Campus Area Networking
Technologies for routing
packets from one LAN to
another
Layer 3 Communication
S
S
R
R
S
S
Network - Layer 3
The network layer establishes the route
between the sending and receiving
stations. The node to node function of the
data link layer (layer 2) is extended
across the entire internetwork, because a
routable protocol contains a network
address in addition to a host address.
OSI Reference Model
Application
Presentation
Session
Transport
Network
Data Link
Physical
©”A Guide to Networking Essentials”, 1998, Course Technology.
Routing
BODY
Layer 2
Trailer
Layer 3
Header
Layer 2
Trailer
Routers read packets up to
layer 3
Network Routing
Protocols for
internetworking.
Two major types
Packet switching (or datagram)
Usually layers 3 and 4
Circuit switching
Usually layers 1 and/or 2
Packet switching or
Datagram Protocols
Best effort
Frames take individual routes
Packet assembly devices needed
Error Control
Traffic Management
Buffering
Discard
Node Functions
Message forwarding
Error detection and correction
Traffic management
Router Functions
Routers perform layer 1, 2, and 3 functions
Packet passing
Error correction
Message routing
Including circuit definition
Protocol translation
Firewall functions
(see the tracert function on the TCP/IP stack)
Switches and Routers
Switch
Executes in firmware
Not flexible
Fast execution
Inexpensive
Router
Executes in software
Flexible
Slow execution
Expensive
Any logic that can be executed in software
can also be converted to firmware using ASIC
technology (application specific integrated
circuits).
Routers
From A
From B
Input Buffer
Input Buffer
Processor
Output Buffer
Output Buffer
Input Buffer
Table of
Addresses
To C
To D
Packet Routing
Datagram
Packets proceed along their own route and
must be reordered at the end.
Circuit
Packets all take the same route and arrive in
order
Datagram Logic (IP)
Packet n
Packet 2
Packet 1
3
2
1
3
1
PAD
2
IP
Best Effort
Addressing
Variable packet lengths (1500 bytes or
less)
IPv4 vs IPv6
Frame and Header
The Internet:
IP Addressing – IP v4
32 bits (4 bytes)
Network address + Host address in one
Classes (originally)
A:
B:
C:
126 nets, 3 bytes of client addresses
2 bytes of client addresses (e.g. OU)
1 byte of client addresses (256)
Next step – IPv6
128 bit address space
Why?
IP Header (Layer 3)
Version
Header length
Type of service
Total length
Source port identifier
Fragment offset
Time to live
Protocol
Header checksum
Source address
Destination address
Options + Padding
Data
=4
In bytes
Characteristic of route
Length of the packet
Port identifier for host process
Position (8 byte units) from message start
Allowed seconds
ID of Transport layer protocol (TCP = 6)
32 bits
32 bits
How IP Routing Works
IP
Routing
Circuit Protocols
All packets take the same route
No packet assembly device to reorder
packets
Normally layer 2 connection
May be permanent or switched
Allow guaranteed service quality levels
May be used to carry datagram protocols
Circuit Logic
Source
Destination
Setup
Message & ACK’s
Teardown
Frame Relay
Frames relayed without reconstruction
End to end error control using CRC
error detection at layer 3 level
Variable packet size
Virtual circuit (usually permanent)
Multiple data rates
Multiple quality levels
Frame Relay Pricing
Components
Port speed
Measured as Maximum Bit Rate (56K,
T1, etc.)
Up to DS3 speed (45 Mbps)
Processing quality
Access (lowest)
Burst
Committed
Frame Relay
Processing Quality
Asynchronous Transfer
Mode – layer 2 networking
Cell switched
Equal length cells – 53 bytes
Like machine gun bullets
Fast: Speeds up to 9953 Mbps
Supports Quality of Service classes
Used primarily as a backbone technology
ATM Cell Format
Frame segment
Generic Flow Control
Size
Virtual Circuit (not
used)
Virtual Path Identifier
Virtual Channel Identifier
Payload Type Identifier
Cell Loss Priority
1 = discard eligible
Header Error Correction
Data
4 bit
1 byte
2 bytes
3 bit
1 bit
48 bytes
ATM Traffic Classes (QoS)
Constant Bit Rate (CBR) Real time voice & video
Variable Bit Rate – real
time (rt-VBR)
Variable Bit Rate – non
real time (nrt-VBR)
Available Bit Rate (ABR)
Unspecified Bit Rate
(UBR)
Compressed video &
LAN
LAN internetworking
Non mission critical
bursty Traffic
No guarantee, e-mail,
bulk file transfers
Class of Service CoS) and
Quality of Service (QoS)
In an enterprise network, class of service
(CoS) differentiates high-priority traffic
from lower-priority traffic. Tags may be
added to the packets to identify such
classes, but they do not guarantee
delivery as do quality of service (QoS)
functions, which are implemented in the
network devices.
