Lecture 3
Review of Internet Protocols
Transport Layer
Protocols: HW/SW Interface
Internetworking: allows computers on independent
and incompatible networks to communicate reliably
and efficiently;
Enabling technologies: SW standards that allow reliable
communications without reliable networks
Hierarchy of SW layers, giving each layer responsibility for
portion of overall communications task, called
protocol families or protocol suites
Transmission Control Protocol/Internet Protocol
(TCP/IP)
This protocol family is the basis of the Internet
IP makes best effort to deliver; TCP guarantees delivery
TCP/IP used even when communicating locally: NFS uses IP
even though communicating across homogeneous LAN
2
Services provided by layers
Each layer in protocol stack
provides a “service”
Uses service from lower
layers
Layered protocol
stack
Application-specific
communication
Application layer
Benefits of layering
Isolates complexity
Clearly defined interfaces
Protocols implement
functionality within layer
Service provided
Process-to-process
communication
Transport layer
Connectivity between
network interfaces
Network layer
Point-to-point frame
transmission
Link layer
Transmission of bits in
medium
Physical layer
3
Layered Network Architecture (OSI)
Network
B
A
DATA
7
Application
6
Pre.
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
AH
DATA
PH
DATA
SH
TH
NH
DH
PH
DATA
DATA
DATA
DATA
DATA
Application
7
Pre.
6
Session
5
Transport
4
Network
3
Data Link
2
Physical
1
TCP/IP Model
OSI
7
Application
6
Pre.
5
Session
4
Transport
TCP
3
Network
IP
2
Data Link
1


TCP/IP
Physical
Application
Host-to-Net
ISO OSI (Open Systems Interconnection) not fully implemented
Presentation and Session layers not present in TCP/IP
Protocols
Protocols define communication between
entities
Format and order of messages
Actions taken on transmission and/or receipt of
message or other event
Application layer
Data
Message
Protocols use
headers (and
trailers) for control
information
Naming depends
on layer
Transport layer
Network layer
Link layer
Physical layer
H
Data
Segment
H H
Data
Datagram
H H H
Data
T
Frame
Bit
6
Process-to-process communication
We have a network. How to get between
programs?
Network
7
Process Communication
How do the end systems communicate?
End system
End system
Application layer
Data
Transport layer
H
Network
Application layer
Routers
Transport layer
Data
Data
H
Network layer
H H
Network layer
Data
H H
Link Layer
H H H
Data
Network layer
Data
H H
Link Layer
T
H H H
Physical layer
Data
Data
T
Data
Link Layer
T
H H H
Physical layer
H H H
Data
Data
T
Physical layer
H H H
Data
T
8
Interface-to-interface connectivity
We now have links. How to get across the
network?
9
Datagrams
Datagrams are forwarded independently
C
A
Dest
Out
port
A
3
B
1
...
...
E
B
D
F
10
TCP/IP packet
Application sends
message
TCP breaks into 64KB
segments, adds 20B
header
IP adds 20B header,
sends to network
If Ethernet, broken into
1500B packets with
headers, trailers
Header, trailers have
length field, destination,
window number, version,
...
Ethernet
IP Header
TCP Header
IP Data
TCP data
(≤ 64KB)
11
Communicating with the Server:
The O/S Wall
Problems:
User
CPU
Kernel
PCI Bus
NIC
NIC
• O/S overhead to
move a packet
between network
and application level
=> Protocol Stack
(TCP/IP)
• O/S interrupt
• Data copying
from kernel
space to user
space and vice
versa
• Oh, the PCI
Bottleneck!
12
The Send/Receive Operation
The application writes the transmit data to the TCP/IP sockets
interface for transmission in payload sizes ranging from 4 KB to
64 KB.
The data is copied from the User space to the Kernel space
The OS segments the data into maximum transmission unit
(MTU)–size packets, and then adds TCP/IP header information
to each packet.
The OS copies the data onto the network interface card (NIC)
send queue.
The NIC performs the direct memory access (DMA) transfer of
each data packet from the TCP buffer space to the NIC, and
interrupts CPU activities to indicate completion of the transfer.
