Bentuk Tenses

TENSES

Bentuk-Bentuk Waktu

Secara sederhana, tense berarti bentuk kata kerja yang menunjukkan waktu. Kata kerja itu dapat memberitahu kita:

Bahwa suatu tindakan atau kegiatan dilakukan pada waktu sekarang.

Bahwa suatu tindakan atau kegiatan dilakukan pada waktu lampau.

Bahwa suatu tindakan atau kegiatan dilakukan pada waktu yang akan datang.

A. Present Tense (waktu sekarang)

1) Simple present tense (waktu sekarang sederhana)

Menjelaskan peristiwa yang terjadi di waktu sekarang dalam bentuk sederhana atau suatu pekerjaan/perbuatan yang dilakukan berulang-ulang, atau kebiasaan sehari-hari, atau peristiwa/perbuatan yang tidak ada kaitannya dengan waktu.

bentuk :

I / we / you / they + Infinitive

He / she / it + Infinitive + s

a) Dipakai untuk menyatakan perbuatan yang dilakukan karena kebiasaan

Contoh: I go to school every day. Saya pergi ke sekolah setiap hari

b) Dipakai untuk menyatakan kebenaran umum yang tidak dapat diubah

Contoh: The sun rises in the east. Matahari terbit di sebelah timur

Catatan :

Jika pokok kalimatnya orang ketiga tunggal (he, she, it), maka bentuk dasar kata kerja akan mengalami perubahan :

Pada umumnya bentuk dasar kata kerja (infinitive) ditambah s.

to speak speaks = berbicara

to help helps = membantu

Infinitif yang berakhiran dengan huruf hidup (vokal) ditambah es.

to do does = berbuat, mengerjakan

to go goes = pergi

Infinitif yang berakhiran dengan huruf mati (konsonan) ch,sh,s atau x, ditambah es.

to teach teaches = mengajar, mengajarkan

to wish wishes = mengharapkan, memujikan

Infinitif yang berakhir dengan vokal e, walaupun berakhiran suara huruf z atau j, ditambah s saja.

to use uses = mengguakan, memakai

to change changes = mengubah, menukarkan

Infinitif yang berakhir dengan konsonan y yang didahului oleh huruf mati, y diganti dengan i, lalu ditambah es.

to fly flies = terbang

to study studies = mempelajari

Infinitif yang berakhir dengan konsonan y yang didahului oleh huruf hidup, ditambah s saja.

to buy buys = membeli

to play plays = bermain, memainkan

Infinitif tidak mengalami perubahan apapun jika didahului oleh kata kerja bantu can, could, may, wil, dsb.

Contoh: He can speak English. Ia dapat berbicara bahasa Inggris

2) Present continuous tense (waktu berlangsung sekarang)

Menerangkan suatu perbuatan yang sedang berlangsung pada waktu sekarang.

bentuk :

To be (am, are, is) + present participle (Ing form)

untuk semua pokok kalimat baik jamak maupun tunggal.

a) Dipakai untuk menyatakan perbuatan yang sedang berlangsung.

Contoh: They are studying English now. Mereka sedang mempelajari bahasa Inggris sekarang

b) Dipakai untuk menyatakan perbuatan yang bersifat sementara.

She is reading now but she will write soon. Ia sedang membaca sekarang tetapi ia akan segera menulis

c) Dipakai untuk menyatakan perbuatan yang dimaksud pada waktu yang akan datang.

We are writing again in a few weeks. Kami akan mengirimkan surat lagi dalam beberapa minggu

Kekecualian :

Tidak semua kata kerja boleh dipakai dalam bentuk present continuous tense walaupun kalimatnya diucapkan ketika peristiwa sedang berlangsung. Ada sekelompok penting kata kerja yang biasanya tidak digunakan dalam present continuous :

1. Verbs of emotion, kata-kata kerja yang menyatakan perasaan : to like , to dislike, to refuse,

to wan.t dsb.

Contoh: I like Mr. Brown. Saya suka pada tuan Brown (bukan I am liking Mr. Brown)

2. Verbs of the senses, kata-kata kerja yang menyatakan hal, yang berhubungan dengan pancainder : to feel, to hear, to see, to smell, to taste, dsb.

