iso 7 layer

OPEN SYSTEM INTERCONNECTION (OSI)

I. PENGERTIAN

Masalah utama dalam komunikasi antar komputer dari vendor yang berbeda adalah karena mereka mengunakan protocol dan format data yang berbeda-beda. Untuk mengatasi ini, International Organization for Standardization (ISO) membuat suatu arsitektur komunikasi yang dikenal sebagai Open System Interconnection (OSI) model yang mendefinisikan standar untuk menghubungkan komputer-komputer dari vendor-vendor yang berbeda.

Model-OSI tersebut terbagi atas 7 layer, dan layer kedua juga memiliki sejumlah sub-layer (dibagi oleh Institute of Electrical and Electronic Engineers (IEEE)). Perhatikan tabel berikut:

7th	- Layer : Application	Services
6th	- Layer : Presentation	Services
5th	- Layer : Session	Communications
4th	- Layer : Transport	Communications
3rd	- Layer : Network	Communications
2nd	- Layer : Data-link	Physical connections
1st	- Layer : Physical	Physical connections

Tabel MODEL OSI

Layer-layer tersebut disusun sedemikian sehingga perubahan pada satu layer tidak membutuhkan perubahan pada layer lain. Layer teratas (5, 6 and 7) adalah lebih cerdas dibandingkan dengan layer yang lebih rendah; Layer Application dapat menangani protocol dan format data yang sama yang digunakan oleh layer lain, dan seterusnya. Jadi terdapat perbedaan yang besar antara layer Physical dan layer Application.

II. FUNGSI LAYER

1. Layer Physical

Ini adalah layer yang paling sederhana; berkaitan dengan electrical (dan optical) koneksi antar peralatan. Data biner dikodekan dalam bentuk yang dapat ditransmisi melalui media jaringan, sebagai contoh kabel, transceiver dan konektor yang berkaitan dengan layer Physical. Peralatan seperti repeater, hub dan network card adalah berada pada layer ini.

2. Layer Data-link

Layer ini sedikit lebih “cerdas” dibandingkan dengan layer physical, karena menyediakan transfer data yang lebih nyata. Sebagai penghubung antara media network dan layer protocol yang lebih high-level, layer data link bertanggung-jawab pada paket akhir dari data binari yang berasal dari level yang lebih tinggi ke paket diskrit sebelum ke layer physical. Akan mengirimkan frame (blok dari data) melalui suatu network. Ethernet (802.2 & 802.3), Tokenbus (802.4) dan Tokenring (802.5) adalah protocol pada layer Data-link.

3. Layer Network

Tugas utama dari layer network adalah menyediakan fungsi routing sehingga paket dapat dikirim keluar dari segment network lokal ke suatu tujuan yang berada pada suatu network lain. IP, Internet Protocol, umumnya digunakan untuk tugas ini. Protocol lainnya seperti IPX, Internet Packet eXchange. Perusahaan Novell telah memprogram protokol menjadi beberapa, seperti SPX (Sequence Packet Exchange) & NCP (Netware Core Protocol). Protokol ini telah dimasukkan ke sistem operasi Netware. Beberapa fungsi yang mungkin dilakukan oleh Layer Network

• Membagi aliran data biner ke paket diskrit dengan panjang tertentu
• Mendeteksi Error
• Memperbaiki error dengan mengirim ulang paket yang rusak
• Mengendalikan aliran

4. Layer Transport

Layer transport data, menggunakan protocol seperti UDP, TCP dan/atau SPX (Sequence Packet eXchange, yang satu ini digunakan oleh NetWare, tetapi khusus untuk koneksi berorientasi IPX). Layer transport adalah pusat dari mode-OSI. Layer ini menyediakan transfer yang reliable dan transparan antara kedua titik akhir, layer ini juga menyediakan multiplexing, kendali aliran dan pemeriksaan error serta memperbaikinya.

