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