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Transcript
CS578 IT Architecture Lecture 15, April 25, 2002, Spring 2002 Lecture 16, April 29, 2003, Spring 2003 Infrastructure Architecture Open Systems Interconnection (OSI) Reference Shafay Shamail, Ph.D. Associate Professor Lahore University of Management Science Infrastructure Architecture Lecture 15 April 25, 2002 OSI Reference Model • The OSI Reference Model describes seven layers of related functions that are needed at each end when a message is sent from one party to another party in a network. • An existing network product or program can be described in part by where it fits into this layered structure. • For example, TCP/IP is usually packaged with other Internet programs as a suite of products that support communication over the Internet. • This suite includes the File Transfer Protocol (FTP), Telnet, the Hypertext Transfer Protocol (HTTP), e-mail protocols, and sometimes others. • Although TCP fits well into the Transport layer of OSI and IP into the Network layer, the other programs fit rather loosely (but not neatly within a layer) into the Session, Presentation, and Application layers. Application Layer • Makes sure that the other party is identified and can be reached • If appropriate, authenticates either the message sender or receiver or both • Makes sure that necessary communication resources exist (for example, is there a modem in the sender's computer?) • Ensures agreement at both ends about error recovery procedures, data integrity, and privacy • Determines protocol and data syntax rules at the application level Presentation Layer • Programs in the presentation layer address three aspects of presentation: • Data formats - for example, Postscript, ASCII, or binary formats • Compatibility with the host operating system • Encapsulation of data into message "envelopes" for transmission through the network Session Layer • The Session layer (sometimes called the "port layer") manages the setting up and taking down of the association between two communicating end points that is called a connection. • A connection is maintained while the two end points are communicating back and forth in a conversation or session of some duration. • Some connections and sessions last only long enough to send a message in one direction. However, other sessions may last longer, usually with one or both of the communicating parties able to terminate it • For Internet applications, each session is related to a particular port, a number that is associated with a particular upper layer application. For example, the HTTP program or daemon always has port number 80. Transport Layer • The Transport layer ensures the reliable arrival of messages and provides error checking mechanisms and data flow controls. • The Transport layer provides services for both "connection-mode" transmissions and for "connectionless-mode" transmissions. • For connection-mode transmissions, a transmission may be sent or arrive in the form of packets that need to be reconstructed into a complete message at the other end. Network Layer • The Network layer knows the address of the neighboring nodes in the network, packages output with the correct network address information, selects routes and Quality of Service, and recognizes and forwards to the Transport layer incoming messages for local host domains. • Among existing protocol that generally map to the OSI network layer are the Internet Protocol (IP) part of TCP/IP and NetWare IPX/SPX. Both IP Version 4 and IP Version 6 (IPv6) map to the OSI network layer. Data Link Layer • The Data-Link layer is the protocol layer in a program that handles the moving of data in and out across a physical link in a network. The Data-Link layer is layer 2 in the Open Systems Interconnect (OSI) model for a set of telecommunication protocols. The Data-Link layer contains two sublayers that are described in the IEEE-802 LAN standards: – Media Access Control (MAC) – Logical Link Control (LLC) • The Data-Link layer ensures that an initial connection has been set up, divides output data into data frames, and handles the acknowledgements from a receiver that the data arrived successfully. It also ensures that incoming data has been received successfully by analyzing bit patterns at special places in the frames. Physical Layer • The physical layer supports the electrical or mechanical interface to the physical medium. • For example, this layer determines how to put a stream of bits from the upper (data link) layer on to the pins for a parallel printer interface, an optical fiber transmitter, or a radio carrier. • The physical layer is usually a combination of software and hardware programming and may include electromechanical devices. It does not include the physical media as such. ISDN • ISDN (Integrated Services Digital Network) • is a set of CCITT/ITU standards for digital transmission over ordinary telephone copper wire as well as over other media. • Home and business users who install an ISDN adapter (in place of a modem) can see highly-graphic Web pages arriving very quickly (up to 128 Kbps). • ISDN requires adapters at both ends of the transmission so your access provider also needs an ISDN adapter. • ISDN is generally available from your phone company in most urban areas in the United States and Europe. ATM • ATM (asynchronous transfer mode) • is a dedicated-connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. • Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the transmission path. • Because ATM is designed to be easily implemented by hardware (rather than software), faster processing and switch speeds are possible. • The prespecified bit rates are either 155.520 Mbps or 622.080 Mbps. Speeds on ATM networks can reach 10 Gbps. • Along with Synchronous Optical Network (SONET) and several other technologies, ATM is a key component of broadband ISDN (BISDN). • ATM also stands for automated teller machine, a machine that bank customers use to make transactions without a human teller. FDDI • FDDI (Fiber Distributed Data Interface) • is a set of ANSI and ISO standards for data transmission on fiber optic lines in a local area network (LAN) that can extend in range up to 200 km (124 miles). • The FDDI protocol is based on the token ring protocol. • In addition to being large geographically, an FDDI local area network can support thousands of users. • FDDI is frequently used on the backbone for a wide area network (WAN). • An FDDI network contains two token rings, one for possible backup in case the primary ring fails. • The primary ring offers up to 100 Mbps capacity. If the secondary ring is not needed for backup, it can also carry data, extending capacity to 200 Mbps. The single ring can extend the maximum distance; a