Issues & Need of new protocols
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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 communication
Group Communication
Security
Network Management
Scalability
Transparency
Must be location independent because process can
be migrated leading to change in identifiers
Client server based communication
Must be Simple, Connectionless, support
Request Response behavior
Group Communication
Should support flexible transfer of n data n entities
Security
Messages should be encrypted only if the path
cannot be trusted because it is expensive
Network Management
Adding & removing of node should be done
automatically
Scalability
Protocol should be scalable
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
VMTP
Provides 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 address
Allows 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 Transmission
Packets 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 operations
Idempotent 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
FLIP
Connectionless 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
identifier
Sites on internetwork have more than one
NSAP’s connected by a FLIP Box
FLIP Box
Software 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 Box
Two parameters used
N/w Weight
Security bit
Three calls are provided in FLIP for sending
messages
FLIP_Unicast
FLIP_Multicast
FLIP_Broadcast
Mechanisms provided for sending sensitive
messages -> Security