Data Networks Sharing data through the use of floppy disks is not an efficient or cost-effective manner in which to operate businesses. Sneakernet created multiple copies of the data. Businesses needed a solution that would successfully address the following three problems: • How to avoid duplication of equipment and resources • How to communicate efficiently • How to set up and manage a network Businesses realized that networking technology could increase productivity while saving money.
LANs, MANs, & WANs One early solution was the creation of local-area network (LAN) standards which provided an open set of guidelines for creating network hardware and software, making equipment from different companies compatible. What was needed was a way for information to move efficiently and quickly, not only within a company, but also from one business to another. The solution was the creation of metropolitan-area networks (MANs) and wide-area networks (WANs).
WAN Network Structure WAN is a network of LANs It consists of: • network edge: applications and hosts connected by LANs • network core: Switching nodes (e.g. routers, ATM switches) network of networks • access networks, physical media: Communication links to connect SN
LANs and WANs
Connection of LANs over a large geographical distance
The Internet is the biggest commercial WAN DS3 (45 Mbps) OC3 (155 Mbps) OC12 (622 Mbps) OC48 (2.4 Gbps)
Sprint US backbone network Seattle Tacoma
POP: point-of-presence
to/from backbone Stockton
…
… Kansas City . …
Anaheim
peering
… …
San Jose
Cheyenne
New York Pennsauken Relay Wash. DC
Chicago Roachdale
Atlanta
to/from customers Fort Worth Orlando
Examples of Data Networks
Network History 1940s 1947 1950s late 1960-70s 1977 1981 1984 mid-1980s mid-1980s 1960s-1990.
large, unreliable electromechanical computers the invention of a semiconductor transistor smaller, more reliable computers. mainframe computers; run by punched card programs smaller minicomputers Apple Computer Company introduced the microcomputer IBM introduced its first personal computer. The user-friendly Mac Users with started to share files using modems This was “dial-up” or a “point-to-point” connection. Users would connect to the bulletin boards, leave and pick up messages, as well as upload and download files. Department of Defense (DoD) developed large, reliable, WANs for military and scientific reasons. Instead of only being able to communicate with one other computer many computers could be reached using the same connection.
The DoDs WAN eventually became the Internet.
Networking Components •Devices •Topology •Messages •Protocol •Media
1- Networking Devices Equipment that connects directly to a network segment is referred to as a device. These devices are broken up into two classifications. • end-user devices • network devices End-user devices include computers, printers, scanners, and other devices that provide services directly to the user. Network devices include all the devices that connect the enduser devices together to allow them to communicate. Each individual NIC carries a unique code, called a Media Access Control (MAC) address.
Networking Addresses The addresses are divided into: Physical addresses: is the machine address called Media Access Control (MAC) address. It is a 6 octet hexadecimal number. (ex: 2A:3E:14:23:1C:87) Network addresses: is the LAN address called internet protocol (IP) address. It is a 4 dotted decimal number. (ex: 121.13.0.0) . Application addresses: is the application address called port address. It is a decimal number. Well Known Ports (0 to 1023): (ex: HTTP server port 80) Registered Ports (1024 to 49151): these are usually assigned to applications that a user has chosen to install Dynamic or Private Ports (49152 to 65535): these are assigned dynamically to client applications
Networking Device Icons
LANs
WANs
Repeater A repeater is a network device used to regenerate a signal. Repeaters regenerate analog or digital signals distorted by transmission loss due to attenuation. A repeater does not perform intelligent routing like a bridge or router.
Hub Hubs concentrate connections. In other words, they take a group of hosts and allow the network to see them as a single unit. This is done passively, without any other effect on the data transmission. Active hubs not only concentrate hosts, but they also regenerate signals.
Bridge Bridges convert network transmission data formats as well as perform basic data transmission management. Bridges, as the name implies, provide connections between LANs. Not only do bridges connect LANs, but they also perform a check on the data to determine whether it should cross the bridge or not. This makes each part of the network more efficient.
Workgroup Switch Workgroup switches add more intelligence to data transfer management. Not only can they determine whether data should remain on a LAN or not, but they can transfer the data only to the connection that needs that data. Another difference between a bridge and switch is that a switch does not convert data transmission formats.