dual ring can extend 100 km (62 miles). Category 1 – 5 • Categories of twisted pair cabling systems ANSI/EIA (American National Standards Institute/Electronic Industries Association) Standard 568 is one of several standards that specify "categories" (the singular is commonly referred to as "CAT") of twisted pair cabling systems (wires, junctions, and connectors) in terms of the data rates that they can sustain. The specifications describe the cable material as well as the types of connectors and junction blocks to be used in order to conform to a category. These categories are: Category Maximum data rate Usual application CAT 1 Less than 1 Mbps analog voice (POTS) Integrated Services Digital Network Basic Rate Interface in ISDN Doorbell wiring CAT 2 4 Mbps Mainly used in the IBM Cabling System for token ring networks CAT 3 16 Mbps Voice and data on 10BASE-T Ethernet CAT 4 20 Mbps Used in 16 Mbps Token Ring Otherwise not used much CAT 5 100 Mbps 1000 Mbps (4 pair) 100 Mbps TPDDI 155 Mbps ATM Gigabit Ethernet CAT 5E 100 Mbps 100 Mbps TPDDI 155 Mbps ATM CAT 6 200-250 MHz Super-fast broadband applications Category 1 - 5 • While longer connections for Gigabit Ethernet use optical fiber, the goal is to leverage the CAT 5 twisted-pair wiring most organizations already have in place for connections out to the desktop. (Four pairs of twisted pair are used.) • The two most popular specifications are CAT 3 and CAT 5. While the two cables may look identical, CAT 3 is tested to a lower set of specifications and can cause transmission errors if pushed to faster speeds. CAT 3 cabling is near-end crosstalkcertified for only a 16 MHz signal, while CAT 5 cable must pass a 100 MHz test. • The CAT 6 specification was not yet formally approved by the EIA as of March, 2001, although products are being offered that conform to a proposed specification. A CAT 7 specification is reportedly being considered. Coaxial Cable Coaxial Cable • Coaxial cable is the kind of copper cable used by cable TV companies between the community antenna and user homes and businesses. Coaxial cable is sometimes used by telephone companies from their central office to the telephone poles near users. It is also widely installed for use in business and corporation Ethernet and other types of local area network. • Coaxial cable is called "coaxial" because it includes one physical channel that carries the signal surrounded (after a layer of insulation) by another concentric physical channel, both running along the same axis. The outer channel serves as a ground. Many of these cables or pairs of coaxial tubes can be placed in a single outer sheathing and, with repeaters, can carry information for a great distance. • Coaxial cable was invented in 1929 and first used commercially in 1941. AT&T established its first cross-continental coaxial transmission system in 1940. Depending on the carrier technology used and other factors, twisted pair copper wire and optical fiber are alternatives to coaxial cable. RJ 45 RJ 45 Ethernet • Ethernet is the most widely-installed local area network (LAN) technology. • Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox and then developed further by Xerox, DEC, and Intel. • An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless LANs. • The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. • Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol. Fast Ethernet • Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. • Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second). 10-Gigabit Ethernet provides up to 10 billion bits per second. Point-to-Point Protocol (PPP) • • • • • • • • • PPP (Point-to-Point Protocol) is a protocol for communication between two computers using a serial interface, typically a personal computer connected by phone line to a server. For example, your Internet server provider may provide you with a PPP connection so that the provider's server can respond to your requests, pass them on to the Internet, and forward your requested Internet responses back to you. PPP uses the Internet protocol (IP) (and is designed to handle others). It is sometimes considered a member of the TCP/IP suite of protocols. Relative to the Open Systems Interconnection (OSI) reference model, PPP provides layer 2 (data-link layer) service. Essentially, it packages your computer's TCP/IP packets and forwards them to the server where they can actually be put on the Internet. PPP is a full-duplex protocol that can be used on various physical media, including twisted pair or fiber optic lines or satellite transmission. It uses a variation of High Speed Data Link Control (HDLC) for packet encapsulation. PPP is usually preferred over the earlier de facto standard Serial Line Internet Protocol (SLIP) because it can handle synchronous as well as asynchronous communication. PPP can share a line with other users and it has error detection that SLIP lacks. Where a choice is possible, PPP is preferred. LDAP • • • • • • • • • LDAP (Lightweight Directory Access Protocol) is a software protocol for enabling anyone to locate organizations, individuals, and other resources such as files and devices in a network, whether on the public Internet or on a corporate intranet. LDAP is a "lightweight" (smaller amount of code) version of Directory Access Protocol (DAP), which is part of X.500, a standard for directory services in a network. LDAP is lighter because in its initial version it did not include security features. LDAP originated at the University of Michigan and has been endorsed by at least 40 companies. Netscape includes it in its latest Communicator suite of products. Microsoft includes it as part of what it calls Active Directory in a number of products including Outlook Express. Novell's NetWare Directory Services interoperates with LDAP. Cisco also supports it in its networking products. In a network, a directory tells you where in the network something is located. On TCP/IP networks (including the Internet), the domain name system (DNS) is the directory system used to relate the domain name to a specific network address (a unique location on the network). However, you may not know the domain name. LDAP allows you to search for an individual without knowing where they're located (although additional information will help with the search). An LDAP directory is organized in a simple "tree" hierarchy consisting of the following levels: – – – – – The root directory (the starting place or the source of the tree), which branches out to Countries, each of which branches out to Organizations, which branch out to Organizational units (divisions, departments, and so forth), which branches out to (includes an entry for) Individuals (which includes people, files, and shared resources such as printers)