OUTLINE• Overview• Types of Communication Networks• Communications Layers and Protocols• Network Design and Management• Future Trends
OVERVIEW• Definition of Communications Networks• Layering Concept in Communication Networks and Protocols• Standard Organizations• Brief History of Communication Networks
Definition of Communications Networks• A communication network is a collection of elements connected by using transmission facilities to provide end-users with the capability of exchanging messages and information in a variety of formats, for example, voice, data, and video• The elements could be computers, workstation, routers, switches, private branch exchanges (PBXs) and multiplexers, etc.• Formally called Network Element or the node
• Transmission links may be twisted wire pairs,co-axial cables, and optical cables, radio links, satellite links, or infrared connections.• Operations systems Operate Monitor Manage network resources• People• Network categorization based on geographical dispersion of its components - PAN, LAN, MAN, WAN
LAYERING CONCEPT IN COMMUNICATION NETWORKS AND PROTOCOLS• To facilitate the exchange of information, each network element and user equipment must provide a set of comprehensive functions so that they can communicate with each other in an unambiguous way.• Could be complex to implement and maintain in one package• Breaking up into smaller and more manageable components• Termed layering model Each model contains a group of related communication functions
• A protocol is an implementation of a set of unambiguous rules and procedures used in exchanging information via messages among network elements and end-user devices Advantage of layering approach Easy to develop specialized protocols for each layer Allows for the mixing and matching of many different protocolsDisadvantage Places burden on industry to standardize• Two most important layering approaches - Open Systems Interconnection model - Internet Model
Standard Organizations• Formal standards are typically developed by industry consortia, professional associations, and government organizations.• ISO• ITU-T• ITU-R• IEEE• IETF• 3GPP• 3GPP2• CableLabs• DMTF• OMA• TIA• TM Forum• W3C
BRIEF HISTORY OF COMMUNICATION NETWORKS• The evolution of communications networking is tied to the invention of telegraph, telephony, radio, and computers.• Telephone networks used to connect computers together.• Low speed( data rate)• Telephone lines became quickly insufficient.• Need for dedicated transmission lines thus packet switching.
• ARPANET in the early 1970s and the Internet in the 1980s• PC revolution in 1980• LAN associated equipments routers and bridges were developed• Wireless voice communication in 1970s
TYPES OF COMMUNICATION NETWORKS• PAN• LANs• MANs• WANs
PAN• Personal Area Network• The use of Bluetooth and infra red radiation to create a network• IEEE 802.15 (Bluetooth) provides a so-called wireless PAN by connecting a number of devices around a person• Devices e.g. PDAs, laptops, cellular phones, headphones, mouse, keyboard, and so on.
• short range communications (1–100 m) based on low- cost tiny transceivers.• A Bluetooth network, referred to as a piconet• consists of up to eight simultaneously communicating devices• a piconet can have up to 125 Bluetooth enabled devices, only eight can be active at the same time.• The devices in a piconet can dynamically and in an ad hoc fashion form a network by first choosing a master device that can control other devices, called slaves.• The master acts like an AP -selecting frequencies to be used -controlling the access to these frequencies by the slaves.
• Devices share the same frequency range• Uses FHSS for media access control.• Frequency range (2.4000–2.4835 MHz)• Divided into 79 separate 1-MHz channels• Bluetooth version 1.2 provides a data rate of 1 Mbps, while Bluetooth version 2.0 can provide up to 3 Mbps• Interconnection of piconets is called a scatternet.
• The data rate calculations in wLANs are similar to those discussed under the wired LANs section.• transmission errors play a greater role in wLANs data calc.• interference on the air.• Also the errors cause retransmissions, which, in turn, lower the data rates• 802.11b results in about 85% average efficiency, whereas IEEE 802.11a and 802.11g would give us about 75% average efficiency.• Also consider thePCF, which introduces more delays.