5. Layer Session

Layer Session, sesuai dengan namanya, sering disalah artikan sebagai prosedur logon pada network dan berkaitan dengan keamanan. Layer ini menyediakan layanan ke dua layer diatasnya, Melakukan koordinasi komunikasi antara entiti layer yang diwakilinya. Beberapa protocol pada layer ini: NETBIOS: suatu session interface dan protocol, dikembangkan oleh IBM, yang menyediakan layanan ke layer presentation dan layer application. NETBEUI, (NETBIOS Extended User Interface), suatu pengembangan dari NETBIOS yang digunakan pada produk Microsoft networking, seperti Windows NT dan LAN Manager. ADSP (AppleTalk Data Stream Protocol). PAP (Printer Access Protocol), yang terdapat pada printer Postscript untuk akses pada jaringan AppleTalk.

6. Layer Presentation

Layer presentation dari model OSI melakukan hanya suatu fungsi tunggal: translasi dari berbagai tipe pada syntax sistem. Sebagai contoh, suatu koneksi antara PC dan mainframe membutuhkan konversi dari EBCDIC character-encoding format ke ASCII dan banyak faktor yang perlu dipertimbangkan. Kompresi data (dan enkripsi yang mungkin) ditangani oleh layer ini.

7. Layer Application

Layer ini adalah yang paling “cerdas”, gateway berada pada layer ini. Gateway melakukan pekerjaan yang sama seperti sebuah router, tetapi ada perbedaan diantara mereka. Layer Application adalah penghubung utama antara aplikasi yang berjalan pada satu komputer dan resources network yang membutuhkan akses padanya. Layer Application adalah layer dimana user akan beroperasi padanya, protocol seperti FTP, telnet, SMTP, HTTP, POP3 berada pada layer Application.

III. KOMPONEN JARINGAN DAN PROTOKOL LAYER

1. Layer 1 – Physical

Network components: Repeater Multiplexer Hubs(Passive and Active) TDR Oscilloscope Amplifier

Protocols: IEEE 802 (Ethernet standard) IEEE 802.2 (Ethernet standard) ISO 2110 ISDN

1. Layer 2 – Datalink

Network components: Bridge Switch ISDN Router Intelligent Hub NIC Advanced Cable Tester

Protocols: Media Access Control: Communicates with the adapter card Controls the type of media being used: 802.3 CSMA/CD (Ethernet) 802.4 Token Bus (ARCnet) 802.5 Token Ring 802.12 Demand Priority Logical Link Control error correction and flow control manages link control and defines SAPs 802.2 Logical Link Control

3. Layer 3 (Network)

Network components: Brouter Router Frame Relay Device ATM Switch Advanced Cable Tester

Protocols: IP; ARP; RARP, ICMP; RIP; OSFP; IGMP; IPX NWLink NetBEUI OSI DDP DECnet

4. Layer 4 – Transport

Network components: Gateway Advanced Cable Tester Brouter

Protocols: TCP, ARP, RARP; SPX NWLink NetBIOS / NetBEUI ATP

5. Layer 5 – Session

Network components: Gateway

Protocols: NetBIOS Names Pipes Mail Slots RPC

1. Layer 6 – Presentation

Network components: Gateway Redirector

Protocols: None

1. Layer 7 – Application

Network components: Gateway

Protocols: DNS; FTP TFTP; BOOTP SNMP; RLOGIN SMTP; MIME; NFS; FINGER TELNET; NCP APPC; AFP SMB

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materi pendidikan bahsa inggris

A.                Building Things through Language

In Chapter 1 we argued that language-in-use is about saying, doing, and being. We argued, as well, that by saying, doing, and being we enact certain “games” or “practices” (e.g., committee meetings, a Yu-Gi-Oh! play session, an argument in court, a turf battle between gangs, teaching reading to a firstgrade class, “small talk” with a neighbor, asking someone out on a date) which, in turn, give meaning to our saying, doing, and being. These “games” or practices always belong to social groups (e.g., street-gang members, lawyers, anime fans), cultures (e.g., Americans, African-Americans, Native Americans), or institutions (e.g., universities, schools, governments). So when we enact these “games” or practices, we also sustain these social groups, cultures, and institutions.

