• History, Standards, Design Principles
• Network Component and Addressing.

 
1. Leon-Garcia. Widjaja, "Communication Networks: Fundamental Concepts and Key Architectures," McGraw-Hill, 2000.
2. Douglas Comer, Introduction with TCP/IP: Principles, Protocols, and Architectures," 4th Edition, Prentice-Hall, 2000.
3. Andrew S. Tanenbaum, Computer Networks , Prentice Hall, 3rd ed., 1996.
4. Larry L. Peterson & Bruce S. Davie, Computer Networks: a system approach , 2nd Edition, Morgan Kaufmann, 2000.
5. Internet Drafts and Notes documents available at

http://www.isi.edu/publications.html

Communication line (communication links, transmission line): line that connects with several end points, takes information from one end points and delivers to other end point(s).

Wide Area Network (WAN): a network that spans a large geographical area, often a country or continent, and connects LANs or MANs. It consists of transmission line (called circuits, channels, or trunks) and switching elements (called switching nodes, data switching exchanges or router).

_: The name of a movie starring Goldie Hawn.
_: The rule implemented by a device driver to allow cpu to talk to a peripheral.
_: A set of rules for achieving a global objective exercised by geographically distributed nodes. (Robert Gallager, Prof. EE MIT)

Open System Interconnection (OSI) Reference Model

Served as a framework for communications architecture specification and for specifying protocol standards

Messages Generated for a Simple Web Access

• First, the browser parses the url entered by the user. Get the cs.uccs.edu as domain name. To send HTTP request message to the cs.uccs.edu. It needs the IP address of cs.uccs.edu to fill in the source IP address of IP header for every packet sent to cs.uccs.edu.
• To find out the IP address of cs.uccs.edu, it uses the DNS network services.
• The DNS query (with content such as "what is the IP address of cs.uccs.edu?") is put in UDP segment and the destination IP address of the IP packet carrying this UDP segment is set to 128.198.1.250. From the system configuration, the machine knows the destination IP address of the UDP packet is 128.198.1.250 (DNS server IP).
• The IP packet is sent to the IP module for routing.
• The IP module matches the routing table and found that 128.198.1.250 is not a host in local subnet. Only the default gateway entry is matched.
• It realizes that the IP packet needs to be sent to default gateway for relaying to the DNS server.
• Assume that we do not have arp entry of the default gatewy. We need to send out ARP request to find the MAC address of the gateway. wait tries to find out the MAC (Ethernet) address of the gateway/router of the subnet using ARP protocol.
• The gateway responds with its MAC address using the ARP protoocl message.
• Wait then sends the DNS request to DNS server, ccnucccs.uccs.edu.
• DNS server, ccnucccs.uccs.edu, replies that the IP address of cs.uccs.edu is 128.198.162.68.
• Wait then sets up a TCP connection with cs.uccs.edu.  It takes three TCP messages, SYN, SYN/ACK, ACK, called three-way handshake, to establish a TCP connection.
• Wait then sends the HTTP request message to cs.uccs.edu. Frame 11.
• cs.uccs.edu returns the HTML document in the HTTP response message over 10 ethernet frames. Frames 13,15, 16, 18, 19, 21, 22, 24, 25, 27.  wait replies an ACK every other packets.
• Note that the ~cs522 web page is 12719 byte long.  An TCP packet can only carry 1448 byte data.  Therefore it takes ceil(12719/1448)=9 addtional frames.  The first frame  includes HTTP response header (not part of the 12719 byte HTTP data).
• The informaton field in Ethernet frame can carry a maximum 1500 bytes data.  However, the IP header takes 20 bytes. The TCP header takes 32 bytes.   TCP payload or data field  is left with 1500-20-32=1448 bytes to carry the HTTP response.
• The process of chopping a big message into several smaller packets  by the sender is called segmentation.  The reverse process of assembling these fragmented packets into the original message is called re-assembly.
• Wait's browser parses the HTML document  in HTTP response. Found there are cubannder.JPG, rocky.mid, marble1.jpg, rainbowan.gif media files needed for displaying the web page.  It needs to go back to the web server at cs.uccs.edu to retrieve them.
• Wait set up three additonal TCP connections with port numbers, 1090, 1091, 1092, to retrieve these four images and mid file.  Note that at least packets over 1090 and 1091 interleave, implying that the benefit of concurrent retrieval of files.

