TCP/IP, Connecting LANs

Tom Kelliher, CS 318

Feb. 23, 2000

Administrivia

Announcements

Collect project 1.

Why perl and sockets?

Assignment

Remember reading: Chs. 1--10, 14--16.

From Last Time

OSI Layers.

Outline

1. Introduction to TCP/IP.

2. LANs, connecting LANs.

Coming Up

Socket programming.

Introduction to TCP/IP

Message transmission example:

LANs

Goals:

1. Minimize cost.

2. Have high reliability.

Basics:

1. Point-To-Point networks.
   1. connections --- expensive.

   2. Does not scale well.

   3. Used for long-haul networks.

2. LANs: a shared communication medium.

3. Principle of locality: temporal, physical/spatial.

LAN Topologies

1. Star: what you have with a hub.

   Hub broadcasts everything.

2. Ring.

   Nodes on a ring retransmit data.

3. Bus.

   How can a star be a bus?

Ethernet

1. Shared bus.

2. Speeds: 10 Mbps, 100 Mbps, gigabit.

3. CSMA --- ``carrier'' sense multiple access. Listen before transmitting. Idle.

4. CD --- collision detection. Listen to what you've transmitted.

5. Binary exponential backoff. Upon collision, wait for up to d time units, randomly chosen, before retransmitting.

   The exponential part.

IBM Token Ring

1. What is a token?

2. How do I transmit on the token ring?

3. ``Pass'' nodes.

4. How do I receive? How do I know it's for me?

   Why is this efficient: Layering. The NIC is responsible for determining which host a message is for, etc., not the CPU.

5. Transmitter can do error detection.

``Gluing'' LANs Together

Two connected segments:

Repeaters/Hubs

1. Physical layer devices. Amplify, retime (?) the signal.

2. Connected segments in same collision domain: length restrictions.

3. Forwards everything: noise, damaged frames, frames not destined for the other segment, etc.

Bridges/Switches

1. Data link layer.

2. Connected segments in unique collision domains.

3. Completely reads a frame from one segment, then transmits it to other segment.

4. Bridged hosts don't know they're bridged. Buffering?

5. ``Learning'' bridges forward frames only when necessary, after learning the hosts on each segment.

6. A switch is like a hub, but each host is on its own segment:

   

   • Hub bandwidth: R.

   • Switch bandwidth: . where R is the data rate and P the number of ports.

7. One topology: switch --- hubs --- hosts.

Routers

1. Network layer.

2. Connected segments may differ in: media, physical addressing, frame format.

Host Addressing: IP Addresses

Form:

• 32-bit, dotted decimal
• different from ethernet address (ARP, RARP)
• Class A: 0, 7 bit netid, 24 bit hostid

  0.0.0.0 to 127.255.255.255

• Class B: 10, 14 bit netid, 16 bit hostid

  128.0.0.0 to 191.255.255.255

• Class C: 110, 21 bit netid, 8 bit hostid

  192.0.0.0 to 223.255.255.255

• Domain Name System

Encapsulation

1. Data
2. Application layer
3. TCP/UDP layer --- TCP frame
4. IP layer --- IP datagram
5. Ethernet layer --- ethernet frame: 46--1500 bytes (MTU)

Demultiplexing

Process Communication

How do processes on separate machines communicate?

• Client/Server
• ``Well-known'' addresses
• Multiple telnet clients