- layered networks in the abstract
- TCP/IP reference model
- OSI modle minus physical medium is based on proposal developed by ISO (International Standards Organization)
- OSI model
- seven layers
- a layer should be created where a different abstraction is needed
- each layer should perform a well defined function
- function should be chosen to define international standards
- layer boundaries chosen to minimize information flow across interfaces
- number of layers large enough that distinct functions don't need to be thrown together in same layer, small enough that architecture isn't unwieldy
- Physical Layer
- transmit of raw bits over communication channel
- 1,0 bit communication
- electrical signals, how connection established, how connections torn down
- pins network connector has
- mechanical electrical and timing interfaces
- Data Link Layer
- raw transmission into a line free of undetected transmission errors
- mask real errors so network layer doesn't see them
- data frames
- send back acknowledgement frame
- special sublayer of data link layer
- MAC (Medium Access Control) sublayer
- Network Layer
- controls operation of subnet
- determine how packets are routed from source to destination
- routes based on tables, updatable to reflect machines
- handling congestion
- quality of service
- delay
- transmit time
- jitter
- broadcast networks, routing is simple so this layer is thin for that system
- Transport Layer
- Accept data from above it
- split into smaller units
- determines type of service to provide to session layer
- error free point to point channel is most popular
- type of service determined when connection established
- end to end layer, carries data from source to destination
- Session Layer
- establish sessions
- dialog control keep track of whose turn it is to transmit
- token management prevent parties from attempting same operatio simultaneously
- synchronization
- Presentation layer
- concerned with syntax and semantics of information transmitted
- manages abstract data structures
- allows for higher level data structures to be defined
- Application Layer
- HTTP(hyper text transfer protocol)
- variety of protocols for users
- e-mail, file transfer, network news
- TCP/IP used in ARPANET
- ARPANET was a research network sponsored by the department of defense
- used to connect multiple networks seamlessly
- survive loss of subnet hardware
- survive as long as source/destination functioning
- The Link Layer
- packet switching network
- serial lines
- interface between hosts and transmission links
- Internet Layer
- corresponds roughly to OSI Network layer
- permit hosts to inject packets into any network and travel independently to destination
- may arrive out of order
- snail mail equivalent
- defines official packet format and protocol called IP(Internet Protocol)
- ICMP(Internet Control Message Protocol)
- helps function
- Transport Layer
- layer above the internet layer in TCP/IP
- allow peer entities on source and destination to carry out a conversation
- two end to end transport protocols have been defined here
- TCP
- Transmission Control Protocol
- connection oriented
- byte stream delivered without error to other machine
- reassembles received messages into output stream
- UDP
- User Datagram Protocol
- unreliable connectionless protocol
- one shot client server request reply queries
- used for prompt delivery over accuracy
- speech or video
- The Application Layer
- does not have session or presentation layers
- applications includes the above
- all higher level protocols
- TELNET
- virtual terminal
- FTP
- File transfer protocol
- SMTP
- simple mail protocol
- OSI strength is the model itself used for discussion
- TCP/IP is used as the protocols
- hybrid scheme
- Application
- contains programs
- Transport
- transmit
- Network
- how to combine multiple links into networks
- how to find paths
- Link
- how to send finite length messages
- Physical
- how to transmit bits
- Both are based on the concept of a stack of independent protocols
- functionality roughly similar
- OSI
- differentiation is explicit
- Services
- performs services for layer above it
- defines semantics
- Interfaces
- tells process how to access
- Protocols
- used in a layer and is the layer's own business
- fits with object oriented style programming
- devised before protocols invented, so extremely general
- convergence sublayers have to be grafted on to account for network differences
- supports connection oriented/connectionless
- TCP/IP
- does not distinguish
- have been modeled to make it similar to OSI
- protocols came first model defined afterwards, easy fit
- not useful in describing non TCP/IP networks
- supports connectionless in network, both in transport layer
- Bad Timing
- time of standardization is crucial
- in between research and investment
- TCP/IP already in use by universities by the time OSI appeared
- universities/companies did not want to support
- Bad Technology
- model and protocols are flawed
- very complex
- functions repeated
- Bad Implementation
- complexity means implementations large unwieldy and slow
- OSI associated with poor quality
- TCP/IP was good and free from Berkeley, large user communities/improvements
- Bad Politics
- TCP/IP was seen as part of UNIX
- OSI seen as government control
- Models don't distinguish specifications/implementations
- not much of a guide for design
- not general
- link layer is not really a layer, just an interface
- does not distinguish physical and data layers
- Many protocols ad hoc and distributed free
- TELNET designed for 10 character per second mechanical teletype terminal no gui or mice
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