OSI Layer 3 Network Layer + Subnetting | Week 2 lecture + readings Flashcards
While the ____-____ layer is the software that solves the “how to send from me to nearby” problem, the _____ layer solves “how to send from me to far away.”
While the data-link layer (layer 2) is the software that solves the “how to send from me to nearby” problem, the network layer (layer 3) solves “how to send from me to far away.”
The network layer involves which protocol data unit?
packets(IP) and datagrams (UDP)
the data-link layer involves which protocol data unit?
frames
the physical layer involves which protocol data units?
bits
the transport layer involves which protocol data units?
TCP segments
layer-3 provides communication between networks. True or false?
true
What two major functions does the network layer perform?
Routing and forwarding.
At layer 3, how does routing function?
routing collects network topology into routing tables. It affects the way routers forward traffic.
Forwarding, a layer 3 activity, is what?
The process of handling incoming packets. It forwards packets to the next hop.
The network layer is concerned with what?
The network layer is concerned with point to point delivery.
What is a host?
An end system where traffic starts or finishes (usually)
What is a router?
An intermedia system which passes messages to another network.
____ communicate with other _____ to determine network topology and sometimes are the end points, but mostly are the things inbetween.
routers.
IP is global and unique, and because of this, it is used to provide and deliver what?
Provides: Universal addressing, routing of packets between hosts.
Delivers: Packets from source to destination. End-to-end, not link-to-link.
IP is an unreliable connectionless packet delivery service. True or false?
True
What does unreliable mean, with regards to IP being an unreliable connectionless packet delivery service?
Delivery not guaranteed.
Best effort to attempt to deliver a packet.
Packets may be lost, corrupted, delayed or duplicated.
Acknowledgement of receipt is not required.
Sender/receiver not informed when a packet is lost, etc.
Acknowledgement of packets is a responsibility of higher layer transport protocols such as TCP.
What does connectionless mean, with regards to IP being an unreliable connectionless packet delivery service?
Order is unimportant to IP.
Every packet is treated as its own message.
No ordering relationship between consecutive packets.
Packets are just transmitted individually.
If order is important, this becomes the transport layer’s responsibility (layer 4).
What is IP’s simple failure model?
Packets can be lost, corrupted, delayed, or duplicated. However, simple failure means all errors are treated as packet loss.
What are the network layer functions?
Addressing, routing, and forwarding.
Who manages IP addresses?
ICANN Internet Corporation for Assigned Names and Numbers, who manages some domains directly and authorises some companies to become domain name registrars as well.
What provides a dynamic IP address?
Dynamic Host Control Protocol.
The ___ and ____ layers are responsible for moving messages from end to end in a network.
The network and transport layers are responsible for moving messages from end to end in a network.
What 3 functions does the transport layer (layer 4) perform?
The transport layer (layer 4) performs 3 functions
1. linking the application layer to the network,
2. segmenting
and session management (establishing end to end connection between sender and reciever)
What two functions does the network layer perform?
The network layer (layer 3) performs two functions: routing and addressing. Routing is determining the next computer to which the message should be sent to reach the final destination. Addressing is finding the address of that next computer.
What makes up the Internet Protocol Suite?
Transmission Control Protocol / Internet Protocol (TCP/IP)
Vinton Cerf and Bob Khan developed TCP/IP in what year and where/for what organisation?
1974, for ARPANET (US Department of Defense’s Advanced Research Project Agency network)
What is the world’s most popular protocol set, used by almost all backbone networks (BNs) and Wide Area Networks (WANs)?
TCP/IP
TCP/IP allows reasonably efficient and error-free transmission. True or false?
True. Because TCP performs error checking, it can send large files across sometimes unreliable networks with great assurance that data will arrive uncorrupted.
What transport layer protocol links the application layer to the network layer by performing segmenting?
Transmission Control Protocol, numbering data into smaller PDUs called segments.
What transport layer protocol is responsible for ensuring segments are reliably delivered and in the right order at the destination?
Transmission Control Protocol.
What transport layer protocol performs addressing and routing?
Internet Protocol (IP)
IP software and TCP software is used at each of the intervening computers through which the message passes, with both IP/TCP routing the message to the final destination. True or false?
No, only IP software is used. TCP software needs to be active only at the sender and receiver because TCP is involved only when data comes from or goes to the application layer.
A typical TCP segment has how many bytes and bits of control information within its header?
A typical TCP segment has a 192-bit (24 bytes) header of control information.
How many bits are allocated to the following in a TCP segment header?
Source port
Destination port
Sequence Number
ACK number
Header Length
Unused
Flags
Flow Control
CRC-16
Urgent Pointer
Options
User Data?
Source port - 16 bits
Destination port - 16 bits
Sequence Number- 32 bits
ACK number - 32 bits
Header Length - 4 bits
Unused -3 bits
Flags - 9 bits
Flow Control - 16 bits
CRC-16 - 16 bits
Urgent Pointer - 16 bits
Options - 32 bits
User Data? Varies
ACK = acknowledgement
CRC = Cyclical Redundancy Check
Adds up to 192 bits (24 bytes) of control information
The internet protocol suite is typically thought of a pair IP/TCP. What is the second type of transport layer protocol?
User Data-gram protocol UDP.
What is a UDP PDU (packet) called?
A datagram
UDP checks for lost messages. True or false?
False. Unlike TCP, UDP does not check for lost messages.
How large is an IPv4 address field and what are the maximum number of IPv4 addresses?
IPv4: 4bytes long, there is a maximum of 4.2 billion addresses how 500 million are reserved and cannot be used in the early days of the internet, some small companies received several million IP addresses even when they didn’t need all of them.
How large is an IPv6 address field? How many maximum IPv6 addresses can exist?
IPv6: 16-bytes long.
This provides a theoretical maximum of 3.4 * 10 ^ 38 addresses.
What is Ethernet’s maximum packet size?
1492 bytes.
The maximum size of a TCP message field, if IPv4 is used is 1492 - 24 (size of the TCP header) - 24 (size of the IPv4 header) = 1,444
What is the maximum size of a TCP message field if IPv4 is used over Ethernet?
The maximum size of a TCP message field, if IPv4 is used is 1492 (maximum packet size for ethernet) - 24 (size of the TCP header) - 24 (size of the IPv4 header) = 1,444 bytes.
