Avaya Phones2018-07-24T20:44:30+00:00

Avaya Refurbished Phones

Avaya provides a complete portfolio of business phones and communications endpoints. We offer devices for use at desks, in conference rooms, and across campuses. We support in-office, mobile, remote, and video users. Contact us, we are an Avaya Authorized Partner to start a conversation about the right phones for your business communications.

Get all your essential call-handling features in an affordable, yet highly functional SIP Phone. This phone delivers the top functionalities needed by users in any-size businesses.

Avaya video collaboration stations deliver highly effective engagement throughout your business day. Go beyond a basic video phone with full HD video conferencing, a business phone and unified communications features—all in one touchscreen desktop station.

Help drive better communications and collaboration among office, remote, and mobile workers. These devices use standards-based SIP to bring the most often used and impactful call handling features to workers regardless of where they are located.

Avaya 9650C IP Telephone

Avaya 9650C IP Telephone (700461213)

The Avaya 9650C IP Telephone is designed for users who use the phone for the majority of the day.  It provides wideband audio, a high resolution display, and advanced communication capabilities.

 Avaya 9650C IP Telephone Features

  • Provides a 1×4 VGA color screen
  • Specifically made for navigator telephone users that answer many incoming calls, transfer callers, and monitor bridges appearances throughout the day
  • Supports built-in button module functionality to provide simple one-touch access to bridged appearances, speed dials, and feature keys – 8 physical buttons with shift capability to 16
  • Through its integrated web browser and application interface, the 9650 supports enhanced applications such as LDAP corporate directories and integration with Microsoft Outlook Calendars
  • LEDs built into buttons such as mute, message, and headset provide clear indication to the user
  • Easy-to-use context driven menus with on-screen prompts
  • High-resolution monochrome display
  • Full-duplex speaker and wideband audio handset
  • 4-way navigation cluster, 4 display soft keys
  • Fixed features include message, phone, contacts, menu, call log, speaker, mute, headset, and volume control
  • H.323 firmware (can also be loaded with SIP firmware)

Avaya 9650C Compatibility

  • IP Office R6.0 or higher only on IP500 and IP500 V2 control units
  • H.323 version supported by Avaya Communication Manager R3.0 or later
  • SIP version supported by Avaya Communication R4.0 or later
  • Powered via 802.3af PoE or local 1151 power supply (sold separately; see accessory below)

Avaya 9620L IP Telephone

Avaya 9620L IP Telephone (700461197)

The Avaya 9620L is a full-featured IP telephone made for the everyday phone user.  It provides 3 line appearances and supports up to 12 call appearances or features.

Avaya 9620L Features

  • 3.45″ backlit display
  • 3 line appearances supporting up to 12 call appearances or features
  • 4 softkeys, 4 navigation buttons
  • Built-in full duplex speakerphone
  • Dual message waiting indicators
  • Volume, menu, message, speaker, headset, contacts, and call log buttons
  • Built-in two port Ethernet switch for connection to LAN and collocated PC
  • Supports wideband audio codec
  • Built-in headset interface
  • 9620L vs. 9620 – The 9620L is a low power consumption model (Class 1 PoE device). It has the same functionality as the original 9620 but does not have a USB port or adapter interface for adjuncts. It does not support SIP protocol.

Compatibility

  • IP Office R6.0 or higher only on IP500 and IP500 V2 control units
  • Avaya Communication Manager R3.1 or later – H.323 version supported; SIP not supported
  • Powered via 802.3af PoE (Class 1) or local 1151 power supply (sold separately; see accessory below)

 

Avaya 9620C IP Telephone

Avaya 9620C IP Telephone (700461205)

The Avaya 9620C is a full-featured IP telephone made for the everyday phone user.  It provides a color backlit display with  3 line appearances and supports up to 12 call appearances or features.

Avaya 9620C Features

  • 3.45″ color backlit display
  • 3 line appearances supporting up to 12 call appearances or features
  • 4 softkeys, 4 navigation buttons
  • Built-in full duplex speakerphone
  • Dual message waiting indicators
  • Volume, menu, message, speaker, headset, contacts, and call log buttons
  • Built-in two port Ethernet switch for connection to LAN and collocated PC
  • Supports wideband audio codec
  • Built-in headset interface
  • Adapter interface for add-on support (e.g. 9600 Bluetooth Adapter, 9600 GigE Adapter etc.)

