Network Systems - PowerPoint Presentation, Computer Science Engineering Computer Science Engineering (CSE) Notes | EduRev

Computer Science Engineering (CSE) : Network Systems - PowerPoint Presentation, Computer Science Engineering Computer Science Engineering (CSE) Notes | EduRev

 Page 1


1 
P561: Network Systems 
Tom Anderson 
Ratul Mahajan 
TA: Colin Dixon 
2 
“A good network is one that I never have to think 
about” – Greg Minshall 
True some of the time… 
Course Goals 
Technology Survey 
-? How things work 
-? How they are likely to work in the future 
Design and implementation of network protocols 
Research state of the art 
3 
Project: Fishnet 
Build an ad hoc wireless network in stages: 
-? Step 1: basic communication 
-? Step 2: routing 
-? Step 3: transport and congestion control 
-? Step 4: applications 
Three modes: 
-? Simulation (all nodes in one process) 
-? Emulation (each node in its own process; 
interoperability) 
-? Physical (on a PDA or cell phone) 
Details on the web site; due dates week 3, 5, 7, 10 
4 
Blogs 
By 5pm before each class, add a unique new 
comment on one of the questions posted to the 
web site 
Example Q: Instead of PPR, why not use smaller 
packets? 
Example blog: ? 
Before class, read the other comments 
5 
Reading < Class 
Example: Internet has a TTL (time to live) field in 
each packet 
-? Decremented on each hop 
-? When it gets to zero, router drops packet and sends an 
error packet back to the source 
-? Essential to correct operation of the Internet, and to 
its diagnosis 
6 
Page 2


1 
P561: Network Systems 
Tom Anderson 
Ratul Mahajan 
TA: Colin Dixon 
2 
“A good network is one that I never have to think 
about” – Greg Minshall 
True some of the time… 
Course Goals 
Technology Survey 
-? How things work 
-? How they are likely to work in the future 
Design and implementation of network protocols 
Research state of the art 
3 
Project: Fishnet 
Build an ad hoc wireless network in stages: 
-? Step 1: basic communication 
-? Step 2: routing 
-? Step 3: transport and congestion control 
-? Step 4: applications 
Three modes: 
-? Simulation (all nodes in one process) 
-? Emulation (each node in its own process; 
interoperability) 
-? Physical (on a PDA or cell phone) 
Details on the web site; due dates week 3, 5, 7, 10 
4 
Blogs 
By 5pm before each class, add a unique new 
comment on one of the questions posted to the 
web site 
Example Q: Instead of PPR, why not use smaller 
packets? 
Example blog: ? 
Before class, read the other comments 
5 
Reading < Class 
Example: Internet has a TTL (time to live) field in 
each packet 
-? Decremented on each hop 
-? When it gets to zero, router drops packet and sends an 
error packet back to the source 
-? Essential to correct operation of the Internet, and to 
its diagnosis 
6 
2 
Pop Quiz #1 
How could you use this to determine link latency? 
7 
Pop Quiz #2 
How could you use this to determine link 
bandwidth? 
8 
Pop Quiz #3 
How else could you determine link bandwidth? 
9 
A Systems Approach to Networks 
Most interesting applications of computers require: 
-? Fault tolerance 
-? Coordination of concurrent activities 
-? Geographically separated but linked data 
-? Vast quantities of stored information 
-? Protection from mistakes and intentional attacks 
-? Interactions with many people 
-? Evolution over time 
Networks are no different! 
10 
Network Systems: Design Patterns 
Scale by connecting smaller pieces together 
-? With no central state 
Reliability out of unreliability 
-? In any system with a billion components, many will be 
broken at any point in time 
-? And some will fail in bizarre ways 
Interoperability 
-? No single vendor + quasi-formal specs => often 
unpredictable behavior 
-? Layering to manage complexity 
-? Once standardized, hard to impossible to fix 
11 
An Anecdote 
BGP: protocol to exchange routes between ISPs 
-? Two primary vendors: Cisco and Juniper 
-? Monoculture within a given ISP 
-? Stateful: only send updates; 100K routes exchanged 
When you get a receive an invalid route, what do 
you do? 
