1. Network Fundamentals: Intro to Network Structure and Protocol LAN, WAN, TCP/IP
Chuong Huynh
National Center for
Biotechnology Information,
National Library of Medicine,
National Institute of Health
This is intended to be a very general overview of the concepts in computer networking and communication.
May 21, 2001

2. Outline Basic concepts in communications Understanding Networking.
Understanding Transmission Medium (Network Cables)
Understanding Network Hardware
WAN and LAN
Understanding Network Protocols
Potential topics:
TCP/IP and the Internet
TCP and UDP
Gateway and Routing Protocols
Telnet and FTP
TCP/IP Configuration
TCP/IP and Networks
Domain Name Service
Network File System

3. Basic Concepts in Communication

4. Basic Concepts
Communications – activity associated with distributing or exchanging information
Telecommunications – technology of communications at a distance that permits information to be created any where and used everywhere with little delay
Today it, involves
Data: digital and analog
Voice: spoken word
Video: telelcommunication imaging

5. Essentials for Communications
Must have a message
Message must have a transmitter
Message must have a medium
Message must be understood
Message must have some level of security
Source System
Destination System
Transmitter: modem
Transmission system: public telephone network
Receiver: modem
Destination: server
Source  Transmitter  Transmission  Receiver  Destination 1 2 3 4 5 6
Medium
Workstation/PC
Workstation/PC

6. Essentials for Communications
Text input information
Input data digital bit stream
Transmitted analog signal
Received analog signal
Output data digital bit stream
Text output information
Source System
Destination System
Transmitter: modem
Transmission system: public telephone network
Receiver: modem
Destination: server
Source  Transmitter  Transmission  Receiver  Destination 1 2 3 4 5 6
Medium
Workstation/PC
Workstation/PC

7. Data Communication Tasks
Data System Utilization
Addressing
Multiplexing Capacity Congestion Control
Interfacing
Routing
Router / Server / Media Control / Protocol
Signal Generation
Recovery
Repeater/Amplifier; Propagation; Interoperable
Synchronization
Messsage Formatting
Signal Begins & Ends
Exchange Management
Security
Nature and Timing of Signal
Error Detection & Correction
Network MGT
Signal Distortion Bit Error
Flow Control
Routing Delivery Error Feedback

8. Understanding Networking

9. Big Picture What do you see here for a typical network?
Network - A group of computers connected together in a way that allows information to be exchanged between the computers.
Node - Anything that is connected to the network. While a node is typically a computer, it can also be something like a printer or CD-ROM tower.
Segment - Any portion of a network that is separated, by a switch, bridge or router, from other parts of the network.
Backbone - The main cabling of a network that all of the segments connect to. Typically, the backbone is capable of carrying more information than the individual segments. For example, each segment may have a transfer rate of 10 Mbps (megabits per second: 1 million bits a second), while the backbone may operate at 100 Mbps.
Topology - The way that each node is physically connected to the network.

10. Key Network Terminology Explained (1)
Networks needs to interconnect at a distance by a form of point to point or point to multiple point connected media
A network is a group of computers connected together in such a way as to allow
Networks that are interconnected have proven to be low cost, reliable, and efficient means of communicating at a distance

11. Key Network Terminology Explained (2)
Node: anything connected to the network, usually a computer, but it could be a printer or a scanner
Segment: any portion of a network that is separated by a switch, bridge or a router from another part of a network.
Backbone: the main cabling of a network that all of the segment connect to. Usually, the backbone is capable of carrying more information than the individual segments.
Topology: The way each node is physically connected to the network
Backbone example: E.g. each segment may have a transfer rate of 10Mbps (megabits per second or 1 million bits a second) while the backbone may operate at 100Mbps
Network architecture 

12. Common Topologies - Bus
Bus: each node is daisy-chained (connected one right after the other) along the same backbone. Information sent from a node travels along the backbone until it reaches its destination node. Each end of a bus network must be terminated with a resistor to keep the

