Networking essentials4

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Flow Control in the Transport Layer

Flow control is a function forthe control of the data flow within an OSI layer or between

adjacent layers. In other words it limits the amount ofdata transmittedby the sendingtransport entity to a level, or rate, that the receiver can manage.

Flow control is a good example of a protocol function that must be implemented inseverallayers of the OSI architecture model. At the transport level flow control will allow the transportprotocol entity in a host to restrict the flow of data over a logical connection from thetransport protocol entity in another host. However, one of the services of the network level is toprevent congestion. Thus the network level also uses flow control to restrict the flow of networkprotocol data units (NPDUs).

The flow control mechanisms used in the transport layervary for the different classes of service.Since the different classes of service are determined by the quality of service of the underlyingdata network which transports the transport protocol data units (TPDUs), it is these which

influence the type of flow control used.Thus flow control becomes a much more complex issue at the transport layer than at lowerlevels like the datalink level.

Two reasons for this are:

Flow control must interact with transport users, transport entities, and the networkservice.

Long and variable transmission delays between transport entities.

Flow control causes Queuing amongst transport users, entities, and the network service. Wetake a look at the four possible queues that form and what control policies are at workhere.

The transport entity is responsible for generating one or more transport protocol data units(TPDUs) for passing onto the network layer. The network layer delivers the TPDUs to thereceiving transport entity which then takes out the data and passes it on to the destination user.There are two reasons why the receiving transport entity would want to control the flow ofTPDUs:

The receiving user cannot keep up with the flow of data

The receiving transport entity itself cannot keep up with the flow of TPDUs

When we say that a user or transport entity cannot keep up with the data flow, we mean that thereceiving buffers are filling too quickly and will overflow and lose data unless the rate ofincoming data is slowed.

Fourpossible ways to cope with the problem are: Let it be and do nothing

Refuse any more TPDUs from the network service

Use a fixed sliding-window protocol

Use a credit scheme

There are different issues to be considered with transport flow control over different levels ofnetwork service. The more unreliable the network service provided the more complex flow
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control mechanism that may be needed to be used by the Transport Layer. The credit schemeworks well with the different network services although specific issues need to be addressed aswith a Reliable Nonsequencing Network Service and an Unreliable Network Service.

The credit scheme seems most suited for flow control in the transport layer with all types ofnetwork service. It gives the receiver the best control over data flow and helps provide a

smooth traffic flow. Sequence numbering of credit allocations handles the arrival ofACK/CREDIT TPDUs out of order, and a window timer will ensure deadlockdoes not occur ina network environment where TPDUs can be lost.

Session Layer Performing message synchronization. Messagesynchronization is the coordination of the data transfer between the sending

session layer and the receiving session layer. Synchronization prevents the

receiving session layer from being overrun with data. This transfer is coordinated

with acknowledgement messages (ACKs). ACKs are sent back and forth between

both ends of the transfer and notify of the state of the receiving buffer to accept

additional data.

OR

Another service that is offered as a part of the Session Layer might include data

synchronization. Checksums may also be included at the Session Layer as a part

of data synchronization. A checksum is performed after each packet is transmitted

to see if applying the data from the packet to the file or stream being moved or

transmitted would cause it to have the same checksum as the file on the remote

location up to that point. If it is, then the new data may be added to the local

machine being transferred from the remote site. This is a form of error correction

for transmitted data. A familiar form of checksums in use can be seen in Z-modem

transfers as part of communications or terminal software. The wonderful part of z-

modem transfers is that it becomes possible for an interrupted z-modem download

to be resumed where it left off with a minimal amount of retransmitted data. This

may not be a method used at this layer, but it shows how using a system of

synchronization with each part of the data being transferred can allow for

interruptions to limit the problems associated with having to start the whole

transmission over again.
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DIFFERENCE BETWEEN SWITCH N HUB:-

HUB works on Physical layer where as SWITCH works on data

link layer,HUB based networks are on one collision domain

where as in Switch based network switch divides networks into

multiple collision domains.Switch also maintains MAC address

tables.

A Simple Similie

Hub - Think of a postman with a letter to deliver in a row of

houses, none of the houses have numbers so he has to visit

each house and ask the owner if the letter is for them.