      4 2.783156    wait.uccs.edu         ff:ff:ff:ff:ff:ff     ARP      Who has 128.198.192.1?  Tell 128.198.192.202
      5 2.783698    cs-old-loadbalancing-router.uccs.edu wait.uccs.edu         ARP      128.198.192.1 is at 00:50:80:d1:36:00
      6 2.783717    wait.uccs.edu         ccnuccs.uccs.edu      DNS      Standard query A cs.uccs.edu
      7 2.784022    ccnuccs.uccs.edu      wait.uccs.edu         DNS      Standard query response A 128.198.162.68
      8 2.789416    wait.uccs.edu         cs.uccs.edu           TCP      1089 > www [SYN] Seq=4211769964 Ack=0 Win=32120 Len=0
      9 2.789698    cs.uccs.edu           wait.uccs.edu         TCP      www > 1089 [SYN, ACK] Seq=4202585076 Ack=4211769965 Win=32120 Len=0
     10 2.789737    wait.uccs.edu         cs.uccs.edu           TCP      1089 > www [ACK] Seq=4211769965 Ack=4202585077 Win=32120 Len=0
     11 2.790738    wait.uccs.edu         cs.uccs.edu           HTTP     GET /~cs522/ HTTP/1.0
     12 2.791138    cs.uccs.edu           wait.uccs.edu         TCP      www > 1089 [ACK] Seq=4202585077 Ack=4211770251 Win=31856 Len=0
     13 2.793790    cs.uccs.edu           wait.uccs.edu         HTTP     HTTP/1.1 200 OK

     38 2.834564    wait.uccs.edu         cs.uccs.edu           HTTP     GET /~cs522/cubannder.JPG HTTP/1.0
     39 2.835028    cs.uccs.edu           wait.uccs.edu         TCP      www > 1092 [ACK] Seq=4205667534 Ack=4214663002 Win=31856 Len=0
     40 2.836822    cs.uccs.edu           wait.uccs.edu         HTTP     HTTP/1.1 200 OK
     41 2.837067    wait.uccs.edu         cs.uccs.edu           TCP      1092 > www [ACK] Seq=4214663002 Ack=4205668982 Win=31856 Len=0
     42 2.837050    cs.uccs.edu           wait.uccs.edu         HTTP     Continuation

     73 2.846638    wait.uccs.edu         cs.uccs.edu           HTTP     GET /~cs522/rocky.mid HTTP/1.0
     74 2.847026    cs.uccs.edu           wait.uccs.edu         TCP      www > 1091 [ACK] Seq=4200573118 Ack=4209807636 Win=31856 Len=0
     75 2.847940    wait.uccs.edu         cs.uccs.edu           HTTP     GET /~cs522/marble1.jpg HTTP/1.0
     76 2.848814    cs.uccs.edu           wait.uccs.edu         HTTP     HTTP/1.1 200 OK
 
 

Consist of only four layers: applications, transport, network, and host-network.

Internet, internet, intranet, extranet

• private
• may be connected to the Internet, often by firewall

first proposal fro World-Wide-Web
NSFNET upgrade to T1 (1.544Mbps)
 

Regional Data Network: Colorado SuperNet

Internet Host Growth (Latest Survey Results January 2000 )

Number of Hosts and Domains advertised in the DNS

Who run Internet?

