CSE 120 Lecture Notes - Lecture 16: Wide Area Network, Local Area Network, Packet Switching

48 views5 pages
Digital Signatures
Ex: Bob gave a loan to Alice, Alice signs it to agree to pay Bob back
-Alice encrypts the document, M, using a private key KA, priv and send KA, priv (M) to Bob
-When Bob receives, decrypts using KA, pub
-can ONLY decrypt iff someone uses her public key
-if it works, that must mean that it was encrypted using Alice’s private key
-the only one who knows Alice’s private key is Alice herself!
Note: crypto system worked right, but the assumption made was wrong (human error!)
To sign AND keep private
- Alice sends KB, pub (M, KA, priv (M)) to Bob
- ONLY Bob can decrypt: KB, priv (KB, pub (M, KA,priv (M)))
- Decrypts using KA,pub proving Alice signed it
Networks - set of computing nodes
- Connected by communication links
- Allows data transfer by a sender to a receiver
Internetwork: network of networks!
- “Internet” is a global internetwork!
- Nodes communicate using IP (Internet Protocol)
Types of Networks
By “topology”: ring, star, bus, graph
Ring: to send a message to a node, it goes through its connecting nodes to reach the receiver
- MANY hops
Star: send to the Hub and the Hub forwards to the right receiver
- Note: 2 hops to send message to receiver
Bus: transmit bits to the bus (and an address to the receiver)
- Everyone can hear the message!
- Can “broadcast” if you want EVERYONE to hear your message
Graph: NO regularity
By “geographic coverage”: “how much territory do they span?”
- LAN: Local Area Network (spanning floor, building)
- WAN: Wide Area Network (spanning state, country)
- MAN: Metropolitan “” “” (spanning city)
- DAN: Desk “” “” (spanning your office)
Circuit-switching vs. Packet switching
Circuit: establish a path from A to B
- Once determined, bits flow through the path and through the path ONLY
- Still pay regardless of whether you’re on the line or not!
Packet: forward packets to a node “closer” to B, which then forwards packets
- Maybe the packets NEVER reach B
- Less certain
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 5 pages and 3 million more documents.

Already have an account? Log in
- Much more “efficient’ - you only pay for what you use!
What is a Protocol?
Analogy: OS -> Process as Network -> Protocol
-agreed message format AND transfer procedure
-multiparty, so NO central thread of control!
-Expectations of operation
-if you do blah, I do blah, etc.
Messages:
-header and data: | header | Data |
Data: what sender wants receiver to know
Header: info to support protocol
- Src and dest addresses
- State of protocol operation
- Error control (check integrity)
Ex: Ann sends message to Bob
Protocol:
- Message format: (from,to), message contents
- Transfer procedure: post ON refrigerator (agreed way)
Ex: Ann sengs msg to Bob on the East coast
Header Data
| Address | Message |
Header Data
| From Ann, To Bob | blah |
Layering: Separation of Functions
Ann and Bob
- Don’t have to know ANYTHING about delivery
- Aid postal system by providing addresses
Postal System
- Only has to know addresses and how to deliver
- Doesn’t care about what’s inside the message!
Real Network has 7 Layers of OSI Reference Model
8 User!
7 Application: application protocol (i.e. HTTP)
6 Presentation: syntax, network format (i.e. JPEG)
5 Session: start/stop/manage connections
4 Transport: breaks into logical pieces (segments), reliability, flow control
3 Network: logical addressing (translated to physical address appropriate to the network),
routing
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 5 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Notes+

Unlimited access to class notes and textbook notes.

YearlyBest Value
75% OFF
$8 USD/m
Monthly
$30 USD/m
You will be charged $96 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.