Switch - All the houses are numbered, so the postman knows

where to go, and doesn't have to bother any other home

owners.

What is the difference between a hub and a switch?

Hubs and switches are different types of network equipment that connectdevices. They differ in the way that they pass on the network traffic that theyreceive.

Hubs

The term hub is sometimes used to refer to any piece of networkequipment that connects PCs together, but it actually refers to a multi-portrepeater. This type of device simply passes on (repeats) all the information itreceives, so that all devices connected to its ports receive that information.

Hubs repeat everything they receive and can be used to extend the network.However, this can result in a lot of unnecessary traffic being sent to alldevices on the network. Hubs pass on traffic to the network regardless of theintended destination; the PCs to which the packets are sent use the addressinformation in each packet to work out which packets are meant for them. Ina small network repeating is not a problem but for a larger, more heavily

used network, another piece of networking equipment (such as a switch)may be required to help reduce the amount of unnecessary traffic beinggenerated.

Switches

Switches control the flow of network traffic based on the address informationin each packet. A switch learns which devices are connected to its ports (bymonitoring the packets it receives), and then forwards on packets to the


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appropriate port only. This allows simultaneous communication across theswitch, improving bandwidth.

This switching operation reduces the amount of unnecessary traffic thatwould have occurred if the same information had been sent from every port(as with a hub).

Switches and hubs are often used in the same network; the hubs extend thenetwork by providing more ports, and the switches divide the network intosmaller, less congested sections.

When Should I Use a Hub or Switch?

In a small network (less than 30 users), a hub (or collection of hubs) caneasily cope with the network traffic generated and is the ideal piece ofequipment to use for connecting the users.

When the network gets larger (about 50 users), you may need to use aswitch to divide the groups of hubs, to cut down the amount of unnecessary

traffic being generated.If there is a hub or switch with Network Utilization LEDs, you can use theLEDs to view the amount of traffic on the network. If the traffic is constantlyhigh, you may need to divide up the network using a switch.

When adding hubs to the network (to add more users), there are rules aboutthe number of hubs you can connect together. Switches can be used toextend the number of hubs that you can use in the network.

HubIn general, a hub is the central part of a wheel where the spokes come together. The term isfamiliar to frequent fliers who travel through airport "hubs" to make connecting flights from one

point to another. In data communications, a hub is a place of convergence where data arrivesfrom one or more directions and is forwarded out in one or more other directions. A hub usuallyincludes a switch of some kind. (And a product that is called a "switch" could usually beconsidered a hub as well.) The distinction seems to be that the hub is the place where data comestogether and the switch is what determines how and where data is forwarded from the placewhere data comes together. Regarded in its switching aspects, a hub can also include a router.

1. In describing network topologies, a hub topology consists of a backbone (main circuit) towhich a number of outgoing lines can be attached ("dropped"), each providing one ormore connection port for device to attach to. For Internet users not connected to a localarea network, this is the general topology used by your access provider. Other commonnetwork topologies are the bus network and the ring network. (Either of these could

possibly feed into a hub network, using a bridge.)2. As a network product, a hub may include a group of modem cards for dial-in users, a

gateway card for connections to a local area network (for example, an Ethernet or a tokenring), and a connection to a line (the main line in this example).

SwitchIn telecommunications, a switch is a network device that selects a path or circuit for sending aunit of data to its next destination. A switch may also include the function of the router, a deviceor program that can determine the route and specifically what adjacent network point the data
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should be sent to. In general, a switch is a simpler and faster mechanism than a router, whichrequires knowledge about the network and how to determine the route.

Relative to the layered Open Systems Interconnection (OSI) communication model, a switch isusually associated with layer 2, the Data-Link layer. However, some newer switches alsoperform the routing functions of layer 3, the Network layer. Layer 3 switches are also sometimes

called IP switches.On larger networks, the trip from one switch point to another in the network is called a hop. Thetime a switch takes to figure out where to forward a data unit is called its latency. The price paidfor having the flexibility that switches provide in a network is this latency. Switches are found atthe backbone and gateway levels of a network where one network connects with another and atthe subnetwork level where data is being forwarded close to its destination or origin. The formerare often known as core switches and the latter as desktop switches.

