Rabu, 11 November 2009

FRAME RELAY

Frame Relay

Saat ini saya akan membahas tentang frame relay dimana frame relay itu adalah protokol packet-switching yang menghubungkan perangkat-perangkat telekomunikasi pada satu Wide Area Network (WAN).[1] Protokol ini bekerja pada lapisan Fisik dan Data Link pada model referensi OSI.[2] Protokol Frame Relay menggunakan struktur Frame yang menyerupai LAPD, perbedaannya adalah Frame Header pada LAPD digantikan oleh field header sebesar 2 bita pada Frame Relay.

Keuntungan Frame Relay

Frame Relay menawarkan alternatif bagi teknologi Sirkuit Sewa lain seperti jaringan X.25 dan sirkuit Sewa biasa. Kunci positif teknologi ini adalah:[3]

  • Sirkuit Virtual hanya menggunakan lebar pita saat ada data yang lewat di dalamnya, banyak sirkuit virtual dapat dibangun secara bersamaan dalam satu jaringan transmisi.
  • Kehandalan saluran komunikasi dan peningkatan kemampuan penanganan error pada perangkat-perangkat telekomunikasi memungkinkan protokol Frame Relay untuk mengacuhkan Frame yang bermasalah (mengandung error) sehingga mengurangi data yang sebelumnya diperlukan untuk memproses penanganan error.
  • keuntungan frame relay adalah kita dapat menangaini eror pada perangkat-perangkat saliran komunikasi.
  • Standarisasi Frame Relay

    Proposal awal mengenai teknologi Frame Relay sudah diajukan ke CCITT semenjak tahun 1984, namun perkembangannya saat itu tidak signifikan karena kurangnya interoperasi dan standarisasi dalam teknologi ini. Perkembangan teknologi ini dimulai di saat Cisco, Digital Equipment Corporation (DEC), Northern Telecom, dan StrataCom membentuk suatu konsorsium yang berusaha mengembangkan frame relay. Selain membahas dasar-dasar protokol Frame Relay dari CCITT, konsorsium ini juga mengembangkan kemampuan protokol ini untuk berinteroperasi pada jaringan yang lebih rumit. Kemampuan ini di kemudian hari disebut Local Management Interface (LMI).


Rabu, 28 Oktober 2009

PRONOUNS

PRONOUNS

Possessive Pronouns and Adjectives

1. Forms of Possessive Pronouns and Adjectives

Person Pronoun Adjective
1st singular mine my
2nd yours your
3rd (female) hers her
3rd (male) his his
3rd (neutral) its its
1st plural ours our
3rd plural theirs their

2. Using Possessive Pronouns and Adjectives

A possessive pronoun is used instead of a noun:

Julie's car is red. Mine is blue.

A possessive adjective is usually used to describe a noun, and it comes before it, like other adjectives:

My car is bigger than her car.

Remember:

There are no apostrophes in possessive pronouns and adjectives.

The dog wagged its tail.

It's” is not a possessive pronoun or adjective — it means “it is”:

It's not my dog.

Subject Pronouns

Notes:

  1. The written lesson is below.
  2. Links to quizzes, tests, etc. are to the left.

A verb is an action word.

run
sit
eat
sink
swim
study



The main form of a verb is called the infinitive. In English, infinitives include the word "to."

to run
to sit
to eat
to sink
to swim
to study



The infinitive is the pure form of a verb. The infinitive is like a lump of clay that can be molded to match the subject of the sentence it is used in:

I speak
you speak
he/she speaks

we speak
you-all* speak

they speak

Note: The above forms are called conjugations of the infinitive "to speak."



Regarding the form "you-all" -- this usage is not considered to be standard English. In standard English, the same word is used for both the singular you and the plural you. That is, each of the following is correct:

You have a tail light out, ma'am.
You (kids) have soccer practice at four.



In the first sentence, "you" refers to the singular "ma'am." In the second sentence, "you" refers to the plural "kids." To avoid confusion between you (singular) and you (plural), we will employ the non-standard English usage "you-all" to indicate you (plural). This will be very beneficial to y'all, particularly at the beginning of your studies.