Contoh: I feel heavy in the head. Saya merasa pusing

3. Verbs of thought or opinion, kata-kata kerja yang menyatakan pikiran atau pendapat : to

believe, to expect, to forget, to know, to prefer, to realize, to think, to understand, dsb.

Contoh: I believe your word. Saya percaya akan perkataan anda

4. Verbs of possession, kata-kata kerja yang menyatakan : to own, to belong to, to owe, dsb.

Contoh: He owns two cars. Ia memiliki dua mobil

Cara pembentukan Present Participle

Pada umumnya present participe dibentuk dengan menambahkan ing pada bentuk dasar kata kerja.

Contoh:

to apply applying = menggunakan

to betray betraying = berkhianat, menghianati

to go going = pergi

Jika bentuk dasar kata kerja yang bersuku kata satu dan bertekanan itu berakhir dengan sebuah

huruf mati yang didahului oleh sebuah huruf hidup, konsonan terakhir itu digandakan, lalu ditambah ing.

Contoh:

to cut cutting = memotong

to dun dunning = menagih

to jog jogging = berlari-lari pelan

Jika infinitif yang bersuku kata dua atau lebih itu tekanannya jatuh pada suku kata terakhir

serta berakhiran huruf mati yang didahului oleh sebuah vokal, huruf mati terakhir itu

digandakan lalu ditambah ing.

Contoh:

to allot allotting = membagikan, memberikan

to begin beginning = mulai,memulai

to accur occurring = terjadi

Jika infinitif yang bersuku kata dua itu berakhiran konsonan L yang didahului oleh sebuah

vokal, huruf terakhir L itu digandakan, lalu ditambah ing.

Contoh:

to control controlling = memeriksa, mengawasi

to propel propelling = mendorong, menggerakkan

Jika infinitif bersuku kata satu atau dua itu berakhiran konsonan L yang didahului oleh dua

buah vokal, konsonan L terakhir itu tidak boleh digandakan, hanya ditambah ing saja.

Contoh:

to sail sailing = berlayar, berangkat

to seal sealing = menutup, menyegel

to conceal concealing = merahasiakan, menyembunyikan

Jika infinitif berakhiran vokal e yang didahului oleh konsonan, e harus dihilangkan lalu

ditambah ing.

Contoh:

to come coming = datang

to change changing = mengganti, mengubah, menukar

to ride riding = menunggang, naik (sepeda, mobil,dsb)

Jika infinitif berakhiran vokal e yang didahului oleh vokal i, terlebih dulu ie diganti dengan y lalu ditambah ing.

Contoh:

to die dying = layu (bunga)

to lie lying = berbaring, berdusta

to tie tying = mengikat

3) Present perfect tense (waktu selesai sekarang)

Menerangkan peristiwa yang telah terjadi pada waktu lampau yang masih ada hubungannya dengan masa sekarang namun waktu terjadinya tidak diketahui.

bentuk :

I / we / you / they + Have + Past Participle

He / she / it + Has + Past Participle

a) Dipakai untuk menyatakan suatu kegiatan yang dilakukan pada waktu lampau dan masih ada kaitannya dengan waktu sekarang.

Contoh:

She has taught English since five years ago. Ia telah mengajarkan bahasa Inggris sejak lima

tahun lalu

I have lived here for three years. Saya telah bertempat tinggal di sini selama tiga tahun

b) Menyatakan peristiwa yang telah terjadi

Contoh:

I have seen it. Saya telah melihatnya

c) Menunjukkan suatu perbuatan ulangan pada waktu yang tidak tertentu sebelum sekarang. Sering dipakai kata-kata seperti before, already, ever, never, yet.

Contoh:

I have heard this before. Saya telah mendengar hal ini sebelumnya

I have already seen him. Saya telah menjumpainya

I haven’t ever been there. Saya tak pernah kesana

d) Menunjukkan perbuatan yang selesai pada waktu yang singkat. Dalam hal ini sering dipakai kata-kata seperti at last, finally, just, recently.