In the simplest networks, a switch is not required for messages that are sent and received withinthe network. For example, a local area network may be organized in a token ring or busarrangement in which each possible destination inspects each message and reads any messagewith its address.

difference between switch and router??

A switch sorts and distributes the network packets sent between the devices on a local areanetwork (LAN), while a router is a gateway that connects two or more networks, which can beany combination of LANs, wide area networks (WAN), or the Internet. In addition, a router usestables to determine the best path to use to distribute the network packets it receives, and aprotocol such as ICMP to communicate with other routers. A router is a significantly morecomplicated device than a switch--essentially a specialized computer--and more advancedmodels may use a reconfigurable operating system such as Linux, rather than firmware codeddirectly into the hardware. Both routers and switches operate on layers 2 and 3 of the OSI model.

In an enterprise environment, routers and switches are separate physical devices dedicated to

their specific tasks. However, typical "broadband routers" for the home and small office areactually multifunction devices that combine the capabilities of a router, a switch, and (usually) afirewall into one box. In addition to routingtraffic between the Internet and the LAN, they alsohandleswitchingfor packets between devices on the LAN, and often add additional features suchas port forwarding and triggering, a DMZ, a DHCP server, a DNS proxy, and/or network addresstranslation. In addition, "wi-fi routers" add a wireless access point.

Note: A hub is even simpler than a switch. Instead of inspecting the packets that it encountersand sending them to the correct destination device, it just forwards them to all connected devices.

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1.Switch are said to be l2 device only but Router are said

to be L3 device.

2.Switch is said to be H/W Device.Router are said to be S/Wdevice.

3.Switch perform faster than the router because it is a H/W

Device.

-----------------------------------------------------------------

Switch are basically layer2 device and it works on Hardware

technology with map the mac addresses and it works with

switch table.


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Router is known as layer3 device and works alos on hardware

technology and map the mac addresses. it basically connects

two different networks or netids to each other.it works with

routing table.

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1] Switch is separate collision domain. single broad cast

domain. this breakup collision domain.

Router breakup broadcast domain.

2] Switch hardware oriented. L2 devices. packet transferred

through mac address

Router Software oriented. L3 devices. packet transferred

through ip address

3] Switch connected between same network

Router connected between different network.

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1)switch is considered to be an intellengent device because

there is rare chance of collsion

1)router is an important device becauseit work in network layer third layer of the open system

interconnection layer

2)switch works on data link layer of the osi reference

layer,it works depond on mac address(media access control)

2)router is used to communicate two or

more different network

3)when a switch is connected to the host each time it send

a broadcast ip address and mac address

router is consider to be a software

device

4) but swich is considered to be a hardware device because

it uses a special chip call asic(application specific

integrated circuit)

ENCAPSULATION IN OSI MODEL:-

When a car is built in a factory, one person doesn't do all the jobs, rather it's put into a productionline and as the car moves through, each person will add different parts to it so when it comes tothe end of the production line, it's complete and ready to be sent out to the dealer.

The same story applies for any data which needs to be sent from one computer to another. TheOSI model which was created by the IEEE committee is to ensure that everyone follows theseguidelines (just like the production line above) and therefore each computer will be able tocommunicate with every other computer, regardless of whether one computer is a Macintosh andthe other is a PC.

One important piece of information to keep in mind is that data flows 2 ways in the OSI model,DOWN (data encapsulation) and UP (data decapsulation).

The picture below is an example of a simple data transfer between 2 computers and shows howthe data is encapsulated and decapsulated:


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Explanation :

The computer in the above picture needs to send some data to another computer. The Applicationlayeris where the user interface exists, here the user interacts with the application he or she isusing, then this data is passed to the Presentation layerand then to the Session layer. These threelayer add some extra information to the original data that came from the user and then passes itto the Transport layer. Here the data is broken into smaller pieces (one piece at a time

transmitted) and the TCP header is a added. At this point, the data at the Transport layeris calledasegment.