13. Common Topologies - Ring
Ring: Similar to a bus network, rings have nodes daisy chained, but the end of the network in a ring topology comes back around to the first node, creating a complete circuit. Each node takes a turn sending and receiving information through the use of a token. The token along with any data is sent from the first node to the second node which extracts the data addressed to it and adds any data it wishes to send. Then second node passes the token and data to the third node, etc. until it comes back around to the first node again. Only the node with the token is allowed to send data . All other nodes must wait for the token to come to them.
Similar to a bus network, rings have nodes daisy chained, but the end of the network in a ring topology comes back around to the first node, creating a complete circuit. Each node takes a turn sending and receiving information through the use of a token. The token along with any data is sent from the first node to the second node which extracts the data addressed to it and adds any data it wishes to send. Then second node passes the token and data to the third node, etc. until ti comes back around to the first node again. Only the node with the token is allowed to send data . All other nodes must wait for the token to come to them.

14. Common Topologies - Star
In a star network, each node is connected to a central device called a hub. The hub takes a signal that comes from any node and passes it along to all the other nodes in the network.
A hub does not perform any type of filtering or routing of the data.
A hub is a junction that joins all the different nodes together.
A hub does not perform any type of filtering or routing of the data. A hub is a junction that joins all the different nodes together.

15. Common Topologies - Star
In a star network, each node is connected to a central device called a hub. The hub takes a signal that comes from any node and passes it along to all the other nodes in the network.
A hub does not perform any type of filtering or routing of the data. A hub is a junction that joins all the different nodes together.

16. Common Topologies – Star Bus
Prob. Most common topology used today. Combines elements of the star and bus topologies to create a versatile network environment.
Nodes in particular areas are connected to hubs (and create star topology), and hubs are connected together along the network backbone (like a bus network).
Often you have stars nested within stars.

17. Other network topologies (architecture)
Some basic network topologies not previously mentioned:
One-to-one
Hierarchical
Hybrid
Client-server
Multiple nodes

18. Network Communication Devices
There are different communication devices such as routers, hub, switches and brides. These devices are required to transmit the data between one computer and another.  Based on the infrastructure of your network, you need to use different devices.  Hub and Switch are the LAN devices and the router is a LAN/WAN device.  These devices provide the medium of sending and receiving the data and connect the LAN and WAN segments of a network. 

19. Hubs
Hub is a LAN networking device and every computer in an Ethernet based network is directly connected with the hub. All the computers that are connected to the network share the same bandwidth.  When a hub receives the data packets at one of its port, it distributes the data signals to all the ports in a network.   

20. Bridges
Bridges are the networking devices that divided up the network into different segments to reduce the amount of traffic on each network.  A bridge blocks and forwards the data packets based on their MAC addressees.  Be blocking the unnecessary traffic to enter the other part of the network segments, it reduces the amount of traffic and the other issues such network congestions and the bottleneck.  There are following three common types of the bridges.

21. Switches
A network switch is a LAN/WAN communication device. It joins the multiple computers together in the LAN and WAN.  In the LAN, the switches do not broadcast the data to all the connected computers like the hub.  Based on the IP/MAC addresses of the computer, a switch sends data only to the destined computer.  Switches operate on the data link and network layers of the OSI layers model.  Different models of the switches support the different number of the connected devices.  In the LAN, switches support 10mbps 10/100 mbps or 100mbps data transmission speed.  A switch conserves the bandwidth and offers the grater performance than the hub.

22. Routers
A router is a networking device that is used to connect the two or more logically and physically different networks.  On the internet, the routers plays the functions of sorting and distribution of the data packets based on the IP addresses of the destination router or computer.  Router use the header and forwarding table to choose the best shortest path to transmit the data towards the destination. A router is used to connect the two LANs, two WANs, and LAN with WAN and a LAN with the ISP network. Router uses the ISDN, frame relay, ATM and other communication technologies. A router operates at the network layer of the OSI model.