-? And what do you think happened in practice? 
12 
Page 3


1 
P561: Network Systems 
Tom Anderson 
Ratul Mahajan 
TA: Colin Dixon 
2 
“A good network is one that I never have to think 
about” – Greg Minshall 
True some of the time… 
Course Goals 
Technology Survey 
-? How things work 
-? How they are likely to work in the future 
Design and implementation of network protocols 
Research state of the art 
3 
Project: Fishnet 
Build an ad hoc wireless network in stages: 
-? Step 1: basic communication 
-? Step 2: routing 
-? Step 3: transport and congestion control 
-? Step 4: applications 
Three modes: 
-? Simulation (all nodes in one process) 
-? Emulation (each node in its own process; 
interoperability) 
-? Physical (on a PDA or cell phone) 
Details on the web site; due dates week 3, 5, 7, 10 
4 
Blogs 
By 5pm before each class, add a unique new 
comment on one of the questions posted to the 
web site 
Example Q: Instead of PPR, why not use smaller 
packets? 
Example blog: ? 
Before class, read the other comments 
5 
Reading < Class 
Example: Internet has a TTL (time to live) field in 
each packet 
-? Decremented on each hop 
-? When it gets to zero, router drops packet and sends an 
error packet back to the source 
-? Essential to correct operation of the Internet, and to 
its diagnosis 
6 
2 
Pop Quiz #1 
How could you use this to determine link latency? 
7 
Pop Quiz #2 
How could you use this to determine link 
bandwidth? 
8 
Pop Quiz #3 
How else could you determine link bandwidth? 
9 
A Systems Approach to Networks 
Most interesting applications of computers require: 
-? Fault tolerance 
-? Coordination of concurrent activities 
-? Geographically separated but linked data 
-? Vast quantities of stored information 
-? Protection from mistakes and intentional attacks 
-? Interactions with many people 
-? Evolution over time 
Networks are no different! 
10 
Network Systems: Design Patterns 
Scale by connecting smaller pieces together 
-? With no central state 
Reliability out of unreliability 
-? In any system with a billion components, many will be 
broken at any point in time 
-? And some will fail in bizarre ways 
Interoperability 
-? No single vendor + quasi-formal specs => often 
unpredictable behavior 
-? Layering to manage complexity 
-? Once standardized, hard to impossible to fix 
11 
An Anecdote 
BGP: protocol to exchange routes between ISPs 
-? Two primary vendors: Cisco and Juniper 
-? Monoculture within a given ISP 
-? Stateful: only send updates; 100K routes exchanged 
When you get a receive an invalid route, what do 
you do? 
-? And what do you think happened in practice? 
12 
3 
Another Anecdote 
In 1997 and 2001, a small mis-configuration at one ISP 
disrupted Internet connectivity on a global scale 
-? Nothing prevented one ISP from announcing that it can 
deliver packets for any Internet prefix 
Internet is still vulnerable to this same problem 
-? Over half of all new Internet route announcements are 
misconfigurations! 
-? Until recently, Cisco’s Internet prefix was hijacked on a 
regular basis 
Internet Design Patterns 
Be liberal in what you accept, conservative in what 
you send 
Spread bad news quickly, good news slowly 
Use only soft state inside the network 
Avoid putting functionality into the network unless 
absolutely necessary 
14 
Internet Design Patterns in Practice 
Be liberal in what you accept, conservative in what 
you send 
-? Security suggests the opposite 
Spread bad news quickly, good news slowly 
-? Inconsistent state is a barrier to improving availability 
Use only soft state inside the network 
-? NATs, firewalls, etc. 
