FRAME RELAY

Frame Relay merupakan layanan jaringan komunikasi data dengan teknologi Frame switching yang berkecepatan tinggi untuk menghubungkan satu atau beberapa lokasi ke berbagai lokasi tujuan (point to multi point) baik di dalam ataupun luar negeri pada waktu yang bersamaan. Dalam lalu lintas komunikasi yang padat, Frame Relay jauh lebih efisien daripada sirkit sewa (leased line) yang disediakan khusus untuk satu pelanggan (dedicated), yang umumnya hanya terpakai 10% sampai 20% dari kapasitas lebarpita (bandwidth)-nya. Dalam paket yang berisi data elektronik, masih dilengkapi dengan deteksi kesalahan, dan ada konfirmasi dari penerima yang berbentuk kode, apakah paket dapat diterima secara utuh. Dala paket data terdapat istilah frame (bingkai) yang berfungsi untuk menyatakan batas bingkai sebuah paket. Sedangkan batas frame sendiri ditandai dengan flag, sehingga data akan dibawa sepanjang jalur komunikasi dalam bentuk frame-frame. Berikut ini stuktur dari sebuah frame :

GFI = General Format Identifier
LCN = Logical Channel Number
LGN = Logical Channel Group Number
PKT TYPE ID = packet type identification
FCS = Frame check sequence
DLCI = data link connection Indentifier
C/R = Command/response field bit
(application specific-not modified by network)
FECN = Forward Explicit Congestion notification
BECN = Backward Explicit Congestion notification
DE = Discard Eligibility Indicator
EA = Address Extension
Gambar 1. (a) Struktur dasar frame, (b) Field informasi pada X.25 (c) Struktur frame pada Frame Relay, dan (d) Format header pada Frame Relay

Koneksi LAN to LAN dengan berbagai aplikasi voice, multimedia, video conference dan aplikasi berbasis client-server / telnet / terminal emulation dengan sentralisasi database yang mencakup :
1. File transfer
2. Email
3. Web Intranet
4. Data entry
5. Pengendalian persediaan
6. Payment point
7. Corporate Internet dedicated

Aplikasi transaksional dan interaktif yang mencakup:
1. Online antar cabang
2. Reservasi hotel/tiket pesawat

KEUNGGULAN LAYANAN :
1. Bandwidth minimum yang diperoleh digaransi melalui parameter Committed Information Rates (CIR)
2. Memperoleh garansi bandwitdh dan kelebihan bandwith yang fleksibel
3. Tersedia beragam media akses yang digunakan
4. Ragam pilihan kecepatan sesuai dengan kebutuhan pelanggan
5. Pelayanan aduan gangguan 24 jam sehari dan 7 hari seminggu.
6. Cakupan layanan di seluruh Indonesia dan 220 negara di dunia.

SPESIFIKASI TEKNIS :
1. Tingkat kehandalan tinggi dengan dukungan sistem transmisi Fiber Optic dan network yang handal
2. Lebih ekonomis untuk berbagai tujuan karena menggunakan satu saluran fisik untuk menghubungi ke berbagai tujuan (star)
3. Memungkinkan pengelolaan trafik data yang bersifat bursty
4. Keberagaman pilihan protokol komunikasi dan jenis aplikasi
5. Tingkat keamanan yang tinggi karena merupakan jaringan private

Verbs as Complements

Verbs that are always followed by the infinitive.

Some verbs can take another verb as the complement instead of a noun. Sometimes the verbs functioning as the complement mustbe in the infinitive (to + verb) and sometimes it must be in the gerund ( verb + ing) form.The following verbs are always followed by the infinitive if the complement is a verb.

agree, attempt, claim, decide, demand,

desire, fail, forget, hesitate, hope,

intend, learn, need, offer, plan,

prepare, pretend, refuse, seem, strive

ten, try, want, wish.


- The president will attempt to reduce inflation in the next four years.

- The soldiers are preparing to attack the village.

- Cinthya has agreed to act as a liason between the two countries.


Verbs that are always followed by the gerund.

Other verbs must alwaysbe followed by the gerund. These verbs include:

admit, appreciate, avoid, can’t help, consider,

delay, deny, enjoy, finish, mind,

miss, postpone, practice, quit, recall,

regret, report, resent, resist, resume,

risk, suggest,


- John admitted stealing the jewels.

