pted or altered while in transit between endpoints during an H.323 call. The process employed in H.235 is similar to that used in other IP communications protocols. However, rather than using checksums and CRCs (cyclic redundancy checks), H.235 data integrity uses an encryption mechanism (a hash) to protect the packet's integrity value. In this approach, the integrity checksum value must be encrypted, but not the actual data payload. This reduces the necessary amount of encryption processing. H.235's encryption techniques provide a mechanism to conceal data from eavesdroppers. Without the appropriate decryption algorithm and the key to unlock the encrypted packet, an encrypted packet cannot be viewed even if it is intercepted. However, encryption requires processor-intensive computation and thereby adds delay. Therefore, one must balance the risk that the H.323 call may be compromised Video Communications: The Whole Picture against the need to emulate circuit-switching quality in the session. Of course, there is no practical way to make a session completely secure, SO one must refer to security policies to determine an organization's risk tolerance before deploying H.323. Non-repudiation is the prevention of any party from falsely denying that they have made a commitment or, in the case of H.235, denial that they participated in an H.323 session. The most conventional example of non-repudiation (repudiation prevention) is the requirement of a signature upon delivery of a package or acceptance of a credit card. This is important for service providers who must accurately charge for their services and validate those charges, but it is also important for any organization that desires to verify who participated in any given H.323 session. There are two viable RAS authentication techniques: Symmetric Encryption-Based Authentication and Subscription-Based Authentication. Gatekeepers typically authenticate the client. However, clients can also request the Gatekeeper to authenticate itself. Symmetric Encryption-based Auth