The words "I" "you" "he" "she" "we" "you-all" and "they" are called subject pronouns. Spanish has corresponding subject pronouns. Here's a list of the English subject pronouns and their Spanish equivalents:

yo
I
usted
you
él
he
ella
she
nosotros
we
ustedes
you-all
ellos
they


Spanish subject pronouns are both similar to and different from their English counterparts. Let's examine some of the differences. Look more closely at the English word "you."

You have just seen that this can be translated into Spanish as "usted." But there is also a second way it can be translated. There are two ways the English word "you" can be expressed in Spanish:

usted
you
you


Spanish has a formal and an informal form of the word "you." "Usted" is more formal and is generally used to express respect. "Tú" is more familiar and is used among friends, coworkers, relatives, or when addressing a child.

Speaking to your boss: usted
Speaking to your daughter:
Speaking to your teacher: usted
Speaking to your friend:

usted = you formal

= you informal (familiar)



This same distinction with regard to degree of formality occurs in the plural form as well. When referring to "you-all," there are two choices in Spanish:

ustedes
you-all formal

vosotros
you-all familiar



Once again, the difference lies in the degree of formality conveyed by the speaker. However, the vosotros form is used primarily in Spain. Throughout Latin America, "ustedes" is generally used in both formal and informal situations to refer to "you-all."

Speaking to a group of children
(in Spain): vosotros

Speaking to a group of children
(in Latin America): ustedes

Speaking to a group of strangers
(in Spain): ustedes

Speaking to a group of strangers
(in Latin America): ustedes

Note: usted can be abbreviated Ud. or Vd. ; ustedes can be abbreviated Uds. or Vds.



In many ways, Spanish is more gender-specific than English. We find evidence of this in the subject pronouns. First, look at the word "nosotros." This means "we" in the sense of a group containing at least one male. If the group contains only females, the word "nosotras" is used. So, in Spanish, there are two ways to say "we":

nosotros
we (masculine or mixed group)

nosotras
we (feminine)



This same idea applies to the English word "they":

ellos
they (masculine or mixed group)

ellas
they (feminine)



This same idea also applies to the "vosotros" form:

vosotros
you-all familiar (masculine or mixed group)

vosotras
you-all familiar (feminine)

Note: These forms are used primarily in Spain, not Latin America.



Finally, don't get confused over the difference between talking to a group or talking about a group. Consider the following statement, which could have been made by your Spanish teacher, while standing before the class:

"You-all need to study your Spanish. Those students in the other class don't need to study Spanish. They are studying French. You-all can practice Spanish in Spain. They can practice French in France."



The teacher is talking to the Spanish students and about the French students.

Talking to a group, use "you-all":

ustedes
vosotros
vosotras

Talking about a group, use "they":

ellos
ellas



Here's the complete list of Spanish subject pronouns:

Singular

yo - I
- you (familiar)
él - he
ella - she
usted - you (formal)

Plural

nosotros
we (masculine or mixed gender)
nosotras
we (feminine)
vosotros
you-all (familiar, Spain, masculine or mixed gender)
vosotras
you-all (familiar, Spain, feminine)
ellos
they (masculine or mixed gender)
ellas
they (feminine)
ustedes
you-all (formal in Spain, formal and familiar in Latin America)

SECURITI JARINGAN

JARINGAN KOMPUTER

Jaringan komputer LAN pada suatu organisasi yang membentuk intranet, yang dimana
Server-server saling berkomunikasi menggunakan suatu aturan yang di sebut protokol.Protokol komunikasi di Interenet di kenal dengan nama TCP/IP. TCP/IP bekerja secara
bertingkat atau memiliki layer-layer komunikasi. Protokol TCP/IP merupakan sekumpulan
protokol dengan 2 protokol utamanya adalah TCP dan IP.

Analogi komunikasi di atas seperti 2 orang kepala negara yang saling berkomunikasi
dengan surat. Permintaan aplikasi, misalnya http, sebagai kepala negara A, yang di tujukan
ke server aplikasi (web server), sebagai kepala negara B. Surat dari kepalan negara A
(dengan bahasa A) di terjemahkan dulu ke bahasa Inggris oleh seorang penterjemah,
kemudian di ketik dan di edit oleh sekertaris. Lalu dikirim melalui seorang kurir (jalur
transmisi). Di sisi penerima (negara B), surat tadi akan masuk ke sekertaris dan di proses
adminitrasinya, kemudian di terjemahkan ke bahasa B. Kedua kepala negara tidak seolaholah
saling berkomunikasi (komunikasi peer to peer) dengan bahasanya masing-masing.

