Wide Area Network Wiwin Sulistyo, ST, M.Kom

Packet-Switching vs Circuit-Switching Networks Packet switching is used by the Internet and routed networks The path that is used to send data packets from one point to another through routers is not predetermined if there are multiple paths. For example: you can see that from point A to point B, there exist many paths and ways for packets to travel between the source and destination PCs. If we assume that each router is a LAN, which is not shown, then it is possible for each LAN to experience different bandwidth usage.

Packet-Switching vs Circuit-Switching Networks Figure 7-1:Routed network

Packet Switching When a user at PC A wants to copy a shared file from PC B, the data path is not a set path between specific routers. Packets will be sent from router to router based on the quickest or shortest path. If a router is extremely busy, it will not be used, and a different path will be chosen if one exists. Remember that other users are also sending data packets over the same media and routers as you are using.

Packet Switching Using Figure 7-1, let’s now look at an example of how packet switching works: PC B will send its data to the router that is the least busy; for the first data packet, let us assume that it is Router 6. Now that Router 6 has the data packet, it will look at its routing table and determine that Router 3 might be the best way for it to reach PC A. Router 6 sends the data packet to Router 3, which in turn decides that the best path is to forward the packet on to Router 1. Router 1 will then send the packet to PC A. Now, the second packet might be sent to Router 7, because Router 6 has suddenly become very busy.

Packet Switching Router 7 will receive the data packet and forward it to Router 4, which sends the packet to Router 3. Router 3 checks its routing table and sends the packet to Router 2, which in turn sends the packet on to PC A. PC A will then start assembling the entire data file from the packets received. For the third data packet, let’s say that it is also sent to Router 7, which will send it to Router 5 again. Now let’s say that Router 2 has suddenly gone offline. Router 5 waits to contact Router 2, but eventually times out and sends the data packet back to Router 7, which then tries to send the data packet to Router 4. Router 4 has since determined that Router 2 is offline, and sends the data packet to Router 1. Router 1 sends the data packet to PC A. The fourth data packet is sent to Router 6, on to Router 3, then to Router 1, and finally delivered to PC A.

Packet Switching Let’s look more closely at packets 3 and 4: While packet 3 was detained at Router 5 because of the failure of Router 2, packet 4 was able to be delivered to PC A before the arrival of packet 3. This shows that a packet-switched network is not dependent on packets being delivered in the order in which they were sent. Actually, if there are enough data paths, it is very common for packets to be received out of order. With routable protocols, data packets are numbered so they can be placed back in the proper order to create the original block of data that existed at the sending PC. It would do no good to receive a jumbled database or unreadable document.

Circuit Switching Circuit switching, on the other hand, is the foundation for the telephone system. When you make a telephone call from your home to someone next door or even 1000 miles away, a circuit is opened between your telephone and the telephone to which you are calling. The circuit is not usable by others, so it is 100-percent dedicated for your use. As you speak, your voice is sent over the media to the other telephone and is not broken up or rerouted. One problem with circuit switching is when a circuit fails.

Asynchronous Transfer Mode (ATM) Asynchronous Transfer Mode (ATM) is a technology used mainly as a backbone in the Internet world. ATM technology is suitable for both LAN and WAN connectivity. With ATM technology in place for a LAN, it will be easy to extend the technology to cover a large area if needed, and make a WAN without loss of performance.

Asynchronous Transfer Mode (ATM) ATM can be used to enhance broadband ISDN to allow for the transmission of voice, data, and multimedia packets over the same media simultaneously. ATM will provide for high bandwidth as needed if enough users are implementing the bandwidth. ATM bandwidth ranges from slow speeds, around 12.96 to 25 Mbps using copper media such as category 3 UTP cable, and high speeds around 622.08 Mbps using fiber-optic cable. With advances in technology, ATM speeds can reach 2.488 Gbps.

Asynchronous Transfer Mode (ATM) ATM can be used with physical interfaces such as FDDI and SONET/SDH, this means that in an FDDI or SONET/SDH network, ATM can be used on the network topology for data transmissions.

Synchronous Optical NETwork /Synchronous Digital Hierarchy Synchronous Optical NETwork (SONET) is an American standard that allows the unifying of unlike transmissions into one single data stream. SDH is an international standard designed for the same purpose as SONET. Basically, SONET allows multiple companies to transmit their packets on their network onto a SONET backbone to be transmitted to a remote location.

