<P> An easy way to visualize the transport layer is to compare it with a post office , which deals with the dispatch and classification of mail and parcels sent . A post office inspects only the outer envelope of mail to determine its delivery . Higher layers may have the equivalent of double envelopes , such as cryptographic presentation services that can be read by the addressee only . Roughly speaking , tunneling protocols operate at the transport layer , such as carrying non-IP protocols such as IBM 's SNA or Novell 's IPX over an IP network , or end - to - end encryption with IPsec . While Generic Routing Encapsulation ( GRE ) might seem to be a network - layer protocol , if the encapsulation of the payload takes place only at endpoint , GRE becomes closer to a transport protocol that uses IP headers but contains complete frames or packets to deliver to an endpoint . L2TP carries PPP frames inside transport packet . </P>
<P> An easy way to visualize the transport layer is to compare it with a post office , which deals with the dispatch and classification of mail and parcels sent . A post office inspects only the outer envelope of mail to determine its delivery . Higher layers may have the equivalent of double envelopes , such as cryptographic presentation services that can be read by the addressee only . Roughly speaking , tunneling protocols operate at the transport layer , such as carrying non-IP protocols such as IBM 's SNA or Novell 's IPX over an IP network , or end - to - end encryption with IPsec . While Generic Routing Encapsulation ( GRE ) might seem to be a network - layer protocol , if the encapsulation of the payload takes place only at endpoint , GRE becomes closer to a transport protocol that uses IP headers but contains complete frames or packets to deliver to an endpoint . L2TP carries PPP frames inside transport packet . </P>
ipsec is defined at what layer of the osi model
ipsec is defined at what layer of the osi model
transport layer
transport layer