This document discusses Internet Protocol (IP) which is the fundamental protocol that defines how devices communicate over the internet. IP provides a connectionless datagram service and uses mechanisms like routing tables, fragmentation and reassembly, and addressing to transmit data packets between devices. Key aspects of IP include its use of routing tables to determine the next hop for packets, placing time to live values on packets to prevent looping, and including fragmentation information to reassemble packets at the destination when they are split across networks.

1. M.SANDHIYA (MSC INFO TECH)
NADAR SARASWATHI COLLEGE
OF ARTS AND SCIENCE
INTERNET PROTOCAL

2. Internet Protocol
 The term internet is short for “internetworking”
 interconnection of networks with different network access
mechanisms, addressing, different routing techniques, etc.
 An internet
 Collection of communications networks interconnected by
layer 3 switches and/or routers
 The Internet - note the uppercase I
 The global collection of individual machines and networks
 IP (Internet Protocol)
 most widely used internetworking protocol
 foundation of all internet-based applications

3. Design Issues
 Routing
 Datagram lifetime
 Fragmentation and re-assembly
 Error control
 Flow control
 Addressing


4. Internet Protocol (IP)
 IP provides connectionless (datagram) service
 Each packet treated separately
 Network layer protocol common to all routers
 which is the Internet Protocol (IP)

5. Routing
 End systems and routers maintain routing tables
 Indicate next router to which datagram should be sent
 Static
 Tables do not change but may contain alternative routes
 Dynamic
 If needed, the tables are dynamically updated
 Flexible response to congestion and errors
 status reports issued by neighbors about down routers
 Source routing
 Source specifies route as sequential list of routers to be followed
 useful, for example, if the data is top secret and should follow a
set of trusted routers.
 Route recording
 routers add their address to datagrams
 good for tracing and debugging

6. Datagram
 Datagrams could loop indefinitely
 Not good
 Unnecessary resource consumption
 Transport protocol needs upper bound on datagram life
 Datagram marked with lifetime
 Time To Live (TTL) field in IP
 Once lifetime expires, datagram discarded (not
forwarded)
 Hop count
 Decrement time to live on passing through each router
 Time count
 Need to know how long since last router
 global clock is needed

7. Fragmentation and
Re-assembly
 Different maximum packet sizes for different networks
 routers may need to split the datagrams into smaller
fragments
 When to re-assemble
 At destination
 Packets get smaller as data travel
 inefficiency due to headers
 Intermediate reassembly
 Need large buffers at routers
 All fragments must go through same router
 Inhibits dynamic routing

8. Internet Protocol (IP) Version 4
 Part of TCP/IP
 Used by the Internet
 Specifies interface with higher layer
 e.g. TCP
 Specifies protocol format and mechanisms
 RFC 791
 Dated September 1981
 Only 45 pages
 Will (eventually) be replaced by IPv6 (see later)

9. Internet Protocol (IP) Version 4
 Next header
 Header extension length
 Options
 Type (8 bits), length (8 bits) , option data (variable size)
 type also says what should router do if it does not recognize the option
 Pad1 / Pad N
 Insert one/N byte(s) of padding into Options area of header
 Ensure header is multiple of 8 bytes
 Jumbo payload (Jumbogram)
 Option data field (32 bits) gives the actual length of packet in octets
 excluding the base IPv6 header
 For packets over 216 -1 = 65,535 octets, we use this option
 up to 232 octets
 for large video packets
 Router alert
 Tells the router that the content of packet is of interest to the router
 Provides support for Resource Reservation

10. IP Fragmentation
 In IP, reassembly is at destination only
 Uses fields in header
 Data Unit Identifier – In order to uniquely identify datagram – all
fragments that belong to a datagram share the same identifier
1. Source and destination addresses
2. Upper protocol layer (e.g. TCP)
3. Identification supplied by that layer
 Data length
 Length of user data in octets (if fragment, length of fragment data)
 Actually header contains total length incl. header but data length can
be calculated
 Offset
 Position of fragment of user data in original datagram (position of the
first byte of the fragment)
 In multiples of 64 bits (8 octets)
 More flag
 Indicates that this is not the last fragment (if this flag is 1)