Smack – A Smart Acknowledgement Scheme For Broadcast Messages In

  • July 2020
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SMACK – A Smart ACKnowledgement Scheme for Broadcast Messages in Wireless Networks Problem: Reliable multicast in layer3 is time consuming and costly if made reliable. Objective: - To present a way to utilize simultaneous transmissions to reduce cost of reliable multicast by orders of magnitude. - Can Speed up broadcast, anycast etc applications. How: They use ACK sending in the Physical layer using a single bit. The Access point dedicates OFDM channels to each node so that they can send ACKs in case of wireless broadcasts. ACK less broadcasts are used currently. Process: - The AP assigns ID to each member - Broadcast is sent - All nodes send out a 1 on the sub carrier assigned by the AP to acknowledge - The AP senses medium once and then decodes all the ACKs by sending the medium only once. Protocol Provides: - Robustness against varying signal power - Robustness against interference Yes they were able to back their claims with experimental results.

PortLand: A Scalable Fault-Tolerant Layer 2 Data Center Network Fabric Problem: Lack of scalability, Difficult Management, Inflexible communication and limited support for VM migration in existing Data Center Networks. Explicit problems addressed for future DCNs: a) VM Migration should be easy from 1 physical machine to other in the DCN and it should be transparent to ongoing flows, connections and applications with that VM b) Plug & Play switch support, no configuration required by administrator c) Efficient communication between any two end hosts in the DCN d) No forwarding loops e) Failure detection and recovery should be rapid and efficient Design Points that cater the above problems: Fabric Manager: -Maintains the Network topology in softstate - ARP resolution - Fault management Pseudo MACs: - Another address assigned to each machine other than its Actual MAC. - PMAC addressing such that even the position is ascertained from the address Proxy based ARP: - All ARP requests are intercepted and sent to the Fabric Manager, which replies with the mapping. Distributed Location Discovery: - Switches generate location discovery messages to know their position in network Loop Free forwarding: - Unidirectional flow of messages, either up or down, not lateral. Therefore no loops are formed. Fault tolerant Routing: - If one switch discovers that the neighboring link or node is dead, it informs the FM, which tells all the affected nodes so they recalculate the forwarding table.

VL2: A Scalable and Flexible Data Center Network Problems: 1) Existing networks don’t have enough capacity between sensors 2) Traffic flooding in service affects other services traffic 3) Dynamic VM migration not possible. Solution Requirements: 1) Uniform high capacity, no limitation on channel capacity, only due to NICs 2) Performance Isolation , Traffic of one service shouldn’t be affected by the traffic of any other service. 3) Layer 2 Semantics in DCN Connectivity i.e flat addressing like in Ethernet. Design: VL2 -

Valiant Load Balancing is used for uniform load distribution providing performance isolation Each server given Application Specific Addresses (AAs) and Location Specific Addresses (LAs). The AA to LA mapping is maintained by the Directory System. Providing Transparent VM Migration.

Experimental results solve all the mentioned 3 problems and that too with existing hardware, with VL2 client running on a machine.

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