Different cultures have different conventions about how to make music. But within any culture, each musical performer makes music that both fits those conventions (and, thus, is old) and is unique, played according to the talent and style of that performer (and, thus, is new). The same is true of language. We use the term “grammar” for conventions about how to speak and write. Each time a person uses language, that person does so in ways that fit the conventions (are “grammatical”) and that, at the same time, are unique, expressing what that person has to say and how they have chosen to say it. Like music, what we do with language is always both old and new.

It is pretty clear what it means to make music, but we use language to make meaning, and it is not clear what that means. In the broadest sense, we make meaning by using language to say things that, in actual contexts of use, amount, as well, to doing things and being things. These things we do and are (identities) then come to exist in the world and they, too, bring about other things in the world. We use language to build things in the world and to engage in world building. It is as if you could build a building by simply speaking words. While we cannot build a building by simply speaking words, there are, indeed, things we can build in the world by speaking words that accomplish actions and enact identities.

Let’s take a very simple example. An umpire in a baseball game says “Strike!” and a “strike” exists in the game. That is what the rules of the game allow to happen. It is a strike if the umpire says it is. Similarly, the rules of marriage allow a marriage to actually happen in the world when a properly ordained minister or a judge says “I now pronounce you man and wife.” Umpires actually make strikes happen and ministers actually make marriages happen.

These are what we can call “direct speech acts.” Saying something makes it so, as long as one has said it in the right circumstances (so, “promise” is also a direct speech act, since saying “I promise” in the right settings—e.g., not on a stage as part of a play—makes a promise happen). But there are also things we make happen in the world through language that do not actually require language, but which are much easier to do with language than without it. I can most certainly threaten you through gestures and behavior, but it is often easier to do it in language.

We make or build things in the world through language. Not just strikes, marriages, and threats, but many things. For example, I can make (or break) a relationship with other people through language. If I talk to you in an informal, bonding sort of way, I am “bidding” to have you accept me as a friend, someone with whom you are comfortable. If you talk that way back to me, that sort of relationship becomes “real” (at least for that time and place) and has consequences in the world (e.g., it is now harder for you to turn down my invitation for you to come to my house for dinner).

Whenever we speak or write, we always (often simultaneously) construct or build seven things or seven areas of “reality.” Let’s call these seven things the “seven building tasks” of language. In turn, since we use language to build these seven things, a discourse analyst can ask seven different questions about any piece of language-in-use. Below, I list the seven building tasks and the discourse analysis question to which each gives rise:

1.      Significance

There are things in life that are, by nearly everyone’s standards, significant (for example the birth or death of a child). But for many things, we need to use language to render them significant or to lessen their significance, to signal to others how we view their significance. “Hornworms sure vary a lot in how well they grow” signals that the speaker takes the variation in the hornworms to be significant by the use of the adverb “sure.” This is a marker of attitude or feeling.

“Hornworm growth exhibits a significant amount of variation” signals that the speaker takes the variation in the hornworms to be significant by the use of the phrase “significant amount of variation.” This use of the word “significant” here is a technical term and refers to the statistical tools of an academic discipline.

Discourse Analysis Question: How is this piece of language being used to make certain things significant or not and in what ways?

2.      Practices (Activities)

We have already talked a lot about practices. By a “practice” I mean a socially recognized and institutionally or culturally supported endeavor that usually involves sequencing or combining actions in certain specified ways. Encouraging a student is an action, mentoring the student as his or her advisor in a graduate program is a practice. Telling someone something about linguistics is an action (informing), lecturing on linguistics in a course is a practice. Sometimes the term “activity” is used for what I am calling a practice.