23. Key Network Terminology Explained (3)
Simplex: information flows in only one direction
Half-duplex: information flows in two directions, but only in one direction at a time.
Full-duplex: information flows in two directions at the same time

24. Basic Signal Terminologies
Bit: binary digit, either 0 or 1
Baud (don’t really use anymore; not accurate) = one electronic state change per second
Bit rate – a method for measuring data transmission speed – bits per second
Mbps – millions of bits per second (data speed; measure of bandwidth = total information flow over a given time) on a telecommunication medium
8 bits = 1 byte
Mb – million bits (quantity of data)
MB – million bytes (quantity of data)
Gbps – Billion bits per second (data speed)
Teraflops – trillion operations per second
Kilo K 2^10
Mega M 2^20
Giga G 2^30
Tera T 2^40
Peta P 2^50
Exa E 2^60
Zetta Z 2^70
Yotta Y 2^80
Baud – don’t use; a single state change can involve more than a single bit of data

25. Data Transmission Successful transmission of data depends on:
The quality of the signal being transmitted
Characteristics of the transmission medium
Data rate – bits per second in data communications
Bandwidth – bandwidth or signal is constrained by the transmitter and the nature of the transmission in cycles per second or hertz
Noise – Average level of noise over the communication path.
Error rate – rate at which errors occur where error in 1 or 0 bit occurs
 we will talk about network cables next

26. Understanding Transmission Medium

27. Basic transmission medium concepts
Medium is the physical path between transmitter and receiver in a data transmission system
Guided Medium: waves are guided along a solid medium path (twisted pair, coaxial cable, and optical fiber).
Unguided medium: waves are propagated through the atmosphere and inner/outerspace (satellite, laser, and wireless transmissions).

28. Medium examples by type
Conductive: twisted pairs and coaxial cables
Electromagnetic: microwave
Light: lasers and optical fibers (need clear line of sight)
Wireless – inner/outerspace; satellite (omnidirectional  security issues)

29. Coaxial cable (1)
Widely installed for use in business and corporation ethernet and other types of LANs.
Consists of inter copper insulator covered by cladding material, and then covered by an outer jacket
Physical Descriptions:
 Inner conductor is solid copper metal
 Separated by insulating material
 Outer conductor is braided shielded (ground)
 Covered by sheath material

30. Coaxial cable (2) Applications: Transmission characteristics:
TV distribution (cable tv); long distance telephone transmission; short run computer system links
Local area networks
Transmission characteristics:
Can transmit analog and digital signals
Usable spectrum for analog signaling is about 400 Mhz
Amplifier needed for analog signals for less than 1 Km and less distance for higher frequency
Repeater needed for digital signals every Km or less distance for higher data rates
Operation of 100’s Mb/s over 1 Km.

31. Twisted Pair Cables Physical description: Application:
Each wire with copper conductor
Separately insulated wires
Twisted together to reduce cross talk
Often bundled into cables of two or four twisted pairs
If enclosed in a sheath then is shielded twisted pair (STP) otherwise often for home usage unshielded twisted pair (UTP). Must be shield from voltage lines
Application:
Common in building for digital signaling used at speed of 10’s Mb/s (CAT3) and 100Mb/s (CAT5) over 100s meters.
Common for telephone interconnection at home and office buildings
Less expensive medium; limited in distance, bandwidth, and data rate.

32. Categories of Twisted Pairs Cabling System
Category
Maximum data rate
Usual application
CAT 1
Less than 1 Mbps
analog voice (plain old telephone service) 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 (certify 16Mhz signal)
CAT 4
20 Mbps
Used in 16Mbps Token Ring
Otherwise not used much
CAT 5
100 Mbps
100 Mbps TPDDI
155 Mbps asynchronous transfer mode (certify 100 Mhz signal)
Specs describe cable
Material, type of
Connectors, and
Junction blocks to
Conform to a category
CAT 5 is currently under consideration to be incorporated into the Gigabit Ethernet specification for short distance wiring. While longer connections using 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.