Synchronous Optical NETwork /Synchronous Digital Hierarchy Since many companies might be using different network topologies and protocols, the data streams from each company will most likely differ. SONET allows these companies to transmit their information over SONET without having to conform to a network standard. For example, one company might have a 10-Mbps category-5 Ethernet network using IPX/SPX, while another is using fiber optic with TCP/IP. These can then be combined into a single data stream for transmission over one cable. More companies can be added for transmission over the SONET medium without making any changes to any of the company networks.

Synchronous Optical NETwork /Synchronous Digital Hierarchy SONET can be used as a backbone between unlike systems. This architecture allows for different media types and transmission types to be combined into one stream and sent over a fiber-optic cable at a minimum speed of 54.84 Mbps for SONET-1. SONET is divided into electrical levels that have varying speeds, termed synchronous transport signals (STS).

Synchronous Optical NETwork /Synchronous Digital Hierarchy The highest level is SONET-192 with a speed of 9953.280 Mbps. SDH has no equivalent for SONET-1 at the speed of 51.84 Mbps, but has a low speed of 155.520 Mbps mapping to SONET-3. The different SDH levels are termed synchronous transfer mode (STM). Table 7-1 lists the different levels.

Synchronous Optical NETwork /Synchronous Digital Hierarchy The format for SONET is created by multiplexing all data signals into a single data stream called a synchronous transport signal (STS). The multiplexer is managed by the path terminating equipment (PTE) from various different media and transmission types. shown in Figure 7-2. Now that the STS signal is created, it must be transmitted on the SONET media. The STS transmission is managed by the line terminating equipment (LTE), also shown in Figure 7-2. The LTE will send and receive the STS signal on both ends of the SONET media. Remember that the STS signal is in the form of electrical pulses. The SONET link might not be a single connection from one point to another, and entire segment might be comprised of sections of SONET media. Therefore, to create the sections and have the entire segment appear as one physical link, you use section terminating equipment (STE) to begin and end a section as shown in Figure 7-3.

Synchronous Optical NETwork /Synchronous Digital Hierarchy Figure 7-3:SONET/SDH link

Optical Carrier Level-X The Optical Carrier (OC) standard is used to specify bandwidth for transmissions that are sent over fiber-optic cables. These standards are equivalent to the SONET/SDH standards and will correlate to the bandwidths available for SONET/SDH. One OC channel (OC-1) is 51.84 Mbps, as is STS-1. When multiple channels are used, the bandwidth increases. For example, nine OC channels (OC-9) are comprised of nine OC-1 channels at 51.84 Mbps each. This results in a total bandwidth of 9 x 51.84 Mbps, for a total bandwidth of 466.56 Mbps.

Frame Relay Frame Relay is an architecture that operates at the OSI Physical layer and is independent of all protocols being used over the medium. Frame Relay is for transmitting data only because the transmission speeds are not always constant. Since Frame Relay is not a constant speed, real-time voice or video is impossible.

Frame Relay Frame Relay is a highly efficient method of transmitting data using bandwidth at an optimum level, allowing for bandwidths as high as 2 Mbps. The nodes, which are used to route the frames in the packet-switching network, each use a routing algorithm that can help determine the efficiency of the Frame Relay network. Frame Relay does send frames as variable-length packets that are not all set at the same size before transmission.

Frame Relay If the bandwidth becomes too congested, Frame Relay will drop any frames that it cannot handle. Once the available bandwidth is at a minimum, the source or destination can be notified to slow the transmissions to avoid over-utilization of the bandwidth, which will avoid packets being dropped due to congestion. Although the source or destination is requested to slow the transmissions, the transmissions do not necessarily have to slow.

Fiber Distributed Data Interface (FDDI) The Fiber Distributed Data Interface (FDDI) topology is sometimes referred to as a fast redundant token ring network. FDDI is similar to a token ring network, but there are two rings and the media is fiber-optic cable operating at 100 Mbps. If copper cable is used, such as category 5 at 100 Mbps, the topology is termed Copper Distributed Data Interface (CDDI).

Fiber Distributed Data Interface (FDDI) Two rings are used, the primary ring and the secondary ring. The primary ring is used at all times, and the secondary ring is only used if the primary ring fails. The token is passed on each ring in opposite directions; the reason for this will be apparent shortly.

Fiber Distributed Data Interface (FDDI) FDDI is specifically for WAN use and not for LAN use. FDDI is used to connect multiple sites. Each building or office will have a dual-attachment concentrator (DAC) that allows both rings to be connected to the DAC, or two single attachment concentrators (SAC). The SAC will connect to a single ring, allowing the SAC to be powered down without affecting the ring.