13
Transmitting data across the memory
bus using a standard NIC
http://www.dell.com/downloads/global/power/1q04-her.pdf
14
TCP/IP Processing Path (RX)
Network I/O Processing
TCP requirements Rule of thumb:
1GHz for 1Gbps
1000
GHz and Gbps
100
10
100
Network
bandwidth
outpaces
Moore’s Law
40
10
1
0.1
Moore’s
Law
.01
1990
1995
2000
2003
2005 2006/7
2010
Time
I/O Acceleration Techniques
Architectural Improvement
TCP Offload: Offload TCP/IP Checksum and
Segmentation to Interface hardware or
programmable device (Ex. TOEs)
O/S Bypass: User-level software techniques
to bypass protocol stack – Zero Copy Protocol
(Needs programmable device in the NIC for
direct user level memory access – Virtual to
Physical Memory Mapping. Ex. VIA)
All the high bandwidth NICs today employ some kind of TCP Offload
and O/S Bypass techniques
Multiplexing/de-multiplexing
Multiple processes operate on one computer
Interface address alone is not sufficient to distinguish
Need to (de)multiplex traffic from different processes
5-tuple used for unique identification of connection
IP source address
IP destination address
Transport layer source port
Transport layer destination port
Transport layer protocol
18
TCP/IP packet
MAC
IP
TCP
APP. DATA
Source Port
MAC
Destination Port
Sequence Number
Acknowledgement Number
Header Length and Options
Window Size
Checksum
Urgent Pointer
Options (0 or more 32-bit words)
TCP/IP packet
MAC
Ver.
IHL
IP
APP. DATA
Service Type
Identification
Time to Live
TCP
Total Length
Options and Fragment Offset
Protocol
Header Checksum
Source Address
Destination Address
Options (0 or more 32-bit words)
MAC
TCP/IP packet
MAC
Preamble
IP
TCP
D. Add. S. Add. Leng.
APP. DATA
MAC
CRC
TCP Header: 5-tuple example
5-tuple is reversed for
return communication
sender
Destination port is
(client)
associated with
application
layer protocol (e.g., 80
for HTTP)
Operating system picks
source port randomly
128.119.91.53
74.125.39.99
receiver
(server)
source IP
destination IP
source port
destination port
protocol
source IP
destination IP
source port
destination port
protocol
128.119.91.53
74.125.39.99
35466
80
TCP
74.125.39.99
128.119.91.53
80
35466
TCP
22
Source port number
Position of data
31
28
29
23
24
20
21
15
16
11
12
7
8
3
4
Port numbers
Sequence number
0
TCP header
Destination port number
Sequence number
ACK number
Next expected
data
Data
offset
Reserved
URG
ACK
PSH
RST
SYN
FIN
Acknowledgement number
Checksum
Checksum
Flags for
connection setup
and teardown
Window
Urgent pointer
Options
Data
23
What functionality does TCP provide?
Reliability
Recovery from errors in the network layer
Flow control
Limit transmission rate to not overwhelm receiver
Congestion control
Limit transmission rate to not overwhelm network
24
Reliable data transfer
How can reliability be achieved?
Consider different assumptions for network layer
Case 1: completely reliable network layer
Send segment
Case 2: bit errors in network layer
Add error detection and ACK/NAK
Add sequence number to handle garbled ACK/NAK
Case 3: bit errors and packet loss in network
layer
Timer to trigger retransmission
“Stop-and-wait” protocol
25
Reliable data transfer
Stop-and-wait has low performance
How can we increase throughput?
