Data Communications-Midterm

LAN Ethernet Protocol Architecture

Link-layer protocol consists of two sub-layers (or divides the OSI Data Link layer into 2 sub-layers): Medium Access Control (MAC) Logical Link Control (LLC)

MAC Address

MAC address is within a network. Each port on a router has its own MAC address.

Mobile Network Forecast-Video

Mobile Video Will Generate 66% of Mobile Data Traffic by 2015

Why Segmentation? Disadvantages

More computed on both the sending and receiving ends Duplicates are possible and must be dealt with by detecting and deleting them

Why Multiplexing

Multiple telephone lines between same locations required multiple physical cables With multiplexing, multiple cables can be replaced with one cable

Multiplexing vs. Channel Access Methods

Muxing is a layer 1 operation. Channel access method or multiple access method occurs at layer 2. The language and ideas are very similar but they are different. Muxing is dealing with the physical medium while channel access describes how NICs access the medium. Multiplexing also occurs at the Transport Layer.

Why Ethernet for high speed networks: CSMA/CD (Negative)

Negative CSMA/CD is not an ideal choice for high-speed LAN design because it does not scale well - at high data rates lots of bits are transmitted before and error is realized and retransmission is performed - but there are reasons for retaining Ethernet protocols

IP Address Structure--Network

Network to which the address belongs Commonly associated with an ISP Can be associated with large organization, e.g. a university

TCP Functions--Stop and Wait Mechnisms

No data is sent until receipt of the previous segment is acknowledged and receiver indicates it can accommodate 320 bytes

TCP Functions--Connection Establishment:

No data is sent until receipt of the previous segment is acknowledged and receiver indicates it can accommodate 320 bytes Solution: 3-way Handshake Before communication starts, sender and receiver negotiate a set of sequence numbers to use in TCP

Internet Protocol (IP)

First used on a large scale in Berkeley Software Distribution (BSD) UNIX (UNIS - UNiplexed Information and Computing Service. It would eventually support multiple simultaneous users, and be renamed UNIX) Most common protocol at the Network Layer Estimated usage exceeds 75% of all network traffic Most current uses of the Internet (http, IM, bit-torrent, movie downloads) did not exist at the time of creation of IP Even email was only specified a year later in Aug 1982 in RFC 821 IP does not provide end-to-end reliability, sequencing, etc. These tasks are performed by TCP - it is connection-oriented. (However, UDP is connectionless!)

Multiplexing Diagram

General multiplex scheme: data on lines (channels) are multiplexed into a single fast line; the demultiplexer receives the multiplexed data stream and extracts the original channels to be transferred.

What is a Port

Hardware and software ports Hardware port is typically identified by its connector (USB ports, RJ 45, RJ 11, etc.) Software ports in computer networking are numbered (port 80 = http, port 443 = https, port 25 = SMTP, 22 = Secure Shell, 161 = SNMP)

Ethernet Address Representation

Hexadecimal Notation Address broken up into 12 4-bit blocks Each 4-bit block is represented on the NIC as a hexadecimal digit 0-F or 0-f

Ethernet Address Representation (Hexadecimal Notation)

Hexadecimal notation Address broken up into 12 - 4-bit blocks Each 4-bit block is represented on the NIC as a hexadecimal digit 0-F or 0-f

Hubs

Hubs send data out to all computers Old technology, original Ethernet, but can be useful for network diagnostics

MAC Address

A Media Access Control address (MAC address) is a unique identifier assigned to each NIC for communications at the physical layer. The MAC is a six byte address written in the NIC card in hexadecimal. The first 3 bytes are the Organizationally Unique Identifier or the next 3 bytes are Network Interface Controller specific. Read by layer 2 switches.

Circuit Switching

A circuit is an electronic closed-loop path among two or more points Circuit switched networks typically bill by the minute

Dotted-Decimal Notation

32 bit addresses broken into 4 blocks of 8 bits each Each block converted to decimal representation Decimals are separated by dots

Twisted Pair

8 individual strands of copper wire are organized as four pairs Each pair of wires is twisted around each other Twisting reduces interference Tighter twisting improves data rates

Connection-Data Communication Transmission

A connection is requested The receiver acknowledges and establishes the connection Receiver acknowledges receipt of data Receiver can ask to have the data repeated (automatic repeat request or ARQ)

Gigabit (Layer 3 switched) Ethernet

Is downward compatible; that is, it accommodates the CSMA/CD protocol and Ethernet format and Layer 2 switched implementations. Uses Cat 5e or Cat 6.

