Essential Networking Concepts: TCP, UDP, and Congestion

Differences Between TCP and UDP

• TCP: Connection-oriented, bytes delivered in order, arbitrary length content, flow control matches sender to receiver, and congestion control matches sender to network.
• UDP: Connectionless, messages may be lost, limited message size, can send regardless of receiver state, and can send regardless of receiver network.

TCP Connection Management

Explain using figures where and how the 3-way handshaking is used. Explain using figures how TCP releases connections (refer to the other side of this paper).

• Normal case
• Simultaneous connect

Computing Adaptive Timeout

Keep smoothed estimates of the RTT and variance in RTT. Update estimates with a moving average. Set timeout to a multiple of estimates to estimate the upper RTT in practice.

Max-Min Algorithm

What are the steps for computing the max-min algorithm? For the following figure, assume each consecutive router pair has a flow-capacity of 1 unit. Label each connection.

Additive Increase Multiplicative Decrease (AIMD)

AIMD is a control law hosts can use to reach a good allocation:

• Hosts additively increase rate while the network is not congested.
• Hosts multiplicatively decrease rate when congestion occurs.
• Practically used by TCP.

Understanding ACK Clocking

ACK rate can be used by the sender to set the sender’s data rate:

1. The sender injects a burst of segments into the network.
2. Segments are buffered and spread out on a slow link.
3. ACKs maintain the spread back to the original sender.
4. Sender clocks new segments with the spread, sending at the bottleneck link speed without queuing.

Benefits: Helps the network run with low levels of loss and delay; the network has smoothed out the burst of data segments, and ACK clocking transfers this smooth timing back to the sender.

DNS Resolution Process

What are the steps for DNS resolution to find the IP address for a given hostname? What is the port number?

• Resolution: The computer requests a local name server to resolve the address. The local name server asks the root name server. The root returns the name server for a lower zone. Continue down zones until the name server can answer.
• Port: Runs on UDP port 53.