33. Optical Fibers (1) Physical Description: Applications:
Glass or plastic core of optical fiber = 2to125 µm
Cladding is an insulating material
Jacket is a protective cover
Laser or light emitting diode provides transmission light source
Applications:
Long distance telecommunication
Greater capacity; 2 Gb/s over 10’s of Km
Smaller size and lighter weight
Lower attenuation (reduction in strength of signal)
Electromagnetic isolation – not effected by external electromagnetic environment. Aka more privacy
Greater repeater spacing – fewer repeaters, reduces line regeneration cost
Use of optical fibers over ;
Optical fiber (or "fiber optic") refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire or fiber. Optical fiber carries much more information than conventional copper wire and is in general not subject to electromagnetic interference and the need to retransmit signals. Most telephone company long-distance lines are now of optical fiber.
Transmission on optical fiber wire requires repeater at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have optical fiber wires or cables from the phone company's branch office to local customers (known as local loop).
single mode fiber fiber is used for longer distances; multimode fiber fiber is used for shorter distances.
Repeaters 

34. Optical Fibers (2)
multimode fiber is optical fiber that is designed to carry multiple light rays or modes concurrently, each at a slightly different reflection angle within the optical fiber core. used for relatively short distances because the modes tend to disperse over longer lengths (this is called modal dispersion) .
For longer distances, single mode fiber (sometimes called monomode) fiber is used. In single mode fiber a single ray or mode of light act as a carrier
Multimode has a larger core than single mode optical fiber

35. Wireless Transmission (1)
Frequency range (line of sight):
26 GHz to 40 GHz: for microwave with highly directional beam as possible
30 MHz to 1 GHz: for omnidirectional applications
300MHz to GHz: for infrared spectrum; used for point to point and multiple point application (line of sight)
Physical applications:
Terrestrial microwave – long haul telecommunication service (alternative to coaxial or optical fiber)
Few amplifier and repeaters
Propagation via towers located without blockage from trees, etc (towers less than 60 miles apart)
Starband.com
DirectDuo
DirectPC

36. Wireless Transmission (2)
Satellite is a microwave relay station
Geostationary orbit (22,000 miles) and low orbit (12000 miles)
Satellite ground stations are aligned to the space satellite, establishes a link, broadcast at a specified frequency. Ground station normally operate at a number of frequencies – full duplex
Satellite space antenna is aligned to the ground station establishes a link and transmits at the specified frequency. Satellite are capable of transmitting at multiple frequencies simultaneously, full duplex.
To avoid satellites from interfering with each other, a 4 degree separation is required for 4/6 GHz band and 3 degree for 12/14 GHz band. Limited to 90 satellites.
Disadv: not satellite repair capability; greater delay and attenuation problems.

37. Wireless LAN Wireless LAN
HiperLAN (European standard; allow communication at up to 20 Mbps in 5 GHz range of the radio frquency (RF) spectrum.
HiperLAN/2 operate at about 54 Mbps in the same RF band.
In wireless LAN (WLAN) technology, refers to a family of specifications developed by a working group of the Institute of Electrical and Electronics Engineers (IEEE). There are three specifications in the family: , a, and b.
All three of the above mentioned specifications use CSMA/CD carrier sense multiple access with collision detection (CSMA/CD)as the path sharing protocol. If a source station has a data packet to send, the station checks the system to see if the path medium is busy. If the medium is not busy, the packet is sent; if the medium is busy, the station waits until the first moment that the medium becomes clear. Testing is done repeatedly by the source via a short test message called RTS (ready to send). The data packet is not transmitted until the destination station returns a confirmation message called CTS (clear to send). If two stations send at exactly the same time, CSMA/CD prevents the loss of data that might otherwise occur and provides a system for retrying.
The and b specifications apply to wireless Ethernet LANs, and operate at frequencies in the 2.4-GHz region of the radio spectrum. Data speeds are generally 1 Mbps or 2 Mbps for , and 5.5 Mbps or 11 Mbps for b, although speeds up to about 20 Mbps are realizable with b. The b standard is backward compatible with The modulation used in has historically been phase-shift keying (PSK). The modulation method selected for b is known as CCK (complementary code keying), which allows higher data speeds and is less susceptible to multipath-propagation interference.
The a specification applies to wireless ATM systems and operates at radio frequencies between 5 GHz and 6 GHz. A modulation scheme known as OFDM (orthogonal frequency-division multiplexing) makes possible data speeds as high as 54 Mbps, but most commonly, communications takes place at 6 Mbps, 12 Mbps, or 24 Mbps.

