Difference between revisions of "OLSR"

Revision as of 13:28, 21 August 2012

olsr.org OLSR daemon adalah sebuah implementasi dari protokol Optimized Link State Routing. Sehingga memungkinkan sebuah device jaringan untuk melakukan mesh routing.

OLSR bisa dijalankan jika card WiFi mendukung mode ad-hoc dan juga pada device ethernet biasa. OLSR adalah salah satu dari dua standard Internet untuk Jaringan Mesh. OSLR banyak digunakan dan sudah teruji keandalannya.

Karena OLSR bekerja di lapisan / layer 3, dia sangat portable. Saat ini dapat dijalankan di

Windows (XP and Vista, Windows 7)
Linux (i386, arm, alpha, mips, xscale)
OS X (powerpc, intel, xscale, iPhone)
VxWorks
NetBSD
FreeBSD
OpenBSD
Nokia N900
Google phone (Android, G1)
linux wifi phones (WIP)
laptop
Intel Classmate

OLSR sangat cepat dan menggunakan sedikit CPU time sehingga dapat menghemat batere dari embedded dan portable device.

OLSR sangat scalable. OLSR di jalankan di jaringan komunitas wireless mesh dengan 2000 nodes (Athens wireless network), ~ 600 nodes (berlin FreiFunk.net), Leipzig Freifunk net, ~ 400 nodes (FunkFeuer.at). Sebagai protokol mesh routing yang di operasikan di lapangan, OLSR sering menerima stress test dan cukup solid sejak versi 0.5.6-r7 terlepas apa yang dikatakan oleh protokol lain. Tentunya masih banyak ruang untuk perbaikan.

OLSR di released menggunakan lisensi BSD. Oleh karenanya OLSR sangat mudah untuk dimasukan ke projek anda, terima kasih untuk lisensi yang sangat liberal.

OLSR adalah sebuah project open source, sangat di sarankan agar anda tergabung & ikut aktif mengembangkan.

OLSR adalah routing protocol untuk jaringan mobile ad-hoc. Protokol tersebut bersifat pro-active, table driven dan menggunakan teknik multipoint relaying untuk optimized message flooding. olsrd juga menjalankan link quality extension.

Olsrd dibuat dengan cara terstruktur dan terimplementasi dengan baik sehingga mudah di maintain. di expand dan di porting ke platform lain. Olsrd mempunyai arsitektur plugin yang sangat flexibel.

Mengimplementasikan RFC3626 baik untuk core maupun fungsi tambahannya.

Olsrd mendukung penggunaan plugin yang dapat di load. Hal ini dapat digunakan untuk menangani paket khusus yang dapat di bawa oleh skema OLSR MPR flooding atau fungsi lain yang di inginkan.

Lebih Jauh Dengan OLSR

Optimized Link State Routing Protocol (OLSR) adalah sebuah protocol routing untuk IP yang di optimisasi untuk jaringan mobile ad-hoc, yang juga dapat digunakan pada jaringan wireless ad-hoc. OLSR adalah sebuah protocol link-state routing yang proactif, yang menggunakan message hello dan topology control (TC) untuk mengetahui dan mendiseminasikan informasi link state di seluruh jaringan mobile ad-hoc. Masing-masing node menggunakan informasi topologi untuk menghitung next hop yang dituju untuk semua node di jaringan menggunakan shortest hop forwarding paths.

Fitur yanng spesifik di OLSR

Protocol Link-state routing seperti Open Shortest Path First (OSPF) dan IS-IS akan memilih router tertentu di setiap sambungan untuk melakukan pemberitahuan akan informasi topologi. Dalam jaringan wireless ad-hoc, ada perbedaan pengertian tentang sebuah sambungan, paket dapat dan pergi keluar melalui interface yang sama, oleh karena itu kita perlu melakukan proses yang berbeda untuk mengoptimasi proses pemberitahuan.

Menggunakan message Hello di setiap node akan menemukan informasi tetangga 2-hop dan melakukan pemilihan secara terdistribusi kumpulan dari multipoint relay (MPR). Node akan memilih MPR supaya ada jalur antara tetangga 2-hop melalui sebuah node yang terpilih sebagai MPR. MPR Ini kemudian akan mengambil dan memforward message TC yang berisi MPR yang terpilih. Fungsi MPR membuat OLSR unik dari protokol link state routing dalam beberapa hal: infomasi path forwarding untuk message TC tidak di bagi ke semua node tapi bervariasi tergantung pada source, hanya sebuah subset dari informasi source link state node, tidak semua link dari node di beritahukan hanya node yang merepresentasikan MPR yang terpilih saja.

