OSI

1. OSI Jacek Ilow j.ilow@dal.ca OSI

2. Overview • Wide Area Networking and Telecommunications • Standard Organizations • OSI Model • WAN Technologies • Digital Telephony • QoS • Summary OSI

3. Wide Area Networks machines are spread over a wide geographical region comm channels are furnished by a third party (telephone company, public data networks) channels are of relatively low capacity (tens kbs) channels are error prone, BER=10 E-5 Local Area Networks machines are spread over a “small” geographical region comm channels are privatly owned channels are relatively high capacity (Mbs) channels are relatively error-free, BER=10 E-9 WANs and LANs OSI

4. The Telephone Network • The customer premise equipment • telephone handsets, modems, PBX • transmission facilities • the local (subscriber) loop and the trunk lines • switching facilities • the main function is to interconnect and route • local switching systems (central office) • tandem switches connect trunks to trunks • a toll switch that serves the long distance network OSI

5. Virtual Circuits vs Datagrams OSI

6. Packet vs. Circuit Switching • Packet switching allows multiple users to share data-network facilities and bandwidth, rather than providing specific amounts of dedicated bandwidth to each user. • Traffic passed by packed-switched networks is “bursty” and can be aggregated statisticall to maximize the use of on-demand bandwidth resources. • There is much more overhead associated with packet switching as compared to circuit switching. • Conncetionless character of packet switching in contradistinction to connection-oriented circuit switching allows routing around failed links, whereas in circuit switching the entire circuit would need to be switched OSI

7. Driving force for WAN • More powerful applications have an impact on human productivity • Bandwidth is becoming available to support these applications • Decreased costs to use this bandwidth • Increased computing power • Decreased costs of telecomputing will make gigabit-based applications cost effective OSI

8. Bandwidth requirements of different media types CIF Common Intermediate Format MPEG Moving Pictures Expert Group QCIF Quarter CIF JPEG Joint photographic experts group OSI

9. OSI

10. WAN Technologies • Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH) • a high-speed synchronous carrier system, based on the use of optical fiber technology and a defined digital multiplexing hierrarchy • Frame Relay • a fast relay service, with minimal network support offering bandwidth on demand • Wireless Systems • a wide array of wireless systems designed to support primarilly voice and low-speed data OSI

11. Broadband Signaling • a second-generation signaling technology (based on ISDN and SS7) used to setup and tear down virtual circuits • Asynchronous Transfer Mode • a high speed virtual circuit with cell relay technology • Residential Broadband • video on demand, client-server applications, Internet browsing on the local loop OSI

12. Standards • Standards are required to govern • the physical • electrical • procedural characteristics of communication equipment • The principal disadvantage of standards is that they tend to freeze technology • Standards and Regulation • Voluntary standards (CCITT and OSI) • Regulatory standards (FCC and Industry Canada) • Regulatory use of voluntary standards OSI

13. Terms of Reference • Telecommunications • the technology of communication-at-a-distancethat permits information to be created anywhere and used everywhere • Communication • the transfer of information according to agreed conventions • Standard • a prescribed set of rules, conditions, or requirements concerning definition of terms; classification of components; specification of materials, performance, or operations; delineation of procedures; or measurement of quality describing products and materials • Communication network • set of devices, mechanisms, and procedures by which end-user equipment attached to the network can exchange meaningful information OSI

14. OSI Standard • provides conceptual and functional framework which allows international teams of experts to work productively and independently on standards for each layer of the Ref Model • Bearer services • means to convey information between users without alteration of the content of the message • Connection • a concatenation of transmission channels or telecommunication circuits, switching and other functional units set up to provide for the transfer of signals between two or more points in a telecommunication network, to support a single communication OSI

15. Standards Organizations • CCITT - International Telegraph and Telephone Consultive Committee • committee of the International Telecommunications Union (ITU) which itself is a United Nations treaty organization • Study groups:Network organization; Tariff and accounting principles; Data communications networks; Terminals for telematic services; Switching and signaling; Transmission performance of telephone network and terminals; Transmission systems and equipment; Data transmission over the telephone network; ISDN • As of 1993, CCITT is ITU-TSS (Telecommuni-cation Standardization Sector) in Geneva OSI

16. IOS - International Organization for Standardization • international agancy for the development of standards on the wide range of subject • voluntary, non-treaty organization whose members are designated bodies of participating nations • CCITT has primarily been concerned with data transmission and communication network issues • the lower three layers of the OSI architecture. • ISO has traditionally been concerned with computer communications and distributed processing issues, • layers 4 through 7. • The merger of the fields of data processing and data communications has resulted in considerable overlap in the areas of concern of these two organizations. OSI

17. Communications Architecture • A communications architecture is a structured set of software modules that implement the communications function. • The model provides a framework within which standards at each layer can be developed systematically and in parallel. • Communications standards assure a large market and therefore promote lower costs through competition and mass production. • Standards promote interoperability; that is, standards promote the ability for products from different vendors to work together. Interoperability gives purchasers more flexibility in equipment selection and promotes distributed applications between and among different organizations. OSI

18. OSI Reference Model Application Presentation Session Transport Network Data Link Physical AH User Data PH AH User Data SH PH AH User Data TH SH PH AH User Data NH TH SH PH AH User Data LH NH TH SH PH AH User Data LT LH NH TH SH PH AH User Data LT OSI

19. OSI Reference Model.. Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical Service to layer (N+1) Protocol with peer layer (N) Layer (N) Service to layer (N-1) Comm Path OSI

20. OSI Network Service • Independence of the underlying communications facility: • Network users need not be aware of the details of the subnetwork facilities used. • End-to-end transfer: • All routing and relaying are performed by the network-service provider and are not of concern to the network-service user. • Transparency: • The network service does not restrict the content, format, or coding of user data. OSI

21. OSI Network Service... • Quality of service selection: • The network-service user has some ability to request a given quality of service. • User addressing: • A system of addressing (NSAP addressing) is used that allows network-service users to refer unambiguously to one another. • The essential requirement for internetworking is that the two communicating end users are presented with the same network service; that is, they employ the same set of network-service primitives and parameters. OSI