Avoid putting functionality into the network unless 
absolutely necessary 
•? Ubiquitous middleboxes 
15  16 
A Brief Tour of the Internet 
What happens when you “click” on a web link? 
This is the view from 10,000 ft …  
You at home 
(client) 
www.msn.com 
(server) 
Internet 
request 
response 
 17 
9,000 ft: Scalability 
Caching improves scalability 
We cut down on transfers: 
-? Check cache (local or proxy) for a copy 
-? Check with server for a new version 
Cache 
“Changed?” 
“Here it is.” 
“Have it?” 
“No” 
www.msn.com 
 18 
8,000 ft: Naming (DNS) 
Map domain names to IP network addresses 
All messages are sent using IP addresses 
-? So we have to translate names to addresses first 
-? But we cache translations to avoid next time 
“What’s the IP address for www.msn.com?” 
“It’s 207.68.173.231” 
128.95.2.106 
Nameserver 
128.95.2.1 
Page 4


1 
P561: Network Systems 
Tom Anderson 
Ratul Mahajan 
TA: Colin Dixon 
2 
“A good network is one that I never have to think 
about” – Greg Minshall 
True some of the time… 
Course Goals 
Technology Survey 
-? How things work 
-? How they are likely to work in the future 
Design and implementation of network protocols 
Research state of the art 
3 
Project: Fishnet 
Build an ad hoc wireless network in stages: 
-? Step 1: basic communication 
-? Step 2: routing 
-? Step 3: transport and congestion control 
-? Step 4: applications 
Three modes: 
-? Simulation (all nodes in one process) 
-? Emulation (each node in its own process; 
interoperability) 
-? Physical (on a PDA or cell phone) 
Details on the web site; due dates week 3, 5, 7, 10 
4 
Blogs 
By 5pm before each class, add a unique new 
comment on one of the questions posted to the 
web site 
Example Q: Instead of PPR, why not use smaller 
packets? 
Example blog: ? 
Before class, read the other comments 
5 
Reading < Class 
Example: Internet has a TTL (time to live) field in 
each packet 
-? Decremented on each hop 
-? When it gets to zero, router drops packet and sends an 
error packet back to the source 
-? Essential to correct operation of the Internet, and to 
its diagnosis 
6 
2 
Pop Quiz #1 
How could you use this to determine link latency? 
7 
Pop Quiz #2 
How could you use this to determine link 
bandwidth? 
8 
Pop Quiz #3 
How else could you determine link bandwidth? 
9 
A Systems Approach to Networks 
Most interesting applications of computers require: 
-? Fault tolerance 
-? Coordination of concurrent activities 
-? Geographically separated but linked data 
-? Vast quantities of stored information 
-? Protection from mistakes and intentional attacks 
-? Interactions with many people 
-? Evolution over time 
Networks are no different! 
10 
Network Systems: Design Patterns 
Scale by connecting smaller pieces together 
-? With no central state 
Reliability out of unreliability 
-? In any system with a billion components, many will be 
broken at any point in time 
-? And some will fail in bizarre ways 
Interoperability 
-? No single vendor + quasi-formal specs => often 
unpredictable behavior 
-? Layering to manage complexity 
-? Once standardized, hard to impossible to fix 
11 
An Anecdote 
BGP: protocol to exchange routes between ISPs 
-? Two primary vendors: Cisco and Juniper 
-? Monoculture within a given ISP 
-? Stateful: only send updates; 100K routes exchanged 
When you get a receive an invalid route, what do 
you do? 
-? And what do you think happened in practice? 
12 
3 
Another Anecdote 
In 1997 and 2001, a small mis-configuration at one ISP 
disrupted Internet connectivity on a global scale 
-? Nothing prevented one ISP from announcing that it can 
deliver packets for any Internet prefix 
Internet is still vulnerable to this same problem 
-? Over half of all new Internet route announcements are 
misconfigurations! 
