Layered Protocol architecture
No matter how we slice it, we must arrange
approach to architecture
Interface specs & Architecture
Interface = Service
Large message unit
A stream of bits at
And a series of
Each subsystem comprises a number of independent
hardware/software modules called “entities”.
Across exchange of data and control information at the
same layer level is according to
ce is across
within the same system but
across layer boundary.
For well defined interface points and protocol specification,
accords an open system
Open System Interconnection models.
OSI Protocol refere
Has 7 layers. Other protocol suits based on this may have
lower number of layers.
: Unified virtual terminal layout on
incompatible terminals systems over network. File
Transfer. Remote login. Te
lnet. Remote copy. Program
: Syntax and semantics of information
presented. Encoding data in a standard way. Basically
management of abstract data structures.
: Creation and maintenance of a session on
machines. Dialog control. Traffic bidirectional?
One at a time? Token management problems.
Synchronization issues after machines crash?
: Take the message from the session layer,
split into packets, give them to Network layer and ensure
they arrive at the other end correctly. Split traffic on
multiple transport lines for high throughput.
Multiplex multiple lines on a single transport to save
end layer. Type of service. Error free or no
guarantee? Broadcast? Multicas
Controls the operation of subnet. Figures
out how packets must be routed from source to destination.
Handling of network congestion. Handling of various
: To make the raw transmission facility appear
ven in a buggy environment. Flow control
making sure fast sender does not overwhelm slow
receivers. Error detection and correction. Piggybacking for
acks when they are expensive to make.
: Transmission of raw
bits over communication
major issues are with the interface
procedures and definition of data.
Typically the protocol Architecture would see flows in the
Sender ↔ Router ↔ Receiver
IP Protocol Stack. An alternative to OSI/ISO model. Also
known as TCP/IP Protocol stack.
FTP, HTTP, DNS, POP3, NTP, NNTP,
SNMP, SSH, RTP, rlogin, …
: TCP, UDP, DCCP, …
IP (IPv4, IPv6), ICMP, IGMP, ARP, RARP, ..
: Ethernet, Token
Fi, PPP, SLIP, FDDI,
ATM, Frame Relay, Bluetooth, …
Modems, ISDN, RS232, USB, …
IP address class:
Class A: 0 + 7 network ID bits + 24 host ID bits
Class B: 10 + 14 network ID bits + 16 host ID bits
Class C: 110 + 21 network ID bits + 8 host ID bits
Class D: 1110 + 28 multicast address bits
.local (for class A IDs)
network.network.network.local (for class C IDs)
IP address of a device
MAC address (physical ID)
MAC address is a permanently stamped address. IP
address is stored in a configuration file in the loca
A single network may be split into a multiple
networks for internal use but appear as a single
network to outsider. This is the concept of subnets.
Subnet mask. An address such that when added to
network address (in bitwise
into network + subnet + host address.
e.g. IP address: 188.8.131.52 subnet mask 255.254.0.0
Since the leading bit begins with 0, it’s a Class A
network with address 184.108.40.206
00001100 00001011 00001010 00001001
11111111 11111110 000
00001100 00001010 |
Network is extended by 7 more bits. Therefore, this is
The remaining host part is 0.1.10.9 is the host
IP and subnet masks
are often presented together in
this format. e.g. Network address = 220.127.116.11 ,
subnet mask = 255.255.224.0. In this case, the
network address can be written as 18.104.22.168/19
indicating subnet has 19 bits for the network portion
of address, and has rema
ining 13 bits for host part.
Therefore, total number of subnets =
2 = 6
Total numbe of hosts per subnet =
Classless Interdomain Routing (CIDR)
Classfull addresses waste a lot of addresses. Ideally,
could bunch similar network addresses together
and reduce ARP table considerably. For a good
example, see Tanenbaum
Some distinct networks:
127.0.0.0 is used for loop
(typically in the form of 127.0.0.1)
When host address is either all 0s (4
all 1s (Unix OS standard), it’s considered a
For mobile objects, two addresses: Home
address (permanent), and a care
of address. Used
only for forwarding IP datagrams and admin
functions. Higher layers never use them.
ddresses two types: Foreign agent
address, and Co
located care of address where
mails are sent directly to the device on a foreign
TCP/IP includes a protocol suit ARP (Address
Resolution Protocol) to map IP addresses to physical
addresses by network
administrators. The constructed
table is called ARP cache.
RARP = Reverse Address resolution Protocol permits
the inverse mapping from MAC to corresponding IP
address. Hosts such as diskless workstations only
knows their MAC addresses when booted but not
their IP addresses. This must be obtained from an
RARP server source. (RFC 903 for details).