2. Reasons to use Layers Easier to understand the different tasks of data communication Easier to replace only one part of the whole data communication task stack (BNC / UTP / Fiber / Radio) Easier to study all the roles of data communication (Cisco says) rroosend@xs4all.nl 2
3. Different Models OSI Model Developed by Open Systems Interconnection (OSI) 7 Layers Theoretical base rroosend@xs4all.nl 3 TCP/IP Model De-facto Model developed by DARPA for millitairy computer networks 4 Layers Practical base
18. The Presentation Layer (OSI) Establishes context between Application Layer entities Different syntax and semantics Independence from differences in data representation Transforms data into form that application layer accept Examples: Convert EBCDIC-coded file to ASCII-coded file Serializes objects and other data structures from and to XML rroosend@xs4all.nl 6
19. The Session Layer (OSI) Controls the connections between computers Full-duplex, half-duplex, or simplex operation Checkpointing, adjournment, termination, and restart procedures Graceful close of sessions Implemented explicitly in application environments that use remote procedure calls rroosend@xs4all.nl 7
20. The Transport Layer (OSI) Reliable data transfer services to the upper layers using flow control, segmentation/desegmentation, error control, windowing Five classes of connection-mode transport protocols Class/TP 0 for less reliable to class/TP 4 for most reliable rroosend@xs4all.nl 8
21. The Network Layer (OSI) Functional and procedural means of transferring variable length data sequences Performs network routing functions. Routers operate at this layer using a logical addressing scheme Layer management protocols (ISO 7498/4) Routing protocols Multicast group management Network Layer information and error Network Layer address assignment rroosend@xs4all.nl 9
22. The Data Link Layer (OSI) Functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical Layer Point-to-Point Protocol (PPP) Manages the interaction of devices with a shared medium (Media Access Control sublayer) Manages addressing and multiplexing on multiaccess media (Logical Link Control sublayer) rroosend@xs4all.nl 10
23. The Physical Layer (OSI) Electrical and physical specifications for devices (layout of pins, voltages, cable specifications) Establishment and termination of a connection to a communications medium. Modulation from and to the signals transmitted over a communications channel (coper, fiber, radio, …). Ethernet incorporates both this layer and the Data Link Layer. rroosend@xs4all.nl 11
25. The Application Layer (TCP/IP) Roughly equivalent to the OSI Application, Presentation and Session layers Support the applications and utilities that are the Internet Focuses on network services, APIs, utilities, and operating system environments Examples: DHCP, DNS, HTTP, IRC, POP, SMTP, SSH rroosend@xs4all.nl 13
26. The Transport Layer (TCP/IP) Roughly equivalent to the OSI Transport layer Port identifier in TCP/UDP messages Port identifier and IP address together form a socket Uniquely identified on the Internet by the four-tuplesource port and address, destination port and address TCP provides connection-oriented communication UDP provides connectionless communication rroosend@xs4all.nl 14
27. The Internet Layer (TCP/IP) Roughly equivalent to the OSI Network Layer Provides connectionless transport service across the network Does not provide a mechanism for flow control Examples: IP (IPv4, IPv6), ICMP, ICMPv6, IPsec rroosend@xs4all.nl 15
28. The Network Interface Layer (TCP/IP) Roughly equivalent to the OSI Data Link and Physical Layers Operates over nearly any underlying local or wide area network technology Particularly relevant: The Serial Line Internet Protocol (SLIP, RFC 1055) Point-to-Point Protocol (PPP, RFC 1661) Examples: ARP, RARP, SLIP, PPP, MAC rroosend@xs4all.nl 16
29. TCP/IP versus OSI TCP/IP OSI rroosend@xs4all.nl 17 Application Application Presentation Session Transport Transport Network Internet Network Interface Data Link Physical
