Security and Tunneling Overhead
Certain security and tunneling encapsulations also add overhead to voice packets and
should be considered when calculating bandwidth requirements. When using a virtual
private network (VPN), IP Security (IPsec) will add 50 to 57 bytes of overhead, a significant
amount when considering the relatively small voice-packet size. Layer 2 Tunneling
Protocol/generic routing encapsulation (L2TP/GRE) adds 24 bytes. When using MLP, 6
bytes will be added to each packet. Multiprotocol Label Switching (MPLS) adds a 4-byte
label to every packet. All these specialized tunneling and security protocols must be considered
when planning for bandwidth demands.
For example, many companies have their employees telecommute from home. These
employees often initiate a VPN connection into their enterprise for secure Internet transmission.
When deploying a remote telephone at the employee’s home using a router and a
PBX Off-Premises eXtension (OPX), the voice packets experience additional overhead
associated with the VPN.