1. Remind: CEREAL account!!!
RECITATION 3
Remind: CEREAL account!!!

2. Project 1 Provide TorrentFileHandle.java & …
Important info from .torren file
url of the tracker
Name of file
Length of file
Pieces <hash1,hash2,….hashn>
Piece length

3. Overall Architecture Tracker Web Server Get-announce C A [Seed] Peer
Web page
with link
to .torrent A B C
Peer
[Leech]
Downloader
“US”
[Seed]
Tracker
Get-announce
Web Server

4. Overall Architecture Tracker Web Server Response-peer list C A [Seed]
Web page
with link
to .torrent A B C
Peer
[Leech]
Downloader
“US”
[Seed]
Tracker
Response-peer list
Web Server

5. Overall Architecture Tracker Web Server Shake-hand C A [Seed] Peer
Web page
with link
to .torrent A B C
Peer
[Leech]
Downloader
“US”
[Seed]
Tracker
Shake-hand
Web Server

6. Overall Architecture Tracker Web Server request C A request Peer
Web page
with link
to .torrent
request C A
request
Peer
[Seed]
Peer
[Leech]
Downloader
“US” B
Peer
[Leech]

7. Overall Architecture Tracker Web Server C A pieces [Seed] Peer [Leech]
Web page
with link
to .torrent A B C
Peer
[Leech]
Downloader
“US”
[Seed]
Tracker
pieces
Web Server

8. Project 1 Basics (cont'd)
● Communicate With Peer – Handshake <pstrlen><pstr><reserved><info_hash><peer_id> – General Messages <length prefix [4B dec]><message ID[1B char]><payload> – Request <0013><6><index><begin><length> – Piece: <length prefix> is 0009+X and message ID is 7. The payload is as follows: <index><begin><block> X is block size

9. Sample Question: SWITCHING
Considering a small network of four hosts and three links as depicted in the figure below. A 1MB message is to be sent from A to D. The bandwidth of links is 0.8 Mbyte/second. Propagation delays of the links are negligible.
Host A Host B Host C Host D
(A). Assume that circuit switching is used and the total circuit set-up time is 100 ms, what is the time to send the message from A to D?
(B). Assume that message switching is used and queuing delays are negligible, what is the time to send the message from A to D?

10. Sample Question: SWITCHING+PIPELINING
Considering a small network of four hosts and three links as depicted in the figure below. A 1MB message is to be sent from A to D. The bandwidth of links is 0.8 Mbyte/second. Propagation delays of the links are negligible.
Host A Host B Host C Host D
(C). Assume that packet switching is used, packet size is 240 bytes and header size is 10 bytes, what is the time to send the message from A to D? (WITH PIPELINING)

11. Message Switching (cont’d)
Msg
Header
Transmission
Delay
Time
Msg
Queueing
Delay
Msg A B C D
Routers/switches

12. Pipelining “Parallelogram” for packet switching
Host A
Switch 1
Switch 2
Host B
Packet 1
Packet 2
Packet 3
Time
Packet 4

13. Sample Question: Performance Analysis
For parts A and B, assume host A is connected to B via a point-to-point duplex link which has a data rate of 1 Mbps and propagation delay of 10 msec.
HOST A HOST B
Host A has a large amount of data that must be reliably sent to Host B. Assuming Stop-and-Wait protocol is used to assure reliable delivery, the data frame size is 1000 bytes each, and the ACK frame size is 64 bytes.
(A). Assuming that Host B takes 0 time to process an incoming data and send an ACK frame back to A, what is the smallest time the retransmission timer can be set to at Host A which eliminates unnecessary retransmissions?
(B). Assuming there are no transmission errors, what is the link utilization in the direction from A to B?
Hint:
Link utilization = the time to send a frame without delay and ACK/ the time in A (OR the time to send a frame from A to B + the time an ACK frame back to A)
Link utilization = size of a frame/ (the time to send a frame from A to B + the time an ACK frame back to A)
(C). A new, different channel has a bit rate of 4 Kbps and a propagation delay of 20 msec. For what range of frame sizes does stop-and-wait protocol give an efficiency of at least 50 percent?

14. MAC address Network Interface Card (NIC)
Each NIC has its own MAC address , it is stored on the chip!!
Length of MAC : 48 bites = 6 bytes
For examples: 00:C1:71:01:AB:F0
Prefix: Company ID: 3Com, Netgear …
Postfix: Serial Number
Command to show MAC: ifconfig, ipconfig
NIC -> EISA, ISA, PCI card
Maybe separate into several slide !!!

15. Ethernet Frame Structure
MAC Dest. address
MAC Source address
Type
DATA ….
CRC
Type(2 bytes) specifies the network layer protocol: IP or Novel IPX or ARP or RARP…
CRC: check sum
Broadcast:
MAC Broadcast Address = FF:FF:FF:FF:FF:FF
Host A sends a msg to host B:
MAC dest = MAC B, MAC src = MAC A
NIC -> EISA, ISA, PCI card
Maybe separate into several slide !!!

16. SWITCH can learn the MACs of all nodes
HUB vs. SWITCH
Ethernet Frame
SWITCH can learn the MACs of all nodes
MAC A -> MAC C
DATA
HUB
SWITCH
forward
send
send
NIC -> EISA, ISA, PCI card
Maybe separate into several slide !!! A B C A B C
B can CAPTURE the packet from A to C !!!!
B CAN’T capture the packet from A to C !!!!

17. How to build your own network!
NICs
HUB or SWITCH !!!
2 machines can be connected by using crossover cable!!!
Assign IP address
Static
Dynamic
- Need a picture of DSLmodel
Crossover cable