permasalahan jaringan biasa terjadi pada perangkat yang tersambung dan terputusnya jaringan yang terhubung. komputer yang terhubung jaringan sering kali mengalamai permaslahan jaringan ini disebabkan banyaknya komputer yang terhubung dengan jaringan.

faktor-faktor yang menyebabkan terjadinya kerusakan adalah:

1. Mati atau tidak berfungsinya komponen pada jaringan, dimana bisa saja kerusakan ini desbabkan komponen-komponen yang terdapat pada jaringan contohnya SERVER, WORKSTATION, HUB/SWITCH, KABEL DAN KONEKTOR.

dimana ini semua dapat terjadi karena penyebab diatas. dan cara mengatasinya Periksa satu demi satu kemungkinan-kemungkinan yang ada. Namun kalau ternyata setelah dicoba semua kemungkinan tersebut masih juga belum menyelesaikan masalah, maka kemungkinan ada masalah secara software. Bisa jadi karena registry yang rusak (corrupt) akibat virus, malware, spyware, atau karena instalasi software yang tidak jelas asal-usulnya. contohnya...

1. Periksa HCL untuk menentukan apakah ada driver yang kompatibel dengan Windows XP dan tersedia untuk adaptor nirkabel Anda.

2. periksa alamat IP nya.

3. cek kabel yang terhubung sebagai jaringan.

4. jika menggunakan jaringan wriles cek IP alamatnya.

Selasa, 20 Oktober 2009

Present Perfect


[has/have + past participle]

Examples:

  • You have seen that movie many times.
  • Have you seen that movie many times?
  • You have not seen that movie many times.

Complete List of Present Perfect Forms

USE 1 Unspecified Time Before Now

We use the Present Perfect to say that an action happened at an unspecified time before now. The exact time is not important. You CANNOT use the Present Perfect with specific time expressions such as: yesterday, one year ago, last week, when I was a child, when I lived in Japan, at that moment, that day, one day, etc. We CAN use the Present Perfect with unspecific expressions such as: ever, never, once, many times, several times, before, so far, already, yet, etc.

Examples:

  • I have seen that movie twenty times.
  • I think I have met him once before.
  • There have been many earthquakes in California.
  • People have traveled to the Moon.
  • People have not traveled to Mars.
  • Have you read the book yet?
  • Nobody has ever climbed that mountain.
  • A: Has there ever been a war in the United States?
    B: Yes, there has been a war in the United States.

How Do You Actually Use the Present Perfect?

The concept of "unspecified time" can be very confusing to English learners. It is best to associate Present Perfect with the following topics:

TOPIC 1 Experience

You can use the Present Perfect to describe your experience. It is like saying, "I have the experience of..." You can also use this tense to say that you have never had a certain experience. The Present Perfect is NOT used to describe a specific event.

Examples:

  • I have been to France.
    This sentence means that you have had the experience of being in France. Maybe you have been there once, or several times.
  • I have been to France three times.
    You can add the number of times at the end of the sentence.
  • I have never been to France.
    This sentence means that you have not had the experience of going to France.
  • I think I have seen that movie before.
  • He has never traveled by train.
  • Joan has studied two foreign languages.
  • A: Have you ever met him?
    B: No, I have not met him.

TOPIC 2 Change Over Time

We often use the Present Perfect to talk about change that has happened over a period of time.

Examples:

  • You have grown since the last time I saw you.
  • The government has become more interested in arts education.
  • Japanese has become one of the most popular courses at the university since the Asian studies program was established.
  • My English has really improved since I moved to Australia.

TOPIC 3 Accomplishments

We often use the Present Perfect to list the accomplishments of individuals and humanity. You cannot mention a specific time.

Examples:

  • Man has walked on the Moon.
  • Our son has learned how to read.
  • Doctors have cured many deadly diseases.
  • Scientists have split the atom.

TOPIC 4 An Uncompleted Action You Are Expecting

We often use the Present Perfect to say that an action which we expected has not happened. Using the Present Perfect suggests that we are still waiting for the action to happen.

Examples:

  • James has not finished his homework yet.
  • Susan hasn't mastered Japanese, but she can communicate.
  • Bill has still not arrived.
  • The rain hasn't stopped.

