Issues in ad-hoc networks Miguel Sanchez Nov-2000

Contents Introduction to ad-hoc networks Media access control in wireless networks Routing in ad-hoc networks Wireless Local Area Network standards Research project

What an ad-hoc networks is? It is a network made of wireless nodes No network infrastructure is present Transmission range is limited, not all the destinations can be reached in one hop Multi-hop forwarding is needed to provide any-to-any communication Nodes act as both, end-points and routers

What an ad-hoc networks is for? Cellular networks are infrastructure-based networks When there is no network available, ad-hoc networks can be of help: –Disaster recovery (floods, earthquakes, …) –Space exploration (multiple probes) –Network of sensors (NOS) Even if a network is available: –Meeting rooms (education or business) –Military applications (armies communication)

Why not to have a longer transmission range? A long transmission range can avoid the multi-hop routing By using low power transmissions a double benefit is obtained: –Reduced power consumption (batteries lasting longer) –Increased spectrum reuse (more network throughput)

Contents Introduction to ad-hoc networks Media access control in wireless networks Routing in ad-hoc networks Wireless Local Area Network standards Research project

Media access in wireless networks Dashed circle is a transmitting node Arrows show receiving nodes Dashed-line big circle is the transmission range Nodes than can hear a given transmitter are called neighbors of it

New MAC problems Carrier sense algorithms suffer the hidden terminal problem Some protocols establish a reservation handshake before actually sending the data to avoid this problem

RTS/CTS reservation dialog Unicast only Transmitter sends a RTS packet to the destination node Destination node acknowledges by sending back a CTS packet If CTS is successfully received, then transmitter sends a data packet. If not, backs off and it retries later

Leading idea of our research at the MAC level We question the current approach of letting the hardware features to decide We study both, static and dynamic settings for the transmission range: 1.Optimal transmission range 2.Adaptive power control

Transmission range adjustment We have proposed an heuristic to adjust the transmission range With this method, we can estimate a transmission range for best throughput results In this work we obtain a static value for the transmission range

Our power control algorithm RTS/CTS dialog is a reservation mechanism This dialog always reserve the same area for each transmission Our algorithm uses a variable transmission range and to adapt it depending on the distance to the destination node Each node can use a different power level for each transmission

Contents Introduction to ad-hoc networks Media access control in wireless networks Routing in ad-hoc networks Wireless Local Area Network standards Research project

IETF MANET working group The primary focus of the working group is to develop and evolve MANET routing specification(s) and introduce them to the Internet Standards track Several proposals are available for end-to- end and multicast traffic

Ad-hoc routing 101 Topology changes can happen anytime and at a high pace Two basic approaches: –Proactive (i.e. table-driven routing) –Reactive (i.e. source routing) Some hybrid algorithms, too Mobility scenario not defined Multicast protocols also proposed

More ad-hoc routing problems Scalability, or lack of. Some protocols work ok for tens of nodes but they degrade for hundreds or thousands of nodes Providing QoS in such an scenario seems to be quite a challenge (some proposals exist) Power-conserving routing is also under study (there are some proposals too)

Contents Introduction to ad-hoc networks Media access control in wireless networks Routing in ad-hoc networks Wireless Local Area Network standards Research project

IEEE This working group developed the 1 and 2 Mbps specification Now a new revision, called b, is supported in some new devices, raising the speed to 11 Mbps Two modes of operation (alternative): –Access point based (infrastructure) –Ad-hoc (infrastructure-less)

Wireless LANs It is a commercial reality It is being used as an installation-free setup for some offices Access points provide the necessary connectivity to the wired backbone Ad-hoc mode is supported but not very often used (user has to choose the operating mode when installing the driver)

Contents Introduction to ad-hoc networks Media access control in wireless networks Routing in ad-hoc networks Wireless Local Area Network standards Research project

Operational mode is alternative. Or it is access point based or it is ad-hoc A combined mode will allow better coverage with less access points A mobile node could act as a “helper node” to nearby nodes unable to reach the access point

Some extensions We envision an scenario where a convergence of cellular and ad-hoc networks can bring some benefits for the user This new scenario also brings the necessity of rethink billing systems Multiple access technologies can be present in smarter, new mobile devices, that could use some of these mobile extensions