tcp/ip, associated internet protocols, and routing associated internet... · describe key issues of...

TCP/IP, Associated

Internet Protocols,

and Routing

2

Objectives

Identify the major protocols of the TCP/IP suite from the five-layer Internet model architecture

Compare protocols in relation to their architecture layers

Differentiate between the areas of emphasis for each of the layers in the Internet model architecture

Discuss the challenge of Internetwork addressing and describe how different protocols approach addressing to make it work

Identify differences between TCP and UDP at the transport layer and describe how these relate to IP

Describe key issues of Internet routing and present Internet quality of service issues, covering both policy and class methods

Provide an analysis of voice over IP communications including considerations that must be weighed before implementing deployment

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Overview

“We consider the TCP/IP architecture to be

a five-layer model, of which the top three layers

(application, transport, and Internet)

are most common in the Internet.”

Table 13.1 Major TCP/IP protocols

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Layer 3 (Internet/Network)

Protocols

Node Any device on the network

Examples: switches, routers, workstations, laptops

Switches and routers need not go above layer 3

vs.

Host End-user device

Examples: workstations and laptops

As an end-user node, a host needs to run the entire protocol stack (i.e., layers 1 through 5 in the TCP/IP model)

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Protocols

Communication categories

Location in

TCP/IP ModelCommunications Category

Layer 4Host-to-host where the hosts

are end points of the comms

Layer 3Node-to-node connected

through intervening nodes

Layer 2Directly connected node-to-

node

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Protocols

IP routing

When nodes are not directly connected

Deals with switching decisions—where to send the packet next

IP routing algorithm categories Link state—conditions between a router and the

next hop

Distance vector—possibilities for total path from source to destination

Node-to-node communication

between two directly connected devices

is handled at the data link layer (layer 2)

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Protocols

Address resolutionWhat?

Converting or relating a (logical) host IP address to its network address

Why?

Knowing a host’s (logical) IP address does not mean its network address is known

Knowing an address within a network does not mean the IP address is known

How?

Address resolution protocol (ARP)—converts an IP address to a machine address (i.e., physical address)

Reverse address resolution protocol (RARP)—converts a machine address into its associated IP address

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Protocols

Fig 13.1 – The ARP header

ARP translates layer 3 (IP) addresses into layer 2 (usu. MAC sublayer)

RARP translates layer 2 addresses into layer 3

Both ARP and RARP

use the same header

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Protocols Dynamic host configuration protocol (DHCP)

What?

Assigns host IP addresses and other transmission parameters to devices in an autonomous network

How?

Three address allocation schemes Manual

Network/Server administrator manually enters associations in the DHCP server table for each machine

Machines in the table get the same IP address every log on

Automatic Network/Server administrator enters an address range

DHCP server assigns the permanent IP address at first log on

Dynamic Same as automatic except a new IP address is assigned

every time a machine logs on (i.e., not a permanent IP address assignment)

Commonly used by ISPs

for dial-up connections

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Protocols

Internet control message protocol (ICMP)

ICMP messages are embedded in IP packets

Type number—indicates kind of message problem

Code number—specific details within type

“For hosts to be informed of problems with their

transmission, messages must be transmitted to them by

the parties discovering the problems.”

E.g., Type 3 (“destination unreachable”)—Code options:

0 network unreachable

1 host unreachable

2 protocol not supported

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Protocols

Internet group message protocol (IGMP)What?

Completely different from ICMP

Mechanism that supports IP multicasting Provides temporary “host group” addresses

Adds/deletes members from a group

How?In addition to the normal unique IP address

Temporary group members receive a temporary multicast address

Permanent group members receive a permanent multicast address

Hosts Can belong to more than one group

Do not need to belong to a group to send the group a multicast message

Must belong to a group to receive a multicast message

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Protocols

What is streaming?

Transferring data in such a way that it can be processed as a steady, uninterrupted flow

If data are received at a faster rate than necessary for processing

If data delivery is too slow or, not steady

Not a problem!

Data can be buffered

at receiver and

processed as needed

Ouch!

Flow is interrupted

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Layer 4 (Transport) Protocols

Transport control protocol (TCP)What?

One of the main protocols of the Internet

Developed along with IP to support packet transmissions over the ARPANET

Connection-oriented Guarantees end-to-end packet delivery

Guarantees correct ordering of segmented (fractionalized) packets

How?