TOPIC 5 Multiple Actions at Different Times

We also use the Present Perfect to talk about several different actions which have occurred in the past at different times. Present Perfect suggests the process is not complete and more actions are possible.

Examples:

  • The army has attacked that city five times.
  • I have had four quizzes and five tests so far this semester.
  • We have had many major problems while working on this project.
  • She has talked to several specialists about her problem, but nobody knows why she is sick.

Time Expressions with Present Perfect

When we use the Present Perfect it means that something has happened at some point in our lives before now. Remember, the exact time the action happened is not important.

Sometimes, we want to limit the time we are looking in for an experience. We can do this with expressions such as: in the last week, in the last year, this week, this month, so far, up to now, etc.

Examples:

  • Have you been to Mexico in the last year?
  • I have seen that movie six times in the last month.
  • They have had three tests in the last week.
  • She graduated from university less than three years ago. She has worked for three different companies so far.
  • My car has broken down three times this week.

NOTICE

"Last year" and "in the last year" are very different in meaning. "Last year" means the year before now, and it is considered a specific time which requires Simple Past. "In the last year" means from 365 days ago until now. It is not considered a specific time, so it requires Present Perfect.

Examples:

  • I went to Mexico last year.
    I went to Mexico in the calendar year before this one.
  • I have been to Mexico in the last year.
    I have been to Mexico at least once at some point between 365 days ago and now.

USE 2 Duration From the Past Until Now (Non-Continuous Verbs)

With Non-Continuous Verbs and non-continuous uses of Mixed Verbs, we use the Present Perfect to show that something started in the past and has continued up until now. "For five minutes," "for two weeks," and "since Tuesday" are all durations which can be used with the Present Perfect.

Examples:

  • I have had a cold for two weeks.
  • She has been in England for six months.
  • Mary has loved chocolate since she was a little girl.

Although the above use of Present Perfect is normally limited to Non-Continuous Verbs and non-continuous uses of Mixed Verbs, the words "live," "work," "teach," and "study" are sometimes used in this way even though they are NOT Non-Continuous Verbs.

ADVERB PLACEMENT

The examples below show the placement for grammar adverbs such as: always, only, never, ever, still, just, etc.

Examples:

  • You have only seen that movie one time.
  • Have you only seen that movie one time?

ACTIVE / PASSIVE

Examples:

  • Many tourists have visited that castle. Active
  • That castle has been visited by many tourists. Passive


Past perfect

Past Perfect Simple

had + 3rd column of irregular verbs

Example:
I had spoken

regular verbs: form of have + infinitive + ed

Example:
I had worked


The past perfect simple expresses an action taking place before a certain time in the past.

Form of Past Perfect Simple

PositiveNegativeQuestion
no differences I had spoken. I had not spoken. Had I spoken?

For irregular verbs, use the past participle form (see list of irregular verbs, 3rd column). For regular verbs, just add ed.

Exceptions in Spelling when Adding ed

Exceptions in Spelling when Adding edExample
after final e, only add d love – loved
final consonant after a short, stressed vowel
or l as final consonant after a vowel is doubled
admit – admitted
travel – travelled
final y after a consonant becomes i hurry – hurried

Use of Past Perfect

  • action taking place before a certain time in the past
    (putting emphasis only on the fact, not the duration)

    Example: Before I came here, I had spoken to Jack.

  • Conditional Sentences Type III (condition that was not given in the past)

    Example: If I had seen him, I would have talked to him.

Signal Words

  • already, just, never, not yet, once, until that day (with reference to the past, not the present)
  • If-Satz Typ III (If I had talked, …)




Rabu, 14 Oktober 2009

- SIMPLE PRESENT AND PROGRESSIVE

The simple present expresses daily habits or usual activities, as in (a) and (b). The simple present expresses general statements of fact, as in (c) and (d). In sum, the simple present is used for events or situations that exist always, usually, or habitually in the past, present, and future.

THE PRESENT PROGRESSIVE

(g) Ann can’t come to the phone right now because she is taking a shower.

(h) It’s noon. I am eating lunch at the cafeteria right now.

(i) Jimmy and Susie are babies. They are crying. I can hear them right now. Maybe they are hungry.

