Download CS578 IT Architecture

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)
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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
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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:
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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)