-? Until recently, Cisco’s Internet prefix was hijacked on a 
regular basis 
Internet Design Patterns 
Be liberal in what you accept, conservative in what 
you send 
Spread bad news quickly, good news slowly 
Use only soft state inside the network 
Avoid putting functionality into the network unless 
absolutely necessary 
14 
Internet Design Patterns in Practice 
Be liberal in what you accept, conservative in what 
you send 
-? Security suggests the opposite 
Spread bad news quickly, good news slowly 
-? Inconsistent state is a barrier to improving availability 
Use only soft state inside the network 
-? NATs, firewalls, etc. 
Avoid putting functionality into the network unless 
absolutely necessary 
•? Ubiquitous middleboxes 
15  16 
A Brief Tour of the Internet 
What happens when you “click” on a web link? 
This is the view from 10,000 ft …  
You at home 
(client) 
www.msn.com 
(server) 
Internet 
request 
response 
 17 
9,000 ft: Scalability 
Caching improves scalability 
We cut down on transfers: 
-? Check cache (local or proxy) for a copy 
-? Check with server for a new version 
Cache 
“Changed?” 
“Here it is.” 
“Have it?” 
“No” 
www.msn.com 
 18 
8,000 ft: Naming (DNS) 
Map domain names to IP network addresses 
All messages are sent using IP addresses 
-? So we have to translate names to addresses first 
-? But we cache translations to avoid next time 
“What’s the IP address for www.msn.com?” 
“It’s 207.68.173.231” 
128.95.2.106 
Nameserver 
128.95.2.1 
4 
 19 
7,000 ft: Sessions (HTTP) 
A single web page can be multiple “objects” 
Fetch each “object” 
-? either sequentially or in parallel  
GET index.html 
GET ad.gif 
GET logo.gif 
www.msn.com 
 20 
6,000 ft: Reliability (TCP) 
Messages can get lost 
We acknowledge successful receipt and detect and 
retransmit lost messages (e.g., timeouts); 
checksums to detect corruption 
(lost) 
retransmission 
acknowledgment 
 21 
5,000 ft: Congestion (TCP) 
Need to allocate bandwidth between users 
Senders balance available and required 
bandwidths by probing network path and 
observing the response 
How fast can 
I send? 
 22 
4,000 ft: Packets (TCP/IP)  
Long messages are broken into packets 
-? Maximum Ethernet packet is 1.5 Kbytes 
-? Typical web object is 10s of Kbytes 
Number the segments for reassembly  
1. GET 2. inde 3. x.ht 4. ml 
GET index.html 
 23 
3,000 ft: Routing (IP) 
Packets are directed through many routers 
R 
R 
R 
R 
R H H 
H 
H 
H 
R 
R H 
R 
H: Hosts 
R: Routers 
 24 
2,000 ft: Multi-access (e.g., Cable) 
May need to share links with other senders 
Poll headend to receive a timeslot to send 
upstream 
-? Headend controls all downstream transmissions 
-? A lower level of addressing is used … 
Headend 
Page 5


1 
P561: Network Systems 
Tom Anderson 
Ratul Mahajan 
TA: Colin Dixon 
2 
“A good network is one that I never have to think 
about” – Greg Minshall 
True some of the time… 
Course Goals 
Technology Survey 
-? How things work 
-? How they are likely to work in the future 
Design and implementation of network protocols 
Research state of the art 
3 
Project: Fishnet 
Build an ad hoc wireless network in stages: 
-? Step 1: basic communication 
-? Step 2: routing 
-? Step 3: transport and congestion control 
-? Step 4: applications 
Three modes: 
-? Simulation (all nodes in one process) 
-? Emulation (each node in its own process; 
interoperability) 
-? Physical (on a PDA or cell phone) 
Details on the web site; due dates week 3, 5, 7, 10 
4 
Blogs 
By 5pm before each class, add a unique new 
comment on one of the questions posted to the 
web site 
Example Q: Instead of PPR, why not use smaller 
packets? 
