03-08-2013, 03:17 PM
Protocols and the TCP/IP Protocol Suite
Protocols.ppt (Size: 977 KB / Downloads: 23)
Protocols
Cooperative action is necessary
computer networking is not only to exchange bytes
huge system with several utilities and functions. For examples
error detection
Encryption
Routing
etc.
For proper communication, entities in different systems must speak the same language
there must be mutually acceptable conventions and rules about the content, timing and underlying mechanisms
Those conventions and associated rules are referred as “PROTOCOLS”
Protocol Architecture
Task of data transfer is broken up into some modules
Why?
How do these modules interact?
For example, file transfer could use three modules
File transfer application
Communication service module
Network access module
Simplified File Transfer Architecture
File Transfer Application Layer: Application specific commands, passwords and the actual file(s) – high level data
Communications Service Module: reliable transfer of those data – error detection, ordered delivery of data packets, etc.
Network Module: actual transfer of data and dealing with the network – if the network changes, only this module is affected, not the whole system
General protocol architecture principles that we have seen so far
Layered structure
Protocol stack
Each layer provides services to upper layer; expect services from lower one
Layer interfaces should be well-defined
Peer entities communicate using their own protocol
peer-to-peer protocols
independent of protocols at other layers
if one protocol changes, other protocols should not get affected
Network Access Layer
Exchange of data between the computer and the network
Sending computer provides address of destination
so that network can route
Different switching and networking techniques
Circuit switching
Packet switching
LANs
etc.
This layer may need specific drivers and interface equipment depending on type of network used.
But upper layers do not see these details
independence property
Transport Layer
Reliable data exchange
to make sure that all the data packets arrived in the same order in which they are sent out
Packets nor received or received in error are retransmitted
Independent of network being used
Independent of application
Protocol Data Units (PDU)
User data is passed from layer to layer
Control information is added/removed to/from user data at each layer
Header (and sometimes trailer)
each layer has a different header/trailer
Data + header + trailer = PDU (Protocol Data Unit)
This is basically what we call packet
each layer has a different PDU
Standard Protocol Architectures
Common set of conventions
Nonstandard vs. standard protocols
Nonstandard: K sources and L receivers lead to K*L different protocols
If common protocol used, we design only once
Products from different vendors interoperate
If a common standard is not implemented in a product, then that product’s market is limited; customers like standard products
Customers do not stick to a specific vendor
OSI - The Layer Model
Each layer performs a subset of the required communication functions
Each layer relies on the next lower layer to perform more primitive functions
Each layer provides services to the next higher layer
Changes in one layer should not require changes in other layers
TCP/IP Protocol Suite
Most widely used interoperable network protocol architecture
Specified and extensively used before OSI
OSI was slow to take place in the market
Funded by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)
DoD automatically created an enormous market for TCP/IP
Used by the Internet and WWW
Internet Standards Track
Steps involve increasing amount of scrutiny and testing
Step 1: Internet Draft
Step 2: Proposed standard
Internet Draft approved as an RFC by IESG
must remain at least six months to advance
Step 3: Draft standard
at least two independent and interoperable implementations
must remain at least 4 months
Step 4: Internet standard
Significant operational experience
key difference between ISOC and others
consensus
Internet Assigned Numbers Authority (IANA)
An ISOC entity responsible for all “unique numbers” on the Internet
including IP addresses
Almost all protocols work with numeric parameters
e.g. port numbers, error codes, status codes, message types, options, etc.
the meanings of all numeric codes are mostly specified in RFCs, but number assignment is formalized by IANA