Each segment is sequenced so the data stream can be put back together on the receiving sideexactly as transmitted. Each segment is then handed to theNetwork layerfor network addressing(logical addressing) and routing through the internet network. At theNetwork layer, we call thedata (which includes at this point the transport header and the upper layer information) apacket.

TheNetwork layeradd its IP header and then sends it off to the Datalink layer. Here we call thedata (which includes theNetwork layerheader, Transport layerheader and upper layerinformation) aframe. The Datalink layeris responsible for taking packets from theNetworklayerand placing them on the network medium (cable). The Datalink layerencapsulates eachpacket in a frame which contains the hardware address (MAC) of the source and destination

computer (host) and the LLC information which identifies to which protocol in the prevoiuslayer (Network layer) the packet should be passed when it arrives to its destination. Also, at theend, you will notice the FCS field which is the Frame Check Sequence. This is used for errorchecking and is also added at the end by the Datalink layer.

If the destination computer is on a remote network, then the frame is sent to the router orgateway to be routed to the desination. To put this frame on the network, it must be put into adigital signal. Since a frame is really a logical group of 1's and 0's, the Physical layeris


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responsible for encapsulating these digits into a digital signal which is read by devices on thesame local network.

There are also a few 1's and 0's put at the begining of the frame, only so the receiving end cansynchronize with the digital signal it will be receiving.

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It is a process of adding a header to wrap the data that flows down the OSI model.

Encapsulation Process

Wrapping up of data into a protocol is also known as encapsulation.

1. The Application layer, Presentation layer and Session layer create data fromuser's input.

2. Encapsulation actually starts at layer 4 of the osi model where the Transportlayer convert the data into segments by adding a header containing sourceand destination port numbers.

3. The Network layer convert the segments into packets (or datagram) by

adding a header containing source and destination IP address.

4. The Data link layer convert the packets into Frames by adding a headercontaining source and destination MAC address and a trailer containing theFrame check sequence(FCS)used for verifying the data integrity.

5. The Physical layer convert the frames to bits and it is transmitted through thephysical medium which can be a UTP,

6. OSI Reference Model :-Open Systems Interconnection ( OSI ) is a standard reference model for communicationbetween two end users in a network. The model is used in developing products and

understanding networks. Also see the notes below the figure.
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Illustration republished with permission from The manual Page.

OSI divides telecommunication into seven layers. The layers are in two groups. The upperfour layers are used whenever a message passes from or to a user. The lower three layers areused when any message passes through the host computer. Messages intended for thiscomputer pass to the upper layers. Messages destined for some other host are not passed upto the upper layers but are forwarded to another host. The seven layers are:

Layer 7: The application layer ...This is the layer at which communication partners areidentified, quality of service is identified, user authentication and privacy are considered, andany constraints on data syntax are identified. (This layer is notthe application itself, although

some applications may perform application layer functions.)

Layer 6: The presentation layer ...This is a layer, usually part of an operating system, thatconverts incoming and outgoing data from one presentation format to another (for example,from a text stream into a popup window with the newly arrived text). Sometimes called thesyntax layer.
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Layer 5: The session layer ...This layer sets up, coordinates, and terminates conversations,exchanges, and dialogs between the applications at each end. It deals with session andconnection coordination.

Layer 4: The transport layer ...This layer manages the end-to-end control (for example,determining whether all packets have arrived) and error-checking. It ensures complete data

transfer.Layer 3: The network layer ...This layer handles the routing of the data (sending it in theright direction to the right destination on outgoing transmissions and receiving incomingtransmissions at the packet level). The network layer does routing and forwarding.

Layer 2: The data-link layer ...This layer provides synchronization for the physical leveland does bit-stuffing for strings of 1's in excess of 5. It furnishes transmission protocolknowledge and management.

Layer 1: The physical layer ...This layer conveys the bit stream through the network atthe electrical and mechanical level. It provides the hardware means of sending and receivingdata on a carrier.

The TCP/IP model

TCP/IP is based on a four-layer reference model. All protocols that belong to the TCP/IPprotocol suite are located in the top three layers of this model.

As shown in the following illustration, each layer of the TCP/IP model corresponds to one ormore layers of the seven-layer Open Systems Interconnection (OSI) reference model proposedby the International Standards Organization (ISO).

