For system structure, HDLC is applied to point-to-point or point-to-multipoint structure;
For operation mode, HDLC is applied to half-duplex or full-duplex;
For transmission mode, HDLC is applied to only synchronous transmission;
For transmission rate, HDLC is applied to high-speed transmission.
After initiating the transmission of a frame, HDLC has to finish sending this packet continuously. HDLC can confirm several frames at the same time.
Every frame in HDLC contains the Address field. In the multipoint structure, every secondary node receives only the frame that contains the local node address.
Therefore, a primary node can select other nodes to communicate without removing the link, when selecting a secondary node and communicating with it. That is, a primary node can set up links with multiple nodes at the same time.
For the preceding features, HDLC has high transmission efficiency.
In HDLC, all frames (including response frames) have FCS. The I format is numbered by the window sequence and its transmission reliability is higher than the asynchronous transmission.
HDLC adopts Zero-Bit Insertion to transmit data transparently. The bit combination mode of transmitting information is not limited and easy to implement.
HDLC adopts the uniform frame format to transmit data, commands and response, which is easy to implement.
HDLC finishes various stipulated link operations by changing the code format of the Control field in a frame, and provides the bit-oriented transmission function.
HDLC
As shown in Figure 1, two switchs are connected through POS interfaces running HDLC to transmit IPv4, IPv6, and MPLS packets.
Figure 1 HDLC networking
IP-Trunk
For an IP-Trunk interface, you can configure weights for member interfaces to implement load balancing among member interfaces. There are two load balancing modes, namely, per-destination and per-packet load balancing.
Per-destination load balancing: packets with the same source and destination IP addresses are transmitted over one member link.
Per-packet load balancing: packets are transmitted over different member links.
As shown in Figure 2, two switchs are connected through POS interfaces that are bundled into an IP-Trunk interface to transmit IPv4, IPv6, and MPLS packets.
Figure 2 IP-Trunk networking
