| Comparative Study of M/Er/1 and M/M/1 Queuing Delay Models of the two IP-PBXs Recent countries visiting this post |  |
 | 14 | United States |
 | 6 | United Kingdom |
 | 1 | |
 | 1 | Russian Federation |
 | 1 | Iran, Islamic Republic of |
| Comparative Study of M/Er/1 and M/M/1 Queuing Delay Models of the two IP-PBXs Recent countries visiting this post | |
| 14 | United States |
| 6 | United Kingdom |
| 1 | |
| 1 | Russian Federation |
| 1 | Iran, Islamic Republic of |