Example blog: ? 
Before class, read the other comments 
5 
Reading < Class 
Example: Internet has a TTL (time to live) field in 
each packet 
-? Decremented on each hop 
-? When it gets to zero, router drops packet and sends an 
error packet back to the source 
-? Essential to correct operation of the Internet, and to 
its diagnosis 
6 
2 
Pop Quiz #1 
How could you use this to determine link latency? 
7 
Pop Quiz #2 
How could you use this to determine link 
bandwidth? 
8 
Pop Quiz #3 
How else could you determine link bandwidth? 
9 
A Systems Approach to Networks 
Most interesting applications of computers require: 
-? Fault tolerance 
-? Coordination of concurrent activities 
-? Geographically separated but linked data 
-? Vast quantities of stored information 
-? Protection from mistakes and intentional attacks 
-? Interactions with many people 
-? Evolution over time 
Networks are no different! 
10 
Network Systems: Design Patterns 
Scale by connecting smaller pieces together 
-? With no central state 
Reliability out of unreliability 
-? In any system with a billion components, many will be 
broken at any point in time 
-? And some will fail in bizarre ways 
Interoperability 
-? No single vendor + quasi-formal specs => often 
unpredictable behavior 
-? Layering to manage complexity 
-? Once standardized, hard to impossible to fix 
11 
An Anecdote 
BGP: protocol to exchange routes between ISPs 
-? Two primary vendors: Cisco and Juniper 
-? Monoculture within a given ISP 
-? Stateful: only send updates; 100K routes exchanged 
When you get a receive an invalid route, what do 
you do? 
-? And what do you think happened in practice? 
12 
3 
Another Anecdote 
In 1997 and 2001, a small mis-configuration at one ISP 
disrupted Internet connectivity on a global scale 
-? Nothing prevented one ISP from announcing that it can 
deliver packets for any Internet prefix 
Internet is still vulnerable to this same problem 
-? Over half of all new Internet route announcements are 
misconfigurations! 
-? Until recently, Cisco’s Internet prefix was hijacked on a 
regular basis 
Internet Design Patterns 
Be liberal in what you accept, conservative in what 
you send 
Spread bad news quickly, good news slowly 
Use only soft state inside the network 
Avoid putting functionality into the network unless 
absolutely necessary 
14 
Internet Design Patterns in Practice 
Be liberal in what you accept, conservative in what 
you send 
-? Security suggests the opposite 
Spread bad news quickly, good news slowly 
-? Inconsistent state is a barrier to improving availability 
Use only soft state inside the network 
-? NATs, firewalls, etc. 
Avoid putting functionality into the network unless 
absolutely necessary 
•? Ubiquitous middleboxes 
15  16 
A Brief Tour of the Internet 
What happens when you “click” on a web link? 
This is the view from 10,000 ft …  
You at home 
(client) 
www.msn.com 
(server) 
Internet 
request 
response 
 17 
9,000 ft: Scalability 
Caching improves scalability 
We cut down on transfers: 
-? Check cache (local or proxy) for a copy 
-? Check with server for a new version 
Cache 
“Changed?” 
“Here it is.” 
“Have it?” 
“No” 
www.msn.com 
 18 
8,000 ft: Naming (DNS) 
Map domain names to IP network addresses 
All messages are sent using IP addresses 
-? So we have to translate names to addresses first 
-? But we cache translations to avoid next time 
“What’s the IP address for www.msn.com?” 
“It’s 207.68.173.231” 
128.95.2.106 
Nameserver 
128.95.2.1 
4 
 19 
7,000 ft: Sessions (HTTP) 
A single web page can be multiple “objects” 
Fetch each “object” 
-? either sequentially or in parallel  
GET index.html 
GET ad.gif 
GET logo.gif 
www.msn.com 
 20 
6,000 ft: Reliability (TCP) 
Messages can get lost 
We acknowledge successful receipt and detect and 
retransmit lost messages (e.g., timeouts); 
checksums to detect corruption 
(lost) 
retransmission 
acknowledgment 
 21 
5,000 ft: Congestion (TCP) 
Need to allocate bandwidth between users 
Senders balance available and required 
bandwidths by probing network path and 
observing the response 
How fast can 
I send? 
