Answer to Question #90187 in Computer Networks for Shivam Nishad

Question

Compare the OSI and TCP/IP reference models in computer networks.

Answer 1

OSI and TCP/IP models

In 1982 the International Organization for Standardization (International Organization for Standardization, ISO) with the assistance of ITU-T began the new project in the field of network technologies which was called Open System Intercommunication (OSI). This model is the first shaking to the international standardization of the protocols used at various levels (Day and Zimmerman, 1983). Then it was reconsidered in 1995 (Day, 1995). The interaction which can be supported in the non-uniform environments containing systems of different suppliers is called open. The OSI model establishes the global standard defining the structure of functional levels at open interaction between computers.

The OSI and TCP models have many common features. Both models are based on the concept of a stack of independent protocols. The functionality of levels is also in many respects similar. For example, in each model levels, starting with transport above, provide the through, not depending on network transport service for the processes wishing to communicate. These levels form the supplier of transport. Also in each model levels are higher transport are applied consumers of transport service. 

Application level

Provides transformation of the data specific to each appendix. Is responsible for access of appendices to network.

Protocols

HTTP, Gopher, Telnet, DNS, SMTP, SNMP, CMIP, FTP, TFTP, SSH, IRC, AIM, NFS, NNTP, NTP, SNTP, XMPP, FTAM, APPC, X.400, X.500, AFP, LDAP, SIP, ITMS, Modbus TCP, BACnet IP, IMAP, POP3, SMB, MFTP, BitTorrent, eD2k, PROFIBUS

Presentation level

Carries out the transformation of data of the general character (coding, a compression, etc.) of the applied level to a flow of information for transport level. Is responsible for the possibility of dialogue between applications on different machines.

Protocols

HTTP, ASN.1, XML-RPC, TDI, XDR, SNMP, FTP, Telnet, SMTP, NCP, AFP

Session level

Adds transport function of the convenience of the address, operates dialogue throughout the established communication session. Is responsible for the organization of sessions of data exchange between terminal cars.

Protocols

ASP, ADSP, DLC, Named Pipes, NBT, NetBIOS, NWLink, Printer Access Protocol, Zone Information Protocol, SSL, TLS, SOCKS

Transport level

Carries out free from mistakes, the through transfer focused on work with messages. Divides flows of information into rather small fragments (packages) for transfer them on the network level.

Protocols

TCP, UDP, NetBEUI, AEP, ATP, IL, NBP, RTMP, SMB, SPX, SCTP, DCCP, RTP, TFTP

Network level

Provides routing, and management of loading of the channel of transfer provides the raw route of transfer consisting only of final points. Is responsible for the division of users into groups. At this level, there is a routing of packages on the basis of transformation of MAC addresses to network addresses. Network level provides also the transparent transfer of packages on the transport level.

Protocols

IP, IPv6, ICMP, IGMP, IPX, NWLink, NetBEUI, DDP, IPSec, ARP, RARP, DHCP, BootP, SKIP, RIP

Datalink level

Carries out the transfer, free from mistakes, on a separate communication channel. Provides creation, transfer, and reception of frames of data. This level serves inquiries of network level and uses service of physical level for reception and transfer of packages. The IEEE 802.x specifications divide channel level into two subtotals: management of logical channel (LLC) and management of access to the environment (MAC). LLC provides service of a network level, and the subtotal of MAC regulates access to the divided physical environment.

Protocols

ARCnet, ATM, DTM, SLIP, SMDS, Ethernet, FDDI, Frame Relay, LocalTalk, Token ring, StarLan, WiFi, L2F, L2TP, PPTP, PPP, PPPoE, PROFIBUS, STP

Physical level

Carries out the real physical transfer of bits of data. Receives packages of data from overlying channel level and will transform them into optical or electric signals, the corresponding 0 and 1 binary streams. These signals are sent through the transfer environment to reception knot. Mechanical and electric/optical properties of the environment of transfer are defined at the physical level and include:

Type of cables and sockets

·        Distributing of contacts in sockets

·        The encoding scheme of signals for values 0 and 1

Protocols

RS-232, RS-422, RS-423, RS-449, RS-485, ITU-T, xDSL, ISDN, T-carrier (T1, E1), модификации стандарта Ethernet: 10BASE-T, 10BASE2, 10BASE5, 100BASE-T (включает 100BASE-TX, 100BASE-T4, 100BASE-FX), 1000BASE-T, 1000BASE-TX, 1000BASE-SX

TCP/IP Stack

The TCP/IP model is called also the DARPA model (reduction from Defense Advanced Research Projects Agency, the organization in which network projects were developed in due time, including the TCP/IP protocol and which stood at the origins of the Internet) or model of the Ministry of Defence of the USA (the model DoD, Department of Defense, the DARPA project worked by request of this department).

The TCP/IP model was developed for the description of a stack of protocols of TCP/IP (Transmission Control Protocol/Internet Protocol). It was developed much earlier, than the OSI model – in 1970 a necessary set of standards was developed and by 1978 the fact that today we call TCP/IP was finally issued. Later the stack was adapted for use in local networks. At the beginning of 1980, the protocol became a UNIX OS component. The same year there was a joint network Internet.

Stack of protocols of TCP/IP — a set of network protocols on which the Internet is based. Usually, in TCP/IP stack, the OSI models unite the top 3 levels (applied, representative and session) in one — applied. As the unified protocol of data transmission is not provided in such stack, functions by definition like data are transferred to the appendix.

Unlike the reference OSI model, the TCP/IP model more is guided by ensuring network interactions, than by rigid division of functional levels. For this purpose, she recognizes the importance of the hierarchical structure of functions but provides to designers of protocols sufficient flexibility in realization. Respectively, the reference OSI model is suitable for an explanation of the mechanics of intercomputer interactions much better, but the TCP/IP protocol became the main gateway protocol.