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Should I Use Hubs or Switches in 3Com NBX Configurations?

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Forget The general rule to use a switch when installing 30 or more telephones or installing T1.5 lines. The emphasis is "general." The NBX product presents an opportunity and challenge to the installing company unlike a traditional telephone system since, the NBX is a converged product. This meaning that telephones and local area network (LAN) devices will operate on the same cabled ethernet infrastructure. It is up to the installing company to ask the right kinds of questions and to do the site survey before presenting a sales quotation with or without LAN switches.

Hubs are obsolete. One experienced VAR commented "Never, never deploy an NBX with Hubs, we always use switches."

In traditional telephony there is still alive and well a scientific method known as "traffic engineering" that is used to calculate and answer questions such as of how many telephone lines or people to answer calls do I need ? In the data world there is bandwidth, packets, latency, and utilization. In the converged world of the NBX we must view the network as a whole and identify the traffic, applications used by the customer, and the existing methods implemented.

The device count is a quick indicator to decide on implementing switches but not conclusive. Devices are telephone lines, telephones, servers, PCs, Macs, network printers, and anything else that uses a dedicated LAN connection, so taking inventory is necessary. Next, identify any DOS, accounting, or data intensive applications in use. Then, determine if the internet connection is analog, dual analog, ISDN, dsl, F-T1.5, T1.5, T3, etc. In the site survey find all the hubs in use. There are usually some in hiding because someone didn't want to install a cable. After you find the hubs collect them, trash them, and forget them. Not to sound harsh, but the amount of effort and countless manhours spent troubleshoot Hub problems needs to end with any NBX installation. If you never get an NBX, get rid of your Hubs and move on to better things.

If the customer is willing, run Transcend Network Supervisor to discover the network and take a look at the traffic using the monitoring feature. Don't just rely on Transcend, get out and walk around, ask questions, and find out how the network is installed. Another general rule is most businesses are busy at 10:00 am and 2:00 pm. Assuming this is so, observe the existing hubs in place. Are the collision lights constantly on? Is response time slow? What do the users have to say?


Personally, it's beyond me why business owners even allow hubs in their network. (Yes, I know, these are cost factors.) Anyway, here are some indicators that are good reasons to go ahead and buy the switch(es):

  • Pressing a line button on the NBX seems slow in delivering audible dial tone
  • Hub collision lights are always on
  • Print activity on LAN is too slow
  • Response time in application is too slow
  • Internet or voice connections are dsl, T1.5, or T3
  • Telecommuter(s) are in place for the NBX
  • You deploy a VoIP solution
  • Users complain of echo on NBX
  • Users complain of noise on telephone calls (Analog Lines)
  • Excessive Error Log messages: exceeded pkt resend count reseting
  • Users complain of 'audio distortion/garbling'
  • Voice Mail ports go into the HUNG state
  • Latent Message Notification lights/alerts of new voice mail messages
  • Attacks from WAN inbound knock down internet access & telephone system (IP)

the Group recommends the 3Com 1100 switches (3C16950/3C16951). 3C16951 shown below. Be sure to disable "auto negotiation" on any NBX or shared NBX connections going in the switch(es) and this will also enable "Half Duplex." Also, connect the NBX 100 Uplink port to the 1100 switch port (10 Mbps). The 1100 switches are manageable using Transcend Network Supervisor, have matrix ports for connecting another switch or the optional matrix card (3C16960) capable of connecting four (4) switches, and support IEEE 802.1p and 802.1Q standards for packet prioritizaiton. These 1100 series switches have plenty of other features and optional cards. They are great solutions that will perform in the NBX converged environment.


the Group configurations listed and discussed are actual customer sites installed by an authorized 3Com NBX 100 dealer.

Customer: Mail Order Company
Networking environment: Windows 95/98, Windows NT, DOS retail application, QuickBooks Pro LAN, two (2) NT Client workstations and three (3) DOS retail workstations
NBX System: Call Center with queuing, 6 lines x 8 telephones, 4 port x 30 Minutes APX
Internet: SDSL connection


  • One office building has 3 telephones and PCs linked to a 3Com 8-port Office Connect Hub which is connected to a port on the 1100 switch (3C16951)
  • Previous to the NBX installation- prior Hub had constant collision lights and response time worsened when reports printed
  • Previous to the 1100 switch installation- delayed dial tone after pressing a Line (CO) button on NBX telephones
  • NT server connected to port 13 (10/100 Mbps) on the 1100 switch
  • After the 1100 switch installation- reports print immediately, response time improved, no delay in getting dial tone on the NBX telephone Central Office (CO) lines

Customer: Telecommunications Service Company
Networking environment: Windows 95/98 peer to peer, Macintosh OS 9, high printing on network printer HP LaserJet 5M, QuickBooks PRO (not LAN version)
NBX System: 4 lines x 6 telephones, 4 port x 30 Minutes APX, CO Lines ISDN- BRI connected to Panasonic DSHS and using four 2500 ports connected to the NBX 100 CO Line ports
Internet: 3Com LAN 56K Modem


  • Monthly report printing of accounting reports is approximately the same volume of paper monthly. Printing time for monthly reports went from 26 minutes to 4 minutes after implementing 1100 switch (3C16951)
  • iMacs DV are smoking on this configuration !
  • Internet sharing via the LAN 56K Modem seemed to improve among 3 users


  • Upgraded NBX software to release 2.6.3 (9/2000)
  • 3Com Firewall 25 added (10/2000)

Customer: Private Parochial School
Networking environment: Windows NT throughout computer LAB and school (77 workstations)
NBX System: 4 lines x 29 telephones, 1 DSS/BLF adjunct, 12 x 80 APX, seven (7) hubs, external paging system connected to NBX to page speakers in classrooms, outdoors, and maintenance areas in addition to paging telephones in all classrooms
Internet: analog telephone line shared


  • No brainer! 7 hubs connect to 7 ports (10 Mbps) on 1100 switch (3C16951)
  • NT server moved to port 13 (10/100 Mbps)
  • Transcend Network Supervisor implemented for network monitoring
  • The 3Com 1100 switch implemented for damage control (Updates will be posted here after school starts)


  • Transcend showing PCs in classroom and printers as source of heavy traffic. Monitoring setup shows "High Traffic" on the IP addresses associated with the classroom. Also discovered hub installed by students in the teachers lounge as another traffic bottlekneck. Students use "color" printers. (10/2000)
  • Upgraded NBX software to Release 2.6.3 (10/2000)
  • Deployed 3Com 1100/3300 switches (3C16950 and 3C16951) with matrix cable (3C16965) and fiber modules (7/2001)

Customer: Transcription Services Company
Networking environment: Novell, Windows 95/98, multiple DOS applications on IVR Servers
NBX System: 6 lines x 18 telephones, 8 x 20 APX
Internet: dedicated lines (dsl currently being added to replace dedicated analog lines)


  • Echo constant problem
  • Delayed dial tone after pressing a Line (CO) button on NBX telephones
  • Hubs- collision lights on frequently
  • Implemented 1100 switchs (3C16950 and 3C16951) with matrix cable (3C16965)


  • No System lockups since power protection added. (6/2000)
  • Network traffic congestion virtually "non-existent." (6/2000)
  • Echo is minimal. (6/2000)