Contoh:

The time has at last arrived. Akhirnya telah tiba waktunya

Finally, she has started to sing. Akhirnya, ia mulai menyanyi

I have just spoken to him. Saya baru saja berbicara dengannya

4) Present perfect continuous tense (waktu selesai sedang berlangsung sekarang)

Menyatakan perbuatan yang dimulai pada waktu lampau dan masih berlangsung hingga sekarang.

bentuk :

I / we / they + Have + Been + Present Participle

He / she / it + Has + Been + Present Participle

Contoh:

I have been staying at his place this month. Saya telah sedang tinggal di rumahnya sebulan ini

We have been waiting for you since eight o’clock. Kami telah sedang menantikan anda sejak pukul delapan

She has been studying English for over three years. Ia telah sedang mempelajari bahasa Inggris selama lebih dari tiga tahun

B. Past Tense (waktu lampau)

1) Simple past tense (waktu lampau sederhana)

Menerangkan peristiwa yang terjadi atau tindakan kegiatan, perbuatan dan atau pekerjaan yang dilakukan pada waktu lampau dalam bentuk sederhana dan diketahui pula waktu terjadinya peristiwa atau pekerjaan yang dilakukan itu.

bentuk :

I / we / you / they + Past Tense

he / she / it + Past Tense

a. Dipakai untuk menyatakan perbuatan yang selesai dilakukan pada waktu lampau.

Contoh: I saw a good film last night. Saya menonton film yang baik tadi malam

He went to Surabaya last week. Ia pergi ke Surabaya minggu lalu

2) Past continuous tense (waktu berlangsung lampau)

Menyatakan peristiwa atau perbuatan yang sedang berlangsung pada waktu lampau pada saat peristiwa yang lain terjadi atau perbuatan yang lain dilakukan

bentuk :

I / he / she / it Was + Present Participle

We / you / they Were + Present Participle

a) Menyatakan perbuatan yang sudah dimulai dan masih berlangsung ketika perbuatan lain menyusul pada waktu lampau.

Contoh: While I was bathing in the river I heard a fearful cry. Ketika saya sedang mandi di sungai itu, kudengar jeritan yang menakutkan

When you called me, I was listening to the radio. Ketika anda menelepon saya, saya sedang

mendengarkan radio

b) Menyatakan perbuatan yang sedang terjadi pada waktu lampau.

Contoh: He was watching television all afternoon yesterday. Ia sedang menonton televisi sepanjang sore kemarin

3) Past perfect tense (waktu selesai lampau)

Menerangkan suatu perbuatan yang sudah selesai dilakukan pada waktu lampau, atau menjelaskan dua peristiwa yang telah terjadi, tetapi menegaskan peristiwa mana yang terlebih dahulu terjadi.

bentuk :

Had + Past Participle

a. Dipakai untuk menyatakan suatu perbuatan yang telah selesai sebelum suatu perbuatan lain dilakukan pada masa lampau.

Umpamanya, pertimbangkan dua buah peristiwa yang berikut:

On Sunday morning, I painted my car. Pada hari Minggu pagi, saya mengecat mobil saya

At lunch-time, my brother arrived. Pada waktu makan siang, saudara laki-laki saya tiba

Namun untuk menggabungkan kedua peristiwa itu, kita menggunakan past perfect tense :

Contoh: When my brother arrived, I had painted my car. Ketika saudara laik-laki saya tiba, saya telah mengecat mobil saya

Tegasnya past perfect harus digunakan apabila waktu suatu perbuatan lampau adalah lebih lampau daripada perbuatan lainnya. Perbuatan yang pertama selesai kita gunakan past perfect dan perbuatan kedua kita gunakan simple past tense.

Contoh: The train had left before I arrived. Kereta api telah berangkat sebelum saya tiba

I had copied the lesson before she came home. Saya telah mengutip pelajaran itu sebelum ia

pulang

4) Past perfect continuous tense (waktu sedang berlangsung selesai lampau)

Menyatakan perbuatan yang sudah dimulai dan masih berlangsung pada waktu lampau.

bentuk :

Had + Been + Present Participle

a. Bentuk ini dipakai untuk menunjukkan perbuatan yang berlangsung terus pada waktu lampau.

Contoh: When I finished my dinner, Peter had been playing chess. Ketika saya selesai makan, Peter telah sedang bermain catur

C. Future Tense (waktu yang akan datang)

1) Simple future tense ( waktu akan datang sederhana )

bentuk :

I / we + Shall + Infinitive

You / they / he / she / it + Will + Infinitive

a) Dipakai untuk menyatakan perbuatan yang akan dilakukan pada waktu yang akan datang.

