▁ ▁a = fmt p : 1 0 1 ▁ 0 - 1 6 ▁ ▁a = pt ime : 2 0 ▁ ▁a = enc ryption : optional ▁ ▁a = send rec v ▁ ▁The ▁phone ▁receives ▁the ▁answer ▁from ▁the ▁proxy ▁and ▁now ▁there ▁can ▁be ▁a ▁two - way ▁secure ▁call : ▁▁ ▁S IP / 2 . 0 ▁ 2 0 0 ▁Ok ▁ ▁Via : ▁S IP / 2 . 0 / T LS ▁ 1 7 2 . 2 0 . 2 5 . 1 0 0 : 2 0 4 9 ; branch = z 9 h G 4 b K - s 5 kc qq 8 jq j v 3 ; r port = 6 2 4 0 1 ; rece ived = 6 6 . 3 1 . 1 0 6 . 9 6 ▁ ▁From : ▁" 1 2 3 " ▁< si ps : 1 2 3 @ iet f . org >; tag = m og k xs r hm 4 ▁ ▁To : ▁< si ps : * 9 7 @ iet f . org ; user = phone >; tag = 2 3 7 5 9 2 6 7 3 ▁ ▁Call - ID : ▁ 3 c 2 6 9 2 4 7 a 1 2 2 - f 0 ee 6 w cr v kc q @ s nom 3 6 0 - 0 0 0 4 1 3 2 3 0 A 0 7 ▁