TechEncyclopedia, 2003(class of service)
QoS
Layer 4 Responsibilities:
Connection
Establish and release connections
Control between endpoints to avoid overflow
Multiplexing
Crash recovery (protection buffering)
Data transfer
Packet splitting
Expedited delivery
Transport - Layer 4
The transport layer is responsible for overall
end to end validity and integrity of the
transmission. The lower data link layer (layer
2) is only responsible for delivering packets
from one node to another. Thus, if a packet
gets lost in a router somewhere in the
enterprise internet, the transport layer will
detect that. It ensures that if a 12MB file is
sent, the full 12MB is received.
TCP and UDP
Transmission Control
Protocol
Connection oriented
Assures that packets
arrive in order and
that they are correct.
User Datagram Protocol
Connectionless
Sends packets out
without confirming
that they arrive
TCP Header (layer 4)
Source port (16 bits)
Ports of communicating processes
“
Destination port (16 bits)
Sequence Number (32 bits)
Offset
Location of current fragment in
message
Number of frame to be
acknowledged next
Number of 32 bit words in header
Reserved
Not used
Acknowledgement Number (32 bits)
Flags
Window
Checksum (16 bits)
Urgent Pointer
Number of frames sender can
accept without buffer overflow
Ethernet/TCP/IP Header
Structure
UDP Routing
Layer 5 Responsibilities
Dialog management
Synchronization of checkpoints for error
recovery
Activity management to assure complete
action messages
Session - Layer 5
Coordinates communications. Determines
one-way or two-way communications and
manages the dialogue between both
parties; for example, making sure that the
previous request has been fulfilled before
the next one is sent. It also marks
transmitted data with checkpoints to allow
for fast recovery in the event of a
connection failure.
Example:
Ethernet/TCP/IP Stack
OSI Layer
5-7. User File
Layers
Transfer
(FTP)
Internet Protocols
Simple TELNET Routing
Simple Network
Mail
Information Management
Transfer
(RIP)
(SNMP)
(SMTP)
4.Transport Transmission Control
User Datagram (UDP)l
(TCP)
3. Network Address
Internet Internet Control Message
Resolution
Protocol (ICMP)
(ARP)
(IP)
2.Data Link
Ethernet, Token Ring, etc.
1.Physical
Twisted Pair, Fiber, Coax, Wireless
Backbone Protocols
Out to the WAN “cloud”
Station
CSU/DSU
Router/
Gateway
Firewall
LAN
Backbone
CSU/DSU:
Digital Service Unit/Channel Service Unit
CSU/DSU Wide area
access
The Channel Service Unit terminates the
external line at the customer's premises.
It also provides diagnostics and allows for
remote testing.
The Digital Service Unit does the actual
transmission and receiving of the signal
and provides buffering and flow control.
The DSU and CSU are often in the same
unit.
Dual Ring Topologies
(FDDI & SONET)
Dual Ring Operation
Rerouted Ring
FDDI
Fiber Distributed Data Interface
Common Backbone Technology
Two Fiber Cables
Dual Ring Configuration
4500 byte frame limit
100 Mbps
Priority Access
Multiple Frame Transmission
200 km (single mode fiber)
SONET
Synchronous Optical NETwork
Backbone technology used by phone
company.
Layer “1”
Externally synchronized
810 byte frame
Dual ring topology
Time division multiplexing
Multiple simultaneous data streams
SONET CIRCUITS
Service
VT-1.5
OC-1
STS-1
OC-3
STS-3
OC-12 STS-12
OC-48 STS-48
OC-192 STS-192
OC-768 STS-768
Speed (Mbps)
1.7
51.84
155.52 (3 STS-1s)
622.08 (4 STS-3)
2488.32 (16 STS-3)
9953.28 (64 STS-3)
39813.12 (256 STS-3)
OC (Optical Carrier) refers to the optical signal, and STS
(Synchronous Transport Signal) refers to the electrical
signal
ATM
Asynchronous Transfer mode
53 byte cell
5 byte header / 48 bytes of data
Single path for all packets in a message
Dedicated circuit
Quality of Service Priorities
Typical SONET and ATM use
as backbone technologies
Internetworking