LANs• A LAN is used to connect a number of computers and other devices in a small, local, area such as a room, a floor, or a building.• Computers could be - servers (Web server, e-mail server, fileserver, or print server) -client (which shares the files, printers, and servers with other client computers in the same LAN)• hub/ switches for connecting servers and client• Network Interface Card (NIC) in each node -provides the physical layer and data link layer functions
• Network Operating System (NOS) - handles all network functions -performs data link -network -application layer functions - acts as the application software e.g. NOS are MS Windows Server and Linux Server
• Ethernet, specified in the IEEE 802.3 is the commonly used standards in LAN technology• Two different implementation of Ethernet - Traditional (or shared) using CSMA/CD -Switched using Forwarding Table• In putting together a LAN, perhaps the most important aspect to watch for is the effective data rate - which is the maximum speed in bits that the hardware layers (i.e. physical and data link layers) can provide.
• Three major components of the effective data rate :- The nominal data rate that depends on the physical layer properties. E.g. the nominal rate for a 100Base-T Ethernet is 100 Mbps- The error rate of the circuit, which is a critical factor in determining retransmissions, therefore reducing the transmission efficiency- The efficiency of data link layer protocol• The packet size, which plays an important role in these calculations, depends on the type of the traffic on the LAN
• LAN traffic include -number of small Web application specific (i.e., Hypertext Transfer Protocol, HTTP) - the e-mail application-specific (i.e., SMTP, or Simple Mail Transfer Protocol) messages - followed by a large number of larger packets• This results in about 97% efficiency for the Ethernet frames with 33 bytes overhead• Calculating the effective data rate for a whole LAN - consider the efficiency of the media access control
• The Ethernet’s media access mechanism works well in low-traffic LANs -resulting typically in a 50% capacity utilization.• The total effective data rate for a 100Base-T will be calculated as follows: -50% capacity × 97% efficiency × 100 Mbps rate = 485 Mbps (for the whole LAN)• With 10 computers in the LAN, each computer’s effective data rate would be 485/10 = 48.5 Mbps.
• The effective rates for switched Ethernets are much higher due to the significant improvements (up to 95%) in capacity utilization - since there is no sharing in this architectureNB: switched Ethernet is not affected by the traffic due to the availability of dedicated circuits for each computer
Improving LAN performance• There needs to be continuous monitoring and, if necessary, to make changes to improve performance• The two bottleneck -server- circuit.
Server Bottleneck• A key indicator to determine whether the server is a bottleneck is the utilization of the server -say over 70%, then it is likely the server is the bottleneck.• Eliminate bottleneck by upgrading -hardware (CPU, memory, storage, etc.) - software (operating system, applications, etc.)• If the server utilization is low, then the bottleneck is the circuit
Circuit Bottleneck• Improving the circuit capacity, say from 100Base-T to 1000Base-T may help• The are other methods of improving performance of a LAN-dividing a LAN into two or more segments,-reducing the network demand by scheduling certain applications during off hours
WIRELESS LANS• When the computers on a LAN are connected via unguided media, eliminating the cables, the resulting LAN is called a wireless LAN (wLAN).• LAN technologies based on the radio transmission• The IEEE 802.11 series of standards, also referred to as the Wi-Fi technology
• Earliest version IEEE 802.11b• Later IEEE 802.11a after commercialisation of 802.11b even though preceded it• Followed by IEEE 802.11g• Now IEEE 802.11n• IEEE 802.15 – (PAN) limited range and data rate.• Each new version improves Data rates Security
