Transcript protocol_intro

Introduction to Network Protocols
Kang Li
CSx760 Computer Networks
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Outline
 Administrative trivia’s
 TA Class Account
 [email protected]
 TA Individual Contact Information
 Arsham Mesbah <[email protected]>
 Yingfeng Wang <[email protected]>
 What is a network protocol?
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What is a Network Protocol?
 A network protocol is about Format
 Data Format
 Routine (Action) Format
 A network protocol defines the format and the
order of messages exchanged between two or
more communicating entities, as well as the actions
taken on the transmission and/or receipt of a
message or other event.
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The Protocol Stack and Ways to Traverse It
 Protocol stack
 collection of protocols
implementing a series of layers
 Traverse
 Bottom-up
 Top-down
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Top-down by examples
What happens when you type in a web page
Your computer
?
www.google.com
Internet
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Application Layer
Turn the typed in URL into HTTP Get Request
Your computer
Get http://www.google.com
HTTP 1.1
Host: www.google.com
Connection: keep-alive
…
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Application Layer (cont.)
Finding the right IP address: DNS
Where is www.google.com?
Local
Domain Name Server
(129.95.50.2)
Your computer
(129.95.50.53)
What’s the IP address for www.google.com?
Oh, it is 216.239.53.100
What if the local DNS server doesn’t know?
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Transport Layer (TCP)
Break message into packets (TCP segments),
and deliver them (in order and reliably)
Your computer
Get http://www.google.com
HTTP 1.1
Host: www.google.com
Connection: keep-alive
…
3 w.goog
2 p://ww
1 Get htt
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Network Layer (IP)
Address each packet so that it can traverse the
network from the sender to the destination.
Your computer
(128.192.4.122)
www.google.com
(216.239.51.100)
Destination
216.239.51.100
source
data
128.192.4.122 1 Get htt
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Network Layer (cont.)
Getting to the Campus backbone (static routing)
Your computer
(128.192.4.122)
Default route
Local
router
(128.192.4.1)
Please send my packet to 216.239.51.100
UGA
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Network Layer (cont.)
Getting to the Internet (intra-domain routing)
Each router forward packets toward the destination
Peach Net
CS department
UGA Campus Network
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Network Layer (cont.)
Getting through the Internet (inter-domain routing)
Qwest
Sprint
PeachNet
Level3
Exodus
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Link Layer
Address each IP packet with hardware address so
that it be deliver to the next hop
Local
router
(128.192.4.122)
Your computer
(128.192.4.122)
Dst MAC
Hardware Address
(08:00:20:9D:01:1E)
Src MAC
IP Packet
Hardware Address
(00:03:E4:3D:A8:00)
How to know the next hop’s
hardware address?
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UGA
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Link and Physical Layer
OC-3
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Summary of the Example
 Top-down Traverse of 5 layers
 Application:
HTTP
 turn the typed in URL into Get
Request
 Transport:
TCP
 break message into segments, make
in-order and reliable delivery
 Network:
IP
 routing of datagram from source to
destination
 Link:
Ethernet/Wavelan
 data transfer between neighboring
network elements
 Physical:
 bits “on the wire”
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What’s inside
 Network Protocols are about format and the order
of messages exchanged.
 What are the challenge of designing protocols?
 Or, why some protocols are complicated?
 You need to know why a particular format or order is
chosen.
 Here is the same example …
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What if the Data gets Lost?
Problem: Lost Data
GET index.html
Internet
Solution: Timeout and Retransmit
GET index.html
Internet
GET index.html
GET index.html
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What if the Data Doesn’t Fit?
Problem: Packet size
 On Ethernet, max IP packet is 1.5kbytes
 Typical web page is 10kbytes
Solution: Fragment data across packets
ml
x.ht
inde
GET
GET index.html
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What if the Data is Out of Order?
Problem: Out of Order
ml
inde
x.th
GET
GET x.thindeml
Solution: Add Sequence Numbers
ml 4
inde 2
x.th 3
GET 1
GET index.html
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What if receiver has no resources (flow control)?
Problem: Overflowing receiver buffers
PUT remix.mp3
Internet
Solution: Receiver advertised window
PUT remix.mp3
Internet
16KB free
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What if Network is Overloaded?
Problem: Network Overload
Solution: Buffering and Congestion Control
 Short bursts: buffer
 What if buffer overflows?
 Packets dropped and retransmitted
 Sender adjusts rate until load = resources
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What if the Data gets Corrupted?
Problem: Data Corruption
GET index.html
Internet
GET windex.html
Solution: Add a checksum
0,9 9
6,7,8 21
X
4,5 7
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Questions?
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