Compatibility

  • IP Office R6.0 or higher only on IP500 and IP500 V2 control units
  • H.323 version supported by Avaya Communication Manager R3.1 or later
  • SIP version supported by Avaya Communication R4.0 or later
  • Powered via 802.3af PoE (Class 1) or local 1151 power supply (sold separately; see accessory below)

Avaya 9621G IP Telephone

avaya 9621g ip telephone 700480601

Avaya 9621G IP Telephone (700480601)

The Avaya 9621G is a full-featured IP telephone.  It features a tiltable touch screen display and Gigabit connectivity.

Avaya 9621G Features

  • 3.7 x 2.1 inch color touchscreen display
  • 4 position adjustable tilt display
  • Fixed features include speaker, mute, headset, contacts, home, history, message, phone, forwarding, volume
  • Wideband audio and wideband speakerphone
  • Dual message waiting indicators 360-degree visual alert for incoming calls and voice mail
  • Bluetooth and DECT headset support with optional adapter
  • Built-in two port Ethernet (10/100/1000 Mbps) switch for connection to LAN and collocated PC
  • Built-in headset interface

Compatibility

  • H.323 version supported by Avaya Communication Manager 3.1.4 or later
  • SIP version supported by Avaya Communication Manager 6.0 with Avaya Aura Session Manager 6.0 or Avaya Midsize Business Template 5.2.1
  • Also compatible with IP Office 6.1 or higher only on IP500 or IP500 V2 control units
  • The Avaya 9621G can be powered via 802.3af PoE (Class 1) or local PoE injector (sold separately; see accessory below)

Avaya BM12 Button Module

Avaya BM12 Button Module (700480643)

The Avaya BM12 button module provides 24 additional programmable line and feature buttons for Avaya 9600 series IP telephones.

Avaya BM12 Features

  • Provides 24 additional buttons using two pages of 12 call appearances/features each
  • Buttons can be used for additional lines for incoming calls, outgoing calls, and calling features

Compatibility

  • The Avaya BM12 is compatible with the Avaya 9608, 9611G, and 9641G IP phones
  • Also compatible with the Avaya 9408 and 9508 digital phones (NOTE: When using with the 9408/9508, an 1151D1 power supply is required – see accessory below)
  • Can add up to three button modules per phone

Avaya 9650 IP Telephone

Avaya 9650 IP Telephone (700383938)

The Avaya 9650 IP Telephone is designed for users who use the phone for the majority of the day.  It provides wideband audio, a high resolution display, and advanced communication capabilities.

Avaya 9650 Features

  • Specifically made for navigator telephone users that answer many incoming calls, transfer callers, and monitor bridges appearances throughout the day
  • Supports built-in button module functionality to provide simple one-touch access to bridged appearances, speed dials, and feature keys – 8 physical buttons with shift capability to 16
  • Through its integrated web browser and application interface, the 9650 supports enhanced applications such as LDAP corporate directories and integration with Microsoft Outlook Calendars
  • LEDs built into buttons such as mute, message, and headset provide clear indication to the user
  • Easy-to-use context driven menus with on-screen prompts
  • High-resolution monochrome display
  • Full-duplex speaker and wideband audio handset
  • 4-way navigation cluster, 4 display soft keys
  • Fixed features include message, phone, contacts, menu, call log, speaker, mute, headset, and volume control
  • H.323 firmware (can also be loaded with SIP firmware)

Compatibility

  • IP Office R6.0 or higher only on IP500 and IP500 V2 control units
  • H.323 version supported by Avaya Communication Manager R3.0 or later
  • SIP version supported by Avaya Communication R4.0 or later
  • Powered via 802.3af PoE or local 1151 power supply (sold separately; see accessory below)

Avaya SBM24

Avaya SBM24 Button Module

(700383417, 700426737, 700462518)

The Avaya SBM24 button module provides 24 additional programmable line and feature buttons for Avaya 9600 series IP telephones.