On transmission TCP divides messages that are too large for IP into segments and numbers

so they can be correctly ordered at the recipient

For reliability, TCP end receivers send acknowledgements back to the sender

If an acknowledgement is not received within a given time, the package is re-sent

Packets with checksum failures are not acknowledged, and eventually re-sent

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Transport control protocol (TCP)—problems

For applications that depend on speedy packet

delivery in steady data streams

Applications will experience slow-down from router

processing requirements

If packets are lost or defective, subsequent packets are

withheld from the application until the replacement arrives

For real-time, streaming audio, streaming video,

or voice transmissions, TCP will not do

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User datagram protocol (UDP)What?

Second of two protocols available at the TCP/IP transport layer

Connectionless oriented “Best effort” delivery—packet delivery is not guaranteed

Packet ordering is not guaranteed

Significantly faster than TCP

How?

UDP handles segments of a transmission independently [handling packet segments on the transport layer the same as how IP handles datagrams at the IP layer

UDP adds a transport layer to the data segment that contains the destination and source port addresses

UDP supports real-time, streaming audio,

streaming video, and voice transmissions.

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Layer 5 (Application) Protocols

Hypertext transfer protocol (HTTP)What?

Leftmost part of a URL (http://)

Indicates the protocols (service) being used on the Web page

Commonly used to view websites and to retrieve a variety of data from a Web server

Connectionless—no connection between client and server after the request is carried out

Stateless—each request is treated without reference to previous requests

By specifying the data type in the http message header,

http can transport any data type

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How?

Http uses the services of TCP and IP to

actually move data between the browser

and the server

Http at the web server operates over the

well-known TCP port 80

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Common gateway interface (CGI)What?

Accessing a database or producing dynamic Web pages requires running a server-side program

CGI defines an open standard that allows Web servers and server-side programs to interact

Commonly used to view websites and to retrieve a variety of data from a Web server

How?

Independent of any programming language

CGI defines How a Web server can supply input information to a program it is running

How the program must return its results to the server

How a dynamic document is to be constructed as a result

Programs can be written in any programming language

that supports the CGI standard

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File transfer protocol (FTP)What?

Establishes rules for transferring data between an ftp server and a client

Users can download a file from an ftp server and upload a file to an ftp server

Used to download large data sets where the receiver is interested in the data but not concerned with presentation

How?

Users interact with the server to obtain data sets but do not interact with the data

In many instances, a password is required to log on to an ftp server before data can be moved in either direction

Transfers can be initiated by graphical user interface programs or line commands

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Simple network management protocol (SNMP)What?

Assists in managing networks remotely by

Enabling monitoring and controlling of network nodes

Collecting performance data, and

Administering cost, configuration and security measures

How?

SNMP is implemented on a network device by a software module

A network management system (NMS) hardware/software combination aids network management using data provided through SNMP

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E-mail protocols

Sending

Simple mail transfer protocol (SMTP)

Receiving

Post office protocol (POP)

Internet message access protocol (IMAP)

Clients use one or the other

not both

Homes

Small businesses

Remote connections

Large networks

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E-mail protocols

Sending

Simple mail transfer protocol (SMTP)

When you connect to the Internet

to send e-mail, client software uses

your connection provider’s SMTP server

to send your messages.

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E-mail protocolsReceiving

Post office protocol (POP) Downloads e-mail to computer’s e-mail client inbox

Disconnects as soon as e-mail is downloaded

Internet message access protocol (IMAP) More complex, more sophisticated than POP

Allows… Multiple clients to simultaneously connect to same inbox

Clients can use/manipulate multiple mailboxes and folders on same server

Clients can search e-mail on server besides inbox

Clients can remain connected to the server

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TelnetWhat?

Client/server software protocol

Originally designed to emulate a computer or terminal connected to a mainframe via a phone line

It functions as though a direct connection (terminal-to-mainframe) was in place

Widely used for line-by-line commands

Not encrypted—vulnerable to hacking!

Telnet is being replaced by secure shell (SSH)

which provides encrypted communications

between two hosts over unsecure networks

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Other layer 5 protocols

Voice over IP (VoIP) “Telephone calls over the Internet”

Carries voice over packet switched IP networks

H.323 Part of a group of standards covering multimedia

communications over a variety of network types

Originally designed to handle multimedia communications over LANS that had no inherent quality of service (QoS) capability

H.323 compliance ensures vendor multimedia interoperability

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Internet Routing

Routing

Each step along the way is called a hop

Layer 3 addresses identify devices on the route

Routing protocols support layer 3 addresses

Lookup tables indicate where to send packets next

Static—created/maintained by system administrators

Dynamic—created/maintained by routers

Determining the path a packet should take

while traveling from source to destination

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Internet Routing

Routing categorizations Predetermined or determined on-the-fly

Will every packet follow the same route (virtual circuit) or, will each packet’s next hop be determined by the router (connectionless)?