ASCII

ASCII - American Standard Code for Information Interchange

IP Address--Address Class

Address Class Specifies network size Initially 5 classes (2 rarely used) Class A largest organizations Class B large organizations (such as VCU) Class C small businesses

Ethernet Fields

Allows receiver to synchronize with sender Bit pattern produces a periodic waveform in the medium when encoded by the physical layer using Manchester encoding

Dynamic IP Addressing

An IP address is 'leased' to a device An IP address from a pool is assigned to a node for a number of hours. When the device disconnects or when the lease expires the IP address is returned to the pool of available IPs

Analog Singals

Are made up of sign waves. Sign waves have three properties: Amplitude, Frequency, and Phase.

Ethernet Fields Error Detection:

As the packet moves from source to destination, errors can be introduced Ethernet uses CRC-32, which can detect: 100% of the errors affecting 32 or fewer bits 99.99999998% of errors involving more than 33 bits

TCP Segmentation

At the receiving end, TCP collects all fragments from IP, reassembles them into the original data and passes it to the receiving application Divide data into segments of 64K or less (called Segmentation) These segments are sometimes called datagrams A sequence number is assigned to each datagram Sequence numbers help the receiving host order segments when they are received out of order

802.3 Medium Notation

Because there are so many options, the standard notation format has been established:<data rate in Mbps><signaling method><maximum segment length in hundreds of meters><T for twisted pair><F for fiber>

Layer 2 Switches--Cuts Through

Begins repeating the frame as soon as it recognizes the destination MAC address but does not check the FCS (CRC) for errors. Faster than Store and forward, but increased chance of error

Binary Numbers Overview

Binary numbers are extremely important in data communications IP addresses use binary numbers Used to compute subnet sizes, broadcast addresses etc. Maximum computer network size depends upon the number of bits available IP addresses are grouped in octets so you need to be able to convert from 8-bit binary numbers to decimal and vice-versa

Role of Destination Address:

Can immediately ignore packet without correct destination address Saves time by not reading every packet

Computer Networks in Business

Chevron (CIO magazine, 2002) Electronic level monitors in tanks at filling stations and satellite communication links between filling stations and the inventory management system ensures that stations never run out of gas The system has all but eliminated "retains," the aborted delivery because the tank is too full

Class D Networks

Class D Networks The first 4 bits are "1110" so that the first octet ranges from 224-239 or 11100000-11101111 These are Multicasting addresses - not much multicast is done on the Internet, but if you want to multicast you use a class D IP destination address. Class D has is no specific concept of a network ID and host ID as in classes A, B and C. So, the full range of multicast addresses is from 224.0.0.0 to 239.255.255.255. Since multicast addresses represent a group of IP devices (sometimes called a host group) they can only be used as the destination of a datagram; never the source.

Solutions--eliminates address classes

Classless Inter-Domain Routing (CIDR) Defined in RFC 1519 Focus here on addressing component of RFC Address blocks can be of arbitrary length (any power of 2) Primarily benefits medium-sized organizations Too big for Class C (~250 hosts) Too small for Class B (~65,000 hosts)

Multiplexing

Combines multiple channels of information on a common transmission medium

Features of Computer Networks--Many of the basic principles have not changed for over 4 decades!

Common set of technologies support all networked computer applications Therefore, any device attached to the network can perform these functions

Data to Signal--How Can we send Data

Convert it to a signal that represents a stream of bits (binary 0 or 1)

TCP/IP Stack

Core Technologies: TCP - Transmission Control Protocol IP - Internet Protocol Integrates two popular sets of technologies: TCP/IP Ethernet Modern Computer Networks use 4-Layers

Crossover Cable

Crossover cable- The wire connected to pin 1 on one side will no longer be connected to pin 1 on the other side. Four wires will "cross over" in a crossover cable. Specifically, the wiring of pins 1, 2, 3, and 6 are "crossed-over" to pins 3, 6, 1, and 2. Used to connect like devices.

Dynamic Host COnfiguration Protocol

DHCP is a protocol for automatic assignment of IP addresses in an organization's network.

Uder Diagram Protocol (UDP)

Defined in RFC 768 (1980) Many applications do not need TCP In these cases, if we can avoid TCP, we eliminate the overhead of keeping track of sequence numbers, window sizes etc.