The present progressive expresses an activity that is in progress (is occurring, is happening) right now. The event is in progress at the time the speaker is saying the sentence. The event began in the past, is in progress now, and will probably continue into the future. FORM: am, is, are + -ing.


Using The Present Perfect Progressive And The Difference Between The Present Perfect Progressive And The Present Perfect.

Let's say that your friend calls you up and wants to take you out for dinner. You really don't feel like going because it started to rain early in the morning, and now it is very wet outside. It is too wet to go out. You are afraid of driving when the roads are so wet and slippery. You do not know the exact time the rain started, but you want to tell your friend that the rain started in the past (in this situation, early in the morning) and is still continuing. It is still raining. You would probably say

It has been raining all day, and the streets are too wet to go out now.

This grammar is called the present perfect progressive. It is used to say that something started in the past, and it is still happening. It is often used to answer how long questions with for and since.

So, how do you make the present perfect progressive? Good question! Here's how you make it:

It
has
been
raining
subject+have or has+been

+

verb with -ing

Again, the present perfect progressive is used when an activity started in the past and continues until now. For example, you may ask a college professor you met at a conference, "How long have you been teaching?" Professor Brown can answer, "I have been teaching for 23 years."

If you read our lesson on the present perfect, you would know that the present perfect cannot use a specific time, like yesterday (if you haven't read it, you can read it now). The present perfect progressive works the same way: you cannot use a specific time. Therefore, I have been teaching at Columbia University today is incorrect.

However, just like the present perfect, you can use the words since and for.

If you read our present perfect lesson, you might ask yourself, "What is the difference between the present perfect progressive and the present perfect?" That's another good question! Take a look at these 2 sentences:

Present Perfect ProgressiveI have been teaching at Columbia University for 23 years
Present Perfect

I have taught at Columbia University for 23 years.

The answer is very simple: there is NO DIFFERENCE. If you remember correctly, there are 2 kinds of present perfect:

SINCE or FOR?ExampleMeaning
1NO since or forI have smoked. NOT SURE it continues

The person smoked in the past (we don't know when), and he/she may still smoke, but we do not know.

2YES, there is since or forI have smoked for 12 years. SURE it continues

The person started to smoke 12 years ago, and he/she still smokes.

Do you see what the meaning of the second kind of present perfect is? It is the same meaning as the present perfect progressive! That's right! When the present perfect has since or for, it has the same meaning as the present perfect progressive!

As you can see, the present perfect has 2 meanings. However, the present perfect progressive has only 1 meaning: it started in the past and continues until now.

There is one more thing you must remember: some verbs usually do NOT have -ing. For example, we say I know you. We would never say I am knowing you. That's because know canNOT have -ing. Verbs that cannot have -ing are called stative verbs. Here is a list of stative verbs. The words on the following list rarely have -ing. Therefore, they are rarely used with the present perfect progressive.

STATIVE VERBS

knowunderstandowepossessbe
have*belongcontainequalresemble
tendperceivesupposebelievedecide
concludepreferlovelikeseem
*have with the meaning of possession: I have a pen.

Because these verbs cannot be used with the present perfect progressive, you can just use the present perfect with since or for:

INCORRECT

We have been knowing you for a long time.
CORRECTWe have known you for a long time.

In order to summarize the present perfect progressive and the present perfect, look at the following chart:

present perfect NO since or for I have lived in Korea. Not sure if this person still lives in Korea; the time is also unknown.
present perfect WITH since or forI have lived in Korea since 1997.We are sure this person still lives in Korea; we also know the time.
present perfect progressive I have been living in Korea since 1997.We are sure this person still lives in Korea; we also know the time.

The second and third sentences above have identical meanings. The first and second sentences have (potentially) different meanings even though they look almost the same.

You may be asking, "Which one should I use? When should I use the present perfect progressive, and when should I use the present perfect with since or for?"

Actually, for some verbs, it doesn't matter, for example, the verb live (see above). However, for many verbs, if you want to say that the action started in the past and continues until now, it is better to use the present perfect progressive. Take a look at the following examples:

NOT natural

We have painted our house since last night.
NaturalWe have been painting our house since last night.

example:

Directions: Rewrite the following sentences with the present perfect progressive. The first one has been done for you.


1. Jack is cooking. He started to do this 4 hours ago.

Jack has been cooking for 4 hours.