Contoh: I shall go to Bogor tomorrow. Saya akan pergi ke Bogor besok

b) Dipakai untuk membuat suatu janji pada waktu yang akan datang.

Contoh: He will meet you by ten. Ia akan menemui anda menjelang pukul sepuluh

c) Dipakai untuk menunjukkan syarat.

Contoh: He will give you a good dictionary if you go with him. Ia akan memberi anda sebuah kamus yang baik jika anda pergi bersamanya

d) Dipakai untuk memohon kepada seseorang untuk melakukan sesuatu.

Contoh: Will you please help me to get the book. Tolong ambilkan buku itu untuk saya

2) Future continuous tense (waktu sedang berlangsung akan datang)

bentuk :

Shall / will + Be + Present Participle

a. Dipakai untuk menunjukkan suatu perbuatan yang akan sedang terjadi.

Contoh: I shall be working at nine o’clock tomorrow morning. Saya akan sedang bekerja pada pukul sembilan besok pagi.

At this time next year, Agus will be travelling in Japan. Tahun depan pada waktu ini, Agus akan

sedang mengadakan perjalanan di Jepang.

3) Future perfect tense (waktu selesai akan datang)

bentuk :

Shall / will + Have + Past Participle

a. Dipakai untuk menyatakan perbuatan yang sudah dimulai pada waktu lampau, dan segera selesai pada waktu yang akan datang

Contoh: John will have done his work by the end of this week. John akan selesai mengerjakan

pekerjaannya menjelang akhir minggu ini

4) Future Perfect Continuous Tense (waktu sedang berlangsung selesai akan datang)

bentuk :

Shall / will + Have + Been + Present Participle

Adalah future perfect tetapi perbuatan itu ada kemungkinan dilanjutkan pada waktu yang akan

datang.

Contoh: By the end of this year we shall have been studying German for three years. Menjelang akhir tahun ini kami akan sudah mempelajari bahasa Jerman selama tiga tahun

D. Past future tense (waktu akan datang lampau)

1) Past future tense (waktu yang akan datang pada waktu lampau)

bentuk :

I / we + Should + Infinitive

You / they / he / she / it + Would + Infinitive

a) Menyatakan perbuatan yang akan dilakukan pada waktu lampau

Contoh: He would buy a car the previous day. Ia akan membeli mobil sehari sebelumnya

b) Menyatakan perbuatan yang akan dilakukan bila syaratnya dipenuhi, pada waktu lampau.

Contoh: He would come if you invited him. Ia akan datang jika anda mengundangnya

2) Past future continuous tense (waktu yang akan sedang terjadi pada waktu lampau)

bentuk :

I / we + Should + Be + Present Participle

you / they / he / she / it + Would + Be + Present Participle

a. Dipakai untuk menyatakan perbuatan yang akan sedang dilakukan pada waktu lampau.

Contoh: I should be taking an examination at this time the following day. Saya akan sedang menempuh ujian hari berikutnya pada waktu ini

3) Past future perfect tense (waktu yang akan sudah selesai pada waktu lampau)

bentuk :

I / we + Should + Have + Past Participle

You / they / he / she / it + Would + Have + Past Participle

a. Dipakai untuk menyatakan suatu pengandaian yang tidak mugkin terjadi karena syaratnya yang tidak terpenuhi sudah pasti, namun hanya sebagai bayangan saja seandainya syarat terpenuhi pada waktu lampau.

Contoh: He would have graduated if he had studied hard. Ia akan sudah tamat sekolah seandainya ia telah belajar giat (namun sekarang ia tidak lulus karena ia tidak belajar giat)

4) Past future perfect continuous tense (waktu yang akan sudah sedang berlangsung pada waktu lampau)

bentuk :

I / we + Should + Have + Been + Present Participle

you/they/he/she/it + Would + Have + Been + Present Participle

adalah future perfect continuous dalam bentuk lampau.

Contoh: By the end of this month last semester, Siti would have been studying medicine at Pajajaran University for five years. Menjelang akhir bulan ini semester yang lalu, Siti akan sudah belajar ilmu kedokteran di Universitas Pajajaran selama lima tahun

Ringkasan Enam Belas Bentuk Waktu

Present Tense

1) Simple present

Positif : I swim, You swim, He swims

Negative: I do not swim, You Do not swim, He does not swim

Pertanyaan: Do I swim?, Do you swim?, Does he swim?