Fiber Distributed Data Interface (FDDI)

Fiber Distributed Data Interface (FDDI) Functional FDDI example

Tx/Ex-Carrier The T-carrier and E-carrier are both digital mediums for which to transmit voice, data, or images. The T-carrier is used in the United States, Japan, and Australia, whereas the E-carrier is used in Europe, Mexico, and South America.

Tx/Ex-Carrier

Serial Line Internet Protocol dan Point-to-Point Protocol SLIP dan PPP adalah dua protocol komunikasi yang digunakan untuk menghubungkan sebuah computer ke jaringan yang jauh melalui koneksi serial dengan menggunakan MODEM. Sehingga memungkinkan sebuah computer dapat menjalankan aplikasi-aplikasi jaringan dari tempat dimana dia berada. Dan protocol-protokol tersebut biasanya digunakan untuk koneksi ke internet.

SLIP (Serial Line Internet Protocol) Merupakan protocol komunikasi yang digunakan untuk membangun koneksi dengan TCP/IP melalui sebuah serial interface ke remote network. Dirancang untuk berkoneksi dengan server UNIX melalui saluran telepon, dengan Dial-Up. Dan merupakan salah satu protocol pertama yang memungkinkan koneksi ke remote network melalui saluran telepon.

SLIP (Serial Line Internet Protocol) SLIP tidak menyediakan: Software compression Password encryption Multiple network protocol Tidak menyediakan deteksi error pada saat session setup Alamat DHCP Metode authentication

PPP (Point-to-Point Protocol) Merupakan protocol yang terletak pada lapisan Data Link yang digunakan untuk enkapsulasi paket dari network layer untuk dilewatkan melalui jalur Synchronous dan Asynchronous. PPP dirancang untuk: Encapsulasi paket-frame untuk pengiriman ke multiple network layer melalui point-to-point link. Network protocol multiplexing Session negotiation Data compressing negotiation. Mendukung multiple protocok, antara laian: TCP/IP, IPX/SPX, DECnet.

PPP (Point-to-Point Protocol) Untuk PPP yang mengirimkan data melalui serial point-to-point link, menggunakan 3 komponen yang saling melengkapi, antara lain: Protocol High Level data Link Control (HDLC), yang melakukan enkapsulasi data pada saat ditransmisikan. Protokol Link Control Protocol (LCP), yang melakukan pembangunan, pengujian dan konfigurasi koneksi data link. Bermacam-macam Network Control Protocol (NCP), yang digunakan untuk konfigurasi pada protocol komuniasi yang berbeda.

PPP (Point-to-Point Protocol) Prose kerja pada PPP PPP menggunakan 3 komponen diatas untuk melakukan komunikasi. PPP awalnya akan mengirimkan frame LCP untuk pengujian dan konfigurasi data link. Hal dilakukan untuk membangun link dan negoisasi, dimana ada beberapa pilihan/opsi tambahan yang dibutuhkan untuk memudahkan koneksi. Selanjutnya melakukan negosiasi protokol authentication, dan biasanya protokol yang digunakan adalah Challenge Handshaking Authentication Protocol (CHAP) dan Password Authentication Protocol (PAP). Selanjutnya client mengirimkan frame NCP untuk konfigurasi dan set up protokol network layer yang digunakan pada sesi tersebut. Setelah sesi diatas selesai, setiap protokol jaringan dapat melewatkan data melalui koneksi tersebut. HDLC digunakan untuk melakukan encapsulasi aliran data yang lewat melalui koneksi PPP. Koneksi link masih aktif selama frame LCP atau NCP menutup koneksi, atau terjadi error / external event seperti user mengakhiri link.

PPP (Point-to-Point Protocol) PPP Framing PPP frame menentukan format data yang diencapsulasi sebelum dikirimkan ke jaringan. PPP memberikan standard framing yang memungkinkan koneksi ke bermacam-macam standard server PPP karena semua vendor menggunakan format yang sama. PPP menggunakan HDLC sebagai dasar encapsulation framing untuk koneksi serial.

PPP (Point-to-Point Protocol) Perangkat PPP PPP mampu beroperasi dengan beragam data terminal equipment/data circuit terminating equipment (DTE/DCE). Contoh perangkat, standard EIA/TIA 232 (modem) Authentication Protocols Protokol-protokol authentikasi : PAP, CHAP, MS-CHAP. Dengan protokol authentikasi kita bisa memberikan level security. Proses protokol authentikasi pada PAP: Protokol PAP bekerja sangat mirip dengan proses login client ke server pada suatu jaringan jaringan. Client melakukan authentikasi untuk dirinya dengan mengirimkan username dan password ke server. Server kemudian membandingkan inputan dari client tersebut dengan informasi yang tersimpan pada dirinya. Pada protokol autentikasi CHAP dan MS-CHAP memiliki cara kerja tersendiri untuk melakukan proses autentikasi.

