hw1 text answers

1:  The transport layer's job is to ensure all the data reaches its destination in the proper order.  This layer for web browsing uses the protocols TCP or UDP.  It determines an IP and port (together, a socket) on the sender and receiver through which data is transmitted and received.  The transport layer receives data from the application layer and ensures its proper transmission in segments, and using TCP, each host also sends acknowledgment messages when it receives segments.  So, when I access a web page, my browser (application layer) requests from the web server, and this data transfer is managed at the transport layer.  If a different protocol were not used, the hosts would be unable to communicate as to when a message was received, and I may flood the server with requests (because my system did not receive an acknowledgment from the server) or it may flood me with data (because it doesn't know I received the webpage).

2:  A horizontal relationship at the data link layer involves both sides recognizing each other's MAC address as well as having compatible network cards and speeds.  The purpose of this relationship is to translate the physical layer (physically being connected by a cable) to being able to properly send data from one device to the other by ensuring compatibility and the proper physical addresses of each machine.  This relationship is only from one device to another but it makes all of the individual links work properly.

3:  Layer 3 (Network) properly routes packets to the destination machine in the optimal fashion for Layer 4 (Transport) to ensure they are ordered and acknowledged.  Layer 2 (Data Link) confirms physical compatibility and MAC addresses between individual devices to allow Layer 3 to then create the optimal routing scheme and addresses.

4:  Modularity and standardization are important because compatibility is needed at all layers even when introducing new technologies.  New network technologies still need to be able to communicate with old ones and different manufacturers need to be able to communicate with one another -- for example, many systems would fail to work properly if Windows and UNIX machines used different standards for their MAC or IP addressing, and if a new network protocol is introduced in the future, it still needs to be compatible with the old.