TCP/IP plays a dual role in internet communications, in that I mean TCP/IP are two different protocols that play their own part in internet communications. First the TCP (Transmission Control Protocol) is considered the higher layer protocol that manages the assembling of messages or files in order to transfer the packets over the internet and then reassemble the message back to its original state when it reaches its destination. The IP (Internet Protocol) also considered the lower layer and is basically the protocol that is responsible for ensuring that the packet/s reaches the correct destination (Rouse, SearchNetworking: Definition - TCP/IP (Transmission Control Protocol/Internet Protocol), 2008).
The IP data transfer over the internet role is to carry a data load with an IP header broken down into bits in order to be transmitted over the network, once the bits arrive at its destination the bits are reassembled into the original packet or file (Unuth, 2012).
DHCP (Dynamic Host Configuration Protocol) is designed to allow IT network administrators to manage IP addressing from a central location by assigning IP addresses by an automated process rather than having to manually enter them into each device that requires one. This process makes it much easier for IT administrators to distribute IP addresses (Rouse, 2008).
The DNS (Domain Name System) role is critical for resolving internet host names into IP addresses and IP addresses back into host names because humans are not going to remember all IP addresses for every website on the internet so DNS helps with the common names used for websites that everyone is familiar with (Davidowicz, 1991).
The role that SSH (Secure Shell) plays in data exchange is that both ends of the connection, client/server, are protected by using an authenticated digital certificates, also encrypted passwords are used (Rouse, 2005).
Davidowicz, D. (1991). DNSSEC. Retrieved from...