Karena link-state routing membutuhkan database topologi yang tersinkronisasi di seluruh jaringan, OSPF dan IS-IS melakukan penyebaran informasi topologi menggunakan algoritma yang reliabel. Algoritma demikian sangat sulit di implementasikan dalam jaringan wireless ad-hoc, oleh karena-nya OLSR tidak peduli masalah reliabilitas, cukup melakukan penyebaran informasi topologi sesering mungkin untuk memastikan bahwa database tidak sampai tidak terupdate dalam perioda yang lama.

Keuntungan

Being a proactive protocol, routes to all destinations within the network are known and maintained before use. Having the routes available within the standard routing table can be useful for some systems and network applications as there is no route discovery delay associated with finding a new route.

The routing overhead generated, while generally greater than that of a reactive protocol, does not increase with the number of routes being created.

Default and network routes can be injected into the system by HNA messages allowing for connection to the internet or other networks within the OLSR MANET cloud. Network routes are something reactive protocols do not currently execute well.

Timeout values and validity information is contained within the messages conveying information allowing for differing timer values to be used at differing nodes.

Kritik Terhadap OLSR

The original definition of OLSR does not include any provisions for sensing of link quality; it simply assumes that a link is up if a number of hello packets have been received recently. This assumes that links are bi-modal (either working or failed), which is not necessarily the case on wireless networks, where links often exhibit intermediate rates of packet loss. Implementations such as the open source OLSRd (commonly used on Linux-based mesh routers) have been extended (as of v. 0.4.8) with link quality sensing.

Being a proactive protocol, OLSR uses power and network resources in order to propagate data about possibly unused routes. While this is not a problem for wired access points, and laptops, it makes OLSR unsuitable for sensor networks that try to sleep most of the time. For small scale wired access points with low CPU power, the open source OLSRd project showed that large scale mesh networks can run with OLSRd on thousands of nodes with very little CPU power on 200 MHz embedded devices.

Being a link-state protocol, OLSR requires a reasonably large amount of bandwidth and CPU power to compute optimal paths in the network. In the typical networks where OLSR is used (which rarely exceed a few hundreds of nodes), this does not appear to be a problem.

By only using MPRs to flood topology information, OLSR removes some of the redundancy of the flooding process, which may be a problem in networks with moderate to large packet loss rates[2] – however the MPR mechanism is self-pruning (which means that in case of packet losses, some nodes that would not have retransmitted a packet, may do so). Messages

OLSR makes use of "Hello" messages to find its one hop neighbors and its two hop neighbors through their responses. The sender can then select its multipoint relays (MPR) based on the one hop node that offers the best routes to the two hop nodes. Each node has also an MPR selector set, which enumerates nodes that have selected it as an MPR node. OLSR uses topology control (TC) messages along with MPR forwarding to disseminate neighbor information throughout the network. Host and network association (HNA) messages are used by OLSR to disseminate network route advertisements in the same way TC messages advertise host routes. Hello

Olsr-hello-packet.png Topology control (TC)

Olsr-tc-packet.png Other approaches

The problem of routing in ad-hoc wireless networks is actively being researched, and OLSR is but one of several proposed solutions. To many, it is not clear whether a whole new protocol is needed, or whether OSPF could be extended with support for wireless interfaces.[3][4]

In bandwidth- and power-starved environments, it is interesting to keep the network silent when there is no traffic to be routed. Reactive routing protocols do not maintain routes, but build them on demand. As link-state protocols require database synchronisation, such protocols typically use the distance vector approach, as in AODV and DSDV, or more ad-hoc approaches that do not necessarily build optimal paths, such as Dynamic Source Routing.

For more information see the list of ad-hoc routing protocols.

OLSR versi 2

OLSRv2 is currently being developed within the IETF. It maintains many of the key features of the original including MPR selection and dissemination. Key differences are the flexibility and modular design using shared components: packet format packetbb, and neighborhood discovery protocol NHDP. These components are being designed to be common among next generation IETF MANET protocols. Differences in the handling of multiple address and interface enabled nodes is also present between OLSR and OLSRv2. Implementations

OLSR.ORG – Downloadable code for OLSR on GNU/Linux, Windows, Mac OS X, FreeBSD and NetBSD systems. Features a great deal of documentation, including an informative survey of related work.
NRL-OLSR – Open source code of NRL-OLSR. Works on Windows, MacOS, Linux, and various embedded PDA systems such as Arm/Zaurus and PocketPC as well as simulation environments ns2 and OPNET., http://cs.itd.nrl.navy.mil/focus/
SOURCEFORGE.NET-OLSR – Created by MOVIQUITY and based on studies within the project Workpad, it offers a code in C# to deploy a MANET (Ad-Hoc, Meshnet) with protocol OLSR. Developed for WM 6, Win XP and can be adapted to other platforms using NET Framework and Compact http://sourceforge.net/projects/wmolsr/

Referensi

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