• IEEE 802.11b designed to connect easily to Ethernet.• The physical layer specifications are based on the spread spectrum technology where the energy carrying the signal is spread over a rather large band of the frequency spectrum• There are two versions: -Direct Sequence Spread Spectrum (DSSS)-Frequency Hopping Spread Spectrum (FHSS)• A wLAN architecture has a simple star topology where the computers equipped with wireless NICs are connected through an access point• Uses Access Points (AP) or Ad-doc mode• Devices using AP must use same channel
• IEEE 802.11b has 3 channels for AP• APs connected through Ethernet LANs• Roaming between APs• APs installation geographical needs traffic needs• IEEE 802.11b uses a scheme to avoid collisions for accessing the medium• Uses CSMA/CA.• uses two complementary MAC methods together: -the mandatory Distributed Coordination Function (DCF), a.k.a., Physical Carrier Sense Method- the optional Point Coordination Function (PCF), a.k.a., Virtual Carrier Sense Method
DCF• A node listens to the medium to make sure that an existing transmitting node has finished, before transmission• Uses the stop-and-wait Automatic Repeat Request (ARQ)• The ACK/NAK (Acknowledgment/Negative Acknowledgment) frames are sent a short time
PCF• Solves the famous hidden node problem in wireless networks• two devices may not be able to detect each other’s signals, even though both can hear the AP.• Node sends Request-To-Send signal to the AP, requesting allocation of a channel in a time period.• The AP responds with a Clear-To-Send signal containing the duration that the channel is reserved.• The device starts transmitting its messages
• IEEE 802.11a completed after IEEE 802.11b standardised and commercialised• IEEE 802.11a operates in so called unlicensed information infrastructure• Total bandwidth of 300 MHz• 4-12 channels (20MHz each) depending on configuration• Faster data rates up to 54Mbps• However, limited range 50m (150ft)
• Advantages of IEEE 802.11a• Capacity of LAN is increased• IEEE 802.11a combined with IEEE 802.11b can support more users with higher data rates• Disadvantages of IEEE 802.11a• Range is considerably limited. i.e., more IEEE 802.11a APs to cover the same area covered by one IEEE 802.11b AP.• Although packet format are very similar, physical layer schemes and frequency bands are quite different. i.e., 802 .11a and 802.11b are not compatible.
• IEEE 80.11g created to solve interoperability problem• Combines 802.11a and 802.11b• 802.11g offers data rate up to 54Mbps with 50m• 802.11b and 802.11g all operate in 2.4GHz band• All 802.11g devices downgraded to 802.11b, when 802.11g APs detects 802.11b device in a network• 802.11g Provides 3-6 channels depending on configuration• Employs Orthogonal Frequency Division Multiplexing (OFDM)
• Newer version, 802.11n allows the use of multiple antennas simultaneously• Uses Multiple Input Multiple Output (MIMO)• More efficient and reliable scheme• Supports up to 300Mpbs data.
Data Rate Calculation• The data rate calculations in wLANs are similar to those discussed under the wired LANs section• However, in wLANs, transmission errors play a greater role in the data rate calculations due to the potential interference on the air• 802.11b results in about 85% average efficiency• IEEE 802.11a and 802.11g would give us about 75% average efficiency.• Based on the assumption that a typical 802.11 overhead is about 51 bytes and the average packet length is a mix of short and full length packets.
• PCF introduces more delays.• As a result, MAC in wLANs operates with about up to 85–90% of capacity• The effective data rate for a network based on the 802.11b NICs and APs can be calculated as: 85% efficiency × 85% capacity × 11 Mbps = 9.6 Mbps• With 10 devices, each device would get 9.6 Mbps/10 devices = 960 Kbps.• For 802.11a and 802.11g, we would get about 34.4 Mbps data rate total.