2.
My brother drives. He started to do this in 1968.

3. Carol lives in Morocco. She went there last month.

4. Timothy rides a bus to school. He started to do it when his car broke down.

5. Ping plays tennis. She started to do this when she was young.

6. Mick Jagger sings rock music. He started to do this 40 years ago with the Rolling Stones.

7. James knows how to repair a computer. He learned how to do it a long time ago.

8. Doctors and researchers look for a cure for cancer. They started to do this more than 100 years ago.

9. Patients use anesthesia during childbirth. They started to do this in the mid-1800s.

10. I am reading this lesson. I started to do this 10 minutes ago.

Answer:

1. Jack is cooking. He started to do this 4 hours ago.

Jack has been cooking for 4 hours.

2.
My brother drives. He started to do this in 1968.

My brother has been driving since 1968.

My brother has been driving for 33 years.

3. Carol lives in Morocco. She went there last month.

Carol has been living in Morocco for a month.

Carol has been living in Morocco since last month.

4. Timothy rides a bus to school. He started to do it when his car broke down.

Timothy has been riding a bus to school since his car broke down.

5. Ping plays tennis. She started to do this when she was young.

Ping has been playing tennis since she was young.

6. Mick Jagger sings rock music. He started to do this 40 years ago with the Rolling Stones.

Mick Jagger has been singing rock music with the Rolling Stones for 40 years.

7. James knows how to repair a computer. He learned how to do it a long time ago.

James has known how to repair a computer for a long time.

**Know cannot have -ing, so we use the present perfect with for which has the same meaning as the present perfect progressive.

8. Doctors and researchers look for a cure for cancer. They started to do this more than 100 years ago.

Doctors and researchers have been looking for a cure for cancer for more than 100 years.

9. Patients use anesthesia during childbirth. They started to do this in the mid-1800s.

Patients have been using anesthesia during childbirth since the mid-1800s.

10. I am reading this lesson. I started to do this 10 minutes ago.


OTHER & ANOTHER

OTHER, ANOTHER

These words refer to something different, remaining, or additional. They are placed before the noun. Another is used with singular nouns, other with singular or plural.

Plural: There are other jobs you could try.
Singular: Where's the other packet of cereals?

Singular: Have another cup of tea.


Other is an adjective meaning 'different'.
Another expresses quantity, something extra or additional.
Have the other cup of tea, not this cup.
Have another cup of tea, not just the one cup.

Some other and another are synonymous (they mean the same), true, but other and another are not. Another is a spelling fused from two words, an other, meaning not the same thing in meaning, shape or form, whereas other can mean same meaning, shape or form; e.g., not that shoe, the other shoe; not that shoe, but another shoe, something different.

On the other hand...speaking about a different perspective

The other day...speaking about a different day.
-It was raining the other day.

Another refers to something that is additional.

-I ate a cookie for dessert and I want another one (one more).
-I need another glass of water.
Reply With Quote

Selasa, 13 Oktober 2009

tugas artikel VOIP

VOIP

Voice over Internet Protocol (VoIP) adalah teknologi yang mampu melewatkan trafik suara, video dan data yang berbentuk paket melalui jaringan IP. Dalam komunikasi VoIP, pemakai melakukan hubungan telepon melalui terminal yang berupa PC atau telepon.

Di Era Globalisasi saat ini kita dapat melihat revolusi besar-besaran dalam system komunikasi
di seluruh dunia: diamana setiap orang mulai menggunakan PCs dan Internet untuk mencari
pekerjaan, berkomunikasi satu sama lain, untuk menukar data (seperti ganbar, suara, dan
dokumen). Dan terkadang berbicara satu sama lain menggunakan applikasi Netmeeting atau
Internet Phone.Dan untuk masa yang akan datang bagaimana penggunaan secara real−time
vocal communication: VoIP.