38. Network Hardware

39. Hubs
A hub is the place where data converges from one or more directions and is forwarded out in one or more directions.
Seen in local area networks
Reference to
equipment
Nowadays you see hubs with switches; but basically the hub is the place where data comes together while the switch determines how and where data is forwarded from the place where data comes together.

40. Gateways
A gateway is a network point that acts as an entrance to another network. On the internet, in terms of routing, the network consists of gateway nodes and host nodes.
Host nodes are computer of network users and the computers that serve contents (such as Web pages).
Gateway nodes are computers that control traffic within your company’s network or at your local internet service provider (ISP)

41. Routers
A router is a device or a software in a computer that determines the next network point to which a packet should be forwarded toward its destination.
Allow different networks to communicate with each other
A router creates and maintain a table of the available routes and their conditions and uses this information along with distance and cost algorithms to determine the best route for a given packet.
A packet will travel through a number of network points with routers before arriving at its destination.

42. Bridge
a bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or token ring).
A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs).
bridge
In telecommunication networks, a bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or token ring). You can envision a bridge as being a device that decides whether a message from you to someone else is going to the local area network in your building or to someone on the local area network in the building across the street. A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs).
In bridging networks, computer or node addresses have no specific relationship to location. For this reason, messages are sent out to every address on the network and accepted only by the intended destination node. Bridges learn which addresses are on which network and develop a learning table so that subsequent messages can be forwarded to the right network.
Bridging networks are generally always interconnected local area networks since broadcasting every message to all possible destinations would flood a larger network with unnecessary traffic. For this reason, router networks such as the Internet use a scheme that assigns addresses to nodes so that a message or packet can be forwarded only in one general direction rather than forwarded in all directions.
A bridge works at the data-link (physical network) level of a network, copying a data frame from one network to the next network along the communications path.
A bridge is sometimes combined with a router in a product called a brouter.

43. What is the difference between?
Bridge: device to interconnect two LANs that use the SAME logical link control protocol but may use different medium access control protocols.
Router: device to interconnect SIMILAR networks, e.g. similar protocols and workstations and servers
Gateway: device to interconnect DISSIMILAR protocols and servers, and Macintosh and IBM LANs and equipment

44. Switches
Allow different nodes of a network to communicate directly with each other.
Allow several users to send information over a network at the same time without slowing each other down.

45. WANs and LANs

46. Major Categories of Networks
Local Area Networks (LAN)
A network of computers that are in the same general physical location, within a building or a campus.
Metropolitan Area Networks (MAN)
Wide Area Networks (WAN)
Issues of size and breadth.

47. Data Communications Through WANs (1)
WANs were developed to communicate over a large geographical area (e.g. lab-to-lab; city-to-city; east coast-to-west coast; North America-to-South America etc)
WANs require the crossing of public right of ways (under control and regulations of the interstate commerce and institute of telephone and data communications established by the gov’t and international treaties).
WANs around the world relies on the infrastructure established by the telephone companies (“common carrier”) or public switched telephone network (PSTN).
WANs consists of a number of interconnected switching nodes (today = computers). Transmission signals are routed across the network automatically by software control to the specified destination. The purpose of these nodes are to route messages through switching facilities to move data from node to node to its destination.