Signals

Detectable transmitted energy that can be used to carry information or A time-dependent variation of a characteristic of a physical phenomenon, used to convey information

Transmission Impairments

Distortion Delay Signals travel at different speeds through media (higher frequency is possible in the center so a message sent at different frequencies can arrive at different times) Environment Weather, terrain, structures, other signals Electromagnetic Interference (EMI) Attenuation loss of signal (measured in dBs) Noise External interference, heating, cross-talk (measured in dBs)

Switching

Eliminates the need for point-to-point direct connections between every node in a network

Using Broadcast Method

Ensures Packet reaches destination Simplifies the technology Increases the processing load on the network and each device

Why Segmentation? Advantages

Errors are less likely in smaller segments Less retransmission if error is introduced into a segment during transmission Easier for routers to hold smaller segments in memory if outbound router is busy

CSMA/CD Ethernet Process

Ethernet and CSMA/CD (IEEE 802.3) Four step procedure If medium is idle, transmit If medium is busy, listen until idle and then transmit If collision is detected, cease transmitting After a collision, wait a random amount of time before retransmitting

Packet Receipt in Ethernet

Ethernet operation is based on broadcast Signal is transmitted to all stations connected to the medium All computers on the network get the packet But only PC B opens it

Ethernet (MAC) Address Representation

Example: go to command prompt (cd/) then enter c>ipconfig /all

Layer 3 Switches

Implement the packet-forwarding logic of the router in hardware at the Network layer - Layer 3. Implementation can be either Packet-by-packet or flow based. Packet-by-packet switching operates like a traditional router. Logic is in hardware and achieves an order of magnitude increase in performance over the software-based routers. A flow-based switch identifies flows of IP packets that have the same source and destination and uses this information to develop connection-oriented flows that speed up the forwarding process.

Differential Manchester Encoding

In Differential Manchester again the code changes in the data period. A 0 is represented by a transition at the beginning of the data period and a transition in the mid. A 1 is represented by a no transition in the beginning of the period and a transition in the mid.

Manchester Encoding (2)

In Manchester and Differential Manchester the code changes in the data period, the amount of time required to transmit one bit. In Manchester IEEE 802.3, a 1 is expressed low to high and a 0 high to low. Widely used in Ethernet and RFID applications.

TCP Functions Reliability Continued...

In addition to ACKs, reliability requires a checksum in the TCP header. If a segment is damaged, the receiver simply discards it, waits for the time out, and the sender resends the segment.

CDM

In code division multiplexing, each sending receiving pair has a unique coding scheme. In this way, multiple messages can be sent over the same channel are decoded by different receiving stations.

Trunking

In the context of VLANs, Cisco use the term "trunking" to mean "VLAN multiplexing" - carrying multiple VLANs through a single network link by using a "trunking protocol". To allow for multiple VLANs on one link, frames from individual VLANs must be identified. The most common and preferred method, IEEE 802.1Q, adds a tag to the Ethernet frame header, labeling it as belonging to a certain VLAN.

SDM

In wired communication, space-division multiplexing simply implies different point-to-point wires for different channels. In wireless communication, space-division multiplexing is achieved by multiple antenna.

Factors Favoring Packet Switching over Ciorcuit Switching

Increase in interactive data traffic increases "burstiness" of data (i.e., high ratio of peak usage to mean usage) Packet switching enables efficient utilization of communication links by averaging needs among large numbers of users Allows for multitasking (concurrent access to the communication network) Up to 100 times more efficient than circuit switching

"Bursty Traffic"

Increasing interactive data traffic increases "burstiness" of data

Technology Milestone-Telegraph

Information carried as electrical signals over wires Patented in the United States in 1840 by Samuel F. B. Morse

Frame

LLC sub-layer frames data in a PDU MAC sub-layer frames data again by adding: MAC control Destination MAC address Source MAC address LLC Frame Check Sequence is Cyclic Redundancy Check (CRC)

Functions of the Network Layer

Layer responsible for transferring packets from the source device to the destination device via one or more networks.

