udp_ip

(a)
Server
PC Router (2,1) (1,3) r PPP
(1,1)
s
(2,2)
Ethernet
w
Workstation
(1,2)
(b)
Server HTTP TCP/UDP IP
Network interface
PC HTTP Router IP
Network interface
TCP/UDP IP
Length = 1200 ID=9876 3rd bit = 0 1200, ID 9876, 0, offset = 350
Network Interface 2
Network Interface 3
Diverse network technologies
UDP/IP : Unreliable Datagram Service
DATA 0 4 8 16 19 Destination Port UDP Checksum
Total length Flags Protocol Source IP address Destination IP address Options Padding Fragment offset Header checksum
UDP Checksum Calculation
0 8 16 Source IP Address Destination IP Address 00000000 Protocol = 17 UDP Length 31
UDP pseudoheader
• • • • •
UDP checksum detects for end-to-end errors Covers pseudoheader followed by UDP datagram IP addresses included to detect against misdelivery IP & UDP checksums set to zero during calculation Pad with 1 byte of zeros if UDP length is odd
Distributed applications HTTP Reliable stream service connectionless packet transfer SMTP DNS RTP User datagram service ICMP
TCP
UDP
IP
Network Interface 1
UDP Datagram
0 Source Port UDP Length 16 Destination Port UDP Checksum 31
•
Data
•
0-255
– Well-known ports
256-1023
– Less well-known ports
•
1024-65536
– Ephemeral client ports
IP Fragmentation -Each data link layer protocol has its own maximum frame size limit -IP layer will divide the datagram into smaller units if th d t it the datagram exceeds th maximum d the i packet size limit imposed by the data link layer
A
B
Internet Process y
Process 1
…
Network Service
Process n
UDP/IP : Unreliable Datagram Service (Lossy and no bandwidth guarantee) TCP/IP: Reliable Stream Service (but no bandwidth guarantee) )
data
IP Upd U d header header
data
Process 1 buffer
…
Process n
queue
UDP P
Input Processing
Output Processing
Input queue
IP P
IP output processing
IP input processing
Source and destination port p numbers – Client ports are ephemeral – Server ports are well-known well known – Max number is 65,535 UDP length – T t l number of bytes in Total b fb t i datagram (including header) – 8 bytes ≤ length ≤ 65,535 UDP Checksum – Optionally detects errors in UDP datagram
Example: a pe
Length=4000, ID = 9876, 3rd bit of flags = 0, offset = 0
Length=1400, ID=9876, 3rd bit=1,offset =0

Length = 1400, ID=9876, 3rd bit = 1, offset = 175
31 UDP
Source Port UDP Length
Version IHL Type of service
Identification Time to live
IP
UDP Datagram
Process X
Process X
message essage
message essage
IP Upd U d header header
Total length flag
Protocol Source IP address S dd Destination IP address Options Padding
UDP
identification
Time to live
Fragment offset
Header checksum
IP
Fragmentation
output queue
• Wh t is a datagram protocol What i d t t l
– Receiving and transmission are datagrambased (if b ff i not enough t accept th b d buffer is t h to t the entire data frame from the application program, program a returning error will occur – De-multiplexing is done based only on the destination port (i.e. Only be one queue for all sources. It is impossible to have a separate queue for each source (Why?).
Transport Layer Protocols
UDP/IP TCP/IP
Point-to-Point Link
Link bandwidth is fixed and reliable A B
Internet End-to-End Virtual Link
Process x
Bandwidth is unpredictable (time varying) and lossy. Link bit error rate is low, loss only due to congestion.
• • •
•
Total length: define the total length (header plus data) of the IP datagram in bytes. Fragmentation offset: this 13-bit field indicates the relative position (in bytes) of this fragment with respect to the whole datagram. Flags: th Fl three bits, fi t bit reserved, second bit when set, th i l bit first bit: d d bit: h t the ip layer should h ld not fragment the datagram. If the length exceeds the maximum size limit, an ICMP error report packet will be sent back. The 3rd bit: when set, the g g datagram is not the last fragment and more to come. Identification: IP layer will generate an ID number for each datagram it receives from the upper layer.
Network interface
Ethernet
PPP
Figure 2.15
IP Fragmentation
0 4 8 16 19 24 31