2) Present continuous

Positif : I am swimming, You are swimming, He is swimming

Negative: I am not swimming, You are not swimming, He is not swimming

Pertanyaan: Am I swimming?, Are you swimming?, Is he swimming?

3) Present perfect

Positif : I have swum, You have swum, He has swum

Negative: I have not swum, You have not swum, He has not swum

Pertanyaan: Have I swum?, Have you swum?, Has he swum?

4) Present perfect continuous

Positif : I have been swimming, You have been swimming, He has been swimming

Negative: I have not been swimming, You have not been swimming, He has not been swimming

Pertanyaan: Have I been swimming?, Have you been swimming?, Has he been swimming?

Past Tense

1) Simple past

Positif : I swam, You swam, He swam

Negative: I did not swim, You did not swim, He did not swim

Pertanyaan: Did I swim?, Did you swim?, Did he swim?

2) Past continuous

Positif : I was swimming, You were swimming, He was swimming

Negative: I was not swimming, You were not swimming, He was not swimming

Pertanyaan: Was I swimming?, Were you swimming?, Was he swimming?

3) Past perfect

Positif : I had swum, You had swum, He had swum

Negative: I had not swum,You had not swum, He had not swum

Pertanyaan: Had I swum?, Had you swum?, Had he swum?

4) Past perfect continuous

Positif : I had been swimming, You had been swimming, He had been swimming

Negative: I had not been swimming, You had not been swimming, He had not been swimming

Pertanyaan: Had I been swimming?, Had you been swimming?, Had he been swimming?

Future Tense

1) Simple future

Positif : I shall swim, You will swim, He will swim

Negative: I shall not swim, You will not swim, He will not swim

Pertanyaan: Shall I swim?, Will you swim?, Will he swim?

2) Future continuous

Positif : I shall be swimming. You will be swimming, He will be swimming

Negative: I shall not be swimming, You will not be swimming, He will not be swimming

Pertanyaan: Shall I be swimming?, Will you be swimming?, Will he be swimming?

3) Future perfect

Positif : I shall have swum, You will have swum, He will has swum

Negative: I shall not have swum, You will not have swum, He will not have swum

Pertanyaan: Shall I have swum?, Will you have swum?, Will he have swum?

4) Future perfect continuous

Positif : I shall have been swimming, will have been swimming, He will have been swimming

Negative: I shall not have been swimming, You will not have been swimming, He will not have been swimming

Pertanyaan: Shall I Have been swimming?, Will you have been swimming?, Will he have been swimming?

Past Future Tense

1) Past future

Positif : I should swim, You would swim, He would swim

Negative: I should not swim, You would not swim, He would not swim

Pertanyaan: Should I swim?, Would you swim?, Would he swim?

2) Past future continuous

Positif : I should be swimming, You would be swimming, He would be swimming

Negative: I should not be swimming, You would not be swimming, He would not be swimming

Pertanyaan: Should I be swimming?, Would you be swimming?, Would he be swimming?

3) Past future perfect

Positif : I should have swum, You would have swum, He would have swum

Negative: I should not have swum, You would not have swum, He would not have swum

Pertanyaan: Should I have swum?, Would you have swum?, Would he have swum?

4) Past future perfect continuous

Positif : I should have been swimming, You would have been swimming, He would have been swimming

Negative: I should not have been swimming, You would not have been swimming, He would not have been swimming

Pertanyaan: Should I have been swimming?, Would you have been swimming?, Would he have been swimming?

Referensi : www.englishtutorial.co.cc

Passive Voice

Ada dua bentuk “voice” dalam bahasa Inggris, active voice dan passive voice. Active voice menunjukkan apa yang dilakukan oleh subjek, contoh:

* The secretary wrote a letter (Sekretaris menulis sebuah surat)

Passive voice menunjukkan apa yang dilakukan terhadap subjek. Contoh:

* The letter was written by the secretary (Surat ditulis oleh sekreatir)

Bentuk

Kalimat pasif dibuat dengan kata kerja “to be” dan kata kerja bentuk ke-3. Berikut beberapa tenses bahasa Inggris utama yang digunakan dalam passive voice.

