Do you mean Cat5 cable? If so - that's not good enough (only rated up to 100mbps) and is probably >10 years old and will need replacing. Cat5e will suffice but Cat6 has better shielding from interference so is the one to go for.
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.