Sliding window
Allow multiple segments “in-flight”
26
Sliding window example
data
Sent,
acknowledged
Sent, not yet
acknowledged
Ready,
not yet
sent
Received,
acknowledged,
sent to application
Free
buffer
acknowledgements
Sequence numbers
Received,
Received,
acknowledged,
not yet
not yet sent to
acknowledged
application
Free
buffer
Acknowledgement numbers
sender
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
receiver
1 2 3 4 5 6 7 8 9 10
S=1
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
A=4
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
A=6
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
S=2
S=3
S=4
S=5
S=6
S=7
timer for S=6
timer for S=7
1 2 3 4 5 6 7 8 9 10
A=2
S=8
S=9
S=6
S=7
A=6
A=10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
27
UDP: bare bones protocol
Ports, length, checksum
Source port number
Destination port number
Length
Checksum
31
28
29
23
24
20
21
15
16
11
12
7
8
3
4
0
Checksum is optional
28
29
Source and destination
address
Datagram length
Upper layer protocol
Identifies TCP, UDP, etc.
Time to live
Protection against accidental
loops
Header checksum
Version
Header
length
31
28
29
23
24
20
21
Type of service
Identifier
Time to live
15
16
11
12
7
8
3
4
IP header
0
Internet Protocol
Datagram length
Flags
Upper layer
protocol
Fragment offset
Header checksum
Source address
Destination address
Options
Data
Protection against bit errors
Fragmentation possible
Link layer limited to some
datagram size (min. MTU is
576 bytes)
30
Other IP aspects
Routing
Application layer
Determines forwarding
Domain Name
System (DNS)
ICMP
Error handling
Transport layer
Link layer
Address resolution (ARP)
Dynamic IP addresses (DHCP)
Application layer
Domain names (DNS)
Network layer
Routing protocols
(OSPF, RIP,
BGP)
Forwarding
Information
Base (FIB)
Internet
Protocol
(IP)
Transport layer
Network address translation
(NAT)
New IP version: IPv6
Internet
Control
Message
Protocol
(ICMP)
Address
Resolution
Protocol (ARP)
Link Layer
Physical layer
31
Network systems
Data is switched between network stacks
...
...
...
Network system
Transport layer
Transport layer
Transport layer
Network layer
Network layer
Data link layer
Data link layer
Data link layer
Physical layer
Physical layer
Physical layer
Link
Link
Link
...
Network layer
32
Classification of network systems
Network system differ by level of protocol
processing
Link
Physical
Physical
network
system
Link
Physical
DLC
MAC
LLC
Bridge
DLC
MAC
LLC
Network
Router
Network
Transport
...
Gateway
Transport
...
33
Example network system: NIC
Network interface card / adapter connects to
link
Block diagram:
Adapter
Memory
Link
Physical
MAC
End system
bus interface
DMA
Microprocessor
34
Example network system: switch
Switch connects multiple links
Block diagram:
Interconnection
Memory
Switch
DMA
Adapter 1
Proc
Memory
...
Switch
Proc
DMA
MAC/
PHY
MAC/
PHY
Link
Link
Adapter N
35
Example network system: switch
System may differ by system architecture
Example: share memory vs. distributed
Memory
memory
Interconnection
Switch
Proc
...
DMA
MAC/
PHY
Link
Switch
Adapter 1
Proc
DMA
MAC/
PHY
Adapter N
Link
36
Application requirements
Different applications have different
requirements:
Internet browsing
Scientific data archiving
Telephony
Internet TV
First-person shooter game
Real-time surgery
Delay-tolerant networking
Throughput
Low
High
Low
High
Low
High
Low
Delay
Large
Medium
Minimal
Minimal
Minimal
Minimal
Large
Jitter
Insensitive
Indifferent
Sensitive
Sensitive
Very sensitive
Very sensitive
Insensitive
Packet loss
Unacceptable
Unacceptable
Low
Low
Unacceptable
Unacceptable
Acceptable
37
Throughput preservation
Throughput performance
Ensure network system can handle link rates at all
points
Delay/jitter
Ensure network system processes traffic quickly
Packet loss
Ensure sufficient buffer space and fast processing
Most network system design focus on
bandwidth
38
Packet rate vs. data rate
Data rate states total number of bits per
second
Each packet requires specific processing
Packet rate sometimes more meaningful
What is the packet rate for a 10Gbps link?
Distinguish small packets and large packets
39
System design for throughput
What are the differences between these
systems?
How do they affect throughput preservation?
Processor
Memory
Processor
Bus
Bus
Link
adapter
Memory
Link
adapter
DMA unit
40