Dengan tuntutan perkembangan zaman yang cukup pesat yang jelas membutuhkan saran pendukung yang bisa diandalkan dari faktor efisiensi, kecepatan dan biaya maka penelitian terus dilakukan yang diawalin dengan kemampuan mengirimkan suara melalui Internet hanya merupakan eksperimen dari beberapa orang atau perusahaan kecil. Ini dimulai dengan perusahaan seperti Vocaltech dan kemudian pada akhirnya diikuti oleh Microsoft dengan program Netmeeting-nya. Pada saat itu jaringan komputer Internet masih sangat lambat. Di rumah-rumah (khususnya di Amerika) masih digunakan dial-up dengan kecepatan 36,6K. Backbone Internet pun masih kecil. Aplikasi yang bersifat menghabiskan bandwidth, seperti misalnya suara atau video, masih sangat terbatas penggunaannya di pusat penelitian yang memiliki bandwidth besar.
Seiring dengan berpacunya perkembangan teknologi yang cukup pesat hingga tak dapat terbendung, pada saat ini jaringan komputer Internet sudah masuk ke rumah-rumah dengan kecepatan yang cukup besar. Leased line lebih murah dibandingkan dahulu. Alternatif lain, seperti Wireless LAN, memberikan layanan dengan pita bandwidth yang besar dengan harga yang masih terjangkau oleh perusahaan kecil. Aplikasi yang berbau multimedia mulai dapat digelar di atas Internet. IP telephony menjadi memungkinkan dijalankan dengan menggunakan infrastruktur Internet. IP telephony dapat dibagi menjadi dua kategori; Internet Telephony dan VoIP. Perbedaan dari keduanya adalah Internet telephony menggunakan jaringan Internet yang umum (public internet),
sementara VoIP menggunakan jaringan privat meskipun masih menggunakan teknologi yang sama (Ada juga pengertian lain yaitu VoIP merupakan teknologi yang digunakan, yaitu Voice over IP. Sementara itu IP telepony terkait dengan layanan (service)). Teknologi lain pun, seperti Asynchronous Transfer Mode (ATM) juga dapat digunakan untuk telephony. Namun biasanya aplikasinya juga masih disebut atau digolongkan kedalam IP telephon

Prinsip dasar dari Voip berupa pengiriman sebuah sinyal ke remote destination/tujuan yang dapat dilakukan secara digital, dimana sebelum dilakukan pengiriman data yang berupa sinyal analog terlebih dahulu diubah ke bentuk data digital dengan ADC (analog to digital converter), kemudian ditransmisikan, dan dipenerima dilkukan kembali konversi dari data digital ke data analog dengan DAC (digital to analog converter). Begitu juga dengan VoIP, digitalisasi voice dalam bentuk packets data, dikirimkan dan dikonversi kembali dalam bentuk voice dipenerima.
Format digital lebih mudah dikendalikan ataupun diproses ; dalam hal ini dapat dikompresi, dan dapat diubah ke format yang lebih baik.dan data digital lebih tahan terhadap noise daripada analog.
TCP/IP networks dibuat atas packet-packet IP yang terdiri atas header (berfungsi mengatur komunikasi) dan memuat data yang akan dikirim: VoIP menggunakan tekhnologi ini untuk melewati jaringan dan sampai di tujuan. Untuk Lebih jelasnya bisa kita lihat dalam gambar 1. diagram dibawah ini.


Gambar-1

Untuk infrastruktur pengaplikasian Voip untuk pertama kalinya (sering disebut voip tardisional) pada umumnya dapat dilihat pada gambar 2.


Komponen-komponennya antara lain:
• Internet infrastructure
• Wireless Internet equipments
• Internet Telephony Gateway
• PABX


Untuk infrastruktur pengaplikasian Voip Setelah mengalami perkembangan dan banyak digunakan saat ini pada umumnya dapat dilihat pada gambar 3.



Protokol Penunjang Jaringan VoIP
Ada beberapa protokol yang menjadi penunjang jaringan VoIP, antara lain :

Protokol TCP/IP (Transfer Control Protocol/Internet Protocol); merupakan sebuah protokol yang digunakan pada jaringan Internet. Protokol ini terdiri dari dua bagian besar, yaitu TCP dan IP.

Application layer ;Fungsi utama lapisan ini adalah pemindahan file. Perpindahan file dari sebuah sistem ke sistem lainnya yang berbeda memerlukan suatu sistem pengendalian untuk mengatasi adanya ketidak cocokan sistem file yang berbeda – beda. Protokol ini berhubungan dengan aplikasi. Salah satu contoh aplikasi yang telah dikenal misalnya HTTP (Hypertext Transfer Protocol) untuk web, FTP (File Transfer Protocol) untuk perpindahan file, dan TELNET untuk terminal maya jarak jauh.