Tenses

Simple present:

Present continuous:

Simple past:

Past continuous:

Present perfect:

Past perfect:

Future:

Future continuous:

Present conditional:

Past conditional:


Subject

Flowers

Flowers

Flowers

Flowers

Flowers

Flowers

Flowers

Flowers

Flowers

Flowers


Verb “to be”

are

are being

were

were being

have been

had been

will be

will be being

would be

would have been


Verb III

planted every year

planted now.

planted last year

planted last summer.

planted here for 10 years.

planted until last year.

planted next year.

planted during the summer.

planted if we had seeds.

planted if we had had seeds.

By

Untuk menyatakan apa penyebab sebuah tindakan pasif, kita bisa menggunakan by. Contoh:

* This photo was taken by my friend.
* I was given this by my brother.

Seringkali tidak diperlukan untuk menyatakan penyebab tindakan pasif, khususnya jika dipahami dengan jelas atau tidak relevan. Sebagai contoh:

* The meeting was cancelled (pertemuan itu dibatalkan). (Informasi penting yang ingin disampaikan adalah pembatalan pertemuan, bukan siapa yang membatalkannya.)

* These boots were made in Italy (sepatu-sepatu boot ini dibuat di Italia). (Informasi yang penting dalam kalimat ini adalah bahwa sepatu-sepatu tersebut dibuat di Italia, bukan siapa yang membuatnya).

Born

Ketika berbicara tentang kelahiran orang tertentu atau suatu peristiwa, kita menggunakan bentuk pasif “to be born”. Contoh:

* I was born in Iran.
* The twins were born just last year.

Get

Get bisa digunakan menggantikan to be pada situasi dimana sesuatu terjadi. Contoh:

- Our flight got cancelled = Our flight was cancelled.
- I got paid today = I was paid today.

Get tidak bisa digunakan pada situasi-situasi umum dan apabila bersama dengan kata kerja yang menyatakan keadaan (bukan tindakan). Contoh:

- He is liked by a lot of people. - Benar
- He gets liked by a lot of people. - Tidak benar
- She is known to be a hard-working employee. - Benar
- She gets known to be a hard-working employee.- Tidak benar

Get digunakan lebih sering dalam bahasa Inggris informal.

—

Rujukan:
http://www.1-language.com/englishcourse/unit58_grammar.htm

Frame Relay, x.25 and TDM,FDM,CDM

Frame Relay is a CCITT(Consultative Committee for International Telegraph and Telephone. International organization responsible for the development of communications standards. Now called the ITU-T. See ITU-T.) and American National Standards Institute (ANSI) standard that defines the process for sending data over a public data network (PDN). It is a data-link technology that is streamlined to provide high performance and efficiency. It operates at the Physical an Data Link Layers of the OSI model but it relies on upper-layer protocols such as TCP for error correction.

Note that Frame Relay defines the interconnection process between your customer premises equipment (CPE) (also known as data terminal equipment - DTE), such as a router, and the service provider’s local access switching equipment (known as data communications equipment - DCE).

Frame Relay provides a means for multiplexing many logical data conversations (referred to as virtual circuits) by assigning each pair of DTEs connection identifiers. The service provider’s switching equipment constructs a table mapping connection identifiers to outbound ports. When a frame is received, the switching device analyzes the connection identifier and delivers the frame to the associated outbound port. The complete path to the destination is established prior to the sending of the first frame.


Frame Relay Terminology

Following are some terms that are used frequently when discussing Frame Relay:
Local access rate—The clock speed (port speed) of the connection (local loop) to the Frame Relay cloud. It is the rate at which data travels into or out of the network.
Data-link connection identifier (DLCI)—A number that identifies the logical circuit between the source and destination device. The FR switch maps the DLCIs between each pair of routers to create a PVC.
Local Management Interface (LMI)—A signaling standard between the CPE device and the FR switch that is responsible for managing the connection and maintaining status between the devices. LMIs may include support for a keepalive mechanism, which verifies that data is flowing; a multicast mechanism which can provide the network server with its local DLCI; multicast addressing, providing a few DLCIs to be used as multicast (multiple destination) addresses, and the ability to give DLCIs global (whole Frame Relay network) significance, rather than just local significance (DLCI used only to the local switch); and a status mechanism, which provides an ongoing status on the DLCIs known to the switch.
There are several LMI types and routers need to be told which LMI type is being used. Three types of LMIs are supported:
cisco—LMI type defined jointly by Cisco, StrataCom, Northern Telecom, and DEC
ansi—Annex D defined by ANSI standard T1.617
q933a—ITU-T Q.933 Annex A


Frame Relay Terminology (cont.)