Router Routers have all the capabilities of the previous devices. Routers can regenerate signals, concentrate multiple connections, convert data transmission formats, and manage data transfers. They can also connect to a WAN, which allows them to connect LANs that are separated by great distances. None of the other devices can provide this type of connection.
“The Cloud� The cloud is used in diagrams to represent where the connection to the internet is. It also represents all of the devices on the internet.
2-Network Topologies Network topology defines the structure of the network. One part of the topology definition is the physical topology, which is the actual layout of the wire or media. The other part is the logical topology, which defines how the media is accessed by the hosts for sending data.
Physical Topologies
Bus Topology A bus topology uses a single backbone cable that is terminated at both ends. All the hosts connect directly to this backbone.
Ring Topology A ring topology connects one host to the next and the last host to the first. This creates a physical ring of cable.
Star Topology A star topology connects all cables to a central point of concentration.
Extended Star Topology An extended star topology links individual stars together by connecting the hubs and/or switches. This topology can extend the scope and coverage of the network.
Hierarchical Topology A hierarchical topology is similar to an extended star. However, instead of linking the hubs and/or switches together, the system is linked to a computer that controls the traffic on the topology.
Mesh Topology A mesh topology is implemented to provide as much protection as possible from interruption of service. Each host has its own connections to all other hosts. Although the Internet has multiple paths to any one location, it does not adopt the full mesh topology.
Logical Topologies The logical topology of a network is how the hosts communicate across the medium. The most common types of logical topologies are: Broadcast Unicast Multicast Token passing.
Unicast
Broadcast
Multicast
Token Passing Topology Token passing controls network access by passing an electronic token sequentially to each host. When a host receives the token, that host can send data on the network. If the host has no data to send, it passes the token to the next host and the process repeats itself. Two examples of networks that use token passing are Token Ring and Fiber Distributed Data Interface (FDDI).
3-Network Protocols Protocol suites are collections of protocols that enable network communication from one host through the network to another host. A protocol is a formal description of a set of rules and conventions that govern a particular aspect of how devices on a network communicate.
4-Messages Data on the internet is transferred in ASCII code
4-Messages A messsage “How are you� is transferred as?
4-Message Format
... ..
As A d s
L
... ..
Data
Payload
5-Media LAN media: •Wired: copper cables (twisted pair, coaxial,…) , optical cables. •Wireless: wireless LAN (WLAN) WAN media: •Wired: MPLS, Frame relay,…. •Wireless: 3G, WiMax
Bandwidth
Measuring Bandwidth
LAN Media
WAN Media
Throughput Throughput refers to actual measured bandwidth, at a specific time of day, using specific Internet routes, and while a specific set of data is transmitted on the network. Unfortunately throughput is often far less than the maximum possible digital bandwidth of the medium that is being used. The following are some of the factors that determine throughput: • • • • • • •
Internetworking devices Type of data being transferred Network topology Number of users on the network User computer Server computer Power conditions
Transfer Time Calculation
Why do we need the OSI Model? To address the problem of networks increasing in size and in number, the International Organization for Standardization (ISO) researched many network schemes and recognized that there was a need to create a network model that would help network builders implement networks that could communicate and work together and therefore, released the OSI reference model in 1984.
Don’t Get Confused. ISO - International Organization for Standardization OSI - Open System Interconnection IOS - Internetwork Operating System The ISO created the OSI to make the IOS more efficient. The “ISO” acronym is correct as shown. To avoid confusion, some people say “International Standard Organization.”
The OSI Reference Model 7 Application 6 Presentation 5 Session
The OSI Model will be used throughout your entire networking career!
4 Transport 3 Network 2 Data Link 1 Physical
Memorize it!
Layer 7 - The Application Layer 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
This layer deal with networking applications. Examples: • Email • Web browsers PDU – Protocol Data Unit (Application Data)
Layer 6 - The Presentation Layer 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
This layer is responsible for presenting the data in the required format which may include: • Encryption • Compression PDU - Formatted Data
Presentation Layer
• Text • Data ASCII EBCDIC Encrypted
• Sound • Video MIDI MPEG QuickTime
• Graphics • Visual Images TIFF JPEG GIF
Layer 5 - The Session Layer 7 Application 6 Presentation 5 Session 4 Transport
This layer establishes, manages, and terminates sessions between two communicating hosts.
