protocols used by network systems are not effective to distributed system special requirements are...
TRANSCRIPT
Protocols For Distributed Systems
Protocols used by network systems are not effective to distributed system
Special requirements are needed here. They are in cases of:
Transparency Client server based communicationGroup CommunicationSecurityNetwork ManagementScalability
Issues & Need of new protocols
Transparency
Must be location independent because process can be migrated leading to change in identifiers
Client server based communicationMust be Simple, Connectionless, support Request Response behavior
Group CommunicationShould support flexible transfer of n data n entities
SecurityMessages should be encrypted only if the path cannot be trusted because it is expensive
Network Management
Adding & removing of node should be done automatically
ScalabilityProtocol should be scalable
Introduction of Protocols
Two Communication Protocols are designed to achieve higher throughput & fast response in distributed system & to solve the issues mentioned
VMTP: Versatile Message Transport Protocol
FLIP: Fast Local Internet Protocol
VMTPProvides Group Communication , Security & efficient Client Server Communication
Connectionless protocol supports Request-Response behavior between Client & Server
Entities identified by 64-bit identifier which is unique, stable & independent of host addressAllows entities to be migrated & handled independent of network layer addressing
Portion of entity identifier space reserved for group identifiers , identify a group of zero or more entities
VMTP provides Selective TransmissionPackets of message divided into packet group which contains maximum of 64 kilobytes of segment data(viewed as a sequence of segment block having 512 bytes
32 bit mask in segment
When a packet is received , delivery mask ORed together to obtain a bit map
VMTP uses a rate-based flow control mechanism
Packets in a packet group are spaced out with in for packet gaps to reduced the arrival rate at Receiver
Allows Client Server Communication
Optimization is used in VMTP -> differentiate between idempotent & non idempotent operationsIdempotent operation-> executions can be repeated no: of times without their being any side effect
VMTP provides rich collection of optional facilities -> expands its functionality & efficiency in various site
FLIPConnectionless protocol used in AMEOBA Distributed Systems
Features are Transparency, Security, easy Network Management, Group Communication & C-S Communication
Identifies entities as Network Service Access Points(NSAP’s) with location independent 64-bit identifierSites on internetwork have more than one NSAP’s connected by a FLIP Box
FLIP BoxSoftware Layer OS corresponding to sites
Run on a separate communication process
Routing table is maintained-> dynamic cache mapping NSAP address on data-link address
FLIP messages are transmitted between NSAP’s
Path is selected on the basis of information stored in routing table of each FLIP BoxTwo parameters used N/w Weight
Security bit
Three calls are provided in FLIP for sending messages
FLIP_UnicastFLIP_MulticastFLIP_Broadcast
Mechanisms provided for sending sensitive messages -> Security