SKR 5302: Advanced Distributed Computing

4. Chapter 4: Inter-process Communication

UDP datagram communication

UDP datagrams are sent without acknowledgement or retries

Issues relating to datagram communication

Message size: not bigger than 64k in size, otherwise truncated on arrival
blocking: non-blocking sends (message could be discarded at destination if there is not a socket bound to the port ) and blocking receives (could be timeout)
Timeout: receiver set on socket
Receive from any: not specify an origin for messages

Failure model

omission failure: message be dropped due to checksum error or no buffer space at sender side or receiver side
ordering: message be delivered out of sender order
application maintains the reliability of UDP communication channel by itself

TCP stream communication

The API to the TCP

Provide the abstraction of a stream of bytes to which data may be written and from which data may be read

Hidden network characteristics

Issues related to stream communication

Matching of data items: agree to the contents of the transmitted data
Blocking: send blocked until the data is written in the receiver’s buffer, receive blocked until the data in the local buffer becomes available
Threads: server create a new thread when it accept a connection

Failure model

Integrity and validity have been achieved by checksum, sequence number, timeout and retransmission in TCP protocol
Connection could be broken due to unknown failures
- Can’t distinguish between network failure and the destination process failure
- Can’t tell whether its recent messages have been received or not