48. Data Communications Through WANs (2)
WANs originally implemented circuit switching and packet switching technologies. Recently, frame relay and asynchronous transfer mode (ATM) networks have been implemented to achieve higher operating and processing speeds for the message.
WAN transmission speeds are _______
WAN are owned by the common carrier in the U.S. and governement in most foreign countries.
Interconnected devices, I.e. LANs or Personal Computers (PC) or Workstation or Servers can be (usually are) privately owned by companies.
The range for WAN transmission will vary: 56 Kb/s to Mb/s

49. Circuit Switching Technologies
Circuit switching is a dedicated communications path established between two stations or multiple end points through nodes of the WAN
Transmission path is a connected sequence of physical link between nodes.
On each link, a logical channel is dedicated to the connection. Data generated by the source station are transmitted along dedicated path as rapidly as possible.
At each node, incoming data are routed or switched to the appropriate outgoing channel without excessive delay. However, if data processing is required, some delay is experienced.
Example of circuit switching above is the telephone networks.
Communication path established between two

50. Packet Switching Technologies
It is not necessasry (as in circuit switching) to dedicate transmission capacity along a path through the WAN rather data are sent out in a sequence of small chucks, called packets.
Each packet, consisting of several bits is passed through the network from node to node along some path leading from the source to the destination
At each node along the path, the entire packet is received, stored briefly, and then transmitted to the next node.
At destination all individual packets are assembled together to form the complete text and message from the source. Each packet is identified as to its place in the overall text for reassembly.
Packet switching networks are commonly used for terminal-to-computer and computer-to-computer communications.
If packet errors occur, the packet is retransmitted.

51. Frame Relay Techniques
Packet switching was developed at a time (1960’s) when digital long distance transmission facilities exhibited a relatively high error rate compared to today’s facilities. A large amount of overhead was included for error detection and control. Each packet included additional bits and each node performed additional processing to insure reliable transmission.
Frame relay has removed the overhead bits and additional processing. It has become unnecessary to invoke these overhead checks and thereby enables higher capacity transmission rates.
Frame relay takes advantage of these high rates and low error rates.
Frame relay networks are designed to operate efficiently at user data rates of 2 Mb/s and higher. (packet switching originally designed with a 64 Kb/s data rate to the end user).
Frame relay achieves these higher rates by stripping out most of the overhead involved with error control.

52. Asynchronous Transfer Mode (ATM)
ATM also referred to as “Cell Relay”
Evolution from frame relay and circuit switching.
Major differences: Frame relay uses variable length packets called “frames”. ATM uses fixed length packets called “cells”.
ATM provides little overhead for error control like frame relay, and depends on inherent reliability of the transmission system and on higher layers of logic in the end systems to identify and correct errors.
ATM is designed to operate in range of 10s to 100 Mb/s compared to frame relay (2 Mb/s)
ATM allows multiple virtual channels with higher data rates for transmission paths. Each channel dynamically sets on demand.

53. ISDN and Broadband ISDN Technology
Integrated services digital network (ISDN) was intended to be a world wide public telecommunication network to replace existing public telecommunication networks and deliver a wide variety of services.
ISDN has standardized user interfaces, implemented a set of digital switches and paths supporting a broad range of traffic types and providing a value added processing service
ISDN is multiple networks, but integrated to provide user with single, uniform accessibility and world wide interconnection.
First generation ISDN was narrowband, 64 Kb/s channel of switching and circuit switching orientations. Frame relay resulted from the ISDN narrowband efforts.
Second generation is broadband ISDN. It supports high data rates of 100s Mb/s and has a packet switching orientation. ATM resulted from the broadband ISDN efforts.
What is the third generation speed for ISDN?

