Chapter 1Introduction

Protocol

• Protocol (New Oxford American Dictionary): The official procedure or system of rules governing affairs of state or diplomatic occasions.

• Protocol Suite: Collection of protocols– TCP/IP: originated from ARPANET Reference Model (ARM)

• Protocol Architecture (or Reference Model): How protocols of a suite relate to each other and how they divide up the tasks– ISO protocol architecture– Xerox’s XNS – IBM’s SNA

Internet Architecture• Clark recounts that the primary goal was to “develop

an effective technique for multiplexed utilization of existing interconnected networks.”

• Secondary Goals:– Internet communication must continue despite loss of networks or

gateways.– The Internet must support multiple types of communication services.– The Internet architecture must accommodate a variety of networks.– The Internet architecture must permit distributed management of its

resources.– The Internet architecture must be cost-effective.– The Internet architecture must permit host attachment with a low

level of effort.– The resources used in the Internet architecture must be accountable.

Circuit and Packet Switching

• Circuit Switching– Network meant Telephone networks up to the

1960s.

• Packet Switching– Chunks of data– Multiplexing– Statistical multiplexing

Virtual Circuits

• Per-flow state in each router• Examples– X.25: until 1990s• logical channel identifier (LCI) or logical channel

number (LCN)

– Frame Relay– DSL (Digital Subscriber Line)– Cable Modem

Datagrams

• Identifying information of source and final destination carried in each packet

• Per-connection state in routers not needed• Eliminates complicated signaling• Designers loved the idea

Message Boundaries

OSI (Open Systems Interconnection) Model defined by ISO (International Standardization Organization)

End-to-end argument

• End-to-end argument (for TCP/IP)– Correctness and completeness can be achieved by

implementing at the end-points– “dumb” network and “smart” end-points

• Fate Sharing: (related concept)– Maintain state with the end-points, so that

connection will fail iff at least one end-point fails– (assumes there is always some path available

between the end-points)

Encapsulation

Encapsulation

Demutliplexing

Port numbers

• 16-bit nonnegative numbers (i.e., range 0–65535)

• well-known port numbers (0–1023) • registered port numbers (1024–49151)• dynamic/private port numbers (49152–65535)

Terminology

• internet: multiple networks connected together, using a common protocol suite.

• Internet: collection of hosts around the world that can communicate with each other using TCP/IP

• intranet: private internet• extranet: intranet with access to a group of

partners and associates

Iterative Server

• I1. Wait for a client request to arrive.

• I2. Process the client request.

• I3. Send the response back to the client that sent the request.

• I4. Go back to step I1.

Concurrent Server

• C1. Wait for a client request to arrive.

• C2. Start a new server instance to handle this client’s request. This may involve creating a new process, task, or thread, depending on what the underlying operating system supports. This new server handles one client’s entire request. When the requested task is complete, the new server instance terminates. Meanwhile, the original server instance continues to C3.

• C3. Go back to step C1.

History of Software Releases supporting TCP/IP

Attacks Involving the Internet Architecture

• Spoofing• Denial-of-service (DoS)• Owing the system: converting to zombie or

bot• Malicious software (malware)

Questions to Ponder

• If you are designing TCP from scratch, how will you design it differently?

• As an end-user what do you think are the biggest drawbacks of the current Internet?