The types of services performed and protocols used at each layer within the TCP/IP model aredescribed in more detail in the following table.

Layer Description Protocols

Application Defines TCP/IP application protocols and how hostprograms interface with transport layer services to usethe network.

HTTP, Telnet, FTP,TFTP, SNMP, DNS,SMTP, X Windows, other


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application protocols

TransportProvides communication session management betweenhost computers. Defines the level of service and statusof the connection used when transporting data.

TCP, UDP, RTP

Internet

Packages data into IP datagrams, which contain sourceand destination address information that is used toforward the datagrams between hosts and acrossnetworks. Performs routing of IP datagrams.

IP, ICMP, ARP, RARP

Networkinterface

Specifies details of how data is physically sent throughthe network, including how bits are electrically signaledby hardware devices that interface directly with anetwork medium, such as coaxial cable, optical fiber, ortwisted-pair copper wire.

Ethernet, Token Ring,FDDI, X.25, Frame Relay,RS-232, v.35

For more information about ARP, IP, ICMP, IGMP, UDP, and TCP, see Understanding TCP/IP.Note

The OSI reference model is not specific to TCP/IP. It was developed by the ISOin the late 1970s as a framework for describing all functions required of anopen interconnected network. It is a widely known and accepted referencemodel in the data communications field and is used here only for comparisonpurposes.

OR

TCP/IP Reference ModelThe TCP/IP model does not same as OSI model. There is no universal agreement regarding howto define TCP/IP with a layered model but it is generally agreed that there are fewer layers thanthe seven layers of the OSI model.TCP/IP model define 4 layers that are as follows:

1) Internet layer :Packet switching network depends upon a connectionless internetwork layer. This layer is knownas internet layer, is the linchpin that holds the whole design together. Its job is to allow hosts toinsert packets into any network and have them to deliver independently to the destination. Theymay appear in a different order than they were sent in each case it is job of higher layers torearrange them in order to deliver them to proper destination.

The internet layer specifies an official packet format and protocol known as internet protocol.The job of internet layer is to transport IP packets to appropriate destination. Packet routing isvery essential task in order to avoid congestion. For these reason it is say that TCP/IP internetlayer perform same function as that of OSI network layer.

2) Transport layer :In the TCP/IP model, the layer above the internet layer is known as transport layer. It is
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developed to permit entities on the source and destination hosts to carry on a conversation. Itspecifies 2 end-to-end protocols1)TCP (Transmission Control Protocol)2)UDP (User Datagram Protocol)

1) TCPIt is a reliable connection-oriented protocol that permits a byte stream originating on onemachine to be transported without error on any machine in the internet. It divides the incomingbyte stream into discrete message and passes each one onto the internet layer. At the destination,the receiving TCP process collects the received message into the output stream. TCP deals withflow control to make sure a fast sender cannot swamp a slow receiver with more message than itcan handle.

2) UDP

It is an unreliable, connectionless protocol for applications that do not want TCPs sequencing onflow control and wish to offer their own. It is also used for client-server type request-reply

queries and applications in which prompt delivery is more important than accurate delivery suchas transmitting speech or video.

Application Layer :In TCP/IP model, session or presentation layer are not present. Application layer is present onthe top of the Transport layer. It includes all the higher-level protocols which are virtual terminal(TELNET), file transfer (FTP) and electronic mail (SMTP).

The virtual terminal protocol permits a user on one machine to log into a distant machine andwork there. The file transfer protocol offers a way to move data efficiently from one machine toanother. Electronic mail was used for file transfer purpose but later a specialized protocol wasdeveloped for it.

The Application Layer defines following protocols

File Transfer Protocol (FTP)It was designed to permit reliable transfer of files over different platforms. At the transport layerto ensure reliability, FTP uses TCP. FTP offers simple commands and makes the differences instorage methods across networks transparent to the user. The FTP client is able to interact withany FTP server; therefore the FTP server must also be able to interact with any FTP client. FTPdoes not offer a user interface, but it does offer an application program interface for file transfer.The client part of the protocol is called as FTP and the server part of the protocol is known asFTPd. The suffix "d" means Daemon this is a legacy from Unix computing where a daemon is a

piece of software running on a server that offers a service.