• "Nobody?"
• Standards: Internet Engineering Task Force (IETF)
• Names: Internic (US), RIPE (Europe)
• IP Numbers: Internet Assigned Numbers Authority (IANA)
• Operational coordination: Internet Engineering Planning Group (IEPG)
• Networks: Internet Service Providers (ISPs), Network Access Points (NAPs)
• Fiber: Telephone companies (mostly)
• Content: Companies, universities, individuals

• San Francisco NAP, Pacific Bell
• Chicago NAP, Ameritech and Bellcore
• New York NAP, Sprint
• Washington DC NAP, MFS

Ameritech NAP Architecture

very high speed Backbone Network Services (vBNS)

Internet Addresses and Domain Names

• Every organization connecting to the Internet must have a unique identifier. This identifier is known as the Internet address.

e.g. Internet address Domain/ Machine name
UCCS 128.198.X.X uccs.edu
Sanluis (DS3100) 128.198.2.62 sanluis.uccs.edu
HP 15.X.X.X hp.com
hpcslb 15.19.2.160 hpcslb.col.hp.com
• Internet address also called IP address since it is used by IP to route msgs.
• In addition to a numerical identifier, most organizations also get what is known as a domain name.
• It is through the Internet address and the domain name that the organization's hosts will become known throughout the Internet.
• Used to be an organization must register with the Internet Address Naming Authority (IANA) authority that assigns Internet addresses and domain names.

Internet Addresses

• 32 bit addresses (running out, future IPv6 has 128 bit address)
• almost every network interface card has one
• some machines have more than one Internet address
• has more than one network card, each connected to a subnet
• A machine's Internet address may
• change (in dial up ISP, its users share limited no. of addresses, say 254)
• have lots of them (WWW servers, firewall machines)
• have none (some routers)
• American Registry for Internet Numbers, ARIC, at http://www.arin.net is responsible for managing IP addresses in North/South America, the Caribbean and sub-Saharan Africa.
• ARIN charges an end user$2500 one time for /19 (=32 c-class) address space, or 8196 hosts. But it charges ISP $2500 each year for the same address space. Something funny here.

Classful Internet Addresses Formats

The Internet address are expressed in (4 number) dotted notation.
Machine hpcslb.col.hp.com has 15.19.2.160 as its internet address.
Is it belong to a class A network? What is its netid value? hostid value?
Machine sanluis.uccs.edu has 128.198.2.62 as its internet address.
        Is it belong to a class A network? What is its netid value? hostid value?
Machine cli.com has 192.31.85.1 as its internet address.
        Is it belong to a class A network? What is its netid value? hostid value?

rfc1375.txt discusses the limitation of IP address formats & the growing demand.

IP Address Classes

 

Class	first octet	hosts per network	nets	used (7/96)
Class A	<128	16M	128	95
Class B	128...191	65334	16384	5892
Class C	192...223	254	2M	128378
Class D	224...239		268M	dynamic
Class E	240...255		138M	reserved

Class D addresses are called call IP multicast addresses or group addresses that are dynamically assigned.
• The original policy was to allow a C-class network address (256 IP addresses) to a domain name applicant. With explosion of applications, there is a concern of IP addresses is running out.

How to Avoid Shortage of IP addresses

• Four approaches:
• Extend size of IP address: The proposed IP protocol (IPv6) will have 128 bits IP address.
• Allocate network with IP address ranges that are multiple of class C size instead of a large class B size.

Require subnet mask and a network address  to idenfiy this type of  network.
This is so called Classless and Subnet address concept.
• Monitor the usage and take back if not used.
• Don't allocate if we do not have to.
• It turns out that many domain names are hosted by ISP's and shared their IP addresses. There is no need to give out C-class address individual. The new policy separates the application of IP address and that of domain name. The IP addresses are not running out in near future.
• Network Solutions Inc. was trusted by NSF for assigning domain names. But they are not doing a good job. There are proposals to allow multiple companies to assign domain name.
• Most ISP or web hosting companies has web pages that facilitate the search of avavailability of domain name. Check out Tabnet web page for searching the domain names.
• The Domain Name is picked by the organization.
• A domain name is simply a character string that maps to the Internet address. It is easier for humans to remember than a unique set of numbers.