Next hop routing A router table only contains entries that tell the packet

what the next hop will be

Network-specific routing Routers select from a list of layer 3 addresses for routing decisions

Link state or, distance vector Is the router focused on next hop (link state) or,

full path (distance vector)?

Interior or exterior Are the routing protocols used entirely within a self-contained

(autonomous) network (interior) or are the protocols used between networks (exterior)?

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Internet Routing

Interior routing protocols (aka interior gateway protocols [IGP])

Open shortest past first (OSPF) Link state next hop technique

Uses Dijkstra’s algorithm to determine “shortest distance” (i.e., least cost, fastest, most reliable, etc.)

Routing information protocol (RIP) Dynamic distance vector method based on hop counts

Uses Bellman-Ford (or Dijkstra’s) algorithm

Each router creates a table that lists every other network within the system that it can reach

Problem with RIP: smallest hop count is not always best route!

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Internet Routing

Exterior routing protocols (aka exterior gateway protocols [EGP])

Border gateway protocol (BGP) (also exterior BGP [EBGP])

The major exterior routing protocol of the Internet

Supports classless inter-domain routing (CIDR)

Runs on border routers providing translation services between autonomous networks

Gateways connecting an organization to the Internet are typically border routers running BGP

BGP is also used as an interior protocol (IBGP)

in large corporate networks

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UDP and TCP Revisited

Layer responsibilities

TCP/IP model—

layersResponsibility

Layer 4 – Transport

Process-to-process communications

between hosts at end points

[end-to-end]

Layer 3—InternetPacket delivery between nodes

not directly connected

Layer 2—data linkPacket delivery between

directly connected nodes

TCP

UDP

The Internet is unreliable at the Internet layer

because IP is an unreliable service

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Transport layer protocols

TCP

Complicated, but reliable

UDP

Simple, but unreliable

Reliable service—guaranteed delivery

Unreliable service—delivery is not guaranteed

When reliability is needed

When reliability is not needed

+ IP

+ IP

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Internet transport design philosophy Minimal control at the hops where routing occurs—no addressing

above layer 3

Overall control at the end points where layer 4 addressing is required to identify hosts

Transport layer design concerns Flow control

Prevents a sender from overwhelming a receiver by sending data too fast

Congestion Deals with “traffic jams” at nodes (e.g., router feeding too many links)

Error control Discovering and correcting faulty packets

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Ports Every host has two types of ports

Physical (hardware)—where devices are attached

Virtual (software)—numbers that track processes Two-byte numbers (divided into ranges by IANA)

Well-known ports 0 to 1,023

Registered ports 1,024 to 49,151

Dynamic range 49,152 to 65,535 (processes, as needed)

Sockets Virtual identifier

A virtual connection to a process running on a host

Combination of the (virtual) port number and the (virtual) IP address

UDP

69 TFTP

161 SNMP

TCP

20 FTP

25 SMTP

80 HTTP

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User Datagram Protocol (UDP)

Unreliable, connectionless transport service

Simple, fast, little overheadFig 13.2

The UDP header

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Transport Control Protocol (TCP) Reliable, connection-oriented transport service

A connection is established in a three-step process (“three-way handshake”):

1. Host 1 (e.g., client) sends a connection request to Host 2 (e.g., server)

2. Server sends a confirmation packet to client

3. Client confirms packet receipt; connection is established

Connection termination occurs separately in each direction

Client sends a termination packet to server that is acknowledged; this ends client-to-server connection

Server still needs to terminate the server-to-client connection

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Transport Control Protocol (TCP)

Reliable, connection-oriented transport service

Fig 13.3 - The TCP header

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Quality of Service on the Internet

Service Level Agreement (SLA) specifying Quality of Service (QoS) A formal contract between a business and

a communications provider

Provides

Levels of service that will be provided

Under what conditions

At what cost

“Quality of service (QoS) for any communication system is

that it provides an acceptable level of network performance

relative to application need.”

