In grid networks, there are different communication pairs between senders and receivers, where they communicate simultaneously. These different simultaneous communications are called multiple-pair communications. In multiple-pair communications, an identical link that is shared on paths of different communications may exist. The link is called a common link. A controller of multiple-pair communications needs to know the link available bandwidth of the common link, which may limits the available bandwidth in simultaneous multiple-pair communications, for scheduled communications. An objective of scheduling is to complete all required communications as quickly as possible when each traffic demand is given. A conventional scheme is not able to estimate the link available bandwidth of a common link. This paper proposes a scheme for estimating an available bandwidth in simultaneous multiple-pair communications, which is called a simultaneous available bandwidth. To achieve this, the proposed scheme estimates the link available bandwidth of a common link by synchronizing packet streams at the common link if any common link exists and the bandwidth limits the simultaneous available bandwidth. The proposed scheme employs the metrics that are used to estimate the path available bandwidth of a single-pair communication in the conventional scheme, to synchronize packet streams. This paper formulates an optimal adjustment width of transmission time of a packet stream to synchronize packet streams when a target synchronization ratio is given.