Avaya SBM24 Features

  • Provides 24 additional lines for incoming calls, outgoing calls, and calling features

Compatibility

  • Compatible with Avaya 9630, 9630G, 9640, 9640G, 9650, an 9650C IP telephones
  • IP Office R6.0 or higher – Can add up to 3 SBM24 modules per phone; up to 42 SBM24s per system
  • Avaya Communication Manager R4.0 or higher – Can add up to 3 SBM24 modules per phone
  • Avaya Communication Manager below R4.0 – Support for one SBM24 per phone

 

Avaya 9641G IP Telephone

 Avaya 9641G IP Telephone (700480627)

The Avaya 9641G IP phone is a multi-line premium deskphone ideally suited for people who spend considerable amounts of time on the phone and who rely on intelligent communications and productivity enhancing capabilities. The 9641G has a color graphical display, larger touch screen and, high definition audio quality.

Avaya 9641G Features

  • 4.1 x 2.3 inch color touchscreen display
  • Configurable line/feature buttons
  • 4 position adjustable tilt display
  • Fixed features include speaker, mute, headset, contacts, home, history, message, phone, forwarding, volume
  • Wideband audio and wideband speakerphone
  • Dual message waiting indicators
  • 360-degree visual alert for incoming calls and voice mail
  • Bluetooth and DECT headset support with optional adapter
  • USB application support
  • Built-in two port Ethernet (10/100/1000 Mbps) switch for connection to LAN and collocated PC
  • Supports up to three Avaya BM12 button modules
  • Built-in headset interface

Compatibility

  • H.323 version supported by Avaya Communication Manager 3.1.4 or later
  • SIP version supported by Avaya Communication Manager 6.0 with Avaya Aura Session Manager 6.0 or Avaya Midsize Business Template 5.2.1
  • Also compatible with IP Office 7.0.36 or higher only on IP500 or IP500 V2 control units
  • The Avaya 9641G can be powered via 802.3af PoE (Class 1) or local PoE injector (sold separately; see accessory below)

 

 

Avaya 9640G IP Telephone

Avaya 9640G IP Telephone (700419195)

The Avaya 9640G IP Telephone is designed for workers who conduct much of their business on the phone moving from one call to the next. It delivers advanced communications capabilities including wideband audio, Gigabit connectivity, and a brilliant high resolution color display.

Avaya 9640G Features

  • 3.8″ color backlit display
  • 6 line appearances supporting up to 24 call appearances or features
  • 4 softkeys, 4 navigation buttons
  • Built-in full duplex speakerphone
  • Dual message waiting indicators
  • Volume, menu, message, speaker, headset, contacts, and call log buttons
  • Built-in two port Gigabit Ethernet switch for connection to LAN and collocated PC
  • Supports wideband audio codec
  • Supports up to 3 Avaya SBM24 Button Modules for expansion
  • 2 adapter interfaces for add-on support (e.g. 9600 Bluetooth Adapter, 9600 GigE Adapter etc.)
  • Built-in headset interface

Compatibility

  • IP Office R6.0 or higher only on IP500 and IP500 V2 control units
  • H.323 version supported by Avaya Communication Manager R3.0 or later
  • SIP version supported by Avaya Communication R4.0 or later
  • Powered via 802.3af PoE (Class 2) or local PoE Injector (sold separately; see accessory below)

Avaya 9640 IP Telephone

 Avaya 9640 IP Telephone (700383920)

The Avaya 9640 IP Telephone is designed for workers who conduct much of their business on the phone moving from one call to the next. It delivers advanced communications capabilities including wideband audio and a brilliant high resolution color display.

Avaya 9640 Features

  • 3.8″ color backlit display
  • 6 line appearances supporting up to 24 call appearances or features
  • 4 softkeys, 4 navigation buttons
  • Built-in full duplex speakerphone
  • Dual message waiting indicators
  • Volume, menu, message, speaker, headset, contacts, and call log buttons
  • Built-in two port Ethernet switch for connection to LAN and collocated PC
  • Supports wideband audio codec
  • Supports up to 3 SBM24 Button Modules for expansion
  • 2 adapter interfaces for add-on support (e.g. 9600 Bluetooth Adapter, 9600 GigE Adapter etc.)
  • Built-in headset interface

Compatibility

  • IP Office R6.0 or higher only on IP500 and IP500 V2 control units
  • H.323 version supported by Avaya Communication Manager R3.0 or later
  • SIP version supported by Avaya Communication R4.0 or later
  • Powered via 802.3af PoE (Class 2) or local PoE Injector (sold separately; see accessory below)

 

Avaya 9611G IP Telephone

Avaya 9611G IP Telephone (700480593)

The Avaya 9611G IP phone is a full-featured Gigabit IP desk phone that provides 24 programmable line and feature buttons.  It is the perfect choice for everyday office workers like salespeople, executives, and operators.

