COE768: Computer Networks (Final Exam Review)

What special role does 255.255.255.255 have as an IP address?

Local broadcast to all hosts in the current network.

What special role does NetID.(All 1s) have as an IP address?

Directed broadcast to all hosts in network NetID

What are the three fashions to deliver IP packets?

Unicast (one to one)

Broadcast (one to all in network)

Multicast (one to selected few in network)

Multicast uses which type of IP addressing?

Class D (224.0.0.0 to 239.255.255.255)

What is the purpose of a switch?

Take the signal from one device and switch the path to another device.

What layer does a switch operate on?

Layer 2 (data link)

What layer does a hub operate on?

Layer 1 (physical)

What does a hub do?

Broadcast data packets to all devices connected.

How does a switch know what port to send the packet to?

MAC table, using the address of the destination

What does a switch do if it's MAC table does not have the port for the given value?

It broadcasts the frame to all ports.

What is the goal of switched ethernet?

To allow easy expansion of the network

During the spanning tree algorithm, which host is the root?

The host with the smallest MAC address.

What is a VLAN?

Virtual local area network. Splits LAN into multiple broadcast domains.

Tagged vs. untagged VLAN

Tagged: Multiple VLANs can be supported using a single switch port, TAG field is added to the frame indicating the VLAN ID.

Untagged: Need distinct ports for separate VLANs

What controls the tag field?

Switches

Define access ports

Switch ports connected to end devices

Define trunk ports

Switch ports connected to other switches.

Define MACA

Multiple access with collision avoidance, like CSMA/CD but for wireless. Meant to overcome the hidden terminal problem

Steps of MACA

1. Sender sends request to send (RTS) to destination

2. Destination sends clear to send (CTS) to all nodes in range, occupied for a set time

3. Sender sends frame

Define exposed terminals

A node that is not the destination, and is visible to the source, but not visible to the destination.

Define hidden terminal

A node that could also be transmitting to a destination node while being invisible to the source.

Define CSMA/CA and its purpose

Carrier sense multiple access with collision avoidance.

1. Minimize collisions

2. Retransmit with stop and wait (exponential backoff)

3. Interframe spaces

Purpose of interframe spaces

IFS is the insertion of small gaps, SIFS for high priority (shorter), DIFS for low priority (longer)

CSMA

CSMA is like CSMA in ethernet, channel sensing is performed by all wifi radios.

CA (part of CSMA/CA)

Difference in the exponential backoff in CSMA/CD compared to CSMA/CA

CSMA/CA is okay with longer wait times if it means less collisions. Starting set is [0-7] and then doubles every failed attempt.

Two main roles of the router in the network layer

Routing (finding the optimal path across the network)

Forwarding (using routing tables to determine the next hop)

Difference between Datagram model and Virtual circuit model of IP

VC all fragments take the same path due to the connection, in datagram each fragment may take a different path.

Define frame relay

Example of virtual circuit model

Store and forward switching

Routers receive packets and store temporarily while it figures out what to do

T/F: Over the course of a transmission, the IP address doesn't change

True

T/F: Over the course of a transmission, the MAC address in the DLL header does change

T

Formula to find block size

floor((MTU-20)/8)*8

Class A IP addresses

1.0.0.0-127.0.0.0

0-127, Subnet Mask of 255.0.0.0,

Class B IP addresses

128.0.0.0-191.255.0.0

128-191, Subnet Mask of 255.255.0.0

Class C IP addresses

192.0.0.0-223.255.255.0

192-223, Subnet Mask of 255.255.255.0

Class D IP addresses

224.0.0.0 - 239.255.255.255 Multicast

Class E IP addresses

240-255, used for Experimental Addressing

Meaning of 255.255.255.255

Broadcast to local network