Telephone Service

Post-Dial Delay

"Most ISDN intra-LATA calls complete in less than a second." (, 1997-05-05)

90% of all calls complete in 1 second after the last dialed digit; 90% of all calls through connect (talking is possible) in under 150ms. (

The calls were placed between H.324 terminals via synchronous V.34 modems. The times below are post-dialing until receipt of the CONNECT signal from the modem, so these times are dominated by modem negotiation. It takes about 5 more seconds for an H.245 session to come up and audio to commence and another second or so for the first video key frame to arrive. An intra-LATA call takes about 14 seconds post-dialing till connect; however, it seems like I've seen 30 to 60 seconds for some international calls. ( (Paul Long))

Post Dial Delay (measured as the duration between the "Last Digit Dialed by Calling Party" and "Onset of Audible Network Response at Calling party" depends basically on the following parameters

  1. Type of call (whether direct dialed or "database lookup required", e.g.., 800 or 900 number);
  2. Type of signaling available (SS7 now quite ubiquitous, earlier much more MF trunking between switches with gradual migration in early 90s), and
  3. Number of intervening switches.

Further, it can be quite sensitive to whether or not there is an access tandem via which the call is coming in - particularly since (at least during the roll out phase) SS7 was not as widely available at all switches. Some actual numbers could be as follows:

Anyone recall the early 90s when 800 number portability came around, requiring close to ubiquitous SS7 deployment - that's when the post dial delay started dropping dramatically across the board in the US.

Raj Bansal, Nokia

Network Utilization

"For PSTN, if you count just the T1s connecting 4E switches, utilization averages almost 30%." (Andrew Odlyzko, AT&T)

Social Issues and Usability



Dial tone 350+440 continuous
Ringback (Normal) 440+480 2.0s on, 4.0s off
Ringback (PBX) 440+480 1.5s on, 4.5s off
Busy signal 480+620 0.5s on, 0.5s off
Congestion (toll) 480+620 0.2s on, 0.3s off
Reorder (local) 480+620 0.3s on, 0.2s off
Receiver off-hook 1400+2060 0.1s on, 0.1s off
Nickel Signal 1700+2200 0.060s on
Dime Signal 1700+2200 0.060s on, 0.060s off X2
Quarter Signal 1700+2200 33ms on, 33ms off, 5 times repeating

         1209 1336 1477 1633
     697   1    2    3    A
     770   4    5    6    B
     852   7    8    9    C
     941   *    0    #    D

Interesting Numbers

ANI (announces number)212 958 xxxx
long announcement (Columbia library hours) 212 854 3533
CO verification212 939 9901
LD carrier name1 700 555.4141
Gives alot of code numbers, then your ANI1-800-487-9240 (disconnected)
Announce your number800-346-0152 (disconnected, but provides disconnect announcement)


Feature Description Activate Deactivate
Three-way calling "With Three-Way Calling you can easily add a third person, local or long-distance, to another call. Each person can leave the conversation by hanging up and you will remain connected to the other person. You can also remove the third person at any time by pressing the switch-hook once. To disconnect the entire three way conversation, just hang up." (BA) switchhook, (three short tones), dial, switchhook
*69 "*69 gives you the number, date and time of your last incoming call and the option to dial that party back." *69 -
Call waiting "The brief Call Waiting tone is easily recognizable while you're on the phone: you have the option to take the new call -- or not. To switch over to the new call, just click once on your receiver. To switch back to the first call, click again... and so on." (USWest) - *70
Call Waiting Deluxe "With Call Waiting Deluxe, if you're on the phone and another call comes in, with the touch of a button, you can:
  • Switch between calls as you would with regular Call Waiting
  • Send the incoming caller directly to your Voice Messaging service;
  • Send the incoming caller to a pre-recorded "Please Hold" message;
  • Join the caller with your current call so that all three of you can talk;
  • Disconnect from the first caller to take the second call.
Caller id "Your Caller ID Display Unit shows you the name and number of incoming callers. Caller names, numbers, plus call date and time are stored for later retrieval."
Call waiting id "Identify who's calling when you're already using the phone line Make a call management choice -- answer the new call, or let it go to your US WEST Voice Messaging Service."
Call following "Call Following allows you to send your calls to any phone, from any location, so now your calls can follow you anywhere. You will be prompted to enter both the area code and the telephone number to forward your calls to. Although the area code must be included for local as well as long distance forwarding, there is no charge to forward calls to a local number. Forwarding to long distance numbers will result in long distance charges being billed to your account." *78
Caller id with Privacy+ "A pre-recorded message explains to callers that you would like them to identify themselves by recording their name for you. Once you hear the distinctive Caller ID with Privacy + ring and listen to the recorded name, you have the option to take the call - or not. If you don?t take a call, the caller hears a message explaining that you?re not available. If you have a Voice Messaging service, the caller has the option to leave you a message. ... Your friends and family can skip the Caller ID with Privacy + process by entering your four digit code whenever they hear the Caller ID with Privacy + message. Once they enter the code they will be sent directly to you rather than having to identify themselves." *78
Call forwarding *72
Call forwarding selective (forward up to 15 numbers) *63 *83
Custom (distinctive) ringing for up to three numbers: short, short; short, short, long; short, long, short
Call rejection blocks up to 15 numbers *60 *80
No solicitation Your No Solicitation message will play during the most common hours for telephone solicitation - from 8am to 9pm. You can ensure that certain callers - up to 25 - can automatically bypass your No Solicitation message. ("You have reached a number that does not accept solicitations. If you are a solicitor, please add this number to your do-not-call list and hang up now. Otherwise, please press one, or stay on the line.") "Three types of entries are allowed: Area Codes (e.g., 612): Calls from that area code will skip the No Solicitation message. Area Codes followed by 3-digit prefixes (e.g., 612-111): Calls from that area code/prefix combination will skip the No Solicitation message. Specific 10-digit telephone numbers (e.g., 612-111-1111): Calls from that number will skip the No Solicitation message. You may have up to 25 entries on your list. Frequent callers will automatically be added to your list. In order to be automatically added, a caller with a valid 10-digit number must call and press 1 at the No Solicitation message 5 times within 7 days." (USWest) *78
Do not disturb "Your new Do Not Disturb service has automatically been activated with a pre-set schedule. Your phone will not ring between 10 pm and 6 am, 7 days a week. You can decrease the time it takes for family and friends to reach you by setting up a 4-digit Privileged Caller Code. Your friends and family can break through your Do Not Disturb screening immediately by entering this code as soon as they hear the Do Not Disturb greeting." *78
Call curfew "Blocks all outgoing and incoming calls during late-night and very early morning hours - either by a pre-set schedule, or a schedule you customize according to your household?s needs. Gives you added peace of mind by allowing you to program up to 20 authorized phone numbers for people you want to call to or hear from, even if CallCurfew is active. hedule for CallCurfew has already begun blocking incoming and outgoing calls from 10 p.m. to 6 a.m. Sunday through Thursday, and 11 p.m. to 7 a.m. Friday and Saturday. You may specify up to 20 Authorized Telephone Numbers. Only calls to or from these phone numbers will go through when CallCurfew is turned on." (USWest)

Other Resources

Private Line, "a journal of inquiry into the telephone system"

J. Van Bosse, Signaling in Telecommunication Networks, Wiley, 1997. ISBN 0-471573779

T1 line costs per month: $1,732.75 + $223.48