Avaya 9611G Features

  • 2.8 x 2.1 inch color display
  • 3 pages of 8 buttons with dual LEDs (24 programmable keys), 4 soft keys 4-way navigation cluster
  • Fixed features include phone, messages, contacts, history, home, headset, speaker, volume, mute
  • Wideband audio
  • Built-in full duplex speakerphone and built-in headset interface
  • Dual message waiting indicators
  • Built-in two port Ethernet (10/100 Mbps) switch for connection to LAN and collocated PC
  • Supports up to three Avaya BM12  button modules

Compatibility

  • Compatible with IP Office 8.0 (42) or higher
  • H.323 version supported by Avaya Communication Manager 3.1.4 or later
  • SIP version supported by Avaya Communication Manager 6.0 with Avaya Aura Session Manager 6.0 or Avaya Midsize Business Template 5.2.1
  • Also compatible with IP Office 7.0.36 or higher only on IP500 or IP500 V2 control units
  • The Avaya 9611G can be powered via 802.3af PoE (Class 1) or local PoE injector (sold separately; see accessory below)

Avaya 9630G IP Telephone

 Avaya 9630G IP Telephone (700405673)

The Avaya 9630G IP phone is made for the essential telephone user.  It features 6 line appearances, wideband audio, and Gigabit connectivity.

Avaya 9630G Features

  • 3.8″ backlit display
  • 6 line appearances supporting up to 24 call appearances or features
  • 4 softkeys, 4 navigation buttons
  • Built-in full duplex speakerphone
  • Dual message waiting indicators
  • Volume, menu, message, speaker, headset, contacts, and call log buttons
  • Built-in two port Gigabit Ethernet switch for connection to LAN and collocated PC
  • Supports wideband audio codec
  • Supports up to 3 Avaya SBM24 Button Modules for expansion
  • 2 adapter interfaces for add-on support (e.g. 9600 Bluetooth Adapter etc.)
  • Built-in headset interface

Compatibility

  • IP Office R6.0 or higher only on IP500 and IP500 V2 control units
  • H.323 version supported by Avaya Communication Manager R3.0 or later
  • SIP version supported by Avaya Communication R4.0 or later
  • Powered via 802.3af PoE (Class 2) or local PoE Injector (sold separately; see accessory below)

Avaya 9608 IP Telephone

Avaya 9608 IP Telephone (700480585 )

The Avaya 9608 IP phone is a full-featured IP desk phone that provides 24 programmable line and feature buttons.  It is the perfect choice for everday office workers like salespeople, executives, and operators.

Avaya 9608 Features

  • 3.2″ x 2.2″ monochrome display
  • 3 pages of 8 buttons with dual LEDs (24 programmable keys), 4 softkeys, 4-way navigation cluster
  • Fixed features include phone, messages, contacts, history, home, headset, speaker, volume, mute
  • Wideband audio
  • Built-in full duplex speakerphone and built-in headset interface
  • Dual message waiting indicators
  • Built-in two port Ethernet (10/100 Mbps) switch for connection to LAN and collocated PC
  • Supports up to three Avaya BM12 button modules

Compatibility

  • H.323 version supported by Avaya Communication Manager 3.1.4 or later
  • SIP version supported by Avaya Communication Manager 6.0 with Avaya Aura Session Manager 6.0 or Avaya Midsize Business Template 5.2.1
  • Also compatible with IP Office 7.0.36 or higher only on IP500 or IP500 V2 control units
  • The Avaya 9608 can be powered via 802.3af PoE (Class 1) or local PoE injector (sold separately; see accessory below)

 

Avaya 8503 ISDN VOICE TERMINAL

Features:

  • 3 call appearance (rubber dome) buttons 9 fixed feature buttons, 3 with secondary functions Includes easy-to-use fixed key features 12 one-touch speed dial numbers
  • Memory
  • Conference/Ring
  • Drop/Test
  • Transfer/Pause
  • Hold buttons
  • Adjunct jack

System Requirements/Compatibility:

  • DEFINITY ECS G2 or G3
  • TN556B BRI ISDN line circuit card
  • Compatible with “custom” IDSN service from your local phone company

Avaya 8520 ISDN VOICE TERMINAL

The 8520T voice/data terminal is used with the ISDN communication system through a 4-wire T-interface. The 8520T voice/data terminal offers the following:

Features:

  • 20 programmable buttons, ISDN terminal
  • 9 fixed feature buttons
  • Large supertwist LCD; 7-lines, 24-characters
  • Call logs keep track of 60 recent calls
  • Built-in speakerphone
  • Speakerphone which can also be optioned as a listen-only Speaker
  • Volume control
  • Improved acoustic quality with the K-type handset
  • Adjunct jack for adjunct equipment
  • Touch-tone dialing. Ten softkeys and four display control buttons located on either side of the Directory, a Call Log which lists the most recent incoming and outgoing calls, the Self-Test feature, and a personalized ringing pattern for the voice/data terminal.

System Requirements/Compatibility:

  • DEFINITY ECS G2 or G3
  • TN556B BRI ISDN line circuit card
  • Compatible with “custom” ISDN service from local service providers

Avaya 8528 ISDN VOICE TERMINAL

Features:

  • 28 programmable buttons for call appearance or call management features, ISDN terminal
  • 9 fixed feature buttons
  • Large LCD; 2-lines, 24-characters
  • Call logs keep track of 30 recent calls
  • Built-in speakerphone

System Requirements/Compatibility:

  • DEFINITY ECS G2 or G3
  • TN556B BRI ISDN line circuit card
  • Compatible with “custom” ISDN service from local service providers

Avaya 8403

The Avaya Definity 8403 phone enhanced design and functionality make it an excellent phone for any business. The multiline digital terminal is an ideal solution for Definity system customers who need flexible yet economical call-handling capabilities throughout their business. The Avaya 8403 terminal multiple line appearances provide expanded call coverage and other advanced voice communications.

For example – one-touch access to dedicated feature buttons such as Conference, Hold, Mute, and Transfer lets your employees work faster and more efficiently. The rocker-type Volume Control easily adjusts the ring, handset, or speaker volume, and the red LED Message waiting light instantly alerts users to messages. The Feature button allows quick access – via the dialpad – to 12 additional features of the telephone system.

In addition, the listen-only, built in Speaker provides convenient off-hook dialing and listening.

Features:

  • 3 programmable call appearance/feature buttons
  • 8 fixed feature buttons
  • Listen-only speakerphone

System Requirements/Compatibility:

  • 2-wire TN2181 16-ports circuit card for DEFINITY G3V2 Systems and higher
  • 2-wire TN2224 24-ports circuit card for DEFINITY Release 5.0 and higher
  • 4-wire TN754C circuit card for System 75 and earlier DEFINITY communications systems

Avaya 8405 DISPLAY

Features:

  • 5 programmable call appearance/feature buttons
  • 2-line, 24-character Liquid Crystal Display (LCD)
  • 9 fixed feature buttons
  • 2-way speakerphone
  • 4 “Soft Keys” that activate 12 different system features

System Requirements/Compatibility:

  • 2-wire TN2181 16-ports circuit card for DEFINITY G3V2 Systems and higher
  • 2-wire TN2224 24-ports circuit card for DEFINITY Release 5.0 and higher
  • 4-wire TN754C circuit card for System 75 and earlier DEFINITY communications systems

Avaya 8405 NON DISPLAY

The Definity 8405 Basic phone comes with a listen-only speakerphone, Conference, Mute, Speaker, Transfer, Shift, Drop, Hold and Test. The phone provides access to multiple lines for call handling, call coverage, bridging, conferencing, and more.