54. Local Area Network
Small interconnected of personal computers or workstations and printers within a building or small area up to 10 Kms.
Small group of workers that share common application programs and communication needs.
LANs are capable of very high transmission rates (100s Mb/s to G b/s).
LAN equipment usually owned by organization. Medium may be owned or leased from telephone company provider or common carrier.
PC or Workstation interconnected to medium (twisted pair; fiber optics; etc) through concentrators to servers. LAN is interconnected with other networks via switches and router/gateways.
Advanced LANs using circuit switching are available. ATM LANs, fibre channel baseband, and broadband LANs are being used. Etc.
Ethernet
Token Ring

55. What is ethernet?
A group of standards for defining a local area network that includes standards in cabling and the structure of the data sent over those cables as well as the hardware that connects those cables.
Independent of the network architecture
Flavors of ethernet
IEEE Ethernet Specification
Great detail specifying cable types, data formats, and procedures for transferring that data through those cables
IEEE Token Ring Specification
The standards put down in writing what happens at the very basest level of network communication: that which actually travels through the wires and hardware.

56. Network Interface Card (NIC)
Every computer and most devices (e.g. a network printer) is connected to network through an NIC. In most desktop computers, this is an Ethernet card (10 or 100 Mbps) that is plugged into a slot on the computer motherboard.

57. How does Ethernet work?
Using MAC addresses to distinguish between machines, Ethernet transmits frames of data across baseband cables using CSMA/CD (IEEE 802.3)

58. What is a MAC Address?
Media Access Control (MAC) Address – are the physical address of any device, e.g. a NIC in a computer on the network. The MAC address has two parts of 3 bytes long. The first 3 bytes specify the company that made the NIC and the second 3 bytes are the serial number of the NIC.

59. What is a Token Ring?
All computers are connected in a ring or star topology and a binary digit or token passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time.

60. How do Token Rings work?
Empty information frames are continuously circulated on the ring.
When a computer has a message to send, it inserts a token in an empty frame (this may consist of simply changing a 0 to a 1 in the token bit part of the frame) and inserts a message and a destination identifier in the frame.
The frame is then examined by each successive workstation. If the workstation sees that it is the destination for the message, it copies the message from the frame and changes the token back to 0.
When the frame gets back to the originator, it sees that the token has been changed to 0 and that the message has been copied and received. It removes the message from the frame.
The frame continues to circulate as an "empty" frame, ready to be taken by a workstation when it has a message to send.

61. Understanding Network Protocols

62. Protocols of Computer Communications and Networks
Protocol are used for communication between computers in different computer networks. Protocol achieves:
What is communicated between computers?
How it is communicated?
When it is communicated?
What conformance (bit sequence) between computers?
Key elements of a protocol are:
SYNTAC: Data format and signal levels
SEMANTICS: Control information for coordination and error handling
TIMING: Synchronization, speed matching, and sequencing
Examples of protocols:
WAN Protocol: TCP/IP
LAN Protocol: Media Access Control; Contention; Token Passing

63. Protocol Architecture
Architecture provides high degree of cooperation between two computers.
Example:
INSERT DIAGRAM of file transfer 
Structure of protocols architecture:
file transfer module contains all logic for file transfer applications (transmitting passwords, file commands, and file records). Need is to transmit the files and commands reliably.
Some sorts of reliability are relevant to a variety of applications (e.g. , document transfer)
Met by separate communication service modules that can be used by a variety of applications. Communication service modules assumes two computer systems are active and ready for data transfer, and keeps track of data being exchanged to assure delivery.
A structured set of modules are used that implements the communication functions.

64. ISO/OSI Reference Model (1)
Open Systems Interconnection
No one really uses this in the real world.
A reference model so others can develop detailed interfaces.
Value: The reference model defines 7 layers of functions that take place at each end of communication and with each layer adding its own set of special related functions.
Flow of data through each layer at one
It is use to guide product implementors so that their products will consistently work with other products.