- Would you mind not smoking in this office?

- Michael was considering that building in its present condition.


Note : These sentences are made negative by adding the negative particle not before the infinitive or gerund.

- John decided not to buy the car.

- We regretted not going to the party last night.

The following verbs can be followed by either the infinitiveor the gerund with no change in meaning.

begin, can’t stand, continue, dread, hate,

like, love, prefer, start.


- He started to study after dinner, OR, He started studying after dinner.

- Joan hates to ride her bicycle to school, OR, Joan hates riding her bicycle to school.


Verbs + prepositions followed by the gerund

approve of , be better of, count on, depend on,

give up, insist on, keep on, put off,

rely on, succeed in, think about, think of,

worry about.
The following expressions contain the preposition to. The word to in these expressions must not be confused with the to in the infinitive. These verb + preposition expressions must also be followed by the gerund.

object to, look forward to, confess to.


- Marry insisted on taking the bus instead of the plane.

- Fred confessed to stealing the jewels.

- Henry is thinking of going to France in August.

Adjectives, Nouns, and Pronouns

Adjectives + prepositions followed by the gerund

Accustomed to, afraid of, capable of, fond of,

Intent on, interested in, successful in, tired of.


- Jean is not capable of understanding the predicament.

- Alvaro is intent on finishing school next year.

- Craig is fond of dancing.


Nouns + prepositions followed by the gerund

choice of , excuse for, intention of, method for,

possibility of, reason for, (method of),


- George has no excuse for dropping out of school.

- There is no reason for leaving this early.

- Connie has developed a method for evaluating this problem.


Any time a preposition is followed directly by a verb, the verb will be in the gerund form.

- After leaving the party. Ali drove home.

- He should have stayed in New York instead of moving to Maine.


Adjective followed by the infinitive

anxious, boring, dangerous, hard,

eager, easy, good, strange,

pleased, prepared, ready, able*,

usual, common, difficult.

*able means the same as capable in many instance, but the grammar is very different. While able is followed by the infinitive, capable is followed by of + [verb + ing].

- These students are not yet able to handle such difficult problems\

- These students are not yet capable of handling such difficult problem.


Examples of adjectives followed by infinitive

- Muhammad is anxious to see his family.

- We are ready to leave now.

- It is difficult to pass this test.


Some verbs can be followed by either the infinitive or gerund, but the meaning changes.

stop, remember, forget.


- John stopped studying. {John is not going to study anymore}

- John stopped to study. {John stopped doing something in order to study}


Pronouns before the gerund or infinitive:

allow, ask, beg, convince, expect, instruct,

invite, order, permit, persuade, prepare, promise, remind, urge, want.


Subject + verb + complement form {pronoun / noun} + [to + verb]. . .

- Joe asked Marry to call him when she woke up.

- We ordered him to appear in count.

- You should prepare your son to take this examination.


However, before the gerund, a noun or pronoun must appear in the possessive form.

Subject + verb + possessive form {noun / pronoun} + [verb + ing]. . .

- We understand your not being able to stay longer.

- He regrets her leaving.

- We object to their calling at this hour.


Pronouns


Subject : a, you, she, he, it, we, you, they.

Complement : me, you, her, him, it, us, you, them.

Passive Adjective : my, your, her, his, its, our, your, their.

Possesive : mine, yours, hers, his, its, ours, yours, theirs.

Reflective : myself, yourself, herself, himself, itself, ourselves, yourselves, themselves.
Diposkan oleh aditha_citra's blog di 06:36

Exercises

Execrice :

1. This pen isn’t working. Please give me another. (singular)
2. If you’re still thirsty. I’ll make another pot of coffee.
3. This dictionary has a page missing. Please give me the other. (the last one)
4. He does not need those books. He needs the others. (all the remaining)
5. There are thirty people in he room. Twenty are from Latin America and the other are from other countries.
6. Six people were in the store. Two were buying meat. Another was looking at magazines. Another was eating a candy bar. The other were walking around looking for more food. (notice the verbs)
7. This glass of milk is sour. Another glass of milk is sour too.
8. The army was practicing its drills. One group was doing artillery. The other was practicing combat tactics.
9. There are seven student from Japan. The others are from Iran, and others are from other places.
10. We looked at four cars today. The first two were far too expensive, but the other one were reasonably priced.