Features:

  • 5 programmable call appearance/feature buttons
  • 9 fixed feature buttons
  • 2-way speakerphone
  • 5 call appearance/feature buttons
  • LED Message Waiting Light
  • Conference, transfer, mute, and hold built-in
  • 2 and 4 Wire Connectivity
  • Two Way Speakerphone
  • Avaya 8405B Non Display Digital Set Requirements

System Requirements/Compatibility:

  • 2-wire TN2181 16-ports circuit card for DEFINITY G3V2 Systems and higher
  • 2-wire TN2224 24-ports circuit card for DEFINITY Release 5.0 and higher
  • 4-wire TN754C circuit card for System 75 and earlier DEFINITY communications systems

Avaya 8410 DISPLAY

Features:

  • 10 programmable call appearance/feature buttons
  • 2-line, 24-character Liquid Crystal Display (LCD)
  • 9 fixed feature buttons
  • 2-way speakerphone
  • 4 “Soft Keys” activate 12 different system features

System Requirements/Compatibility:

  • 2-wire TN2181 16-port circuit card for DEFINITY G3V2 Systems and higher
  • 2-wire TN2224 24-port circuit card for DEFINITY Release 5.0 and higher
  • 4-wire TN754C circuit card for System 75 and earlier DEFINITY communications systems

Avaya 8410 NON DISPLAY

Great price on this digital 2 wire phone with 10 call appearances with built in display.

Features:

  • 10 programmable call appearance/feature buttons
  • 9 fixed feature buttons
  • 2-way speakerphone
  • 2-line, 24 character display
  • 4 soft keys activate 12 different functions
  • Conference, transfer, drop, and hold built-in

System Requirements/Compatibility:

  • 2-wire TN2181 16-port circuit card for DEFINITY G3V2 Systems and higher
  • 2-wire TN2224 24-port circuit card for DEFINITY Release 5.0 and higher
  • 4-wire TN754C circuit card for System 75 and earlier DEFINITY Communications Systems

Avaya 8411 DISPLAY FAX/DATA PORT

Features:

  • 10 programmable call appearance/feature buttons
  • 2-line, 24-character Liquid Crystal Display (LCD)
  • 9 fixed feature buttons
  • 2-way speakerphone
  • 4 “soft keys” located under the display activate 12 different system features
  • Built-in 25-pin RS-232 connector for PassageWay Direct Connection
  • Plug in local fax machine or analog product

System Requirements/Compatibility:

  • Requires one of the following circuit cards:
  • 2-wire 16-port digital station circuit card (TN2181)
  • 2-wire 24-port digital station circuit card (TN2224)
  • 4-wire 8-port digital station circuit card (TN754C)

Avaya 8434 34 BUTTON DISPLAY

Features:

  • 34 programmable call appearance/feature buttons
  • 2-line, 40-character Vacuum Fluorescent Display (VFD)
  • 2-way speakerphone
  • 5 “Soft Keys” activate 15 different system features

System Requirements/Compatibility:

  • DEFINITY G3V3 (or higher)
  • 1151A1 Auxiliary Power Supply, Local Auxiliary Power supply or bulk power supply
  • Requires one of the following circuit cards:
  • 2-wire 16-port digital station circuit card (TN2181)
  • 2-wire 24-port digital station circuit card (TN2224)
  • 4-wire 8-port digital station circuit card (TN754C)

Avaya 18 BUTTON

Features:

  • 16 buttons for outside lines or programmable features
  • Fixed feature buttons such as Hold, Conference, Transfer, Drop and Intercom access
  • Built-in speakerphone
  • Built-in port allows for direct connection of standard devices, such as answering and fax machines
  • Slide out tray with user’s instructions
    System Requirements/Compatibility:

  • Compatible with all releases of PARTNER ACS
  • Compatible with Release 3.0 or higher of PARTNER, PARTNER Plus and PARTNER II

Avaya Partner 18d

Features:

  • 16 buttons for outside lines or programmable features
  • 2-line, 24-character display, adjustable and back lit
  • Fixed feature buttons such as Hold, Conference, Transfer, Drop and Intercom access
  • Built-in speakerphone
  • Built-in port allows for direct connection of standard devices, such as answering and fax machines

System Requirements/Compatibility:

  • Compatible with all releases of PARTNER ACS
  • Compatible with Release 3.0 or higher of PARTNER, PARTNER Plus and PARTNER II

Avaya 34 BUTTON BIS DISPLAY

Features

  • 32 programmable buttons for outside lines or programmable features
  • 2-line, 24-character display, adjustable and back lit
  • 46 functional buttons
  • Fixed feature buttons such as Hold, Conference, Transfer, Drop and Intercom access
  • Built-in port allows for direct connection of standard devices, such as answering and fax machines and built-in speakerphone

System Requirements/Compatibility:

  • Compatible with PARTNER ACS and PARTNER II systems
  • Compatible with Release 2.0 and higher of PARTNER Plus system