Committed information rate (CIR)—The rate, in bits per second, that the Frame Relay switch agrees to transfer data.
Committed Burst (Bc)—The maximum number of bits that the switch agrees to transfer during any Committed Rate Measurement Interval (Tc).
Excess Burst—The maximum number of uncommitted bits that the Frame Relay switch will attempt to transfer beyond the CIR. Excess Burst is dependent on the service offerings available by your vendor, but is typically limited to the port speed of the local access loop.
Forward explicit congestion notification (FECN)—When a Frame Relay switch recognizes congestion in the network, it sends an FECN packet to the destination device indicating that congestion has occurred.
Backward explicit congestion notification (BECN)—When a Frame Relay switch recognizes congestion in the network, it sends a BECN packet to the source router instructing the router to reduce the rate at which it is sending packets.
Discard Eligibility (DE) Indicator—When the router detects network congestion, the FR switch will drop packets with the DE bit set first. The DE bit is set on the oversubscribed traffic; that is, the traffic that was received after the CIR was met.



Frame Relay Data Link Connection Identifier

Frame Relay virtual circuits are identified by data link connection identifiers (DLCIs). DLCI values are typically assigned by the Frame Relay service provider (for example, the telephone company).

Frame Relay DLCIs have local significance. That is, the values themselves are not unique in the Frame Relay WAN. Two DTE devices connected by virtual circuit might use a different DLCI value to refer to the same connection.

Frame Relay Frame Format

The Frame Relay frame is shown n the graphic. The flags field indicate the beginning and end of the frame. Following the leading flags field are two bytes of address information. Ten bits of these two bytes make up the actual circuit ID (called the DLCI, for data link connection identifier).

The 10-bit DLCI value is the heart of the Frame Relay header. It identifies the logical connection that is multiplexed into the physical channel. 3 of the remaining bits in the field provide congestion control. The forward explicit congestion notification (FECN) bit is set by the Frame Relay network in a frame to tell the DTE receiving that frame that congestion was experienced in the path from source to destination. The backward explicit congestion notification (BECN) bit is set by the Frame Relay network in frames traveling in the opposite direction from frames encountering a congested path. The notion behind both of these bits is that the FECN or BECN indication can be promoted to a higher-level protocol that can take flow control action as appropriate.

The discard eligibility (DE) bit is set by the DTE to tell the Frame Relay network that a frame has lower importance than other frames and should be discarded before other frames if the network becomes short of resources. Thus, it represents a very simple priority mechanism. This bit is usually set only when the network is congested.


Frame Relay Frame Field Descriptions

Flags - Delimits the beginning and the end of the Frame Relay frame.

Address - Contains the following information:
DLCI Value - Indicates the data link connection identifier (DLCI) value. Consists of the first 10 bits of the Address field.
Extended Address (EA) - Indicates the length of the Address field. While Frame Relay addresses are currently all 2 bytes long, the EA bits allow for the possible extension of address lengths in the future. The 8th bit of each byte of the Address field is used to indicate the EA.
C/R - Bit that follows the most significant DLCI byte in the Address field. The C/R bit is not currently defined.
Congestion Control - The three bits that control the Frame Relay congestion notification mechanisms. These are the FECN, BECN, and DE bits, which are the last 3 bits in the Address field.

Data - Variable-length field that contains encapsulated upper-layer data.

FCS - Frame Check Sequence (FCS), used to ensure the integrity of transmitted data.


Frame Relay Addressing

Assume two PVCs, one between Atlanta and Los Angeles, and one between San Jose and Pittsburgh. Los Angeles uses DLCI 12 to refer to its PVC with Atlanta, while Atlanta refers to the same PVC as DLCI 82. Similarly, San Jose uses DLCI 12 to refer to its PVC with Pittsburgh. The network uses internal proprietary mechanisms to keep the two locally significant PVC identifiers distinct.