65. ISO/OSI Reference Model (2)
File Transfer, , Remote Login 
ASCII Text, Sound (syntax layer) 
Establish/manage connection 
End-to-end control & error checking
(ensure complete data transfer): TCP 
OSI divides telecommunication into seven layers. The layers are in two groups. The upper four layers are used whenever a message passes from or to a user.
The lowest three layers (Up to network layer) are used when any message passes through the host computer.
Message intended for this computer pass to the upper layers.
Message destined for some other host are not passed up to the upper layers but are forwarded to another host.
Physical layer: Bit stream through network at electrical/mechanical level
Routing and Forwarding Address: IP 
Two party communication: Ethernet 
How to transmit signal; coding
Hardware means of sending and 
receiving data on a carrier

66. What is TCP/IP?
Transmission Control Protocol (TCP) – uses a set of rules to exchange messages with other Internet points at the information packet level
Internet Protocol (IP) – uses a set of rules to send and receive messages at the Internet address level
Is the predominate network protocol in use today (Other includes OSI Model) for interoperable architecture and the internet.
TCP/IP is a result of protocol research and development conducted on experimental packet switched network by ARPANET funded by the defense advanced research projects agency (DARPA). TCP/IP used as internet standards by the internet architecture board (IAB).

67. TCP/IP Five Independent Levels
HTTP / FTP / Telnet /
SMTP / SLIP / PPP 
Application Layer: contains the logic needed to support the various user applications. Separate module are required for each application.
Host-to-host or transport Layer: collection of mechanisms in a single and common layer
Internet Layer: IP provides the routing functions across the multiple networks
Network access layer: concerned with access to and routing data across a network for two end systems attached to the same network.
Physical Layer: covers physical interface between PC or workstation and a transmission medium or network
TCP keep track of the
individual packets 
And reassemble
IP handles actual 
delivery of packets
There are several higher layer application protocols that use TCP/IP to get to the internet. They include World Wide Web’s Hypertext Transfer Protocol; File Transfer Protocol (FTP); Telnet (Telnet) [ allow you to logion to remote computers], Simple Mail Transfer Protocol (SMTP)
These and other protocols are often packaged together as a suite.
TCP keep track of the individual packets that a message is divided into for efficient routing through the internet

68. TCP (example) Web Server: serves HTML pages
TCP layer in the server divides the file into one or more packets, numbers the packet, then forward packets individually to IP.
Note: each packet has the same destination IP address, it may get routed differently through the network.
TCP (on the client) reassembles the individual packets and waits until they have arrived to forward them as a single file.
Connection-oriented protocol

69. IP
Connectionless protocol (I.e. no established connection between the end points that are communicating.)
Responsible for delivery the independently treated packet !!!!
TCP responsible for reassembly.

70. Associated TCP/IP Protocols & Services
HTTP
This protocol, the core of the World Wide Web, facilitates retrieval and transfer of hypertext (mixed media) documents. Stands for the HyperText Transfer protocol
Telnet
A remote terminal emulation protocol that enables clients to log on to remote hosts on the network.
SNMP
Used to remotely manage network devices. Stands for the Simple Network Management Protocol.
DNS
Provides meaningful names like achilles.mycorp.com for computers to replace numerical addresses like Stands for the Domain Name System.
SLIP/ PPP
SLIP (Serial Line Internet Protocol) and PPP (Point to Point Protocol) encapsulate the IP packets so that they can be sent over a dial up phone connection to an access provider’s modem.

71. Considerations?

72. Examples
Multimedia (audio/video stream) Bioinformatics Educational CD’s as an example of extending network capacity

73. Further Readings
Basics: Complete Idiots Guide to Networking, 3rd Edition (Wagner and Negus)
Practical Network Cabling (Freed and Derfler)
Networking books by William Stallings:
Business Data Communications
Operating Systems: Internals and Design Principles
Data & Computer Communications
Local and Metropolitan Area Networks
High-speed networks TCP/IP and ATM Design Principles
Online Audio/Video Recording of Networking Class: