11/ 3 Mon

IP Address

Network #

Host #

         ;                             ;                             ;    

Subnet #

Subnet host #

         ;                         & nbsp;           &n bsp;           &nb sp;           &nbs p;           ( à< /span> subnet mask )

Special Addresses

Prefix	Suffix	Address Type	Purpose
All 0’s	All 0’s	This computer	Bootstrap (Real address is not available)
Network #	All 0’s	Network	Used to refer to a network(network id)
Network #	All 1’s	Directed broadcast	Broadcast in a determined network
All 1’s	All 1’s	Limited broadcast	Broadcast in local net
127	Any	Loop back	testing

11/5 Wen

Professor explain the project

2 programs

1 – Directory Server

         ;     Dialog-based

2 – Phone Program

         ;     Includes Directory Client , Ringer Client/Server, Play Server/Voice Client

Two threads:

1 – receive samples in the UDP and put them in Jitter buffer

1 – play samples in Jitter buffer

IP Packets

Because the internet connects heterogeneous networks, a router will copy the packets arriving in one network and copying them in another

To accommodate heterogeneity, an internet must define a hardware independent packet format.

IP Packet == IP datagram

IP Packets are the basic unit of communication in the internet.

Ether Header

IP Header

IP Data( UDP Packet, TCP Packet, ICMP Packet )

IP Packet Header

0 34         ;         78         ;                  16         ;                         & nbsp;           &n bsp;           &nb sp;    31

Ver	Header Len	Service type		Total Length
ID				Flags(4bit)	Fragment Offset
Time to live			Type	Header Checksum
Source IP
Destination IP

Version – 4 bits

- Correct version is 4.

- New version is 6 (still not widely used)

Header Length

- It is usually 20 bytes (this number is in words of 4 bytes or 5 bytes)

- If IP options are used then the header will be longer

Service type

- Priority (It is usually ignored)

Total Length

- # Bytes in the packet including header

ID – monotonically increasing number different in each packet

- coming from the same source

- same source 64K Identifiers

Flag

– Do not fragment bit. If set then, Router should not fragment packet

- Last fragment bit. Set to 1 if this packet is the last fragment.

Fragment offset

- Position of this packet the original packet if it was fragmented.

H

R

         ;                         & nbsp;           &n bsp;      MTU=500

         ;                         & nbsp;           &n bsp;           &nb sp;           &nbs p;             ;                         & nbsp;           

Id=5(Off=0, LF=1)	Id5 500 (off=0)	LF=0
IP=1500 bytes	Id5 500 (off=500)	LF=0
	Id5 500 (off=1000)	LF=1

Reassembly is done at destination and not in the routers.

Do not fragment bit is used to find the PATH MTU.

11/7 Fri

Time to live

- The max number of seconds the packet should remain in the internet.

- It is decremented by 1 every second the packet starts in the router

- It is decremented by 1 every time the packet is routed by a router

If the TTL fields reaches 0 the packet is discarded and an ICMP message “Time expired” is sent to the source.

Since the TTL fields is 8 bits long, the max number of seconds the packet can be in the interrupt will ?

The packet can be routed 255 times max.

This prevents a packet being forwarded forever.

IP Type

- It tells the protocol on top of IP that is encapsulated in the data: TCP, UDP, ICMP

Header checksum

- checksum of the IP header to check possible errors

Source IP

- IP address of source host

Destination IP

- IP address of destination host

Source and Destination do not change during the transit of the IP Packet.

The header may have additional information known as “IP Option”.

Example of IP Options

- Record Route

Add the IP address of the router to the header every time the packet is routed.

- Strict Routing

Loose Follow the routing path indicated in the header

IP Options are used in Network diagnostics.

IP semantics

- IP is connectionless

+ A datagram contains the destination and the identity of packet. The IP packet is “self contained”. The packet contains everything it needs to reach its destination.

+ Each IP Packet (datagram) is handled independently.

- Routers can change at any time.

- IP datagrams can be

+ delayed

+ duplicated

+ delivered out of order

+ lost

- IP is a “best effort” delivery protocol.

That means that the network hardware and protocol will do “their best” to deliver packets but errors may occur

- The motivation for IP being so flexible is to accommodate all possible networks.