• wLAN requires a careful determination of the number of APS and their placement• The placement affects Coverage of area• Number of APs important to handle traffic in network• A site survey to determine the potential location of the APs should include the measurement of potential interference from external sources• Trial and error may be necessary for making sure that the signal strength is acceptable in all areas
• directional antennas, instead of Omni directional antennas, may be used• 15% overlap between APs should be engineered forSmoothnessTransparent roaming
• Security is great concern in wLAN Transmitted in the air Easily captured and JeopardizedMeasures to counter insecurity Service Set Identifier Transmits in plain text and can easily be intercepted Security and privacy guaranteed by Wired Equivalent Privacy (WEP) Require users to configure a key manually into the device (NIC and APs) all messages will be encrypted by using this WEP key Key between 40 and 128 bits The longer the key, the harder to break if the algorithm is the same
The Extensible Authentication Protocol is an advanced security feature that requires a login and a password to a server. Wi-Fi Alliance, an industry group providing certification for the 802.11-based equipment• Wi-Fi Protected Access (WPA) used in the certification process.• IEEE 802.11i was designed to provide secured communication of wLANs in a more comprehensive way• enhances the WEP in the areas of encryption, authentication, and key management.
CAMPUS NETWORKS• Bridges, routers, switches, and gateways are used for connecting LANs together via higher speed circuits, more commonly fiber optical cables.• Bridges lost their place to switches Switches cheaper and powerful• Router operate with different data link layer protocol with the same network layer protocol• Gateways operate at the network layer protocol connecting LAN with different data link and Network layer protocol• Each LAN has its own subnet designation.
HUB ROUTER ROUTER HUB HUB ROUTER ROUTER HUB• A campus network with routers connecting its LANs.
• The architecture of diagram above is easier to manage but it tends to impose more delays than bridging due to the Layer 3 processing.• Could be improved by connecting each hub of the LANs to a switch via a separate circuit (and get rid of all the routers). -Meaning more cables but less devices to worry about• Switched operation will make performance improve significantly.• The down side is that, the use of a single central switch introduces a reliability problem - when the switch fails, the whole network goes down.• Improve the configuration even further - higher performance and a more intelligent switch even - eliminating the hubs• Allowing us to create VLANs segment through software and assigning computers to them.
• Computers can be assigned to any segment regardless of location• provides a more flexible network management - creating project groups and assigning resources to them• Multi-switch virtual LAN configurations are also possible by using several switches -complex and costly - used for larger campus networks• CAN largely data centric• Additional software and/or hardware changes in the end- user equipment - can transmit voice and video as well
• Voice over IP (VoIP) and multimedia-specific protocols and features that rely on a common network layer protocol• PBX (a.k.a. PABX)• Latest trend in PBX development is IP PBX• Switches calls between VoIP on Local line• A single line for data access, VoIP and traditional telephone
MANS AND WANS• If network element are spanning from 3 to 30 miles, the network is typically called a MAN• If covering a province, a country, or even across countries, the network is called a WAN• Typically, these networks are built by using dedicated circuits leased from common carriers.• A WAN containing the dedicated circuits is called a dedicated circuit WAN.
• The services provided by common carriers can be classified as :-circuit-switched services- packet-switched services• E.g. of dedicated digital circuits are T-Carrier services, E-Carrier service, etc• Lease organization charge a monthly flat fee that depends on the capacity and length of the circuit• The line is dedicated to the customer with the rights of unlimited use of the circuit.
• T-Carrier services most commonly in North America• E-Carrier service in Europe and elsewhere. - T1 circuits provide 1.544 Mbps data rate (equivalent of 24 voice channels, 64 Kbps data rate) - T3 circuits offer 44.376 Mbps data rate (28 T1 lines).• For higher data rates, common carriers offer dedicated circuits based on the Synchronous Optical Network (SONET) technology -an ANSI standard in the United Sates for optical fiber transmission in Gbps range• Hierarchy of data rates in SONET starts with OC-1 (optical carrier level 1) at 51.84 Mbps.• OC-192 providing almost 10 Gbps data rate.
