Commit a5807308 authored by wx002's avatar wx002

ch5 done

parent e237c538
This chapter is going into details of the 5 layer network model, focusing on the link layer.
Link Layer:
Some important terminology for the link layer.
- Node: any device that runs a link-layer. Ex: hosts, routers, switches, and Wi-Fi access points
- Links: communication channels that connect adjacent nodes along the communication path
- link-layer frame: the node which transmitting node encapsulates the datagram within this frame
- Basic service of link layer: move datagram from one node to the next adjacent node over a single communication link
Bellow are some of the services provided by the Link Layer:
- Framing: all network layer datagram gets pack into a link layer frame
- Link Access: medium access control (MAC) protocol specifies the rules by which a frame is transmitted onto the link
- Reliable delivery: guarantees to move each network-layer datagram across the link without error
- Error detection and correction: detect bit errors and drop frame since no need to forward error datagram
- Part of the link layer is implemented in software running by CPU as well as the network adapter in hardware, AKA NIC(network interface card)
Error detection and Correction:
This goes into regarding Link Layer's error detection and correction services. Specifically, it focus on bit-level error detection and correction.
This does not guarantee error free datagram packets, it only detect a finite number of errors using various algorithms.
Forward error correction (FEC): ability of the receiver to both detect and correct errors
Types of checks:
- parity bit: simplest form of error detection. An extra bit is sent within the packet to keep track of its parity
- two-dimensional parity: similar to previous, except apple to rows and columns
- checksums
- CRC
Multiple Access Link and Protocols:
There are two types of links.
- point-to-point link: single sender at one end of the link and a single receiver at the other end of the link
- broadcast link: multiple sending and receiving nodes all connected to the same, single, shared broadcast channel
There are rules for sharing broadcast channels in networks, known as multiple access protocols. This is how nodes regulate transmission in shared broadcast channels.
When two nodes are transmitting at once, its a collide and no receiver can tell what is happening, so it is important to keep only one node is transmitting while others wait.
Multiple Access Protocol Categories:
- channel partitioning protocols: divide it into slots for each node
- random access protocols: All nodes can talk, and it keeps retransmitting until a single frame is successfully transmitted
- taking-turns protocols: each node take turn transmitting consist of the following rules:
- Listen before speaking
- If someone else begins talking at the same time, stop talking
This capable handle collision errors.
Switched LAN:
route packet based on link layer frame using network switches instead of using routing algorithms. There is addresses for network layer and link layer, consist of the ARP(Address Resolution Protocol), which is the mechanism to translate IP address into link-layer address.
Link layer address is refer as:
- LAN address
- physical address
- MAC address
VLAN:
This section focus on modern usage of VLAN configuration.
virtual local area networks (VLANs): a switch that sup-ports VLANs allows multiple virtual local area networks to be defined over a single physical local area network infrastructure.
It targets the following problems:
- Lack of traffic isolation
- Inefficient use of switches
- Managing users
Reflection:
This chapter goes in depth about the transport layer, and describe various application of transport layer in modern use. It is very interesting to see packet go through error checking on the link layer. Also, this chapter provide a great explanation for the ARP Wireshark lab. It was definitely interesting to see modern usage of VLAN configuration due how complex network really is in modern use.
Question
1. all of the above
2. step 5
3. runs directly on top of IP
4. Chooses the gateway that has the smallest cost.
5. The SNMP protocol specifies the actions a network manager should take in
response to a specific set of network fault conditions.
6. The SNMP protocol specifies the actions a network manager should take in
response to a specific set of network fault conditions.
7. To allow a managed device to request and receive a set of initial values for MIB
objects in the managed device
8. 1.2.840.11356
9. 2**32 - 1
T/F
1. T
2. F
3. F
4. F
5. F
6. F
7. T
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