prototype and connection would take more processing time so only EAC
uses mobility enhanced version of ATM for providing may be used and once the number of base stations in an
connection control functions. ATM connection reaches a limit, a new connection may

1060-3425/98 $10.00 (C) 1998 IEEE

be established to reduce the bandwidth overhead caused by needs to initialize connection tree and numbers. It also
connection extension. This limit can be decided and needs to allow spare capacity as only one of the many
dynamically varied based on the acceptable amount of paths is in use at a time. However, it can support fast
traffic in wireless network and the tolerable amount of mobility and is capable of generating very low handoff
connection processing overhead in ATM network [11]. delay. Dynamic routing requires searching for the common
Since above schemes are designed for different ancestor switch of current and new paths between the
configurations, it is difficult to compare them users. After the search, only the part of the connection
quantitatively. However, a qualitative comparison is made which is between the common ancestor switch and the
here (table 1) based on some important issues such as current base station, needs to be modified. In doing so, it
amount of wireless traffic introduced, handoff delay, may produce very high handoff delay.
routing loops, and the control complexity involved in the
implementation of a connection routing scheme. The 6. Triangular routing and possible loop
schemes used in this comparison are NCEH (New formation
Connection Every Handoff), BAHAMA (based on
connection extension), Connection tree approach, Extending a connection through base stations can cause
Dynamic rerouting (finding the common ancestor switch forwarding loops, where one or more base stations may be
and then rerouting the connection), and RAC/EAC. involved more than once in the path from the original
NCEH will create least wireless traffic at the expense base station to the current base station. This can occur if a
of significant overload caused by setting up a connection mobile user moves to a previously visited base station,
at every handoff, leading to high handoff delay. BAHAMA which is still involved in forwarding ATM cells to the
will create significant wireless traffic due to forwarding mobile user [11].
from original base station to the new location. However, An example of triangular routing is shown in Figure
the handoff delay is low due to the connection extension 10(a). The extended connection involves base stations W,
involving only base stations. Connection tree approach X, and Y. After the user moves to the cell served by Z,

Table 1. A qualitative comparison of connection rerouting schemes

_________________________________________________________________________________
NCEH BAHAMA C-TREE DYNAMIC RAC/EAC
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Amount of excess None Large Small None Small
wireless traffic
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Handoff delay High Low Least High Low
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Undetected No Yes No No No
routing loop
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Spare capacity Least Most Most Least Least
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Control Simplest Complex Complex Complex Complex
complexity
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Type of mobility Slow Slow Fast Slow Fast
supported
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
VPI/VCI translation No Yes No No No
at a base station
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Need to initialize No No Yes No No
connection tree
-------------------------------------------------------------------------------------------------------------------------------------------------------------------

1060-3425/98 $10.00 (C) 1998 IEEE

and if Z accepts the request, then it will create inefficient Also the growing demand of real time and multimedia
utilization of wireless link bandwidth. This triangular services over the Internet may justify the deployment of
routing can be avoided, if Z (before accepting a request for wireless ATM.
connection extension) checks for triangular and circular
(loop) routes that may be formed after the connection REFERENCES
extension is accepted. So, if Z will look into the list of [1] A. S. Acampora and M. Naghshineh, “An Architecture
base stations (supplied with extension request), which and Methodology for Mobile-Executed Handoff i n
have been visited and are currently part of the extended Cellular ATM Networks”, IEEE Journal on Selected Areas
connection. Looking into the list, which in this case in Communications, vol. 12, no. 8, Oct. 1994.
[2] K. Y. Eng, M. J. Carol, M. Veeraraghavan, E. Ayanoglu,
would be <<W, X, Y>>, Z finds that W is its neighbor
C. B. Goodworth, P. Pancha, and R. A. Valenzuela,
so it will send a request to W to reroute the connection. If “BAHAMA: A Broadband Ad-Hoc Wireless ATM Local-
W accepts the request, then it will stop forwarding ATM Area Network”, in Proc. IEEE Int. Conf. Comm., June
cells to X. After receiving all the ATM cells which were 1995.
in the pipeline, the simplified (or short-circuited) route is [3] T. Imielinski, and H. F. Korth, “Mobile Computing”,
as shown in Figure 10(b). Kluwer Academic Publishers, 1996.
[4] D. B. Johnson, “Scalable Support for Transparent
7. Conclusion and further prospects Mobile Host Internetworking”, Wireless Networks, Vol.
1 (1995).
Wireless ATM is an emerging technology where ATM [5] C. Oliveira, J. B. Kim, T. Suda, “Quality-of-Service
cells are transmitted over wireless channels and part(s) of Guarantee in High-Speed Multimedia Wireless
Networks”, in Proc. IEEE Int. Conf. Comm., June 1996.
the ATM connection lies in the wireless network. This
[6] D. Raychaudhuri, L. J. French, R. J. Siracusa, S. K.
introduction of ATM in wireless environment creates Biswas, R. Yuan, P. Narasimhan, and C. Johnston,
many interesting challenges. These include how to “WATMnet: A Prototype Wireless ATM System for
maintain the end-to-end ATM connection as the user Multimedia Personal Communication”, in Proc. IEEE Int.
moves from one location to the other, how to provide Conf. Comm., June 1996.
quality of service, and the choice of transport protocol if [7] D. Raychaudhuri and N. D. Wilson, “ATM-based
needed to support mobile computing environment. Transport Architecture for Multiservices Wireless
The paper discusses issues in wireless ATM that must Personal Communication Networks”, IEEE Journal o n
be considered before it can be deployed in the Internet Selected Areas in Comm., vol. 12, no. 8, Oct. 1994.
environment. It’s an emerging area and is beginning to get [8] A. S. Tanenbaum, “Computer Networks”, Third Edition,
a lot of attention in ATM as well as wireless Prentice Hall, 1996.
[9] U. Varshney, “A Scheme for Connection Management i n
communities. Some of the working models have been
Wireless ATM Networks”, in Proc. First NDSU
built using off-the-self components to show that wireless Workshop on ATM Networking, Fargo, ND, Aug. 1996.
ATM is feasible with existing technology. Author [10] U. Varshney, “Supporting Mobility using Wireless
believes that increased radio bandwidth allocation, ATM”, IEEE Computer, Jan. 1997.
emerging reliable and QoS oriented MAC protocols along [11] U. Varshney, “Two Connection Re-Routing Schemes for
with wireless ATM based transport protocols will all Wireless ATM Environment”, in Proc. IEEE
justify the use of wireless ATM in the Internet International Conference on Universal Personal
environment to support mobile computing applications. Communications (ICUPC ‘97), Oct. 1997.

W X W X

Y Y
Z Z

Figure 10: (a) An example of triangular routing (b) Eliminating triangular routing

1060-3425/98 $10.00 (C) 1998 IEEE