3Com S7906E Configuration Manual page 720

Holding Time: If no hello packets are received from the neighbor within the holding time, the
neighbor is considered down.
PDU Length: Total length of the PDU in bytes.
Priority: DIS priority.
LAN ID: Includes the system ID and a one-byte pseudonode ID.
Figure 1-8 shows the hello packet format on the point-to-point networks.
Figure 1-8 P2P IIH format
Instead of the priority and LAN ID fields in the LAN IIH, the P2P IIH has a Local Circuit ID field.
LSP packet format
The Link State PDUs (LSP) carry link state information. LSP involves two types: Level-1 LSP and
Level-2 LSP. The Level-2 LSPs are sent by the Level-2 routers, and the Level-1 LSPs are sent by the
Level-1 routers. The level-1-2 router can send both types of LSPs.
The two types of LSPs have the same format, as shown in Figure 1-9.
1-9