Jaringan wireless adalah jaringan komputer yang cukup rentan dengan kendala. Bahkan terkadang problem yang muncul sering kali membingungkan. Walau demikian, saat ini teknologi wireless sudah menjadi teknologi jaringan yang banyak diterapkan.Hali ini terutama karena kelebihanya yang memiliki jarak jangkau.

Penggunaan teknologi jaringan wireless cukup membantu, terutama untuk menjangkau area yang jauh/luas. Namun, dibalik keuntungan tersebut, ada faktor-faktor yang membuat implementasi jaringan wireless tidak semudah ketika menggunakan kabel. Pada saat  menerapkan wireless, menghubungkan satu perangkat ke perangkat yang lain akan dipengaruhi banyak faktor. Antara lain, LoS (Line of sight), site 1 dengan site yang lain harus bisa saling melihat dan tanpa halangan.

Selain itu, ada beberapa hal penting yang harus diperhatikan ketika membangun jaringan nir kabel, antara lain:

Wireless Band

Memilih band bertujuan untuk menentukan standart protokol yang akan digunakan oleh wireless interface. Selain itu, band juga menentukan data rates yang bisa dilewatkan, channel frequencies dan lebar channel. Ada beberapa macam band pada router mikrotik, yaitu:

  • 2Ghz-only G, bekerja di frekuensi 2,4Ghz, hanya menggunakan protokol  802.11g.
  • 2Ghz-only N, bekerja di frekuensi 2,4Ghz, hanya menggunakan protokol  802.11n.
  • 2Ghz-b, bekerja di frekuensi 2,4Ghz. Menggunakan protokol 802.11b dengan data rate maksimum 11 Mbit/s.
  • 2Ghz-b/g, juga bekerja di frekuensi 2,4Ghz. Menggunakan protokol 802.11b dan 802.11g. protokol 802.11g hampir sama seperti 802.11b akan tetapi melakukan transmisi dengan basis OFDM seperti 802.11a sehingga protokol 802.11g bisa mencapai 54 Mbit/s.
  • 2Ghz-b/g/n, bekerja di frekuensi 2,4Ghz. Menggunakan protokol 802.11b, 802.11g dan 802.11n. Pengembangan dari standart protokol 802.11, ditambah dengan kemampuan multiple-input multiple-output (MIMO). Dengan tambahan fitur MIMO ini, secara teori maksimal data rate yang bisa dicapai adalah 300 Mbit/s.
  • 5Ghz-a, bekerja di frekuensi 5 Ghz. Menggunakan protokol 802.11a, maximum data rate yang bisa dicapai adalah 54 Mbit/s.
  • 5Ghz-a/n, bekerja di frekuensi 5 Ghz. Menggunakan protokol 802.11a dan 802.11n.
  • 5Ghz-only N, bekerja di frekuensi 5 Ghz dan hanya menggunakan protokol  802.11n.

Jika kita perhatikan, ada beberapa pilihan band yang menggunakan lebih dari satu protokol. Jika kita setting sebuah interface wireless dengan band yang menggunakan lebih dari satu protokol, maka interface wireless tersebut memberikan pilihan kepada client, protokol mana yang support dengan perangkat client tersebut. Contohnya adalah band 2Ghz-b/g/n.

Frekuensi

Wireless LAN menggunakan radio frekuensi yang membutuhkan media rambat yang juga harus bersih atau tanpa gangguan. Gangguan bisa berupa halangan seperti pohon, gedung, tembok, kaca atau interferensi frekuensi dari perangkat lain di sekitarnya.

Agar terbentuk link wireless yang bagus, gangguan ini harus dihindari. Hal pertama yang harus dilakukan dilakukan adalah site survey terlebih untuk mengetahui kondisi lapangan secara fisik maupun penggunaan frekuensi yang sudah ada. Misalnya, adanya halangan berupa bukit, gedung, pohon, tembok, kaca dsb yang harus dihindari. Kita harus mengetahui juga frekuensi-frekuensi yang ada disekitar. Hal ini nantinya bisa untuk meminimalisir terjadinya interferensi/overlapping.

Alokasi frekuensi sudah diatur dalam regulasi di setiap wilayah dan negara. Di Indonesia, untuk keperluan wireless LAN sudah dalokasikan dalam ISM Band pada frekuensi 2,4GHz dan 5,8GHz. Lebih detail nya, untuk 2,4GHz dibagi dalam beberapa channel dengan lebar channel masing – masing 22MHz.

Begitu juga dengan yang 5GHz. Frekuensi 5Ghz juga dibagi menjadi beberapa channel.

Di mikrotik, tiap channel ditampilkan dengan nilai tengah frekuensi-nya. Misal pada band 2,4GHz, channel1 = 2412 ,dsb.

Kembali ke masalah interferensi. Di mikrotik ada beberapa tool yang bisa digunakan untuk melakukan scanning frekuensi.

    • Tool Scanner, double klik interface wlan > atur mode=station, band, dan frekuensi > klik scan .
    • Tool Snooper, double klik interface wlan > atur mode=station, band, dan frekuensi > klik snooper.

    • Tool Frequency Usage, double klik interface wlan > atur mode=station, band, dan frekuensi > klik Freq. Usage

Dari hasil survey tersebut,kita bisa menentukan penggunaan frekuensi pada perangkat kita agar tidak interferensi dengan yang lain. Berdasarkan pembagian channel pada 2,4GHz, dengan lebar channel standard, bisa dilihat ada beberapa channel yang saling overlapping. Hal ini lah yang harus dihindari agar tidak saling mengganggu dan wireless link terbentuk dengan baik. Misal, dari hasil scan ternyata sudah banyak yang menggunakan frek 2412 (channel 1) , maka kita bisa gunakan frek 2437 (channel 6). Kenapa tidak menggunakan 2417 (Ch.2) saja ? bukankah 2412 (Ch.1) dan 2417 (Ch.2) sudah beda.?Coba lihat lagi gambar pembagian channel tadi, antara 2412 (Ch.1) dan 2417 (Ch.2) ternyata masih overlapping, saling menganggu. Jika digambarkan lagi, agar tidak saling mengganggu bisa gunakan 2412 (Ch.1), 2437 (Ch. 6), 2462 (Ch. 11)

Nah, kalo untuk frek 2484 (Ch.14) merupakan channel yang tidak standard. Perangkat seperti gadget,laptop biasanya tidak support.

Mikrotik support untuk 2484 (ch.14). Akan tetapi kita tetap tidak boleh menggunakan frekuensi tersebut dengan sembarangan. Walaupun secara teknis perangkatnya support, tapi penggunaan frekuensi di luar alokasi jelas menyalahi aturan. Jadi mari gunakan frekuensi sesuai regulasi yang ada. Agar tidak saling mengganggu di frekuensi lain.

Tips diatas untuk pemilihan penggunaan frekuensi pada Band 2,4GHz. Bagaimana dengan 5GHz ?. Berbeda dengan pembagian channel pada 2,4GHz, pembagian channel pada 5GHz tidak ada yang saling overlapping. Untuk mengcover laptop atau gadget, bisa gunakan frek 5725 – 5785 MHz. Kebanyakan gadget saat ini support di frekuensi tersebut. Produk Mikrotik juga sudah support baik untuk band 2,4GHz atau 5GHz. Support juga untuk custom freq dan custom channel width. Tapi sekali lagi, gunakan frekuensi dengan bijak. Jangan menyalahi regulasi.

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