Components in MANs/WANs• There are special equipments such as - Channel Service Unit -Data Service Unit• To be installed at the end of each dedicated circuit• routers and switches - to create a network owned and maintained by the organization itself
Architectural Decisions• Network designers must determine the best architecture that fits the application at hand• factors to consider: -delay, throughput, reliability, and the cost.• Ways of connecting the locations via dedicated lines. -ring, star, and mesh topologies are the basic dedicated circuit architectures
• ring and star architectures are most cost-effective -result in less dedicated circuits to lease• mesh architecture is more costly -requires many more circuits• performance (throughput, delay) - mesh the best, followed by star and then ring• From the reliability point of view -mesh architecture is best - ring worst since network relies on a central node
• To bring the down the cost of a mesh -a partial mesh architecture can be used - where only certain pair of nodes are connected directly• The nodes that are not directly connected communicate with each other through other nodes
• Enterprises that cannot afford to put together their own dedicated circuit-based network rely on switched services provided by the common carriers• end-user equipment are connected via temporary, not dedicated,• The connection is no longer available once session is complete
• first leases a short connection from each of its locations to the nearest Point of Presence (POP) of the service provider• An end-user equipment in the enterprise is required to break its message to be transmitted into smaller segments, called packets and attach the address of the destination equipment
• Packet-switching technologies• X.25 is the oldest standardized packet- switched protocol -standardized by ITU-T (CCITT at the time)• Frame relay -operates at rates higher than those of X.25 up to 45 Mbps• Asynchronous Transfer Mode (ATM).
The Internet• The Internet is a network of networks -an interconnection of thousands of LANs, campus networks, MANs, and WANs• Networks and computers connected to an Internet Service Provider• Many ISPs are connected to each other via bilateral agreements and connections• Networks connected in hierarchical structure.
• There is a payment-compensation scheme established by the ISPs.• ISPs are classified into three tiers: -Tier 1 ISPs, the largest ones -Tier 2 ISPs, buy connectivity from Tier 1 ISPs -Tier 3 ISPs, buy connectivity from Tier 2 ISPs• ISPs at the same level usually do not charge each other for exchanging messages.• This is called peering.
COMMUNICATIONS LAYERS AND PROTOCOLS• Write short notes on the following• APPLICATION LAYER FUNCTIONS AND PROTOCOLS• WWW Applications and Related Protocols• E-Mail Applications and Related Protocols• TRANSPORT LAYER FUNCTIONS AND PROTOCOLS• NETWORK LAYER FUNCTIONS AND PROTOCOLS• DATA LINK LAYER FUNCTIONS AND PROTOCOLS• PHYSICAL LAYER FUNCTIONS AND PROTOCOLS
FUTURE TRENDS• GIGABIT ETHERNET TRENDS -The 10 Gbps Ethernet -Sophisticated physical layer and required several years of activities -current 10 Gbps Ethernet applications are mostly in WAN and carrier networks -interconnect servers in data centers in enterprise system
• The standardization activities for enterprise networking is IEEE 802.3 HSSG.• NEXT GENERATION INTERNET- projects directed to develop the technologies that will be part of the next generation of the Internet- Internet2, China’s Next Generation Internet, CA*net - common features include the use of IPv6 - a backbone in multiples of 100 Gbps data rates - efficient multimedia transmission with adequate QoS parameter values
-tools and protocols to facilitate new applications such as videoconferencing• Internet2 is a consortium that includes major U.S. universities, corporations, government agencies and laboratories, and international organizations -focus on advanced network applications -such as remote access to unique scientific instruments -new network capabilities such as IPv6 -middleware -high performance networks linking member institutions
• The purpose of CNGI project is to promote China’s status in the Internet technology.• A key aspect of CNGI is the immediate adoption of IPv6 to solve the IPv4’s address shortage problem• China showcased CNGI at the 2008 Summer Olympics in broadcasting the events• CA*net is a Canadian approach to the next generation Internet
• 4G CELLULAR NETWORKS• 4G refers to a new type of wide area wireless systems that will provide - more bandwidth - will use packet switching based on the IPWIRELESS AD HOC NETWORKS AND WSNS - include numbers of nodes (PDAs, laptops, sensors, etc.) with varying functionalities and power levels.
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