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COMS W3156: Software Engineering, Fall 2001
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Title: COMS W3156: Software Engineering, Fall 2001
1
COMS W3156Software Engineering, Fall 2001
- Lecture 5 Tools and Networking
- Janak J Parekh
- janak_at_cs.columbia.edu
2
Administrativia
- Recitation tomorrow most likely early afternoon
- Permanent time yet to be set (hopefully by
classtime) - Late group proposals
- Well have to return assignments tomorrow
- Requirements will be out tomorrow night, barring
unforeseen problems - Notes going out between noon and 1pm, soon 9am
3
Next class
- We go object-oriented in a big way
- Read UML chapters 3-5, Schach chapter 12
- Object-oriented specification using UML
technologies what you will be doing for the next
milestone - Were skipping around to prepare for milestones
- Might want to consider reading chapters 1-2 of
UML pretty short, useful intro
4
Todays class
- Finish up chapter 5 analytical tools
- Networking basics
5
Stepwise refinement (I)
- Based on the principle of functional abstraction
- Worry about the high-level details first, smaller
problems can be dealt with later - Useful for specification, design and
implementation - In implementation, though, you sometimes need the
smaller pieces first
6
Stepwise refinement (II)
- Purchase order system
- Add purchase orders
- Edit/delete purchase orders
- Print purchase orders
- Fulfill purchase orders
- Now, drill down one level
7
Stepwise refinement (III)
- Add purchase orders
- Get input from user
- Validate input
- Compute totals on PO
- Add to database
- Edit/delete similar to previous
- Print purchase orders
- Request which to print from user
- Format for printout
8
Stepwise refinement (IV)
- Fulfill purchase orders
- Identify purchase order to fulfill
- Have user enter quantity shipped
- Determine if purchase order is completely
fulfilled - Now, one drills down, and down, and down
- I dont particularly like Schachs example, but
the process is valid
9
Cost-benefit analysis
- Is it worth computerizing? Not always
- Not straightforward intangible benefits
- Need to make assumptions
- Complex science, mostly outside of the scope of
this course well touch upon it during chapter 9
10
Software metrics (I)
- Many different kinds
- Lines of code (LOC), or thousand-lines-of-code
(KLOC) - MTBF
- Person-months of work, turnover
- etc.
11
Software metrics (II)
- Five fundamental metrics
- Size (KLOC others in chapter 9)
- Cost ()
- Duration (months)
- Effort (person-months)
- Quality ( of faults detected)
- Must be measured per each phase
- Note Metrics are controversial
12
Networking
- Introduction to networking essentials
- History and background
- Layers of networking abstraction
- LAN networks Ethernet
- WAN networks Internet
- TCP/IP addressing, routing, transmission, DNS
- Socket programming
- See http//www.novell.com/info/primer/primer.html
- How much do you know?
13
History and background
- We define modern computer networks to be
packet-based networks encapsulate data in
small packets that are sent out one-at-a-time - Compare to a telephone, which has a complete
circuit you can include many more parties in the
conversation - This stemmed out of DARPA research ARPAnet in
the 70s and 80s - TCP/IP eventually made public, led to Internet
14
Networking abstraction
- Similar to functional abstraction, but slightly
different - Many different models OSI reference model
- Most include (example)
- physical/hardware electric signals (Ethernet)
- network deal with nodes addressing (IP)
- transport transmit data efficiently and reliably
(TCP) - application allow programs to communicate
(sockets) - Protocol language on many different levels
www.ietf.org
15
LAN Ethernet
- Physical and electronic transmission medium
- Very cheap and popular, available in 10, 100, and
1000Mbps varieties - Communication via CSMA/CD
- Shout the message to everyone else
- If confusion, shut up for a bit, then try again
- Many, many others
16
WAN Internet
- Really not analogous to Ethernet
- Once known as the ARPAnet
- Internet comprised of many local networks
interconnected using large telecommunication
links - Links generally digital-circuit-based, over which
packet-based networks are run - http//www.cs.bell-labs.com/who/ches/map/gallery/i
sp-ss.gif
17
TCP/IP
- Transmission Control Protocol/Internet Protocol
- Its a misnomer
- IP is solely responsible for addressing and
routing computers across the Internet - TCP is a means of transmitting data over IP, and
not the only one (UDP, ICMP, GRE, ) - IP is the most popular protocol today
- Current version is IPv4, but new one out (IPv6)
18
IPv4 (I)
- Addressing and routing protocol
- Defines packets to be delivered to or routed
between machines - Each node on an IPv4 network has a 4-byte address
- Commonly represented using quad notation, e.g.
www.xxx.yyy.zzz
19
IPv4 (II)
- Each packet contains source IP address,
destination IP address, checksum, length, and
other fields - Gruesome details at http//www.ietf.org/rfc/rfc079
1.txt?number0791 - This is a request-for-comment (not anymore for
IP) all standard Internet protocols are defined
by an RFC - John Postel father of the Internet
- IP will attempt to deliver this packet for you to
the destination node
20
Subnets and routing (I)
- How can IP deliver? Two possibilities
- Target machine is locally reachable, i.e.,
connected via LAN - Give that machine the packet
- Target machine is not local
- Give the packet to a router, i.e., a machine that
knows where it should go - Subnetting determines which machines are local
and which arent
21
Subnets and routing (II)
Janakscomputer
Other Columbia networks
CS network (128.59.16.0-128.59.23.255)
Router
Router
Router
Columbias network (128.59.x.y)
Big-ass router
Big-ass router
note this isstrictly approximate
OC3(155Mbps)
OC3(155Mbps)
Applied Theory andthe Internet
Internet2(other research inst)
22
Subnets and routing (III)
- tracert/traceroute will do what its name implies
- Uses packet time-to-live field increments it and
sees how far it goes
23
TCP
- Transmission Control Protocol
- Mechanism of handling reliable transmission of
data over IP connection - Packets delivered in order
- Retransmission if one is not received on the
other side - Ports to handle many connections
24
UDP
- User Datagram Protocol
- Not connection-oriented send the packet and
forget about it if the other side doesnt
receive it, or its out of order, oh well, let
the program worry about it - Also has port construct
25
Servers and services
- Both UDP and TCP allow for listening to ports
for incoming data (TCP inbound connections) - Common ones include
- 21 ftp
- 23 telnet
- 25 smtp (mail)
- 80 www
- 110 pop3
- Most OSs allow 65,535 ports!
- Try telnet www.columbia.edu 80
26
Naming computers DNS
- Domain Name System
- We have lots of nodes with IP addresses
- Can you remember 128.59.23.10?
- Instead, we name each machine (hostname), and
then have servers that keep track of a
name-to-IP-address mapping - Distributed
27
So, how do you do all this?
- Well, you could write the packets yourself
- Instead, we use the operating system (or
language)s API to automate things - Sockets (they plug into ports ?)
- http//web2.java.sun.com/docs/books/tutorial/netwo
rking/sockets/index.html for Java - http//world.std.com/jimf/papers/sockets/sockets.
html for C/C (or Google) - quite a bit trickier
28
Philosophy of socket programming
- Server
- Establish a server socket
- Listen and accept new incoming connections
- Talk
- Hangup
- Repeat
- Client
- Create a client socket (or socket)
- Try to connect to server
- Talk
- Hangup
- Often send strings of data over sockets
29
Lets do it!
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