CSMA/CD Disadvantages

Not scalable due to broadcasting Limited to about 250 users Network may not be available when needed Switching and over-provisioning are used to solve this problem

OSI Model:

OSI - Open Systems Interconnection Architecture Early networks involved vendor defined networking technologies: SNA, DECnet, Netware, Ethernet, Appletalk Created communication islands Strong need to ensure interoperability

Technology Milestone-Multiplexing

One wire carries multiple signals In 1874, the quadruplex telegraph developed by Thomas Edison transmitted two messages in each direction simultaneously, for a total of four messages transiting the same wire at the same time

Technology Milestone-Circuit Switching

One wire connects to multiple destinations March 10, 1891, Strowger switch patented

TCP Port Assignment Sender--

Operating system assigns one of the free ports to an application that requires network connectivity

TCP Functions Multiplexing:

Operating systems support multi-tasking Running more than one application concurrently A combination of the host's IP address and a port address together is called a socket A pair of sockets uniquely identifies each connection

Mobile Network Forecast-Data

Overall Mobile Data Traffic is Expected to Grow to 6.3 Exabytes / Month by 2015

Packet Switching

Packet switches are called routers Routers are devices used to interconnect two or more networks Packet switched networks typically bill by the MB

Packetization Overview

Packetization is breaking down a message into small pieces (called packets) these packets then independently traverse the network to their destination where they are delivered and reassembled Each packet has two parts Data to be delivered Overhead required for successful delivery and integration with other packets

Ethernet

Patented in 1977 by Robert M. Metcalfe Ethernet is a low-cost, high-speed communication technology for small networks Most common data link layer technology for LANs An Ethernet network can be up to 100 meters in radius and have up to 250 devices

The Transport Layer can deal with Segments and Segmentation:

Problem: The maximum packet size in IP is 65,536 (64K) bytes Solution: When an application needs to send a larger amount of data : Sender breaks data into smaller blocks Receiver reassembles these blocks

The Transport Layer Can Provide Reliable Service:

Problem: The network and lower layers can lose packets - packets are sent to the correct computer with "best effort" Solution: Using Acknowledgment Numbers, all data is acknowledged as being received.

Network Systems and Data Communications Analysts' Salary and Job Growth

Projections by the Bureau of Labor Statistics (2006 - 2016) Network systems and data communications analysts 2006 employment: 262,000 2016 projected employment: 402,000 Growth (23rd among all occupations): 140,000 Growth rate: 53% (highest among ALL occupations)

Fiber Optic

Properties: A thin strand of glass Can carry large volume of data over long distances Weighs much less than copper Throughput is thousands of times greater than copper Uses: Dominant in long distance communications Aggregate traffic is carried over fiber

`ATIS Definition

Providing transparent transmission of a bit stream over a circuit built from some physical communications medium*

Quadrature Amplitude Modulation (QAM)

Quadrature amplitude modulation (QAM) The two carrier waves, usually sine waves, are out of phase with each other by 90° and are called quadrature components — hence the name of the scheme. QAM wave is a combination of both phase modulation and amplitude modulation.

Checksums Continued...

Remember The checksum in IPv4 is only for the header (and there is no checksum in IPv6). This leaves only the Frame Check Sum at the Data-link layer. Ethernet frames are 1518 octets, but IP has capacity of 64K octets - lots of room for error!

Data

Representation of facts in a formalized manner suitable for communication, interpretation, or processing by humans or by automatic means

Rollover Cable

Rollover cable - all 8 wires in the cable are "rolled over" to another pin at the other end of the cable with the wire on pin 1 attaching to pin 8, pin 2 attaching to pin 7, and so on. Most commonly used to connect a computer terminal to a router's console (administrative command) port. This cable is typically flat (and has a light blue color) to help distinguish it from other types of network cabling.

Layer 2 Switches--store and forward

Routes it to appropriate output line after checking the FCS (CRC)

Packet Switching

Routing data using addressed packets so that a channel is occupied only during the transmission of the packet Network resources are allocated as needed First packet transmission occurred on Oct 29, 1969, in California Used extensively in computer networks

What is Multiplexing

Sending multiple signals simultaneously on the same medium Multiple TV channels on one coax cable All the different signals in the air space (e.g., Wi-Fi, cellphone, FM, AM, etc.)

Digital Signal

Signals in which information is represented in discrete steps

Technology Milestone-Packet Switching

Signals sent and switching performed only when information ready to be transferred Highly efficient compared to circuit switching First ARPANET transmission on Oct. 29, 1969

Analog Signal

Signals that have a continuous nature, and not discrete or pulsed

The Transport Layer Can Provide Multiplexing:

Solution: By combining port and IP addresses (a socket), the transport layer (TCP) can distinguish between different applications running on the same IP address.