Hyper Text Transfer ProtocolHTTP permits applications such as browsers to upload and download web pages. It makes use ofTCP at the transport layer again to check reliability. HTTP is a connectionless protocol thatsends a request, receives a response and then disconnects the connection. HTTP delivers HTMLdocuments plus all of the other components supported within HTML such as JavaScript, Visualscript and applets.


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Simple Mail Transfer ProtocolBy using TCP, SMTP sends email to other computers that support the TCP/IP protocol suite.SMTP provides extension to the local mail services that existed in the early years of LANs. Itsupervises the email sending from the local mail host to a remote mail host. It is not reliable foraccepting mail from local users or distributing received mail to recipients this is theresponsibility of the local mail system.

SMTP makes use of TCP to establish a connection to the remote mail host, the mail is sent, anywaiting mail is requested and then the connection is disconnected. It can also return a forwardingaddress if the intended recipient no longer receives email at that destination. To enable mail to bedelivered across differing systems, a mail gateway is used.

Simple Network Management ProtocolFor the transport of network management information, SNMP is used as standardized protocol.Managed network devices can be cross examined by a computer running to return details abouttheir status and level of activity. Observing software can also trigger alarms if certain

performance criteria drop below acceptable restrictions. At the transport layer SNMP protocoluses UDP. The use of UDP results in decreasing network traffic overheads.

4) The Host to Network Layer:Below the internet layer is great void. The TCP/IP reference model does not really say suchabout what happen here, except to point out that the host has connect to the network using someprotocol so it can transmit IP packets over it. This protocol is not specified and varies from hostto host and network to network.

A firewall is a part of a computer system or network that is designed to block unauthorizedaccess while permitting authorized communications. It is a device or set of devices configured topermit, deny, encrypt, decrypt, orproxy all (in and out) computer traffic between differentsecurity domains based upon a set of rules and other criteria.

Firewalls can be implemented in either hardware or software, or a combination of both. Firewallsare frequently used to prevent unauthorized Internet users from accessing private networksconnected to the Internet, especially intranets. All messages entering or leaving the intranet passthrough the firewall, which examines each message and blocks those that do not meet thespecified security criteria.

There are several types of firewall techniques:

1. Packet filter: Packet filtering inspects each packet passing through the

network and accepts or rejects it based on user-defined rules. Althoughdifficult to configure, it is fairly effective and mostly transparent to its users.In addition, it is susceptible to IP spoofing.

2. Application gateway: Applies security mechanisms to specific applications,such as FTP andTelnet servers. This is very effective, but can impose aperformance degradation.
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3. Circuit-level gateway: Applies security mechanisms when aTCP or UDPconnection is established. Once the connection has been made, packets canflow between the hosts without further checking.

4. Proxy server: Intercepts all messages entering and leaving the network. Theproxy server effectively hides the true network addresses.

A metropolitan area network(MAN) is a largecomputer networkthat usually spans a cityor a large campus. A MAN usually interconnects a number oflocal area networks (LANs)using a high-capacity backbone technology, such as fiber-optical links, and provides up-linkservices to wide area networksand the Internet.

The IEEE 802-2001 standard describes a MAN as being: A MAN is optimized for a largergeographical area than a LAN, ranging from several blocks of buildings to entire cities.MANs can also depend on communications channels of moderate-to-high data rates. A MANmight be owned and operated by a single organization, but it usually will be used by manyindividuals and organizations. MANs might also be owned and operated as public utilities.They will often provide means for internetworking oflocal networks. Metropolitan areanetworks can span up to 50km, devices used are modem and wire/cable }}

What Is a MAC Address?

The MAC address is a unique value associated with a network adapter. MAC

addresses are also known as hardware addresses or physical addresses. They

uniquely identify an adapter on a LAN.

MAC addresses are 12-digit hexadecimal numbers (48 bits in length). By convention, MACaddresses are usually written in one of the following two formats:

MM:MM:MM:SS:SS:SS

MM-MM-MM-SS-SS-SS

The first half of a MAC address contains the ID number of the adapter manufacturer.