2 Data Link
Example: • Client Software ( Used for logging in)
1 Physical
PDU - Formatted Data
3 Network
Session Layer
Service Request
Service Reply
Vocabulary of two processes
Layer 4 - The Transport Layer 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
This layer breaks up the data from the sending host and then reassembles it in the receiver. It also is used to insure reliable data transport across the network. PDU - Segments
Layer 3 - The Network Layer 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
Sometimes referred to as the “Cisco Layer”. Makes “Best Path Determination” decisions based on logical addresses (usually IP addresses). PDU - Packets
3
Network Layer Path selection based on network addresses (e.g. IP addresses)
Segmentation and reassembly Multiplexing of network connections (block formation)
Error detection and possibly correction
Possibly flow control at network level
Network Layer
Provision of the “best“ route
Layer 2 - The Data Link Layer 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
This layer provides reliable transit of data across a physical link. Makes decisions based on physical addresses (usually MAC addresses). PDU - Frames
Layer 1 - The Physical Layer 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
This is the physical media through which the data, represented as electronic signals, is sent from the source host to the destination host. Examples: • CAT5 (what we have) • Coaxial (like cable TV) • Fiber optic PDU - Bits
Host Layers 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
These layers only exist in the source and destination host computers.
Media Layers 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical
These layers manage the information out in the LAN or WAN between the source and destination hosts.
Why Another Model? Although the OSI reference model is universally recognized, the historical and technical open standard of the Internet is Transmission Control Protocol / Internet Protocol (TCP/IP). The TCP/IP reference model and the TCP/IP protocol stack make data communication possible between any two computers, anywhere in the world, at nearly the speed of light. The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions, even a nuclear war.
2 Models Side-By-Side 7 Application 6 Presentation
Application
5 Session 4 Transport
Transport
3 Network
Internet
2 Data Link
Network Access
1 Physical
IEEE 802.3
RTP
ICMP
IP
IEEE 802.4
SNMP
UDP
ARP
IEEE 802.2
BOOTP/ DHCP
TFTP
DNS
LDAP
WWW
IMAP
POP3
SMTP
RLOGIN
Telnet
FTP
TCP
IEEE 802.5
FDDI
ATM
Frame Relay
X.25
PPP
noi t aci nu mmo Cl aci t r e V
Computer 1
Computer 2
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Application
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Presentation
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Session
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Session
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Transport
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Transport
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Network
3
Network
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Data Link
2
Data Link
1
Physical
1
Physical
Horizontal Communication
Concept of Encapsulation Receive
Send Layer n+1 n+1 Header
n+1 Header
n + 1 Data
n + 1 Data
Layer n n Header
n Data
n Header
n Data
Encapsulation through TCP/IP layers
Sending and Receiving Data in the Layer Model Receive
Send Data
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Data
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Data
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Data
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Horizontal / Virtual Communication in the Layer Model Receive
Send
Virtual Communication: Layer 3 can communicate with Layer 3. The exchange of information takes place in the respective header.
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Data
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Data
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Daten
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SANs A SAN is a dedicated, highperformance network used to move data between servers and storage resources. Because it is a separate, dedicated network, it avoids any traffic conflict between clients and servers. This method uses a separate network infrastructure that relieves any problems associated with existing network connectivity.
Virtual Private Network A VPN is a private network that is constructed within a public network infrastructure such as the global Internet. Using VPN, a telecommuter can access the network of the company headquarters through the Internet by building a secure tunnel between the telecommuter’s PC and a VPN router in the headquarters.
3 Types of VPNs Access VPNs – Access VPNs provide remote access to a mobile worker and small office/home office (SOHO) to the headquarters of the Intranet or Extranet over a shared infrastructure. Intranet VPNs – Intranet VPNs link regional and remote offices to the headquarters of the internal network over a shared infrastructure. Intranet VPNs differ from Extranet VPNs in that they allow access only to the employees of the enterprise. Extranet VPNs – Extranet VPNs link business partners to the headquarters of the network over a shared infrastructure using dedicated connections.