itec801 distributed systems
Post on 01-Jan-2016
21 Views
Preview:
DESCRIPTION
TRANSCRIPT
1
ITEC801Distributed Systems
Protocols
Coulouris chapter 3
ITEC 801 Protocols 2
Important Things
Things to get from this set of slides What is a protocol? What are protocols for? Why we have many protocols What is the difference between connection-
oriented and connectionless
ITEC 801 Protocols 3
Protocols
Inter-process communication is at the heart of distributed systemsIPC depends on protocolsa protocol is simply the rules by which the communication is carried outa network communications protocol defines all the messages (and their ordering) for a communication
ITEC 801 Protocols 4
Protocol
Protocol definitions include Error detection Message length Message structure etc
Protocol implementations may be in hardware or software
ITEC 801 Protocols 5
How Do Protocols Work?
Transmission of data over network broken down into discrete systematic steps
At each step, certain actions take place
Each step has its own rules and procedures which cannot take place at any other step
ITEC 801 Protocols 6
Protocol Functioning
Steps must be carried out in a consistent order on every computer in the network Sending Computer: Steps carried out-Top
down. Receiving Computer: Steps carried out
bottom-up.
ITEC 801 Protocols 7
Protocols
ITEC 801 Protocols 8
Protocol
There are many protocols
Each protocol has a different purpose and accomplishes different task
Several protocols work together in what is known as a Protocol Stack
Levels of the protocol stack map on to layers of the OSI model
ITEC 801 Protocols 9
Layered Protocols
Computer network protocols are layered
each layer has its own function
for example: Network level: IP Transport level: TCP. Application level
RPC Remote method Invocation (RMI) Message oriented Middleware (MOM)
ITEC 801 Protocols 10
Internet Protocols (some)
IP ICMP
TCP UDP
Network
Transport
Teln
et
FTP
HTTP
Use
r app
s
SN
MP
TFT
P
Use
r app
s
UpperLayers
ITEC 801 Protocols 11
Need for a Protocol Stack
Require a high degree of cooperation between two computer systems that communicate
Activities include: Path determination/conveying control information
to network Ascertaining destination status Ascertaining destination application status Determining format
ITEC 801 Protocols 12
Need for a Protocol Stack
Single module versus multiple modules.
We could implement all communication in a single piece of software
too unwieldy and hard to maintain
ITEC 801 Protocols 13
Internet Protocol Stack: TCP/IP
Standard routable enterprise networking protocol
Technology for connecting dissimilar systems
ITEC 801 Protocols 14
TCP/IP layers:
Application: user interface to Internet.Transport: Transmission Control Protocol (TCP): Connection
oriented reliable communications for applications. User Datagram Protocol (UDP): connectionless
Network: Internet Protocol: For routing and addressing. (RFC 791)Network Interface layer: Inserting/removing frames from network.
ITEC 801 Protocols 15
OSI Reference Model
Defines seven layersPhysical: Concerned with transmission of unstructured bit stream over physical medium.Data link: Reliable transmission of information across physical link.Network: Provides upper layer independence from data transmission/switching technologies.
ITEC 801 Protocols 16
OSI Reference Model
Transport: reliable transfer of data between end points.Session: Control structure for communication between application.Presentation: Independence to application process from data representation.Application: Access to environment.
ITEC 801 Protocols 17
OSI Reference Model
ITEC 801 Protocols 18
Connection-Oriented versus Connectionless
Protocols can be connection–oriented OR Connectionless
Connection oriented: A logical connection is set up between sender and receiver before they actually communicate
Connectionless: Sender and receiver communicate without establishing a logical connection
ITEC 801 Protocols 19
Connection-Oriented
Setup phase when the connection is created
Communication phase during which the communications happens
Pull-down phase when the connection is terminated
ITEC 801 Protocols 20
Protocol Terminology
Entity: active elements in each layer
Peer Entities: Entities in same layer but on different machines
Entities in layer N implement a service used by layer N+1 N layer: Service provider N+1 layer: service user
ITEC 801 Protocols 21
Protocols
Each layer provides service at an access point : SAP (Service Access Point) Each SAP has a unique address that
identifies it.
Agreed set of rules at Interface between any two layers
ITEC 801 Protocols 22
Protocols
Information block passed by layer N+1 to layer N through SAP: Interface Data Unit (IDU)IDU Block= SDU (Service Data Unit) + Control (ICI)ICI: Interface Control InformationSDU information passed along network to peer entity up to layer N+1
ITEC 801 Protocols 23
Protocols
Control: some guidelines for layer N to do its Job.
Processing on SDU by layer N results in PDU (Protocol Data Unit)
PDU = SDU+ Header
PDUs generated at different layers given a different name
ITEC 801 Protocols 24
ICI SDU
SAP
ICI SDU
SDUHeader N-PDU
Layer N+1
Interface
Layer N
Relation Between Layers at an Interface
top related