Link Layers

Flashcards about Link Layers based on lecture notes.

What are hosts and routers referred to as in the context of link layers?

Nodes

What is a layer-2 packet called, which encapsulates a datagram?

Frame

What is the primary responsibility of the link layer?

Transferring datagrams from one node to a physically adjacent node over a link.

What are the key functions provided by the link layer regarding framing and link access?

Encapsulating datagram into frame, adding header and trailer and channel access if shared medium.

What type of addresses in frame headers identify source and destination nodes in the link layer?

MAC addresses

What is the purpose of flow control in the context of link layer services?

Pacing between adjacent sending and receiving nodes.

What are the primary causes of errors that the link layer's error detection mechanism aims to address?

Signal attenuation and noise

Where is the link layer typically implemented in a host?

Network Interface Card (NIC)

What does EDC stand for in the context of error detection?

Error detection and correction bits

How reliable is error detection in link layer protocols?

The protocol may miss some errors, but rarely.

What type of errors does single bit parity checking primarily detect?

Detect single bit errors.

What are the two main types of links discussed in the context of multiple access links?

Point-to-point and broadcast (shared)

What happens when two or more nodes transmit simultaneously over a shared broadcast channel?

Interference and collision

What are some examples of channel partitioning methods in MAC protocols?

Time Division (TDMA), Frequency Division (FDMA), Code Division Multiple Access (CDMA)

What is the key element that differentiates CSMA/CD and CSMA/CA from ALOHA protocols?

Carrier sensing

What is the primary function of a MAC address?

Used locally to get frame from one interface to another physically connected interface (same subnet)

What is the typical length of a MAC address in most LANs?

48-bit

What is the main question that ARP (Address Resolution Protocol) aims to resolve?

To determine interface’s MAC address, knowing its IP address.

How does a node determine the MAC address of another node on the same LAN using ARP?

It broadcasts an ARP query containing the target IP address

In an ARP broadcast, which nodes receive the ARP query?

Each node on the LAN receives the ARP query.

What action does the target node take upon receiving an ARP query in the ARP protocol?

B replies to A with an ARP response, giving its MAC address.

When routing to another subnet, what information does node A need to know about router R?

To send data to a destination on another subnet, it needs to know the IP and MAC address of the first hop router (gateway).

When sending a datagram to B via router R, how does A construct the link-layer frame?

A creates link-layer frame with R's MAC address as the destination MAC.

How does router R creates the link-layer frame when forwarding the datagram to B?

The destination MAC address is B's MAC address.

What is the historical significance of Ethernet in the context of LAN technologies?

First widely used LAN technology

What are the two main physical topologies discussed for Ethernet?

Bus and Switched

What is the primary function of an Ethernet switch?

Examine incoming frame’s MAC address, selectively forward frame to one-or-more outgoing links.

What are the characteristics of a switched Ethernet network regarding connections, collisions, and transmission mode?

Hosts have dedicated connections to switch, switches buffer packets, no collisions due to full duplex.

How does a switch keep track of which hosts can be reached through which interfaces?

Each switch has a switch table with MAC address of host, interface to reach host, and time stamp.

How does a switch 'learn' the location of a sender when a frame is received?

records sender/location pair in switch table.

What are the two possible actions a switch can take when forwarding a frame?

Flood or selectively send on one link

How do interconnected switches learn to forward frames to the correct destination?

By self learning

What is the key difference between routers and switches in terms of the layer at which they operate?

Routers are network-layer devices and switches are link-layer devices.

What is the goal of the 'synthesis' section regarding a day in the life of a web request?

To identify, review, and understand protocols at all layers involved in a seemingly simple scenario: requesting a www page.

What information does a connecting laptop need, and which protocol is used to obtain it?

Connecting laptop needs to get its own IP address, address of first-hop router, and address of DNS server- use DHCP.

Before sending an HTTP request, what two key pieces of addressing information are required, and which protocols provide them?

Before sending HTTP request, need IP address of www.google.com- DNS. To send frame to router, need MAC address of router interface - ARP.

Encapsulation of DNS query

DNS UDP IP Eth Phy

What type of connection does the client first establish with the web server before sending an HTTP request?

The client opens a TCP connection to the web server before sending the HTTP request.