TCP (Transmission Control Protocol) ; Dalam mentransmisikan data pada layer Transpor ada dua protokol yang berperan yaitu TCP danUDP. TCP merupakan protokol yang connection-oriented yang artinya menjaga reliabilitas hubungan komunikadasi end-to-end. Konsep dasar cara kerja TCP adalah mengirm dan menerima segmen– segmen informasi dengan panjang data bervariasi pada suatu datagram internet. TCP menjamin realibilitas hubungan komunikasi karena melakukan perbaikan terhadap data yang rusak, hilang atau kesalahan kirim. Hal ini dilakukan dengan memberikan nomor urut pada setiap paket yang dikirimkan dan membutuhkan sinyal jawaban positif dari penerima berupa sinyal ACK (acknoledgment). Jika sinyal ACK ini tidak diterima pada interval pada waktu tertentu, maka data akan dikirikamkan kembali. Pada sisi penerima, nomor urut tadi berguna untuk mencegah kesalahan urutan data dan duplikasi data. TCP juga memiliki mekanisme fllow control dengan cara mencantumkan informasi dalam sinyal ACK mengenai batas jumlah paket data yang masih boleh ditransmisikan pada setiap segmen yang diterima dengan sukses. Dalam hubungan VoIP, TCP digunakan pada saat signaling, TCP digunakan untuk menjamin setup suatu call pada sesi signaling. TCP tidak digunakan dalam pengiriman data suara pada VoIP karena pada suatu komunikasi data VoIP penanganan data yang mengalami keterlambatan lebih penting daripada penanganan paket yang hilang.

User Datagram Protocol (UDP) ; UDP yang merupakan salah satu protocol utama diatas IP merupakan transport protocol yang lebih sederhana dibandingkan dengan TCP. UDP digunakan untuk situasi yang tidak mementingkan mekanisme reliabilitas. Header UDP hanya berisi empat field yaitu source port, destination port, length dan UDP checksum dimana fungsinya hampir sama dengan TCP, namun fasilitas checksum pada UDP bersifat opsional.UDP pada VoIP digunakan untuk mengirimkan audio stream yang dikirimkan secara terus menerus.UDP digunakan pada VoIP karena pada pengiriman audio streaming yang berlangsung terusmenerus lebih mementingkan kecepatan pengiriman data agar tiba di tujuan tanpa memperhatikan adanya paket yang hilang walaupun mencapai 50% dari jumlah paket yang dikirimkan. (VoIP fundamental, Davidson Peters, Cisco System,163) Karena UDP mampu mengirimkan data streaming dengan cepat, maka dalam teknologi VoIP UDPmerupakan salah satu protokol penting yang digunakan sebagai header pada pengiriman data selainRTP dan IP. Untuk mengurangi jumlah paket yang hilang saat pengiriman data (karena tidakterdapat mekanisme pengiriman ulang) maka pada teknolgi VoIP pengiriman data banyak dilakukan pada private network.

Internet Protocol (IP); Internet Protocol didesain untuk interkoneksi sistem komunikasi komputer pada jaringan paket switched.Pada jaringan TCP/IP, sebuah komputer diidentifikasi dengan alamat IP. Tiap-tiapkomputer memiliki alamat IP yang unik, masing-masing berbeda satu sama lainnya. Hal ini dilakukan untuk mencegah kesalahan pada transfer data. Terakhir, protokol data akses berhubungan langsung dengan media fisik. Secara umum protokol ini bertugas untuk menangani pendeteksiankesalahan pada saat transfer data. Untuk komunikasi datanya, Internet Protokol mengimplementasikan dua fungsi dasar yaitu addressing dan fragmentasi. Salah satu hal penting dalam IP dalam pengiriman informasi adalah metode pengalamatan pengirimdan penerima. Saat ini terdapat standar pengalamatan yang sudah digunakan yaitu IPv4 denganalamat terdiri dari 32 bit. Jumlah alamat yang diciptakan dengan IPv4 diperkirakan tidak dapatmencukupi kebutuhan pengalamatan IP sehingga dalam beberapa tahun mendatang akan diimplementasikan sistim pengalamatan yang baru yaitu IPv6 yang menggunakan sistim pengalamatan 128 bit.

Jumat, 09 Oktober 2009

Pertamax

Jujur blog ini di buatin... HAHAHAHA ,,,