The peer ID. This is used as a unique
ID to identify a remote entity and to associate
links to it. For example, for 'normal' PPP, there
is one entry in the link table. For Multilink
PPP there are one or more multiple links.
In either case the Link table is indexed
by Link index (one per link) and by Peer ID.
When one or more entrys in the link table
has the same Peer ID, then these entries
form a group for use either for Multilink
PPP, or as a rotary group.