 22 
4,000 ft: Packets (TCP/IP)  
Long messages are broken into packets 
-? Maximum Ethernet packet is 1.5 Kbytes 
-? Typical web object is 10s of Kbytes 
Number the segments for reassembly  
1. GET 2. inde 3. x.ht 4. ml 
GET index.html 
 23 
3,000 ft: Routing (IP) 
Packets are directed through many routers 
R 
R 
R 
R 
R H H 
H 
H 
H 
R 
R H 
R 
H: Hosts 
R: Routers 
 24 
2,000 ft: Multi-access (e.g., Cable) 
May need to share links with other senders 
Poll headend to receive a timeslot to send 
upstream 
-? Headend controls all downstream transmissions 
-? A lower level of addressing is used … 
Headend 
5 
Different kinds of addresses 
Domain name (e.g. www.msn.com) 
-? Global, human readable 
IP Address (e.g. 207.200.73.8) 
-? Global, works across all networks 
 Ethernet (e.g. 08-00-2b-18-bc-65) 
-? Local, works on a particular network 
Packet often has all three! 
a 
IP Hdr HTTP Payload TCP Hdr HTTP Hdr Ethernet Hdr 
Start of packet End of packet 
 26 
1,000 ft: Framing/Modulation 
Protect, delimit and modulate payload as a signal 
For cable, take payload, add error protection (Reed-
Solomon), header and framing, then turn into a 
signal 
-? Modulate data to assigned channel and time (upstream) 
Sync / Unique Payload w/ error correcting code Header 
 27 
Protocols and Layering 
We need abstractions to handle complexity and interfaces to 
enable interoperability. Protocols are the modularity of 
networks. 
A protocol is an agreement dictating the form and function 
of data exchanged between parties to effect 
communication 
-? Examples: ADSL, ISDN, DS-3, SONET, Frame Relay, PPP, BISYNC, HDLC, 
SLIP, Ethernet, 10Base-T, 100Base-T, CRC, 802.5, FDDI, 802.11a/b/g/n, ATM, 
AAL5, X.25, IPv4, IPv6, TTL, DHCP, ICMP, OSPF, RIP, IS-IS, BGP, S-BGP, CIDR, 
TCP, SACK, UDP, RDP, DNS, RED, DECbit, SunRPC, DCE, XDR, JPEG, MPEG, 
MP3, BOOTP, ARP, RARP, IGMP, CBT, MOSPF, DVMRP, PIM, RTP, RTCP, RSVP, 
COPS, DiffServ, IntServ, DES, PGP, Kerberos, MD5, IPsec, SSL, SSH, telnet, HTTP, 
HTTPS, HTML, FTP, TFTP, UUCP, X.400, SMTP, POP, MIME, NFS, AFS, SNMP, 
… 
 28 
Layering and Protocol Stacks 
Layering is how we combine protocols 
-? Higher level protocols build on services provided by 
lower levels 
-? Peer layers communicate with each other  
Layer N+1 
e.g., HTTP 
Layer N 
e.g., TCP 
Home PC www.msn.com 
 29 
Example – Layering at work 
We can connect different systems: interoperability 
TCP 
IP 
Ethernet 
TCP 
IP 
CATV 
IP 
 IP 
Ethernet 
 CATV 
host host 
router 
djw // CSEP561, Spring 2005  30 
Layering Mechanics 
Encapsulation and decapsulation 
Hdr 
Hdr Data 
Data 
+ 
+ 
Layer N+1 PDU 
becomes 
Layer N ADU 
Messages 
passed 
between 
layers 
Read More
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