is adds to the cost of deploying the network elements, as the MSP must install only equipment that supports MACsec. Figure 11-14 illustrates the basic differences between IPsec and MACsec implementations, and how MACsec is a "hop-by-hop" approach, whereas IPsec is an "end-to-end" approach because the inter- vening nodes never see the data in the clear. On the other hand, MACsec encrypts the data as it goes onto a link and decrypts it at the other end, SO the data is in the clear at transit nodes. Figure 11-14 does not intend to suggest that both approaches should be implemented together. Grandmaster Router Slave layer layer layer layer IPsec tunnel IP layer IP layer IP layer IP layer MACsec tunnel MACsec tunnel layer layer layer layer layer layer layer layer Figure 11-14 IPsec Versus MACsec Having the data in the clear is not regarded as the best security, but for packet-based timing, it is an advantage because it allows T-BC and T-TC to offer on-path support as the timing signal transits the node. The downside to encrypting the transport of PTP messages is that the encryption and decryption processes of messages can introduce variable delay that could affect time accuracy. More details about that are provided in the upcoming section "MACsec." Prong C: Architectural Guidance This prong includes architectural approaches to increase the reliability of the timing signal by im- plementation and design. The possible methods include the following: Redundant grandmasters, in case of failure or compromise of the primary source. Redundant links, in case of failure or the link being compromised. Redundant time sources and paths (for example, by using multiple, independent sources of time). This form of deployment is not that common in the case of mobile timing; normally, op- erators only deploy redundancy of GMs and paths/links. This book has dealt with many of these issues under separate topics. Prong D: Monitoring and Management This prong includes monitoring and management methods for ensuring the security, accuracy, an