• hierarchical, dot-separated names
• multi-level delegation, each organization can assign names (prefix to its assigned organization domain name) to its constituents.
• by country or by type of organization (in us)
• needs to be overhauled (63% of all domains are .com)
• Top-level domains:2 letters: countries; 3 letters: type of organization

Domain	Usage	Example	# of Hosts (1/97)
com	commercial	mci.com	3965417
edu	US 4yr college	cs.uccs.edu	2654129
net	network provider	vbns.net	1548575
mil	US military	arpa.mil	655128
gov	US non-mil. government	whitehouse.gov	387280
org	non-profit orgs	linux.org	313204
us	us geographical	reston.va.us	587175
jp	japan	flab.fujitsu.co.jp	734406
uk	united kingdom	cs.ucl.ac.uk	591624

• Host domain name are mapped to IP address by Domain Name Service(DNS). This could be a many-to-many mapping.
• Both www.cs.uccs.edu and owl.uccs.edu are mapped to 128.198.2.69
• www.cs.uccs.edu may be mapped to machine 128.198.8.250 in the future.
• When we send IP packet out, we need IP address in the packet header.
• Domain Name Servers (more than two in a domain) provide DNS service.
• Java applet security problem related to DNS.
• IP address mapped to Ethernet card MAC address via ARP protocol, one-to-one.

• Hierarchy of redundant domain name servers with time-limited cache
• redundant to improve reliability and efficiency
• time-limited cache to avoid stale data.
• Each server know the (9) root servers
• Each root servers know at least two DNS servers in a domain.
• Each host can be configured to query more than one DNS server.
• better know which one is faster and less congested.

• Data Link Layer Protocol: Point-to-Point (PTP), Serial Line Interface (SLIP)
• Network layer data: IPv4, IPv6,
• Network layer routing: ICMP, IGMP, OSPF, PIM
• Transport layer: TCP, UDP.
• Information access: HTTP, FTP, TELNET
• File sharing: NFS, DFS
• Electronic Mail: SMTP, POP
• Real time service: Real-timeTransport Protocol (RTP)
• Time: Network Time Protocol (NTP)

• Guarantee data delivery
• retransmission data in case of loss
• data are delivered in sending order
• Use sequence number for keeping track of msg sending status
• Use window concept dynamically adjusting the number of msgs sent for
• flow control: avoid overruning slow receiver

receiver "advertise" the window size.
• congestion control: avoid network overload
• Sender probes for available bandwidth:
• slow start: add segment size for each ACK received, which allows exponentially open the window size
• when msg lost (detected via time-out mechanism), reduce the window size
• Heavy overhead:
• 20 bytes header
• Connection oriented: requires three-way handshake to establish a connection; no data sent before that

• Add "ports" concept to differentiate processes, which use network services within a host.
• add payload checksum. IP only has header checksum.
• checksum: digit sequence computed from the data for verification purpose.
• senders compute it and put in a special field typical at the end of a msg.
• receivers recompute in from the data and compare against the checksum sent. If they are not the same, transmission error is detected.
• Very little overhead: 8 byte header
• For prompt delivery and performance.
• Used by RTP and NFS
• Datagram: data can be sent right away without waiting for a connection to be setup. It is also called connection less.
• Does not guarantee delivery of data.

Simple Web Access Example: Step1

• Someone requests a document using a browser (Web Client) on a computer connected to Internet
• Type in a URL, http://www.netcraft.co.uk/Survey/
• The browser parses the URL, obtains domain name of url, www.netcraft.co.uk
• Asks Domain Name Server (DNS) for translating the domain name to the IP adddress
• With IP address, the client computer sets up an HTTP connection to the server

• Browser sends ASCII characters string to server

GET /survey/ HTTP/1.0
User-agent: Mosaic for X windows/2.4
Accept: text/plain
Accept: text/html
Accept: image/*
• httpd server parses the request according to HTTP

interpret rest of the metainfo for browser capabilities
retrieve c:/InetPub/wwwroot/survey/default.htm
send information back using HTTP/1.0 format

• Server replies information using HTTP/1.0 format

• Server close file, network connection, wait for next request