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Quality of Service (QoS)

Components Bandwidth

Latency (delay)

Jitter

Packet loss

Related measures Reliability

Sequencing

Error rate

Data rate

Throughput

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Quality of Service (QoS)—application requirements E-mail and file transfers

Reliable, complete, error free

Bandwidth, latency, jitter relatively unimportant

Browser web page rendering Complete, error free, greater bandwidth

Latency, jitter relatively unimportant

Streaming audio Latency, jitter can distort sound

Lost packets are not so important

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Streaming video

Sensitive to jitter, delays; needs bandwidth, throughput

Lost packets are not so important

Video conferencing

Demands high bandwidth for audio and video

Okay to sacrifice video packets if audio is maintained

Internet telephony (VoIP)

Jitter can render calls unintelligible

Latency and some packet loss might be okay,

but not if competing against PSTN service

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Quality of Service (QoS)—policy and class methods

Integrated services (IntServ) Capacity (bandwidth reservation) is key

Resource reservation protocol (RSVP) requests capacity for an end-to-end route before the flow begins with three response classes1. Guaranteed—capacity is available on every route hop

No packet loss; specified max delay and jitter, guaranteed bandwidth

2. Controlled—uses statistical division multiplexing to make a heavily loaded route behave as if it were lightly loaded

Typically provides constant service for a given flow

3. Best effort— operation without reservation (as if no IntServ)

No bandwidth is reserved

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Differentiated services (DiffServ)

Tries to alleviate processing burden of IntServ

Aggregates flow at the edge routers

Core routers need not analyze flow requirements

or track flow states

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Multiprotocol label switching (MPLS) An IntServ—DiffServ hybrid

Provides guarantees where warranted without a large processing burden

All routers involved must be MPLS enabled

Fig.13.4 The MPLS header

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VoIP

Voice over IP (VoIP) (also “IP telephony”)

Method for transmitting voice over an IP network (usually Internet)

VoIP considerations for practical use Must behave like a PSTN telephone call

(i.e., circuit switched service)

Severe latency and jitter can render IP telephony unusable

Packet sequencing is an issue, but there can be no waiting Service will not tolerate waiting for dropped/out-of-order

packets

UDP must maintain flow without waiting for packet issues

Connect, use, and disconnect are required (like telephone)

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VoIP

Voice over IP (VoIP) (also “IP telephony”)

If there is no congestion, VoIP calls work smoothly

When congestion occurs, all the other problems come to the fore

Solution involves hardware and software supported by protocols

“In the end, the main problem for VoIP

is congestion, a traffic volume vs. bandwidth issue.”

46

VoIP

VoIP methods to offset congestion Voice digitizing at each end

Analog-to-digital converter (ADC) in combination with a digital-to-analog converter (DAC) configured

As a standalone box for connection to a phone

On a card in a computer

Built into a digital phone

Compression techniques to reduce bandwidth requirements

Protocols with connection-oriented signaling To exchange call management information for establishing

connections and managing the call

To provide familiar telephone features (ring tones, busy signals, etc.)

Together the ADC/DAC is

called a codec (coder/decoder)

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VoIP

VoIP connection-oriented signaling-related protocols H.323

Part of ITU-T applications layer (H.32x) suite of protocols for multimedia communications

Session initiation protocol (SIP) From Internet Engineering Task Force (IETF)

Designed specifically for VoIP

Handles call maintenance, termination, and other signaling features

Used for interactive multimedia sessions

Media gateway control protocol (MGCP) and megaco Gateway protocols that allow interconnection of IP and non-IP networks

(e.g., PSTN)

Physically Call agent (media gateway controller) sets up and terminates calls

A media gateway converts voice to packets and back

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VoIP

VoIP call transport QoS

Issues that protocols must handle

Latency

Jitter

Packet loss

Sequencing

Protocols for handling issues

Real-time transport protocol (RTP)

Real-time transport control protocol (RTCP)

Secure real-time transport control protocol (SRTCP)

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VoIP

VoIP—Real-time transport protocol (RTP) How it works

RTP numbers and stamps each voice packet

End host assembles packets in sequence

End host knows if packets are lost Packets are forwarded as they are received

Out-of-sequence packets are ignored (dropped)

Other notes RTP + (H.323 or SIP) cell phone “push to talk”

SRTCP adds encryption and authentication

Caveat No end-to-end transport protocol

can guarantee real-time flow transport

tcp/ip, associated internet protocols, and routing associated internet... · describe key issues of...

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