Exercise : Simple Present and Present Progressive

1. Something smells very good.
2. We are eating dinner at seven o’clock tonight.
3. He practices the piano every day.
4. They are driving to school tomorrow.
5. I believe you.
6. Maria has a cold.
7. Jorge is swimming right now.
8. John hates smoke.
9. Jill always gets up at 6:00 A.M.
10. Jerry is mowing the lawn now.


Execrice : Simple Past Tense and Past Progressive

1. Gene was eating dinner when his friend called.
2. While Maria was cleaning the apartment, her husband was sleeping.
3. At three o’clock this morning. Eleanor was studying.
4. When Mark arrived, the Johnsons were having dinner, but they stopped in order to talk to him.
5. John went to France last year.
6. When the teacher entered the room, the students were talking.
7. While Joan was writing the report, Henry was looking for more information.
8. We saw this movie las night.
9. At one time, Mr. Roberts owned this building.
10. Joes was writing a letter to from the present perfect.


Exercise : Present Perfect and Simple Past

1. John wrote his report las night.
2. Bob has seen this movie before.
3. Jorge has read the newspaper already.
4. Mr. Johnson has worked in the same place for thirty-five years, and he is not planning to retire yet.
5. We haven’t begun to study for the test yet.
6. George went to the store at ten o’clock this morning.
7. Joan has travelled around the world.
8. Betty wrote a letter last night.
9. Guillermo called his employer yesterday.
10. We have not seen this movie yet.


Exercise : Past Perfect and Simple Past

1. The policeman read the suspect his right after he had arrested him.
2. After John had washed his clothes. He began to study.
3. George had waited for one hour before the bus came.
4. Maria entered the university after she had graduated from the community collage.
5. Jeanette washed the pipettes after she had completed the experiment.
6. Jane sent a letter to her university after she had received her scholarship check.
7. After the stewardesses has served launch to the passengers, they sat down.
8. The car had flipped ten times before eat landed on eats roof.
9. We corrected own paper after we had taken de quiz.
10. John had lived in Miami for one ear, when his parents came to visit.

Keamanan Jaringan

Beberapa Ancaman dan Serangan
• Tujuan utama dengan adanya keamanan adalah untuk membatasi akses informasi dan sesumber hanya untuk pemakai yang memiliki hak akses.
• Ancaman keamanan:
o Leakage (Kebocoran) : pengambilan informasi oleh penerima yang tidak berhak
o Tampering : pengubahan informasi yang tidak legal
o Vandalism (perusakan) : gangguan operasi sistem tertentu. Si pelaku tidak mengharap keuntungan apapun.
• Serangan pada sistem terdistribusi tergantung pada pengkasesan ke saluran komunikasi yang ada atau membuat saluran baru yang menyamarkan (masquerade) sebagai koneksi legal
• Penyerangan Aktif, Secara aktif memodifikasi komunikasi atau data
o Pemalsuan atau pengubahan Email
o TCP/IP Spoofing

Beberapa Metode Penyerangan
• Eavesdropping, mendapatkan duplikasi pesan tanpa ijin
• Masquerading, Mengirim atau menerima pesanmenggunakan identitas lain tanpa ijin mereka
• Message tampering,
o Mencegat atau menangkap pesan dan mengubah isinya sebelum dilanjutkan ke penerima sebenarnya. “man-in-the-middle attack” adalah bentuk message tampering dengan mencegat pesan pertama pada pertukaran kunci enkripsi pada pembentukan suatu saluran yang aman. Penyerang menyisipkan kunci lain yang memungkinkan dia untuk mendekrip pesan berikutnya seelum dienkrip oleh penerima
• Replaying, menyimpan pesan yang ditangkap untuk pemakaian berikutnya.
• Denial of Service, membanjiri saluran atau sesumber lain dengan pesan yang bertujuan untuk menggagalkan pengaksesan pemakai lain

Keamanan Transaksi Elektronik
Keamanan sangat dibutuhkan pada kebanyak transaksi
• E-commerce
• Banking
• E-mail

Transaksi elektronik dapat aman jika dilindungi dengan kebijakan dan mekanisme keamanan. Contoh : Pembeli harus dilindungi terhadap penyingkapan kode credit number selama pengiriman dan juga terhadap penjual yang tidak bersedia mengirim barang setelah menerima pembayaran. Vendor harus mendapatkan pembayaran sebelum barang dikirim, sehingga perlu dapat memvalidasi calon pembeli sebelum memberi mereka akses

Kebijakan dan Mekanisme Keamanan
• Pemisahan antara kebijakan dan mekanisme keamanan akan membantu memisahkan kebutuhan implementasinya
o Kebijakan menspesifikasikan kebutuhan
o Mekanisme menerapkan spesifikasi kebijakan tersebut
• Berdasar spesifikasi dari OSI, sebuah layanan (kebijakan) keamanan meliputi :
o Access Control, Perlindungan terhadap pemakaian tak legak
o Authentication, Menyediakan jaminan identitas seseorang
o Confidentiality (kerahasiaan), Perlindungan terhadap pengungkapan identitas tak legak
o Integrity, Melindungi dari pengubahan data yang tak legak
• Untuk mencapai layanan keamanan tersebut, mekanisme-mekanisme yang dapat diterapkan :
o Enkripsi
 Digunakan untuk menyediakan kerahasiaan, dapat menyediakan authentication dan perlindungan integritas
o Digital Signature
 Digunakan untuk menyediakan authentication, perlindungan integritas, dan non-repudiation
o Algoritma Checksum/Hash
 Digunakan untuk menyediakan perlindungan integritas, dan dapat menyediakan authentication
o Satu atau lebih mekanisme dikombinasikan untuk menyediakan security service

Berikut adalah contoh program yang dapat menghasilkan kunci Public/Private Key dengan menggunakan algoritma RSA :

import javax.net.*;
import javax.net.ssl.*;
import java.security.*;
public class getPublicPrivateKey {
public static void main(String[] args) {
try {
//1024-bit Digital Signature Algorithm (DSA)
KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA");
keyGen.initialize(1024);
KeyPair keypair = keyGen.genKeyPair();
PrivateKey privateKey = keypair.getPrivate();
PublicKey publicKey = keypair.getPublic();
System.out.print("Public Key : " + publicKey);
System.out.print("Private Key : " + privateKey);
// Generate a 576-bit DH key pair
keyGen = KeyPairGenerator.getInstance("DH");
keyGen.initialize(576);
keypair = keyGen.genKeyPair();
privateKey = keypair.getPrivate();
publicKey = keypair.getPublic();
System.out.print("Public Key : " + publicKey);
System.out.print("Private Key : " + publicKey);
// Generate a 1024-bit RSA key pair
keyGen = KeyPairGenerator.getInstance("RSA");
keyGen.initialize(1024);
keypair = keyGen.genKeyPair();
privateKey = keypair.getPrivate();
publicKey = keypair.getPublic();
System.out.print("Public Key : " + publicKey);
System.out.print("Private Key : " + privateKey);
}catch (java.security.NoSuchAlgorithmException e) {}
}
}

Digital Signature
• Didasarkan pada suatu ikatan tanda (yang tak dapat dirubah) ke suatu pesan atau dokumen yang hanya diketahui oleh si penandatangan.
• Hal ini dapat dicapai dengan cara mengenkrip sebuah pesan terkompresi (digest) dengan menggunakan private key
• Digest memiliki ukuran yang tetap yang dihasilkan dari sebuah secure digest function.


Contoh ilustrasinya :
• A ingin menandatangani dokumen M, sehingga penerima dapat yakin bahwa M adalah berasal dari A.
• A menghitung digest dokumen dengan fungsi Digest(M).
• A mengenkrip digest dengan private keynya, dan ditambahkan ke M, sehingga menghasilkan {Digest(M)}KApriv.
• B menerima dokumen tersebut dan mengambil M dan menghitung Digest(M).
• B mendekrip dengan {Digest(M)}KApriv menggunakan KApub dan membandingkan isinya dengan hasil perhitungan Digest(M). Jika sama, tandatangan adalah valid.