PPTP (Point-to-Point Tunneling Protocol) Sebuah protokol jaringan yang menyediakan kemanan transfer data dari remote client ke sebuah privat server dengan menciptakan multiprotocol virtual private network (VPN). PPTP digunakan pada jaringan TCP/IP sebagai alternative untuk metode dial-up. System ini memungkinkan komunikasi yang aman pada multiprotocol melalui suatu jaringan pablik, seperti internet. PPTP sebenarnya ekstensi dari PPP, dimana PPP melakukan encapsulasi paket PPP kedalam IP datagram untuk ditransmisikan. Sehingga memungkinkan system yang menggunakan PPP memiliki fitur-fitur keamanan yang dimiliki oleh teknologi VPN.

PPTP (Point-to-Point Tunneling Protocol) Cara kerja PPTP: VPN menyediakan tunnel melewati jaringan public dengan jalur komunikasi yang aman. PPTP dapat menentukan routing paket untuk melewati jalur public secara aman menuju suatu jaringan privat. Tiga proses pada PPTP untuk membangun koneksi dengan jalur yang aman. Dimana setiap proses yang lengkap pada masing tahapan secara berurutan, seperti dibawah ini:

PPTP (Point-to-Point Tunneling Protocol) PPP connection and communication, PPTP menggunakan PPP berkoneksi dengan remote network. Setelah terkoneksi, PPP juga melakukan enkripsi paket data yang dilewatkan antara remote host dan local machine. PPTP control connection, ketika sesi PPP sudah terbentuk, PPTP menciptakan sebuah control koneksi antara client dengan PPTP remote server. Proses tersebut disebut dengan tunneling. PPTP data tunneling, PPTP menciptakan IP datagram PPP untuk dikirimkan. PPP mengenkripsi paket, yang dikirimkan melalui tunnel ke PPTP server. PPTP server kemudian mendekripsi paket PPP, mengurai IP datagram, dan merutekan ke host yang dimaksud.

ISDN (Integrated Service Digital Network) Sistem komunikasi telepon digital yang memungkinkan melakukan transmisi data secara simultan ujung ke ujung. Dirancang untuk komunikasi dengan cepat, digunakan untuk komunikasi small office dan home user. Ide dasar diawali tahun 1950, dikenalkan 1972. Konsep dasar diawali dengan perkembangan perangkat koneversi analog/digital pada pelanggan yang memungkinkan layanan suara dan data dikirimkan melalui jalur tungal.

ISDN (Integrated Service Digital Network) ISDN Chanels: Sirkuit transmisi ISDN terdiri dari sekumpulan logika data channel, sehingga memungkinkan data dan suara dibawa lewat channel tersebut. Dua tipe channel yang digunakan pada ISDN koneksi tunggal: B channels (bearer channels): Memiliki Bandwidth 64Kbps per channel. Spesifikasi B channel dijelaskan pada H channel, antara lain: H0384Kbps (6 B  channels). H101472Kbps (23 B channels). H111536Kbps (24 B channels). H121920Kbps (30 B channels, the European standard).

Kelebihan-kelebihan dari ISDN: D channels (data channels): Menangani 16 Kbps (BRI) atau 64 Kbps (BRI) Memungkinkan B channel melewatkan data dengan cermat. Biasanya layanan ISDN berisi dua B channel dan sebuah D channel. Kelebihan-kelebihan dari ISDN: Kecepatan transmisi data yang lebih tinggi dibanding dial up. Menyediakan multiple digital Channel pada saat yang bersamaan untuk melewatkan data melalui jalur telepon regular. Mendukung multiple device set up dalam satu link. Koneksi lebih jelas karena data dikirimkan dalam format digital. Karena ISDN menggunakan beberapa channel yang terpisah, maka D channel digunakan untuk pensinyalan yang akan menghilangkan administrative overhead. Sehingga semua informasi yang dikirimkan dalam aliran bit.

PSTN (Public Switch Telephone Network) Dirancang untuk system switching analog untuk routing voice call Menggunakan modem untuk berkoneksi ke remote network melalui jalur PSTN Bandwidth 56Kbps.