Advantages of Layering

Specializes technology development Separation of functionality Simplification in upgrades Change from IPv4 to IPv6 does not require change in email clients or browsers Simplification in adding new technology Adding wireless network capability does not require change in web site addresses (URLs)

Logical Link Layer

Specifies method of addressing and controls the exchange of data Independent of topology, medium, and medium access control Three functions: Multiplexing - via Service Access Points Flow control Automatic Repeat Request (ARQ)

ASCII Binary Representation of Text

Standard method to convert characters to binary is ASCII code Numbers 0-127 represent common characters Letters to binary conversion

TCP Port Assignment Receiver--

Standard ports are assigned by the Internet Assigned Numbers Authority (IANA)

Straight Through Cable

Straight through cable - is used to connect a PC to a switch. The wire connected to pin 1 on one side is connected to pin 1 on the other side and pin 2 to pin 2 and so forth. Also called a "Patch" cord. Used to connect PC to network.

OSI Model

Strengths Very good basis to understand data networks Clearly specifies concept of a network layer Each layer provides defined services to the layer immediately above it And depends upon specified services from the immediately below it Weaknesses No one supplier has an entire solution

IP Address-Class Address Problem:

Unavailability of IP address blocks of reasonable size Class A, B, and C system failed to fit the requirements of most users. Explosive growth of routing tables

Switches

Switches only send the data to the intended destination This speeds up the network, at extremely low cost The directory of connections is called the forwarding table forwarding table is initially empty By reading the addresses of incoming frames, the switch builds and updates a forwarding table

Synchronous Optical Networking

Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are essentially the same. In packet-oriented data transmission, a packet frame usually consists of a header and a payload. The header is transmitted first, followed by the payload (and possibly a trailer, such as a CRC). In synchronous optical networking, this is modified slightly. The header is termed the overhead, and instead of being transmitted before the payload, is interleaved with it during transmission. Part of the overhead is transmitted, then part of the payload, then the next part of the overhead, then the next part of the payload, until the entire frame has been transmitted. The internal structure of the overhead and payload within the frame differs slightly between SONET and SDH, and different terms are used in the standards to describe these structures. Their standards are extremely similar in implementation, making it easy to interoperate between SDH and SONET at any given bandwidth. SONET/SDH are used in Asynchronous Transfer Mode (ATM) frames

TCP Functions--Flow Control:

TCP Flow Control provides a mechanism for the Receiver to control the maximum rate the Sender provides data

TCP Error Detection and Recovery

TCP does both error detection and error recovery using the sequence number and acknowledgement number Sequence = recovery ACK = detection

Connection Establishment-Three-way-hand-shake:

TCP only (Not applicable to UDP) Before data is transmitted: Sender transmits a TCP segment with the synchronization bit set (SYN=1). The objective here is to negotiate the sequence number. The sender suggests a number. Recipient responds with a TCP segment with both the SYN and ACK bits set (SYN/ACK) Sender responds with ACK Sender sends a finish (FIN) bit to takedown the connection

TCP Functions: Reliability

TCP provides a mechanism to ensure packet delivery

IP Addresses

The Internet Protocol requires each device that connects to the Internet to have a unique IP address An IP Address is a 32-bit value Unlike MAC (Ethernet) addresses, IP addresses are assigned by network administrators

OSI Architecture

The OSI architecture (model) is a logical structure for communications networks, standardized by the International Organization for Standardization (ISO) An effort by the ISO to standardize computer networks The "language" of the network professionals

TCP Overview of Operation

The application layer creates the data to be sent and passes it to its TCP module for transmission TCP fragments the data, adds sequence numbers to the fragments and hands them off to the Internet/ Network layer (IP) At the receiving end, TCP collects all fragments from IP, reassembles them into the original data and passes it to the receiving application

Connectionless Data Communication Transmission

The data is sent and we hope it arrives at its destination. There is no feedback from the destination to indicate whether it arrived or not.

Layering

The hierarchical arrangement of functionality such that lower layers provide functions and services that support the functions and services of higher layers

Business Data Communications

The movement of information from one computer application to an application on another computer by means of electrical or optical transmission systems

HOP Count

The number of hops a packet has taken toward its destination (it is kept in the packet header). Note: A packet with an exceedingly large hop count is discarded.

