Compare

1 Port, 2 Port, 4 Port, 8 Port

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No, Yes

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Yes

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Yes

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Yes

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Yes

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Asterisk, Elastix, FreeBPX, FreeSWITCH, IP BRICK, trixbox, YATE

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YES

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Euro ISDN, Network or CPE, AT&T 4ESS, CAS Voice Modes

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5 Years From Manufacturer

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Allo

Yealink

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SIP-T21P E2

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2 VoIP accounts, Call hold, mute, DND, One-touch speed dial, hotline, Call forward, call waiting, call transfer, Group listening, SMS, emergency call, Redial, call return, auto answer, Local 3-way conferencing, Direct IP call without SIP proxy, Ring tone selection/import/delete, Set date time manually or automatically, Dial plan, XML Browser, action URL/URI, Integrated Screenshots, RTCP-XR

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SIP RFC3261, TCP/IP/UDP, RTP/RTCP, HTTP/HTTPS, ARP/RARP, ICMP, DNS (A record, SRV, NAPTR), DHCP, PPPoE, SSH, TFTP, NTP, STUN, SIMPLE, LLDPMED, LDAP, TR-069, 802.1x, TLS, SRTP

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SIP v1 (RFC2543), v2 (RFC3261), NAT transverse: STUN mode, Proxy mode and peer-to-peer SIP link mode, IP assignment: static/DHCP, HTTP/HTTPS web server, Time and date synchronization using SNTP, UDP/TCP/DNS-SRV(RFC 3263), QoS: 802.1p/Q tagging (VLAN), Layer 3 ToS
DSCP, SRTP for voice, Transport Layer Security (TLS), HTTPS certificate manager, AES encryption for configuration file, Digest authentication using MD5/MD5-sess, OpenVPN, IEEE802.1X, IPv6

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2 line keys with LED, 6 features keys: message, headset, redial, tran, mute, hands-free speakerphone, 6 navigation keys, Volume control keys

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Support for G.711µ/a, G.722 (wide-band), G.723 (pending), G.726-32, G.729 A/B, in-band and out-of-band DTMF (In audio, RFC2833, SIP INFO)

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English, German, Italian, French, Spanish, Portuguese, Russian, Croatian, simplified and traditional Chinese, Korean, Japanese and more

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FCC: Part 15 (CFR 47) Class BCE : EN55022 Class B, EN55024, EN61000-3-2, EN61000-3-3, EN60950-1RCM: AS/ACIF S004; AS/NZS CISPR22/24; AS/NZS 60950; AS/NZS 60950.1