We use language to get recognized as engaging in a certain sort of practice or activity. For example, I talk and act in one way and I am engaged in formally opening a committee meeting; I talk and act in another way and I am engaged in “chit-chat” before the official start of the meeting.

When we think about practices, we confront a significant “chicken and egg”sort of question. What we say, do, and are in using language enacts practices. At the same time, what we say, do, and are would have no meaning unless these practices already existed.

Which comes first then: A practice like committee meetings or the language we use to carry out committee meetings, our committee ways of talking and interacting? Is this a “committee meeting” because we are speaking and acting this way, or are we speaking and acting this way because this is a committee meeting? The practice of committee meetings gives meaning and purpose to our language in the meetings and our language in the meetings enacts the committee meeting and makes it exist.

The answer to this chicken and egg question is this: Language and practices “boot strap” each other into existence in a reciprocal process through time. We cannot have one without the other.

This does, of course, raise the question of how new practices arise. Often new practices are variants of old ones, ones people have changed or transformed. At other times, new practices start by people borrowing elements of their other older practices to make something new. That is why computer interfaces look like and are talked about as “desktops.” We use something old to understand and build something new.

Discourse Analysis Question: What practice (activity) or practices (activities) is this piece of language being used to enact (i.e., get others to recognize as going on)?

3.      Identities

We use language to get recognized as taking on a certain identity or role, that is, to build an identity here and now. For example, I talk and act in one way and I am speaking and acting as “chair” of the committee; at the next moment I speak and talk in a different way and I am speaking and acting as one peer/colleague speaking to another. Even if I have an official appointment as chair of the committee, I am not always taken as acting as the chair, even during meetings. I have to enact this identity at the right times and places to make it work.

We often enact our identities by speaking or writing in such a way as to attribute a certain identity to others, an identity that we explicitly or implicitly compare or contrast to our own. We build identities for others as a way to build ones for ourselves. For example, it is impossible to enact a racist identity for oneself without building in speech or writing some sort of inferior identity for people of another “race.”

Discourse Analysis Question: What identity or identities is this piece of language being used to enact (i.e., get others to recognize as operative)? What identity or identities is this piece of language attributing to others and how does this help the speaker or writer enact his or her own identity?

4.      Relationships

We use language to signal what sort of relationship we have, want to have, or are trying to have with our listener(s), reader(s), or other people, groups, or institutions about whom we are communicating. We use language to build social relationships. For example, in a committee meeting, as chair of the committee, I say “Prof. Smith, I’m very sorry to have to move us on to the next agenda item” and signal a relatively formal and deferential relationship with Prof. Smith. On the other hand, suppose I say, “Ed, it’s time to move on.” Now I signal a relatively informal and less deferential relationship with the same person.

Discourse Analysis Question: What sort of relationship or relationships is this piece of language seeking to enact with others (present or not)?

5.      Politics (the distribution of social goods)

We use language to convey a perspective on the nature of the distribution of social goods, that is, to build a perspective on social goods. For example, if I say “Microsoft loaded its operating system with bugs,” I treat Microsoft as purposeful and responsible, perhaps even culpable. I deny them a social good. If I say, on the other hand, “Microsoft’s operating system is loaded with bugs,” I treat Microsoft as less purposeful and responsible, less culpable. I am still denying them a social good, but I have mitigated this denial. If I say, “Like all innovative pieces of software, Microsoft’s operating system has bugs,” I grant Microsoft a social good (being innovative) and even make the bugs a sign of this, rather than a problem. How I phrase the matter has implications for social goods like guilt and blame, legal responsibility or lack of it, or Microsoft’s bad or good motives.

Social goods are potentially at stake any time we speak or write so as to state or imply that something or someone is “adequate,” “normal,” “good,” or “acceptable” (or the opposite) in some fashion important to some group in society or society as a whole. In Chapter 1, I defined perspectives on the distribution of social goods as “politics.”

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