Transport Layer

The primary purpose of the transport layer is to provide data to the application layer such that, apart from time delay, the application layer receives the data as if it were being offered by the local device.

Manchester Encoding

The problem with a stream (series) of 1s or 0s is that it's easy to get lost; that is, simply representing 0s and 1s with continuous steams or series of +5V or -5V is that it is subject to bit creeping; in other words it is NOT self-synchronizing or self-clocking . There are coding schemes that are self-clocking such as Manchester and Differential Manchester.

Noise and Signals

The received signal can be seriously distorted by noise. The receiver has to be able to interpret the result correctly for reliable data transmission. Repeater - reconstitutes the actual binary transmission Amplifier - boosts the received signal

Packet Switching Network-HOP

The trip a packet takes from one router to another.

Static IP Addressing

There are a limited number of IP addresses There are more devices on the network then IP addresses Devices are constantly being added and removed from the network

Transport Layer-Protocols (TCP)

Transmission Control Protocol (TCP) Connection Oriented RFC 793 (Sep 1981) Most popular protocol, highly reliable host-to-host protocol over packet switched networks

Media Types and Properties

Twisted-pair (copper) Fiber Optic (glass) Interacts with the environment Provides a transmission path that propagates a signal Enables efficient transmission (movement) of signals

Functions of the Data Link Layer (Addressing & Error Detection)

Two primary functions: Addressing (switching) Encapsulates packets (network layer PDUs) into frames and MAC addressing (switches) Error Detection Detect and discards errors that may occur in the Physical Layer

Why Ethernet for high speed networks: CSMA/CD (Positive)

Use of switched Ethernet (layer 2 switches) can eliminate collisions greatly reducing the negative resulting from a standard implementation of CSMA/CD. IEEE 802.3 is well understood; vendors have experience building networks using this standard. Easy for customers to understand and integrate with existing systems

Class E Networks

Used for experimental purposes only and you cannot assign these IP addresses to your devices. Four left most bits of the left most octet of a "Class E" network is reserved as "1111".

Transport Layer Protocols--Connectionless User Datagram Protocol (UDP)

User Datagram Protocol (UDP) RFC 768 (Aug 1980) For simpler tasks

VLAN

VLAN = Virtual LAN VLANs provide the ability to define broadcast domains without the constraint of physical location. For example, instead of making all of the users on the third floor part of the same broadcast domain (because they're on the same Hub), you might use VLANs (by replacing the hubs with layer 2 switches) to make all of the users in the HR department part of the same broadcast domain.

Copper Wire

Very good conductor of electricity (Silver is best; however, it is very expensive!) Relatively abundantly available

CSMA/CD Advantages

Very simple to implement, therefore inexpensive and fast Alternatives are complex

Packetization Requires:

We now know that data is sent as packets Packetization requires: specifying user commands (e.g., http://...) segmentation and reassembly of packets Identifying and locating packet destination error control and correction signaling Much of this information needs to be included with the data in what is called a frame.

CSMA/CD Collision

What if multiple senders want to send data at the same time? The outcome is called a collision; its solution is called Carrier Sense Multiple Access with Collision Detection

Ethernet (Packet in the Medium)

When PC A wants to send data to PC B, it first adds B's address to the frame Like putting a letter in an envelope and putting a To: address on top The frame is then sent into the medium Similar to dropping the letter into the mailbox

Router

When a router receives a packet, there are 3 possibilities: The host destination is on the router's network The host destination is not on the network, but the router's routing table has an entry for where to forward the packet The host destination is not on the network and the router's routing table does not have an entry for where to forward the packet

Switch Operations--Flooding

happens when the switch's forwarding table has no entry for the frame's destination MAC address. The switch then sends out the frame to every single port on the switch except for the one from the host the frame came in on. Unknown unicast frames are always flooded.

Circuit Switching

connection (circuit) is established before any data is sent and circuit is "owned" until end of transmission and parties disconnect.

Computer Networks--Applications:

email, IM , browser, client-server

Address Resolution Protocol

is a protocol used for resolving network layer addresses into link layer addresses.

Switch Operations--Forwarding

is performed when a switch's forwarding table has an entry for the frame's destination MAC address. The frame is then sent to the port with that MAC address host.

Switch Operations--Filtering

is performed when the switch's forwarding table has an entry for both the source and destination MAC addresses, and both the source and destination MAC addresses found in the forwarding table are on the same port.