These IDs are regulated by an Internet standards body (see sidebar). The second

half of a MAC address represents the serial number assigned to the adapter by the

manufacturer. In the example,

00:A0:C9:14:C8:29

The prefix

00A0C9

indicates the manufacturer is Intel Corporation.

Why MAC Addresses?

Recall that TCP/IP and other mainstream networking architectures generally adopt

the OSI model. In this model, network functionality is subdivided into layers. MAC

addresses function at the data link layer (layer 2 in the OSI model). They allow

computers to uniquely identify themselves on a network at this relatively low level.
http://en.wikipedia.org/wiki/Circuit-level_gatewayhttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/Proxy_serverhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Wide_area_networkhttp://en.wikipedia.org/wiki/Wide_area_networkhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/IEEEhttp://en.wikipedia.org/wiki/LANhttp://en.wikipedia.org/wiki/Local_networkhttp://en.wikipedia.org/wiki/Local_networkhttp://en.wikipedia.org/wiki/Modemhttp://compnetworking.about.com/library/glossary/bldef-adapter.htmhttp://compnetworking.about.com/library/glossary/bldef-lan.htmhttp://compnetworking.about.com/library/glossary/bldef-osi.htmhttp://en.wikipedia.org/wiki/Circuit-level_gatewayhttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/Proxy_serverhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Wide_area_networkhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/IEEEhttp://en.wikipedia.org/wiki/LANhttp://en.wikipedia.org/wiki/Local_networkhttp://en.wikipedia.org/wiki/Modemhttp://compnetworking.about.com/library/glossary/bldef-adapter.htmhttp://compnetworking.about.com/library/glossary/bldef-lan.htmhttp://compnetworking.about.com/library/glossary/bldef-osi.htm


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MAC vs. IP Addressing

Whereas MAC addressing works at the data link layer, IP addressing functions at the

network layer (layer 3). It's a slight oversimplification, but one can think of IP

addressing as supporting the software implementation and MAC addresses as

supporting the hardware implementation of the network stack. The MAC address

generally remains fixed and follows the network device, but the IP address changesas the network device moves from one network to another.

IP networks maintain a mapping between the IP address of a device and its MAC address. Thismapping is known as the ARP cache orARP table.ARP, the Address Resolution Protocol,supports the logic for obtaining this mapping and keeping the cache up to date.

DHCP also usually relies on MAC addresses to manage the unique assignment of IP addresses todevices.

OR

Short for Media Access Control address, a hardware address that uniquely

identifies each node of a network. In IEEE 802 networks, the Data Link Control (DLC)layer of the OSI Reference Model is divided into two sublayers: the Logical Link

Control (LLC) layerand the Media Access Control (MAC) layer. The MAC layer

interfaces directly with the network medium. Consequently, each different type of

network medium requires a different MAC layer.

On networks that do not conform to the IEEE 802 standards but do conform to the OSIReference Model, the node address is called theData Link Control (DLC) address.
http://compnetworking.about.com/library/glossary/bldef-arp.htmhttp://compnetworking.about.com/library/glossary/bldef-arp.htmhttp://compnetworking.about.com/library/glossary/bldef-dhcp.htmhttp://www.webopedia.com/TERM/M/node.htmlhttp://www.webopedia.com/TERM/M/network.htmlhttp://www.webopedia.com/TERM/M/IEEE.htmlhttp://www.webopedia.com/TERM/M/DLC.htmlhttp://www.webopedia.com/TERM/M/DLC.htmlhttp://www.webopedia.com/TERM/M/OSI.htmlhttp://compnetworking.about.com/library/glossary/bldef-arp.htmhttp://compnetworking.about.com/library/glossary/bldef-dhcp.htmhttp://www.webopedia.com/TERM/M/node.htmlhttp://www.webopedia.com/TERM/M/network.htmlhttp://www.webopedia.com/TERM/M/IEEE.htmlhttp://www.webopedia.com/TERM/M/DLC.htmlhttp://www.webopedia.com/TERM/M/DLC.htmlhttp://www.webopedia.com/TERM/M/OSI.html

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