Frame Relay Operation - LMI

Frame Relay signaling reports the status of PVCs. the original Frame Relay signaling specification is called Link Management Interface (LMI - also known as Local Management Interface). LMI was proposed by the Frame Relay Forum. Subsequently, the American National Standards Institute (ANSI) and the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) have standardized slightly different versions of LMI. (ITU-T was formerly called CCITT)

The main purpose for the LMI process is:
PVC status - What is the operational status of the various PVCs that the router knows about.
Transmission of keepalive packets to insure that the PVC stays up and does not shut down due to inactivity.

The router must be programmed to choose which LMI type encapsulation will be used.
Options are:

IETF Encapsulation Type
Cisco Encapsulation Type


Inverse ARP

The Inverse ARP mechanism allows the router to automatically build the Frame Relay map. The router learns the DLCIs that are in use from the switch during the initial LMI exchange. The router then sends an Inverse ARP request to each DLCI for each protocol configured on the interface if the protocol is supported. The return information from the Inverse ARP is then used to build the Frame Relay map.

Frame Relay Mapping

The router next-hop address determined from the routing table must be resolved to a Frame Relay DLCI. The resolution is done through a data structure called a Frame Relay map. This data structure may be statically configured in the router, or the Inverse ARP feature can be used for automatic setup of the map.


Frame Relay Operation - Switching

The Frame Relay switching table consists of four entries: two for incoming port and DLCI, two for outgoing port and DLCI. The DLCI could, therefore, be remapped as it passes through each switch; the fact that the port reference can be changed is why the DLCI is “locally significant."


Frame Relay Operation

Frame Relay is a Layer 2 protocol that describes how the DTE device communicates with and connects to a Frame Relay switch. A summary of how this protocol operates follows:
You order Frame Relay service from a service provider, or you create a private Frame Relay cloud.
Each router, either directly or through a CSU/DSU, connects to the Frame Relay switch.
When the CPE router is enabled, it sends a Status Inquiry message to the FR switch. The message notifies the switch of the router’s status, and asks the switch for the connection status of the other remote routers.
When the FR switch receives the request, it responds with a Status message that includes the DLCIs of the remote routers to which the local router can send data.
For each active DLCI, each router sends an Inverse ARP request packet introducing itself and asking for each remote router to identify itself by replying with its network-layer address.








Frame Relay Operation (cont.)

For each DLCI that each router receives an Inverse ARP message about, the router will create a map entry in its Frame Relay map table that includes the local DLCI and the remote router’s network-layer address, as well as the state of the connection. Note that the DLCI is the router’s locally configured DLCI, not the DLCI that the remote router is using. Three possible connection states appear in the Frame Relay map table:
Active state—Indicates that the connection is active and that routers can exchange data.
Inactive state—Indicates that local connection to FR switch is working, but the remote router’s connection to FR switch is not working.
Deleted state—Indicates that no LMI is being received from the FR switch or no service between the CPE router and FR switch is occurring.

If Inverse ARP is not working, or the remote router does not support Inverse ARP, you need to configure the routes (DLCIs and IP addresses) of the remote routers. This configuration is referred to as static maps and is discussed later in the “Configuring Frame Relay” section.
Every 60 seconds, the routers exchange Inverse ARP messages.
Every ten seconds or so (this is configurable), the CPE router sends a keepalive message to the FR switch. The purpose of the keepalive message is to verify that the FR switch is still active.

The router will change the status of each DLCI, based on the response from the FR switch




















Time-division multiplexing (TDM)—Information from many sources has bandwidth allocation on a single media. Circuit switching uses signaling to determine the call route, which is a dedicated path between the sender and the receiver. By multiplexing traffic into fixed time slots, TDM avoids congested facilities and variable delays. Basic telephone service and Integrated Services Digital Network (ISDN) use TDM circuits


Frequency-division multiplexing.
Technique whereby information from multiple channels can be
allocated bandwidth on a single wire based on frequency.

X.25 - ITU-T standard that defines how connections between DTE and DCE are maintained for remote terminal access and computer communications in PDNs (Public Data Networks). X.25 specifies LAPB, a data link layer protocol, and PLP, a network layer protocol. Frame Relay has to some degree superseded X.25. See also Frame Relay, LAPB, and PLP.