Transcript Handout_TCP_IP_Part3_BigPicture_Part1

Chapter 5 – Big Picture
Dr. V.T. Raja
Oregon State University
Chapter 5 – Big Picture
Minimum Information Needed by a Computer in a TCP/IP Network
Identify minimum information
needed by any computer that is
installed on (or dials into) a
TCP/IP network
Some of the minimum information
can be provided by ___________
file, or via a server such as _____
server.
Example illustrating Big Picture
Example: Assume the following:
All computers have been provided minimum info
specified in previous slide
Client A requests a web page from Web Server D.
Client A is connected to Router R, which is
connected to Server D.
TCP/IP are the transport and network layer
protocols, and Ethernet is the data link layer
protocol.
Example (Continued)
Client A knows IP address of Server D, and AL
address of D (www.D.edu).
This implies that client A has already requested IP of D
from DNS in the past, and now has the IP of D in its
address table.
Assume each device has the DL address of its
immediate neighbor(s).
This implies that both A and D have already issued ARP
messages to determine DL of R in the past, and now
have the DL address of R in their respective address
tables.
Similarly, R has the DL address of A and D in its address
tables.
Example illustrating Big Picture
(Continued)
IP of A is 16.32.64.33; Subnet mask of A is 255.255.255.128
IP of R is 16.32.64.128;
IP of D is 16.32.64.129;
Assume NIC address of A is 00-A0-B0-C0-A4-54-6A;
NIC address of R is 00-E0-B0-C0-E4-45-6E;
NIC address of D is 00-D0-B0-C0-D4-75-7D
Assume there are no errors in transmission
Question: Describe the data flow (across the
different layers in the 5-layer model) for the web
request made by Client A to Web Server D.
Description of data flow at Client A
User’s request is translated to HTTP
format; passed to TL.
Transport Layer:
TCP is protocol used in this layer
TCP performs ‘Packetizing’ (i.e., breaks
message into smaller sized packets);
Since DL protocol is Ethernet each
frame has a maximum of 1492 bytes.
Since message is a web page request, it
probably fits within one packet.
Transport Layer at Client A
(Continued)
TCP prepares TCP header which
includes:
Source and Destination Port ID indicating
software used at source and to be used at
destination. Being a web application –
Default Source/Dest. Port ID would be 80.
Packet numbers (here there is probably only
one packet)
TCP passes [TCP|HTTP|User Data] to
NL of client A.
Network Layer at Client A
(Continued)
IP is the protocol used in this layer.
IP performs addressing and routing.
IP determines NIC address 00-E0-B0-C0-E4-456E of next hop device “R” (from address table) and
IP address (16.32.64.129) of final destination
(Web Server D) from address table.
If addresses are unavailable in address table, ARP
is used for determining NIC address of R, and
DNS is used for determining IP of D.
Network Layer at Client A
(Continued)
NIC address of R is passed to DLL of client A.
IP prepares IP header, sample contents of IP
header include:
Source (Client A’s) IP (16.32.64.33) and Destination
(Web Server D’s) IP (16.32.64.129) addresses
Routing (e.g., next hop device) information is decided
using subnet mask addresses, subnet mask algorithm,
and routing software (where appropriate). Note that
client A and router R are not on same subnet.
IP passes [IP|TCP|HTTP|User Data] to data link
layer of client A.
Data Link Layer at Client A
(Continued)
Ethernet is protocol used at Data Link
Layer.
Ethernet performs Media Access
Control (MAC), Message Delineation
(MD), and Error Detection (ED)/Error
Correction (EC)
Data Link Layer at Client A
(Continued)
Ethernet creates DL Header and DL Trailer packets, which
include:
Source (Client A’s) DL address (00-A0-B0-C0-A4-54-6A)
Receiver’s (Router R’s) DL address (00-E0-B0-C0-E445-6E)
MAC is specified (i.e., CSMA/CD)
Value (i.e., 32-bit remainder obtained using CRC-32) that
helps R determine if there were any errors during
transmission
Info on how R should perform EC (i.e., Stop-and-wait
ARQ)
MD info (i.e., length of frame is specified in header)
Data Link Layer and Physical
Layers at Client A (Continued)
DL passes [DLH|IP|TCP|HTTP|User
Data|DLT] to DLL of R via PL.
Physical Layer: Transmission media
passes packets to DL layer of R; if there is
a collision during transmission, MAC is
performed as per CSMA/CD rules.
(Complete this answer by describing
data flow across different layers at
router R and at final destination).